ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V002T00A001. doi:10.1115/POWER-ICOPE2017-NS2.

This online compilation of papers from the ASME 2017 Power Conference Joint With ICOPE-17 (POWER2017-ICOPE-17) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

I&C, Digital Controls, and Influence of Human Factors

2017;():V002T06A001. doi:10.1115/POWER-ICOPE2017-3616.

Advances in computer hardware over the past several decades have helped to expand the capabilities of boiler control systems in power generating applications. These greater capabilities have supported a proliferation of computer controlled boiler functions and, in many cases, replaced human operator functions with automated functions. Nevertheless, the human operator remains a central piece in many modern boiler control systems. One reason the operator is still present in the control room is that computer controls and human operators each have distinct advantages. Consequently, a boiler control system design should balance the best integration of automatic and operator control functions while balancing various requirements and design goals. The following question should then be answered: what roles or functions should be given to the operator vs. to the computer controls?

We will address this question by considering the guidance of relevant codes and standards, which have historically influenced control system design for large boilers in power generating applications. An analysis is performed on current and historically relevant standards and codes, including NFPA 85 and its predecessors, to consider how the guidance has changed along with control system technology. The analysis examines provisions directed toward manual and automatic controls to better understand the types of operations that are best-suited for manual functions versus automatic functions. Over time, NFPA 85 and its predecessors responded to the growing automation capabilities by requiring more automatic controls. While the emphasis placed on automatic controls for safety functions has grown, these standards suggest a balance or combination of automatic and manual controls for safety functions. These concepts are considered relative to those of Inherently Safe Design commonly applied in the chemical process industry.

Commentary by Dr. Valentin Fuster

Plant Construction Issues and Supply Chain Management

2017;():V002T07A001. doi:10.1115/POWER-ICOPE2017-3117.

HPR1000 is a kind of third-generation advanced nuclear technology, which was developed independently by China. It plays an important role in nuclear markets all over the world. For mass construction, besides quality and safety, enhancing process management and construction period optimization should be taken into consideration, such as design interface control in turbine & generator (TG) package, to improve comprehensive competitiveness for HPR1000. The existing Interface Control Manual (ICM) is a good means used to control design interface, however there is no standard model to establish ICMs for HPR1000. Taking the system of condensation water extraction (TFE) for example, after analysis on the design interfaces between TFE and other related systems, a standard design interface module can be built for TFE. Other standard design interface modules can be built in the same way, so the standard ICM for HPR1000 can be formed by combining the standard design interface modules of every system. (CSPE)

Topics: Design , Optimization
Commentary by Dr. Valentin Fuster
2017;():V002T07A002. doi:10.1115/POWER-ICOPE2017-3656.

Conventional methods for man-hour evaluation of purchase management include purchase package subtotal method and total purchase price proportion method, etc., however, these methods are limited to effectively analyze the man-hour of the procurement management in complicated industrial projects, such as nuclear power plants. Based on the experience of data collection in several nuclear power plant projects, a novel model for evaluating the equipment procurement management man-hour is proposed based on the Work Breaking-down Structure (WBS) in this paper. The unit standard man-hour for each WBS element is rigorous defined by statistical investigation of the data collection, then a set of specified adjust coefficients are applied to calculate the man-hour of the purchase contract management. The model is then analyzed and verified by a realistic equipment procurement contract, where the calculated results agree well with the practical experience. Moreover, the new model is employed to a nuclear power plant project in progress in China, both the man-hour of the equipment procurement management and the human resource demand are calculated to support the reasonable human resource arrangement for the entire construction period, which plays significant role in price quoting and cost control of procurement in Engineering-Procurement-Construction (EPC) projects. Finally, each result of a single-project obtained base on the new model can be accumulated for evaluating the multi-projects human resource demand and distribution.

Topics: China , Nuclear power
Commentary by Dr. Valentin Fuster
2017;():V002T07A003. doi:10.1115/POWER-ICOPE2017-3662.

A novel dynamic model and refined method for implementation of the Earned Value Management (EVM) on nuclear power equipment procurement is proposed in this paper. The EVM is known as an efficient and accurate method for progress and cost control in most of the civil engineering systems; however, there is lack of literatures on the EVM for precisely measuring the procurement progress in large-scale complex industrial projects, such as nuclear power plant systems. A novel dynamic measurement model based on the EVM is first established for evaluating the progress and performance of purchasing the nuclear power equipment, including specified details of operating procedure by quantitative valuing each schedule node based on work breaking-down structure (WBS) elements; then the dynamic model is analyzed and verified by a realistic contract of nuclear power equipment procurement. Furthermore, a nuclear power project under construction is studied and the equipment procurement progress is evaluated by applying the novel dynamic measurement model. Finally, the deviation of equipment procurement contract execution is presented by calculating the performance of progress and cost, which helps identify and analyze the delay risks. The dynamic measurement model has been applied in an abuilding nuclear power plant since January 2015, the results of applying the new model providing significant support to the progress and cost control of equipment procurement and bringing considerable profits to the project management. Based on the investigation and results of the above project, the new dynamic model is viable to be employed in future projects of nuclear power plant as a practical reference for applying the EVM in procurement management.

Topics: Nuclear power
Commentary by Dr. Valentin Fuster

Plant Operations, Maintenance, Aging Management, Reliability and Performance

2017;():V002T08A001. doi:10.1115/POWER-ICOPE2017-3023.

The cation conductivity in water-steam cycle has been significantly increased as external heating units presented on trends in large capacity and high parameters. Real test has been carried out to demonstrate the TOC concentration in feedwater has been increased as the external heating increases. The presence of organic acid would significantly reduce the pH of the condensate and result in general corrosion, pitting and environment assisted cracking. For the cogeneration thermal power stations in which make-up water were produced with traditional ion exchange system and Integrated Membrane Technology separately, the main factors affecting cation conductivity of steam are residues of the organics in raw water and dynamic variation about bacterial reproduction in reducing environment, respectively. If gel type anion resin had been replaced with macroporous strong base anion resin, the remaining TOC in traditional ion exchange system could be significantly reduced. And if non-oxidative bactericide had been dosed before or after Ultrahigh Purity Filter, bacteria could be effectively killed. For heat-supply units, the actual rates of makeup water, denote with “N%”, are always more than the design value. So it is very important in this scenario to revise the ceiling values of TOC for makeup water, which should be divided by N, to allow that ceiling value to match the actual rate of makeup water. For drum boilers and once-through boilers which superheated steam pressure are greater than 18.3 MPa, in order to guarantee the cation conductivity (25 °C) values of feed water less than the standard of 0.10 μ S/cm, TOC values in feed water should be under 50μ g/L.

Commentary by Dr. Valentin Fuster
2017;():V002T08A002. doi:10.1115/POWER-ICOPE2017-3035.

The bottlenecks which in developing high-efficiency Ultra Super Critical (USC) coal power technology is analyzed under the background of great pressure of reducing CO2 emission on coal power industry. The development of 700°C Advanced Ultra Super Critical (A-USC) technology has been much slower than expected mainly due to the material limitations. Double reheat systems increase the efficiency at the cost of significant increases in expense and complexity. A cross compound unit with an elevated and conventional turbine layout greatly shorten the expensive high-temperature piping, significantly cutting the piping costs as well as reduce pressure drops and heat losses which increase the efficiency and the performance-price ratio of the power unit. Engineering study demonstrates the feasibility and advantages of this design. Existing 600 °C materials and equipment manufacturing capabilities were applied to the double reheat unit with the elevated and conventional turbine-generator layout, and adding other mature energy-saving technologies which had succeed in Shanghai Waigaoqiao No.3 Power plant to achieve a net efficiency of 49.8% (6849Btu/kWh, Lower Heating Value (LHV)). Combined with a series of innovative technologies that can improve the operating efficiency and keep the efficiency from decreasing, the annual net efficiency can achieve 48.8% (LHV). This efficiency level is high enough to meet the strict CO2 emission standard (636g/kWh) issued by Environmental Protection Agency (EPA) of the USA, showing significant demonstration of reducing CO2 emission.

Topics: Coal , Turbines
Commentary by Dr. Valentin Fuster
2017;():V002T08A003. doi:10.1115/POWER-ICOPE2017-3045.

Wind based electric generation is one of the fastest growing energy sources in the world. With rapid development of wind farms, many challenges have emerged with respect to the reliability and availability of the in-service equipment. Additionally, with increasing size of wind turbine blades, both onshore and offshore, the serviceability and maintainability of the equipment poses its own unique challenge. There is also an inherent risk from the economics of energy production, which dictates that low-cost manufacturing methods are employed to produce cost-effective machines.

In our experience, there are additional risks associated with supply chains and limited availability and understanding of damage mechanisms and reliability data of the myriad manufacturers and models of turbines, blade design and associated equipment. Failure of different components results in different outage times and therefore impact operational and maintenance (O&M) costs in different ways. Achieving high availability targets requires a robust O&M plan.

The authors will highlight operational risks of large wind turbines and methodologies to improve reliability and availability for wind farms.

Commentary by Dr. Valentin Fuster
2017;():V002T08A004. doi:10.1115/POWER-ICOPE2017-3063.

Coal-fired power generation will continue to be the cornerstone of China’s energy sources in the coming decades and advanced ultra-supercritical technology is the future of coal-fired power generation. This paper selects double reheat cycle design for study and incorporates back pressure extraction steam turbine (BEST) into current cycle design, which used to drive boiler feed water pump and feed regenerative heaters. This design prevailed in US in 1960s and gradually was replaced by condensing turbine due to less efficiency benefits at subcritical steam condition. Reinvention of BEST design in current double reheat cycle is an evitable choice, because the efficiency advantage is improved at USC steam condition.

BEST configuration incorporated into current double reheat cycle and advanced cycle is developed to compare with other two conventional systems in this study. Thermodynamic simulation at design and off-design condition shows that BEST configuration has an obvious efficiency advantage at design load, but the advantage decreases at partial load. BEST expansion line and reheat pressure is integrated in cycle heat rate optimization. Genetic algorithm is chosen to implement the optimization and exergy analysis method is utilized to evaluate BEST expansion line optimization results. Finally, BEST design limitation and future work is practically concluded.

Topics: Heat , Design , Optimization , Cycles
Commentary by Dr. Valentin Fuster
2017;():V002T08A005. doi:10.1115/POWER-ICOPE2017-3087.

South Carolina Electric and Gas (SCE&G) Wateree Station is a pulverized coal fired power generation facility consisting of two Riley supercritical units (3,549 psi 1,005/1,005°F, 2,850 klb/hr) and two General Electric G2 tandem compound four flow three casing reheat steam turbines.

Commentary by Dr. Valentin Fuster
2017;():V002T08A006. doi:10.1115/POWER-ICOPE2017-3229.

Changes in misorientation with deformation were measured by various misorientation analysis methods using the electron backscattered diffraction (EBSD) method, and quantitative assessments were attempted to estimate the amount of strain or damage. Misorientations were correlated with macroscopic plastic or creep strains for comparative well-strained materials such as austenitic stainless steels.

Ni-base superalloys used for components requiring high temperature strength such as gas turbine blades, have low ductility with precipitation of the γ’ phase in grains, therefore the change of crystal orientation was considered to be extremely suppressed in comparison with austenitic stainless steels. In addition, it was anticipated that the extremely large grains of Ni-base superalloys made it difficult to properly assess the damage as misorientation. However, with the current advances in the EBSD acquisition systems in conjunction with scanning electron microscopy, it has become possible to make unprecedented resolved measurements of the local crystal structure distribution at a millimeter scale.

In particular, in order to assess the damage of gas turbine blades, the complex blade inner cooling system complicates the distribution of temperatures and stresses in the blades, which implies that it is required to assess the influence of geometry at stress concentrated regions in addition to the condition of temperatures, stresses and creep fatigue wave forms.

To date, in the case of the conventional casting material or the same geometry notched specimen of the directionally solidified (DS) superalloy, the average misorientation which means the grain reference orientation deviation (GROD) within grains in a certain predetermined evaluation area including the notch increases linearly up to the initiation of creep cracks regardless of the testing temperatures, strain rates and the effect of fatigue under the creep dominant condition. However, the different notch geometry of the DS superalloy shows the different characteristics of the misorientation development.

This paper focuses on a misorientation parameter which can assess the creep crack initiation life independent of the geometry at stress concentrated regions. In order to assess the creep crack initiation life at various stress concentrated areas of the DS superalloy, the development of a unified life assessment method independent of the individual notch geometries was discussed. As a result of this study, a parameter dividing the GROD by the initial notch opening value, φ0, was proposed and it was confirmed that the proposed parameter, GROD/φ0 shows similar characteristics with the relative notch opening displacement (RNOD) curves which correspond to the local strain energy and the initiation of creep crack at the notch tip independent of the geometry at a stress concentrated region.

Commentary by Dr. Valentin Fuster
2017;():V002T08A007. doi:10.1115/POWER-ICOPE2017-3232.

A method for speed matching of the second rotor (R2) with equal power for two rotors was proposed to improve the performance of the counter-rotating fan under off-design conditions. In this method, the speed of R2 is adjusted until the power of R2 is equal to the power of the first rotor (R1). The fan performance during constant speed operation and during R2 speed matching operation is presented and discussed using theoretical analysis, numerical simulation, and experimental research. The results show that R2 speed matching improves the power and efficiency characteristics of R2. Thus, the pressure rise and power characteristics of the fan were improved. The load of R2 under low flow rates condition was decreased, and the pressure rise and efficiency of R2 under high flow rates condition were increased. The blocking condition margin increased from 37.2% to 48.0%, and the high-efficiency working range of the fan increased from 33.2% to 37.9%.

