Effect of droplet characteristics on vapor film renewal and heat transfer behaviors on high-temperature slab surface in continuous casting

Abstract

In the secondary cooling zone of continuous casters, the cooling intensity for the high-temperature slab is affected by the formation and renewal behaviors of vapor and liquid films on the slab surface, which is directly related to the ability of the droplets penetrating the vapor film effectively. The velocity and size of droplets have an important influence on their penetration behavior, but there is still a lack of understanding regarding on these. Additionally, the renewal behavior of vapor film is not easily observed by experimentally. Based on these, a two-dimensional numerical model is developed to simulate the process of multiple droplets impacting on the high-temperature slab. Results demonstrate that the slab surface experiences the film boiling phenomenon, and the vapor and liquid films undergo formation, deformation, and renewal processes when multiple high-velocity tiny droplets impact on the high-temperature slab. The average heat flux on the slab surface during the film boiling stage increases with an increase in droplet velocity, thereby intensifying the heat transfer process between multiple droplets and the high-temperature slab. With increasing the droplet size, the average heat flux on the slab surface initially rises before subsequently diminishing. In this study, the slab surface experiences maximum average heat flux at a droplet velocity of 50 m/s and a droplet diameter of 0.04 mm, indicating optimal heat transfer performance between the droplets and the high-temperature slab.