Effect of geometrical parameters on slug behaviour and two phase pressure drop in microchannel T-junctions

Abstract

Geometric parameters of a microchannel such as cross-sectional area, shape and aspect ratio are important factors in determining the two phase flow characteristics. Two phase flow analyses were carried out experimentally for microchannel T-junction geometries at low values of capillary number. Three hydraulic diameters were used, namely 250, 400 and 550 μm, while the aspect ratio was varied between 0.1 to 1. Experiments were performed for the gas volume flow rate ranging from 2 to 30 ml/min while the liquid volume flow rate ranged between 0.1 to 10 ml/min. Slug length was estimated from the processing of high speed images of slug flow and pressure drop was simultaneously recorded. For constant mass flux in rectangular channels, an increase in the aspect ratio leads to an entrapment of continuous phase at the corner. This influences the transport characteristic of such channels. The effects of aspect ratio on slug length and pressure drop are reported. A simplified scaling model based on the geometric parameters of microchannels as well as gas and liquid flux is proposed which agrees reasonably well (within ±15%) with the present experimental data as well as data available in literature. A flow based pressure drop prediction model was developed which agrees well (within ±10%) with the experimentally measured two phase pressure drop. It is believed that a priori information on slug length and pressure drop in a given flow through a microchannel will help to design the flowing system better.