| Hydrogen energy is a kind of clean and renewable new energy,which is expected to solve the energy crisis and environmental pollution problems faced by human society.As a new energy equipment in the core of hydrogen energy application,PEMFC has the advantages of rapid startup,zero emission,high energy conversion efficiency and high power density,and can be widely used in transportation,fixed and portable fields.At present,the heat balance of PEMFC is one of the key factors restricting the further development of PEMFC,and reasonable cooling channel structure and uniform cooling water flow distribution in the stack can stabilize the internal temperature of the battery,thus improve the battery output performance and prolong the battery life.In this paper,taking the PEMFC liquid cooling system as the research object,the polarization curves of PEMFC at different temperatures are measured based on the test platform,and the numerical simulation method is used to explore the internal flow and heat transfer characteristics of PEMFC and the internal flow distribution characteristics of PEMFC stack under different cooling channels.The Z-type structure is designed and optimized according to the non-uniform distribution of cooling water flow in the stack.Firstly,the PEMFC test platform is built,and the step-by-step voltage conversion method is used to measure the PEMFC polarization curve by changing the working temperature.The results show that the polarization curve measured by the experiment is consistent with the theoretical polarization curve,and the voltage and current density is highly nonlinear in the activated polarization region,and the relationship between voltage and current density is basically linear in the ohmic polarization region.in the concentration polarization region,the voltage and current density is highly nonlinear.In addition,in the operating temperature range of 333-353 K,the output performance of PEMFC increases with the increase of temperature.Then,the basic hydrodynamics model,electrochemical reaction model and polarization control equation in PEMFC simulation are described,which provides a theoretical basis for subsequent single cell and stack simulation research.At the same time,the accuracy of the model is verified by comparing the polarization curves obtained by test and simulation under the same working conditions.The research results show that when the battery voltage is 0.6 V,the relative error of current density between test data and simulation results is 2.78%,and the relative error between test data and simulation results under other voltage conditions is less than 3.13%.The accuracy of the calculation model is high.Secondly,a three-dimensional non-isothermal single cell model is established,and the internal flow and heat transfer process of PEMFC with serpentine gas channels with four different cooling channels is numerically simulated under the operating voltage of 0.6V.The results show that the distribution uniformity of cooling water is A,D,C and B type from inferior to excellent.The pressure in the four kinds of channel decreases gradually along the direction of cooling water flow,and reaches the minimum at the outlet of cooling water,in which the pressure gradient in type B channel is the largest,and the pressure drop at inlet and outlet is much higher than that of the other three channels,while the increase of pressure drop in type C channel is the smallest.There is a large local hot spot on the surface of A-type runner,the highest surface temperature is the highest,and the temperature distribution uniformity is the worst.The maximum temperature of C-type runner and D-type runner is slightly higher than that of B-type runner,and the temperature distribution uniformity of C-type runner is the best.The maximum temperature of proton exchange membrane of type A channel is the highest and the uniformity is the worst.The maximum temperature of proton exchange membrane of type C channel and type D channel is slightly higher than that of type B channel,and the uniformity of temperature distribution is slightly worse than that of type B channel.The average water content of proton exchange membrane in type An is the lowest,while that of proton exchange membrane in type B is the highest and slightly higher than that in type C.at the same time,the temperature on the proton exchange membrane directly affects its water content,thus affecting the proton conductivity.The highest temperature in the PEMFC is located in the cathode catalytic layer,and the lowest temperature is located in the anode cooling channel.The overall temperature of the battery is Atype flow channel,D-type flow channel,C-type flow channel and B-type flow channel from high to low.Then,a three-dimensional simplified PEMFC stack model is established,and the difference of cooling water flow in U-shaped structure and Z-shaped structure is studied.The effects of inlet velocity,inlet velocity distribution,the number of cooling plates and the number of inlet and outlet of main pipe on the flow distribution and pressure variation characteristics in the stack are analyzed.The results show that the flow distribution in U-shaped structure is opposite to that in Z-shaped structure,and the distribution of cooling water in Z-shaped structure is more uniform.In addition,the variation law of inlet manifold pressure of U-shaped structure is the same as that of Z-shaped structure,while that of outlet manifold is opposite.The increase of inlet velocity reduces the uniformity of flow distribution and increases the pressure fluctuation in the stack.When the inlet velocity 2 is greater than the inlet velocity 1,the uniformity of flow distribution in the stack can be improved and the pressure fluctuation in the stack can be reduced.The greater the inlet velocity1,the worse the uniformity of flow distribution and the greater the pressure fluctuation.The increase of the number of cooling plates in the stack will reduce the uniformity of flow distribution and increase the pressure difference in the inlet and outlet main pipe.The uniformity of the flow distribution in the single-inlet and double-outlet structure is the best,and the pressure in the outlet main pipe first increases and then decreases,followed by the double-inlet and single-outlet structure,and the pressure in the inlet main pipe increases at first and then decreases,and the uniformity of flow distribution in the single-inlet and single-outlet structure is the worst.Finally,in order to improve the uniformity of cooling water flow distribution in Z-type structure,three kinds of stack structures with different inlet header configurations are designed and compared with the original structure.The results show that the conical inlet main pipe can effectively improve the defect of flow distribution in Z-type structure,and improve the uniformity of flow distribution.Among the three optimized structures,the uniformity of flow distribution in Z-c structure is the best.The second is Zmurb structure,and the worst is Zmura structure. |
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