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 dropletboiling 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 highlyunlikely 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 mediumhigh 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.