Pool Boiling Heat Transfer From Enhanced Surfaces to Dielectric Fluids

Pool boiling heat-transfer measurements were made using a 15.8 mm o.d. plain copper tube and three copper enhanced surfaces: a Union Carbide High Flux surface, a Hitachi Thermoexcel-E surface and a Wieland Gewa-T surface. The dielectric fluids were Freon-113 and Fluorinert FC-72, a perfluorinated organic compound manufactured to cool electronic equipment. Data were taken at atmospheric pressure, and at heat fluxes from 100 W/m² to 200,000 W/m². Prior to operation, each test surface was subjected to one of three aging procedures to observe the effect of surface past history upon boiling incipience. For Freon-113 the enhanced surfaces showed a two to tenfold increase in the heat-transfer coefficient when compared to a plain tube, whereas for FC-72 an increase of two to five was measured. The High Flux surface gave the best performance over the range of heat fluxes. The Gewa-T surface did not show as much of an enhancement at low fluxes as the other two surfaces, but at high fluxes its performance improved. In fact, it was the only surface tested which delayed the onset of film boiling with FC-72. The degree of superheat required to activate the enhanced surfaces was sensitive to both past history of the surface and to fluid properties.