Topics: Design , Rotors
Commentary by Dr. Valentin Fuster
2017;():V002T08A008. doi:10.1115/POWER-ICOPE2017-3258.

In many parts of the world, the impact of renewable energy, especially from intermittent sources as wind and solar is continuously increasing. In Germany, the share of renewable energy in electricity production is believed to increase from 32.5% in 2015 to 50% in 2030. In order to operate an electrical system and control the mains frequency, the power supply must match the consumption at any time. Ancillary services like primary and secondary control are used to balance the system on a time-scale of several seconds up to 15 minutes. Those control reserves are usually provided by thermal power plants. Particularly in times of high shares of fluctuating renewable feed-in, thermal power plants are turned off or operated at minimum load to avoid electricity production at low electricity prices. However, an amount of about 3000 MW of fast responding primary control need to be provided in the European network of transmission system operators for electricity grid to maintain stable operation even in case of two simultaneous large unit outages. This requirement leads to situations, where thermal power plants are operated in minimum load below their marginal cost to provide control reserves even if there is a surplus of energy in the grid. Operation in low load while at the same time providing control reserves leads to new challenges. As the relation between energy production and the thermal storage capacities provided by the metal and fluid mass in the boiler is decreasing with the load, the ability of responding to control demands is naturally slowed down. Dynamic simulation of the thermodynamic power plant process turned out to be an efficient method to investigate such operational modes. Using comprehensive process models coupled with a control system model, equipment adaptions or control system updates can be evaluated in order to provide faster responses. By increasing the specific amount of ancillary services per unit, the number of units necessary to provide the total amount of primary and secondary control could be reduced in situations with energy surplus.

Commentary by Dr. Valentin Fuster
2017;():V002T08A009. doi:10.1115/POWER-ICOPE2017-3269.

The U.S. electric utility industry continues to undergo dramatic and accelerating transformation. Reliability and resiliency are a key focus. A number of important issues including cyber and physical security challenges, aging infrastructure, and low natural gas prices continue to be of concern. Significant advances in technology, and prolonged regulatory uncertainty are also contributing factors.

Electric utilities are now making substantial investment in renewable resources and other technologies needed for renewables integration. This means a reduction in investment in generation assets and an increase in the transmission and distribution grids. There is also increased investment in providing customers with solutions to lower their costs, reduce their carbon footprint and provide control over their energy management.

The transformation ultimately demands significant increases in power plant generation operating capabilities and higher levels of equipment reliability while reducing O&M and capital budgets. Achieving higher levels of equipment reliability, with such tightening budget and resource constraints, requires a very disciplined approach to maintenance and an optimized mix of the following maintenance practices:

• Preventative (time-based)

• Predictive (condition-based)

• Reactive (run-to-failure)

• Proactive (combination of 1, 2 and 3 + root cause failure analysis)

Preventive maintenance (PM) is planned maintenance actions taken to ensure equipment is capable of performing its required functions. PM tasks are generally time-based, depending on the availability of condition monitoring data through a predictive maintenance (PdM) program.

Traditionally, PdM is largely performed by maintenance technicians in the field with handheld devices. Resource constraints usually mean that often weeks or even months elapsed between readings on the same piece of equipment. This approach has limitations with data volume, velocity, variety, and veracity.

Significant recent advances in sensor and technology associated with the Industrial Internet of Things (IIoT) have enabled the transformation of critical power plant assets such as steam turbines, combustion turbines, generators, and large balance-of-plant equipment into smart, connected power plant assets. These enhanced assets, in conjunction with analysis and visualization software, provide a comprehensive on-line conditioning monitoring solution that enables both a reduction in time-based PM tasks and also automation of PdM tasks.

This paper describes an approach by Duke Energy to apply smart, connected power plant assets to greatly enhance its fossil generation equipment reliability program and processes. It will outline the value that is currently being realized and will also examine additional opportunities.

Commentary by Dr. Valentin Fuster
2017;():V002T08A010. doi:10.1115/POWER-ICOPE2017-3309.

Owing to the growing environmental concerns, super-critical and ultra-supercritical coal-fired power plants dominate the electricity generation with the demand of near-zero air pollutant emission in China. Therefore, it is highly expected to assess the environmental impact and optimize the design at global and local levels. Exergoenvironmental analysis is a valid approach to investigate the formation of environmental impacts (EIs) associated with energy conversion systems at the component level. It generates information crucial for designing systems with a lower overall environmental impact, based on life cycle assessment (LCA) and exergy analysis.

A 600 MW supercritical coal-fired system with and without dust, SO2 and NOx mitigation controls was analyzed. Heat transfer in the boiler, condenser (CND), low pressure cylinder (LP), air preheater (APH) show high potential to decrease the environmental impact due to high exergy destructions. The deaerator (DEA), induced draft fan (IDF), forced draft fan (FDF) should be focussed on construction design and manufacturing optimization. Purification units reveal high benefit for reducing EI produced by coal combustion, but there is a large space for the EI saving for it. The specific EI of electricity in China is much greater than European.

Commentary by Dr. Valentin Fuster
2017;():V002T08A011. doi:10.1115/POWER-ICOPE2017-3323.

A 150kW organic working fluid radial turbine designed for the low temperature waste heat with temperature of 150 ∼ 200°C using R600a as working fluid was selected. Under the condition of same inlet temperature and rotational speed, the mixture R600a(iso-butane) / R601a(iso-pentane) with different compositions was adopted for the CFD numerical simulation to obtain the aerodynamic performance and the detailed flow of the organic working fluid radial turbine. The results show that the mixture R600a / R601a can broaden the output power range and increase the efficiency of the radial turbine compared with the pure working fluid. The output power of the organic working fluid radial turbine increases from 54.03kW to 129.6kW as the R600a composition increases from 0.1 to 0.9. The optimal composition of R600a / R601a was obtained for relatively higher efficiency of the organic working fluid radial turbine. The results can provide a reference for the selection of working fluid for radial turbine of the low temperature heat source.

Commentary by Dr. Valentin Fuster
2017;():V002T08A012. doi:10.1115/POWER-ICOPE2017-3412.

In pulverized coal-fired plant, the U-type bend is commonly used in flue gas and pulverized coal pipe system to due to the constraints of outer space. And gas-solid two-phase flow exists in these pipelines. The erosion of the pipe has significant effect on the safety and reliability of pipelines. In present paper, the erosion characteristics of U-type bend were investigated through CFD (Computational Fluid Dynamics) method. The wear distribution on the pipe wall was obtained. And the particle flow characteristics in U-type bend were analyzed. The influence of inlet velocity, mass loading rate and particle size on the erosion rate was studied as well. Result suggested that the maximum erosion rate increases exponentially with the increase of inlet velocity. And maximum erosion rate increases linearly with the increasing mass loading rate. Increasing particle size can aggravate the wear on the pipe wall.

Commentary by Dr. Valentin Fuster
2017;():V002T08A013. doi:10.1115/POWER-ICOPE2017-3417.

A cooling suction air with water spray has been used for the gas turbine. The cooling efficiency depends on spray properties and surrounding conditions. The aim of this study is to know spray properties and to clarity an influence of spray nozzle type on the cooling efficiency. A Phase Doppler Anemometry (PDA) is used for measurements. This measurement system is able to measure size and velocity of each droplet. A pin type nozzle, two different hole type nozzles are tested. The distribution of spray properties for the pin type nozzle becomes asymmetry due to the existence of pin. Its spray spreads widely and has broad size distribution in all spray area. Spray spreading area of hole type nozzles is narrow. Small particles gather on the spray center and large particles gather in the spray outer edge. Properties of each nozzle are also discussed for evaluating the cooling efficiency.

Commentary by Dr. Valentin Fuster
2017;():V002T08A014. doi:10.1115/POWER-ICOPE2017-3422.

In recent years an increasing number of coal-fired power plants are forced to take part in load cycling to balance the electricity demands and supplies in China. Therefore, the investigation of energy consumption characteristics of power plants during transient processes is necessary and valuable. In this paper, the loading up processes of a power plant with several formats of load commands, such as linear, parabolic, sine and exponential functions were simulated, and the energy consumption characteristics of the power plant were presented. Furthermore, the operation characteristics including flexibility, safety and generation cost were compared. Results show that: when the unit increases load with the same average cycling loading rate, the max difference of standard coal consumption rates is 1.03 g/(kW h), which decreases with the increase of average cycling rate. The excellent signal formats have the following features: the instantaneous cycling rates are small in the ending of a transient process while they have high values in the beginning and mid-stage of the process. (CSPE)

Commentary by Dr. Valentin Fuster
2017;():V002T08A015. doi:10.1115/POWER-ICOPE2017-3431.

As power plant combustion turbines (CTs) are pushed towards higher thermal efficiencies, increased attention is being given to operating requirements for their fuel gas supply such as the maximum allowable rate-of-change in pressure. It is important to perform detailed analyses for multi-unit plants to ascertain whether pressure transient events, such as those caused by initial trip of one or two combustion turbines, will cause additional combustion turbines to trip off. In this paper, single and dual CT trips were postulated in a near-realistic combined cycle power plant. Predictions of the gas flow behavior, along with propagation and superposition of pressure waves, was carried out using the method of characteristics (MOC) for compressible flows. Specifically, the rate of change in fuel gas supply pressure to each CT was monitored and compared against a typical manufacturer limit of 0.8 bar/s. Instances where simulations showed this threshold exceeded were noted, since such events correspond to automatic valve closure that would shut down one more CT and thereby further reduce plant electrical output.

The overall goal of fuel gas transient analyses is to improve pipeline designs, iteratively when necessary, such that those additional trips are avoided. To that end, this paper presents several simulation cases to illustrate pressure transient phenomena and to show the impact of various pipeline design alterations, some of which caused 40% reductions in the worst pressure rate-of-change during simulations.

Commentary by Dr. Valentin Fuster
2017;():V002T08A016. doi:10.1115/POWER-ICOPE2017-3440.

In order to improve solid particle erosion (SPE) resistance for steam turbine blades and nozzles, in corporation with Kobe Steel, Ltd., evaluation of hard coatings of TiN and TiAlN deposited by the Arc Ion Plating (AIP®) process was performed to verify applicability to an actual steam turbine. The results of high-temperature steam oxidation tests and room-temperature sand erosion tests showed that the TiAlN coating had high-temperature stability superior to that of the TiN coating, and erosion resistance far superior to that in the case of the conventional CrC thermal spray coating and boronizing treatment. High-temperature fatigue and creep tests showed that the characteristic strength of the blade material with the TiAlN coating was equal or superior to that of the base blade material.

On the basis of the results of comprehensive evaluation, it was confirmed that the TiAlN hard coating has excellent applicability to an actual steam turbine and it was successfully applied to steam turbine blades of power plants in Japan.

Commentary by Dr. Valentin Fuster
2017;():V002T08A017. doi:10.1115/POWER-ICOPE2017-3444.

In order to keep a high efficiency of a gas turbine, it is important to make a suitable maintenance. Gas turbine nozzle guide vanes (NGVs) and turbine rotor blades deteriorate through a long-time operation due to various causes such as a particle attachment, erosion, and a thermal stress. In the present study, a numerical investigation has been carried out to clarify the influence of the NGV and the rotor blade deterioration on aerodynamics in a 3-stage gas turbine. Geometries of the NGV and the rotor blade were measured from a real gas turbine using a 3-D scanner. The first stage NGVs and rotor blades usually deteriorate seriously and are usually replaced at certain intervals. Two kinds of the geometries of the NGV and the rotor blade of the first stage were obtained, which are the new ones before use and the used ones to be replaced. For the second stage and the third stage, the geometries before use were used in the computations. The numerical results show that the isentropic efficiency of the first stage increases and that of the second stage decrease due to the deterioration of the first stage. The efficiency of the third stage is not affected significantly. The mechanisms are discussed from the observation of the flow fields.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2017;():V002T08A018. doi:10.1115/POWER-ICOPE2017-3458.

In order to clarify the mechanism of fatigue crack growth in alloy 625, which is a candidate material for use in advanced ultra supercritical power plants, the crack tip damage zone formation after a crack growth test conducted in high temperature steam was investigated. It was observed that the oxide thickness at the crack tip tended to increase with decreasing cyclic loading frequency. The crack path was a mix of transgranular and intergranular fractures. According to the grain reference orientation deviation (GROD) maps, it was revealed that the density of geometrically necessary dislocations (GNDs) in the matrix along the crack path and ahead of crack tip increased with an increase in the fatigue crack growth rate (FCGR) due to environmental effects. It was observed that (1) mobile dislocations at the crack surface were blocked due to the thick oxide layer, resulting in an increase in the density of GNDs, and (2) an increase in the density of GNDs might induce stress concentration at the crack tip, deformation twinning, and the acceleration of FCGRs.

Commentary by Dr. Valentin Fuster
2017;():V002T08A019. doi:10.1115/POWER-ICOPE2017-3534.

Safe and efficient operation of a power plant is the system designers’ target. Regenerative system improves the Rankine Cycle efficiency of a power station. However, it is quite difficult to monitor the regenerative system’s performance in an accurate, economical and real-time way at any operation load. There are two main problems about this. One is that most model based on numerical and statistics approaches cannot be explained by the actual operation mechanism of the actual process. The other is that most mechanism models in the past could not be used to monitor the system performance accurately at real-time.

