The Thickness of the Liquid Microlayer Between a Sliding Bubble and a Heated Wall: Comparison of Models to Experimental Data

Sliding vapor bubbles are known to create high heat transfer coefficients along the surfaces against which they slide. The details of this process remain unclear and depend, in part, on the evolution of the liquid microlayer that forms between the bubble and the surface, as the bubble grows by evaporation. A mechanistic model of the microlayer thickness verified by direct observation of the microlayer thickness is needed. This paper describes a comparison of measurements from a recent set of experiments to the results of microlayer models from literature and to the predictions of a new model presented here for the first time. The measurements were produced by a laser-based method developed to measure the thickness of the liquid microlayer between a cap-shaped sliding bubble and an inclined heated wall. Microlayer thicknesses of $22–55μm$ were obtained for saturated FC-87 and a uniform-temperature surface inclined at 2–15 deg from the horizontal. The basis of each model, input requirements, limitations, and performance relative to this data set is discussed. A correlation is developed based on the structure of the lubrication theory. It collects the measured microlayer thickness presented as a microlayer Reynolds number to within $±10%$⁠. This correlation depends only on bubble volume, inclination, and a bubble shape factor, all of which can be determined experimentally to within reasonable accuracy.