Effect of inlet sub-cooling on heat transfer and flow stability in a hybrid heat sink

Abstract Inlet sub-cooling of fluid has significant influence on stability and heat transfer process during flow boiling in microchannel heat sinks for devices generating high heat flux. A computational study of a hybrid microchannel-microgap heat sink section has been performed for constant high heat flux condition with varying water inlet sub- cooling. Results of the transient two-phase analysis reveal that at saturated inlet condition ( ∆T in = 0 K), heat sink shows better temperature uniformity and hotspot mitigation capabilities but had high pressure fluctuations due to flow reversal resulting in flow boiling instability. By increasing sub-cooling ( ∆T in = 5 K and ∆T in = 10 K), the pressure fluctuations reduced considerably but developed non-uniform, high surface temperatures in heat sink due to delay in onset of boiling, which can cause hotspots. Increasing the subcooling also resulted in increase in heat transfer coefficient (h) in heat sink, particularly in downstream microgap section. The study corroborated the importance and effect of inlet sub-cooling on heat transfer performance and flow stability of a hybrid heat sink with two-phase flow.