This paper focuses on solving these two problems and finds a better way to monitor the regenerative system’s performance accurately in a real-time by the analysis of the mechanism models and numerical methods. It is called the dominant factor method. Two important parameters (characteristic parameter and dominant factor) and characteristic functions are introduced in this paper. Also, this paper described the analysis process and the model building process.

In the paper, the mathematics model building process is based on a 1000MW unit’s regenerative system. Characteristic functions are built based on the specific operating data of the power unit. Combing the general mechanism model and the characteristic function together, this paper builds up a regenerative system off-design mathematical model. First, this paper proved the model accuracy by computer simulation. Then, the models were used to predict the pressure of the piping outlet, the temperature of the outlet feedwater and drain water of heaters in a real-time by computers. The results show that the deviation rate between the theoretical predictions and the actual operation data is less than 0.25% during the whole operation load range. At last, in order to test the fault identification ability of this model, some real tests were done in this 1000MW power plant during the actual operation period. The performance changes are identified via the difference between the predict value and the real time value. The result of the tests shows that the performance’s gradient change and sudden change could be found by the model result easily.

In order to verify the adaptability of the model, it was used for another 300MW unit, and done some operation test. The results show that this method can also be used for the 300MW unit’s regenerative system. And it can help the operator to recognize the fault heater.

The results of this paper proved that the dominant factor method is feasible for performance monitoring of the regenerative system. It can be used to monitor and find the fault of the regenerative system at any operation load by an accurate and fast way in real-time.

Commentary by Dr. Valentin Fuster
2017;():V002T08A020. doi:10.1115/POWER-ICOPE2017-3715.

Artificial intelligence (AI) has played an increasingly important role in condition monitoring and machinery fault diagnosis in power generation plants. However, the accuracy and reliability of any AI-based machinery fault diagnosis is highly dependent on the quality and quantity of the input data fed to the AI model. The hypothesis of this paper is that AI-based fault diagnosis can be further improved by taking into account all the available sensor inputs of the machine. In short, the more sensor inputs fed into the AI model, the more accurate and reliable the outcome of the fault diagnosis. This paper proposes an application of Dempster-Shafer (DS) evidence theory for sensor fusion to improve the accuracy of decision-making in machinery fault diagnosis, by fusing all the available vibration signals measured on different axes and locations of the test machine. Vibration signals from different axes and locations of a machinery faults simulator were collected by multiple accelerometers simulating various machinery health conditions, namely healthy, unbalance, misalignment and foundation looseness. The accuracy of fault diagnosis using a different number of sensor inputs was then investigated. Analysis results showed that by combining more sensor inputs using a DS-based algorithm can improve fault detection accuracy from an average of 63% to 83%. In conclusion, the multi-sensor fusion algorithm can be applied to increase the accuracy and reliability of AI-based fault diagnosis.

Commentary by Dr. Valentin Fuster
2017;():V002T08A021. doi:10.1115/POWER-ICOPE2017-3716.

This paper presents a case study in managing the dilemma of whether to resume or stop the operation of a power generation gas turbine with suspected blade faults. Vibration analysis is undertaken on the vibration signal of the gas turbine, to obtain an insight into the health condition of the blades before any decision is made on the operation of the machine. Statistical analysis is applied to study the characteristics of the highly unstable blade pass frequency (BPF) of the gas turbine and to establish the baseline data used for blade fault assessment and diagnosis. Based on the excessive increase observed on specific BPF amplitudes in comparison to the statistical baseline data, rubbing at the compressor blade is suspected. An immediate overhaul is therefore warranted, and the results from the inspection of the machine confirm the occurrence of severe rubbing at the compressor blades and labyrinth glands of the gas turbine. In conclusion, statistical analysis of BPF amplitude is found to be a viable tool for blade fault diagnosis in industrial gas turbines.

Commentary by Dr. Valentin Fuster
2017;():V002T08A022. doi:10.1115/POWER-ICOPE2017-3760.

In the course of the past decade, there has been increased attention and focus on the challenges facing power plant owners in managing/optimizing performance of their power generating assets. The challenges include aging power plants, changing mix of assets in fleets used for power production, aging workforce, attrition, capturing and retaining knowledge, recruiting new talent, technological changes, obsolescence, economics, environmental regulations, and others. These challenges have resulted in a paradigm shift, creating a need for power plant owners to do more with less, while simultaneously maximizing their operating revenues and return on investment.

This paper provides an overview of the challenges facing the power industry as it grapples with these challenges, and knowledge management strategies to effectively harness the power of human resources, power plant processes and technological advances/tools in managing/optimizing the performance of power generating assets.

Commentary by Dr. Valentin Fuster

Renewable Energy Systems: Solar, Wind, Hydro and Geothermal

2017;():V002T09A001. doi:10.1115/POWER-ICOPE2017-3077.

Nowadays, the management level and information construction of wind power industry are still relatively backward, for example, the existing maintenance models for wind farm are much too single, and corrective maintenance strategy is the most commonly used, which means that maintenance measures are initiated only after a breakdown occurs in the system. Moreover, the wind farm spare parts management is out-dated, no practical and accurate spares demand assessment method is available. In order to enrich the choices of maintenance methods and eliminate the subjective influence in the demand analysis of spare parts, a spare parts demand prediction method for wind farm based on periodic maintenance strategy considering combination of different maintenance models for wind farms is proposed in this paper, which consists of five major steps, acquire the reliability functions of components, establish the maintenance strategy, set the maintenance parameters, maintenance strategy simulation and spare parts demand prediction. The discrete event simulation method is used to solve the prediction model, and results demonstrate the operability and practicality of the proposed demand forecasting method, which can provide guidance for the actual operation and maintenance of wind farms.

Commentary by Dr. Valentin Fuster
2017;():V002T09A002. doi:10.1115/POWER-ICOPE2017-3155.

A successful transition to a low carbon future requires that power be generated all of the time, 24/7, not just when the sun is shining. But few clean emissions power technologies can operate 24/7. Concentrated solar power (CSP) can because it can store thermal energy at 10–20% of the cost of batteries1 and can then burn fuel when its solar resource is exhausted. However, many see first generation CSP as too costly, complex, risky, and economical only at utility scale.

Alternatively, by mimicking the all-factory, standardized, modular approach of wind and PV, next generation CSP with low-cost dry thermal storage (e.g., firebrick, not molten salts), and using no water/steam (just hot air) may give CSP the potential to fulfill on its promise of baseload affordability.

This technical paper summarizes an Engineering and Cost Feasibility Study2 funded by the US Department of Energy as well as presents a new breakthrough power generation product based on the Brayton power tower system called 247Solar Plants™. Design, construction, and operation are all simplified with greatly reduced costs and increased deployment speeds.

Such modular CSP systems can be installed as single units or 100s of modules at utility scale. The microturbines used by the system stabilize grids by responding nearly instantly, similar to battery response time, to changing power demands and voltage fluctuations, while offering dispatchable, reliable electricity. The redundancy of multiple modules in a single project increases capacity factor, operational flexibility, and project reliability.

The DOE Study shows that such a system may be able to achieve the two key DOE targets included: 1) a capacity factor of at least 75%, of which >85% would be solar with <15% from fuels; and LCOE3s <9ȼ/kWh. Indeed, LCOEs under 6ȼ/kWh may be possible with further development and widespread deployment.

Topics: Solar energy
Commentary by Dr. Valentin Fuster
2017;():V002T09A003. doi:10.1115/POWER-ICOPE2017-3162.

Numerical simulation was made for high-temperature solar and thermal receivers of pressurized air for solar micro gas turbine system. The solar / biomass hybrid gas turbine was considered to generate 30kW to 100kW power. The gas turbine system was provided with the concentrated solar light from the dish reflector at the solar receiver and the combustion heat from the biomass synthesis gas at the thermal receiver. Numerical model was developed to the solar receiver and the thermal receiver to reveal their thermal potential.

The solar receiver was a close loop concentric annuli to receive highly condensed solar light of 1,000kW/m2. The inner cylinder was made of high-temperature resistance ceramic irradiated by the condensed light on the inner side. The liner was inserted between the inner cylinder and the outer shell. The pressurized air passes the many holes of the liner to impinge the outer surface of the irradiation wall. These impinging jets caused high heat transfer coefficient on the irradiation wall and alleviates the thermal distribution in the receiver aisle. The liner and the outer shell were made by the high temperature resistance INCONEL alloy.

The thermal receiver was also a close loop annuli. This uses the same part as the solar receiver and the biomass gas combustor combined to it. The combustor comprises of the liner and the center tube, installed to the inside of the ceramic cylinder. The biomass gas was provided to the gap between liner and the center tube, and the oxidant air to the outer side of the liner. The biomass gas was spouted from the many holes of the liner and mixed with the oxidant air. The resulted hot combustion gas impinged directly to the inner side of the ceramic cylinder. The impingement of the hot combustion gas thinned the thermal boundary layer and enhanced the heat transfer on the ceramic wall. The thermal receiver was designed to attain the preferable heat transfer performance by the inner impinging jet of the hot combustion gas as well as the outer impinging jet of the pressurized air.

Three dimensional numerical model was developed to the solar receiver and the thermal receiver considered in the present study using ANSYS FLUENT. Parameter study showed that the exit air from the solar receiver was heated above 1200K or higher presently, and was continued to search better condition and better configuration of the system to obtain higher temperature. The numerical simulation revealed that the distance from the jet nozzle (linear holes) and the heat transfer surface is critical to the thermal distribution. The concept of the new solar and thermal receivers was confirmed on their usefulness; the multiple impinging jet effectively enhanced the heat transfer on the ceramic wall of the solar receiver and the thermal receiver to reduce the thermal inhomogeneity near the heat transfer surface with pressure loss of order 800Pa.

Commentary by Dr. Valentin Fuster
2017;():V002T09A004. doi:10.1115/POWER-ICOPE2017-3170.

Development of the renewable source of energy has become an area of interest due to increasing power demand and fixed fossil fuels in the universe. To increase efficiency of the renewable source of energy like, hydro power become important. In the present work, adaptive feedforward fuzzy PID controller has been developed for position control of the electrohydraulic actuation turbine IGV system. Electrohydraulic turbine governing systems are superior to the electromechanical governing system due to the high power availability, very good controllability, self lubrication property etc. NACA 0012 aerofoil blade configuration has been considered for the turbine IGV system due to the less lift force which lead to the less effort required to governing action. Low cost proportional valve control electrohydraulic system configuration has been considered. Simulation study has been carried in Matlab Simulink environment. The system IGV position control has been studied for step, sinusoidal and arbitrary position demand.

Commentary by Dr. Valentin Fuster
2017;():V002T09A005. doi:10.1115/POWER-ICOPE2017-3194.

Renewable energy technologies and sources have been playing a key role in reducing CO2 emissions and its footprint. Solar energy which is one of the major renewable energy sources can be utilized by means of solar Photovoltaic (PV) or solar collectors. Concentrating solar collectors supply thermal energy from medium to high grade where as non-concentrating collectors (flat plate) delivers low-grade thermal energy. The use of thermofluids with boiling temperatures lower than water, allows the operation of low grade solar thermal systems on an Organic Rankine Cycle (ORC) to generate both mechanical and heat energy. At the same time, the selection of an appropriate thermofluid is an important process and has a significant effect both on the system performance and the environment. Hydrofluoroethers (HFEs) are non-ozone depleting substances and they have relatively low global warming potential (GWP). In this study, a solar ORC is designed and commissioned to use HFE 7000 as a thermofluid. The proposed system consists of a flat-plate solar collector, a vane expander, a condenser and a pump where the collector and the expander are used as the heat source and prime mover of the cycle respectively. The performance of the system is determined through energy analysis. Then, a mathematical model of the cycle is developed to perform the simulations using HFE-7000 at various expander pressure values. Experimental data indicates that the efficiency and the net mechanical work output of the cycle were found to be 3.81% and 135.96 W respectively. The simulation results show that increasing the pressure ratio of the cycle decreased the amount of the heat that is transferred to HFE 7000 in the collector due to the increased heat loss from the collector to the environment. Furthermore, the net output of the system followed a linear augmentation as the pressure ratio of the system increased. In conclusion, both the experimental and theoretical research indicates that HFE 7000 offers a viable alternative to be used efficiently in small scale solar ORCs to generate mechanical and heat energy.

Commentary by Dr. Valentin Fuster
2017;():V002T09A006. doi:10.1115/POWER-ICOPE2017-3210.

The heat flux on the receiver tube is non-uniform because of uneven solar flux and receiver structure, which causes overheating and thermal stress failure of receiver and affected safe operations of the Concentrated Solar Power (CSP) system. In order to reduce the temperature difference in receiver tube wall and improve the efficiency of CSP system, the ternary eutectic salt LiF-NaF-KF (46.5-11.5-42 wt.%, hereafter FLiNaK), which has a better high thermal stability than that of nitrate salts at operating temperature of 900 °C, is selected as HTF, and heat transfer performance of FLiNaK in a corrugated receive tube with non-uniform heat flux is simulated by CFD software in the present work. The numerical results reveal that the non-uniform heat flux has a great influence on the temperature distributions of the receive tube and FLiNaK salt. Compared with the result of bare tube, the corrugated tube can not only significantly reduce the temperature difference in tube wall and salt by improving the uniformity of temperature distribution but also enhance the heat transfer of the salt, where the heat transfer coefficient increases with the Reynolds number and heat flux. Moreover, the enhanced effect of the corrugated tube depends on both the pitch and the height of ridges. It is found that the heat transfer coefficient of the salt gets a maximum when the ratio of the height of ridge to the pitch is 0.2. The research presented here may provide guidelines for design optimization of receiver tube in CSP system.

