Experimental study on flow boiling heat transfer in manifold microchannel heat sinks with different numbers and widths of manifolds

Abstract

Flow boiling in manifold microchannel heat sink (MMCHS) has demonstrated lower pressure drop and more uniform temperature distribution. In this work, the effects of manifold number and width on the flow boiling heat transfer and pressure drop characteristics of deionized water in MMCHS are experimentally investigated. Flow boiling tests are conducted on five MMCHSs with inlet manifold numbers of 2, 3, and 5, and manifold widths of 0.5 mm, 1 mm, and 1.5 mm, under the mass flow rates ranging from 1 g/s to 3 g/s and inlet subcooling degrees ranging from 10 °C to 30 °C. At low heat fluxes, reducing number of manifolds contributes to expanding the boiling area and improving HTC. For heat sinks with large manifold number and width, increasing mass flow rate results in a decrease in HTC before the dry-out occurs. The heat transfer deterioration is related to the non-uniform rewetting in microchannels. Increasing manifold width enhances the wall rewetting, delaying the heat transfer deterioration and achieving an improvement of up to 31.2 % in HTC. The "vapor trapping" phenomenon is observed in microchannels near the ONB, resulting in an increase in wall temperature and pressure drop, which can be eliminated by increasing mass flow rate and decreasing inlet subcooling degree. With the increase of manifold number and width, the pressure drop decreases and the COP increases. Under the mass flow rate of 3 g/s and inlet subcooling degree of 20 °C, increasing manifold number and width reduces the pressure drop by up to 74.8 % and 84.7 %, respectively. Considering the average COP in the stage of fully developed boiling as a measure of the comprehensive performance, increasing the number and width of manifolds improves the comprehensive performance by up to 292.6 % and 398.5 %, respectively.