Experimental study of loss coefficients for laminar oil-water two-phase flow through micro-scale flow restrictions

Abstract

Micro-scale flow restrictions have significant effect on the flow performances in microfluidic devices, porous media and biological processes. Two pairs of micro channels were fabricated by microfluidic method to experimentally investigate the irreversible pressure losses of laminar oil–water two-phase flow through two micro-scale flow restrictions. The hydraulic diameters of these two micro-scale flow restrictions are 72 μm and 33 μm, respectively. The oil contents of oil–water mixture vary from 0 % to 100 % and all the flow patterns are dispersed. By comparing the pressure drops between a micro channel with a built-in micro-scale flow restriction and the one without micro-scale flow restriction for a pair of micro channels, the irreversible pressure losses through a micro-scale flow restriction were determined. The results indicate that the local irreversible pressure loss is principally generated from the frictional dissipation effect instead of the acceleration and capillary effects for dispersed oil–water two-phase flow through the micro-scale restrictions with identical contraction and expansion geometries. As a dimensionless expression of irreversible pressure loss, the dependencies of local loss coefficient on the dimensionless parameters such as capillary number, Knudsen number, Reynolds number and restriction area ratio are concerned and discussed for the laminar oil–water two-phase flow through micro-scale flow restrictions. A new expression of local loss coefficient was proposed for laminar oil–water flow through a whole micro-scale flow restriction, by which the prediction results show good consistency with the experimental data.