heat transfer enhancement due to air bubble injection into a horizontal double pipe heat exchanger

if an air flow is injected into a liquid fluid, many ambulant air bubbles are formed inside the fluid. air bubbles move inside the liquid fluid because of the buoyancy force, and the mobility of these air bubbles makes sizable commixture and turbulence inside the fluid. this mechanism was employed to enhance the heat transfer rate of a horizontal double pipe heat exchanger in this paper. however it can be used in any other type of heat exchanger. especially, this method can be expanded as a promising heat transfer improvement technique in automotive cooling system, for instance in radiator which contains of water or other liquid fluid. bubbles were injected via a special method. present type of air bubbles injection and also the use of this mechanism for double tube heat exchanger have not been investigated before. results are reported for varying bubble inlet parameters. the main scope of the present work is to experimentally clarify the effect of air bubble injection on the heat transfer rate and effectiveness through a horizontal double pipe heat exchanger.