Modeling Study On Transport Characteristics And Performance Of Solid Oxide Fuel Cells

Solid oxide fuel cell(SOFC)is a promising and efficient energy conversion device with energy conversion efficiency up to 70%,which provides a new energy storage and conversion method,and it can be applied to small and medi?m-sized distribution power generation systems,combined heat and power systems,etc.SOFC has excellent fuel flexibility,as an alternative fuel for hydrogen,natural gas or methane has the advantages of low cost,abundant natural reserves.Direct internal reforming solid oxide fuel cells(DIR-SOFC)fueled with natural gas or methane have higher system efficiency and lower operating costs.However,there are few experimental studies on DIR-SOFC,and due to the excessively high operating temperature and the excessively small cell size,it is difficult to experimentally measure the key parameters within the SOFC.Therefore,the numerical simulation method was used to study the distribution of key parameters in SOFC and DIR-SOFC,and the effect of operating parameters on the performance of SOFC and DIR-SOFC was investigated.The main research work carried out in this paper are as follows:(1)A three-dimensional multi-physics fully coupled n?merical model of SOFC was established.The model coupled mass transfer,heat transfer,species transfer,moment?m transfer,charge transfer and electrochemical reaction.The model was solved using commercial finite element software COMSOL 5.3.(2)An anode supported planar single SOFC experimental setup with effective active surface 4 cm×4 cm was established.The current density-voltage performance curves of SOFC fed with hydrogen and DIR-SOFC fed with methane were tested for model validation,respectively.(3)The prediction accuracy of cell performance with Fick model,dust-gas model and Stefan-Maxwell model was compared.The internal transport properties of SOFC fed with hydrogen such as species concentration,temperature,current density,flow field and over-potential distribution was examined with the developed model.Moreover,the effect of flow configuration,operating temperature as well as fuel flow rate on SOFC performance was studied systematically.The results show that the temperature of the cell components gradually increased,the activation overpotential gradually decreased,the hydrogen and oxygen mole fractions gradually decreased,the current density gradually decreased,and the concentration overpotential increased gradually along the length of the cell length during the downstream operation.Increasing fuel flow rate and operating temperature,power density increased.The temperature increased from 1023 K to 1073 K?1123 K,the maxm?m power density increased from 0.33 W/cm~2 to 0.50 W/cm~2?0.69 W/cm~2.(4)Regarding methane steam reforming(MSR)as the internal reforming mechanism,the species concentration,temperature and current density distribution within DIR-SOFC fed with methane were simulated.Moreover,the effects of methane concentration,water vapor concentration,operating temperature,fuel flow rate,and flow direction on DIR-SOFC performance were investigated with the established model.It is found that the coupling of the electrochemical reaction and the methane steam reforming reaction leads to different distributions of temperature and speicies concentration at different fuel flow rates and operating loads.There are three temperature distributions along the cell length,namely,gradually increases,gradually increases after first decreases in the fuel inlet region,and gradually decreases.When the fuel flow is 50 NmL/min and 100 NmL/min,the hydrogen mole fraction gradually decreases after first increases in the fuel inlet region along the cell length and the hydrogen mole fraction gradually increases along the cell length when the fuel flow is 200 NmL/min.Increasing methane concentration,operating temperature and fuel flow rate,the power density increased simultaneously.