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ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V002T00A001. doi:10.1115/POWER2018-NS2.
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This online compilation of papers from the ASME 2018 Power Conference (POWER2018) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Heat Exchanger Technologies

2018;():V002T07A001. doi:10.1115/POWER2018-7104.

Steam surface condensers may require several different relief devices for safe operation. Atmospheric relief devices are typically utilized for the safe relief of over-pressure on the shell-side (LP steam). This is to protect and prevent steam surface condensers, often including steam turbine exhaust hoods, from exceeding specified design pressures. In addition to shell-side safety devices, relief devices for the tube-side (cooling water), such as water box pressure & vacuum relief, venting and air removal valves, all perform a similar function.

This paper provides a thorough background to all the types of condenser safety relief devices currently available. The latest applicable standards, codes and guidelines for these safety relief devices are reviewed, in conjunction with the current methodology for the correct design and sizing of such devices. Several sample calculations and working examples for the correct sizing of safety devices are provided for reference. The paper includes a review of the relative attributes and considerations for the appropriate selection of each of these types of safety devices, e.g. rupture discs versus atmospheric relief valves for shell-side protection. The paper concludes with a comprehensive review of the latest guidelines for the installation, operation, and maintenance for these safety devices, including guidance on other aspects such as preferred locations, exhaust & vent piping, routine inspection, and testing requirements.

Commentary by Dr. Valentin Fuster
2018;():V002T07A002. doi:10.1115/POWER2018-7148.

Scarcity and restrictions in the use of cooling water has prompted power plant developers to explore multiple sources of cooling mediums to condense turbine exhaust steam in a steam surface condenser. The cooling mediums can have different chemistries dictating selection of different tube and tubesheet materials. The flowrate, inlet temperature and temperature rise for the cooling mediums can be different. Some cooling mediums may not be available during certain times of the year. The resulting steam surface condenser will include multiple smaller tube bundles of various sizes operating with different flowrates and temperatures.

The challenges in designing a condenser that employs multiple sources of cooling medium with different chemistries, flowrates and inlet temperatures are enormous. To ensure reliable operation a number of thermal, hydraulic and mechanical design issues must be carefully evaluated. Determining performance of the entire condenser at off-design conditions with variations in flowrates and inlet temperatures of one or more cooling water streams (or absence thereof) can be complicated.

This paper highlights the major concepts that need to be addressed while designing a steam surface condenser that employs multiple sources of cooling medium to condense the turbine exhaust steam. Critical thermal, hydraulic and mechanical design issues that can impact the performance and reliability of the overall condenser are addressed.

Commentary by Dr. Valentin Fuster
2018;():V002T07A003. doi:10.1115/POWER2018-7348.

In 2014, the Turkey Point Nuclear Power Plant experienced a hole and a steam leak through the shell of the Unit 4, #3B Low Pressure (LP) Feedwater Heater (FWH) near the drains outlet nozzle. Although the location of the hole in the shell was below the centerline of the heater in the Drain Cooler (DC) Zone, a video probe inspection through the drains outlet nozzle revealed that the cause of the leak was actually a hole through the DC top plate, which then allowed the steam to penetrate into the DC zone and erode the shell. The shell was able to be repaired in 2014, however there was not enough time to try to fix the hole in the top plate at that time. During a planned refueling outage in 2017, an access window was cut into the shell and the DC boundary repaired using a custom fit plate to cover the hole and prevent further leakage of steam into the DC zone. The unusual configuration of the DC sealing plates in that area made the repair challenging, but overall the repair was successful and the FWH was able to be returned to service.

Additionally, during the maintenance outage, two leaking tubes were discovered on the periphery of the bundle near one of the Steam Inlet Nozzles. In order to determine the source of the tube failure, a video probe inspection of the shell side of the heater was conducted. It was determined that Foreign Material (FM) was the cause of the failures. By removing the steam inlet piping elbow, the Foreign Material was able to be retrieved and removed from the heater.

Commentary by Dr. Valentin Fuster
2018;():V002T07A004. doi:10.1115/POWER2018-7406.

The traditional organic Rankine cycle (ORC) is operated below critical point. However, the specific heat of the working fluid undergoes tremendous change near the critical point. This can improve the thermal performance of the system due to the enhancement of heat transfer coefficient within the heat exchanger. However, the strong temperature dependence of thermo-physical properties of the working fluid especially at near the critical point requires much more efforts in designing a heat exchanger. Hence, more elaborate calculation involving stepwise integration is needed as far as accuracy is concerned. Therefore the heat exchanger is divided into several segments. The outlet temperatures of the first segment serve as the input parameters for the second segment, and the process is carried out further on. The fluid properties are calculated with the actual bulk temperature of each segment. With increasing number of segments, better resolution of temperature distribution of both heat source and working fluid within the heat exchanger is achieved. In the present study, a plate heat exchanger was numerically examined by using R-245fa as a working fluid at a supercritical condition. The effects of the working pressure and mass flow rate were examined in detail. For all cases in this study, the maximum of the total heat transfer rate was achieved by a working pressure of 3700 kPa, especially close to critical pressure. It is found that at a working pressure of 4000 kPa and mass flow rate ranging from 1 kg/s to 1.75 kg/s, the total heat transfer rate was independent of the mass flow rate.

Commentary by Dr. Valentin Fuster
2018;():V002T07A005. doi:10.1115/POWER2018-7417.

In previous references, no study has been done on the optimization of rotary regenerative air preheaters (RAPHs) used in coal-fired power plants yet. The key structure parameters of RAPH include rotor radius, fluid section angles and matrix layer heights. In this study, work on the multi-objective design optimization of an RAPH was conducted by combing the thermal hydraulic calculation program which is developed to calculate the temperature and the pressure drop and the non-dominated sorting genetic algorithm (NSGA-II). The maximum heat transfer rate and the minimum friction, namely minimum outlet gas temperature and pressure drop, are considered as the conflicting objectives in the multi-optimization. The layer heights, rotor radius, angles of fluid sections and heights of matrix layers are involved in the design variables in the optimization. The optimization includes three cases in which the rotor radius upper limits are 7 m, 8 m and 9 m respectively. Sets of the Pareto-optimal front points were obtained for the different cases. The obtained optimal air-preheaters with larger upper limit of rotor radius would have better Pareto results. The optimum rotor radius is the upper limit value for different design range of rotor radius. The air-preheaters with larger upper design limit of rotor radius would have better Pareto results. In other words, if the upper design limit of rotor radius is too small, all the Pareto points in this case could not satisfy the performance requirements of heat transfer and friction, and the only way is to increase the upper design limit of rotor radius. The ratio of each optimum fluid section angle is determined by the fluid flow rate of each section.

Commentary by Dr. Valentin Fuster
2018;():V002T07A006. doi:10.1115/POWER2018-7563.

Kansas City Power & Light’s (KCP&L) Hawthorn Unit #5 is a coal fired power plant that was originally built in 1969. In 2000, the condenser had new condenser tube bundles installed with Admiralty tubes during the Hawthorn rebuild project. An evaluation of the unit in 2014 identified the potential for the conversion from open to closed cycle cooling. At the same time of the evaluation, multiple failures, causing high silica (derates), required action again in 2016. With improvements in condenser technology, and after evaluation of all the options available — including investment payback — it was decided to rebundle the condenser once again to improve the heat transfer surface area, and to anticipate the (future) requirement for the unit to operate at a higher design pressure on the circulating water side.

