The effects of a sliding air bubble on heat transfer from an inclined surface

Abstract

An investigation into the effect of a single sliding air bubble on heat transfer from a submerged, inclined surface has been performed. It is known that bubbles, both vapour and gas, can increase heat transfer rates from adjacent heated surfaces. However, the mechanisms involved are dynamic and complex and, in some cases, poorly understood. Although numerous studies exist for free rising bubbles, research on their effects on heat transfer are limited. Even fewer studies have been performed in relation to sliding bubbles. A comprehensive review of the available existing literature is presented. The present study utilises high speed, high resolution, infrared thermography to measure the two dimensional surface heat transfer adjacent to a sliding bubble. The three dimensional bubble position and shape in two planes are simultaneously recorded with two high speed digital cameras. Fluid velocity in a plane parallel to the surface is computed using a high speed particle image velocimetry system. The equipment is mounted to a purpose built tilting water tank to observe the bubble as it slides. Computer code was developed to analyse and combine the data in a virtual three dimensional environment. Accurate, repeatable bubble volumes of 0.05, 0.1, 0.2 and 0.4 ml were released onto a surface inclined at 30° to the horizontal.