Micro pin fins with topologically optimized configurations enhance flow boiling heat transfer in manifold microchannel heat sinks

The manifold microchannel heat sink (MMCHS) is a promising design for heat dissipation in high power electronics. However, the configuration of the microchannels in MMCHS is generally rectangular straight channels, which would limit the further improvement of heat transfer performance. Topology optimization has been proven to be an effective approach to design single-phase heat sinks, which only depends on the iterative algorithm. In this work, we first design three single-phase heat transfer structures (2D) by a density-based topology optimization method, and then systematically investigate the two-phase flow and heat transfer characteristics of MMCHS (3D configurations that are converted based on 2D designs). The thermohydraulic performances of three topologically optimized MMCHS obtained by varying the constrained pressure drop (named TOC-I, TOC-II and TOC-III for simplicity) and the baseline rectangular MMCHS are compared. The results show that the flow paths in the TOCs exhibit root-like configurations and the number of pin fins increases with the increase in constrained pressure drop (i.e., TOC-III has the most complex flow path). Due to the differences in velocity distribution and channel width among various configurations, churn flow and confined bubbly flow are observed in BC and TOCs, respectively. Compared to BC, the maximum average heat transfer coefficients of TOC-I, TOC-II and TOC-III are increased by 40%, 62% and 87%, respectively. The TOC-I has the lowest pressure drop due to the minimum number of pin fins and the relatively large channel width. The maximum values of Figure of Merit (FOM), a parameter usually employed to analyze the comprehensive performance of MMCHS, for TOC-I, TOC-II and TOC-III are 1.72, 1.77 and 1.8 at Qb= 1000 W/cm2, respectively. Moreover, TOC-I and TOC-III have the best comprehensive performance at 300 W/cm2≤ Qb ≤ 800 W/cm2 and 900 W/cm2 ≤ Qb ≤ 1000 W/cm2, respectively.