Surface Design Factors in the Evaporative Cooling of Electronic Components

Variations in the size and orientation of a surface cooled by evaporation of a liquid are reflected in the measured heat transfer characteristics. Nucleate boiling curves from tests of "Freon-113" in contact with two sizes of heated flat plates in different positions are used to demonstrate the comparative characteristics. For low levels of heat flux, the lowest surface temperatures are exhibited by the larger of the heated plates facing downward. At higher fluxes, the lowest temperatures observed are those of the larger plates facing upward. The slope of the boiling curve for any size plate becomes progressively greater as the plate is shifted from the face-down position through the vertical to the face-up position. The facility with which bubbles can escape from a heated surface is proposed as a significant determinant of heat transfer characteristics.