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Advanced Energy Systems

2003;():3-9. doi:10.1115/IMECE2003-42300.

The feasibility of a compact, reliable, low-cost, and efficient cryocooler capable of delivering 1 Watt of cooling at 10K using less than 1kW of input power has been demonstrated analytically. The technology promises to provide highly efficient refrigeration for temperatures as low as 4K, and to be particularly beneficial for temperatures below 30K. The technical approach is to apply a high-efficiency thermodynamic cycle to a compact and reliable small-scale system by implementing a modern microprocessor into a mechanically innovative machine. The innovations of the design include “floating” piston expanders and electro-magnetic “smart” valves, which eliminate the need for mechanical linkages and reduce the input power, size, and weight of the cryocooler in an affordable modular design. It is predicted that a three-stage cryocooler operating with 15-bar helium could produce 2W of cooling at 10K while requiring less than 1kW of compressor power. A laboratory prototype is currently under development, with testing to be completed in the Fall of 2003.

Commentary by Dr. Valentin Fuster
2003;():11-18. doi:10.1115/IMECE2003-42375.

Thermoacoustic refrigeration employs inert gases as the working fluid and uses high intensity sound waves to pump heat energy. The major components of the system are the resonator, the acoustic driver, the heat exchangers and the stack. The useful thermoacoustic process for cooling in the system takes place between the gas particles and the stack. The system was designed and constructed. Experimental studies on the gas-stack heat transport and the Streaming Reynolds Number, which play crucial roles in the heat transport behavior, were studied. Input signals for the experiments, for the data acquisition system was from thermocouples and pressure transducers. Results from the study were used to make recommendations for the system. It was observed that for a given frequency, the heat transfer increases with drive ratio. Results from the comparison of the heat losses for a stainless steel stack and a stack built of thermoplastic material show that the plate heat losses can be significantly reduced if the stack with thermoplastic material is used for the system.

Commentary by Dr. Valentin Fuster
2003;():19-24. doi:10.1115/IMECE2003-42576.

As commercial building on-site power generation technologies mature to the point of becoming “off-the-shelf” products, the importance of effective heat recovery is demonstrated time and time again in applications where three to six year paybacks typically are necessary to convince building owners to purchase and install these new technologies. This paper explores the effectiveness and economic benefit of different methods of utilizing recoverable heat from on-site power generation equipment in commercial buildings (Cooling, Heating and Power systems – CHP). An optimal configuration of heat recovery options is explored based on analysis of heat recovery from microturbine(s) exhaust to support commercial building heating and cooling/dehumidification needs. Benefits of recovering heat for space heating/domestic hot water production and to support desiccant dehumidification vs. absorption cooling are studied in five different building types (large supermarket, large retail store, medium size office building, full service restaurant and quick service restaurant). Buildings are evaluated at four different geographical locations, allowing additional study of the climatic conditions on the optimum heat recovery system configuration for specific building types. A sophisticated model, incorporating performance algorithms of state-of-the-art power generation, dehumidification and absorption cooling equipment, is used for calculating annual energy/cost savings for CHP systems and optimization of basic parameters, such as generator size/number and heat recovery equipment selection.

Commentary by Dr. Valentin Fuster
2003;():25-32. doi:10.1115/IMECE2003-42629.

This paper deals with application of a heat pump as a part of the dedicated outside air system (DOAS) unit. DOAS systems are known to provide the energy cost savings by dehumidifying the fresh ventilating air in conjunction with the energy and heat recovery systems and also in parallel with the sensible cooling system. The energy cost savings associated with these systems results from operating the sensible cooling systems at higher evaporating temperatures which results in a higher coefficient of performance for the sensible chiller, lower pumping costs and lower capital costs. It is found that the operation of DOAS unit with the radiant panel cooling systems raises the energy cost savings even more significantly. Using hourly weather data, the energy cost saving analysis is performed for several geographical locations and estimated cost savings exceed well above 30 percent of the corresponding commercial building operational costs using the traditional VAV systems for most of the locations in USA.

Topics: Heat pumps
Commentary by Dr. Valentin Fuster
2003;():33-38. doi:10.1115/IMECE2003-42655.

Heat pump water heaters can cut electricity consumption, comparing with the conventional electric resistant water heating tanks by half. A conventional heat pump water heater (HPWH) requires a water circulating pump to sample water temperature every 15 minutes in the tank and to draw water to a condenser-water heat exchanger outside the tank, if water temperature is below the set point. The pump would be on at least once every 15 minutes, 24 hours a day. The novel design presented in this study was to insert the condenser coil through the opening on the top of the water tank. This design eliminated the need of the water circulating pumps, and thus greatly improved the reliability of the HPWH systems. Two types of condenser coil designs were considered; one was a bayonet tube (tube-in-tube) and one was the “U” tube. Previous test data indicated that “U” tube design performed better than the bayonet tube condenser coil, and thus only “U” tube condenser coil was considered in the study. With straight “U” tubes inserted into the tank, it was found that the convective heat transfer was not strong enough to break water temperature stratification in the tank, which resulted in a temperature differential of 16°C (30°F) from top to bottom. However, when the coil was built in “L” shape, the water stratification disappeared. A computational fluid dynamics code, CFD, was used to study the straight and L shaped condenser coils. Results from CFD simulation were compared with the experimental data and found they were close to each other.

Commentary by Dr. Valentin Fuster
2003;():39-48. doi:10.1115/IMECE2003-42767.

A 3D electrothermal model is used to simulate and optimize Si/SiGe superlattice heterostructure micro-coolers. The model considers thermoelectric/thermionic cooling, heat conduction and Joule heating. It also includes non-ideal effects, such as contact resistance between metal and semiconductor, substrate/heatsink thermal resistance, the side contact resistance. The simulated results match very well with the experimental cooling curves for various device sizes ranging from 60×60μm2 up to 150×150μm2 . It is found that the key factor limiting maximum cooling is metal semiconductor contact resistance. The maximum cooling could be doubled if we remove the metal-semiconductor contact resistance. The thin film Si/SiGe superlattice micro-coolers can provide cooling power density over 500 W/cm2 as compared with a few W/cm2 of bulk Bi2 Te3 themoelectric coolers. This micro-cooler experimentally demonstrated a maximum cooling of 4.5°C at room temperature and 7°C of cooling at 100°C ambient temperature. It is a promising candidate for microprocessor spot cooling.

Commentary by Dr. Valentin Fuster
2003;():49-56. doi:10.1115/IMECE2003-42870.

The emerging Distributed Energy Resources (DER) program envisions extensive use of small to midsize turbines for on-site power production. Their output decreases substantially at warm ambient conditions when it is most needed. Therefore inlet air cooling had received much scrutiny as a way to avoid this degradation. This study examines three approaches to inlet air cooling: evaporative cooling; mechanical vapor compression refrigeration; and waste heat powered absorption refrigeration. The benefits and limitations of each process were documented. Ammonia absorption refrigeration is shown to deliver the greatest benefit to continuosly operating turbines at very favorable installed and operating cost. The most economical process identified included an ammonia refrigeration cycle integrated directly into the combustion turbine cycle. This cycle was designed and modeled, and analyzed with ambient temperature conditions for six geographic areas (Boston, Atlanta, Los Angeles, Honolulu, Phoenix, and Chicago). Annual benefits for each area are detailed.

