• Energy Research

Abstract In this study, a novel proton exchange membrane fuel cell (PEMFC) system is proposed, which uses organic working fluid to cool the fuel cell stack directly and recovers the waste heat by combining with an Organic Rankine Cycle (ORC) system. A thermodynamic model of each component and subsystem is established for the combined PEMFC-ORC system. The influence of the PEMFC stack inlet temperature and current density, the ORC working fluid, superheat temperature and saturation pressure on the system performance is studied. The flow and distribution of energy and exergy in the whole PEMFC-ORC system are analyzed comprehensively. It is found that the system performance indicators reach the optimum when the stack inlet temperature is about 343.15 K. Lower current density improves the system efficiency, but reduces the system power density. R245fa shows the best performance among the five organic working fluids investigated for the designed ORC system. Higher superheat temperature and saturation pressure of the organic working fluid in the cycle improves the ORC efficiency. The PEMFC stack has the largest exergy loss in the system, and the cathode side heater and air compressor also contribute much to the large power and exergy loss. The optimization of these components should be the focus of system performance improvement.

Abstract In this study, a novel proton exchange membrane fuel cell (PEMFC) system is proposed, which uses organic working fluid to cool the fuel cell stack directly and recovers the waste heat by combining with an Organic Rankine Cycle (ORC) system. A thermodynamic model of each component and subsystem is established for the combined PEMFC-ORC system. The influence of the PEMFC stack inlet temperature and current density, the ORC working fluid, superheat temperature and saturation pressure on the system performance is studied. The flow and distribution of energy and exergy in the whole PEMFC-ORC system are analyzed comprehensively. It is found that the system performance indicators reach the optimum when the stack inlet temperature is about 343.15 K. Lower current density improves the system efficiency, but reduces the system power density. R245fa shows the best performance among the five organic working fluids investigated for the designed ORC system. Higher superheat temperature and saturation pressure of the organic working fluid in the cycle improves the ORC efficiency. The PEMFC stack has the largest exergy loss in the system, and the cathode side heater and air compressor also contribute much to the large power and exergy loss. The optimization of these components should be the focus of system performance improvement.

Abstract Proton exchange membrane fuel cells are usually connected in series to form a fuel cell stack in order to satisfy the power demand of the practical applications. It is necessary to investigate the designs of the fuel cell stack to achieve the uniformity of reactant distributions and maximize the performance of the fuel cell stack. In this study, a fuel cell stack model is established based on the flow network method. The pressure and mass distributions of the reactant gas and coolant streams are determined by the flow network method incorporating the cross flow effect and the minor losses. The temperature distributions are also considered, and the individual cell performances in the fuel cell stack are obtained. The optimization of the fuel cell stack is also carried out after the stack model is validated by the experimental data. The flow channels are optimized in terms of the stack net power considering the pumping power losses and the cooling channels are optimized in terms of minimum power consumption for the same amount of cooling effect. Finally, the optimal designs for the fuel cell stack are obtained.

Abstract Proton exchange membrane fuel cells are usually connected in series to form a fuel cell stack in order to satisfy the power demand of the practical applications. It is necessary to investigate the designs of the fuel cell stack to achieve the uniformity of reactant distributions and maximize the performance of the fuel cell stack. In this study, a fuel cell stack model is established based on the flow network method. The pressure and mass distributions of the reactant gas and coolant streams are determined by the flow network method incorporating the cross flow effect and the minor losses. The temperature distributions are also considered, and the individual cell performances in the fuel cell stack are obtained. The optimization of the fuel cell stack is also carried out after the stack model is validated by the experimental data. The flow channels are optimized in terms of the stack net power considering the pumping power losses and the cooling channels are optimized in terms of minimum power consumption for the same amount of cooling effect. Finally, the optimal designs for the fuel cell stack are obtained.

Abstract In this study, a novel proton exchange membrane fuel cell (PEMFC) system is proposed, in which a composition adjustment organic Rankine cycle (CAORC) system is integrated. The waste heat from both PEMFC stack and after-burner is recovered by CAORC system to realize the maximum output power conversion from system waste heat. Based on 3D construction method of thermodynamic cycle, the system thermodynamic model is established to evaluate the performance of the proposed PEMFC-CAORC system. The effects of PEMFC operating temperature, current density and high evaporation temperature are analyzed. The system energy and exergy efficiencies are 39.44% and 47.60% at the PEMFC operating temperature of 358 K and current density of 0.6 A cm−2. As the PEMFC operating temperature rises, its performance can be further improved, and the system energy and exergy efficiencies at 368 K reach 40.36% and 48.72%. As the PEMFC current density increases, the system net power increases while both efficiencies drop. To improve the CAORC performance specifically, the evaporation temperature in the after-burner is suggested to be high enough, and genetic algorithm is used to optimize key parameters of the CAORC. The mixture of Benzene and Toluene are the optimum zeotropic fluid type for all optimization cases investigated, while its proportion, separation dryness and evaporation temperature vary in different PEMFC operating conditions. Compared with the original results, the CAORC thermal efficiency increases by over 4% with genetic algorithm optimization.