How do the fluid dynamics change for gravity-destabilized film flow on structured surfaces? An experimental investigation using light-induced fluorescence

Abstract

Liquid film flow is the dominant flow regime in distillation and absorption processes within structured packings. Extensive research has been carried out to improve the understanding of the involved fluid dynamics. Up to now, these investigations mainly focused on gravity-stabilized film flow, i.e., the liquid phase flows over a packing in counter-current flow with a gas phase. In contrast, gravity-destabilized film flow is studied much less frequently although this type of flow applies to about half of the cases in a column with structured packings. Here, the liquid runs along the underside of the packing, also in counter-current flow with the gas phase. To close the gap in the experimental data, this contribution investigates the fundamental fluid dynamics of gravity-destabilized liquid film flows on a smooth plate, a 2D wave texture, and a 3D pyramidal texture. Results on critical convective inclination angle, drained liquid mass flow, and liquid film thickness without counter-current gas flow are reported and compared to numerical results from literature. In the experiments, the Reynolds number is varied from 28.4 to 113.5 using a surfactant-modified aqueous system. The 2D structure showed decreased liquid flow stability compared to the smooth surface. However, the 3D structure seems to have a stabilizing effect on the flow.