A numerical investigation of the thermal–hydraulic performance during subcooled flow boiling in MMCs with different manifolds

Abstract

Thermal management of high-heat-flux electronics has been a critical bottleneck for integrated circuit miniaturization and increased power density, and manifold microchannel (MMC) heat sinks are expected to be an efficient near-junction thermal solution. A numerical investigation based a self-developed solver has been conducted to explore the effects of manifold geometries on the thermal–hydraulic performance of MMC heat sinks during subcooled flow boiling, and phase, pressure, and mass distribution among microchannels are analyzed combined with temperature distribution. Heat flux makes little difference on the mass maldistribution among microchannels of MMCs regardless of single-phase and flow boiling, and flow patterns in the outlet manifolds of Z-type MMCs changes from bubbly flow, slug flow to vapor columns with segmented bubbles with increasing heat fluxes. As for the effect of manifold numbers, both the maximum temperature and the pressure drop decrease with increasing manifold numbers, and a relatively uniform distribution of mass and void fraction has been found for all cases of HU-type MMCs regardless of heat fluxes with the best thermal–hydraulic performance at N = 10. However, the thermal performance of Z-type MMCs would improve firstly and then flatten out with increasing manifold number, while the pressure drop presents an opposite trend. The differences in thermal–hydraulic performance are attributed to the longer flow path in Z-type manifolds, and the increasing manifold number presents a higher manifold pressure drop and thus would worsen the mass maldistribution. As for tapered manifolds, a tapered ratio of 0.33 could provide a slightly lower base temperature than the original case with a pressure drop decreased by over 25 %, and the pressure drop fluctuation at high heat fluxes could be suppressed by 70 % with significantly improved flow boiling stability. This work can serve as a basis for the further optimization of subcooled flow boiling in MMC heat sinks, and the results indicate that both an even mass distribution among microchannels and a desirable inlet/outlet port ratio for improved flow field are of great importance for the manifold design applied in MMC heat sinks for two-phase heat dissipation.