Heat transfer mechanism and flow pattern during flow boiling of water in a vertical narrow channel - experimental results

Experimental investigations on flow boiling phenomena in a vertical narrow rectangular microchannel with the hydraulic diameter d(h) = 0.48 mm were carried out. The experiments were performed under fluid-inlet subcooled conditions with de-ionised and degassed water for different mass fluxes. Investigations on pressure drop and heat transfer during single- and two-phase flow have been carried out. Moreover, flow visualisation of the two-phase flow patterns along the channel was performed using a digital high-speed video camera. The present work outlines local heat transfer coefficients for three mass fluxes (200, 700 and 1500 kg m(-2) s(-1)) and heat fluxes (30-110, 35-150 and 65-200 kWm(-2)) during two-phase flow. The visual observations were used to obtain a better insight about the heat transfer mechanisms. The goal of this work is to find the circumstance of the best heat transfer circumstance in microchannels. (c) 2007 Published by Elsevier Masson SAS.