Modeling of Subcooled Liquid Film Boiling on a Smooth Horizontal Cylinder Using the VOF Method

A study of film-boiling processes of liquid subcooled to saturation state was conducted using numerical modeling based on the Volume of Fluid (VOF) method and the Lee model for describing heat and mass transfer at the interphase surface. During film boiling, a stable vapor film is formed between the wall and the liquid, eliminating their direct contact, which leads to low heat-transfer intensity. Under conditions of subcooling of the liquid to the saturation state, the intensity of film boiling increases significantly. Despite a thorough understanding of the heat and mass transfer mechanisms involved in this phenomenon, the development of new, more accurate models remains an active area of research. The efforts of researchers are driven by the need to accurately describe the cooling dynamics of high-temperature bodies and predict the onset conditions for high-intensity boiling regimes. Physical models explaining the emergence of these modes are still at the development stage. To verify and clarify them, there is insufficient information about the local characteristics of the vapor film and the features of free convective flow in subcooled liquid. The use of the VOF method allows for detailed tracking of changes in the interphase surface directly during the numerical simulation process. The article presents the results of modeling film boiling of water on the surface of a cylinder with a diameter of 2 mm with superheating of the wall up to 400 K and subcooling of the liquid up to 20 K. The discrepancy between the obtained simulation data and the experimental results published in literary sources does not exceed 10%. Information is provided on the distribution of film thickness, heat flux on the wall, and the interphase surface. According to the simulation, even with slight subcooling, the vapor is not “evacuated” from the vapor cavity, while evaporation is observed on one part of the interphase surface, and condensation on the other. The results of modeling taking into account buoyancy forces, associated with temperature nonuniformity in a subcooled liquid, and without taking them into account practically coincide, which indicates that the natural convection flow is formed mainly due to mass forces caused by difference in phase densities. The obtained data can be useful for creating more accurate empirical models describing the process of stable film boiling in subcooled liquid. All calculations were performed using the ANES CFD code developed at the Department of Engineering Thermal Physics of the National Research University MPEI.