Analysis And Optimization Of The Flow Field Characteristics Of The Nozzle For The Floatation Drying Of Lithium-ion Batteries Electrode

The drying process is an important process in the manufacturing of lithium-ion battery electrodes.The flow field characteristics of the nozzle are the key factors affecting the quality and efficiency of the electrode drying process.Floatation nozzle is a such nozzle that uses impinging jet to achieve high heat and mass transfer rates.Compared with the traditional slot or round nozzles,the floatation nozzle can realize the simultaneous doublesided slot coating and drying processes of the lithium-ion battery electrode,which can greatly improve the quality and efficiency of the electrode drying.In addition,the floatation nozzle can also avoid the friction between the idle roller and the electrode in the singlesided coating/drying processes.However,the heat transfer and pressure characteristics of the floatation nozzle remain unclear due to the complexity of the steady-state characteristics of the flow field and the vortical structure dynamics of the floatation nozzle,and the coupling between the flow field and the deformation of the flexible substrate.These complexity makes it difficult to achieve the fast and uniform drying and stable floatation of the electrode.Besides,the design of the floatation nozzle and drying process is difficult,long cycle and high cost in engineering applications.Therefore,this paper focuses on the analysis and optimization of the flow field characteristics of the nozzle for the floatation drying of lithium-ion battery electrode.The main innovations include:The steady heat transfer and pressure characteristics of the floatation nozzle are revealed:The steady-state flow field of the floatation nozzle is modeled,and a solution method for the coupling of the flow field and the deformation of the flexible substrate is proposed.It is found that the steady flow field of the floatation nozzle can be divided into three typical regions,and the heat transfer and pressure characteristics are significantly different from those of the slot nozzle through the simulation and experimental analysis.The deformation of the flexible substrate will change the separation distance between the floatation nozzle and the substrate,which results in the movement and disappearance of the recirculation flows in the flow field.In addition,it is found that the maximum heat transfer coefficient of the flexible substrate is 14.0% lower than that of the rigid substrate,however,the average heat transfer coefficient is 3.40% higher.Finally,the results show that the Reynolds number and slot width are the most important parameters affecting the wall deformation,heat transfer and pressure.The evolution of vortical structure and the mechanism of wall heat transfer of the floatation nozzle are revealed.Large eddy simulation and proper orthogonal decomposition are used to analyze the formation,development,merging and breaking of vortical structure.The coherent structure,transient characteristics,heat transfer and pressure characteristics of floatation nozzle and slot nozzle are compared,and the intrinsic relationships between the flow field near the wall and temperature field are revealed.It is found that the high-order modes are needed to identify the main dynamic characteristics of the vortical structure for the floatation nozzle.The primary vortices originating from the outside of the jet shear finally break into higher strength but smaller scale vortices,while the primary vortices originating from the inside of the jet shear layer finally merge into lower strength but larger scale vortices.The heat transfer enhancement of the floatation nozzle and the slot nozzle in the stagnation region and the wall jet region are mainly due to the convection of the fluid flow,but the heat transfer in the secondary stagnation region of the floatation nozzle can only be realized by movement of the recirculation flows.The performance evaluation method of the heat transfer and pressure of the floatation nozzle is developed.A performance evaluation indicator of the floatation nozzle which can effectively distinguish the width direction and the longitudinal direction is established,and the accuracy of the performance evaluation indicator is illustrated by the comparison between the results of the slot jet and the round jets array.Compared with the traditional performance evaluation indicator,the accuracy of the proposed uniformity evaluation indicator is increased by 56.67%,and the accuracy of the proposed comprehensive performance evaluation indicator is increased by two times.It is found that the main factors affecting the uniformity of the floatation nozzle are the edge effects,the turbulent intermittence and the interaction between the jet and jet.The main factors affecting the average performance include the size and strength of the recirculation flows,the impingent of the jet on the wall,etc.It is found that the comprehensive performance of the traditional floatation nozzle and the floatation nozzle with effusion holes are better than that of the floatation nozzle with injection holes,and the optimal weight coefficient range of the floatation nozzle with effusion holes is larger than that of the traditional floatation nozzle through the comparative analysis of the three types of the floatation nozzlesThe analysis model of the drying oven structure and optimization model of the nozzle for the lithium-ion batteries electrode are developed.It is found that the structure of the air inlet box has little effect on the air homogenization effect,and the flow field near the wall controlled by each floatation nozzle in the drying box has little effect on each other.Based on the above findings,a mathematical model for the optimization of the effusion holes arrangement of a single floatation nozzle is developed,and the effects of the number of effusion holes on the uniformity and average performance of heat transfer and pressure characteristics,and the comprehensive performance are analyzed.An adaptive Kriging model for the optimization of the comprehensive performance of the floatation nozzle with effusion holes is proposed.It is found that the comprehensive performance of the optimized floatation nozzle is improved by 17.16%,the uniformity of Nu and Cp is increased by 13.51% and 31.31%,respectively,but the mean value of Nu and Cp is reduced by 1.17% and 22.52%,respectively,as compared with that of the traditional floatation nozzle.In this paper,the analysis and optimization of the flow field characteristics of the nozzles for the floatation drying of lithium-ion batteries electrode are carried out.The mathematical analysis and optimization model of the flow field,heat transfer and pressure of the floatation nozzle are established,which can provide an accurate and reliable mathematical tool for the engineering designers.The steady-state characteristics of the heat transfer and pressure,the evolution of the vortical structure and the wall heat transfer mechanisms of the floatation nozzle are revealed.It is important to guide the design and optimization of the drying process and equipment of lithium-ion batteries,as well as for the manufacturing of paper drying and other roll to roll processes.