Experimental study of slug flow for condensation in a single square microchannel

Abstract

Local condensation heat transfer for slug flow in a single silicon square microchannel is investigated. Chromel–alumel microthermocouples are located in the rectangular microgrooves formed in the silicon wafer and covered with Pyrex glass for measuring the surface temperature. Various condensation flow patterns are identified in the microchannel: mist flow, churn flow, annular flow, slug flow, liquid ring flow, and annular/bubbly flow. Our attention is focused on the analysis of local heat transfer, and hydrodynamic characteristics of slug flow because it is one of the basis two-phase flow pattern in condensation in the microchannel. Experimental results obtained from images processing show that bubbles velocity is significantly influenced by the departure of each new bubble followed with the new liquid slug from the microchannel entrance. The coalescence phenomena between the neighboring bubbles contribute to increase the bubbles velocity. The experimental data are compared with condensation heat transfer correlations from the literature. Existing correlations are found to over predict both local and average condensation heat transfer, except the correlation of Dobson and Chato which gives the good predictions of the average heat transfer with maximum deviation of 10% at high mass fluxes.