An experimental investigation on characteristics of liquid film thickness of gas-liquid Taylor flow in square/rectangular microchannel applied in microreactor

Abstract

Microchannel reactors employing Taylor flow is 1 – 3 orders of magnitude higher than traditional reactor in handling gas-liquid reaction processes, which has found important applications in oxidation, hydrogenation, chlorination, fluorination and absorption involved in chemical industry. Liquid film thickness of gas-liquid Taylor flow in circular microchannel has been widely investigated, whereas the variation and distribution of liquid film thickness in square/rectangular microchannel are lack of comprehension. In the present work, experiments were conducted to investigate the variation of liquid film thickness in square channels with hydraulic diameter Dh = 0.3, 0.5, 0.7, 1.0 mm, and rectangular channels with a depth of 0.5 mm and widths of 0.3, 0.5, 0.7, 1.0 mm under the condition of air-water and the addition of surfactant Tween-20. The liquid film thicknesses were measured using a laser focus displacement meter (LFDM), the bubble shapes and velocities were compared using high speed photography. The experimental results illustrate that the dimensionless bubble diameter in square/rectangular microchannels can be divided into initial stage, reduction stage and stable stage with the increasing of capillary number Ca. The initial, reduction and stable stage of the dimensionless bubble diameter are all influenced by the channel hydraulic diameter, aspect ratio, asymmetry effects and surface tension coefficient of working fluid. In square channels with Dh = 0.3, 0.5, 0.7, and 1.0 mm, the dimensionless bubble diameter enters the reduction stage at Ca = 0.019, 0.015, 0.011, and 0.009, respectively. Besides, an empirical formula of dimensionless bubble diameter was developed using the dimensionless groups Ca, Re, Bo, and Li/Dh to describe the characteristics of liquid film thickness in square/rectangular microchannel.