Effects of microbubble injection on natural convection heat transfer from a vertical heated plate

Abstract

This paper describes effects of microbubble injection on natural convection heat transfer from a vertical heated plate in water. Thermocouples are used for the temperature measurement and an image processing technique is used for obtaining the bubble diameter, the bubble velocity and the bubble layer thickness. The working fluid used is tap water. and li drogcn bubbles generated b electrolysis of the water are used as the inicrobubbles. For a constant bubble flow rate and a constant wall heat flux, in the laminar and transition regions. the heat transfer coefficient is significantly increased by the microbubble injection (The ratio of the heat transfer coefficient with bubble injection to that without injection is I .6-2.0 in both regions). The heat transfer enhancement in the laminar region results from both the forced-cons cction and mixing effects due to microbubbic injection. On the other hand, the heat transfer cnhaiemncnt in the transition region is iiiainlv affected b' acceleration of the transition to turbulence due to microbubblc injection. © 2012 The Japan Society of Mechanical Engineers.