Enhanced heat sink performance utilizing capillary driven evaporation

Heat sinks with the same form factor, but lower thermal resistance than currently available are desirable in many applications. For example, they would benefit the electronics packaging industry by accommodating increased heat dissipation in reduced form factors. An enhanced longitudinally-finned heat sink that exploits evaporative cooling to significantly reduce its thermal resistance was modeled, fabricated and tested. A 1 mm-thick layer of (porous) sintered copper powder coated the entire (32 mm x 28 mm x 14 mm) heat sink and (porous) sintered copper powder legs were immersed in an underlying water reservoir maintained at the temperature of the base of the heat sink. The assembly was placed in a wind tunnel in the fully-shrouded configuration and (dry) nitrogen with (upstream) velocities ranging from 1 m/s to 4 m/s flowed through the heat sink. Capillary forces maintained a thin, evaporating film of water. Due to the high latent heat of evaporation of water, large thermal resistance reductions are observed. The thermal resistance of the coated heat sink was 3.4 to 4.7 times lower than that of an uncoated heat sink of the same geometry. Both heat sinks were tested over a range of 0 W to 20 W heat loads when (upstream) velocity equaled 2 m/s and over an (upstream) velocity range from 1 m/s to 4 m/s when heat load was 15 W. The sintered heat sink was tested with increasing power at 2 m/s until the heater burned out at 59 W. At this heater input, the sintered heat sink reached 43oC above the ambient temperature. To achieve the same temperature rise, the control heat sink required only 12 W of power, almost five times less. External flow over a coated flat plate was also investigated and similar reductions in thermal resistance observed.