Numerical Simulation Of Evaporation And Heat Transfer When Droplet Impact On A Heated Surface

The droplet impact on heated surface is a common physical phenomenon. In the process of droplet evaporation, due to its higher thermal efficiency then the traditional technology of air and water cooling without evaporation, it is widely used in many fields of the industry and agriculture. The process, which has attracted the attention of many scholars for the variability of dynamic characteristics and the complexity of evaporation and heat transfer, belongs to the typical free surface flow problem. Getting the accurate scientific explanation of the process of droplet impact and evaporation can provide more detailed and comprehensive theoretical basis for strengthening the heat transfer. In the existing research, the discussion about the droplet evaporation and heat transfer in the transient heating process was still less and also lack of systematic and comprehensive.Using the CLSVOF interface tracking method and droplet non-equilibrium evaporation UDF program, a two-dimensional axisymmetric model was established and simulated the droplet impact on heated surface, in order to analyze the conditions of droplet evaporation and heat transfer in the transient heating process. Taking the droplet dynamic deformation process as a reference, the paper compared the simulation results with the experimental data to validate the accuracy and effectiveness of the model.Numerical simulation of the single droplet and double droplets impact successively on a heated surface in the non-equilibrium evaporation process were done respectively, and the relationship between the internal flow field, droplet morphological evolution, temperature field and pressure field was analyzed. Discussed the influence of the impact between the double droplets to the evaporation and heat transfer, and put out the reasons of why the vortexes appeared in the whole process. It was found that the three-phase contact point was the place where the internal disturbance was the most severe, the liquid started to evaporate and the evaporation rate was the largest.The paper analyzed the influence of the different parameters to the droplet spreading coefficient and evaporation in the non-equilibrium evaporation process, which contains the surface temperature, impact velocity, droplet diameter and static contact angle of the single droplet impact, and the vertical spacing and upper part of droplet impact velocity of the double droplets impact. The results showed that, in the droplet transient heating process, the larger impact velocity and droplet diameter, the smaller static contact angle and droplet vertical spacing, the larger upper part of droplet impact velocity can make the droplet spreading coefficient increase, but the influence to the droplet oscillation period was not consistent. And the surface temperature had small effect on the droplet spreading coefficient. At the same time, the larger surface temperature, impact velocity and upper part of droplet impact velocity, the smaller droplet diameter, static contact angle and droplet vertical spacing can make the droplet temperature rise faster and contributed to the droplet evaporation.