Search

A novel element for gas–liquid contact, a plate with rectangular windows was designed to enhance absorption process. This paper describes some experimental observations of free-surface flows arising when thin liquid film flows through the window. Dozens of windows with different geometries and six fluids with Ka varying from 52 to 3000 were used to investigate the flow mechanism. Various free-surface flow patterns composed of droplets, columns, sheets and their combinations were observed in the window region with increasing liquid flow rate. At a critical flow rate, liquid film was able to full fill the window and unique wavy trains were observed (named as twin-liquid films). To characterize the film formation conditions, an empirical equation based on experimental data was proposed. Hysteresis phenomenon was manifested by obviously different flow rate for the film formation and breaking. Multiple and dynamic flow structures shown here would broaden traditional knowledge of liquid flow in packed columns and clarify the mechanism of mass transfer intensification for the perforated packings. [ABSTRACT FROM AUTHOR]

A novel element for gas–liquid contact, a plate with rectangular windows was designed to enhance absorption process. Coexistence and interaction of wall‐bounded films and confined free films named as “twin‐liquid films” were observed on the plate. Volume of fluid (VOF) method was used to simulate its flow behavior. Flow phenomena such as flow around a step‐in, jet impingement, varicose waves, and sinuous waves were observed. Different from thin films flow on an unperforated plate, larger mean velocity, thinner film thickness, more intensive capillary waves, and stronger vorticity on the free surfaces were detected inside the window, and the disturbances could propagate over the whole plate. Three‐dimensional simulation results generally agreed with our experimental observations and further demonstrated complex wavy structures both inside and outside the window. The results would broaden traditional knowledge of liquid films flow and clarify the mechanism of mass transfer intensification for the plate with windows. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1458–1468, 2018 [ABSTRACT FROM AUTHOR]

• An improved VOF-based subgrid-scale model for mass transfer simulation. • Complicated time-periodic flow behavior of asymmetric twin-liquid films. • Several interesting concentration patterns produced by vortices. • Global mass transfer enhancement by large waves and vortices. Twin-liquid films are a combination of wall-bounded films and confined free films. The asymmetric flow is investigated with the VOF method. A new integration algorithm is developed for interfacial mass transfer (Pe =8400) with the subgrid-scale model [1]. Due to the dynamic balance of the surface tension and the spanwise inertia force, periodic interface oscillation at the lower edge of the window is observed. Then the capillary waves in the window become asymmetric, which induces different flux distributions on two sides of the lower wall, accompanied by large waves and vortices. The vortices extrude a scalar plume (local high concentration liquid) from the interface into the liquid bulk and roll it up once or twice in a reverse direction, significantly promoting the mixing and diffusion of scalar in the liquid bulk. As a result, the local mass transfer rate can be enhanced by 100%∼400% on the lower wall. [ABSTRACT FROM AUTHOR]

• Twin-liquid film flow has been observed on a spoked rotating disk reactor. • Interplay between the confined free film and wall-bounded film leads to mass transfer intensification. • The circumferential length of the opening window should be accommodated to fluid viscosity. Spoked rotating disk reactor is a common gas–liquid mass transfer equipment for highly viscous fluids. The hydrodynamics of the twin-liquid film on the disk is numerically investigated. The simulated film thickness, which agrees well with the experimental results, shows that film flow patterns shift at different rotational speeds. The alternation between the windows and spokes brings diverse film flow pattern, i.e. , twin-liquid film, where a confined free film and a wall-bounded film coexist and interplay. The twin-liquid film results in 70% thinning of the film thickness and 30% increase in the surface renewal frequency compared to the wall-bounded film. Based on the trajectory of the tracking particles, intense velocity fluctuations within the twin-liquid film can be observed. Given the pressure gradient within the opening window increasing exponentially with fluid viscosity, we suggest that the circumferential length of the open window be proportional to fluid viscosity. The results demonstrate good adaptability of the optimization strategy, which can guide the scaling-up of the spoked rotating disk reactors for highly viscous fluids. [ABSTRACT FROM AUTHOR]

• A novel way (open windows) for mass transfer intensification. • Symmetric and antisymmetric flow distributions found inside the window. • Two synergetic mechanisms for mass transfer intensification. • The maximum local mass transfer rate increases by 2–6.5 times. Many investigations find that mass transfer efficiency decreases dramatically with increasing viscosity, which poses challenges to the industrial processes with the highly viscous mixture. We use liquid films on a vertical plate with windows to address this problem. The hybrid twin-liquid films combine the motility of free-falling films with the stability of wall-bounded films. In this study, the film thickness distributions are measured experimentally, and the detailed hydrodynamics and mass transfer process are studied with numerical simulations. The results reveal the hydrodynamic and mass transfer behaviors of highly viscous twin-liquid films. Due to gravity acceleration inside the window, the maximum velocity of liquid films increases by 2.5–16 times, and the maximum local mass transfer rate increases by 2–6.5 times in our simulations. We conclude that compared with conventional methods, open windows significantly enhance mass transfer in viscous liquid films without additional cost. [ABSTRACT FROM AUTHOR]