Extensive research has been conducted on pool boiling using heaters larger than the capillary length. For large heaters and/or high gravity conditions, boiling is dominated by buoyancy, and the heat transfer is heater size independent. Much less is known about boiling on small heaters and at low gravity levels. The ratio of heater size L_(h) to capillary length L_(c) is an important parameter in the determination of heater size dependence on heat transfer. As the ratio L_(h)/L_(c) decreases due to a decrease in either heater size or gravity, surface tension forces become dominant. It is proposed that transition from buoyancy to surface tension dominated boiling occurs when the heater size and bubble departure diameter are of the same order. Previous work in variable gravity with flat surfaces has shown that the heat transfer was heater size independent only when the ratio L_(h)/L_(c) was considerably larger than 1. An array of 96 platinum resistance heater elements in a 10X10 configuration with individual elements 0.7X0.7 mm~(2) in size was used to vary heater size and measure the heat transfer. The threshold value of L_(h)/L_(c) above which pool boiling is heater size independent was found to be about 2.8.
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