Numerical assessment of the drag force and Nusselt number during droplet impingement onto a particle

Abstract

The dynamics of droplet impingement onto solid particles play a crucial role in various engineering applications, yet a fundamental understanding of the intricate momentum and heat transfer characteristics within the processes remains unclear. In this work, we numerically investigate and quantify the drag force and Nusselt (Nu) number during the process using a volume of fraction model. After model validations, it is employed to simulate the processes of molten iron ore spreading over a coke particle for demonstration. The results show that the drag force exhibits rapid initial growth, followed by significant fluctuations marked by two peaks, ultimately decreasing to a low value. The Nu number undergoes a sharp ascent to an immediate peak, followed by a two-stage decline with varying rates. Furthermore, the effect of three key operating parameters is quantified. The comparative analysis unveils that a larger droplet size significantly contributes to an augmented drag force, especially during the first peak. The Nu numbers under various droplet sizes follow a similar trajectory, rising and then decreasing until the wetter surface reaches the maximum. The larger droplets show a slower Nu number decrease. A higher initial droplet position can remarkably increase the drag force and Nu number with more rapid fluctuations. Conversely, the effect of gas velocity under the symmetrical and steady flow field is limited and can be practically disregarded. The present work reveals the fundamental characteristics of momentum and heat transfer process during droplets impact particles.