Molecular dynamics simulation of nanodroplet impacting on high-temperature plate wall

Abstract

The process of droplet impacting on a high-temperature wall is a common occurrence in both daily life and industrial instruments. Most of the present researches investigated this phenomenon experimentally or in the macroscopic view. To explore the heat transfer mechanism after nanodroplet impact on hige-temperature surface, the molecular dynamics simulation was carried out to investigate droplet evolution and the influence of surface temperature on its evolution. Droplets containing 10,741 argon atoms impacted on the copper plates with temperatures of 85 K, 150 K, 200 K, 250 K, and 300 K, respectively. The number of droplet evaporation atoms was statistically obtained, the droplet barycenter displacement was analysed, the droplet density and temperature inner distributions were acquired. It is shown that the droplet presents different characteristics on the wall with different temperatures. The droplet spreads stably on the wall at 85 K as shown in Figure 1(a), while when the teperature of the wall rises to 150K, the droplet evaporates slowly and completelyas shown in Figure 1(b), and for the wall temperatures 200 K, 250 K and 300 K, the Leidenfrost phenomenon is found for the droplet is suspended above the wall as shown in Figure (c)(d)(e).. For the temperature conditions when the Leidenfrost phenomenon occurs, the higher of the wall temperature, the faster the droplet evaporating, the earlier of the detachment moment from the wall, the greater the droplet detaching velocity, and the larger the final suspending droplet volume. By analyzing the density and temperature distribution of the droplet at the moment when it detaches from the wall, it is found that the evaporation process is faster and a thicker vapor layer is generated due to the higher heat flux of the high-temperature wall, which will hinder the heat exchange, so that the average temperature of the droplet is lower and the average density is smaller.