A Model of Transition from Stable Film Boiling to an Intense Heat Transfer Regime

The article presents the basic statements of the hypothesis put forward on the factors causing the occurrence of intense heat transfer regime during film boiling of subcooled liquid. A new relationship for the temperature difference corresponding to the moment at which transition to fast cooling regime occurs is derived. This relationship takes into account the thermophysical properties of cooled surface and roughness scale on it, the thermophysical properties of cooling liquid and its subcooling. The model has been verified against experimental data under the conditions of free bulk motion of liquid. Unlike our previously published model versions, the liquid subcooling is now taken into account in a more natural way, namely, by the cooling liquid properties and its flow dynamics rather than by introducing empirical corrections. Separate attention is paid to experimental data on cooling metal bodies with the known surface irregularity scale, because the developed relationship depends quite strongly on it. For verification purposes, we collected experimental data on the cooling of spherical and cylindrical samples made of stainless steel, nickel, and copper with various coatings (chromium carbide, gold, and silver), carbon steel, titanium, and FeCrAl and zirconium alloy in water, ethanol, and water–ethanol mixtures with different concentrations. Additional experiments on cooling a copper ball with nickel coating in subcooled water were carried out. For verifying the model, we used experimental data of other researchers on cooling in subcooled water of heated bodies made of zirconium, stainless steel, Inconel, and Zircalloy. The calculation carried out using the newly developed mode has demonstrated good agreement between the obtained results and predominant amount of experimental data.