The current 1″ OD Admiralty Brass tubes and Muntz metal tube sheets were replaced with 7/8″ OD Titanium tubes and solid Titanium tube sheets. The waterboxes were also replaced with new carbon steel boxes, internally coated with a high solids epoxy lining, together with sacrificial anodes for cathodic protection. The new tube bundles and waterboxes were both designed for a higher design pressure. This was due to the possibility of a future cooling tower installation that would require an increased design pressure for the circulating water system. This Case Study Paper reviews the background to the requirement for new condenser tube bundles and waterboxes, compares the existing and replacement designs, reviews the installation process, and provides a summary of the project lessons learned. It is also intended to be of use to Plants that are considering changing from open to closed cooling cycle.

Commentary by Dr. Valentin Fuster

Plant Performance

2018;():V002T09A001. doi:10.1115/POWER2018-7108.

A method for the speed matching of the second rotor (R2) with equal power for two rotors was proposed to avoid the overload of the second motor under low flow rate and the rapid decrease in pressure-rise and efficiency of R2 under high flow rate. The speed matching of two-stage rotors is proposed and analyzed to improve the stability margin of the counter-rotating fan (CRF). The fan performances during constant speed operating and during the speed matching operating are presented and discussed using experimental research. The results show that, the speed matching of R2 operating decreases the load of R2 under low flow rate and increases the pressure-rise and efficiency of R2 under high flow rate. Thus, the efficient working range and the blocking condition margin are increased. Reducing n1 and increasing n2 under low flow rate can regulate the position of unstable working line leftward without reducing the pressure-rise of the fan. Thus, the stability margin of the CRF is expanded.

Topics: Rotors
Commentary by Dr. Valentin Fuster
2018;():V002T09A002. doi:10.1115/POWER2018-7137.

For over two decades, there has been considerable interest in and research devoted to the use of artificial intelligence (AI) for maximizing the value of power generating assets.

AI may be thought of as application of intelligence in a systematic and rational manner to power plant equipment, components and processes for self-learning and solving complex problems. AI techniques are increasingly finding applications in the power industry in addressing issues related to performance, reliability, availability, maintenance, automation, cybersecurity, workforce, and others.

In the past several years, pace has accelerated in AI techniques, largely stemming from increased speed and power in computing, advances in technology, and utilization of algorithms. The Industrial Internet of Things (IIoT) is rapidly gaining ground by leveraging AI, digital assets and data analytics in managing and optimizing plant operations and performance of power generating assets.

This paper provides an overview of how AI techniques are being utilized to maximize the value of power generating assets and prognosis for future use of AI in the power industry.

Commentary by Dr. Valentin Fuster
2018;():V002T09A003. doi:10.1115/POWER2018-7176.

Increasing the share of intermittent renewable energy sources in a power system poses challenges in terms of increased net load variability and maintaining grid stability and security. Operational flexibility of coal-fired power plants in China has played an essential and promising role in accommodating these nonequilibrium in the power grid. In the study, focusing on condensate throttling coupled with thermal storage tank measures, dynamic simulations of an entire 660 MW supercritical coal-fired power plant were developed via the GSE software. Then, the dynamic characteristics of main thermodynamic parameters and output power were described and compared, and operational flexibility performances of these measures were discussed. It turns out that: when condensate water flowrate decreases, the largest power ramp rate, power capacity, and energy capacity are 12.68 MW min−1, 12.76 MW, and 1084.70 MJ, respectively, and when condensate water flowrate increases, the largest power ramp rate, power capacity, and energy capacity are −5.49 MW min−1, −5.65 MW, and −695.94 MJ, respectively, which means condensate throttling without thermal storage tank measure is more suitable for power-up regulation than power-down regulation, but the shortest duration time is 130 s, which will restrict the operational flexibility regulation. However, coupling with thermal storage tanks, the deaerator water level can maintain a longer time. Meanwhile, at feedwater bypass 60% coupled with thermal storage tank, the largest power ramp rate, power capacity, and energy capacity are −3.62 MW min−1, −3.81 MW, and −897.31 MJ, respectively, and at condensate water bypass 60% coupled with thermal storage tank, the largest power ramp rate, power capacity, and energy capacity are 7.74 MW min−1, 7.88 MW, and 1829.38 MJ, respectively, and these parameter values are greater than condensate water flowrate directly increases or decreases 60%, which means condensate throttling coupling with thermal storage tanks can improve operational flexibility performances. The work is expected to reveal the performance parameters and strategies to provide detailed guidance of using turbine energy storage to improve operational flexibility of the coal-fired power plants.

Commentary by Dr. Valentin Fuster
2018;():V002T09A004. doi:10.1115/POWER2018-7191.

Compressed air and gas are the lifeline of power plants. Deficient or unstable supply of air and gas can result in huge costs and revenue losses of plants. Thus, the accurate determination of performance of the compressors plays important role in prediction of the plant performance. In order to provide reliable and low cost operation for end users, an uncertainty analysis of volume flow, pressure ratio, and power consumption have been investigated and implemented to accurately determine the effect of the compressors to the plant performance. Mathematical models for the uncertainty treatments are proposed based on the ASME test code, and both the systematic errors originating from the measurement instruments and random errors rooted from the raw data are taken into consideration. Moreover, the approach of the uncertainty propagation is also presented through data reduction equations in this paper to evaluate the final performance. Both the rigorous numerical model and sophisticated data acquisition system instrumented in the test facility are employed to conduct the uncertainty analysis for a multi-stage centrifugal compressor. Comprehensive error sources such as ambient conditions, inter-stage pressures and temperatures, and rotational speeds are identified and studied for the final tolerance of the pressure ratio and power consumption of the whole compressor. The test uncertainty results of the compressor can help to improve the power plant field design and demonstrate quality assurance and quality control. Moreover, the tolerance analysis introduced in this paper can be extended to each component of the power plant system to optimize the performance of the whole power plant.

Commentary by Dr. Valentin Fuster
2018;():V002T09A005. doi:10.1115/POWER2018-7246.

Performance improvement of heat recovery systems has huge potential for energy conservation but puzzles researchers due to the nonlinear coupled properties. The traditional modelling approaches focus on individual components, which introduces numerous non-independent variables and further complicates the system optimization. In this contribution, through the thermo-electric analogy method, the equivalent power flow diagram is built based on the system layout, then the corresponding governing equations are derived according to the circuitous philosophy, which reveals the overall transfer and conversion laws of heat. Then, by analyzing the pressure variations of fluids in various components, the flow resistance balance equations are established, which describes the pressure distribution in circulation loop. Moreover, through combining with the coupling relations between the temperatures and pressures of fluids, the inherent physical constraints among operating parameters are revealed by introducing few intermediate variables, which provides convenience for model computation. On this basis, through reasonably matching the mass flow rates of working fluids, the net power generation is maximized under variable working conditions. The optimization results indicate the parameters variation of flue gas significantly impacts the optimal operating state of system, while the empirical constant backpressure operation strategy apparently deviates from the optimums, and the most deviation reaches 8.2%.

Commentary by Dr. Valentin Fuster
2018;():V002T09A006. doi:10.1115/POWER2018-7269.

Optimized operation of gas turbines is discussed for a fleet of eleven LM2500PE engines at a Statoil North Sea offshore field i n Norway. Three engines are generator drivers whilst eight engines are compressor drivers. Several of the compressor drive engines are running at peak load (T5.4 control), hence the production rate is limited by the available power from these engines. The majority of the engines discussed run continuously without redundancy, hence gas turbine uptime is critical for the field’s production and economy.

