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 dh=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 kW m−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.