Local instantaneous heat transfer around a single elongated bubble in inclined pipes

The instantaneous convective heat transfer rate resulting from the passage of a single elongated bubble propagating in an inclined pipe with a constant translational velocity is examined experimentally for various pipe inclinations and liquid flow rates. Local instantaneous heat transfer rates in the upper and lower parts of the pipe were determined using wall temperature measurements by an IR camera. The ensemble-averaged values of the heat transfer rate are presented as a function of the distance from either the bubble tip or bottom. Optical sensors synchronized with the IR camera were used for this purpose. Possible mechanisms that govern the enhancement of the heat transfer rate during the passage of an elongated bubble are discussed.