Numerical Simulation Studies On The Flow And Heat Transfer Process Of Droplet Impacting On The Vertical Wall

Spray cooling is a highly efficient cooling method which is applied widely to the scientific fields such as petrochemical industry,energy environment,and aerospace industry,etc.The droplets impinging the vertical wall is a common phenomenon in the process of spray cooling.In the process of droplets impact onto the vertical wall,the free surface of droplet is constantly changing.Under the influence of the high temperature wall,the phase change and gas-liquid two-phase flow always happens.It makes the phenomenon more difficult and complicated.In this paper,the flow and heat transfer process of droplets impinging the vertical wall is studied by numerical method,and then the parameter analysis is conducted.The specific research contents and conclusions are as follows:(1)Established a two-dimensional geometric model of the process of droplet hitting the vertical wall.Then the VOF model is used to capture the gas-liquid interface,the CSF is selected to calculate the surface tension.The geometry reconstruction technology is used to construct the interface.The FLUENT software is applied to simulate this process and then compare the simulation results with the experiment to verify the model accuracy.(2)Simulating the process of droplets impinging the vertical wall,and performing flow and heat transfer analysis on the inside of the droplets.The research shows that when the droplet spreads out on the wall,with the influence of gravity and wall adhesion,the speed of the upper three-phase contact point gradually decreases to zero,and then goes down slowly along the vertical wall.The speed of the lower three-phase contact point is increasing continually with strong disturbance and largest heat flux.The wall heat average flux increases first and then becomes stable.(3)The effects of various parameters on the dynamic behavior and heat transfer during the droplet impact on the vertical wall are analyzed.The results show that:a)with the larger the initial velocity of the droplet,the drops spread larger distance in both the upper and lower side and moves faster.The heat exchange capacity increases,when the droplet is fully spread in the lower three-phase contact point,the heat flux density achieves a maximum;b)with the larger the impact angle,the drops spread larger distance in both the upper and lower side while moves lower.The heat exchange capacity increases,when the droplet is fully spread in the lower three-phase contact point,the heat flux density achieves a maximum;c)with the larger the diameter of the droplet,the drops spread larger distance in both the upper and lower side while moves lower.The heat exchange capacity increases,when the droplet is fully spread in the lower three-phase contact point,the heat flux density achieves a minimum;d)with the larger the static contact angle,the drops spread larger distance in both the upper and lower side but the spreading speed doesn't change much;e)with the larger the surface tension coefficient,the drops spread shorter distance in the upper side and moves faster;f)the wall temperature has little effect on the spreading of the droplets,the higher the wall temperature,the larger the heat exchange capacity and the higher the heat flux density at the lower three-phase contact point when the droplet is fully spread.