Study On The Optimization Of Bipolar Plate Channel And The Flowrate Control In VRB

As a green energy, the all vanadium redox flow battery has been greatlly concerned by researchers, depending on its adavantages of unlimited shelf life, long life, fully discharged (100%) and instant recharge. Researchs in this area has made great progress. We know, with many achievements, there are lots of papers and reports about all vanadium redox flow battery, but when it comes to the control of electrolyte flowrate and the optimization of bipolar plate channel, papers and reports can not be easily found. Importantly, this two factors really affect the performance of the battery. It is significant to do the research of electrolyte flowrate in order to get the optimal flowrate and to do the optimal design of the bipolar plate channel.Using Gibbs free energy, Nernst equation and the electrochemical reaction of the electrolyte, we can get the stack modle of the all vanadium redox flow battery. In this model, we find the stack voltage and the stack power are functions of the operating conditions, which include the vanadium concentrations, the proton concentration, the current, the temperature and the electrolyte flowrate. There is a discuss about how the operating conditions influencing the stack performance. As a result, the current has inverse ratios with the charge-discharge time of the stack, voltage efficiency and energy efficiency; the vanadium ion concentration has direct ratios with the charge-discharge time of the stack, voltage efficiency and energy efficiency; the sulfuric acid concentration and flowrate have direct ratios with the voltage efficiency and energy efficiency, but no relationship with the charge-discharge time of the stack. Additionally,it is acceptable to consider the temperature constant during the operation for its small change, helpful to calculation.The whole model of all vanadium redox flow battery are composed of the electrochemical model of the stack and the mechanical model of the external pipes and the channels in the stack. An efficient control strategy of the battery must optimize the power electrochemically exchanged the stack power while minimizing the losses. So, we study the electrolyte flowrate based on the two models established, and find the optimal flowrate is the function of the state of charge (SOC). It is possible to use the real-time control flowrate,according to the SOC of the redox flow battery, in order to get the optimum value of energy efficiency. To simplify the system installation and to cut the cost, we can replace the real-time control flowrate with the optimal flowrate for SOC=90%. But the energy efficiency this way is lower than that of the real-time control flowrate. That should be considered comprehensively, to balance the advantages and disadvantages.The main functions of the redox flow battery's bipolar plate channel are as follows:deliver the electrolyte to every part of the single cell equaly; ensure the electrolyte ejected smoothly after the reaction. The electrolyte in single cell will not be supplied partly, if there is a maldistributed electrolyte. That will make the performance of the single cell not playing totally, and then affect the performance of the whole redox flow battery system. So it is significant to optimize the bipolar plate channel of the all vanadium redox flow battery in this paper.The bipolar plate channel structure of the all vanadium flow battery is optimized in this paper, according to two traditional and frequently-used bipolar plate channel structures:straight parallel channel and snakelike channel, in order to improve the performance of the all vanadium flow battery's single cell. The bipolar plate flow field is studied in numerical simulation and theoretical analysis ways. The compare between the optimized channel structure and the traditional channel structures, according to the research result, testify that the performance of the optimized channel structure is better than the traditional ones.