Commentary by Dr. Valentin Fuster
2017;():V002T09A007. doi:10.1115/POWER-ICOPE2017-3263.

The objective of this work is to analyze the dynamics and regimes of cold gas-solid flow in a biomass gasifier that is built at North Carolina Agricultural and Technical State University and to identify its corresponding ranges of operating conditions. The value of the minimum fluidization velocity Umf ≈ 8 cm/s has been found experimentally in a series of measurements of a pressure drop in the fluidized bed filled with Gledart type-B silica sand for the range of superficial gas velocities between 0 and 40 cm/s. To complement the experimental results, a set of three-dimensional numerical simulations of the isothermal gas-solid flow based on Eulerian-Eulerian approach has been performed. The analysis of the fluidization characteristics such as axial void fraction distributions has allowed us to evaluate the dependence of the bed expansion ratios from the flow superficial velocity. Good agreement between experimental and numerical results for the considered operating conditions of the gasifier has been observed.

Commentary by Dr. Valentin Fuster
2017;():V002T09A008. doi:10.1115/POWER-ICOPE2017-3307.

In this paper, a 3-D numerical model is proposed to investigate the capability of generating high operating temperature for a modified solar cavity receiver in large-scale dish Stirling system. The proposed model aims to evaluate the influence of radiation intensity on the cavity receiver performance. The properties of the heat transfer fluid in the pipe and heat transfer losses of the receiver are investigated by varying the direct normal irradiance from 400W/m2 to 1000W/m2. The temperature of heat transfer fluid, as well as the effect of radiation intensity on the heat transfer losses have been critically presented and discussed. The simulation results reveal that the heat transfer fluid temperature and thermal efficiency of the receiver are significantly influenced by different radiation flux. With the increase of radiation intensity, the efficiency of the receiver will firstly increase, then drops after reaching the highest point. The outlet working fluid temperature of the pipe will be increased consistently. The results of the simulations show that the designed cylindrical receiver used in dish Stirling system is capable to achieve the targeted outlet temperature and heat transfer efficiency, with an acceptable pressure drop.

Commentary by Dr. Valentin Fuster
2017;():V002T09A009. doi:10.1115/POWER-ICOPE2017-3308.

As most of wind farms are located at remote places with the large areas, it is difficult to manage wind farms and carry on the monitoring and diagnosis of wind turbines. Spot check is an effective way for the management of wind farm. The existing spot check information management systems are lack of effective management of data and further analysis functions, which makes the spot check data have not been fully used in judging the state of equipment. And the traditional spot check equipment has only simple functions including temperature and vibration detection. In order to solve the above problems, this paper develops a wind turbine spot check information management system. The spot check information management system manages the spot check routes, maintenance shifts, spot check staffs and other information. The spot check data can be uploaded to information management system via the wireless LAN. It can receive and deal with different kinds of signals such as vibration, temperature, noise and image signal. At the same time, it has the functions of vibration data analysis, trend analysis and prediction, fault diagnosis and so on, to judge the state of wind turbine. It can also export different kinds of spot check data report conveniently. According to field test, this spot check information management system can reasonably assign spot check tasks. And it can help to find the problem in time and reduce the maintenance cost.

Topics: Wind farms
Commentary by Dr. Valentin Fuster
2017;():V002T09A010. doi:10.1115/POWER-ICOPE2017-3320.

The expander is a key component of the Organic Rankine Cycle (ORC) power generation system, which has great influence on the system performance. Based on an experiment on a ORC system using the dry working fluid R600a, the thermodynamic parameters at the inlet and outlet of the scroll expander, and the output power under the experimental conditions were obtained. The performance of the scroll expander under variable operating conditions was studied. The effect of the superheat amount, inlet temperature, and inlet pressure on the performance of the scroll expander was analyzed. The results show that the scroll expander has good performance under variable operating conditions. The inlet pressure has the greatest influence on the performance of the scroll expander, followed by the inlet temperature, while the working fluid superheat has the least effect. A change in inlet pressure of about 50kPa results in about 20W of output power at the same inlet temperature variation range. While a change in inlet temperature of about 20 ° C can result in about 15W of output power at the same inlet pressure variation range. The results can provide a reference for the design and operation of the scroll expander. (CSPE)

Topics: Fluids
Commentary by Dr. Valentin Fuster
2017;():V002T09A011. doi:10.1115/POWER-ICOPE2017-3346.

In this work, the detailed model of intermediate temperature solid oxide fuel cell (IT-SOFC) and gas turbine (GT) hybrid system with biomass gas (wood chip gas) as fuel was built, with the consideration of fuel cell potential loss such as polarization loss and heat loss. Detailed performance of key component such as reformer, fuel cell and gas turbine of the hybrid system was studied under different biomass gas fuel compositions and steam/carbon ([S]/[C]) ratios. The results show that the hybrid system can reach the efficiency of 59.24% under the designed working condition. The biomass gas from different sources and processes usually have varied fuel concentrations, especially for methane (CH4), hydrogen (H2), carbon monoxide (CO) and water (H2O), which could significantly affect the performance of hybrid system. Results show that the change of H2 proportion has the most significant influence to system output power, CO and CH4 have similar influence trend. System electrical efficiency increases slightly with the change of H2 proportion while decreasing significantly with the increase of CO and CH4 proportion. The increasing composition of CH4, H2 and CO in biomass gas fuel benefits the output power of hybrid system, but results in the higher risk of overheat as well, which might cause safety problems. The composition of water in biomass gas affects the [S]/[C] ratio of system, and results show that maintaining the [S]/[C] ratio at a certain level can guarantee the temperature of key components in the hybrid system below the limits, which can satisfy the safety standards. The results show this technology has a good application prospect. (CSPE)

Commentary by Dr. Valentin Fuster
2017;():V002T09A012. doi:10.1115/POWER-ICOPE2017-3482.

In this paper, the thermal performance of steam receiver in tower-type solar power plants has been performed using the tower-type solar receiver design program developed by Shanghai boiler works Co Ltd. In the program, the integrated effect of three types of heat transfer, i.e. heat conduction, convection and radiation, in the process of heat transfer of receivers has been considered. With integrating the characteristics and the working conditions of receivers of both steam and molten salt, the developed program can be used to perform the thermal performance calculations for the receivers of both working fluids. The proposed program was validated through Solar Two project and the satisfactory results achieve. A steam receiver in a tower-type solar power plant with double superheats is selected as an example for thermal performance calculation. In view of the receiver operating in subcritical status, the thermal performance calculation is carried out for two sections, the one for evaporation and that for superheat. In evaporation section, the working fluid is circulated with a circulating pump at a very high circulating ratio. At the outlet of panels, the qualities of working fluid can reach to maximum about 0.35. Besides, the great difference of qualities of working fluid at the outlet of panels is observed. Even for some pipes of some panels, the working fluid at the outlet is in liquid phase. The distribution of metal temperature at fin end of panels in the evaporation region varies dramatically from place to place and reaches to over 520 °C. In superheat region, the temperature of the outer front crown of tubes is concerned. The highest front point temperature of pipe, which reaches to maximum over 660 °C, is in the middle region of the last parts of the primary superheat pass. The thermal efficiency distribution of the receiver, including the evaporation and the superheat regions, are also performed. The results show that the averaged efficiency is about 86%. Besides, the phenomenon of negative thermal efficiency happens in both two regions. That is because the solar incidence cannot compensate the natural heat loss due to incident radiation reflection, the pipe wall infrared radiation and convective heat loss.

Commentary by Dr. Valentin Fuster
2017;():V002T09A013. doi:10.1115/POWER-ICOPE2017-3506.

Ocean and wind energy require reliable, efficient electric conversion systems to be viable resources. Direct drive electric generators offer both benefits; however, it is difficult to generate the required torque at the low speeds typical of these resources. In this DOE sponsored project, ABB US Corporate Research partnered with Resolute Marine Energy (RME) and Texas A&M University to investigate the suitability of direct drive electric power generation for a paddle-type wave energy converter (WEC). This WEC provides high torque in a relatively chaotic, oscillating manner and requires a machine capable of handling high peak torques of approximately 40,000 N·m at speeds typically not exceeding 3 rpm. The baseline concept uses a hydraulic power take-off coupled with a generator and convertor; a direct drive electric solution may be beneficial. As a first step in designing a suitable direct drive generator for this application, we have begun with a smaller scale prototype targeting one tenth of the speed and torque, and we investigated a machine topology that may be promising in the operating regime of the full-scale machine. To this end, we designed and tested an integral generator and magnetic gear which is rated at 3,800 N·m at 30 rpm and completed a paper design for a machine of the required scale. This paper describes the mechanical design and testing of the prototype machine and provides some reflection on necessary design changes for the full-scale machine.

Topics: Torque , Machinery
Commentary by Dr. Valentin Fuster
2017;():V002T09A014. doi:10.1115/POWER-ICOPE2017-3520.

This paper presents a novel method of integrating Phase Change Materials (PCMs) and Silicone oil within the Evacuated solar Tube Collectors (ETCs) for application in Solar Water Heaters (SWHs). In this method, heat pipe is immersed inside the phase change material, where heat is effectively accumulated and stored for an extended period of time due to thermal insulation of evacuated tubes. The proposed solar collector utilizes two distinct phase change materials (dual-PCM), namely Tritriacontane paraffin and Erythritol, with melting temperature 72°C and 118°C respectively. The integration of Silicone oil for uniform melting of the PCMs, utilizes the convective heat transfer inside the evacuated tubes, as this liquid polymerized material is well known for its temperature-stability and an excellent heat transfer medium. The operation of solar water heater with the proposed solar collector is investigated during both normal and stagnation (on-demand) operation. The feasibility of this technology is tested via small scale and large scale commercial solar water heaters. Beyond the improved functionality for solar water heater systems, the results from this study show show efficiency improvement of 26% for the normal operation and 66% for the stagnation mode compared with standard solar water heaters that lack phase change materials and silicone oil. The benefit of this method includes improved functionality by delayed release of heat, thus providing hot water during the hours of high demand or when solar intensity is insufficient such in a cloudy day and during night time.

Commentary by Dr. Valentin Fuster
2017;():V002T09A015. doi:10.1115/POWER-ICOPE2017-3538.

This paper proposes new seismic-based methods for use in the wind energy industry with a focus on wind turbine condition monitoring. Fourteen Streckeisen STS-2 Broadband seismometers and two 3D sonic anemometers are deployed in/near an operating wind farm to collect the data used in these proof-of-principle analyses. The interquartile mean (IQM) value of power spectral density (PSD) of the seismic components in 10-minute time series are used to characterize the spectral signatures (i.e. frequencies with enhanced variance) in ground vibrations deriving from vibrations of wind turbine subassemblies. A power spectral envelope approach is taken in which the probability density function of seismic PSD is developed using seismic data collected under normal turbine operation. These power spectral envelopes clearly show the energy distribution of wind-turbine-induced ground vibrations over a wide frequency range. Singular PSD lying outside the power spectral envelopes can be easily identified, and are used herein along with SCADA data to diagnose the associated sub-optimal turbine operating conditions. Illustrative examples are given herein for periods with yaw-misalignment and excess tower acceleration. It is additionally shown that there is a strong association between drivetrain acceleration and seismic spectral power in a frequency band of 2.5–12.5 Hz. The long-term goal of the research is development of seismic-based condition monitoring (SBCM) for wind turbines. The primary advantages of SBCM are that the approach is low-cost, non-invasive and versatile (i.e., one seismic sensor monitoring for multiple turbine subassemblies).

Commentary by Dr. Valentin Fuster
2017;():V002T09A016. doi:10.1115/POWER-ICOPE2017-3550.

Low-temperature heat sources are ubiquitous. Harvesting this heat in an efficient and cost-effective way improve overall systems efficiency and reduce energy costs. Numerous studies shed light on these sources and technologies to utilize low-temperature heat. This paper evaluates the technical and economic feasibility of low-temperature Stirling Engine (SE) powered by hot water energy from evacuated tube solar water heater for distributed power generation when excess hot water energy is available. Evacuated tube solar collector provides hot water on-demand. When hot water is not consumed domestically, a SE is used to utilize the untapped heat from the solar water heater. The objective of this study is to evaluate the energy savings by using a SE to recover untapped heat from solar collectors. Thermal performance of the selected evacuated tube was measured experimentally under local weather conditions for different periods in summer and winter in the Mediterranean region and then simulated on hourly basis for a whole year to estimate the energy and hot water temperature output. Three different cases were taken to assess the potential of energy savings using SE to generate power namely, typical homes, office buildings and schools. SE is modeled using the most advanced third-order design analysis method. Air, helium, and hydrogen are used as working fluids in the SE at different charging pressures. Results obtained from solar collector’s thermal performance for the three cases are integrated with the results achieved from Stirling engine simulation of the various working fluids and pressures to evaluate the engine performance based on a dynamic approach. The study also investigates the economic feasibility of using Stirling engines for power generation from such low-temperature, intermittent heat sources. Results show that using hydrogen as working fluid is the most feasible. Typical schools show the most economical case to recover heat.

Commentary by Dr. Valentin Fuster
2017;():V002T09A017. doi:10.1115/POWER-ICOPE2017-3564.

