ISSN Online: 2377-424X
International Heat Transfer Conference 12
Water Boiling on Highly Superheated Hemispherical Samples
Abstract
The results of experimental and theoretical study of
destruction of the vapor film on highly superheated
hemispheric surface immersed into water, which is subcooled relative to the saturation temperature, are presented. The diameter of the hemisphere is 10 mm. The tests were conducted at atmospheric pressure at a temperature of the heated surface of 700-1100 K and water subcooling relative to the saturation temperature of 20-85 K. The clean, oxidized and coated with low-conductive film samples made of copper, brass, and stainless steel were used. Behavior of the vapor film and the parameters of the film boiling, as well as those during
destruction of the film were observed by means of video camera and special gauges. In the tests, thickness of the vapor film, frequency and amplitude of the interface oscillations, sound effects, accompanying destruction of the film, pressure pulsation near the film surface, temperatures of the hemisphere and the liquid were measured. It was recognized that, depending on the heating surface condition (the clean one or with a low-conductive coating), the surface superheating, and water subcooling, different types of the film destruction and transition to the bubble boiling take place, that is, the gradual with vapor release at the free surface of the liquid and the explosive one with a single or multiple vapor jet ejection into the liquid pool. The physical model of the
explosive vapor film destruction, which takes into account the wave effects on the interface, is proposed.