Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.
Experiments were performed using laser extinction method to measure the thickness of the liquid layer formed by growing flattened bubbles between two parallel plates for gap sizes of 0.5, 0.3, and 0.15 mm. Water, toluene , ethanol and HFE7200 were used as the test fluid. A high-speed camera was used to simultaneously measure the bubble growth process and determine the bubble forefront velocity. Vapour bubbles that are generated by boiling in the present mini-gap grows exponentially due to the rapid evaporation of the thin liquid layer, which, in contrast to the steady situations considered previously, makes the phenomena highly transient. Based on the experimental data (together with the previous results for water and toluene) and scaling arguments, a non-dimensional correlation in terms of capillary number and Bond number is proposed.