The objective of the paper is to study the design and optimization of Kaplan hydro turbines for very low head (less than 3 meters), with a particular emphasis on the use of rim-drive electrical generators. The work is based on Computation Fluid Dynamics (CFD) analysis of a variety of design parameters for maximum output power and efficiency. Two designs are presented in the paper. One is a 90-cm (35-inch) diameter vertical-oriented Kaplan hydro turbine systems as an intended product capable of generating over 50 kW. The other is a smaller, 7.6-cm (3-inch) diameter horizontal-oriented system for prototyping and laboratory verification. Both are analyzed through CFD based on Large Eddy Simulation (LES) of transient turbulence. Certain design for the runner and the stator as well as guide vanes upstream of the turbine were studied to get the most from the available head. The intent is to use 3D-printing manufacturing techniques, which may offer original design opportunities as well as the possibility of turbine and water conduit design customization as a function of the head and flow available from a specific site.

Commentary by Dr. Valentin Fuster
2017;():V002T09A018. doi:10.1115/POWER-ICOPE2017-3618.

A steady state model of a supercritical organic Rankine cycle (SORC) was created in MATLAB and validated. Fluid properties were obtained using NIST REFPROP. Various working fluids were tested, including pentane (R601), isopentane (R601a), butane (R600), isobutane (R600a), butene, and cis-butene. Pentane and isopentane have not been of focus for SORCS at these temperatures. Varying turbine inlet temperatures ranging from 170 to 240°C were tested with the heat source provided by a medium temperature geothermal reservoir. A parametric analysis was performed on varying inlet pressure and turbine inlet temperature in comparison to first law efficiency, second law efficiency, effectiveness, and net work produced to analyze the overall and exergetic performance of each fluid. Optimum first law efficiency ranged from 17 to 22%. Cis-butene and pentane performed the best in all performance factors analyzed. Pentane and isopentane performed the best at pressures near or below their critical point. It was also found that near the critical temperature, a subcritical ORC has better performance than an SORC. This study is beneficial for not only geothermal energy but for applications that can provide operating temperatures between 170 to 240°C.

Commentary by Dr. Valentin Fuster
2017;():V002T09A019. doi:10.1115/POWER-ICOPE2017-3675.

Hydrogen as a clean alternative energy carrier for the future is required to be produced through environmentally friendly approaches. Use of renewables such as wind energy for hydrogen production is an appealing way to securely sustain the worldwide trade energy systems. In this approach, wind turbines provide the electricity required for the electrolysis process to split the water into hydrogen and oxygen. The generated hydrogen can then be stored and utilized later for electricity generation via either a fuel cell or an internal combustion engine that turn a generator. In this study, techno-economic evaluation of hydrogen production by electrolysis using wind power investigated in a windy location, named Binaloud, located in north-east of Iran. Development of different large scale wind turbines with different rated capacity is evaluated in all selected locations. Moreover, different capacities of electrolytic for large scale hydrogen production is evaluated. Hydrogen production through wind energy can reduce the usage of unsustainable, financially unstable, and polluting fossil fuels that are becoming a major issue in large cities of Iran.

Commentary by Dr. Valentin Fuster
2017;():V002T09A020. doi:10.1115/POWER-ICOPE2017-3684.

Undeveloped small hydropower generation sites are abundant throughout the water conveyance infrastructure and natural rivers in the United States. Due to its small scale, micro-hydro development requires substantial upfront capital costs, maintenance and operation costs for customized engineering and construction. The significant investments required for developing small hydropower are inhibiting for utilities, residential and commercial users to adopt. An inexpensive energy storage system and a well-designed power controls system can be integrated with small hydropower sites to increase its cost-effectiveness and reliability. This paper introduces the concept of storing low-power generated from small hydro turbines during long off-peak periods and dispatching at high-power as grid-quality electricity during peak periods. The use of an ultra-low cost thermal energy storage (ULCTES) system is examined. Boosting the power output for small hydro generation allows commercial users to avoid significant demand charges during operation, making small hydro an attractive cost saving strategy and therefore breaking down the cost barrier. The ULCTES operates much like a bulk power production unit and a peaker plant, in which it is capable of dispatching constant power over a long period during peak periods when conventional sources are unavailable. Improvements in system reliability and economic value are evaluated using microgrid optimization software HOMER Energy. In particular, two cases are studied with variations in types of end users and energy management goals. Energy costs savings, demand charges savings and renewable energy penetration are determined. Distributed energy storage systems are shown to reduce energy costs and increase the renewable energy penetration for commercial users. With ULCTES, microgrids have the flexibility to manage fluctuating renewable energy generation as well as respond to rapidly changing loads on a daily basis. A larger hydroelectricity system is shown to be more feasible with distributed energy storage systems for isolated users without any connection to the grid.

Commentary by Dr. Valentin Fuster
2017;():V002T09A021. doi:10.1115/POWER-ICOPE2017-3756.

Marine and hydrokinetic (MHK) turbine development projects use power converters to convert harnessed variable power to grid compatible constant frequency AC. Using power converters in similar projects such as harnessing tidal energy through bi-directional rotor blades, or by using direct-drive technology for harnessing tidal and ocean wave energy, are rapidly expanding all around the world. However, power converters are known to have the lowest mean-time-to-failure among turbines’ components and have significant impact on increasing the cost of energy, especially at larger MHK turbine scales. This work proposes the potential of a novel MHK turbine drivetrain with three main modules. The first module is an “energy harnessing module” to harness variable hydrokinetic power. The waterwheel with a large catchment area is effective in harnessing low head, free flowing hydrokinetic energy. The second module is a novel “speed controlling module” that is a replacement of currently used power converters; it is the focus of this work. It produces a constant speed output from a variable input speed. Finally, the third module is the “power generating module” that generates grid-compatible constant-frequency electricity. The test results showed the superior performance of the proposed speed converter in obtaining constant speed frequency output from a variable input speed range.

Commentary by Dr. Valentin Fuster
2017;():V002T09A022. doi:10.1115/POWER-ICOPE2017-3758.

The goal of this study is to evaluate and compare the thermodynamic performance of three feasible hybrid solar power tower-desalination plants for co-generation of power and fresh water. In these hybrid configurations, either multi effect desalination (MED) or thermal vapor compression (TVC)-MED unit is integrated to the Rankine cycle power block. The particular focus is on comparison between single plant and hybrid plants in terms of energy efficiency and penalty in power production to determine the more efficient configuration. The achieved results showed that integration of MED unit to the power cycle is thermodynamically more efficient, due to less reduction in power production and efficiency than the TVC-MED configurations. Also, for hybrid solar tower-MED plat, the average penalty in power production was between 9.27% and 12.88% when fresh production increased from 10000 m3/day to 31,665 m3/day. Another important finding showed the specific power consumption (specific power penalty) of the hybrid plant decreases with increasing the fresh water production. Especially at higher fresh water production, this specific power consumption was competitive to other desalination technologies such as reverse osmosis. The proposed hybrid solar tower-MED plant offers different benefits such as possibility of eliminating the cooling system requirement of the cycle as it can be replaced by the MED unit.

Commentary by Dr. Valentin Fuster

Risk Management, Safety and Cyber Security

2017;():V002T10A001. doi:10.1115/POWER-ICOPE2017-3086.

According to FM Global proprietary data, power-gen gas turbine losses have consistently represented a dominant share of the overall equipment-based loss value over the past decade. Effective assessment of loss exposure or risk related to gas turbines has become and will continue to be a critical but challenging task for property insurers and their clients. Such systematic gas turbine risk assessment is a necessary step to develop strategies for turbine risk mitigation and loss prevention. This paper presents a study of outage data from the Generating Availability Data System (GADS) by the North American Electric Reliability Corporation (NERC). The risk of forced outages in turbines was evaluated in terms of outage days and number of outages per unit-year. In order to understand the drivers of the forced outages, the influence of variables including turbine age, capacity, type, loading characteristic, and event cause codes were analyzed by grouping the outage events based on the chosen values (or ranges of values) of these variables. A list of major findings related to the effect of these variables on the risk of forced outage is discussed.

Commentary by Dr. Valentin Fuster
2017;():V002T10A002. doi:10.1115/POWER-ICOPE2017-3526.

Valuation is the process by which potential worth of transactions between two or more parties can be evaluated. The work products of a valuation are sets of calculated metrics. Application areas include valuations of electric power and building energy systems. Uncertainty can manifest while exercising a valuation in the form of natural variability, lack of knowledge, and random events. In the context of the valuation process, risk is the combination of these sources of uncertainty and their consequences. This paper lists sources of uncertainty and discusses how the valuation process might better support decision making in the presence of such uncertainty and risk.

Commentary by Dr. Valentin Fuster

Steam Turbine-Generators, Electric Generators, Transformers, Switchgear, and Electric BOP and Auxiliaries

2017;():V002T11A001. doi:10.1115/POWER-ICOPE2017-3100.

The aerodynamic and mechanical performance of the last stage was numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solution and Finite Element Analysis (FEA) coupled with the one-way and two-way fluid-structure interaction models in this work. The part-span damping snubber and tip damping shroud of the rotor blade and aerodynamic pressure on rotor blade mechanical performance was considered in the one-way model. The two-way fluid-structure interaction model coupled with the mesh deformation technology was conducted to analyze the aerodynamic and mechanical performance of the last stage rotor blade. One-way fluid-structure interaction model numerical results show that the location of nodal maximum displacement moves from leading edge of 85% blade span to the trailing edge of 85% blade span. The position of nodal maximum Von Mises stress is still located at the first tooth upper surface near the leading edge at the blade root of pressure side. The two-way fluid-structure interaction model results show that the variation of static pressure distribution on long blade surface is mostly concentrated at upper region, absolute outflow angle of long blade between the 40% span and 95% span reduces, the location of nodal maximum displacement appears at the trailing edge of 85% blade span. Furthermore, the position of nodal maximum Von Mises stress remains the same and the value decreases compared to the oneway fluid-structure model results.

Commentary by Dr. Valentin Fuster
2017;():V002T11A002. doi:10.1115/POWER-ICOPE2017-3147.

The Ultra-high Voltage (UHV) transmission has become an important developing direction of the Internet of Energy. Aiming at the influence of the Ultra-high Voltage transmission on the steam turbine, the primary frequency control (PFC) and low-load operation of units are analyzed emphatically. A coordination principle is proposed to guide operating personnel to modify PFC parameters. First, the PFC parameters are calculated qualitatively based on the proposed principle according to the units of Zhejiang province-China. Second, as the important embodiment of the PFC ability, the PFC capacity of a unit is illustrated from the angle of control valve opening, condensate throttling and feed water bypass and the removing high-pressure heater. Third, several measures are put forward to help increase the economical efficiency and safety when units are working in low-load due to the access of UHV. Finally, the future developing directions and the problems which need to be solved are discussed. The research of the effect of the UHV transmission on the steam turbine has great significance for the application of UHV and the Internet of energy (CSPE).

Topics: Steam turbines
Commentary by Dr. Valentin Fuster
2017;():V002T11A003. doi:10.1115/POWER-ICOPE2017-3152.

Shafting is one of the key units of large steam turbine generator set, its dynamic characteristics directly affect the technical level and operation effect of the new type large capacity Turbine-generator unit. The forces acting on the disc and the shaft are complex in operation. A composite rotor has various dynamic characters for a large capacity nuclear power Turbine-generator comparing with general rotor for its different structure. Numerical simulation was carried out to a composite rotor for a large capacity nuclear power T-G set, so as to analyze the influence of different length to diameter ratio on the vibration characteristics of the low pressure rotor and to study the effect of Interference Amount Between disc and shaft by using the three-dimensional finite element analysis in order to meet the requirements of the good vibration characteristics of the rotor. Firstly, the geometric model of the rotor is set up, and then the element model of the shafting is built, finally natural frequency of the rotor is calculated by using the mechanical module. Vibration characters such as the natural frequency and corresponding mode were obtained by analysis of vibration for the disc and shaft. The effect of the interference fit on critical speeds of the rotors are analyzed preliminarily. The results show that critical speeds of T-G rotor vary sensitively with magnitude of interference. (CSPE).

Commentary by Dr. Valentin Fuster
2017;():V002T11A004. doi:10.1115/POWER-ICOPE2017-3163.

The reliability design and compliance methods for a complete set of 1000MW ultra-supercritical thermal generating units were presented. In twenty-first century, with the rapid development of installed capacity of 1000MW ultra-supercritical thermal generating units in China, at the end of 2015, there are eighty-three 1000MW ultra-supercritical thermal generating units which were put into operation in China, China has become the country which posses the most 1000MW ultra-supercritical thermal generating units in operation. In order to meet the high reliability requirements of 1000MW ultra-supercritical thermal generating units which have been put into operation, the reliability design methods for a complete set of 1000MW ultra-supercritical thermal generating units are needed in engineering. The calculation formula of the availability deducted planned outage hours from period hours and the reliability calculation models of 1000MW ultra-supercritical thermal generating units were proposed, simultaneously with the calculation and compliance methods for the equivalent availability factor design value of 1000MW ultra-supercritical thermal generating units. The statistical formulas of the reliability characteristic, statistical results for the unit derating factor of 1000MW ultra-supercritical thermal generating units were given, together with the calculation examples and verification examples of equivalent availability factor design value for 1000MW ultra-supercritical thermal generating units. The relative error’s range of the equivalent availability factor design values is between −0.55% to 3.37%, base on the statistical results for reliability of 123-year operation data of eighteen 1000MW ultra-supercritical thermal generating units in 8 thermal power stations. Among them, the absolute value of relative error’s range of equivalent availability factor design values for 120 unit years operation data is less than 1%. Results shows that the calculation accuracy of the equivalent availability factor EAF of 1000MW ultra-supercritical thermal generating units is high precision by using the reliability design methods are given. These reliability design methods may be using in quantitative calculation of the design value of equivalent availability factor, which therefore may serve as a reference for reliability design and improvement of 1000MW ultra-supercritical thermal generating units.

