Multi Physical Field Coupling And Performance Optimization Of Solid Oxide Fuel Cell

Solid oxide fuel cell(SOFC)is an electrochemical energy conversion device that directly converts chemical energy into electrical energy.It has the advantages of high energy conversion efficiency,flexible fuel selection,flexible structure design and low catalyst cost.The internal electrochemical reaction and transport process of SOFC is extremely complex,involving chemical transport,electrochemical reaction,electron and ion transport,momentum transfer,heat transfer and mass transport.Numerical simulation of multiple physical fields is an economical and effective method to understand the basic mechanism of physical and chemical processes of SOFC and to optimize the design.In order to improve the electrochemical performance of SOFC,a multi physical coupling model was established to optimize the operating conditions and geometric structure of SOFC.Firstly,the model of coupled momentum transfer,mass transfer,heat transfer and electrochemical reaction was established,which was verified by experiments.Structured electrolyte was prepared flexiblely by the 3D printing technology.The impact of structural design on cell performance was further analyzed by means of simulation.The experimental results show that the performance of the cell with structured electrolyte surface was improved by 46.22% when the effective area was increased by 18.57% compared with the planar cell.The structural design of electrolyte surface mainly reduces the area specific resistance by reducing the ion resistance and increasing the effective reaction area,so as to improve the output power of the cell.The simulation results of different structured designs showed that the ion resistance had the greatest impact on the cell performance,followed by the effective reaction area.The regression relationship of the cell performance and influencing factors was as follows: △P=0.17×△A-0.474×△T+0.758.Compared with planar SOFC,tubular SOFC has the characteristics of high mechanical strength,high thermal shock resistance,simplified sealing technology and high modular integration performance.It is suitable for the construction of large capacity power station.The new 3D printing technology also provides the feasibility for the integrated preparation of tubular stack.In this part,according to the tubular stack prepared by 3D printing technology,the models of single tube cell,honeycomb three tubular stack,independent channel three tubular stack and seven tubular stacks were established to study the cell output performance under different stack structures and operating conditions.The simulation results showed that the maximum power density of honeycomb three tubular stack was lower than that of independent channel three tubular stack of the same size due to ionic resistance and failure of internal mass transfer channel.The results showed that the performance of the cell increased with the increase of operating temperature,hydrogen content,effective current collecting area of cathode and the decrease of tube diameter.The maximum power density deviation of single tube,independent channel three tubular stack and seven tubular stack was less than 1.3%,and the cell output power increased with the number of tubes in multiples.The results provided a theoretical basis for further expanding the tubular stack,optimizing the structure and operating conditions of the tubular stack.Based on the research in the previous part,the scale of the tubular reactor was expanded.A multi tubular stack model with inlet and outlet settings was established to optimize the manifold design and structural parameters.The results showed that tube configuration in arrangement of equilateral triangle had better mass transfer performance and higher power density than square configuration.The fluid concentration and uniformity in the stack can be improved by decreasing the diameter of the stack,increasing the widths of the fluid distribution domain and the diameter of the inlet and outlet of the stack.In order to balance the concentration distribution inside and outside the tube,an optimal tube spacing existed.Compared with the straight configuration of the anode and cathode inlet and outlet settings,the Z configuration of the cathode inlet and outlet and the inverted N configuration of the anode inlet and outlet settings were conducive to the flow and mass transfer in the stack and improve the output power density of the cell.The research results of this paper provided a fully coupled multi physical field model,which supplied a theoretical basis for the design of fuel cell electrolyte structure and tubular stack structure.