Experimental Study of the Vapor Film Behavior on a Highly Heated Surface Immersed Into Subcooled Water

Results of the experimental studies of the vapor film behavior on a highly heated hemispherical surface immersed into water subcooled relative to the saturation temperature are presented. Transition from film to nucleate boiling was studied with the use of high-speed videocamera. Temperature characteristics of the vapor-film collapse, pressure pulses, acoustic effects, and vapor-film thickness were measured, as well. The decisive influence of the material and condition of the heating surface and the degree of water subcooling on the mode of transition (explosion-like, quiet, or intermediate one) was confirmed. The explosion-like mode of the vapor-film collapse is accompanied by ejection of vapor jets (single or multiple) and pressure pulses with an amplitude of up to 1 MPa. A structure of the pulse packs under multiple jets ejection was investigated. Synchronous measurements of the pressure pulses and an area of the direct cold liquid contact with a hot surface made it possible to determine a time delay between an instant of the contact and the pressure pulse. Typical value of this time lag was several tens microseconds. The dependence of the pulse frequency and the number of pulses on the hemisphere temperature was obtained.