Experimental study on single phase flow and boiling heat transfer in microchannels at high flow rates

Official URL: http://192.168.1.20/record=b1302891 (Table of Contents)

With the increasing speed and decreasing size of microprocessors and microchips the sizes of their heat sinks are continuously shrinking from mini size to micro size. The most practical and extensively used micro heat sinks are plain microchannels. They find application in many areas. The proposed study aims at filling the gap in single-phase fluid flow and boiling heat transfer in microchannels at high mass velocities in the literature. This thesis presents a two-part study. In both part, fluid flow was investigated over a broad range of mass velocity in a microchannel with different inner diameters. De-ionized water was used as working fluid, and the test section was heated by Joule heating. The wall temperatures and pressure drops were measured and processed to obtain heat transfer coefficients, Nusselt numbers, and friction factors as output. It was found that existing theory for developing flow in conventional scale could fairly predict experimental data on developing flows in microscale for both laminar and turbulent conditions. In the second part of the study, boiling heat transfer experiments have been carried out for the same microchannel configurations. Heat transfer coefficients and qualities were deduced from local temperature measurements. It was found that high heat removal rates can be achieved at high flow rates under subcooled boiling conditions. It was observed that heat transfer coefficients increase with mass velocity, whereas they decrease with local quality and heat flux. Moreover, experimental heat flux data were compared with partial boiling correlations and fully developed correlations.