Two of the compressor drive engines are instrumented with a new static P2 probe in order to have an inlet depression measurement and thus be able to monitor compressor air flow. Compressor air flow has been used as an additional parameter to efficiency, in order to have better analysis methods and better documentation of deterioration rates. The performance gain with online water wash at high water-to-air ratio and upgraded inlet air filter systems, as well as successful operation at longer intervals between offline wash/maintenance stops are thus documented.

An approach for developing a compressor map for mass flow based on field measurements, predictions and deterioration has been performed, as well as correction methods for engine load and ambient conditions in order to be able to compare performance points in various conditions and engine control modes. When monitoring compressor air flow, the Reynolds number effects on axial compressor performance can be analyzed.

Understanding the gas turbine performance deterioration is of vital importance. Trending of its deviation from the engine baseline facilitates load-independent monitoring of the gas turbine’s condition. Instrument resolution and repeatability are key factors in order to have reasonable results on the performance analysis. Based on previous tests and analysis, the compressor air flow rate is the most sensitive parameter for detecting performance deterioration. Unfortunately, gas turbines for offshore operation, are normally not equipped with any air flow measurement devices.

Commentary by Dr. Valentin Fuster
2018;():V002T09A007. doi:10.1115/POWER2018-7276.

High-temperature Gas-cooled Reactor Pebble-bed Module (HTR-PM) is under construction in Shidao Bay, Shandong of China. It is supposed to be the world’s first pebble-bed modular commercial demonstration plant for High Temperature Gas-cooled Reactor (HTGR). In HTR-PM project, water-Rankine cycles have been used in the power conversion system. Meanwhile, supercritical carbon dioxide (S-CO2) Brayton cycle has shown great potentials for future HTGR technology.

Comparing with typical helium Brayton cycle, in S-CO2 cycle where critical properties of carbon dioxide are utilized, compressor work may reduce significantly and thermal efficiency may improve greatly. Furthermore, the general sizes of S-CO2 cycle equipment, such as heat exchanger and turbine, would be orders of magnitude smaller than water-Rankine system at similar power output. Therefore, parameters study of S-CO2 were conducted in this paper for future HTGR.

Firstly, a physical model of S-CO2 Brayton cycles was built and the performance of cycles were analyzed. Secondly, compression ratio, temperature ratio, the inlet temperature of turbine, inlet parameters of compressor, and recuperated effectiveness were discussed as key cycle parameters. For heat capacities of CO2 are significantly different as a function of temperature and pressure, flow recompression was considered. Calculation was based on a split-flow cycle configuration. The split flow ratio was also analyzed. Finally, the parameters of S-CO2 cycle were optimized for HTGR. In conclusion, S-CO2 Brayton cycle will be a good option for future HTGR.

Commentary by Dr. Valentin Fuster
2018;():V002T09A008. doi:10.1115/POWER2018-7375.

In this work, the energy efficiency of the lithium-ion batteries (LIB) with graphite anode and LiFePO4 cathode (G/LFP) at different nominal capacities and charge/discharge rates is studied through multiphysics modeling and computer simulation. After characterizing all the heat generation sources in the cell, the total heat generation in LIBs is calculated and the charge/discharge efficiency plots at different temperatures are obtained. Since G/LFP LIBs have a wide range of applications in passenger and commercial electric vehicles (EVs), the result of this study assist engineer toward more efficient battery pack design.

Commentary by Dr. Valentin Fuster
2018;():V002T09A009. doi:10.1115/POWER2018-7385.

Digital power plant is the theory and method to improve the operating quality of power plant by quantifying, analyzing, controlling and deciding the physical and working objects of power plants in the whole life cycle. Signals and management information of power plants will be digitized, so as to realize information exchange reliably and accurately and large-scale distributed resource sharing based on the network technology. Then optimization decisions and scientific guidance for plant operation will be proposed by intelligent expert system based on the digital resources. Therefore, the foundation of digital power plant is system modeling and performance analysis. However, there are some problems in the process of the modeling performance analysis of digital power plant. For instance, each unit of the system model has different dimensions and different type of mathematical description, and the data or information used for modeling are defined differently and belong to different enterprises, who do not want to share their information. Metamodeling is potential to solve these problems. It defines the specification to describe a unit and the relationship between different elements. Compared with traditional modeling methodologies for thermal systems, metamodeling makes the model more standardized, and the relationship of the model elements is more explicit and better understood by the co-simulation partners. In this paper, the collaborative modeling and simulation platform for digital power plant has been established based on the metamodeling method and the performance of the target plant has been analyzed from different aspects via field data. The metamodeling method consists of three parts: syntax definition, model development and algorithm definition. The result shows that the collaborate modeling and simulation platform can be used to reduce costs, decrease equipment failure rate, and improve plant output, so as to guarantee the safety and increase economics.

Topics: Power stations
Commentary by Dr. Valentin Fuster
2018;():V002T09A010. doi:10.1115/POWER2018-7407.

The evaluation of power plant uprates has traditionally been based on the definition of several ‘typical’ operating modes based on historical data and a — more or less detailed — model of the plant that is compared in current configuration against the same base model including the modifications under consideration. For the economic assessment of the uprate, annual operating hours are allocated to the operating points, and fuel savings and/or additional output predicted by the model due to the modifications are evaluated against the expected investment cost. In this study, the authors demonstrate that this classic approach contains risks in several aspects, in particular:

• the representativeness of the ‘typical’ operating modes,

• the accuracy of the model, and

• the correctness of the assumptions in the allocation of operating hours.

Utilizing the example of an actual uprate of a heat recovery steam generator (HRSG) in a large utility plant of an Austrian steel company, a new approach for an evaluation based on ‘big data’ is presented that uses a full year of operational data in hourly granularity for both, the verification of the accuracy of the plant model, and the evaluation of the effect of the uprate. The authors also provide details of the underlying technologies that allow for both, excellent match of operational data with a fully-fledged heat balance software and fast evaluation of tens of thousands of calculation cases.

Topics: Power stations
Commentary by Dr. Valentin Fuster
2018;():V002T09A011. doi:10.1115/POWER2018-7479.

Statistical analytics, as a data extraction and fault detection strategy, may incorporate segmentation techniques to overcome its underlying limitations and drawbacks. Merging both techniques shall provide a more robust monitoring structure to address the proper identification of normal and abnormal conditions, to improve the extraction of fundamental correlation among variables, and to improve the separation of both main variation and natural variation (noise) subspaces. This additional feature is key to limit the false alarm rate and to optimize the fault detection time when it is implemented on industrial applications.

This paper presents an analysis to determine whether a segmentation approach, as a previous step of detection, enhances the fault detection strategies, specifically the principal component analysis performance. The data segmentation criteria assessed in this study includes two approaches: a) Sources (well) of the transmitted natural gas and b) Promigas’ natural gas pipeline division defined by the Energy and Gas Regulation Commission (CREG in Spanish).

The performance assessment of segmentation criteria was carried out evaluating the false alarm rate and detection time when the natural gas transmission network presents faults of different magnitude. The results show that the implementation of a segmentation criteria provides an advantage in terms of the detection time, but it depends of the fault magnitude and the number of clusters. The detection time is improved by 25% in the case scenario I, when transition zones are considered. On the other hand, the detection time is slightly better with less than 10% in the case scenario II, where the segmentation is geographical.

