Three Dimensional Numerical Modeling Of Energy Conversion Performance And Flow Channel Optimization In Direct Methanol Fuel Cell

The Direct Methanol Fuel Cell(DMFC)is a sustainable power source,which could directly convert the chemical energy in the fuel to electric energy with a high efficiency and no pollution generated.This master thesis focuses on the optimization of energy conversion performance in DMFC setup.The effect of operating conditions as well as flow channel configurations on internal flow characteristics are well investigated by using numerical method.The study covers the establishment of three-dimensional numerical model;the flow patterns and distributions for methanol in different operating conditions;the relationship between current output and working parameters;the influence of channel number on DMFC performance;flow field optimization based on concentration distributions in passes;the comparison of different channel configurations on energy conversion performance.The main results of this dissertation are listed as follows:(1)A kind of three-dimensional numerical model was constructed for modeling the energy conversion process in DMFC.Through theoretical analysis,this study used the mass and momentum conservation equations,species transport equation and electrochemical equation to construct the theoretical model.It was subsequently solved by commercial software Fluent,which was based on the finite volume method(FVM).The well matching between numerical results and experimental data verified the accuracy and availability of this model.(2)This study has analyzed the effect of main operating parameters on DMFC performance.The results showed that the increasing of inlet velocity was an effective method to accelerate the internal flow fields,and further improve the mean concentration and distribution uniformity of methanol on internal planes.The frontier for optimal operating conditions for DMFC performance was proposed by calculating the growth ratio of current density output.(3)This study has analyzed the effect of channel number on DMFC performance.The results showed that more number of passes could lead to more uniform internal distributions of reactants.The corresponding consumption of methanol in catalyst layer would be also increased so as to obtain a large current density output.(4)A convergent-type flow channel for optimizing channel configurations was explored.This designing scheme was inspired by the variation of methanol concentration in channel layer.The investigation on internal flow fields showed that the DMFC equipped with convergent-type flow channel could produce larger electricity comparing to other types,and a better performance could be obtained with a narrower channel width.