Convective boiling in microchannel heat sinks with spatially-varying heat generation

Two-phase microchannel heat sinks are promising for VLSI chip cooling, but little is known about their ability to minimize the impact of chip hotspots (regions of very high heat generation). The wall temperature distribution is governed in part by the coupling between the pressure drop and the saturation temperature, whose distributions will change in the vicinity and downstream of a region of high heat generation. This study theoretically examines the heat transfer and fluid flow characteristics of two-phase flow in microchannels with hydraulic diameters of 150∼450 micrometers for strongly varying wall heat flux conditions. The theory developed aims to help minimize the pressure drop in the two-phase region and to provide the foundation for optimizing channel dimensions to reduce temperature variations. The results suggest that a two-phase microchannel heat sink should be arranged so that downstream is located near the hotspot to minimize the pressure drop in two-phase flow region and maximum wall temperature. This work is particularly promising for a practical closed loop microchannel cooling system that competes directly with heat pipe technology and is based on an electroosmotic pump.