Proton Exchange Membrane Fuel Cell Energy Conversion And Heat Mass Transfer Enhancement Study

Proton exchange membrane fuel cell technology has been applied in the field of vehicles,electronic devices,and mobile power.To improve the energy conversion efficiency of hydrogen fuel cells and promote their industrialization,there is an urgent need to analyze more essentially the heat and mass transfer characteristics and the physical mechanisms of energy transfer and conversion inside the system.Energy conversion as well as heat and mass transfer in proton exchange membrane fuel cells are complex multi-physical field coupled processes,and the thermodynamic analysis of this process from the spontaneity of the reaction process is less studied at present.Therefore,this thesis introduces the generalized Carnot theorem based on Gibbs’ principle and Nernst’s principle,analyzes the energy transfer and conversion process between chemical energy and electrical energy,and then analyzes the factors affecting the heat and mass transfer performance inside the proton exchange membrane fuel cell based on the enhanced heat and mass transfer theory,and uses these influencing factors as the main variables,and comparatively analyzes and studies these factors on the performance of the proton exchange membrane fuel cell The degree of influence of these factors on the performance of the proton exchange membrane fuel cell was studied in a comparative analysis.First,the electrochemical reaction process is analyzed based on Gibbs’ principle and Nernst’s theory,and the generalized Carnot theorem is applied to reveal the physical mechanism of energy transfer and conversion efficiency.The results show that during the normal operation of the proton exchange membrane fuel cell system,the energy transfer and conversion process between chemical energy and electrical energy inside the system is a thermodynamic coupling between the spontaneous heat transfer process and the generalized force work process of electrons from disorder to an order under the electrochemical potential gradient,and the essence is that the spontaneous heat transfer process drives the non-spontaneous generalized force work process of electrons from disorder to order.Secondly,for the enhanced heat exchange process and the enhanced mass transfer process of the reaction gas in the proton exchange membrane fuel cell system,the thermodynamic coupling mechanism,the field synergy principle,and the diffusive mass transfer theory of the gas is applied to the theoretical analysis of the above processes.The results show that the cooling flow channel is taken as an isolated system,and the cooling process in the cooling flow channel is a thermodynamic coupling mechanism of the non-spontaneous heat transfer process driven by the spontaneous mass transfer process.Based on the field synergy principle,the smaller the synergy angle between the velocity field and concentration field gradient in the gas flow channel,the stronger the synergy between the velocity vector and the concentration gradient,and the enhanced convective mass transfer in the gas flow channel.Finally,the heat and mass transfer characteristics of the proton exchange membrane fuel cell system were simulated and analyzed by Fluent software with cooling water temperature,water flow rate,different gas flow channel cross sections,and different pressure conditions as independent variables.The results show that the cathode catalytic layer is the main heat-producing zone of the electrochemical reaction,and the temperature is symmetrically distributed along both sides of the catalytic layer,so that the appropriate reduction of the cooling water temperature can effectively improve the cell performance,and increasing the cooling water flow rate can change the state of fluid motion and strengthen the convective heat transfer of the cooling water.The heat transfer demand within the system;when the operating pressure is increased,the mass transfer performance of the gas flow channel on the anode side is significantly enhanced,however,the mass transfer performance of the gas flow channel on the cathode side is not sensitive to the operating pressure.Compared with the rectangular cross-section,the mass transfer performance of the flow channel with triangular cross-section is the best,and the mass transfer performance of the flow channel with hexagonal cross-section is the worst,and the field synergy principle has theoretical guidance for strengthening convective mass transfer.