Topics: Absorption , Turbines
Commentary by Dr. Valentin Fuster
2003;():57-65. doi:10.1115/IMECE2003-42957.

This report demonstrates the successful development of a design method reducing oil circulation ratio (hereafter OCR) in swing compressors, based on calculations from a simplified model and an actual experiment. The developed OCR analysis tool features the addition of oil circulation flow rate circuit to the oil supply circuit that diagnoses the pump, the oil feeding passage, and the bearings by electrical circuit. The oil circulation flow rate is affected by refrigerant flow. In consideration of the complementary effects of refrigerant gas and oil circulation flow rate, including wall impingement of oil droplets, the gravity of oil droplets, and buoyancy, calculations can be conducted as separation efficiency ratio. In the experiment, the behavior of oil droplets in refrigerant in a compressor outfitted with pressure-proof glass was observed with a high-speed camera. It was thereby ascertained that the predicted speed of oil droplets and the actual speed in the compressor were almost the same. The effects of a drop in oil level during operation due to the oil circulation flow rate can be taken into account, something previously impossible with conventional circuits. The conclusive analytical precision of OCR is a range of 30–115Hz with a margin of error of ±0.3wt%. Using this method, design points that have substantial impact on OCR reduction can be clarified. With structural changes to the motor-rotor as suggested from the analysis, OCR can be reduced. Consequently, a significant reduction in the period necessary for compressor development has been achieved.

Topics: Design
Commentary by Dr. Valentin Fuster
2003;():67-76. doi:10.1115/IMECE2003-43070.

A hybrid pulse-tube/reverse-Brayton cryocooler is being developed that integrates a regenerative, pulse-tube upper stage with a recuperative, reverse-Brayton lower stage using a flow rectification system consisting of check-valves and buffer volumes. This system shows the potential for high performance with high reliability and low mass, and simple electrical, mechanical, and thermal integration. The turbine in the reverse-Brayton stage will be supported on hydrostatic gas bearings. The performance of the hybrid cryocooler system is strongly dependent upon the performance of these bearings; in particular their stiffness and mass flow consumption. This is a unique application of hydrostatic bearings; the miniature bearings are operating at cryogenic temperatures using high pressure helium. This paper describes the theoretical model that was developed to predict journal bearing performance as geometry and operating conditions change. The model is verified against experimental measurements of stiffness and mass flow consumption for a prototypical set of journal bearings. The model is subsequently used to optimize a set of journal bearings for the cryogenic turbine and parametrically investigate the effect of journal bearing clearance on system performance.

Commentary by Dr. Valentin Fuster
2003;():77-85. doi:10.1115/IMECE2003-43184.

A new thermodynamic cycle has been developed for the simultaneous production of power and cooling from low temperature heat sources. The proposed cycle combines the Rankine and absorption refrigeration cycles, providing power and cooling as useful outputs. Initial studies were performed with an ammonia-water mixture as the working fluid in the cycle. This work extends the application of the cycle to working fluids consisting of organic fluid mixtures. Organic working fluids have been used successfully in geothermal power plants, as working fluids in Rankine cycles. An advantage of using organic working fluids is that the industry has experience with building turbines for these fluids. A commercially available optimization program has been used to maximize the thermodynamic performance of the cycle. The advantages and disadvantages of using organic fluid mixtures as opposed to an ammonia-water mixture are discussed. It is found that thermodynamic efficiencies achievable with organic fluid mixtures, under optimum conditions, are lower than those obtained with ammonia-water mixtures. Further, the refrigeration temperatures achievable using organic fluid mixtures are higher than those using ammonia-water mixtures.

Topics: Cooling , Fluids , Cycles
Commentary by Dr. Valentin Fuster
2003;():87-95. doi:10.1115/IMECE2003-43289.

The gas-fired Generator-Absorber heat eXchanger (GAX) heat pump is being considered for space conditioning in residential and light commercial applications. In order to meet the national building codes for ammonia absorption heat pumps, a secondary fluid is used to interface with the air-coils. Proper choice of a secondary fluid maximizes the economic advantage of the GAX heat pump. The secondary fluid transfers the heating and cooling loads from the absorption heat pump to and from outdoor and indoor air-coils. The physical properties of secondary fluids influence the heat transfer performance in the heat-exchange equipment and hence the effective lift, thereby determining the cycle coefficient of performance (COP). Additionally, the pumping power for each fluid varies depending on the density and viscosity at operating temperatures. The variation in cycle COP and pumping power as a result of fluid properties is ultimately manifested as changes in electric and natural-gas cost. An analysis was carried out to evaluate six secondary fluids for a GAX absorption heat pump. A performance model was developed to simulate the secondary-fluid flow loops and the absorption heat pump. The utility costs for heating and cooling were determined for a typical building. The effects of ambient conditions and local utility rates were determined by modeling the annual utility costs in four cities: Atlanta, Chicago, Los Angeles, and New York. These four cities provided wide variations in heating and cooling requirements, and utility rates for natural gas and electricity. The results from this study provide a basis for selecting secondary fluids for heat pumping in different locations.

Commentary by Dr. Valentin Fuster
2003;():97-101. doi:10.1115/IMECE2003-43544.

The paper presents an absorption system with compact heat exchangers (micro-channels), working with ammonia water solution, driven by either solar or electrical energy. The construction of the solar panels includes heat pipes, and they are able to provide hot water with a maximum temperature of 130°C. The cooling capacity of the system ranges from 5 to 10 kW. The system is designed for comfort the technological air conditioning, providing inside air temperatures in the range of 10°C to 20°C. The project promotes ammonia as an ecological and natural refrigerant and aims to experimentally evaluate the thermal performances of each component of the system (condenser, evaporator, absorber and vapor generator) and of the entire system. The next step consists in a theoretical versus experimental comparison of data. The thermal performances refer to heat transfer coefficients in micro-channels on water ammonia side, as well as on the airside, and to the performance coefficient for various working conditions.

Commentary by Dr. Valentin Fuster
2003;():103-108. doi:10.1115/IMECE2003-43603.

In this paper, a methodology for the study of a fuel cell cogeneration system and applied to a university campus is developed. The cogeneration system consists of a molten carbonate fuel cell associated to an absorption refrigeration system. The electrical and cold-water demands of the campus are about 1,000 kW and 1,840 kW (at 7°C), respectively. The energy, exergy and economic analyses are presented. This system uses natural gas as the fuel and operates on electric party. In conclusion, the fuel cell cogeneration system may have an excellent opportunity to strengthen the decentralized energy production in the Brazilian tertiary sector.

Commentary by Dr. Valentin Fuster
2003;():109-117. doi:10.1115/IMECE2003-43628.

