Particle-resolved simulations of local liquid spreading in packed beds: Effect of wettability at varying particle size

Packed beds are widely used to perform solid-catalyzed gas-liquid reactions, e.g., hydrodesulfurization, oxidation, and hydrogenation. The overall performance of packed beds is often governed by local liquid spreading. In the present work, the dynamics of liquid spreading through a randomly packed three-dimensional bed is investigated using particle-resolved volume-of-fluid simulations. The effect of particle surface-wettability ( theta) at varying particle diameter ( d(p)) on the relative contributions of forces governing the dynamics of liquid spreading is analyzed using the Ohnesorge (Oh(I)), Weber ( We(I)), and AB(I) (proposed in the present work) numbers. With the help of simulated liquid spreading and these numbers, we show that the contribution of inertial force is significant at the beginning of liquid spreading irrespective of theta as well as d(p) and promotes lateral liquid spreading (AB(I) > 1, We(I) > 1). Once the dominance of inertial force diminishes, the capillary force leads to a substantial increase in the lateral spreading (AB(I) > 1, We(I) < 1). In the final stages, the gravitational force dominates restricting the lateral liquid spreading (AB(I) < 1). Furthermore, we have proposed a regime map constructed using AB(I) and We(I), which provides a relationship between different forces and the resultant liquid spreading at breakthrough. We also show that the dominance of capillary force (AB(I) > 1, We(I )< 1) results in the highest lateral spreading, whereas the flow dominated by inertial (AB(I) > 1, We(I) > 1) and gravitational force ( AB(I) (sic) 1) leads to intermediate and least lateral liquid spreading, respectively.