Single-Phase and Two-Phase Pressure Drops over Return Bend in Rectangular Microchannel

Abstract

The purpose of this study is to investigate the effects of a return bend and liquid properties on the pressure drop for gas-liquid two-phase flows in a horizontal rectangular microchannel having a hydraulic diameter of 0.25 mm. To know liquid properties effects, distilled water, pure ethanol, 49 wt% ethanol aqueous solution and HFE 7200 were used as the test liquid, while nitrogen gas as the test gas. To determine the effects of curvature radii of 0.875 mm and 0.500 mm in the return bend, pressure distribution upstream and downstream tangents of the bend was measured for single-phase and two-phase flows. From the pressure distribution data, the friction factor within the bends was determined. The bend friction factor for single-phase flow could be correlated with Reynolds number and the curvature ratio of the bend, while that for two-phase flows with the single-phase friction factor and a two-phase multiplier, being a function of gas volume flow fraction, Bond number and Lockhart-Martinelli parameter defined for the bend.