A mathematical model is formulated in this paper for the prediction of the heat rejection rate, assuming that the total heat transfer area of the mesochannel condenser is made up of 2 different areas, corresponding to superheated vapor state and the two-phase flow state. Each of these areas is considered as an independent heat exchanger (Mamani et al., 1999). The tested mesochannel condenser, manufactured by a Romanian company for automotive air-conditioning systems, is made of aluminum, based on an extrusion process; an oven brazing process was used for the headers to tubes joints. Maximum heat rejection rate represents the criteria used in order to optimize the geometrical configuration of the condenser. This theoretical study resulted in an optimized geometrical configuration of the mesochannel condenser (Heun et al., 1996a; Heun et al., 1996b). Experimental research has been carried out using a mesochannel condenser of optimized geometrical configuration. In order to ensure a quasi-state operating regime, the air-cooled mesochannel condenser was mounted inside an air loop, having multiple regulating and control means for the following parameters: inlet air dry bulb temperature, inlet air wet bulb temperature, and inlet air flow rate. The authors of the present paper develop a comparative analysis of theoretical vs. experimental heat rejection rate and heat transfer coefficient for an ammonia air-cooled mesochannel condenser.

Commentary by Dr. Valentin Fuster
2003;():119-124. doi:10.1115/IMECE2003-43888.

A mathematical model of a reversing valve was developed in order to evaluate the losses and for determining the effects of a reversing valve, on the performance of a heat pump. This mathematical model of the reversing valve was tested using the experimental data of Fang and Nutter (1999). The theoretical predictions made by this model agreed with that of the experimental data. Further, the mathematical model isolated the pressure losses due to friction; pipe-fittings, mass-leakage and heat transfer from the total losses. The evaluation of constituent losses assisted in detecting a faculty reversing valve, and also determining the effect of mass leakage and heat leakage on the compressor work input and COP of the heat pump.

Commentary by Dr. Valentin Fuster
2003;():125-130. doi:10.1115/IMECE2003-43920.

There is a strong industry focus on packaged CHP systems for small scale applications where the design time for unique installations cannot be justified. Distributed generators such as microturbines, reciprocating engines and fuel cells can all now be purchased as CHP products. The development of these products will bring the energy, environmental and economic savings realized in larger applications to the smaller consumers. CHP systems traditionally operate most effectively and give the shortest payback when operated continuously at full output in a baseloading application. This is in conflict with a typical commercial building whose energy requirements vary extensively over daily, weekly and seasonal time periods. Just as CHP is not expected to supply the entire energy requirements of the industrial sector, so CHP should be looked at as merely part of the energy mix for the commercial sector as the capital cost of CHP equipment is typically higher compared to its alternatives and there are technical complications to supply a heating or cooling to power ratio away from design values. An economic CHP system must therefore have a capacity much lower than the peak load of the building to ensure high utilization of the system so that the larger capital investment can be recovered through energy cost savings as quickly as possible. In the absence of a year round continuous demand for either hot or chilled water a commercial CHP system must offer a diverse range of outputs so that the waste heat from the generator can be utilized as mush as possible particularly since the generator component is likely to dominate the capital cost of the installation. This paper proposes that the outdoor, or ventilation air stream into a building provides an excellent capacity match for CHP equipment packaged as a CHP Dedicated Outdoor Air System (CHPDOAS). Ventilation air has the largest temperature and humidity difference with indoor air of any stream of air in the building and so reduces the heat and mass transfer surface areas in the equipment. Also since the ventilation air is only a fraction of the total air flow rate that is being conditioned the CHP system can overcool the air in the summer or overheat the air in the winter and the effect is simply the reduce the cooling or heating workload of the conventional equipment since the ventilation air is then mixed with the bulk of the air remaining in the building before being conditioned. This means that the CHP system can run its generator for longer hours and at higher loads than would have been possible if the outlet conditions were set at space neutral or space supply conditions.

Commentary by Dr. Valentin Fuster
2003;():131-139. doi:10.1115/IMECE2003-55332.

A preliminary design of a polygeneration system, conceived for a four-star hotel located on the Mediterranean coast, is presented in this paper. For this system, a single fuel is used to produce cold, heat, power and water from an internal combustion engine integrated and optimized with heaters, absorption units and a reverse osmosis desalination plant. The proposed system is the result of minimizing a multiobjective function of energy (cold, heat and power) and water consumption, in order to reach a more efficient and sustainable management of the installation. The hotel covers its internal demand of energy and water and reaches important overall energy efficiency improvements thanks to the integration of all the systems. An economic analysis has also been performed. The overall system has been modeled by means of data provided by manufacturers and also by means of efficiency curves available in the literature.

Topics: Heat , Reverse osmosis
Commentary by Dr. Valentin Fuster
2003;():141-150. doi:10.1115/IMECE2003-55397.

Effective utilization of low-enthalpy energy resources in heating, ventilating, and air-conditioning (HVAC) of sustainable buildings require a careful optimization to assure the most economical coupling of HVAC systems with low-enthalpy energy resources. In one of the two separate prior studies an optimization algorithm for the optimal coupling of heat pumps and radiant panel heating and cooling systems was developed. In the second prior study an optimization algorithm for driving ground source heat pumps with wind turbines was developed. In this study these two algorithms were combined for a compound utilization of alternative energy resources. This paper describes the optimization algorithms, emphasizes their importance in achieving a cost effective combined application, and discusses the results obtained from the examples given.

Commentary by Dr. Valentin Fuster
2003;():151-161. doi:10.1115/IMECE2003-41048.

In thermodynamics the sign convention normally used is energy added to a system in the form of heat is taken as positive and that added in the form of work is taken as negative – HIP to WIN (heat in positive – work in negative). This is a common sign convention although some texts specify that all forms of energy added to a system as heat or work are positive. However, regardless of the sign convention adopted for heat and work interactions, later in the same text the specified convention is abandoned in favor of magnitudes or absolute values. This occurs particularly in relation to cycle analyses in which the absolute value is used for energy transfers. Generally for reversible cycles there is no proof as to why the ratio of energy added/rejected via heat transfer equals the ratio of the absolute temperatures of the thermal reservoirs. To promote sign convention consistency, this paper develops the appropriate relationship between energy transfers and thermal reservoir temperatures for reversible cycles and applies the result to power producing and power consuming engineering devices.

Topics: Thermodynamics
Commentary by Dr. Valentin Fuster
2003;():163-172. doi:10.1115/IMECE2003-41167.

In this paper we develop an analytical and graphical formulation of the constructal law of maximization of flow access in systems with heat and fluid flow irreversibilities and freedom to change configuration. The flow system has global objective (e.g., minimization of global flow resistance) and global constraints (e.g., overall size, and total duct volume). The infinity of possible flow structures occupies a region of the two-dimensional domain of “global performance versus freedom to morph.” This region of “nonequilibrium” flow structures is bounded by a line representing the best flow structures that are possible when the freedom to morph is limited. The best of all such structures are the “equilibrium” structures: here the performance level is the highest, and it does not change even though the flow architecture continues to change with maximum freedom. The universality of this graphical and analytical presentation is illustrated with examples of flow structures from three classes: flow between two points, flow between a circle and its center, and flow between one point and an area. In sum, this paper presents an analytical and graphical formulation of the constructal principle of thermodynamic optimization of flow architecture under global constraints. The place of this new and self-standing principle in the greater framework of thermodynamics is outlined.

