Numerical study of flow and heat transfer during a high-speed micro-drop impact on thin liquid films

Abstract

Numerical simulation of high-speed micro-droplet impingement on thin liquid film covering a heated solid surface has been carried out. Effect of droplet Weber number and liquid film thickness on the characteristics of flow and heat transfer has been investigated using the coupled level set and volume of fluid method. The code is validated against both the experimental and numerical results from the literature. Results show that the crown dynamics is mostly affected by variations in the initial film thickness but is weakly influenced by changes in the Weber number. The liquid within the film can be categorized as three regions based on the heat transfer distribution: the static film region, the transition region, and the impact region. The transient local wall temperature shows three stages: first stage when the temperature decreases rapidly, followed by a second stage in which the temperature starts to rise and then becomes almost constant in the third stage. After drop impact, the local Nusselt number continuously increases until reaching a maximum value, and then decreases approaching the initial impact stage. Our analysis of the change in Weber number shows that larger Weber number contributes to intense temperature variation at the crater core relative to other radial locations. Lastly, the results reveal that the thinner liquid film leads to lower wall temperature and hence, higher average Nusselt number.