Study On The Performance Of Novel PEMFC System Based On Organic Rankine Cycle Waste Heat Recovery

Proton exchange membrane fuel cell(PEMFC)has the advantages of high efficiency and cleaness,and has attracted wide attention in recent years.However,a large amount of waste heat is generated and dissipated during its reaction process,resulting in a serious waste of fuel energy and limiting the further improvement of efficiency.In this study,novel coupling schemes of organic Rankine cycle(ORC)system and PEMFC system are proposed to convert PEMFC’s low-temperature waste heat into high-grade power,thus improving the overall efficiency of the combined system.Based on the integration of thermodynamic modeling and analysis methods of PEMFC system,the following studies on system performance are carried out:Firstly,the ORC organic working fluid is directly connected to PEMFC stack for boiling cooling,and a novel vehicular PEMFC-ORC combined system is designed.The system thermodynamic model is established,and the system’s performance variations and energy distributions under different operating conditions are obtained and analyzed.The system’s overall performance is optimal at the stack inlet temperature of 343.15 K.As the stack current density increases,the system’s net power and power density increase,but the efficiencies decrease.Among the five selected ORC working fluids,R245 fa has the best overall performance.The cathode loop heater and air compressor have the largest power consumption and exergy loss,which are the main sources of system’s parasitic energy loss.Secondly,a novel PEMFC-CAORC combined system is proposed by coupling the component adjustment organic Rankine cycle(CAORC)system with PEMFC system,which avoids the anode nitrogen accumulation and improves the humidification effect by using high-temperature and high-humidity exhaust gas.Under basic operating conditions,the CAORC system improved the energy and exergy efficiency of the combined system by 6.23% and 7.51%,respectively.In the range of simulated operating conditions,the combined system’s efficiency increases continuously with PEMFC operating temperature,and decreases with current density.In addition,the genetic algorithm is adopted to further optimize the combination of key parameters of CAORC system to achieve a better match between CAORC system and multitemperature heat source,and the thermal efficiency is increased by more than 4%.Finally,to verify the boiling cooling effect of organic working fluid,four PEMFC cooling plates are designed,and the boiling evaporation process of pure organic working fluid is simulated with CFD method.According to the simulation results,the designed cooling plates can control the average temperature and maximum temperature difference in a reasonable range,and meet the cooling requirements of PEMFC.In addition,the distributions of phase,temperature and pressure in plates with different flow channels are compared and analyzed,and the guidance for cooling flow channel’s optimal design is proposed.