Research On Water And Heat Management Of Proton Exchange Membrane Fuel Cell

With the rapid development of economy,fossil fuels have been consumed in large quantities,and the corresponding environmental pollution problems have become increasingly severe.How to reduce the consumption of fossil fuels and realize the efficient and clean use of energy is a century-old problem facing mankind.Fuel cell can directly convert the chemical energy in the fuel into electrical energy through an electrochemical reaction.Because it is not restricted by the Carnot cycle,has high energy conversion efficiency,and does not pollute the environment.So it is considered to be the most promising energy conversion device to replace traditional energy supply devices.Among them,Proton Exchange Membrane Fuel Cell(PEMFC)not only has the general advantages of fuel cells,but also has outstanding advantages such as low operating temperature,no electrolyte loss,high specific power,and fast start-stop response.It has become a research hotspot of scientific researchers.In this thesis,combined with the working characteristics of PEMFC and uses COMSOL Multiphysics software to carry out a numerical simulation study on the PEMFC water and heat management from two aspects of cell operating parameters and material physical parameters.Firstly,this thesis around the complex "three transfers and one reaction" process in the operation of PEMFC,a three-dimensional steady-state PEMFC model is established based on the conservation equations in the basic fluid mechanics and electrochemical reaction models.And verify its correctness by comparing with the previous experimental results.The results show that the simulation results are consistent with the experimental results under the same conditions.The maximum error of current density and average electrolyte temperature are 2.05% and 0.6%,respectively.Which proves that the established numerical model is correct and can be used for subsequent research.Secondly,this thesis studied the influence of cell material physical parameters on fuel cell performance by changing the PEMFC cathode GDL porosity.In this thesis,four models with porosity varying along the cell thickness and six models with porosity varying along the cell length were established respectively and study the effects of different cathode GDL porosity on fuel cell performance.The results show that the cell limiting current density is directly proportional to the cathode GDL average porosity,and is basically independent of the porosity gradient.The existence of cathode GDL porosity gradient can effectively improve the uniformity of water,oxygen and current distribution.The proper humidity conditions of the fuel cell inlet gas can effectively optimize PEMFC water and heat management,thereby improving the cell performance.In this thesis,the humidification temperature of inlet gas is selected to study the influence of operating parameters on fuel cell performance.By changing the humidification temperature of the cathode and anode inlet gas between 313.15K-363.15 K,the influence of the humidification temperature on the cell performance was studied during symmetric humidification and asymmetric humidification.It is found that for the symmetric humidification model,there is a threshold for the influence of humidification temperature on current density and cell temperature.Within the humidification temperature range studied in this thesis,the best imported gas humidification temperature is 333.15 K.For the asymmetric humidification model,under high working voltage,increasing the humidification temperature of the cathode and anode inlet gas will help to improve the cell performance,and changing the humidification temperature of the anode gas has a greater impact.When changing the humidification temperature of the cathode and anode,the current density increased by43.7% and 58.4%,respectively.Under low working voltage,the influence of humidification temperature on cell performance changes.The current density decreases with the increase of the humidification temperature,and changing the humidification temperature of the cathode gas has a greater impact.When changing the humidification temperature of the cathode and anode,the current density decrease by 19.7% and 1.3%,respectively.