Modeling And Heat Transfer Efficiency Analysis Of Vanadium Redox Flow Battery Stack

In the smart grid system,the existing micro network infrastructure calls for increasing high demand on efficiency and flexibility of the large storage devices.Large power grid energy storage battery not only needs to meet the requirements of high efficiency,long charge and discharge cycles and less investment cost,but also needs to have the capability of rapid response when the input or load change.Compared with the conventional batteries,Vanadium Redox Flow Battery has the advantages of good electrochemical reversibility,high efficiency,deep charge and discharge,power and capacity can be designed independently.Therefore,it get much attention in large-scale energy storage system.Stack is the core of Vanadium Redox Flow Battery,and the existing models seldom include the thermodynamic model of the stack.In order to better understand the characteristics of stack,the construction of the stack model is realized by the thermodynamic simulation software Thermolib,and the main research contents are as follows:Initially,the research background,significance,domestic and international status,the classical models and applications of Vanadium Redox Flow Battery are introduced.On the premise of no additional cost and research time,in order to better understand the properties of the battery,building a model is an effective method.However,there is still lack of relevant research on the thermodynamic modeling of the stack.The detailed analysis of three-dimensional geometric model,electric model and electro chemical model lay a foundation for building stack model.Subsequently,Vanadium Redox Flow Battery stack is established by Thermolib.In order to build the stack model,we introduce these main parameters of NASA coefficients,heat capacity coefficients and Anthony constants.Then,the current module,power module,positive and negative electrode module,temperature module and heat exchanger module are modeled respectively,moreover,the heat exchanger module on the parallel flow and counter flow two cases are established.Consequently,the important characteristics of the stack are analyzed in detail.Firstly,the state of charge in a charge/discharge cycle is simulated,and the curve shows that due to the high efficiency of the stack,a linear trend is presented.Then,change of the stack voltage with time under different current intensity and the optimal control flow rate of the stack have been analyzed.Another important state parameter of stack is the enthalpy which represents the system energy.The thermal model can be used to study the properties of stack,so as to provide reference for the structure design of Vanadium Redox Flow Battery.Finally,at certain heat transfer coefficient,the heat transfer efficiency of parallel flow and counter flow heat exchangers modules which can be used to reduce the temperature of stack is analyzed.In the course of operation,the temperature of stack increases regardless of external conditions.The change of temperature has a direct influence on the speed of chemical reaction and battery performance.The kernel idea of the stack heat exchanger optimization is to get the temperature of the stack as a function of time,and to establish the function relationship between heat transfer efficiency and NTU,heat and cold fluid temperature and power.Under the constraints of these functions,the optimal conditions are analyzed.