Numerical analysis of heat transfer characteristics of small droplets impacting on wall

Abstract

The phenomenon of small droplets impacting on the wall is widely used in fields such as spray cooling. In recent years, the research on the behavior of droplets impacting on a wall has been extensively concerned by scholars. However, current research mainly focuses on the flow and heat transfer characteristics of large droplets (millimeters) impacting on a hot wall. Since the dynamic and thermodynamic characteristics of small droplets (micrometers) impacting on the hot wall are significantly different from those of large droplets, the research on the behavior of small droplets impacting on the hot wall will further facilitate the understanding of the heat transfer mechanism. In order to study the heat transfer process of small droplets impacting on the hot wall (non-boiling zone), a two-dimensional transient model of droplets impacting on the wall is established, and the phase field method is used to analyze the convective heat flux and heat conduction heat flux in the heat transfer process of small droplets. The effect of velocity, wettability and droplet size on the heat transfer characteristics of droplets impacting on the wall are explored. The simulation results show that the phase field method is feasible in studying the behavior of small droplets impacting on the wall. Furthermore, the research results show that the initial stage of droplet impacting on the wall is “cold spot”, which is conducive to the heat transfer between the small droplet and the wall. The peak heat flux during the small droplet impacting on the wall is near the three-phase contact point, and it is on the order of 10<sup>5</sup>–10<sup>6</sup> W/m<sup>2</sup>. The influence of wall wettability and droplet size on the conductive heat flux during the small droplets impacting on the wall are more significant, while velocity and droplet size have a significant influence on convective heat flux. In most cases, the conduction heat flux of small droplets impacting on the wall is about 10<sup>3</sup>–10<sup>5</sup> W/m<sup>2</sup>, and the convective heat flux is about 10<sup>4</sup>–10<sup>6</sup> W/m<sup>2</sup>. The convective heat flux is larger than the conduction heat flux, and it plays a dominant role in the whole process of heat transfer. The above conclusions are helpful in enriching the heat transfer mechanism of small droplets impacting on the hot wall, and implementing the spray cooling and other technologies.