Commentary by Dr. Valentin Fuster
2003;():173-181. doi:10.1115/IMECE2003-41285.

The major alternatives for producing work from the chemical energy of fuels include combustion systems and fuel cells. Combustion systems are subject to several performance limiting constraints. Key amongst these is the fact that combustion is an uncontrolled chemical reaction and is typically highly irreversible. The requirement to operate below the metallurgical limit adds to the irreversibility or exergy consumption in practical combustion systems. Furthermore, the use of heat exchangers, which must have finite temperature differences between fluid streams, compounds the exergy consumption. The fuel cell conversion system is a major alternative to combustion systems. It operates as a direct conversion device and is often cited as having a potential for 100% second-law efficiency. Realistically, however, the chemical reactions involved are not reversible. More importantly, the available fuel resources must be reformed to make the chemical energy of the fuel convertible to work; such processes require significant exergy input that must be factored into the determination of the overall exergy conversion efficiency attainable. This paper gives a first- and second-law analysis of the alternate systems for conversion of fuel exergy to mechanical work thus providing a more realistic comparison of the potential of both systems.

Topics: Fuels
Commentary by Dr. Valentin Fuster
2003;():183-188. doi:10.1115/IMECE2003-41299.

Complete analysis of thermodynamic systems generally requires knowledge of the property values of substances at different states. Performing such analysis on the computer is facilitated if the equations of state for the substances are available in relatively simple analytic forms. This article presents a procedure for formulation for the thermodynamic properties of pure substances using two primary sets of data, namely the pvT data and the specific heat data such as the constant-pressure specific heat, cp , as a function of pressure and temperature. By developing a correlation of the pvT data in the virial form of equation of state, an appropriate corresponding correlation can be determined for the specific heat of the substance on the basis of the laws of thermodynamics. The resulting equations of state take on remarkably simple analytic forms that give accurate predictions over the range of input data employed.

Commentary by Dr. Valentin Fuster
2003;():189-194. doi:10.1115/IMECE2003-41365.

In the present study, the production characteristics of the hydrates from methane, xenon and their mixed gases and the application of a hydrate production technology for the separation of mixed gases such as CO2 and helium gases are discussed. Methane, xenon and CO2 can form hydrates. On the other hand, helium can’t produce the hydrate. Therefore, by using the hydrate production technology, CO2 could be separated from the mixed gases of CO2 and helium as the CO2 hydrate. In the present paper an autoclave experiment apparatus is used for the production of the hydrate.

Commentary by Dr. Valentin Fuster
2003;():195-202. doi:10.1115/IMECE2003-41708.

Worldwide, the main power source to produce electric energy is represented by fossil fuels, principally used at the present time in large combustion power plants. The main environmental impacts of fossil fuel-fired power plants are the use of non-renewable resources and pollutants emissions. An improvement in electric efficiency would yield a reduction in emissions and resources depletion. In fact, if efficiency is raised, in order to produce an amount unit of electric energy, less fuel is required and consequently less pollutants are released. Moreover, higher efficiency leads to economic savings in operating costs. A generally accepted way of improving efficiency is to combine power plants’ cycles. If one of the combined plants is represented by a fuel cell, both thermodynamic efficiency and emissions level are improved. Fuel cells, in fact, are ultra-clean high efficiency energy conversion devices because no combustion occurs in energy production, but only electrochemical reactions and consequently no NOx and CO are produced inside the cell. Moreover, the final product of the reaction is water that can be released into the atmosphere without particular problems. Second generation fuel cells (Solid Oxide FC and Molten Carbonate FC) are particularly suitable for combining cycles, due to their high operating temperature. In previous works, the authors had analyzed the possibility of combining Molten Carbonate Fuel Cell (MCFC) plant with a Gas Turbine and then a MCFC with a Steam Turbine Plant. Results obtained show that both these configurations allow to obtain high conversion efficiencies and reduced emissions. In the present work, a comparison between MCFC-Gas Turbine and MCFC-Steam Turbine is conducted in order to evaluate the main advantages and disadvantages in adopting one solution instead of the other one.

Commentary by Dr. Valentin Fuster
2003;():203-207. doi:10.1115/IMECE2003-41876.

Hydrogen is expected as a clean and renewable alternative to the conventional hydrocarbon fuels. Because the only possible pollutants from the hydrogen combustion are nitrogen oxides (NOx ), it is crucial to reduce the NOx emission in the hydrogen utilization. The rich-lean combustion is well known as a technique to reduce the emission of the Zel’dovich NO from the continuous combustion burners for such as gas turbines and boilers. Because the Zel’dovich NO occupies a large part of the total NOx emission, the rich-lean combustion is quite effective to reduce the NOx emission. However, the NOx reduction effect of the rich-lean combustion has not yet been proven for the hydrogen fuel, while the effect has been demonstrated for the hydrocarbon fuels. On the other hand, the prompt NO is emitted from the hydrocarbon combustion especially under the fuel-rich conditions. Though the amount of the prompt NO is quite small for premixed or diffusion combustion, it could be a relatively significant part in the total NO emission from the rich-lean combustion due to the decreased Zel’dovich NO. The authors estimate that hydrogen is more suitable for the rich-lean combustion compared with hydrocarbons, because hydrogen does not emit the prompt NO even under the fuel-rich conditions which necessarily exist in the rich-lean combustion. This research proposes the rich-lean combustion as a method to reduce the NOx emission from hydrogen combustion and experimentally analyzes the characteristics using a coaxial rich-lean burner with varying the mixture conditions.

Commentary by Dr. Valentin Fuster
2003;():209-216. doi:10.1115/IMECE2003-42573.

Diagnosis of energy systems mainly consists of detecting and locating anomalies that cause reduction in the system efficiency or can cause major failures. This is an important task due to its economic implications. The attention is here focused on the anomalies that affect the system efficiency. The problem of their location is not easy to solve, due to some ‘disturbs’ that make propagate the effects of an anomaly throughout the system. These effects are caused by the dependence of the components’ behavior on their operating conditions. Moreover they can be amplified by the intervention of the control system and the variations in ambient conditions, fuel quality and plant load. A technique for highly complex system has been proposed in [1]. This procedure, based on the hypothesis of small malfunctions, consists of the progressive elimination of the disturbs, so that the anomalies could be more clearly highlighted. In this paper, a procedure particularly suitable for the application to operating plants is adopted to overcome the hypothesis of small malfunction. It consists of a combination of two techniques: 1) the use of neural networks for the elimination of the malfunctions [2] induced by the dependence of efficiency of components on the operating conditions and 2) the successive application of the analysis to several operating conditions selected within the plant case history.

Commentary by Dr. Valentin Fuster
2003;():217-228. doi:10.1115/IMECE2003-42816.

