Numerical Simulation Of Flow Characteristics And Heat Transfer Performance After Droplet Impact On Flat Liquid Film

The phenomenon of droplet impact can be seen everywhere in our daily life and industrial production, so the study of the internal mechanism of this phenomenon can bring important theoretical basis for practical engineering application. In this paper, there is numerical simulation of single droplet impingement on flat liquid film with splashing and numerical simulation of fluid dynamics characteristics after double droplets impact on flat liquid film; and also numerical simulation of heat transfer performance and its influencing factors after double droplets impact on flat liquid film in hot wall with CLSVOF method. The main contributions are as follows:(1) The numerical simulation results of single droplet impacting the flat liquid film show that:the fluid interface instability caused by velocity discontinuity inside the liquid film is the main reason for the splash, and the results show air bubble entrainment phenomenon could be captured successfully. When the droplet diameter is small, there is no small air bubbles. And it is found that the greater the droplet diameter, the longer the time of air bubble disappear, the earlier splash after drop impact on flat liquid film, the more secondary droplets and small bubbles generated, the greater the diameter and of the coronary spray.(2) The numerical results of two droplets with different horizontal distance simultaneously impacting on flat liquid film show that:double droplets with different speed impacting the liquid film will form the surface fluctuation、crown spray, produce secondary droplet and two surface waves collided form jet of center liquid membrane, jet rift s and secondary droplets will happen. We number determine whether the spray tip has splash. When We number is small, it does not produce secondary droplet splash. With the increase of the We number, the thickness of space liquid film and more secondary droplets are generated. With the increase of the We number, spray height and jet height s larger, and the spray height and jet height fell ahead of time also increasing with the We number. The change of droplets’ distance has little effect of spray height in the beginning, after a period of time, the greater the droplets’ spacing, the smaller spray height, after that, and the smaller the droplets’spacing, the smaller spray height. For jet height, at the first of the impact, the greater the distance between double droplets, the smaller the jet height, after a period of time, the greater the distance between double droplets, the bigger the jet height. (3) The numerical simulation results of double droplets impacting on flat liquid film at different vertical distance between the two droplets show that:when droplet spacing is different, spray shapes appear very different, and the thickness of liquid film has little influence on the spray shapes, but has a great influence on the time of air bubble disappear. The greater the thickness of liquid film, the longer the time of bubbles disappear; the bottom diameter of spray increases with time gradually, and the greater the thickness of liquid film, the smaller bottom diameter of the spray; When the spacing is large, the diameter at the bottom of the spray increases first, then decreases, finally, and increased.(4) The numerical simulation results of double droplets impacting on flat liquid film in hot wall at different vertical distance between the two droplets show that:the average heat flux density of the wall increases with the rise of impact velocity and the influences of vertical spacing between two droplets, droplet diameter and liquid film thickness on the average heat flux density are small. The average heat flux density in the impact area decreases with the increasing of the thickness of liquid film, vertical spacing between double droplets and the droplet diameter, while the average heat flux density in the border area increases with the increasing of the thickness of liquid film and vertical spacing between double droplets. The average heat flux density in the border area decreases with the increasing of droplet diameter firstly, then increases with the increasing of droplet diameter. The fluctuation range of average heat flux density in the border area decreases with the increasing of the thickness of liquid film, vertical spacing between double droplets and the droplet diameter.