EFFECTIVE COOLING OF ELECTRONIC COMPONENTS BY BOILING PHASE-TRANSITION IN MICROGRAVITY

Boiling heat transfer on a miniature heater has been studied under mic rogravity conditions during the IML 2 Space Shuttle Mission in 1994. T hese experiments are simulations for the application of the direct coo ling of small electronic devices by boiling heat transfer in space. Th is becomes very important due to high thermal loads of modern electron ic components. The results of this investigations are: Even at microgr avity the heat transfer coefficients are very high and are even higher compared with other heater geometry. A remarkable influence of the gr avity on the nucleate boiling heat transfer could not be observed, onl y in the transition and film boiling region a reduction up to 50% was found. Several boiling modes have been observed during the experimenta l runs depending on the subcooling of the liquid, the liquid state, an d the overall heat flux. Surface tension, wetting behavior, coalescenc e processes, the momentum of bubble formation, and thermocapillary con vection play the most important role in boiling. The general statement can be made: boiling can be applied for cooling processes in microgra vity. (C) 1997 International Astronautical Federation. Published by El sevier Science Ltd.