Confined Boiling Heat Transfer Over a Saturated Porous Structure

Abstract

An experimental investigation was performed to study the confined boiling heat transfer characteristics over a saturated porous structure using distilled water as the working fluid. A thin stainless steel resistive foil stretched between two copper electrodes was used to heat a saturated porous plate with an effective pore size of 50 gm. The temperature distribution on the foil heater was measured using a high speed thermal imaging camera. The effect of the gap height between the heater and the porous plate on the heat transfer was investigated for gap heights ranging from 0 um to 1000 um and for heat fluxes ranging from 11.7 kW/m2 to 58.3 kW/m2. It was observed that the highest heat transfer rate was obtained at a gap height of approximately 600 pm. The main heat transfer mechanism is thought to be confined boiling in the small gap between the heating surface and the saturated porous structure. It was observed that the effect of the subcooled liquid temperature did not have a significant effect on the heat transfer. The effect of the pore size in the porous plate was investigated by repeating the measurements with a porous plate of 200 gm pore size. It was observed that the thermal resistance for the plate with a 200 gm pore size was significantly higher than the plate with 50 gm pores for gaps less than 300 gm. At a larger gap height of 600 gm, similar heat transfer performances were obtained for the two porous media.