Flow Boiling of Water at Sub-Atmospheric Pressure in Staggered Micro Pin-Fin Heat Sink

Flow boiling of deionized (D.I.) water through staggered micro pin-fin heat sink was studied. The device had an array of staggered circular pin fins with diameter of 150 mu m, and both the transverse and longitudinal pitches 450 mu m. The pin fin array covered an area of 1 cm x1 cm, and pin height was 200 mu m. Mass fluxes of 624 kg/m(2)s and 1248 kg/m(2)s, heat fluxes ranged from 20 W/cm(2) to 300 W/cm(2), and inlet temperatures of 50 degrees C and 60 degrees C were tested. All tests were conducted in a closed flow loop with pressure below atmospheric. Flow patterns were visualized by high speed camera. Unstable boiling pattern with single phase flow and two phase flow alternatively occupying micro channel was observed for 1248 kg/m2s with inlet temperature of 50 degrees C. Bubbles initiated at upstream nucleation sites expanded to triangular wakes for stable two phase flow.