Boiling heat transfer on large diamond and SiC heaters: The influence of thermal wall properties

Pool boiling experiments were performed on large synthetic diamond and SiC substrates with integrated heating and temperature sensor elements. The boiling fluid was pure water at atmospheric pressure. The two heating substrates were identical with regard to geometry and design, and were mainly comparable in terms of surface roughness and static contact angle. This enabled the influence of the thermal heating wall properties on the resulting heat transfer to be investigated directly. The extraordinarily high value of the thermal conductivity of the synthetic diamond heater led systematically to higher mean heat transfer rates within the nucleate boiling regime compared to the SiC material. Strong thermal fluctuations due to the growth and detachment of vapor bubbles were recorded for both heaters. Indications for the existence of a local heat flux reversal from the liquid to the wall have been found by means of re-condensation phenomena and direct temperature measurements during boiling.