Experimental and numerical analysis of quasi-static bubble size and shape characteristics at detachment

When investigating the physical mechanisms responsible for pool boiling heat transfer, individual bubbles are commonly assumed to be spherical. This is done in order to ease the computational expense when solving the Navier–Stokes equations. However, bubbles are observed to deviate from spherical depending on fluid properties, cavity sizes and gravitational field strengths. Since it is bubble detachment volume that dictates ebullition frequency, improvements in detachment size and shape predictions would improve nucleate pool boiling heat and mass transfer models. Recent studies have shown that a numerical treatment of the capillary equation’s detachment criterion – which is a result of an interfacial pressure balance analysis – generates profiles corresponding to axis-symmetric quasi-static bubbles for adiabatic conditions. In the present work, this criterion is validated for heat induced bubbles providing the basis for a full analysis of size and shape characteristics of a detaching vapour bubble. A volume detachment correlation is validated for heat induced vapour bubbles and detachment correlations for other size and shape characteristics such as bubble height, width, apex principal radius of curvature, contact angle, and degree of sphericity are developed. Furthermore, a local stress analysis reveals detachment regimes and bubble profile regions.