Numerical Simulation On Dynamics Of Droplet Impacting On Flat Hot Solid Surface

The free surface flow problems are commonly found out in the fields of chemical, metallurgy, aviation and aerospace and material science. In this process, the position of the free surface changes along with the movement of liquid, moreover, the movement of the free surface has a great influence on the system. These problems which are inherent in the nonlinear changes coupled with phase change that may occur in the process of impact make it extremely difficult to be dealt with, so it has become a great concern in the field of fluid dynamics.FLUENT which is one of the Computational Fluid Dynamic software has three common calculation multiphase models: VOF model, Mix model and Euler model. Two-phase fluid which including droplet and air that involved when droplet impacting on isothermal flat solid surface. There is no mass transfer, and dynamics of droplet interface need to be examined crucial, so VOF model is the most appropriate one. Volume of Fluid Method that advanced by Hirt and Nichols, the basic idea of which is that a volume fluid function which satisfies convection function, is defined in whole flow flied. When the cell is empty, the function equals 0; when the cell is full, the function equals 1; when the cell contains interface, the function between 0 and 1.For the case that droplet impacting on isothermal flat surface, theory model is founded. Flow dynamics of droplet is assumed to be axis-symmetric, VOF model in FLUENT of CFD software is applied, and whole dynamics of droplet after impacted on flat surface is simulated. In order to validated the model, simulated results are compared with experimental data. By altering concerned parameters, dynamics of droplet on flat surface are analyzed. Influence of parameters including mesh size of calculation, feature of surface, impact velocity, viscosity, diameter size and surface tension of droplet on dynamics is studied in detail. For the case that droplet impacting on heated flat surface, by founding physical and mathematical model, influence of parameters such as temperature of surface, droplet and surroundings, impacting velocity, diameter size of droplet on heat transfer and evaporation performance is analyzed.The results has shown that despite of error in simulated results, by compared with experimental data, VOF method could capture the key feature of droplet dynamics when spreading and recoiling. The flow state is seriously influenced by the wettability of surface, namely contact angle at the wall. In the spreading phase, the bigger contact angle is, the smaller spreading diameter of droplet and heat transfer are, and the slower evaporation speed is. The bigger impact velocity is, the bigger spreading diameter of droplet and heat transfer are, and the faster evaporation speed is. The bigger diameter size is, the bigger spreading diameter of droplet and heat transfer are, and the slower dynamics of droplet is and the evaporation speed are. The bigger surface tension coefficient is, the smaller spreading diameter range is, and the time to spread and recoil is decreased. The influence of the surface temperature, droplet and surroundings initial temperature on the heat transfer is significant. The higher surface temperature is, the more heat transfer between droplet and surface, the faster evaporation speed is. The higher droplet and surrounding temperature are, the less heat transfer between droplet and surface, the faster evaporation speed is.