The Computation Of Thermal Stress And Failure Probability In Planar Solid Oxide Fuel Cell Within Multi-Field Coupling

Solid oxide fuel cell(SOFC),a new environmently friendly and efficient device which can achieve conversion directly from chemical energy to power,has become a significant investigated project.However,the structural strength and sealing technology of SOFC under high temperature still have some problems to solved,so that SOFC has not achieved the commercial applications.The numerical simulation has become an essential approach to investigate SOFC,because the state of SOFC in service process can not get using the current experiment test.In this paper,the three dimensional numerical model of SOFC within thermalflow and electrochemical reaction coupled has proposed to predict the temperature distribution and stress distribution in the whole cycle included of the heat-up stage,the operation stage and the cooling stage,using computational fluid dynamics and finite element method.The influence of operating parameters on the temperature distribution and the stress distribution in operation stage of SOFC has discussed.And,the conclusions of this paper are as follows:(1)The temperature gradient in heat-up stage and cooling stage are greater than that in operation stage,and the induced stress of SOFC is also large,and the thermal stress is larger in PEN and sealant.PEN and sealant in service process of SOFC suffer large,complex stress,and the failure probability is very close to 1 in the late heat-up stage and operation stage.Therefore,the PEN and sealant are the most vulnerable parts of the SOFC failure.(2)Comparing the counter-flow and co-flow,there is a smaller difference between the maximum temperature and the minimum temperature of SOFC with the counter-flow,which has a more uniform temperature distribution and smaller temperature gradient than with the coflow,and the overall average temperature of SOFC with counter-flow is not much different from that with co-fow.The stress distribution is similar to the temperature distribution from the whole SOFC,which illustrate that the thermal stress is mainly caused by the change of temperature,the different thermal expension coefficient between the materials and the external constraint.From the local point of view,the temperature gradient of SOFC with co-flow is larger than that with counter-flow,leading to larger stress in SOFC with co-flow.Therefore,the counter-flow is more appropriate flow pattern for SOFC.(3)With counter-flow,the temperature distribution trend is not changed with the increase of fuel gas and air flow rate,but the maximum temperature and the average temperature are both decrease,and the thermal induced stress is also reduced.In general,changing the air flow rate can adjust the temperature level of SOFC.(4)With the increase of hydrogen content in fuel gas or oxygen content in the air,the temperature will increase in SOFC,the increase rate of temperature will gradually become slower,and the performance of SOFC will be improved.But,the temperature gradient will increase with the higher temperature,so that the thermal induced stress also will increase.Therefore,selecting the appropriate operation parameters considering the practical operating environment of SOFC is essential.