| The basic heat transfer characteristics of simulated microelectronic chips were investigated with direct immersion cooling in Freon-TF (R-113). The basic heater was 4.5 mm x 4.5 mm electrically heated foil. The studies of plain heaters included natural convection, nucleate boiling, and critical heat flux. Water was included as a working fluid for natural convection. Ultrasonic agitation and heat sinks were studied as enhanced cooling methods.;Data for natural convection were also obtained for in-line and staggered arrays of flush heaters with varying distance between heaters. Heat transfer coefficients for the upper heaters are below those for the lower heaters, with the differences diminishing as the vertical or horizontal spacings increase. For the protruding heaters, the upper heaters have higher coefficients than the lower heaters.;There were negligible effects of width and protruding for fully developed boiling, as expected. Boiling inception occurred earlier with the top heaters than with the bottom heaters.;The effects of heater height for critical heat fluxes agree generally with reported data. Critical heat flux increases with decreasing width. Correlations for the effects of height and width were developed.;The height effect for single flush heaters agrees qualitatively with the conventional theory of natural convection, however, even the widest heaters have coefficients higher than predicted due to leading edge effects. The heat transfer coefficient increases with decreasing width. Correlations were developed for this effect which was as much as 150%. The protruding heaters have about 15% higher coefficients than the flush heaters.;Turning to enhancement, ultrasonics was effective at low heat fluxes. Established boiling and critical heat flux were less affected.;Small holes or small fins were machined in brass bars and copper studs (detachable) which were used as boiling heat sinks. Enhancement of the brass heat sinks was lower than that of the copper heat sinks due to the lower thermal conductivity. Boiling curves were also generated for heat sinks made from the Thermoexcel-E and High Flux surfaces. The best performance was obtained with the High Flux surface. |
