High speed video recording of bubble formation with pool boiling

The images of the video sequence are analysed manually or by special semiautomatic evaluation programs to obtain the number and location of active nucleation sites and some selected results for bubble departure diameter and frequency. Results for the bubble formation on a horizontal copper tube in boiling propane for an intermediate pressure from low to high heat fluxes are discussed, e.g. the cumulative site densities vary from 2 mm−2 at low heat fluxes to 70 mm−2 for high heat fluxes. Additionally, the fluctuation by time and in the location on the tube is recorded. Because of the large amount of data, different automatic methods to analyse the single images have to be developed. A new template-based method for the evaluation of the video sequences allows the nearly automatic identification of the individual bubble on its nucleation site, and to track its growth and movement along the heated tube surface during the following images. First results show that the bubbles sliding up the superheated tube surface grow at a similar rate as those staying on their nucleation site. Their contribution for the vapour production in model assumptions has to be revised.