Heat Transfer Enhancement for Laminar Natural Convection due to Micro-bubble Injection

A micro-bubble injection is one of the most promising techniques of enhancing the heat transfer for laminar natural convections of liquid. However, flow and heat transfer structures for laminar natural convections of water with micro-bubbles have not yet been fully understood. The purpose of this study is to clarify the effects of the micro-bubble injection on the laminar natural convection of water along a vertical heated plate using thermocouples and a Particle Tracking Velocimetry (PTV) technique. The experimental results show that the heat transfer coefficients with micro-bubble injection are higher compared with those without micro-bubble injection as the bubble flow rate increases or the wall heat flux decreases. It is concluded from the velocity measurements that the heat transfer enhancement for the laminar natural convection results from the significant increases in the liquid mean rise velocities and the liquid RMS velocities due to micro-bubble injection.