Topics: Reliability , Design
Commentary by Dr. Valentin Fuster
2017;():V002T11A005. doi:10.1115/POWER-ICOPE2017-3165.

Low frequency oscillation is one of the most important factors that restrict the tie-line power flow of network. Its effective suppression is necessary to ensure safety and stability of the power system. The conventional power system stabilizer (PSS) is still insufficient in suppressing consider the frequency range and types of oscillation, so it is necessary to study the auxiliary suppression of the oscillation from the turbine side by using the electro-mechanical coupling theory. In this paper, a governorside power system stabilizer (GPSS) based on active power signal is designed, and its working principle, system structure and parameter setting method are introduced, the effective response frequency boundary of oscillation is also analyzed. Theoretical analysis and simulation results show that this GPSS can suppress in the whole frequency range of low frequency oscillation, and it is suitable as an auxiliary means of low frequency oscillation suppression. (CSPE)

Topics: Signals
Commentary by Dr. Valentin Fuster
2017;():V002T11A006. doi:10.1115/POWER-ICOPE2017-3230.

Fast valving of ultra-supercritical unit has great effects on over-speed prevention, load-shedding control, transient stability analysis of electrical system and other security problems. The purpose of fast valving is to maintain the stability of power system once fault or load shedding of unit occurs in the electric power system. Therefore, it is of great significance to study the reliability of fast valving for ultra-supercritical unit. In this paper, the KU ( short shedding) logic condition of SIEMENS T3000 system is analyzed as the research object of fast valving. The unit can be avoided over speed by monitoring the unit load and fast valving under faulty grid conditions based on the KU control. A series of measures will be taken after KU is triggered, for instance the governing valving will be closed quickly and the DEH (digital electro-hydraulic) control of the steam turbine will be switched to speeding control mode. On the other hand, the unit will return to normal operation if the transient fault of power grid disappears. The key contributions of this thesis include three parts: Firstly, based on the analysis of control characteristics of ultra-supercritical unit and protective logic and triggered conditions of KU function, a novel dynamic model by coupling the fast valving of steam turbine and the transient stability of generator is established by applying the PSCAD software. Then, the dynamic response process of ultra-supercritical unit is simulated and calculated by adopting the coupling dynamic model when KU function is triggered. Also the influence factors and reliability of fast valving are analyzed under transient fault conditions. Finally, two optimized measures by increasing the time delay and the speed of quantitative judgment are put forward to reduce risks and avoid the misoperation of signal distortion which may be caused by the power transmitter under transient fault conditions. The results of this study can not only help to evaluate the reliability of fast valving function scientifically in power grid transient fault, but also guide the technicians to analyze the stability of the power grid.

Commentary by Dr. Valentin Fuster
2017;():V002T11A007. doi:10.1115/POWER-ICOPE2017-3319.

For the natural oil circulation power transformer, the hot spot temperature and winding temperature should be within prescribed limits so as to ensure its life and reliability. Temperature rise of inner windings not only depends on the transformer loss, but relates to oil flow closely. Therefore, whether the oil flow of transformer and oil flow distribution rules among the three windings can be predicted or not, relates to success or failure of the winding temperature rise research. According to the structural characteristics of transformer, a three-dimensional computational model including windings and external radiators was built by a three-dimensional modeling software. Initially, from the view of flow, the flow resistance of natural oil circulation power transformer windings has been calculated and analyzed using the CFD methodology, and the resistance characteristic curves about high voltage windings, middle voltage windings, low voltage windings, radiators and pipelines were fitted respectively by the least square method. And then, on the basis of above, the porous media model was applied to simplify the integral model of transformer so as to build a three-dimensional coupled porous media-pure fluid computational model. Meanwhile, the author calculated porosities and linear resistance coefficients of high voltage, middle voltage and low voltage windings. At the end of this paper, to obtain the relationship of oil flow distribution among three windings, the pressure loss was calculated by numerical simulation. Compared with the theoretical calculation results which was based on the part of experimental data, the numerical calculation results are in agreement with these data. And the error between them is within 6 percent. Therefore, the feasibility and accuracy of calculation method, which was used to calculate oil flow of natural oil circulation power transformer windings by the porous media model, has been verified as well. There are two kinds of conventional method to calculate oil flow, including an empirical method and an experimental method. On the one hand, although the former kind of method can be applied conveniently, it cannot consider all the factors so that the accuracy cannot be guaranteed. On the other hand, experimental method to calculate the flow can present high accuracy, but the cost of carrying out experimental study is high. Therefore, this paper presents another calculation method aimed to the flow resistance and oil flow by CFD. And the calculation method presented has higher calculation accuracy compared to above. Meanwhile, the new method provides a theoretical reference about oil flow distribution for the design of the power transformer.

Commentary by Dr. Valentin Fuster
2017;():V002T11A008. doi:10.1115/POWER-ICOPE2017-3322.

With the implementation of low-carbon economy policy, clean energy (such as wind and solar energy) has been developing rapidly, and the percentage is increasing year by year; On the other hand, with a steadily growing percentage of residential electricity consumption and commercial electricity consumption, resulting in large electricity load difference between peak and valley, the load related requirements of modern steam power plants are noticeably changing. Whereas the past units being designed in base load now have to take part in peak load, and usually in a low load operation, unable to play its advantages of high efficiency in design load.

In the article the current three main governing methods (i.e. nozzle governing, throttling governing and bypass governing) for steam turbine will be discussed and evaluated under economical criteria focused on the above described challenges for future power generating technologies. A new governing method is Nozzle governing with Overload Valve Regulation, which keeps the advantage that main steam pressure of the Nozzle governing steam turbine is higher under partial load conditions, and weakens the influence of the low efficiency of governing stage on high pressure turbine, effectively improves the efficiency of steam turbine unit under partial load conditions.

In the turbine adopted the new governing method of Nozzle governing with Overload Valve Regulation, the first stage is governing stage, divided into several groups. Main steam from boiler goes through the main stop valve and main steam control valve in sequence, and then turns to the governing stage. When the load is below 85%THA, main steam control valve I, II and III are fully opened, main steam control valve IV is fully closed, and the unit is in sliding pressure operation. When the load is 85%THA, the main steam pressure can reach the rated pressure. With the load increasing, main steam control valve IV starts to open, but the main steam pressure maintains the rated pressure, adjusted to THA when main steam control valve IV is fully opened and the flowrate of governing stage reaches the maximum. In the load more than THA condition, the bypass valve starts to open, the main steam goes through the bypass steam room into the certain stage (as fourth), to meet the requirements of the super load, adjusted to VWO (about 108%THA) when the bypass valve is fully opened.

Through the detailed description about the scheme set and calculation analysis about economy benefit of the new regulation technology of Nozzle governing with Overload Valve Regulation, it shows that with the annual load range of 40%THA–85%THA, the economy of turbine adopted the new regulation technology is better than bypass governing by about 21.6 kJ/kW.h. (CSPE)

Commentary by Dr. Valentin Fuster
2017;():V002T11A009. doi:10.1115/POWER-ICOPE2017-3339.

Based on the rapid development of ultra-supercritical coal-fired units in China, by using material upshift and innovative structural design, such as double barrel cylinder, to improve the steam turbine high pressure and high temperature capability, by using the thermodynamic system optimization and high efficient flow technology to further improve the economy of steam turbine, DongFang has successfully developed a new generation of steam turbine, the parameters reach 35MPa / 615°C/ 630°C/630°C, heat consumption is lower than 6800 kJ/kWh, the generating efficiency of power plant exceeds 50%. This paper also introduces some technical development of future high-efficiency steam turbines at 650°C and 700°C.

Commentary by Dr. Valentin Fuster
2017;():V002T11A010. doi:10.1115/POWER-ICOPE2017-3410.

The nozzle block is one of the most important parts of steam turbine. It puts the steam heat energy into kinetic energy and plays a guiding role to the steam flow. The open integral nozzle block is a very unique structure. Due to the restriction of the large steam passage bending degree and the small nozzle mouth, the traditional process is difficult and the production efficiency is low. This paper mainly studies the structure and processing method of a new open integral nozzle block. The difficulties of the manufacturing process are being solved one by one by the way of developing the five-axis NC program, designing the special tooling and making the process technical solution. The process technical solution is to split the whole complex structure into three main parts which are easy to machine. It can easily realize the surface finishing of the steam passage and guarantee the geometric dimension of each steam blade. The surface roughness of the steam passage can reach Ra0.8. The precision requirements for machining and assembling of the open integral nozzle block can be fully met. It has a wide application prospect in promoting the scientific and technological progress of the new structure and the new process.

Commentary by Dr. Valentin Fuster
2017;():V002T11A011. doi:10.1115/POWER-ICOPE2017-3433.

This paper deals with the real dynamics characteristics of a mistuned steam turbine bladed disk subjected to dry friction forces to better understand the nonlinear mistuning phenomenon. Normal load, which directly affects contact stiffness between interfaces, is chosen as the mistuning parameter. Based on Mindlin model, a forced response analysis of the finite element model of mistuned bladed disk with damped shrouds is performed in ANSYS. Compared with results of other simplified models, a real and complicated nonlinear behavior are observed here. A mass of qualitative analysis is also performed to assess the impact of the mistuning magnitude and excitation level on the vibration. The result shows that, vibration response of bladed disk is affected by excitation and mistuning level significantly. Local amplification coefficient of vibration response in the cases of different mistuning levels is obtained by introducing 10 random mistuned patterns. In addition, frequency splitting phenomena even appears at one of the blades by the contribution of high mistuning levels. According to the calculated results for different excitation levels, the curve of modal damping varying with response amplitude is gained. Lastly, rigidity mistuning is introduced and a combined analysis is performed to investigate the influence of friction damping mistuning on rigidity mistuning in the same 10 random mistuning patterns. The arrangement of dry friction damping mistuning also could be controlled to reduce the local vibration amplification originating from structure mistuning. However, further statistical investigations should be made to gain more information. (CSPE)

Commentary by Dr. Valentin Fuster

Student Competition

2017;():V002T12A001. doi:10.1115/POWER-ICOPE2017-3103.

The increasing world energy demand as a result of society development brings forth a growing environmental concern. The use of high-efficiency alternative systems is becoming progressively more interesting due to economic reasons and regional incentives. The issue of finding the best configuration that minimizes total annual cost is not enough anymore, as the environmental concern has become one of the objectives in the synthesis of energy systems. The minimization of costs is often contradictory to the minimization of environmental impact. Multi-objective optimization tackles the conflicting objectives issue by providing a set of trade-off solutions, or Pareto solutions, that can be examined by the decision maker in order to choose the best configuration for the given scenario. The present work proposes a mixed integer linear programming model for the synthesis of a trigeneration system that must attend the electricity, heat, and cooling demands of a multifamily building complex in Zaragoza, Spain. The objective functions to be minimized are the overall annual costs and the overall annual CO2 emissions, considering investment, maintenance and operation costs. As a first approach, the single-objective configurations for each objective function are evaluated. Then, the Pareto frontier is obtained for the minimization of total annual costs and total annual CO2 emissions, allowing to obtain the best trade-off configuration, which brings results close to the optimal single objectives. It is worth mentioning that the treatment of the energy prices was simplified in order to keep on the same level of detail as energy CO2 emissions, which are given only on an annual basis. On the other hand, the optimization model developed can be further complicated in order to consider more complex situations.

Commentary by Dr. Valentin Fuster
2017;():V002T12A002. doi:10.1115/POWER-ICOPE2017-3186.

Water is one of the major sources of renewable energy and many hydropower plants are working across the world but they require specific values of head and flow rate for their operation and optimum results. There are many sites where limited head and flow rate is available but these resources cannot be exploited due to inefficient technologies. Gravitational vortex turbine (GVT) is a novel technology that is suitable for micro-level power production where low head and flow rate is available. It consists of two main parts: vortex pool for vortex generation and turbine blades. This paper focuses on parametrical analysis of GVT to determine the geometrical characteristics which gives the best performance. These parameters would address; effect of velocity and symmetry of vortex with the ratio of upper diameter of funnel (D) to outlet diameter (d), effect of the angle of rectangular inlet passage on the vortex formation. It will also analyze flow in rectangular passage with constant cross section vs. converging cross section. All of these parameters have major impact on the velocity and symmetry of flow. Results show that outlet of the funnel should be 40% of the upper diameter while highest velocity was achieved when rectangular passage was at 60 degrees with pre-rotational plate at 30 degrees.

Topics: Design , Vortices
Commentary by Dr. Valentin Fuster
2017;():V002T12A003. doi:10.1115/POWER-ICOPE2017-3392.

Renewable energy technologies offer a competitive cost of energy values in large-scale power generations compared with those from traditional energy resources. In 2015, residential and commercial buildings consumed 40% of total US energy consumption. Short and long-term plans have been developed to further employing wind energy technologies for electricity generation. However, there is a significant gap in developing reliable utility-scaled distributed wind energy converters. Employing novel low-cost wind harnessing technologies in these sectors supports the renewable-energy expansion plans.

