Experimental investigation of flow boiling heat transfer of jet impingement on smooth and micro structured surfaces

Abstract

Flow boiling heat transfer experiments using R134a were carried out for jet impingement on smooth and enhanced surfaces. The enhanced surfaces were circular micro pin fins, hydrofoil micro pin fins, and square micro pin fins. The effects of saturation pressure, heat flux, Reynolds number, pin fin geometry, pin fin array configuration, and surface aging on flow boiling heat transfer characteristics were investigated. Flow boiling experiments were carried out for two different saturation pressures, 820kPa and 1090kPa. Four jet exit velocities ranging from 1.1–4.05m/s were investigated. Flow boiling jet impingement on smooth surfaces was characterized by large temperature overshoots, exhibiting boiling hysteresis. Flow boiling jet impingement on micro pin fins displayed large heat transfer coefficients. Heat transfer coefficients as high as 150,000W/m2K were observed at a relatively low velocity of 2.2m/s with the large (D=125μm) circular micro pin fins. Jet velocity, surface aging, and saturation pressure were found to have significant effects on the two-phase heat transfer characteristics. Subcooled nucleate boiling was found to be the dominant heat transfer mechanism.