Commentary by Dr. Valentin Fuster
2018;():V002T09A012. doi:10.1115/POWER2018-7522.

Due to the peculiar physical properties, supercritical carbon dioxide (sCO2) is considered as a promising working fluid in power generation cycles with high reliability, simple structure and great efficiency. Compared with the general thermal systems, the variable properties of sCO2 make the system models obtained by the traditional modelling method more complex. Besides, the pressure distribution in the system will affect the distribution of the fluid properties, the fluid properties influencing the heat transfer process will produce an impact on the temperature distribution which will in turn affect the pressure distribution through the mass flow characteristics of all components. This contribution introduces the entransy-based power flow method to analyze and optimize a recompression sCO2 power generation system under specific boundary conditions. About the heat exchanger, by subdividing the heat transfer area into several segment, the fluid properties in each segment are considered constant. Combining the entransy dissipation thermal resistance of each segment and the energy conservation of each fluid in each segment offers the governing equations for the whole heat transfer process without any intermediate segment temperatures, based on which the power flow diagram of the overall heat transfer process is constructed. Meanwhile, the pressure drops are constrained by the mass flow characteristics of each component, and the inlet and outlet temperatures of compressors and turbines are constrained by the isentropic process constraints and the isentropic efficiencies. Combining the governing equations for the heat exchangers and the constraints for turbine and the compressors, the whole system is modeled by sequential modular method. Based on this newly developed model, applying the genetic algorithm offers the maximum thermal efficiency of the system and the corresponding optimal operating variables, such as the mass flow rate of the working fluid in the cycle, the heat capacity rate of the cold source and the recompression mass fraction under the given heat source. Furthermore, the optimization of the system under different boundary conditions is conducted to study its influence on the optimal mass flow rate of the working fluid, the heat capacity of the cold source and the maximum system thermal efficiency. The results proposes some useful design suggestions to get better performance of the recompression supercritical carbon dioxide power generation system.

Commentary by Dr. Valentin Fuster
2018;():V002T09A013. doi:10.1115/POWER2018-7573.

The increasing share of fluctuating renewable energy sources leads to changing requirements for conventional power plants. The changing characteristics of the residual load requires the conventional fleet to operate with higher load gradients, lower minimum load at improved efficiency levels as well as faster start-ups and provision of ancillary services. Despite the requirements from the electricity market, the value of improving those flexibility parameters is hard to evaluate for power plant operators. In order to quantify the additional benefit that can be achieved by improving flexibility parameters on a certain power plant in a changing market environment, an adjustable load dispatch model has developed for that purpose. Using past electricity market data, the model is validated for typical coal and a typical gas fired power plants by reproducing their operational schedule. In the next step, the model is used to apply parameter changes to the power plants specifications and economic effects are demonstrated. General statements are derived on which flexibility parameter needs to be improved on each power plant type. Furthermore, specific economic evaluations are shown for the reference power plants in order to present the ability of the developed tool to support investment decisions for modernization projects of existing power plants.

Commentary by Dr. Valentin Fuster

Thermal Hydraulics and Computational Fluid Dynamics

2018;():V002T10A001. doi:10.1115/POWER2018-7151.

Erosion wear caused by solid particles is recognized as one of the major concerns for centrifugal pumps. In this paper, a two-way coupled Eulerian-Lagrangian approach is employed to solve the solid-liquid flow in the centrifugal pump. The erosion model developed in the Erosion/Corrosion Research Center (E/CRC), combined with the Grant and Tabakoff particle-wall rebound model, are employed to predict particles behaviors and erosion wear. Three-dimensional transient calculation of the centrifugal pump for solid-liquid flow is carried out to research the performance and erosion wear of centrifugal pump. The influence of concentrations and diameters of solid particles are also investigated. The results show that the existence of solid particles decreases the static pressure and the velocity of liquid. The frequency of impingement and rebound will increase with the increase of the concentrations of solid particles. The middle of the hub and the trailing edge of blades pressure side are the most serious erosion regions.

Commentary by Dr. Valentin Fuster
2018;():V002T10A002. doi:10.1115/POWER2018-7153.

To enhance the efficiency and stable operation, the unsteady pressure fluctuations in a centrifugal pump and the radial force on an impeller are investigated for three different vaned diffuser outlet diameters. The steady-state hydrodynamic performance of the centrifugal pump with three different vaned diffuser outlet diameters was experimentally measured. Numerical simulations were used to obtain the hydrodynamic performance of the experimental centrifugal pump based on the Reynolds-averaged Navier-Stokes (RANS) and turbulence models. The numerical results of the hydrodynamic performance were in agreement with the experimental data. The accuracy of the utilized numerical approach was demonstrated. The unsteady flow characteristics of the centrifugal pump were numerically studied. With increasing diffuser vane outlet diameter, the flow field within the volute became more non-uniform, and the pressure fluctuation was more drastic. Moreover, because of the influence of the non-uniform flow field and the pressure fluctuation, the radial force on the impeller increased.

Commentary by Dr. Valentin Fuster
2018;():V002T10A003. doi:10.1115/POWER2018-7167.

Acid is often injected into porous media to dissolve rock material and enhance flow capability of the rock. Most simulation studies on the propagation of the dissolution front are based on constant injection rate (CIR). Therefore, the objective of this work is to develop numerical model to study acid dissolution front under constant injection pressure (CIP) and also incorporate the effect of fluid temperature on acid–rock interaction. Commercial computational Fluid Dynamics (CFD) software (ANSYS Fluent) is used to solve three-dimensional acid-rock interaction model in cylindrical coordinates. In this work, correlated porosity and permeability distributions are generated. Effect of heat transfer between the injected fluid and the formation on fluid properties and surface reaction rate are accounted for in the model. The study confirmed that all types of acid dissolution patterns exist during constant injection pressure. CIP technique requires lower acid volume to achieve breakthrough in the conical and branched dissolution regimes, than that is required for CIR technique. In dominant wormhole pattern, both techniques require nearly the same acid volume to breakthrough. Thermal interaction between the injected fluid and the formation leads to change of surface reaction rate and physical properties of the fluid, such as viscosity, density, and diffusivity. Injection of cold fluid into heated formation leads to a higher wormhole density as found from experimental studies due to retardation of surface reaction rate. The model developed in this work accurately captures different dissolution patterns. The model shows that the acid volume required for wormhole breakthrough depends on the inlet conditions (CIR or CIP) and the thermal interaction between the injected fluid and formation. This modeling study attempts to answer the critical questions pertaining to the effect of temperature and injection conditions on acid-rock interaction.

Commentary by Dr. Valentin Fuster
2018;():V002T10A004. doi:10.1115/POWER2018-7263.

Coupling of statistical properties from atomistic simulations to continuum is essential to model many multi-scale phenomena. Often, the system under consideration will be homogeneous in two-dimensions (2-D). But due to the existing coupling methods, the property estimation takes place in three-dimensions (3-D) and then averaged to 2-D, which is computationally expensive due to the 3-D convolutions. A direct 2-D pressure or stress estimation model is lacking in literature. In this work, we develop a direct 2-D pressure field estimation method which is much faster than 3-D methods without losing accuracy. The method is validated with MD simulations on two systems: a liquid film and a cylindrical drop of argon suspended in surrounding vapor. This formulation will enable the study of 2-D fundamental phenomena like passive liquid flows in microlayer, as well as facilitate the coupling of atomistic and continuum simulations with reduced computational cost.

Commentary by Dr. Valentin Fuster
2018;():V002T10A005. doi:10.1115/POWER2018-7366.

