Stabilizing Flow Boiling Operation of a Microchannel Heat Sink using a Hybrid Geometric Configuration

Abstract

Two-phase cooling using microchannel heat sinks is a promising solution for the thermal management of microelectronic devices. While conventional straight microchannel heat sinks can dissipate large quantities of heat, they suffer from flow instabilities that result in premature critical heat flux conditions. It therefore becomes necessary to develop heat sinks that offer a stabilized boiling process over a wider range of operating heat flux. In this work, a novel hybrid heat sink developed to attain this objective is first presented. The heat sink involves a hybrid geometric configuration that integrates a $300\mu \mathrm {m} \mathrm {x} 600\mu \mathrm {m}$ microchannel array in the upstream region with a $25\mathrm {m}\mathrm {m} \mathrm {x} 600\mu \mathrm {m}$ microgap in the downstream region of a $25\mathrm {m}\mathrm {m}\mathrm {x}25\mathrm {m}\mathrm {m}$ copper heat sink. Flow boiling experiments are conducted with deionized water at 3 mass fluxes in the range of $100-399\mathrm {k}\mathrm {g}/\mathrm {m}^{2}\mathrm {s}$ and at heat fluxes ranging $\mathrm {f}_{\mathrm {T}}\mathrm {o}\mathrm {m}0-128\mathrm {W}/\mathrm {c}\mathrm {m}^{2}$. The boiling operation is found to be stable across a wide range of moderate to high heat flux. Instabilities are experienced only at low heat flux close to the onset of nucleate boiling. The effect of the downstream microgap surface roughness on the hybrid heat sink flow boiling performance is then investigated. Hybrid heat sinks with microgap surface roughness values of $1.2\mu \mathrm {m}$ and $1.9\mu \mathrm {m}$ are compared with the baseline hybrid heat sink having microgap surface roughness of $0.27\mu \mathrm {m}$. The two-phase heat transfer performance shows a highest improvement of 14.5% with the hybrid heat sinks having roughened microgaps while the pressure drop penalty remained relatively unaffected.