The Dynamics of Bubble Growth at Medium-High Superheat: Boiling in an Infinite Medium and on a Wall

Abstract

At high superheat, bubble growth is rapid and the heat transfer is dominated by radial convection. This has been found, in the case of a droplet boiling within another liquid and in the case of a bubble growing on a heated wall, leading to similar bubble growth curves. Based on an experimental parametric study for the droplet-boiling case, an empirical model was developed for the prediction of bubble growth, within the radial convection dominated regime (the RCD model) occurring only at high superheat. This model suggests a dependence of R∼t1/3—equivalent to a Nusselt number decreasing over time (Nu∼t−1/3), as opposed to R∼t1/2 —equivalent to a highly-unlikely constant Nusselt number, in most other models. The new model provides accurate prediction for both the droplet boiling and nucleate pool boiling cases, in the medium-high superheat range (0.26<Ste <0.41, 0.19<Ste<0.30, accordingly). By comparison, the new RCD model shows a more consistent prediction, than previous empirical models. However, in the nucleate boiling case, the RCD model requires the foreknowledge of the departure diameter, for which a reliable model still is lacking.