Regularities of Stable Film Boiling of a Subcooled Liquid

Different models of stable film boiling of liquids that give heat-transfer characteristics under these conditions are examined. The existing models have been demonstrated to have disadvantages associated with a consideration of certain limiting cases. The model of subcooled liquid film boiling, developed by a research group including the authors of this paper in 2017, takes into account the velocity of natural convection at the liquid/vapor interface. This model demonstrates good agreement with experimental data on cooling of spheres and cylinders, but the expression for the heat-transfer coefficient (HTC) contains an empirical coefficient. A new model of heat transfer during subcooled liquid film boiling based on the Bromley assumptions is proposed. An analysis of the contribution of radiation to heat transfer during film boiling has demonstrated that, according to a rough estimate, the contribution of this factor can be as high as 10% during cooling of high-temperature bodies in water when their surface is superheated to 1000 K. The applicability of the new model of stable film boiling of subcooled liquids and the models examined in this paper was validated by comparison with the authors' experimental data. The test pieces were spheres and cylinders made of different metals (such as stainless steel, nickel, copper, titanium, FeCrAl alloy, zirconium). They were cooled in saturated or subcooled liquids with different thermophysical properties (such as water, ethanol, water-ethanol mixtures of various concentrations, FC-72, nitrogen) at different system pressures. The experimental data agree best of all with the predictions by the newly developed model. The performed comparisons have demonstrated that this model is more accurate (by 10%) compared to other models of heat transfer during cooling of spheres and cylinders in various liquids (such as water, ethanol, FC-72, isopropanol) in the subcooling range from 10 to 180 K at system pressures from 0.02 to 1.00 MPa.