種々の端面形状を有する垂直円柱まわりの膜沸騰(第2報: 膜沸騰下限界点)

概要

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The wall superheat at the lower limit of film boiling of a vertical finite-length silver cylinder, ΔTmin, was determined experimentally by quenching method for saturated and subcooled water at atmospheric pressure. Five kinds of cylinders were tested where the end surface is flat, hemispherical or conical. The following results were obtained from the experiments. (a) For a cylinder with flat end surfaces, ΔTmin has an average value of 136 K for saturated water, irrespective of the aspect ratio, L/D, where L is the length and D the diameter of the test cylinder. ΔTmin increases linearly with an increase in liquid subcooling, ΔTsub, and exceeds always the thermodynamic limit of liquid superheat (about 225K) for water at atmospheric pressure for ΔTsub larger than 12K. This tendency is similar to the cases of a sphere and a horizontal cylinder obtained experimentally by Dhir and Purohit, and Nishio and U emura, respectively. (b)For five kinds of cylinders with various end configurations, ΔTmin is irrespective of the end configurations for saturated water. However, in subcooled water, Δ Tmin of the cylinder with flat end surfaces has a larger value than those with a hemispherical or conical end surface.