Experimental investigation of flow boiling characteristics in microchannel with triangular cavities and rectangular fins

Abstract

Phase change heat transfer in micro heat sink was an effective method to solve the thermal issues of high heat flux micro devices. The geometric structure modification of the micro heat sink could enhance its heat transfer performance obviously. In this paper, a microchannel with triangular cavities and rectangular fins (Tri.C-Rec.F) was fabricated for the purpose of flow boiling improvement. Flow boiling experiments were carried out using pure acetone with a fixed inlet temperature of 29 °C at four mass fluxes 83 kg/(m2⋅s), 147 kg/(m2⋅s), 324 kg/(m2⋅s) and 442 kg/(m2⋅s), effective heat flux ranging from 0 to 101 W/cm2. The flow boiling characteristics of the microchannel Tri.C-Rec.F were studied and compared with those of the conventional rectangular microchannel (R). The physics behind the flow boiling process and the heat transfer enhancement mechanisms of the micro heat sink were explored. Experimental results indicated that the microchannel Tri.C-Rec.F showed significant enhanced heat transfer, reduced onset of nucleate boiling (ONB), and delayed critical heat flux (CHF) compared to the microchannel R because of the increased bubble nucleation and the particular flow boiling phenomena. Moreover, the modified microchannel improved the flow boiling stability distinctly for high mass fluxes. The continuously developing liquid film could enhance the liquid film evaporation, maintain the liquid supplement and prevent partial dryout effectively. The flow disturbance effect of the micro structures and the bubble breaking effect of the micro fins promoted bubble departure and mitigated the flow reversal. The microchannel Tri.C-Rec.F presented a remarkable higher heat transfer coefficient than microchannel R with a maximum increment of 300% and 51.6% at G = =83 and 442 kg/(m2⋅s), respectively. The acceleration, disturbance and separation effects of the micro fins increased the pressure drop, which could be improved by further structural optimization.