Effect of channel width on pool boiling from a microconfigured heat sink

Microelectronics cooling continues to be an area of great technological challenge for thermal engineers. Chip level heat fluxes of 50-100 W/cm² are projected for the year 2000. The problem of high flux removal from individual chips is further exacerbated by the increase in substrate packing densities. In some designs the substrates on which the chips are mounted are stacked very close together. Heat sinks designed for use in these situations therefore have to be very compact. Two-phase liquid immersion cooling of computers is becoming an increasingly favorable heat removal strategy. A re-entrant cavity heat sink has been developed to address these needs. Previous studies on this heat sink have revealed good heat transfer characteristics in fully developed nucleate boiling coupled with negligible overshoots during the transition from natural convection to pool boiling. In confined situations, the vapor generated moves through the channel formed between adjacent substrates. Bubble transport is therefore affected by the channel width. Saturated pool boiling results are presented and discussed for vertically oriented channels of widths ranging from 0.1 cm to 0.6 cm to cover typical values likely to be encountered. The heat source was a sputtered aluminum thin film heater of size 0.9 cm by 0.9 cm. The cavities were laid out over a 2.5 cm by 2.5 cm area. Testing was carried out in FC-72. It was found that the presence of a parallel plate affected the heat transfer performance adversely