Structure of microlayer at water pool boiling for various bubble growth rates

The growth of a single vapour bubble in a saturated pool of boiling water at atmospheric pressure on a transparent heater is investigated experimentally. The study focuses on a several microns thick liquid layer (called a microlayer) that can form between the heater and the bubble. The microlayer profile, the wall temperature distribution and the overall bubble shape are measured simultaneously and synchronously by white light interferometry, infrared thermography and sidewise shadowgraphy. To study the microlayer dynamics for different bubble growth rates, artificial cavities of different sizes were used. These control the wall superheating required for the bubble nucleation, i.e. the nucleation barrier. Both the bubble growth at its inertial stage and the microlayer parameters are found to be almost independent of the applied heat flux and controlled by the nucleation barrier only. The microlayer thickness and its area increase with the nucleation barrier. A model of microlayer formation based on an analogy with the Landau–Levich film deposition is further developed. By using it, the initial microlayer thickness, the time of microlayer formation at a given distance from the bubble centre and the radius of curvature of the bubble foot edge are recovered from the experimental data. The radius of curvature varies in time like the bubble radius, thus suggesting a self-similar bubble growth at its initial inertial stage. The coherency of the above model with the experimental results shows the model’s validity.