Hydrodynamics of countercurrent flows in a structured packed column: Effects of initial wetting and dynamic contact angle

Abstract

Computational countercurrent flow investigation in the structured packed column is a multiscale problem. Multiphase flow studies using the volume of fluid (VOF) method in the representative elementary unit (REU) of the packed column can provide insight into the local hydrodynamics such as interfacial area, film thickness, etc. The interfacial area dictates the mass transfer in the absorption process and hence the overall efficiency of the column. The impacts of a solvent’s physical properties, liquid loads, and static contact angle (SCA) on the interfacial area have been examined previously. In the present study, the dynamic contact angle (DCA) was used to explore the impact of contact angle hysteresis on the interfacial area. The DCA has pronounced impact on the interfacial area (≈10% relative change) for the aqueous solvent of 0.10 M sodium hydroxide (NaOH). The interfacial area shows undulation and does not achieve the pseudo-steady state. In contrast, the interfacial area gets a net pseudo-steady value for aqueous solvent that contains 40% monoethanolamine (MEA) by weight. Wetting hysteresis was also explored via simulations conducted with initially dry and wetted sheets. For the 0.10 M NaOH aqueous solvent, the use of initially wetted sheets led to a slightly higher value of the interfacial area (≈10%) than the use of initially dry sheets at the same liquid load and DCA. As expected, wetting hysteresis reduces with increasing liquid loads, but wetting hysteresis is not significant for 40% MEA aqueous solvent, which might feature lower surface tension and higher viscosity. Overall, the effect of the DCA on interfacial area is not as pronounced as it is found on a flat surface.