Performance Optimization Of Thermally-Regenerative Ammonia-based Flow Battery

As the energy crisis continues to spread today,if the huge amount of low-grade waste heat generated in many fields can be recycled.It will make a great contribution to energy conservation and emission reduction.At present,in the field of low-temperature waste heat recovery,thermally-regenerative ammonia-based flow battery（TRAFB）can meet the requirements of high power density,scalability and low cost in the thermoelectric conversion process well,and has a promising prospect.However,the research on TRAFB is not yet mature,and its power density and potential still need to be improved.Therefore,starting from the simulation study of battery flow channel and internal self-discharge phenomenon,this paper obtained the improvement of battery power density by optimizing the flow channel structure and membrane porosity.On the one hand,a three-dimension（3-D）numerical model has been proposed,the concentration distribution of species in the flow channel of TRAFB and effects of different flow forms on power production were described.The results indicated that dead zones were found in the experimental flow channel,which inhibits the increase of battery power density.Therefore,in order to improve the performance,flow channels of TRAFB have been optimized using silicon rubber sheet channel and copper electrode flow channel.According to the optimization results,it was found that the maximum power density of the battery can be increased by about 33%(12.1 W m^-2),while the pump power consumption only increased by 2.13×10^-2 W m^-2（about 0.5‰of power density）.By comparing the performance of batteries with different flow channels,the general laws of designing flow channel were summarized.That was to minimize the flow dead zones,increase the reaction areas and reduce the distance between electrodes within the allowable range.On the other hand,a two-dimensional numerical model of TRAFB coupling NH₃crossover was established.It was found through the study that the internal resistance of the battery would have a great influence on potential,thus having a great influence on the power density of the battery.Therefore,the internal resistance of the battery under different NH₃ concentrations was calculated through the experimental data,and then the internal resistance was coupled into the model for subsequent simulation.It was found that NH₃ transport in the membrane was mainly carried out by diffusion,convection,but not by electromigration.It was found that increasing the flow rate,increasing the porosity of the membrane and increasing the concentration of NH₃ will increase the transmission flux of NH₃.The porosity of the membrane was selected to optimize the battery.When the porosity of the membrane was adjusted from the initial0.2 to 0.1,the maximum power density of the battery could be increased by about 5%.In this article,after improving the battery through the above two simulation optimization methods,the power density of the TRAFB can be improved.By coupling the two improvements with simple superposition and multiplication,the maximum power density of the optimized battery can be increased by about 40%compared with that before optimization.