A study of gravitational effects on single elongated vapor bubbles

An experimental study was completed on the heat transfer induced by a single elongated vapor bubble rising in vertical, upward, co-current flow at various accelerations. The bubble shape and behavior were also studied under those conditions. Tests were conducted using a flow boiling rig which coupled flow visualization with measurements of the heat transfer and liquid film thickness. The bubble drift velocity was shown to dictate the bubble shape as well as the relative influences of thin film evaporation and turbulent wake heat transfer. When present, vortices shed behind the bubble tail created peaks in the heat transfer coefficient whose magnitude decreased with increasing liquid Reynolds number and acceleration. The vortex frequency was found to be linearly dependent on plunging velocity. A criteria for vortex incipience was proposed. (C) 2016 Elsevier Ltd. All rights reserved.