A novel ducted wind turbine technology, called Wind Tower, for capturing wind power is designed and developed in earlier works. In this work, the Wind Tower structural analysis is conducted to obtain insights to the required materials and optimum components’ dimensions at an expanded range of wind flow regimes. A stable and robust design addresses the need for developing an optimum solution to obtain a maximum output power generation at a minimum cost of energy. It will lead to a maximum return on investment. The results demonstrate a superior structural performance of the Wind Tower Technology. It withstands pressure loads from high wind speed when it is installed as a standalone structure.

Commentary by Dr. Valentin Fuster
2017;():V002T12A004. doi:10.1115/POWER-ICOPE2017-3406.

An experimental investigation of a scaled-down and simplified laboratory model of a transformer cooling system is presented and discussed in this paper. The overall goal of this work was to obtain experimental data for validating cost-effective approximate mathematical models, used in investigations aimed at the development of numerical methods for assessing the operating limits of current transformers and optimizing the designs of next-generation transformers. The laboratory model used in this work was a vertical, single-phase, closed-loop thermosyphon operating with water as the working fluid. The steady and unsteady behaviors of this closed-loop thermosyphon were established and investigated using the following series of power inputs: 50 W, 125 W, 200 W, 125 W, and 50 W. Each of these levels of power input was maintained until steady-state conditions were achieved; and then the excursion to the adjacent power level (up or down, depending on the position in the aforementioned series) was effected. The corresponding experimental results are presented and discussed in this paper. The steady-state experiments with water as the working fluid are used to obtain valuable benchmarking results and also reliable initial conditions for the unsteady experiments. The experiments with excursions from one power level to an adjacent one provide novel results pertaining to unsteady operation of closed-loop thermosyphons. Another novel feature of this work is a demonstration that a simple lumped-parameter formulation can yield good predictions of the overall unsteady behavior of closed-loop thermosyphon systems akin to those used for cooling transformers.

Topics: Cooling systems
Commentary by Dr. Valentin Fuster
2017;():V002T12A005. doi:10.1115/POWER-ICOPE2017-3545.

Solar water heaters (SWHs) are a well-established renewable energy technology that have been widely adopted around the world. In this study we have significantly improved the Evacuated Tube solar Collectors (ETCs) by utilizing the “dry-drawable” Carbon Nanotube (CNT) sheet coatings to increase the solar energy absorption and Phase Change Materials (PCMs) to increase the heat accumulation for application in solar water heaters. The proposed solar collector utilizes a phase change material namely Octadecane paraffin, with melting temperatures of 28°C which is categorized as non-toxic with long-term chemical stability PCM. As PCMs particularly in powder form may not be effective by itself due to the poor heat transfer rate, low thermal diffusivity and thermal conductivity, by combining CNT layers with the high thermal diffusivity and thermal conductivity compare to phase change materials, we are able to overcome the shortcomings of PCMs and design an innovative and efficient solar water heater. With the current technology, we can provide a near ideal black body surface, absorbing a maximum of 98%, between 600–1100 nm, of solar light striking the surface, and providing additional spectral absorption which improves the performance of the solar heater. Applying CNT sheets in conjunction with PCM enables heat storage directly on the collector for a more constant output, even on a cloudy day and prolonged output of heat at night.

Commentary by Dr. Valentin Fuster
2017;():V002T12A006. doi:10.1115/POWER-ICOPE2017-3630.

Ocean compressed air energy storage (OCAES) is a promising large-scale energy storage concept. Different types of OCAES viz. - Diabatic, adiabatic and isothermal are possible based on the handling of heat in the system. In diabatic OCAES, compressed air is cooled in a cooler and heated using external heat source before transport to the expander. In Adiabatic OCAES, heat from the compressed air is stored in a thermal energy storage (TES) and reused to reheat compressed air before sending it to the expander. In Isothermal OCAES, air is compressed and expanded isothermally which results in the least compression work and highest expansion work. These OCAES configurations are assessed using exergy analysis in this paper. The exergy efficiency of individual components, exergy flow and overall efficiencies of diabatic, adiabatic and isothermal OCAES are presented. Results show that adiabatic OCAES shows improved efficiency over diabatic OCAES by storing thermal exergy of compressed air in TES and isothermal OCAES shows significantly higher efficiency over adiabatic and diabatic OCAES.

Commentary by Dr. Valentin Fuster
2017;():V002T12A007. doi:10.1115/POWER-ICOPE2017-3723.

High cycle fatigue (HCF) is the main cause of failure in rotating machinery especially in aircraft engines which results in the loss of human life as well as billions of dollars. More than 60 percent of aircraft accidents are related to High cycle fatigue. Major reason for HCF is vibratory stresses induced in the blades at resonance. Damping is needed to avoid vibratory stresses to reach the failure level. High speed rotating machinery has to pass through the resonance in order to reach the operational speed and chances of failure are high at resonance level. It is therefore required to suppress the vibrations at resonance level to avoid any damage to the structure. Application of coating to suppress vibrations is a current area of research. Various types of coatings have been studied recently. This includes plasma graded coatings, viscoelastic dampers, piezoelectric material damping, and magnetomechanical damping. In this research, the phenomenon of damping using a coating of nickel alloy on a steel beam is studied experimentally and numerically to reduce vibratory stresses by enhancing damping characteristics to avoid aircraft engine and rotating machinery failure. For this purpose, uncoated and nickel alloy coated steel beams are fabricated. The coating procedure was performed using plasma arc method. The beams were then mounted in a cantilevered position and bump and vibration shaker tests were conducted to determine the natural frequencies and mode shapes. One of the most important parameter to measure the damping of a system is the damping ratio. In order to determine the damping ratio, vibration analyzer mode was adjusted in time domain and beam was excited by using a hammer. The vibration analyzer showed the vibration decay as a function of time. Using that decay, damping ratio was calculated by using logarithmic decrement method. In order to investigate and compare the damping characteristics of un-coated and coated beams, forced response method was employed. In this method, beams were excited at 1st and 2nd bending mode natural frequencies using vibration shaker. Results were very encouraging and showed a significant improvement in damping characteristics. The experimental results were then endorsed by numerical results which were achieved by performing modal and forced response analysis using finite element analysis techniques.

Topics: Coatings , Damping , Vibration
Commentary by Dr. Valentin Fuster

Thermal Hydraulics and Computational Fluid Dynamics

2017;():V002T13A001. doi:10.1115/POWER-ICOPE2017-3021.

Based on the domestically developed urea hydrolysis reactor and urea hydrolysis ammonia process, a pilot test of urea hydrolysis was established with 10kg/h ammonia production for the flue gas denitration reductant, to reduce pollution of NOx emission from coal plant and avoid the environmental risk of liquid ammonia.The results show that urea hydrolysis reaction rate was controlled by the temperature monotonically. Steam consumption increases with the increase of pressure, especially when pressure is greater than 0.6 MPa and bring about lower economy. The higher feed concentration, the lower energy loss for the water latent heat of vaporization, and the lower operation cost of device. The maximum ammonia production is 16 kg/h, the hydrolysis conversion is greater than 98%, and the ammonia mass fraction of product gas is 22.6–34% (volume fraction of 28.5–48.0%) during the tests, at the feed concentration of 40–60%, the operating pressure and temperature of 0.6MPa and 160°C.

Topics: Coal
Commentary by Dr. Valentin Fuster
2017;():V002T13A002. doi:10.1115/POWER-ICOPE2017-3171.

Radiation heat transfer is the dominant model of heat transfer in the large scale industry boiler, especially in oxy-fuel combustion condition. Radiative properties of combustion gases and char oxidation in the oxy-fuel condition are obviously different from the air-fuel combustion, due to the N2 replaced by CO2. Through researchers proposed many helpful correlations based on the air-fuel Weighted-Sum-of-Grey-Gases-Model (WSGGM), the absorption coefficients were commonly constant or correlations were discrete by the classical molar ratio of H2O to CO2 (MR), which were mismatching the continuous value of MR in the real furnace. Meanwhile, the discrete MR is also not applied to the computational fluid dynamics (CFD). In this paper, new correlations for the WSGGM are determined as polynomial function of MR and temperature, which can be conveniently employed in Fluent by the form of user-defined-functions in C language. Parameters of model are fitted by total emittances calculated based on the timely HITEMP 2010 database. New correlations are validated by comparing the emittances with line-by-line calculations and other classical models. New correlations are employed in the CFD for the real industrial oxy-fuel combustion with the temperature range of 400–2600K, pressure path-length between 0.01 and 60 bar m. Several assumed test cases have been investigated to evaluate the accuracy of the models. Modified correlations for WSGGM give a better accuracy of the total emittances for the mixed combustion gases in the real furnace. New models including radiative and chemical reaction mechanisms have been employed to CFD modeling of combustion process for a tangentially fired 300MWe utility boiler. The industrial boiler is modeled by a partition meshing method with the hexahedral structured mesh. Due to the atmosphere shift from N2 to CO2, three aspects are essential to be modified for oxy-fuel: radiation model, char oxidation model and homogeneous volatile oxidation model. To investigate the performance of the furnace, air-fuel combustion selected as the conference, three other cases employed are defined as Oxy21 (vol21%, O2), Oxy26 (vol26, O2) and Oxy29 (vol29%, O2), respectively. Temperature profile and heat transfer are investigated for the different test cases. Meanwhile, the simulation and calculation heat transfer in the furnace are also compared. The results show the new modified simulation has an approximate 4–11% lower than the thermodynamic calculation. To achieve an identical heat flux and temperature distributions with the air-fuel case, the molar fraction 29% of O2 is essential for the selected implementation. (CSPE)

Commentary by Dr. Valentin Fuster
2017;():V002T13A003. doi:10.1115/POWER-ICOPE2017-3198.

In this paper, a bi-evaporator compression/ejection refrigeration is experimental investigated to recycle the throttling loss in traditional vapor compression refrigeration cycle by using an ejector. The effects of working parameters on the system performance are mainly analyzed. The results are as follows: the ejector entrainment ratio decreases as the condenser and the high-temperature inlet water temperature increases, but rises with the increasing of low-temperature evaporator inlet water temperature; the system COP rises with the decreasing of inlet water temperature of condenser, and increases with the rise of inlet water temperature of high-temperature evaporator; the inlet water temperature of the condenser and the high-temperature has greater influences on the performance of BCERC system. The system COP increases about 0.25 when the condenser inlet water temperature decreases per 5°C; while the system COP rise about 0.114 as the high-temperature evaporator inlet water temperature increases per 5°C. The low-temperature evaporator inlet water temperature has little effects on the performance of the BCERC system. The results can be references for the design and operation of the BCERC system.

Commentary by Dr. Valentin Fuster
2017;():V002T13A004. doi:10.1115/POWER-ICOPE2017-3212.

This paper proposed an approach to modeling alkali metal reacting dynamics in turbulent pulverized-coal combustion (PCC) using tabulated sodium chemistry. With tabulation, detailed sodium chemistry can be incorporated in large-eddy simulation (LES), but the expenses of solving stiff Arrhenius equations can be avoided. The sodium release rate from a pulverized-coal particle is assumed to be proportional to the pyrolysis rate, as a simplification. The chemical forms of released sodium is assumed to be atomic sodium Na, because atomic sodium is predicted to be the favoured species in a flame environment. A detailed sodium chemistry mechanism including 5 sodium species, i.e., Na, NaO, NaO2, NaOH and Na2O2H2, and 24 elementary reactions is tabulated. The sodium chemistry table contains four coordinates, i.e., the equivalence ratio, the mass fraction of the sodium element, the gas-phase temperature, and the progress variable. Apart from the reactions of sodium species, hydrocarbon volatile combustion has been modeled by a partially stirred reactor concept. Since the magnitude of sodium species is very small, i.e., at the ppm level, and the reactions of sodium species are slower than volatile combustion, one-way coupling is used for the interaction between the sodium reactions and volatile combustion, i.e., the former having no influence on the latter. A verification study has been performed to compare the predictions on sodium species evolutions in zero-dimensional simulations using the chemistry table against directly using the detailed sodium mechanism under various initial conditions, and their agreement is always good. The PCC-LES solver used in the present study is validated on a pulverized-coal jet flame ignited by a preheated gas flow. Good agreements between the experimental measurements and the LES results have been achieved on gas temperature, coal burnout and lift-off height. Finally, the sodium chemistry table is incorporated into the LES solver to model sodium reacting dynamics in turbulent pulverized-coal combustion. Properties of Loy Yang brown coal, for which sodium data are available, are used. Characteristics of the reacting dynamics of the 5 sodium species in a pulverized-coal jet flame are then obtained. The results show that Na and NaOH are the two major sodium species in the pulverized-coal jet flame. Na, the atomic sodium, has a high concentration in fuel-rich regions; while the highest NaOH concentration is found in regions close to the stoichiometric condition. It should be pointed out that the proposed chemistry tabulation approach can be extended to modeling potassium reacting dynamics in turbulent multiphase biomass combustion. (CSPE)

Commentary by Dr. Valentin Fuster
2017;():V002T13A005. doi:10.1115/POWER-ICOPE2017-3227.

