Effects of fluid properties and surface parameters on pool boiling of porous and pin-fin surfaces

The present experimental study investigated the effect of heater size on pool boiling performance for various fluids. Water, methanol and FC-72 were tested at 50 and 70°C saturation temperature on a smooth surface, a porous surface, a pin-fin surface and a structured surface. The boiling test vessel has a 31 mm by 31 mm internal base area and 100 mm height. The sizes of the heating area are: 31×31, 12×12, 9×9, or 6×6 mm². The test results of all the three fluids showed that boiling performance is independent on heater size for 31 mm × 31 mm, 12mm × 12 mm heaters, but the boiling heat transfer coefficients for the smooth surface having 6 mm × 6 mm heating area is approximately 70∼100% higher than those for the 12 mm × 12 mm heating area. The 0.2 mm thick square pin-fins, having 0.2 mm depth and 0.4 mm pitch, yields 2-to-3 folds enhancement of boiling performance in FC-72. For methanol and FC-72, the porous surface yields up to seven folds boiling enhancement as compared with the smooth surface. However, the enhancement ratio of the porous surface, having 0.15 mm average particle diameter, is only 2.3 for water. Boiling phenomena observation by a high speed video system showed that the bubble size depends on surface geometries and fluid properties.