Frictional pressure gradients in two-phase flow in a small horizontal rectangular channel

Abstract

Frictional pressure gradients were measured in a two-phase flow of an air-water mixture in a rectangular channel with a cross section of 19.05 × 3.18 mm, for application to plate-fin compact heat exchangers of the plain fin type. The measurements were conducted with the channel in two horizontal orientations. Adiabatic flows of air-water mixtures near atmospheric pressure were used at mass qualities of 2.5 × 10 −5 to 1.0 and total mass fluxes of 50–2000 kg/(m 2 · s). Pressure gradients were measured with respect to two-phase flow patterns. Unique conditions were found at the transition from bubble or plug flow to slug flow. The data were compared to predictions of two widely used correlation equations. These equations did not adequately correlate the data, and a modified equation were developed for qualities larger than those occuring at the transition to slug flow. The modified two-phase flow pressure gradient correlation covers the parameters of interest for compact heat exchanger application of mass flux from 50 to 350 kg/(m 2 · s) and mass qualities greater than 0.05 (Martinelli parameter less than unity). An existing correlation was found to have good accuracy at mass fluxes above 400 kg/(m 2 · s).