Experimental investigation of flow boiling heat transfer performance in zigzag microchannel heat sink for electronic cooling devices

This study proposes an improved microchannel heat sink with offset zigzag cavities to enhance boiling performance. Flow and heat transfer characteristics are experimentally investigated via a microscale boiling heat transfer visualization system using acetone as the working fluid. At mass fluxes of 285, 402, and 684 kg/(m(2).s) and heat fluxes of 1.31-80.26 W/cm(2), the effects of heat and mass fluxes on flow pattern, heat transfer, wall temperature, and pressure drop of zigzag microchannel heat sink are analyzed and compared with conventional rectangle microchannel heat sink. Results show that the fluctuating amplitude first increases and then decreases with the increment of heat fluxes, thereby causing a quasi-steady and unstable boiling with small fluctuations. Instability becomes increasingly severe for the nucleate boiling area moves toward the inlet and flow reversal intensity increases with heat fluxes under low heat flux. With heat flux increased furtherly. The proportion of steam in the channel increases to reduce fluctuations. Compared with the rectangular microchannel, the zigzag microchannel evidently enhances heat transfer characteristic with lower wall temperature at the onset of nucleate boiling (ONB), higher heat transfer coefficient (HTC) and critical heat flux (CHF) and improves boiling stability by suppressing flow reversal and reducing two-phase pressure drop. The mechanism of zigzag microchannel enhancement boiling performance can be attributed to (1) the improved disturbance of the working fluid, which enhances forced convective boiling heat transfer and mitigates bubble coalescence and flow reversal strength; (2) the continuously developing liquid film and improved wettability maintain a stable liquid film evaporation and delay partial dry out. Increase in mass flux can improve CHF and reduce pressure drop albeit with high wall temperature of ONB. The local HTC is enhanced, except for the low heat fluxes, because the bubbles are condensed by liquid and cannot grow to absorb heat at low heat fluxes.