Enhanced flow boiling heat transfer with three-section sudden expansion microchannels

In this study, a three-section sudden expansion microchannels (TSE-MCs) heat sink was proposed to stabilize the flow boiling and improve the thermal performance of the heat sink exposed to high-heat-flux scenarios. The structural effect of newly designed TSE-MC and operating conditions on the heat transfer coefficient (HTC), pressure drop penalty, and flow instability were experimentally investigated and contrasted with continuous straight microchannels (CS-MCs). The experiments were performed at a saturation temperature of 35.5 °C, the mass flux ranging from 468–1033 kg/m² s, and the heat flux up to ∼132 W/cm². A comparative analysis based on the experimental results was conducted. Compared to CS-MCs, the nucleate boiling in TSE-MCs was initiated in advance with 0.2–1.2 °C reduction of wall superheat. The maximum HTCs at four mass fluxes, which was up to 62784 W/m² K, were enhanced by 18.9–23.6 %. The uniformity of wall temperature was improved and the average wall temperature was reduced. HTCs and visualized results indicated that the dominant mechanism for heat transfer in TSE-MCs was nucleate boiling. Meanwhile, the pressure drop in TSE-MCs was slightly reduced, and pressure drop oscillations were greatly suppressed. The flow reversal in the inlet plenum was completely eradicated, and the performance evaluation criterion (PEC) of TSE-MC outperformed that of CS-MCs and was improved by 79.81 %–86.25 %. Overall, the present work demonstrates the great advantages of the newly proposed TSE-MCs, it offers a reference for the design of microchannel heat sinks for the real high heat flux dissipation applications.