Flow boiling instability and pressure drop characteristics based on micro-pin-finned surfaces in a microchannel heat sink

In this work, flow boiling pressure drop characteristics based on the hydrodynamic instability with deionized water on the micro-pin-finned surfaces in a horizontal narrow microchannel with a hydraulic diameter of 952 µm were investigated. The micro-pin-finned surfaces can be divided into three types based on the size and arrangement of the fins (A30-120/S30-120/A50-120). The experiments were conducted under the mass flux from 200 to 500 kg/m²s and the inlet temperature of 30 to 50 ℃. The two-phase flow patterns on the micro-pin-finned surfaces were captured by a high-speed camera. The flow boiling instabilities in the microchannel are studied, and the two-phase flow pattern, wall temperature, heat fluxes and mass fluxes as well as pressure drop are observed and analyzed. The experiment results show the mass flux has a significant effect on the pressure drop, while it has almost no change with the increasing heat flux in the microchannel heat sink during the nucleate boiling. Besides, the pressure drop of the A30-120 and S30-120 surfaces is less than that of smooth surface due to the effect of hydrophobic surface and bubble drag reduction. The maximum pressure drop of the A30-120 surface is only 0.970 kPa corresponding to the mass flux and critical heat flux (CHF) of 500 kg/m²s and 341.4 W/cm² in this study, respectively. And the overall performance of the micro-pin-finned surfaces is also evaluated in the microchannel heat sink, which can achieve more than a 30% reduction in pressure drop and thermal resistance compared with the smooth surface.