A combined heat, power, and hydrogen (HPH) system consists of a hydrogen production and distribution system that provides hydrogen fuel for vehicles and for fuel cell heat and power systems that meet the energy needs of nearby buildings. This paper describes the analysis of a proposed HPH system that serves a laboratory and the vehicle fleet of an adjacent industrial facility. In the proposed system, hydrogen from a natural gas fuel processor is compressed, stored, and used to fuel fleet vehicles. The hydrogen is also supplied to a building fuel cell system that provides both electricity and hot water for space heating and water heating during peak electrical demand periods. The analysis is based on historical data for vehicle mileage and electricity use, estimates of hot water use for the laboratory, and local utility rates. This data is used in conjunction with a model of system performance and an operating strategy based on the net marginal value of hydrogen for each resource (heat, power, and hydrogen vehicle refueling) to determine the economic and environmental impact of the HPH system. Results show that if the primary goal is vehicle refueling, adding a stationary fuel cell system to create a combined HPH system makes small fleet sizes economical and increases the economic value of the refueling station at all fleet sizes. If the primary goal is to provide building heat and power, adding a vehicle refueling capability increases the economic value provided the fleet size is relatively large. The results also confirm that for the current utility rates at the proposed site, the stationary system should be operated in a peak shaving mode with relatively few operating hours. Finally, the results indicate that application of the HPH system leads to reductions in primary energy use and reductions in emissions of carbon dioxide and oxides of nitrogen in both stationary and vehicular applications. Sulfur dioxide emissions are reduced for stationary applications but increased for vehicular applications. Overall, the HPH system represents a promising approach to facilitate the introduction of both fuel cells and a hydrogen infrastructure.

Topics: Heat , Hydrogen
Commentary by Dr. Valentin Fuster
2003;():229-247. doi:10.1115/IMECE2003-43638.

Recently, a jet engine experiment was added to the Energy Systems Laboratory at Kettering University (formerly GMI). The educational objectives of this experiment are: to familiarize the students with the operation of a turbojet engine, the theory behind the thermodynamic processes involved, and the linear momentum equation; to determine theoretical and measured engine thrust and the efficiencies of the compressor, the combustion chamber, and the turbine; to determine the effect of engine speed on thrust-specific fuel consumption (TSFC) and engine emissions; to analyze the combustion process; and to perform a complete energy balance on the jet engine. The apparatus used is a small TTL model SR-30 turbojet engine capable of kerosene and diesel liquid fuel start and operation. Using an automatic data acquisition system, the students operate the engine at 50,000–75,000 rpm and measure various pressures and temperatures as well as fuel flow rate, air flow rate, engine emissions and engine thrust. The data is then used to calculate the TSFC, component efficiencies and the A/F ratio. By using the linear momentum principle, engine thrust is calculated and compared with the measured value. This paper presents the measured test data and analytical results obtained by using the Engineering Equation Solver (EES). Experimental results compare favorably with theoretical predictions.

Commentary by Dr. Valentin Fuster
2003;():249-262. doi:10.1115/IMECE2003-55040.

A fresh view for explaining the process of osmosis and the phenomenon of osmotic pressure is presented. The process of osmosis was identified and modeled more than 100 years ago. Others have unsuccessfully challenged the original model developed by J.H. van’t Hoff. We revisit the basic equations and assumptions used in the thermodynamic derivation of the osmosis model. And, we propose a small but significantly different view of the traditional theory of osmosis. From this new view of osmosis and the osmosis experiment, we conclude that osmosis occurs at atmospheric pressure. In cellular membranes, flow from the solvent to the solution is related to the vapor pressure difference determined from the concentration difference with Raoult’s law. Furthermore, we suggest that osmotic pressure as determined from the osmosis experiment is related to both the solution properties and the membrane characteristics. We suggest that the difference between experimental and theoretical determination of osmotic pressure can be attributed to capillary action that may occur in some man made membranes.

Topics: Osmosis
Commentary by Dr. Valentin Fuster
2003;():259-265. doi:10.1115/IMECE2003-41087.

A free-piston Stirling engine (FPSE) with a generalized displacer-drive configuration having the displacer sprung to both the engine casing and power piston is described, characterized and analyzed. The analysis includes motion of the moving components, power transmitted from the displacer to the piston and power produced by the gas in the work space, and the effect of the displacer-drive configuration to the engine efficiency. Results are presented, from testing a FPS engine which has a gas spring linking the displacer to the engine casing and the power piston magnetically coupled to a linear alternator. The analysis and analytical prediction of the engine characteristics showed close agreement with the test results.

Commentary by Dr. Valentin Fuster
2003;():267-275. doi:10.1115/IMECE2003-41443.

Computing will be pervasive, and enablers of pervasive computing will be data centers housing computing, networking and storage hardware. The data center of tomorrow is envisaged as one containing thousands of single board computing systems deployed in racks. A data center, with 1000 racks, over 30,000 square feet, would require 10 MW of power to power the computing infrastructure. At this power dissipation, an additional 5 MW would be needed by the cooling resources to remove the dissipated heat. At $100/MWh, the cooling alone would cost $4 million per annum for such a data center. The concept of Computing Grid, based on coordinated resource sharing and problem solving in dynamic, multi-institutional virtual organizations, is emerging as the new paradigm in distributed and pervasive computing for scientific as well as commercial applications. We envision a global network of data centers housing an aggregation of computing, networking and storage hardware. The increased compaction of such devices in data centers has created thermal and energy management issues that inhibit sustainability of such a global infrastructure. In this paper, we propose the framework of Energy Aware Grid that will provide a global utility infrastructure explicitly incorporating energy efficiency and thermal management among data centers. Designed around an energy-aware co-allocator, workload placement decisions will be made across the Grid, based on data center energy efficiency coefficients. The coefficient, evaluated by the data center’s resource allocation manager, is a complex function of the data center thermal management infrastructure and the seasonal and diurnal variations. A detailed procedure for implementation of a test case is provided with an estimate of energy savings to justify the economics. An example workload deployment shown in the paper aspires to seek the most energy efficient data center in the global network of data centers. The locality based energy efficiency in a data center is shown to arise from use of ground coupled loops in cold climates to lower ambient temperature for heat rejection e.g. computing and rejecting heat from a data center at nighttime ambient of 20°C. in New Delhi, India while Phoenix, USA is at 45°C. The efficiency in the cooling system in the data center in New Delhi is derived based on lower lift from evaporator to condenser. Besides the obvious advantage due to external ambient, the paper also incorporates techniques that rate the efficiency arising from internal thermo-fluids behavior of a data center in workload placement decision.

Commentary by Dr. Valentin Fuster
2003;():277-284. doi:10.1115/IMECE2003-41458.

In this paper, multi-criteria analysis and thermo-economic optimization approach is applied to the analysis of a distributed energy system in an urban residential area in Beijing. System Net Present Value (NPV) is taken as the objective to be maximized with simultaneous consideration of the thermodynamic, economic and emission criteria with regarding to CO2 and NOx emissions. Technologies as gas turbine, internal combustion engine, absorption chiller and gas boiler are included in the plant superstructure. For comparison, case with gas boilers for heating, decentralized electric chillers for cooling and all power imported from grids is chosen as the reference.

