| In microscopic view,the flow field structure of all vanadium flow batteries determines the distribution and diffusion of electrolyte solution in the state of the electrode,and affect the mass transfer rate,current density and potential distribution of the electrolyte solution.In macroscopic view,it can control the flow mode,the flow rate and the pressure loss of the vanadium battery.When the mass transfer rate is lower than the rate of the electrode reaction,the concentration polarization will occur,the charging voltage will increase and discharge voltage will decrease,cause the lower energy efficiency.Uneven current density and high local overpotential not only reduce the battery performance,but also lead to the corrosion of the materials,such as bipolar plate and carbon felt electrode.The above phenomenon will affect the overall performance of the vanadium flow batteries.A three-dimensional mass transfer model of vanadium flow batteries was established by using the commercial finite element software.The structure of multistage flow channel was optimal designed and the quantitative analysis was made on the flow rate of electrolyte at each flow channel.And then the flow structure will be adjusted to ensure the uniform distribution of the electrolyte,so that the electrolyte solution was gradually divided in the buffer tank and the electrolyte solution of the carbon felt electrode was uniformly diffused.The uneven degree of the flow rate at the outlet of the distribution was continuously reduced.The concentration polarization caused by uneven distribution of electrolyte solution in the electrode was avoided.The important parameters which cannot be measured in the experiment were obtained by the simulation technology,and the influence on the diffusion of structural changes was directly observed through the cloud image.The multi-channel buffer channel structure was applied to the four groups of 0.55 kW small battery stack,and the performance parameters of the battery stack were compared before and after the adjustment of the channel structure.The experimental results demonstrate that the multi-channel structure can improve the overall performance of the battery. |
