Engineered Micropillar Wicks for Heat Pipe Evaporator

Abstract

This work presents the experiment characterization of thin film evaporation heat transfer of an engineered heat pipe on conventionally manufactured micro-pillar arrays using saturated water as the working fluid. Three engineered copper micro-pillar arrays of 400 μm square pillar width, 500 μm, 800 μm and 1100 μm wall-to-wall spacing and 500 μm pillar height, and one micro-pillar surface of 400 μm square pillar width, 500 μm wall-to-wall spacing and 600 μm pillar height were fabricated using CNC machining. The test samples were provided with primary and secondary reservoirs, and overflow channel to ensure enough liquid supply to the test sample and capillary driven thin film evaporation heat transfer tests. The active heating area of microstructured surfaces had a dimension of 1 cm × 1 cm. The samples were soldered to a custom-built heater block to provide the joule heating. The tests were performed at room temperature (~25 °C) and corresponding saturation pressure (~24 torr). A modular vacuum chamber connected with separate DI water canister was used as the thin film evaporation test facility. A maximum dry-out heat flux of ~ 92 W/cm2 was achieved at a superheat of ~ 31.7 K for the copper micro-pillar arrays of 400 μm square pillar width, 800 μm wall-to-wall spacing and 500 μm pillar height during thin film evaporation of saturated water.