Modeling partition coefficient of liquid droplets impacting on particles by direct numerical simulation

Liquid partition coefficient, defined as the proportion of the liquid volume covered on particle surface to that in bulk phase, is a key parameter in the simulation of liquid-injected fluidized beds. To develop the sub-grid model for liquid partition coefficient as a function of local hydrodynamics, a two-dimensional Volume-of-Fluid (VOF) simulation was conducted to directly resolve droplets impinging, wetting and spreading on particles in a box. The model was first validated by the experiments in literature on the spreading diameter of a droplet impinging on a single particle. Then for a system of multiple droplets particles impinging, we investigated the effects of Weber number, droplet-to-particle (DTP) ratio and particle volume fraction on several characteristic parameters, e.g., ratio of liquid area adhered to particles to the total liquid area, liquid film thickness, the percentage of wetted particle surface area and liquid holdup. All these parameters decrease with increasing Weber number when We = 10 ti 370, and then gradually stabilize. Higher particle volume fraction increases the collisional frequency of droplets and particles, and therefore the ratio of liquid area adhered to particles to the total liquid area. By contrast, DTP is not the dominant factor in liquid partition. Finally a correlation for liquid partition coefficient is proposed as a function of droplet Weber number and particle volume fraction. It may serve as a sub grid model for CFD-DEM or multifluid models in simulation of large-scale liquid-injected fluidized beds.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

Liquid partition coefficient is a key parameter in simulating liquid-injected fluidized beds. A two-dimensional Volume-of-Fluid simulation was conducted to study droplets impinging, wetting and spreading on particles. The model was validated by experiments on droplet spreading diameter. The study investigated the effects of Weber number, droplet-to-particle ratio, and particle volume fraction on various parameters. The results show that these parameters decrease with increasing Weber number and higher particle volume fraction leads to a higher ratio of liquid area adhered to particles. The droplet-to-particle ratio is not the dominant factor in liquid partition.