Performance Optimization And Flow Field Structure Research Of Solid Oxide Fuel Cells

With the rapid growth of population and economy,the global energy consumption is also increasing dramatically.It becomes an increasing hotspot for the research of high efficiency,low cost and environmentally-friendly renewable energy conversion and storage systems.As a new energy generation device based on electrochemical reactions,solid oxide fuel cells(SOFCs)can directly convert chemical energy into electrical energy,and has received widely attention for its advantages of high energy conversion efficiency,low noise level and low pollutant emission.However,the high cost and the low lifetime of SOFCs need to be further solved before commercialization.In addition,the higher operating temperature of SOFC puts higher requirements on the sealing method,and it is difficult to obtain the detailed distributions of key internal parameters by experimental method,which limits the improvement of material performance,determination of structure parameters,optimization of operating conditions and performance improvement of SOFC.Therefore,carrying out SOFC numerical simulation is an effective way to improve the SOFC performance.In this study,the SOFC performance optimization is carried out for single-channel and planar SOFCs,coupled with CFD numerical simulations,agent models,and optimization algorithms.The main contents are drawn as follows:Firstly,a three-dimensional,steady-state CFD model of the anode-supported SOFC is established,which is based on the conservation equations,the electrochemical reaction and the charge transport equations,including the detailed geometry,the model boundary condition settings and the numerical methods adopted.Then,the polarization curves calculated from the simulation are compared with the experimental results to verify the model accuracy.The polarization curves calculated from the numerical simulation are compared with the experimental results from literatures to verify the model accuracy.Numerical calculations were used to obtain the current density,temperature distribution and component concentration distribution under the operating conditions of SOFC,and then the distribution pattern of each physical parameter during the operation of the SOFC is then analyzed.It was found the current density was non-uniformly distributed in the electrode along the height direction,and there was an optimal value of the rib width,so it was necessary to carry out further optimization research.Then,a framework and methodology for improving SOFC performance assisted by computational fluid dynamic(CFD)modeling,artificial neural network(ANN),and genetic algorithm(GA)is presented.Based on the SOFC parameters(operating conditions,geometry parameters and microscopic parameters,etc.),the mapping relationship between the decision variables and objective functions was obtained by Latin hypercube sampling method.Then the 19 widely used intelligence algorithms,e.g.Artificial Neural Network(ANN),Boltzmann Machine(BM),Support Vector Machine(SVM),etc.,were employed to train the databases.Next,the developed ANN surrogate model was used to replace the complicated and timeconsuming CFD model and to predict SOFC’s performance and optimize the power density output.Finally,the system optimization was performed by using genetic algorithm(GA)to maximize the power density.The results showed that the artificial neural network(ANN)achieved the best accuracy(R2=0.99889)in terms of predictions of SOFC performance.Besides,it was found that the optimal SOFC had a better gas concentration distribution which can enhance the mass transfer in the electrode,and thus the SOFC performance was improved.Finally,for solving the problem of non-uniformity of gas flow in planner SOFC distribution,a new tree-shaped channel structure is designed in the external flow field to meet the requirements of high flow field uniformity.It reduces the generation of eddy currents,enhances the flow field mass transfer capability and achieves an increase in the power density of the optimized cell,with a maximum power density increase of 8.16%.In terms of the internal flow field optimization,the horizontal and vertical convergent flow channel structures are designed and compared with the conventional parallel flow channel structure(the based model).It was found that the current density of the vertical convergent flow channel model is 3.27%higher than that of the horizontal convergent flow channel model and 10.55%higher than that of the parallel flow channel model.The vertical convergent flow channel structure has the highest oxygen uniformity index due to the appropriate block configuration,with an increase of 1.23%over the base model.The percentage of increased parasitic power is 0.07%and is therefore negligible.The vertical convergent flow channel structure is significantly better than the parallel flow channel model and the horizontal convergent flow channel model in terms of enhanced mass transfer and improved performance of the planner SOFC.