In this paper, a novel nodalized reduced order model (NROM) has been developed to analyze the linear stability in a heated channel using supercritical water (SCW) as a coolant. The presented reduced order model is developed based on the two-phase flow system approach. The model is much simplified, which reduced the requirement of computational efforts and resources. In the heated channel, the SCW’s density shows a dramatic downfall near the pseudo-critical temperature, based on which it has been divided into n number of nodes. The one-dimension partial differentiation conservation equations of energy, mass and momentum are used and have been linearized by a small perturbation applied on its steady-state solution. These PDEs are converted into the corresponding time-dependent, nonlinear ordinary differential equations (ODEs) by using weighted residual method applied under some appropriate assumptions and approximations. These sets of ODEs (n+1 equations) are then solved analytically by using a state space approach to capture the stability boundary (SB) in terms of trans-pseudo-critical phase change number (Ntpc), pseudo-subcooling number (Nspc) by applying a constant external pressure drop (ΔPtpc) condition across the channel. The NROM results are found to be in good agreement with the methodology and have been verified by numerical simulation. To extend this as a nonlinear stability analysis, the different types of the Hopf Bifurcation regime are also reported.

Commentary by Dr. Valentin Fuster
2018;():V002T10A006. doi:10.1115/POWER2018-7379.

Experimental study of a swirl flow using 3-D Stereo-PIV (Particle Image Velocimetry) that models a gas turbine blade internal cooling configuration is presented. The work is intended to provide an understanding of the advancements of swirl cooling flow methodology utilizing 3-D Stereo-PIV. The study aims at determining the critical swirl number that has the potential to deliver the maximum heat transfer results. In the swirl cooling flow methodology, cooling air is routed to the turbine blades where it passes through the blade’s internal passages lowering the temperature. An experimental setup with seven discrete tangential jets at three different Reynolds numbers is designed to allow detail measurements of the flow. To provide the particles for velocity measurements an oil particle seeder (LAVision) is used. The circular chamber is made of clear acrylic to allow visualization of the flow phenomena. Data is post-processed in DaVis, velocity calculations are conducted in MATLAB, and TechPlot is used for data visualization. This investigation focuses on the continuous swirl flow that must be maintained via continuous injection of tangential flow, where swirl flow is generated with seven inlets and decays with downstream distance. It was also determined that the critical swirl number, Sn, depends greatly on the location and size of the tangential slots.

Commentary by Dr. Valentin Fuster
2018;():V002T10A007. doi:10.1115/POWER2018-7434.

The influence of mesh resolution, the abilities of various eddy viscosity models, and near wall flow treatments on predicting the flow coefficients of poppet valves, operating in water are investigated in this paper. The computational fluid dynamics (CFD) models are solved using STAR-CCM+ 12.04. Grid-convergence is studied first, followed by quantitative assessments of the ability of standard k-ε model, realizable k-ε model, EB k-ε model, Lag EB k-ε model, V2F model and k-ω-sst model, and different wall treatments, such as high y+ wall treatment, two-layer wall treatment and all y+ wall treatment, embedded in the solver. The flow discharge coefficient (Cq) of poppet valves predicted by CFD models are compared to physical measurements. It was demonstrated in the study that grid resolutions normal to the wall and mesh quality are key factors. Advanced near wall flow treatments produce similar or worse predictions when using the standard k-ε model, and the effects of the near wall flow treatments are marginal for the realizable k-ε model. The ability of turbulence models varies greatly in predicting flow in different valves and lift levels. The realizable k-ε model is the optimal option for the considered valve flows giving an acceptable error within ±5%.

Commentary by Dr. Valentin Fuster
2018;():V002T10A008. doi:10.1115/POWER2018-7510.

Static, or motionless, mixers are widely used in applications that involve chemical reactions, heat transfer, blending of fluids, or a combination of these. Within those applications, mixing can affect various parameters such as heat or mass transfer rates, process operating time, cost, safety, and product quality. Therefore, it is crucial to assess the performance of static mixers. In general, their performance is evaluated based on their ability to carry out mixing while minimizing energy loss. To accomplish this, a novel mixing parameter, the M number, is proposed and evaluated. The M number is a unitless parameter that describes the effects of the mixer using entropy change and pressure drop. The parameter is compared to another method of mixing evaluation that relies on Covariance (CoV) change across the mixer. Computational Fluid Dynamics (CFD) is executed using both methods to evaluate two static mixers and compare the results of each method. Potential applications for the M number are discussed and its limitations are noted.

Commentary by Dr. Valentin Fuster
2018;():V002T10A009. doi:10.1115/POWER2018-7544.

Multiphase flows frequently occur in many important engineering and scientific applications, but modeling of such flows is a rather challenging task due to complex interfacial dynamics between different phases, let alone if the flow is oscillating in the porous media. Using humid air as the working fluid in the thermoacoustic refrigerator is one of the research focus to improve the thermoacoustic performance, but the corresponding effect is the condensation of humid air in the thermal stack. Due to the small sized spacing of thermal stack and the need to explore the detailed condensation process in oscillating flow, a mesoscale numerical approach need to be developed. Over the decades, several types of Lattice Boltzmann (LB) models for multiphase flows have been developed under different physical pictures, for example the color-gradient model, the Shan-Chen model, the nonideal pressure tensor model and the HSD model. In the current study, a pseudopotential Multiple-Relaxation-Time (MRT) LBM simulation was utilized to simulate the incompressible oscillating flow and condensation in parallel plates. In the initial stage of condensation, the oscillating flow benefits to accumulate the saturated vapor at the exit regions, and the velocity vector of saturated vapor clearly showed the flow over the droplets. It was also concluded that if the condensate can be removed out from the parallel plates, the oscillating flow and condensation will continuously feed the cold surface to form more water droplets. The effect of wettability to the condensation was discussed, and it turned out that by increasing the wettability, the saturated water vapor was easier to condense on the cold walls, and the distance between each pair of droplets was also strongly affected by the wettability. It’s expected that this study can be used to optimize and redesign the structure of thermal stack in order to produce more condensed water, also this multiphase approach can be extended to more complicated 3D structures.

Commentary by Dr. Valentin Fuster

Water Management for Power Systems

2018;():V002T11A001. doi:10.1115/POWER2018-7281.

Surface tension and solution evaporation of aqueous solutions of sodium lauryl sulfate (SLS), ECOSURF™ EH-14, and ECOSURF™ SA-9 under natural convection is examined through experimental methods. SLS is an anionic surfactant while EH-14 and SA-9 are environmentally-friendly nonionic surfactants.

Surfactants are known to affect evaporation performance of solutions and are studied in relation to water loss prevention and heat dissipation. Surfactants could be useful under drought conditions which present challenges to water management on a yearly basis in arid areas of the world. Recent water scarcity in the greater Los Angeles area, south eastern Africa nations, eastern Australia and eastern Mediterranean countries has high cost of water loss by evaporation. Surfactants are studied as a potential method of suppressing evaporation in water reservoirs. Surfactants are also studied as performance enhancers for the working fluid of heat dissipation devices, such as pulsating heat pipes used for electronics cooling. Some surfactants have been shown to lower thermal resistances and friction pressure in such devices and thereby increase their efficiency.

