Study On The Formation Law Of Temperature Gradient In Preheating Process Of Solid Oxide Fuel Cell

Solid oxide fuel cell(SOFC)stacks are promising power generation devices due to their high effciency and flexible fuel capability.Solid oxide fuel cell operated at600-800 ℃.It must be heated-up to its starting temperature during the preheating process.Therefore,solid oxide fuel cell safely and quickly heated-up to the starting temperature is currently one of the important problem issues that restrict its development.The thermal stress caused by the inconsistency of the temperature rise is one of the important reasons for the failure of SOFC during the start-up process when using hot gas heating the SOFC stack.So it is necessary to study the heat transfer mechanism and the formation law of the temperature gradient of SOFC during the preheating process,so as to provide reference value for the optimization design of the preheating process.According to the conservation of mass,conservation of momentum,conservation of energy equations,and the basic principles and characteristics of SOFC,the numerical model of SOFC in preheating process was established firstly.And the validity of the model has been verified by comparing with the literature.Then the preheating process of SOFC has been simulated through the numerical model,to analyze the temperature distribution and the effect of heating parameters on the temperature rise of SOFC during the preheating process.As a result,the heating characteristics of preheating process were obtained.Heating the SOFC not only requires the formation of a temperature difference between the heating gas and the components,but also requires the formation of a temperature gradient along the channel direction(Z direction)between the inlet and the middle in SOFC.Increasing the inlet heating rate,inlet velocity and backpressure can accelerate the development of temperature gradient along the channnel direction in the SOFC,thus shortening the preheating time.Based on the heating characteristics,an optimal heating scheme was proposed for the inlet heating rate to enable a safe temperature gradient be formed quickly along channel and effectively shorten the preheating time.At the same time,the formation law of the maximum temperature gradient in the preheating process of SOFC was studied in the paper by analyzing the position change law of the maximum temperature gradient in the preheating process of SOFC under different working parameters.The results show that the maximum temperature gradient is always formed in the electrode under the inlet of the heating gas,and the operating parameters of the heating gas can significantly affect the variation of the maximum temperature gradient value.Further study revealed an abnormally high temperature gradient at the SOFC entrance that has been studied in particular by analyzing the entrance effect in the channel and its influence on inlet high temperature gradient at the inlet.The results showed that the abnormal high temperature gradient at the inlet is caused by the inlet effect and the fixed wall temperature boundary condition at the inlet.Finally,based on the analysis results,an improved SOFC heating model was proposed in this paper,which can effectively reduce the high temperature gradient at the entrance.In summary,the heat transfer law and the the formation law of temperature in the preheating process of SOFC were investigated by numerical method.Through the conclusion and the summary of the influencing factors of the temperature gradient,the research contents and results have certain reference value to the optimization of preheating process.