ABSTRACT
High-speed video photography combined with liquid crystal thermography has been used to measure heat transfer near isolated steam or air bubbles sliding along the underside of a sloping, heated plate in water, in simulation of bubbly flow boiling on the lower surface of a tube in a horizontal bundle. The high rate of evaporative cooling under a vapour bubble masks the convective heat transfer that may occur in its wake. The experiments with gas bubbles, in which the evaporative cooling is negligible, show that there is a high rate of convective heat transfer in a very limited region just at the back of a sliding bubble but convection in its wake is only about 30% higher than in single-phase natural convection. There is limited evidence that convective cooling may be much more effective in a swarm of bubbles.