The static surface tensions of the aqueous-surfactant solutions are measured with surface tensiometer using Wilhelmy plate method. The surfactants are shown to lower surface tension significantly from pure water. The surface tension values found at the Critical Micelle Concentration are 33.8 mN/m for SLS, 30.3 mN/m for EH-14, and 30.0 mN/m for SA-9. All three surfactants reduced natural convection water loss over 5 days with SLS showing the greatest effect on evaporation rates. The maximum evaporation reduction by each surfactant from distilled water with no surfactants after 5 days is 26.1% for SLS, 20.8% for EH-14, and 18.4% for SA-9.

Commentary by Dr. Valentin Fuster
2018;():V002T11A002. doi:10.1115/POWER2018-7307.

Power and freshwater demand are increasing as populations around the world keep growing. Due to the environmental impact of using fossil fuels and limited resources, using solar thermal in desalination application is a valuable option. In this paper, an innovative new design of low temperature multi-effect desalination coupled with mechanical vapor compression (LT-MED-MVC) powered by supercritical organic Rankine cycle utilizing a low-grade solar heat source using evacuated tube collectors is analyzed. The proposed design has the potential to desalinate water of high salt concentrations or brine with high salinity more than 100,000 ppm or effluent streams from a power plant with low energy consumption and high efficiency when compared to the previously discussed systems. The performance of the LT-MED-MVC was found to be better than similar systems found in the literature. The specific power consumption for MVC is lower than 4 kWh/m3 for seawater feed salinity of 100,000 ppm, 14 forward feed effects, and a recovery rate of 50%. The overall system efficiency is about 14%. The impact of increasing the number of effects, motive steam temperature, pressure of supercritical-ORC and salt concentration on the specific power consumption, solar collector area, and the system efficiency are also analyzed.

Commentary by Dr. Valentin Fuster
2018;():V002T11A003. doi:10.1115/POWER2018-7318.

A supplemental main steam condenser cooling system is under development, which utilizes a phase change material (PCM). This PCM rejects heat to the cool atmosphere at night until it is fully frozen. The frozen PCM is available for condenser cooling during peak daytime electric demand. Three calcium chloride hexahydrate (CaCl2·6H2O)-based PCMs were selected for development after being characterized using differential scanning calorimetry (DSC). Additives to minimize supercooling and phase separation have demonstrated good performance after long and short-term thermal cycling. Corrosion testing under both isothermal and cycling conditions was conducted to determine long-term compatibility between several common metals and the selected PCMs. Several metals were demonstrated to have acceptably low corrosion rates for long-term operation, despite continual immersion in the selected hydrated salts. A system optimization model was developed, which utilizes a 3D modeling approach called the Layered Thermal Resistance (LTR) model. This model efficiently models the nonlinear, transient solidification process by applying analytic equations to layers of PCM. Good agreement was found between this model and more traditional computational fluid dynamics (CFD) modeling. Next phases of the work includes prototype testing and a techno-economic analysis of the technology.

Commentary by Dr. Valentin Fuster
2018;():V002T11A004. doi:10.1115/POWER2018-7410.

Traditionally, water is used in thermal power plant for heat rejection processes such as in the steam condenser for use in a Rankine cycle. Typically, research has shown that approximately 2 litres of water are required to generate 1 kWh of electricity on a wet-cooling system; which on a bigger scale could translated to more than 11000000 m3 per year of make-up water for a 600 MWe coal-fired plant. The ever-increasing cost of water resources as well as the water resource scarcity have paved a path to dry-cooling systems which alternatively provide a significant cooling potential. However, dry-cooling systems performance are generally driven by the atmospheric conditions which at time do not meet the desired cooling temperatures resulting in significant drop in their performance. Recent developments in cooling technology suggest that hybrid systems (dry-wet) be used to insure good and manageable performances while maintaining the cost of operation at admissible range. In light of the recent draught experienced in South Africa, attention was drawn to evaluation of deluged systems performance as well as water consumption to increase the public awareness in the field. In this study, a deluged bundle was used to experimentally determine the cooling performance characteristic as well as water consumption for performance management. The above is then considered on a bigger scale to in order to open floor for further discussion on future strategies in term of the South African policy on water usage.

Commentary by Dr. Valentin Fuster

Student Competition

2018;():V002T12A001. doi:10.1115/POWER2018-7140.

In recent years, there has been a growing demand for high-power-density direct-drive generators in the wind industry owing to their high reliability, torque per unit volume, and conversion efficiencies. However, direct-drive wind turbine generators are very large, low-speed electric machines, which pose remarkable design and manufacturing issues that challenge their upscaling potential and cost of implementation. With air-gap tolerance as the main design driver, the need for high stiffness shifts the focus toward support-structure design that forms a significant portion of the generator’s total mass. Existing manufacturing processes allow the use of segmented-steel-weldment disk or spoke-arm assemblies that yield stiffer structures per unit mass but tend to be heavier and more expensive to build. As a result, there is a need for a transformative approach to realize lightweight designs that can also facilitate series production at competitive costs. Inspired by recent developments in metal additive manufacturing (AM), we explore a new freedom in the structural design space with a high potential for weight savings in direct-drive generators. This includes the feasibility of using nonconventional complex geometries, such as lattice-based structures as structurally efficient options. Powder-binder jetting of a sand-cast mold was identified as the most feasible AM technology to produce large-scale generator rotor structures with complex geometry. A parametric optimization study was performed and optimized results within deformation and mass constraints were found for each design. The response to the maximum Maxwell stress due to unbalanced magnetic pull was also explored for each design. Further, a topology optimization was applied for each parameter-optimized design to validate results and provide insights into further mass reduction. These novel designs catered for AM are compared in both deflection and mass to conventional rotor designs using NREL’s systems engineering design tool, GeneratorSE. The optimized lattice design with a U-beam truss resulted in a 24% reduction in structural mass of the rotor and 60% reduction in radial deflection. It is demonstrated that additive manufacturing shifts the focus from manufacturability constraints toward lower mass.

Commentary by Dr. Valentin Fuster
2018;():V002T12A002. doi:10.1115/POWER2018-7175.

Direct use of propane and butane in Solid Oxide Fuel Cells (SOFCs) is desirable due to the availability of the fuel source, but is challenging due to carbon coking, particularly on the commercially available Ni+YSZ anode. A novel dual chamber Flame-assisted Fuel Cell (FFC) configuration with micro-tubular SOFCs (mT-SOFCs) is proposed for direct use of higher hydrocarbon fuels. Combustion exhaust for propane and butane fuels is analyzed experimentally and compared with chemical equilibrium. mT-SOFC polarization and power density testing in the FFC configuration with propane and butane fuels is discussed. Peak power and electrical efficiency conditions are assessed by varying the fuel-rich combustion equivalence ratio and flow rate. Carbon deposition and soot formation on the Ni+YSZ anode is investigated with a scanning electron microscope. The results indicate that reasonable power density (∼289 mW.cm−2) can be achieved while limiting soot formation in the flame and carbon deposition on the anode. Electrical efficiency based on the higher heating value of the fuels is analyzed and future research is recommended. Possible applications of the technology include small scale power generation, cogeneration and combined cycle power plants.

Commentary by Dr. Valentin Fuster
2018;():V002T12A003. doi:10.1115/POWER2018-7193.

This paper describes a quantitative methodology to estimate the probability of blade failure modes resulting from typical wear mechanisms in nuclear turbines, which can be used to optimize maintenance. The approach used to model time and spatial dependence of wear mechanisms that affect blades involves the coupling of a Static Bayesian Network to a Dynamic Bayesian Network. This prototype model has been designed to use conditional and time dependent Weibull-like failure rates that can be computed from reliability data bases (failure times and modes, associated causes, row and blade part that failed) to quantify Markov matrixes contained within dynamic nodes.

