Pool boiling heat transfer on bare and microporous surfaces confined in a narrow gap

Abstract

Pool boiling heat transfer on bare and microporous surfaces confined in a narrow gap was investigated using distilled water saturated at 1 atm. A 10 × 10 mm2 test heater was attached to the thin copper sheet with a thickness of 0.2 mm, and the bonded heater and sheet were flush-mounted in the 80 × 80 mm2 insulation block. A glass window was placed at the front of the insulation block for visual observation, and the gap between the block and the window was adjusted by inserting spacers varying thickness from 0.5 mm to infinite. Dried region and liquid sublayer were distinctly observed on the heated surface in a narrow gap at the heat fluxes near the CHF, which is believed to give a clue to understanding the CHF mechanism in pool boiling. Unlike the bare surface, the boiling heat transfer coefficients were maintained at the narrow gaps down to 1 mm on the porous surface.