Heat transfer to bubbles under a horizontal tube

The mechanisms of boiling heat transfer on the outside of a horizontal tube are multifarious and include contributions from site nucleation, micro-layer evaporation and liquid disturbance. Previous work has shown the strong influence of sliding bubbles which disturb the liquid and can leave a thin evaporating layer under the bubble. Results of experiments designed to determine the local temperature profiles around individual bubbles in water as they slide around the periphery of a thin downward-facing curved surface are presented. High-speed video recording of thermochromic paint on the surface followed by hue analysis and processing allowed detailed examination of a small section of the curved surface. The strong influence of liquid disturbance around the bubble on the local heat transfer is demonstrated. Under the low heat flux conditions of the experiments, the liquid layer under the bubble was found to dry out yielding a high-temperature spot which was quenched by the surrounding liquid when the bubble moved away. (C) 1998 Elsevier Science Ltd.