Thin Film Evaporation Modeling of the Liquid Microlayer Region in a Dewetting Water Bubble

Abstract

Understanding the mechanism of bubble growth is crucial to modeling boiling heat transfer and enabling the development of technological applications, such as energy systems and thermal management processes, which rely on boiling to achieve the high heat fluxes required for their operation. This paper presents analyses of the evaporation of “microlayers”, i.e., ultra-thin layers of liquid present beneath steam bubbles growing at the heated surface in the atmospheric pressure nucleate of boiling water. Evaporation of the microlayer is believed to be a major contributor to the phase change heat transfer, but its evolution, spatio-temporal stability, and impact on macroscale bubble dynamics are still poorly understood. Mass, momentum, and energy transfer in the microlayer are modeled with a lubrication theory approach that accounts for capillary and intermolecular forces and interfacial mass transfer. The model is embodied in a third-order nonlinear film evolution equation, which is solved numerically. Variable wall-temperature boundary conditions are applied at the solid–liquid interface to account for conjugate heat transfer due to evaporative heat loss at the liquid–vapor interface. Predictions obtained with the current approach compare favorably with experimental measurements of microlayer evaporation. By comparing film profiles at a sequence of times into the ebullition cycle of a single bubble, likely values of evaporative heat transfer coefficients were inferred and found to fall within the range of previously reported estimates. The result suggests that the coefficients may not be a constant, as previously assumed, but instead something that varies with time during the ebullition cycle.

An investigation of phase change induced Marangoni-dominated flow patterns using the Constrained Vapor Bubble data from ISS experiments

“…In the transition film (also called the thin-film) region, the thickness reduces to the micrometer range, along with a non-monotonically changing interface curvature. The reduction in film thickness enables a shorter conduction path resulting in an increase in phase change rate (Bellur et al, 2020;Lakew et al, 2023). The film thickness further reduces to nano-scale in the adsorbed film region, where the local physics is dominated by intermolecular forces commonly modeled as a disjoining pressure (net pressure reduction).…”

“…The film thickness further reduces to nano-scale in the adsorbed film region, where the local physics is dominated by intermolecular forces commonly modeled as a disjoining pressure (net pressure reduction). In the adsorbed film, the disjoining pressure suppresses evaporation greatly and, in an equilibrium setting, can result in a non-evaporating film of constant thickness (Bellur et al, 2023;Lakew et al, 2023).…”

Nanoscale Meniscus Dynamics in Evaporating Thin Films: Insights from Molecular Dynamics Simulations

“…A meniscus refers to a curved liquid–vapor interface at the edge of a confined space, as illustrated in Figure . For simplicity, evaporating meniscus can be hypothetically divided into three subregions, particularly in the case of wetting fluids. − The first region is the adsorbed layer region, where the solid–liquid–vapor trijunction forms, creating an interface with nearly uniform thickness. The second subregion is the tf region, which connects the meniscus to the adsorbed film.…”

The Influence of Pressure on Local Heat Transfer Rate under the Vapor Bubbles during Pool Boiling

“…Finally, understanding the nature and influence of various parameters on the microlayer evaporation rate is important to develop and fabricate micro-and nanostructured heating surfaces to achieve maximum heat transfer rates and critical heat fluxes during boiling [14][15][16]. However, despite the rather large number of papers devoted to both the experimental study on microlayer evolution and structure [5][6][7][8][9][10][11][12] and the numerical simulation of its evaporation [17][18][19][20], a number of questions remain open. One of such issues is the influence of system parameters (pressure, subcooling degree, gravity level, etc.…”

“…In the present paper, an experimental study on the evolution of a nonstationary temperature field during the pool boiling of ethanol at pressures 12-101.2 kPa was performed. Experimental data were obtained using infrared thermography with high temporal and spatial resolutions, which made it possible to reconstruct the distribution of the heat flux However, despite the rather large number of papers devoted to both the experimental study on microlayer evolution and structure [5][6][7][8][9][10][11][12] and the numerical simulation of its evaporation [17][18][19][20], a number of questions remain open. One of such issues is the influence of system parameters (pressure, subcooling degree, gravity level, etc.…”