The model can be used to make inferences such as the most probable causes of failure in a row and blade part, and visualize the probability as a function of time. It can be also used to determine the riskier location given evidence such as failure mode or the wear mechanisms involved. Also, maintenance tasks acting over time dependent failure functions have been implemented to exemplify the effect of perfect and three kinds of imperfect actions and how they affect the mechanisms and failure mode evolution, given the conditional dependences among them.

Commentary by Dr. Valentin Fuster
2018;():V002T12A004. doi:10.1115/POWER2018-7198.

Cuba’s national pride comes from their projected autonomy as a communist country, although they have been dependent on other countries to supply them with resources since the revolution. However, Cuba has a high capacity for various forms of renewable energy. This study analyzes the impacts of Cuba’s decline in petroleum use and the rise of renewable energy. There is a lack of primary research on Cuba’s energy infrastructure because of government censorship and availability of reliable data, so this study utilizes accounts from Cuban citizens as well as first-hand observations of the country. Research was conducted through interviews, observations, and written accounts of life in Cuba. The decline of Cuba’s use of petroleum has led to an emphasis on sustainability, affecting people’s lifestyles and the economy. The inability to produce enough electricity has created an inequality between those who are involved in tourist industries and those who are not. However, the dawn of renewable energy is helping to close that gap while protecting Cuba’s energy independence and preventing another Special Period.

Commentary by Dr. Valentin Fuster
2018;():V002T12A005. doi:10.1115/POWER2018-7204.

As a promising approach for sustainable development, the distributed energy system receives increasing attention worldwide and has become a key topic explored by researchers in the areas of building energy systems and smart grid. In line with this research trend, this paper presents a case study of designing an integrated distributed energy system including photovoltaics (PV), combined cooling heating and power (CCHP) and electric and thermal energy storage for commercial buildings (i.e., a hospital and a large hotel). The subsystems are modeled individually and integrated based on a proposed control strategy to meet the electric and thermal energy demand of a building. A multi-objective particle swarm optimization (PSO) is performed to determine the optimal size of each subsystem with objectives to minimize carbon dioxide emissions and payback period. The results demonstrate that the proposed method can be effectively utilized to obtain an optimized design of distributed energy systems that can minimize environmental and economic impacts for different buildings.

Commentary by Dr. Valentin Fuster
2018;():V002T12A006. doi:10.1115/POWER2018-7231.

Augmentation in heat transfer is very useful for various engineering and scientific applications due to the call for energy and cost saving. The heat transfer and pressure drop characteristics in annuli of double pipe heat exchanger using helical and plain surface ring turbulators are studied through experimental investigation. The effect of helical surface ring turbulators and plain surface ring turbulators are studied for varied range of pitch ratio (4.0–6.4), Reynolds Number (3,000–10,500) and two different diameter ratios (0.475 and 0.54). Water (hot fluid) flows in the inner tube and air (cold fluid) flows through the annulus. The tests are conducted for air with uniform wall temperature condition. The heat exchanger with least pitch and least diameter ratio is found to exhibit the highest Nusselt number and pressure drop. Results indicate that maximum enhancement is obtained for smallest diameter ratio 0.475 and pitch ratio 4.0 at lowest Reynolds Number. Also, thermal performance factor is always greater than unity for the DPHE using helical surface turbulators. Correlations have been developed for enhancement in Nusselt number and friction factor; show the good agreement with experimental test data within test range.

Commentary by Dr. Valentin Fuster
2018;():V002T12A007. doi:10.1115/POWER2018-7310.

Wind energy and especially offshore wind energy faces an uphill battle in the United States to become a mainstream source of energy generation due to its high price relative to fossil fuels. The wind industry is looking for methods to reduce the costs of energy production by improving the efficiency of wind turbines and reducing their operation and maintenance costs. Correction of yaw error is one way to lower the price of wind energy. Yaw error is the angle between the turbine’s central axis in horizontal plane and the wind flow direction. LIDAR devices are used to correct yaw error, however they are expensive. Therefore, there is a need to develop a return on investment model (ROI) to calculate the cost trade-offs of using such systems. This work reviews how yaw error affects the performance and maintenance costs of wind turbines, discuss the development of an ROI model and provide a case study with two scenarios where LIDAR is used to correct the yaw error of an onshore and an offshore wind farm.

Topics: Errors , Wind turbines , Yaw
Commentary by Dr. Valentin Fuster
2018;():V002T12A008. doi:10.1115/POWER2018-7319.

This study evaluates potential aggregate effects of net-zero energy building (NZEB) implementations on the electrical grid in simulation-based analysis. Many studies have been conducted on how effective NZEB designs can be achieved, however the potential impact of NZEBs have not been explored sufficiently. As significant penetration of NZEBs occurs, the aggregated electricity demand profile of the buildings on the electrical grid would experience dramatic changes. To estimate the impact of NZEBs on the electrical grid, a simulation-based study of an office building with a grid-tied PV power generation system is conducted. This study assumes that net-metering is available for NZEBs such that the excess on-site PV generation can be fed to the electrical grid. The impact of electrical energy storage (EES) within NZEBs on the electrical grid is also considered in this study. Finally, construction weighting factors of the office building type in U.S. climate zones are used to estimate the number of national office buildings. In order to consider the adoption of NZEBs in the future, this study examines scenarios with 20%, 50%, and 100% of the U.S. office building stock are composed of NZEBs. Results show that annual electricity consumption of simulated office buildings in U.S. climate locations includes the range of around 85 kWh/m2-year to 118 kWh/m2-year. Each simulated office building employs around 242 kWp to 387 kWp of maximum power outputs in the installation of on-site PV power systems to enable NZEB balances. On a national scale, the daily on-site PV power generation within NZEBs can cover around 50% to 110% of total daily electricity used in office buildings depending on weather conditions. The peak difference of U.S. electricity demand typically occurs when solar radiation is at its highest. The peak differences from the actual U.S. electricity demand on the representative summer day show 9.8%, 4.9%, and 2.0% at 12 p.m. for 100%, 50%, and 20% of the U.S. NZEB stocks, respectively. Using EES within NZEBs, the peak differences are reduced and shifted from noon to the beginning of the day, including 7.7%, 3.9%, and 1.5% for each percentage U.S. NZEB stock. NZEBs tend to create the significant curtailment of the U.S. electricity demand profile, typically during the middle of the winter day. The percentage differences at a peak point (12 p.m.) are 8.3%, 4.2%, and 1.7% for 100%, 50%, and 20% of the U.S. NZEB stocks, respectively. However, using EES on the representative winter day can flatten curtailed electricity demand curves by shifting the peak difference point to the beginning and the late afternoon of the day. The shifted peak differences show 7.4%, 3.7%, and 1.5% at 9 a.m. for three U.S. NZEB stock scenarios, respectively.

Commentary by Dr. Valentin Fuster
2018;():V002T12A009. doi:10.1115/POWER2018-7390.

