Subcooled pool boiling of water on a downward-facing stainless steel disk in a gap

Pool boiling is experimentally studied on a relatively large downward-facing surface with heated stainless steel disk diameters of D = 100 and 300 mm in confined space at atmospheric pressure using water as the working fluid. The bulk working fluid is subcooled. The gap size s can be adjusted to 10, 15 and 20 mm for D = 100 mm and 0.9–77 mm for D = 300 mm. We found that pool boiling under the present condition is far weaker than that occurring on an upward-facing surface. Furthermore, we found that the larger the diameter of the stainless steel plate, the weaker the pool boiling heat transfer. The heat transfer rate may be predicted by the Kutateladze correlation for s > 20 mm and by its modified form for s < 20 mm for both D = 100 and D = 300 mm. Two different typical bubble circulation motions are found. Type I motion occurs with a probability of 90.9% and type II occurs with a probability of 9.1% according to the statistical calculations. Most coalesced bubble diameters are from 90 to 100 mm for D = 100 mm and from 100 to 200 mm for D = 300 mm.