Computational Fluid Dynamics Modeling of Gas‐Liquid Two‐Phase Flow around a Spherical Particle

Abstract

Microscale studies, which can provide basic information for meso-and macroscale studies, are essential for the realization of flow characteristics of a packed bed. In the present study, the effects of gas velocity, liquid velocity, liquid-solid contact angle, and liquid viscosity on the flow behavior were parametrically investigated for gas-liquid two-phase flow around a spherical particle, using computational fluid dynamics (CFD) methodology in combination with the volume-offluid (VOF) model. The VOF model was first validated and proved to be in good agreement with the experimental data. The simulation results show that the film thickness decreases with increasing gas velocity. This trend is more obvious with increasing operating pressure. With increasing liquid velocity, the film thickness tends to be uniform on the particle surface. The flow regime can change from film flow to transition flow to bubble flow with increasing contact angle. In addition, only at relatively high values does the liquid viscosity affect the residence time of the liquid on the particle surface.

Numerical study of liquid coverage in a gas–liquid–solid packed bed

“…On the contrary, for higher viscosity liquid, film flow appears in most regions of the bed, and the liquid surface coverage on each particle increases. The results are consistent with our previous work (Du et al, 2013) that when liquids flow around a spherical particle, the liquid film thickness becomes thinner for high viscosity liquids but the flow time of this liquid becomes longer. It can be seen that although a better liquid distribution can be obtained inside the packed bed, the liquid coverage on the particle surfaces may be reduced by lowering the liquid viscosity.…”

“…A contact angle of 90 • or greater generally characterizes a surface as nonwettable (hydrophobic), while an angle less than 90 • means that the surface is wettable (hydrophilic). Du et al (2013) observed that the contact angle showed a significant impact on the flow behavior of gas-liquid flow around a spherical particle. Therefore, a similar effect of the contact angle on the flow behavior in a packed bed is expected.…”

“…At the microscopic level, liquid maldistribution is believed to be closely associated with the physicochemical properties of the liquid (density, viscosity, surface tension), liquid and gas flow rates (Onda, Takeuchi, Maeda, & Takeuchi, 1973;Saroha, Nigam, Saxena, & Kapoor, 1998), wettability (Schwartz, Weger, & Dudukovic, 1976), shape and orientation of catalyst particles (Kundu, Saroha, & Nigam, 2001;Ng & Chu, 1987), and local packing structures. Our recent study (Du et al, 2013) has shown that the gas-liquid flow behavior around one spherical particle highly depends on the liquid velocity and liquid properties. The objective of this study is to understand which parameters influence liquid coverage and radial liquid distribution, especially at different locations in a TBR, which are of great importance to the reactor performance.…”

“…2, where liquid water was pumped into the top of the vessel through a rotameter, then distributed into a bed packed with glass bead particles (Du et al, 2013). The experiment was conducted under atmospheric pressure and ambient temperature (293 K).…”

“…Additionally, flow maldistribution, channeling, catalyst wetting, and local temperature variation may occur and significantly affect the overall reactor performance. Such phenomena may arise from systems with disparate parameters (Du, Feng, Xu, & Wei, 2013). Moreover, flow hysteresis, another undesirable flow phenomenon, caused by flow maldistribution in parallel channels in a TBR, is highly influenced by initial start-up conditions and tends to abate after the entire bed is fully wetted.…”