Commentary by Dr. Valentin Fuster
2003;():285-290. doi:10.1115/IMECE2003-42676.

The formalism of the classical thermodynamics, for example Gibbs equations, is routinely and successfully applied to the highly non-equilibrium processes in dynamic systems. Such applications are based on the local equilibrium hypothesis. The presented paper discusses the conditions of the application of this hypothesis. It is shown that the local equilibrium hypothesis is applicable with no limitations to continuous systems. This application is validated by the solution of the Boltzmann equation. This solution was obtained by Enskog, Chapman and Bogolubov. From the Boltzmann equation follows that regardless of the initial state of the system the duration of its approach to the local equilibrium conditions by far less than the time scale of the evolution of the macro properties of the continuous media. This result shows that the local equilibrium is the intrinsic property of this media. Thus it is possible to apply the formalism of the non-equilibrium thermodynamics (the generalized variables, forces and fluxes) to description of the continuous system with no limitations. The derivation of the Carnot theorem is presented to show the effectiveness of such an application.

Topics: Thermodynamics
Commentary by Dr. Valentin Fuster
2003;():291-298. doi:10.1115/IMECE2003-41368.

Fuel Cells have been intensely researched and developed in the recent decade, where especially the fuel cell MEA (Membrane Electrode Assembly) and stack have been the main focus. Now the system control components surrounding the fuel cell have been given more attention. This paper gives a novel system approach of setting up the demands for control components such as valve actuators for a PEM (Proton Exchange Membrane) fuel cell system in order to meet an overall transient system performance criterion. Overall control considerations are treated, and the major time constants of the sub-systems are analyzed. The result is a method for specifying dynamic performance criteria for the individual control components. By proper selection of the components it can be shown that the electric load buffer may be omitted due to the internal capacitance of the fuel cell. Test results from a 2.5 kW PEM fuel cell test facility show close agreement with simulation results from the novel system approach.

Commentary by Dr. Valentin Fuster
2003;():299-305. doi:10.1115/IMECE2003-42145.

Systematic experiments with different cell temperatures, humidification temperatures, pressures and reactant gas flow rates have been carried out to study the effects of different parameters on the performance of a PEM fuel cell with interdigitated flow fields. A 3-D fuel cell model was used to simulate the performance of a PEM fuel cell with interdigitated flow fields. The modeling results were compared with experimental data and the comparison shows a good agreement.

Commentary by Dr. Valentin Fuster
2003;():307-315. doi:10.1115/IMECE2003-42310.

Commonly used ribbed flow-fields such as parallel and serpentine flow-fields in polymer electrolyte fuel cells (PEFC) exhibit limited mass transfer to the part of the diffusion and catalyst layer which is not covered by flow channels, leading to a considerably reduced reactant concentration and increased overpotential losses under the current collector shoulders. In this study, a novel concept is investigated, according to which the traditional ribbed flow delivery systems are replaced with permeable porous fluid distributors, which circumvent drawbacks such as those mentioned earlier. A complex mathematical model, including the conservation of mass, momentum, energy, species and electric current, using Butler-Volmer kinetics for electrochemical reaction rates, is numerically solved in three dimensions, to investigate the impact of different flow configurations on the performance of hydrogen fuel cells. It is found that cells with porous gas distributors generate substantially higher current densities and therefore are more advantageous with respect to mass transfer. Reduction in stack weight is another strong argument for using porous flow distributors in future applications.

Commentary by Dr. Valentin Fuster
2003;():317-326. doi:10.1115/IMECE2003-42817.

The catalyst layer of a proton exchange membrane (PEM) fuel cell is a porous mixture of polymer, carbon, and platinum. The characteristics of the catalyst layer play a critical role in determining the performance of the PEM fuel cell. In this research, sample membrane electrode assemblies (MEAs) are prepared using various combinations of polymer and carbon loadings while the platinum catalyst surface area is held constant. For each MEA, polarization curves are determined at common operating conditions. The polarization curves are compared to assess the effects of the catalyst layer composition. The results show that both Nafion and carbon content significantly affect MEA performance. The physical characteristics of the catalyst layer including porosity, thickness, and apparent Nafion film thickness are investigated to explain the variation in performance. The results show that for the range of compositions considered in this work, the porosity and thickness have little effect on performance but the apparent Nafion film thickness is significant.

Commentary by Dr. Valentin Fuster
2003;():327-332. doi:10.1115/IMECE2003-42886.

The intention of this paper is to present the dynamic models for the MCFC-gas turbine hybrid cycle. This paper analyzes the performance of various components in the hybrid power plant, such as compressor, turbine, recuperator, generator, fuel cell stack etc. The modular simulation models of these components are presented. Based on the dynamic simulation modeling principle, one bottoming hybrid MCFC-Micro turbine cycle was studied to carry out the simulation, the simulation result is reasonable.

Commentary by Dr. Valentin Fuster
2003;():333-343. doi:10.1115/IMECE2003-41958.

A novel liquefied natural gas (LNG) fueled power plant is proposed, which has virtually zero CO2 and other emissions and a high efficiency. Natural gas is fired in highly enriched oxygen and recycled CO2 flue gas. The plant operates in a quasi-combined cycle mode with a supercritical CO2 Rankine-like cycle and a CO2 Brayton cycle, interconnected by the heat transfer process in the recuperation system. By coupling with the LNG evaporation system as the cycle cold sink, the cycle condensation process can be achieved at a temperature much lower than ambient, and high-pressure liquid CO2 ready for disposal can be withdrawn from the cycle without consuming additional power. The net thermal and exergy efficiencies of a base-case cycle are found to be over 65% and 50% respectively, which can be increased up to 68% and 54% when reheat is used. Cycle variants incorporating reheat, intercooling, and reheat+intercooling, as well as no use of LNG coldness, are also defined and analyzed for comparison. The approximate heat transfer area needed for the different cycle variants is also computed. Besides electricity and condensed CO2 , the byproducts of the plant are H2 O, liquid N2 and Ar.

Commentary by Dr. Valentin Fuster
2003;():345-354. doi:10.1115/IMECE2003-42688.

Thermoeconomic diagnosis procedures in the literature rely on the assumption that specific consumption of resources in the components are the key to interpret the effects of malfunctions and then to trace a path towards the sources of anomalies. The main obstacle to a successful application of these approaches is represented by the actual interactions existing among components which cause a propagation of the alteration of component specific consumptions and therefore mask those effects that would allow a direct identification of the origin of malfunction. This paper presents an extensive discussion of potentialities and limits of diagnosis procedures proposed in the literature in distinguishing the effects induced by component interactions from those that are intrinsically generated by the anomaly, which is considered here as the main task to locate effectively causes of malfunctions in energy systems.

Commentary by Dr. Valentin Fuster
2003;():355-364. doi:10.1115/IMECE2003-42689.