The impinging Stream is a novel technique in enhancing heat and mass transfer. In the conventional impinging stream reactor (ISR), as the particles in that reactor are affected by the fluid resistance, the energy of the particles is rapidly decreased after the infiltration of the reverse flow, which leads to the effective mixing of the particles. In this paper, we design an improved impinging stream reactor (IISR) that has different fluid inlet velocity but same mean fluid inlet velocity in a period, which still belongs to definition of impinging stream. In the present study, the flow characteristics in the IISR are investigated using particle image velocimetry (PIV) and computational fluid dynamics. The effects of the fluid inlet velocity in the axisymmetric opposed jets are discussed for equal mean volumetric flow rates of the two jets. The impingement plane and the flow filed of the IISR are measured from captured images using the PIV technique. The two fluid inlet velocity with different sinusoidal variations are applied in the improved impinging stream. Besides, the experimental results show that the impingement plane is moving instantaneously with the two inlet velocity changing dynamically, which expands efficient active areas compared with the conventional impinging stream. Besides, computational fluid dynamics are used in combination with the discrete phase model (CFD-DPM) to predict the flow characteristics within the improved Impinging Stream. The simulation results show that impinging stream flow field can be divided into the inlet, the impact zone, the exit zone and the vortex area. At the same time, the impact zone and the impingement plane is also found to be moving The CFD-DPM results give predictions that are in better agreement with the flow filed pictured by the PIV technique. Because of the complexity of the liquid immersion impinging stream, it is difficult to study the trajectory of the particles in the flow field, so we use the numerical simulation to study the motion of the particles in the immersion IISR. Analysis shows the effective mixing region of the particles can be greatly increased, particles’ motion trajectory can be longer and the heat and mass transfer between the particles and the interphase can be further enhanced. Compared with the conventional ISR, the IISR has obvious advantages. The results point out this improved impinging Stream has a good application prospect in future engineering works.

Commentary by Dr. Valentin Fuster
2017;():V002T13A006. doi:10.1115/POWER-ICOPE2017-3280.

As one kind of serious environmental problems, flow-induced noise in centrifugal pumps pollutes the working circumstance and deteriorates the performance of pumps, meanwhile, it always changes drastically under various working conditions. Consequently, it is extremely significant to predict flow-induced noise of centrifugal pumps under various working conditions with a practical mathematical model. In this paper, a three-layer back propagation (BP) neural network model is established and the number of input, hidden and output layer node is set as 3, 6 and 1, respectively. To be specific, the flow rate, rotational speed and medium temperature are chosen as input layer, and the corresponding flow-induced noise evaluated by average of total sound pressure level (A_TSPL) as output layer. Furthermore, the tansig function is used to act as transfer function between the input layer and hidden layer, and the purelin function is used between hidden layer and output layer. The trainlm function based on Levenberg-Marquardt algorithm is selected as the training function. By using a large number of sample data, the training of the network model and prediction research are accomplished. The results indicate that good correlation is established among the sample data, and the predictive values show great consistence with simulation ones, of which the average relative error of A_TSPL in process of verification is 0.52%. The precision of the model can satisfy the requirement of relevant research and engineering application.

Commentary by Dr. Valentin Fuster
2017;():V002T13A007. doi:10.1115/POWER-ICOPE2017-3347.

Pipelines are widely used in energy power system including thermal power plants and nuclear power plants. In the power system, especially nuclear power plants, as thermal stratification characteristic of nonuniform temperature distribution in the pipe and thermal fatigue such as the low cycle thermal fatigue due to existence of the cycle thermal stress are inevitable, the pipe line system can be destroyed easily and thus affect the normal operation of the power plants. In order to study the pipeline thermal fatigue, the pipeline thermal stress needs to be calculated and therefore the temperature distributions especially the inner wall temperature was needed. The outer wall temperature and working fluid temperature can be obtained with installing measuring tools. The key and difficult point is the estimation of the inner temperature distribution of the pipe. At the same time, in the practical engineering, the pipeline structure with special safety requirements or higher requirements for structural completeness are not allowed to be destroyed by the measuring equipment. Based on the consideration above, this paper presents a method of solving the inverse heat conduction problem, which means the inner temperature distributions can be derived by the outer wall temperature distributions. For the pipe inverse heat conduction problem, this paper applies numerical analysis as the main way. Firstly, the method for transient inverse heat conduction problems applying separation of variables and Duhamel’s theorem is established. As the effects of the random error on the measured outer wall temperature are inevitable, the measured data need to be smoothed before used as an input. The Gram orthogonal polynomial method based on the digital filtering theory is applied in this paper to accomplish the smoothing process. The inverse process is accomplished by using MATLAB programming. Then this method is verified in the experiment with high temperature and high pressure. In order to directly validate the accuracy of the inverse analysis, for the test section, not only the transient outer wall temperature and fluid temperature were measured, but also the time dependent middle layer temperature were measured. Then the middle layer temperature obtained from inverse calculation was compared with the measured data from the experiment. The calculated results show that the accuracy of this method is high. The temperature distributions along the radical direction can be obtained quickly and accurate instantaneous heat load for the structural stress analysis and thermal fatigue analysis can be provided using this method. (CSPE)

Commentary by Dr. Valentin Fuster
2017;():V002T13A008. doi:10.1115/POWER-ICOPE2017-3414.

Ultra low calorific value gas (ULCVG) is hard to be realized by the conventional combustion technology. Most of them are discarded into atmosphere directly, causing the inadvertent waste and serous pollution. Currently, a new type gas turbine with catalytic combustion and rotary regenerator can be used to utilize these fuels and mitigate pollution. Differing from the conventional gas turbine, the chamber and regenerator of the new gas turbine is combined into one component, which is named rotary recuperative type catalytic chamber (RRTCC). The catalytic combustion is applied for RRTCC. The catalytic combustion characteristic of RRTCC is studied using the computational fluid dynamics (CFD). The results indicate that when the inlet velocity is 20 m/s, the methane conversion rate is 90%∼95%, and the corresponding outlet gas temperature is 1030∼1200K. When there is a variation of ±25% in the inlet velocity, the variation of methane conversation rate is −15% and 5% respectively, and the variation of outlet gas temperature is −6% and 2% respectively. Additionally, it is found that the hotspot temperature of combustor wall decreases with the increase of inlet velocity. The lowest value of hotspot temperature is about 1000K, which is higher than the ignition temperature of CH4. Therefore, the existence of hotspot temperature is useful for the catalytic ignition. The temperature distribution on the combustion side exhibits a smoking-pipe-like shape, as well as the recuperative side. The results can provide data reference for RRTCC design.

Commentary by Dr. Valentin Fuster
2017;():V002T13A009. doi:10.1115/POWER-ICOPE2017-3435.

Effective Plume-Chimney Height (EPCH) was a factor engineers used to design and analyse the performance of natural convection in air-cooled heat exchangers particularly in the event of power outage. To date the number of papers in the open literature presenting data on natural convection performance of air-cooled heat exchangers is scarce. The aim of this study is to corroborate the experimental results and theoretical predictions of Effective Plume-Chimney Height (EPCH) using Computational Fluid Dynamics (CFD) in a laboratory-scale air cooled heat exchanger of 457mm × 457mm face area and an industrial-scale test rig of 2.4m × 6.0m face area forced draft air-cooled heat exchanger comprising of a bundle with 4 rows of annular finned tubes in staggered formation operating under natural convection. The CFD software Phoenics 2015 was employed to simulate the electrically-heated air-cooled heat exchanger fitted with a top screen which was built to study the aerodynamics of natural convection of air-cooled heat exchangers. The CFD geometry arrangement and dimensions were schematic in nature, where errors introduced were considered reasonably negligible. The laboratory-scale exchanger model experimental pressure drop data was found to have an insignificant effective plume-chimney height, as predicted by a theoretical equation. It was found that EPCH values calculated from CFD results agree closely to within −0.11m and +0.06m with both experiments and the theoretical prediction, confirming the same conclusion reached in an earlier report. However, for an industrial-scale test rig (ITR) in forced draft mode of large face dimensions the EPCH had been found to be non-negligible in an earlier work. Significant values of theoretical effective plume-chimney height were inserted in the heat transfer and pressure drop simulation that appeared to yield results that agreed with the experimental heat loads. The CFD simulations on the ITR have confirmed the existence of significant effective plume-chimney heights at more than 100 percent of the bundle depth, or the chimney height. The implication is that a solid-walled chimney can appear to have an efficiency of more than 100 per cent, if cold inflow can be prevented or the penetration to the central core hindered. Since the validation of the existence of EPCH by CFD here has used only a set of data from a single source, it is worthwhile to produce more experimental data and analysis to establish the concept for better predictions of air-cooled heat exchanger natural convection performance.

Commentary by Dr. Valentin Fuster
2017;():V002T13A010. doi:10.1115/POWER-ICOPE2017-3447.

Methane hydrate has been paid considerable attention on how to exploit it by efficient and economical methods. A computer modeling approach was used to obtain more detail information during the process of methane hydrate decomposition. A comprehensive Users’ Defined Subroutine (UDS) was used in the FLUENT code to model the methane hydrate dissociation by depressurization. The kinetic model and equilibrium condition were contained in the UDS. The new UDS can model the heat and mass transfer during the decomposition process of methane hydrate. The behavior of the methane hydrate decomposition process in both laboratory-scale simulation and micro channels simulation was investigated in this paper. The laboratory-scale simulation results were compared with ones of the laboratory-scale system studied by Masuda et al. to verify the UDS. Evolutions of methane gas, water and hydrate in the cross micro channels were obtained. The phenomenon of water freezing was predicted by comparing the water temperature and freezing temperature. The results also showed that the dissociation process of gas hydrates as well as the water freezing phenomenon occur not only in the interface between hydrate layer and production zone, but also deep in the hydrate zone.

Commentary by Dr. Valentin Fuster
2017;():V002T13A011. doi:10.1115/POWER-ICOPE2017-3451.

A simplified two dimensional coaxial flow-focusing geometry model was developed for computation domain, and then a volume of fluid based on continuum surface force model was carried out to study the influence of flow parameters on the droplet formation in a coaxial flow-focusing microfluidic device. The effects of flow rates, viscosities and the surface tensions of the three phases which are called the outer fluid, middle fluid and inner fluid on the size and morphology of the droplets were investigated. The results reveal that if the velocity and viscosity of the outer fluid are increased, the sizes of outer and inner droplets become smaller. By increasing the velocity of the middle fluid, the outer droplets become bigger, while the inner droplet size decreases. As the velocity of inner fluid increases, more inner fluid is injected, which leads to an increment with both outer and inner droplet size. Both of the outer and inner droplet sizes become bigger as the outer surface tension coefficients increase, and for the same reason, the increment with the outer surface tension result in an increase with the outer droplet size, but has no effect on the inner droplet size. Similarly, the droplets morphology almost does not vary with the viscosity of both middle and inner fluid. In fact, the principles revealed above are related with the interaction between the viscosity shear stress and the surface tension.

Commentary by Dr. Valentin Fuster
2017;():V002T13A012. doi:10.1115/POWER-ICOPE2017-3527.

The primary objective of the paper is to observe and characterize the flow attributes of gravity-driven dry granular media in vertical cylindrical tubes. Particle packing fractions of ∼60% were the prime focus in the current study as the targeted application is the use of dense particulate media as heat transfer fluids (HTF). Experimental and computational studies were previously conducted to understand the influence of different geometrical parameters on the flow physics [1], [2]. Flowrate, particulate velocity, and packing fraction profiles were studied for different inertial numbers and preliminary observations were made about the corresponding regimes. However, flow characteristics that could have a direct implication on the heat transfer behavior remained unexplored. Hence, the current effort serves as an extension of our previous studies. The three-dimensional computer simulations were conducted by implementing the Discrete Element Method (DEM) for the Lagrangian modelling of particles. Hertz-Mindilin models were used for the soft-particle formulations of inter-particulate contacts. Since the particle contact behavior plays an important role in the conduction heat transfer of these regimes [3], the particle-wall residence times and near-wall packing fractions are studied in the current work. Particle fluctuations, which lead to flow agitation that effect heat transfer [4] are also studied. It was observed that the intermittent nature of the flow resulted in the propagation of wave-like structures in the upstream direction. The characteristics of this phenomenon and its possible influence on the heat transfer physics is also discussed.

Commentary by Dr. Valentin Fuster
2017;():V002T13A013. doi:10.1115/POWER-ICOPE2017-3607.

Air compression is one of the most important processes of air separation. Reliable design, higher performance, low noise, no resonant frequencies in the operating range and economic to manufacture are the goals of compressor design. Although CFD has been widely used in the compressor designs, there are many design considerations need to be addressed during the design. In this paper, the detailed design considerations for compressor configuration, power distribution for each stage, and possible field application issues are discussed in detail. The aerodynamic and structural optimization using CFD and FEA are performed to obtain a high efficiency and wide operating range compressor stage with for robust operation. The new compressor development process addressed in this paper provides the basic design guidance for future new compressor development.

Commentary by Dr. Valentin Fuster
2017;():V002T13A014. doi:10.1115/POWER-ICOPE2017-3789.

Simplified sub-models for coal combustion are widely used in CFD simulation of pulverized coal fired boiler. A large-scale boiler was simulated to investigate the effects of some advanced sub-models. Through calculating several cases using different sub-models, it is known that the predicted ignitability of burners is closely related with the generation of H2. In the case without taking into account H2, the burners show poor ignitability. Using a multi-step mechanism for gas combustion, including char gasification and detailed compositions of volatile largely improve the ignitability of burners. The good ignitability also leads to more heat absorption in boiler and less CO in furnace. CO can be also increased because of the char gasification and detailed compositions of volatiles. Therefore, it is necessary to using multi-step mechanisms for gas combustion, char gasification, and detailed compositions of volatiles to obtain more accurate simulation results.

Commentary by Dr. Valentin Fuster

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