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This paper presents an analysis of a heat pump that uses a solid desiccant dehumidifier to reduce the humidity of the ambient air that flows into the evaporator, with the purpose of decreasing frost formation on the evaporator. The heat pump is analyzed by adding a dehumidifier model to a previously developed heat pump model that includes frost formation. The dehumidifier reduces the amount of energy required for evaporator defrosting, but introduces the need for energy for regenerating the desiccant. The purpose of the analysis is to search for operating conditions and optimum dehumidifier designs for which the use of the dehumidifier results in energy savings. The results show that the use of a dehumidifier may reduce energy consumption if the energetic cost of defrosting the evaporator is high. Other benefits of dehumidification include an increase of the time intervals between defrost cycles, a better stability in the conditions in the controlled space, and the potential for increased reliability and reduced maintenance of the heat pump.

We have used the HCT (hydrodynamics, chemistry, and transport) chemical kinetics code to simulate HCCI (homogeneous charge compression ignition) combustion of methane-air mixtures. HCT is applied to explore the ignition timing, burn duration, N[O.sub.x] production, gross indicated efficiency and gross IMEP of a supercharged engine (3 atm. intake pressure) with 14:1, 16:1 and 18:1 compression ratios at 1200 rpm. HCT has been modified to incorporate the effect of heat transfer and to calculate the temperature that results from mixing the recycled exhaust with the fresh mixture. This study uses a single reaction zone that varies as a function of crank angle. The ignition process is controlled by adjusting the intake equivalence ratio and the residual gas trapping (RGT). RGT is internal exhaust gas recirculation, which recycles both thermal energy and combustion product species. Adjustment of equivalence ratio and RGT is accomplished by varying the timing of the exhaust valve closure in either two-stroke or four-stroke engines. Inlet manifold temperature is held constant at 300 K. Results show that, for each compression ratio, there is a range of operational conditions that show promise of achieving the control necessary to vary power output while keeping indicated efficiency above 50 percent and N[O.sub.x] levels below 100 ppm. HCT results are also compared with a set of recent experimental data for natural gas.

This paper shows the development and use of a transient model for evaluating frost formation on a parallel-plate heat pump evaporator. A frost formation model is derived by applying the equations of conservation of mass, momentum, and energy, as well as empirical correlations, to calculate the growth and densification of the frost layer. The frost formation model is validated by comparison with experimental results. The frost formation model is then incorporated into the evaporator subroutine of an existing heat pump model to calculate performance losses due to frosting as a function of weather conditions and time of operation since the last evaporator defrost. Performance loss calculation includes the effect of air pressure drop through the evaporator and the reduction in evaporator temperature caused by the growth of the frost layer. The results show frost formation parameters and heat pump COP as a function of time and ambient conditions. It is determined that there is a range of ambient temperatures and humidities in which frosting effects are most severe, and this range is explored to calculate heat pump operating conditions. The heat pump analysis results are expected to be useful in predicting optimum defrosting conditions, and to evaluate alternative methods for defrosting.

Vehicle heating requires a substantial amount of energy. Electric vehicles (EVs) generate little waste heat, and using battery energy for heating may consume a substantial fraction of the energy storage capacity, reducing the vehicle range, which is one of the most important parameters in determining EV acceptability. This paper analyzes the applicability of a desiccant dehumidifier for providing comfort heating in an EV with reduced energy consumption. A dehumidifier can reduce the heating load in a vehicle because it adsorbs the water vapor generated by the passengers, thereby avoiding water condensation on the windows without requiring a high external air ventilation rate or a high window temperature. The results indicate that the desiccant dehumidifier can reduce the steady-state heating load by 60 percent or more under typical conditions. The reduction in heating load is such that waste heat may be enough to provide the required heating under most ambient conditions. Desiccant system dimensions and weight appear reasonable for packaging inside an EV.

This paper studies the application of insulated pressure vessels for hydrogen-fueled light-duty vehicles. Insulated pressure vessels are cryogenic-capable pressure vessels that can be fueled with liquid hydrogen (L[H.sub.2]); low-temperature (46 K) compressed hydrogen (C[H.sub.2]) ; or ambient-temperature C[H.sub.2]. In this analysis, hydrogen temperatures, pressures, and venting losses are calculated for insulated pressure vessels fueled with L[H.sub.2] or with low-temperature C[H.sub.2], and the results are compared to those obtained in low-pressure L[H.sub.2] tanks. Hydrogen losses are calculated as a function of daily driving distance during normal operation; as a function of time daring long periods of vehicle inactivity; and as a function of initial vessel temperature during fueling. The results show that insulated pressure vessels have packaging characteristics comparable or better than those of conventional, low-pressure L[H.sub.2] tanks, with greatly improved dormancy and much lower boil-off, and therefore appear to be a good alternative for vehicular hydrogen storage.

This paper presents an analysis of a class of latent thermal energy storage (LTES) system. The analysis is based on a simplified model that allows the system performance to be evaluated in terms of a small set of parameters, while still retaining the main thermodynamic aspects associated with their operation. This analysis therefore permits the broad-based application potential of these systems to be viewed. The paper also discusses the applicability of the model to practical systems. This paper analyzes LTES with multiple energy storage cells and multiple phase-change materials (PCMs). The most general case of infinite energy storage cells and PCMs is solved, for the charge process only, as well as for the overall charge-discharge process. The results yield the optimum phase change temperature, expressed as a continuous function of position along the LTES. The method is equally applicable to the case of a finite number of storage cells. An example of the application of the method to this case is also included. The results show the optimum phase change temperatures for each of the problems being considered, along with the corresponding optimum exergetic efficiencies. The solutions to the optimization problems are surprisingly simple to express, considering the difficulty of the problems, and indicate the potential advantages of using LTES with multiple PCMs.

This paper shows an analysis of the applicability of an adsorption system for electric vehicle (EV) air conditioning. Adsorption systems are designed and optimized to provide the required cooling for four combinations of vehicle characteristics and driving cycles. The resulting adsorption systems are compared with vapor compression air conditioners that can satisfy the cooling load. The objective function is the overall system weight, which includes the cooling system weight and the weight of the battery necessary to provide energy for air conditioner operation. The system with the minimum overall weight is considered to be the best. The results show the optimum values of all the variables, as well as temperatures and amounts adsorbed, for the adsorption and desorption processes. The results indicate that, for the conditions analyzed in this paper, vapor compression air conditioners are superior to adsorption systems, not only because they are lighter, but also because they have a higher COP and are more compact.