Diagnosis procedures primarily aim at locating the control volumes where anomalies occurred. This is not a simple task, since the effects of anomalies generally propagate through the whole system and affect the behavior of several components. Some components may therefore present a reduced efficiency, although they are not sources of operation anomalies, due to non flat efficiency curves. These induced effects are a big obstacle in the use of thermoeconomic techniques for the search of the origin of the anomalies. On the other hand, the real cause of the alteration of component behavior is the modification of its characteristic curve, due to degradation or failures. According to this concept, a new approach, based on an indicator measuring the alteration of the characteristic curve of the component affected by the operation anomaly, is proposed and applied to a test case power plant.

Commentary by Dr. Valentin Fuster
2003;():365-381. doi:10.1115/IMECE2003-43766.

The performance of Stirling engines is subject to limitations resulting from power dissipation in the regenerator. The dissipation is caused by pressure gradients in the regenerator to generate flow. Without this flow the power output would by zero. Hence the dissipation is an essential element of the operation of the engine. Using linearized theory, the equation for pressure in the regenerator is solved for the case of a linear temperature distribution. The regenerator is taken to be thermally perfect. All various are taken to be sinusoidal in time. Expressions are derived for the net power output and the thermal efficiency. The net power output is optimized under various constraints. The constraint yielding the best results is fixed piston amplitude in the compression chamber. Upper bounds on the dimensionless power output are found as function of regenerator void volume and regenerator temperature. These bounds are derived in the limit of zero frequency, and ae independent of the conductance of the regenerator. Both power output and thermal efficiency decrease decreases as frequency and regenerator void volume increase.

Commentary by Dr. Valentin Fuster
2003;():383-391. doi:10.1115/IMECE2003-43856.

Power plant performance deteriorates during operation due to degradation of plant components. This paper deals with the calculation of costs associated with the degradation of selected plant components in a 400 MW pulverized coal-fired subcritical power plant at full and partial load. A commercial process simulator (Gate/Cycle) is used to study the thermodynamic behavior of the plant at various loads. In several case studies, the performance of one or more plant components is deteriorated by altering performance factors (i.e., fouling factor for heat exchangers and isentropic efficiency for turbomachinery). An exergy analysis and a detailed exergoeconomic evaluation are conducted for each case study. Selected exergoeconomic variables defined for each plant component assist in identifying the location of degradation and its effect on the performance and the product coast for single components and the total plant. Such an approach can be applied to process monitoring of a real plant and provides useful information for the diagnosis and assessment of deteriorated power plant performance.

Commentary by Dr. Valentin Fuster
2003;():393-400. doi:10.1115/IMECE2003-43880.

The development of proper tools for power plants production planning is becoming crucial to profitably compete in a deregulated market scenario. Two numerical techniques, the former based on the dynamic programming, the latter on an original real-coded genetic algorithm, are suggested in this paper to optimize the management of cogeneration power plants with thermal storage. Detailed mathematical models are required to simulate plant part-load performance in order to evaluate possible operation plans profitability. Electricity price trends, forecasted from market analyses, are used as input data. Technical constrains and those derived from the market characteristics are included in the optimization problem. The suggested approaches are applied to some possible market situations, typical of different seasons and competition intensities. Results obtained are compared in terms of accuracy and resolution time. Iterative analyses are also performed to assess possible management flexibility improvements resulting from different design choices of the cogeneration system.

Commentary by Dr. Valentin Fuster
2003;():401-409. doi:10.1115/IMECE2003-43887.

Nowadays most HVAC systems for residential building in the Unites States use a single-zone, two-position control system which is simple and easy to manage. However, this two-position control system has its disadvantage due to its unsatisfactory thermal comfort and energy inefficiency. This paper presents a proportional control system for the residential building by setting up the dynamic simulation for the building and the control system. The state-space method is used to model the building system and the simulation code is implemented on MATLAB™. Under this model, optimization of the controller is possible and implemented. The thermal comfort and energy efficiency are compared under the different schemes. It has been found that proportional control is advantageous to the two-position control for the thermal comfort while there is not much different in energy consumption between two control schemes. In this work, the furnace was operated without any minimum run time and under continuous data sampling.

Commentary by Dr. Valentin Fuster
2003;():411-422. doi:10.1115/IMECE2003-43923.

This paper presents the thermodynamic analysis of a coal-based zero-atmospheric emissions electric power plant. The approach involves an oxygen-blown coal gasification unit. The resulting synthetic gas (syngas) is combusted with oxygen in a gas generator to produce the working fluid for the turbines. The combustion produces a gas mixture composed almost entirely of steam and carbon dioxide. These gases drive multiple turbines to produce electricity. The turbine discharge gases pass to a condenser where water is captured. A stream of carbon dioxide then results that can be used for enhanced oil recovery, or for sequestration. This analysis is based on a 400 MW electric power generating plant that uses turbines that are currently under development by a U.S. turbine manufacturer. The power plant has a net thermal efficiency of 42.6%. This efficiency is based on the lower heating value of the coal, and includes the energy necessary for coal gasification, air separation and for carbon dioxide separation and sequestration. The paper also presents an analysis of the cost of electricity (COE) and the cost of conditioning carbon dioxide for sequestration for the 400 MW power plant. Electricity cost is compared for three different gasification processes (Texaco, Shell, and Koppers-Totzek) and two types of coals (Illinois #6 and Wyodak). Cost of electricity ranges from 5.16 ¢/kWhr to 5.42 ¢/kWhr, indicating very little sensitivity to the gasification processes considered and the coal types used.

Commentary by Dr. Valentin Fuster
2003;():425-430. doi:10.1115/IMECE2003-41201.

Traction batteries for hybrid and fuel cell vehicles must maintain temperatures within operational limits for longer battery lifetime and better performance. The uneven battery temperature due to improper heat transfer during discharging/charging could accumulate battery degradation on hot cells resulting in early failure of the battery pack. Current battery systems use a unidirectional coolant flow for battery thermal management. However, due to the nature of the cooling method, the unidirectional cooling systems are prone to show a largest temperature differential ΔTs between the battery cells at fixed flow boundaries, although sophisticated thermal/fluid designs are implemented to make the battery temperature uniform. Here, an innovative battery cooling method ([1]) using a reciprocating cooling flow is proposed. The reciprocating cooling system switches the coolant flow direction periodically by a valve-fan mechanism. By switching the flow direction periodically and thus the cold and hot boundaries of the battery cooling system, the battery cell temperatures are regulated with a very small fluctuation and the temperature differential ΔTs is drastically reduced. In hybrid electric vehicle and fuel cell vehicle applications, the cooling improvement using the new concept would set battery cooling system free of auxiliary air-conditioning system. Parametric study shows that using the reciprocating cooling system for a Li-Ion battery system, an optimum reciprocating period to minimize temperature differential ΔTs and maximum battery temperature Ts,max exists.

Commentary by Dr. Valentin Fuster
2003;():431-436. doi:10.1115/IMECE2003-41893.

