Effects of Bubble Size on Heat Transfer Enhancement for Laminar Natural Convection by Sub-Millimeter Bubbles

Abstract

Sub-millimeter-bubble injection is one of the most promising techniques for enhancing heat transfer for the natural convection of liquids. So far, we have investigated experimentally the heat transfer enhancement by sub-millimeter bubbles. However, the effects of the bubble diameter on the heat transfer have not yet been understood. The purpose of this study is to clarify the effects of bubble diameter on the heat transfer enhancement by sub-millimeter bubbles for the laminar natural convection of water along a vertical heated plate. We conduct temperature measurements using thermocouples and velocity measurements using a Particle Tracking Velocimetry (PTV) technique. We also carry out two-dimensional numerical simulations to comprehensively understand the effects of bubble injection on the flow near the heated wall. Temperature measurements show that the heat transfer coefficient increases with a decrease in the bubble diameter. This is due to a significant increase in the bubble advection effect.