Thin film evaporation modeling of the microlayer region in a dewetting water bubble

Understanding the mechanism of bubble nucleation and growth is critical for optimizing the boiling heat transfer process. The microlayer region formed during bubble departure is known 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 relatively unknown. In the thin film microlayer region, the vapor pressure is balanced by a combination of the capillary, disjoining, and liquid pressure. Thermally driven evaporation in the curved, thin film is suppressed by disjoining pressure at the nano-scale leading to a peak in evaporation flux in the microlayer region. Using the conservation equations with a lubrication approximation coupled with the augmented Young-Laplace equation, 3rd order nonlinear film evolution equation is obtained. The evolution equation solved numerically using the ODE 45 method in MATLAB. A variable wall temperature BC is employed at the solid-liquid interface and is balanced by evaporative heat loss at the liquid-vapor interface. Contrary to most models, the solution begins in the thicker region of the film and proceeds in a direction of reducing film thickness. The adsorbed film thickness is not known a-priori but is an output of the model. The solution method is devoid of tuning parameters or guessed inputs. Experimentally measured film thickness and its derivatives are used as inputsin the thicker region and the model is evaluated to obtain a film profile down to the nano-scale and a corresponding local evaporative flux. The modeling results compare favorably with spatio-temporal experimental measurements of the microlayer. By comparing the film profiles at multiple time steps, the accommodation coefficient could be determined and its influence on the evaporative flux distribution is discussed.