Unique features of electron emission from carbon-based nanostructures are studied to explore direct energy conversion materials and processes. These structures have been shown to produce highly efficient field emission (i.e., high electrical current at low applied fields) for electrical device applications. However, the commensurate transport and conversion of thermal energy has not been previously explored in detail. Understanding these concepts could enable development of devices with efficiencies that exceed those of other direct energy conversion technologies. The electron emission behavior at elevated temperatures, of two diamond-based devices with nanoscale features, is characterized. Bulk current measurements reveal work functions of 1 and 1.3 eV for a boron-doped diamond pyramid array and a phosphorus-doped diamond surface, respectively. An electron energy spectrometer has been designed in order to understand the emission behavior in more detail. The analyzer is integrated with a heat source that enables substrate temperatures up to 1000°C. Spectral measurements indicate higher work functions for both samples.

Commentary by Dr. Valentin Fuster
2003;():437-446. doi:10.1115/IMECE2003-42527.

Data centers today contain more computing and networking equipment than ever before. As a result, a higher amount of cooling is required to maintain facilities within operable temperature ranges. Increasing amounts of resources are spent to achieve thermal control, and tremendous potential benefit lies in the optimization of the cooling process. This paper describes a study performed on data center thermal management systems using the thermodynamic concept of exergy. Specifically, an exergy analysis has been performed on sample data centers in an attempt to identify local and overall inefficiencies within thermal management systems. The development of a model using finite volume analysis has been described, and potential applications to real-world systems have been illustrated. Preliminary results suggest that such an exergy-based analysis can be a useful tool in the design and enhancement of thermal management systems.

Commentary by Dr. Valentin Fuster
2003;():447-454. doi:10.1115/IMECE2003-55001.

This paper introduces the results of transient heat transfer involving a jet of liquid ammonia perpendicularly on a solid substrate of finite thickness containing discrete electronic sources on the opposite surface. The jet was confined by using a cover plate to prevent any evaporation or loss of ammonia during the heat transfer process. The numerical simulation considered both the solid and fluid regions as a conjugate problem. The equations solved in the liquid region included the conservation of mass, conservation of energy, and conservation of momentum. For the solid region, only the heat conduction equation was solved. Computed results included the temperature distribution, local and average heat transfer coefficient, and local and average Nusselt number at the solid-fluid interface. Some of the parameters such as the jet velocity, plate thickness, and plate material were altered to examine the effect that they had on the problem. It was found that the average heat transfer coefficient and a average Nusselt number were high at the initial stages of the transient process and decreased steadily with time until it reached the steady condition. As the plate thickness decreased, and as the jet velocity increased, it was observed that the time it took to reach the steady state condition declined. The time it took to reach steady state condition did not change significantly for different plate materials. However, it did change noticeably for different plate thickness and different Reynolds number.

Commentary by Dr. Valentin Fuster
2003;():455-462. doi:10.1115/IMECE2003-55055.

A general thermodynamic analytical program was developed to investigate the impact of secondary power system (SPS) improvements on mission effectiveness and weapon power generation in a tactical aircraft. Preliminary analysis revealed, among other things, that the engine performance was more sensitive to pneumatic bleed than to shaft power extraction and the use of a More Electric secondary power system resulted in a savings in fuel consumption. Using the total fuel consumption of the conventional aircraft for a typical tactical mission as a baseline, the fuel savings could potentially offer two alternatives to improved performance. The first alternative addresses multiple combat mission legs with varying altitudes and consequently a longer combat duration. The second alternative addresses the use of excess power to activate an airborne weapon platform and subsequent evaluation of thermal management limitations posed by several exploratory concepts. Three different thermal management approaches were considered for a typical airborne solid-state laser based power system with a laser output power of 100 kW. Some of the consequences of using these thermal management concepts on the mission legs in a tactical mission from a time-constraint and mass-constraint points of view are also presented.

Commentary by Dr. Valentin Fuster
2003;():463-467. doi:10.1115/IMECE2003-41699.

For several decades, although many kinds of allocation methods for heat-electricity cost allocation were proposed, there are remarkable differences computed with those methods due to each method having its relative merit and limitation in application. Based on the different roles of anergy and exergy in the heat supply process of cogeneration, two novel methods including the simplified reduced exergy method (SREM) and reduced exergy method (REM) are established by introducing the concept of reduced exergy and available anergy. Those methods consider not only the energy differences in quantity and quality, but also the roles of available anergy and exergy. Some practical conditions for typical units are computed and compared with present methods and existing methods. Calculations verify the feasibility of SREM and REM and indicated that those two methods are more rational, convenient and practical than existing methods in applications.

Commentary by Dr. Valentin Fuster
2003;():469-475. doi:10.1115/IMECE2003-43918.

In order to determine the dimension of a separation column, hydrodynamic and mass transfer models are necessary to evaluate the pressure drop and the height of the global mass transfer unit, respectively. Those parameters are a function of the cross sectional area of the column. The present work evaluates the dependency of the pressure drop and height of the global transfer unit with respect to the cross sectional area of the column, using an absorption column with high efficiency structured packing, in order to recover SO2 in the form of NaHSO3 , as an example. An optimization was done applying Two Film model which is based on the number of global mass transfer units of both gas and liquid, involving the separation efficiency in terms of the height of a global transfer unit. Structured packing, geometrically heaped in a separation column, has been achieving wider acceptance in the separation processes due to their geometric characteristics that allow them to have greater efficiency in the separation processes. Three different structured packing were evaluated in this work. The results show how ININ packing is one of the packings does the best work having the highest separation efficiency because it has the lowest height of the global mass transfer unit and Mellapak packing has the largest capacity because it manages the largest liquid and gas flows. An analysis is done with respect to the pressure drop through the system for all packings considered, and a discussion is presented for each hydrodynamic and mass transfer parameter studied.

Commentary by Dr. Valentin Fuster
2003;():477-490. doi:10.1115/IMECE2003-55402.

A decomposition methodology based on the concept of “thermoeconomic isolation” applied to the synthesis/design and operational optimization of an advanced tactical fighter aircraft is the focus of this research. Conceptual, time, and physical decomposition were used to solve the system-level as well as unit-level optimization problems. The total system was decomposed into five sub-systems as follows: propulsion sub-system (PS), environmental control sub-system (ECS), fuel loop sub-system (FLS), vapor compression and PAO loops sub-system (VC/PAOS), and airframe sub-system (AFS) of which the AFS is a non-energy based sub-system. A number of different configurations for each sub-system were considered. The most promising set of candidate configurations, based on both an energy integration analysis and aerodynamic performance, were developed and detailed thermodynamic, geometric, physical, and aerodynamic models at both design and off-design were formulated and implemented. A decomposition strategy called Iterative Local-Global Optimization (ILGO) developed by Muñoz and von Spakovsky (2000b,c) was then applied to the synthesis/design and operational optimization of the advanced tactical fighter aircraft. This decomposition strategy is the first to successfully closely approach the theoretical condition of “thermoeconomic isolation” when applied to highly complex, highly dynamic non-liner systems. This contrasts with past attempts to approach this condition, all of which were applied to very simple systems under very special and restricted conditions such as those requiring linearity in the models and strictly local decision variables. This is a significant advance in decomposition and has now been successfully applied to a number of highly complex and dynamic transportation and stationary systems. This paper presents the detailed results from one such application, which additionally considers a non-energy based sub-system (AFS).

Commentary by Dr. Valentin Fuster

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