Marine and hydrokinetic (MHK) energy resources with advantages such as predictability and less variability compared to other forms of renewable energies, have been drawing more interest in recent years. One important phase before commercialization of new MHK technologies is to conduct experimental testing and evaluate their performance in a real environment. In this work, a numerical computational fluid dynamics (CFD) method is used to study the fluid flow behavior within a designed water flume for MHK energy technologies. The water flume design parameters were given by the team collaborators at National Renewable Energy Laboratory (NREL) and Colorado School of Mines. The results from this simulation showed the flow characteristics within the test-section of the proposed water flume design. These results can be used for the follow on phases of this research that includes testing scaled MHK prototypes at different flow rates as well as optimizing either the water flume design to obtain more realistic flow characteristics within the test section or the MHK devices to obtain higher performance metrics at lower cost.

Commentary by Dr. Valentin Fuster
2018;():V002T12A010. doi:10.1115/POWER2018-7396.

This paper addresses modeling, design, and experimental assessment of a Gamma type low-temperature differential free-piston Stirling engine. The most advanced third-order design analysis method is used to model, simulate and optimize the engine. Moreover, the paper provides an experimental parametric investigation of engine physical parameters and operating conditions on the engine performance. The experimental test results are presented for a model validation, which shows about a 5% to 10% difference in the simulation results. The aim of this study is to design a Stirling engine capable of harvesting low-temperature waste heat effectively and economically and convert it to power. The engine prototype is designed to increase the engine performance by eliminating the main losses occurred in conventional Kinematic engines. Thus, elastic diaphragm pistons are used in this prototype to eliminate the surface friction of the moving parts, the use of lubricant, and to provide appropriate seals. In addition, flat plate heat exchangers, linear flexure bearing, a stainless-steel regenerator and a polyurethane displacer are outlined as the main components of the engine. Experiments successfully confirm the design models for output power and efficiency. Furthermore, it is revealed that the displacer-to-piston natural frequency ratio is an important design point for free-piston Stirling engines and should be addressed in the design for optimum power output.

Commentary by Dr. Valentin Fuster
2018;():V002T12A011. doi:10.1115/POWER2018-7495.

Human error accounts for about 60% of the annual power loss due to maintenance incidents in the fossil power industry. The International Atomic Energy Agency reports that 80\% of industrial accidents in the nuclear industry can be attributed to human error and 20\% to equipment failure. The Personal Augmented Reality Reference System (PARRS) is a suite of computer-mediated reality applications that looks to minimize human error by digitizing manual procedures and providing real-time monitoring of hazards present in an environment. Our mission is to be able to provide critical feedback to inform personnel in real-time and protect them from avoidable hazards. PARRS aims to minimize human error and increase worker productivity by bringing innovation to safety and procedural compliance by leveraging technologies such as augmented reality, LiDAR, computer machine learning and particulate mapping using remote systems.

Commentary by Dr. Valentin Fuster
2018;():V002T12A012. doi:10.1115/POWER2018-7514.

Military systems greatly depend on the availability of energy. This energy comes mostly in the form of burning fuel in order to produce mechanical work or producing electricity. The ability to extract the most out of these systems aligns with the current focus of energy efficiency, not only in the military, but in society at large. In this research, an infrared camera was used to create an infrared map to infer temperature differences on a gasoline-powered generator at steady state operations. These temperature differences were inputted into an experimental phase during which a digitally-controlled hot plate, water block, variable resistor, and digital acquisitions system were used to measure current output from a single TEG for loads of 1, 10, and 100 Ω, respectively. Data were analyzed and the correlation coefficients determined. These coefficients were modeled a single module and then various array configurations for TEGs in COMSOL. Using the findings, a single commercial 56 mm by 56 mm Be2Te3 TEG can yield 0.72 W of power. Simple calculations yield 72 W of power when 100 modules are joined in 10 sets coupled in parallel with each set containing 10 modules in coupled in series. This would require 560 mm by 560 mm or approximately 2 ft. by 2 ft. of system space to be covered.

Commentary by Dr. Valentin Fuster
2018;():V002T12A013. doi:10.1115/POWER2018-7515.

The U.S. Department of Energy (DOE) has determined that solar power coupled desalination could be the next step in helping to resolve the water-energy nexus. For many decades, integration of concentrating solar power (CSP) electricity generation for combined power and water production has typically utilized the conventional method of steam Rankine cycles. Current research focuses on an enticing innovative method which combines CSP with Brayton cycles and uses supercritical CO2 (sCO2) as a working fluid, allowing for a broader temperature range. This techno-economic study analyzes the power and possible freshwater generation of each cycle and provides a comparison of the techno-economic advantages associated with each technology when applied to desalination processes. The results of this study suggest that recompression-closed Brayton (RCBR) cycle is likely to have the most significant impact in decreasing the levelized cost of electricity (LCOE), almost halving it from combining CSP with the traditional Rankine cycle. Also, to minimize levelized cost of water (LCOW) a smaller scale desalination facility which utilizes multi-effect distillation with thermal vapor compression (MED/TVC) instead of multi-stage flash distillation (MSF) is most applicable. Although the lowest LCOE values are for wet-cooled RCBR with MSF and MED/TVC, in areas where freshwater generation is crucial to be optimized there is only a 0.04 cents/kWh increase for dry-cooled RCBR with MED/TVC to a cost of 9.8 cents/kWh. This suggests the best candidate for optimizing freshwater generation while minimizing both LCOW and LCOE is dry-cooled RCBR with MED/TVC desalination.

Commentary by Dr. Valentin Fuster
2018;():V002T12A014. doi:10.1115/POWER2018-7516.

Concentrating solar power (CSP) plants are one of the main technologies harvesting solar energy indirectly. In CSP systems, solar radiant light is concentrated into a focal receiver, where heat transfer fluid (HTF) as the energy carrier absorbs solar radiation. Thermal energy storage (TES) is the key method to expand operational time of CSP plants. Consequently, thermo-physical properties of the HTF is an important factor in transferring thermal energy. One of the promising chemicals for this purpose is a mixture of molten salts with stable properties at elevated temperatures. However, low thermal properties of molten salts, such as specific heat capacity (cp) around 1.5 kJ/kg°C, constrain thermal performance of CSP systems. Recently, many studies have been conducted to overcome this shortcoming, by adding minute concentration of nanoparticles. In this work, the selected molten salt eutectic is a mixture of LiNO3–NaNO3 by composition of 54:46 mol. % plus dispersing Silicon Dioxide (SiO2) nanoparticles with 10nm particle size. The results from the measured specific heat capacity by modulated differential scanning calorimeter (MDSC) shows a 9% cp enhancement. Moreover, the viscosity of the mixture is measured by a rheometer and the results show that the viscosity of molten salt samples increases by 27% and this may result in increasing the pumping energy of the HTF. Consequently, overall thermal performance of the selected mixture is investigated by figure of merit (FOM) analysis. The interesting results show an enhancement of the thermal storage of this mixture disregard with the viscosity increase effect.

Commentary by Dr. Valentin Fuster
2018;():V002T12A015. doi:10.1115/POWER2018-7547.

Population explosion and rapid industrialization demands increased power production, whereas, environmental concerns are also an issue. The need of time is to develop eco-friendly technology which exploits renewable energy resources. Water is one of the most promising and cheap renewable energy resource. The gross approximate potential of hydro is 128 PW h per year while technically exploitable potential is only 26 PW h per year. Darrieus water turbine (DWT) is like Darrieus wind turbine but it operates in water instead of air. It is an emerging technology for the low head regions. This article focuses on the performance of DWT under different designing parameters i.e. different blade profiles, pitch angle, azimuth angles, tip speed ratio and effect of ducts. It will also focus on the different numerical models used for its simulation. Finally, based on the study an optimum model is selected for practical operations.

Commentary by Dr. Valentin Fuster

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