Surface heat transfer due to sliding bubble motion

Abstract

The presence of a rising bubble in a fluid can greatly enhance heat transfer from adjacent heated surfacessuch as in shell and tube heat exchangers and chemical reactors. One specific case of this is when a bubbleimpacts and slides along the surface. The result is heat transfer enhancement by two main mechanisms:first, the bubble itself acting as a bluff body, and second, the wake generated behind the bubbleleads to increasing mixing. The current research is concerned with measuring the heat transfer from asubmerged heated surface that is subject to a sliding bubble flow. An ohmically heated 25 lm thick stainlesssteel foil, submerged in a water tank, forms the test surface. An air bubble is injected onto the lowersurface of the test plate, it slides along its length and the effects are monitored by two methods. Thermochromicliquid crystals (TLC’s) are used in conjunction with a high speed camera to obtain a time varying2D temperature map of the test surface. A second synchronised camera mounted below the foil recordsthe bubble motion. Tests are performed at angles of 10, 20 and 30 to the horizontal. This paper reportson the enhancement of the heat transfer due to the bubble. It has been found that the angle madebetween the heated surface and the horizontal influences heat transfer by changing the bubble’s motion.In general, a steeper angle leads to a higher bubble velocity, which results in greater heat transferenhancement.