Numerical Simulation And Optimization On Two-Phase Heat Transfer Characteristics Of Small Spray Cooling System

When spray cooling technology is applied to high-power equipment such as small solid-state lasers,the optimization of its operating parameters is an effective means to improve the heat transfer capacity of the system and the operation stability of the equipment.However,in practical application,because there are many factors affecting the heat transfer process of spray cooling system,it is difficult to control a single factor through experiments and the operation cost is high.The heat transfer process of spray cooling system is simulated and analyzed by numerical simulation and orthogonal test,which can optimize the system device and improve the heat transfer capacity of the system.Based on the research and development needs of a small spray cooling device,this paper uses computational fluid dynamics（CFD）to carry out simulation research,and discusses the influence of different operating parameters on the heat transfer performance of the spray cooling system,so as to provide a theoretical basis for the design of the device;At the same time,the process of small droplets impacting the liquid film in the process of spray cooling is simulated to deepen the understanding of spray cooling mechanism.The main research contents and results are as follows:（1）The model of small spray cooling system and the process model of small droplets impinging on liquid film in two-phase region are established.According to the development requirements of small-scale spray cooling system,the heat transfer mechanism model of the cooling system is established by using Euler Lagrange method.The maximum relative error between the simulation results and the experimental results in the literature is 4.3%,which proves the reliability of the model;In order to establish the heat transfer model in the cooling system,the CLSVOF method is used to establish the mathematical model of the process of small droplets impacting the liquid film.The reliability of the model is proved by the visual comparison with the experimental results in the literature.（2）Simulation analysis of operation factors of small spray cooling system.Through single factor simulation and orthogonal simulation,the influence of operating parameters on the heat transfer performance of the system is studied and the operating parameters of the system are optimized.The results show that when the heat flux is 223.98W·cm^-2,the heat transfer performance of the system can be improved by reducing the working fluid temperature,increasing the working fluid flow and injection speed,and reducing the ambient temperature.Among them,the temperature,flow rate and injection velocity of the working medium have obvious effects on the heat transfer process in the two-phase region of the system,while the ambient temperature has little effect;The orthogonal test results show that when the heat flux is constant,the order of significance of the operating parameters on the heat transfer performance of the system is:working fluid flow>injection speed>working fluid temperature.The recommended operating parameters of the optimized experimental system are:working fluid flow 46.88L·h^-1,injection speed 23.4m·s^-1,working fluid temperature 8^oC.（3）Simulation and analysis of the heat transfer process of small droplets impinging on liquid film in spray cooling system.In the process of droplet impacting the liquid film,reducing the droplet temperature,increasing the droplet velocity and reducing the thickness of the liquid film can improve the heat transfer performance of the system.In the process of single factor analysis,the droplet temperature is 8^oC,the droplet velocity is 9 m·s^-1 and the thickness of the liquid film is 30μm,the heat transfer effect of droplet impinging on liquid film is better;When the droplet impinges on the liquid film,when the droplet has an inclination angle,the minimum temperature on the left side of the symmetry axis（in the radial velocity direction of the droplet）is higher than that on the right,and the heat transfer area is higher than that on the right;With the heat transfer process,the difference between the peak values of the heat transfer coefficients on the left and right sides of the symmetry axis decreases.With the decrease of inclination angle,the difference of peak width between two sides of symmetry axis increases.