Effect of Microbubble Injection on Flow and Heat Transfer Characteristics of Surfactant Solution Flow

Koichi ARAGA, Shinnya MORIMOTO, Tatsuro WAKIMOTO and Kenji KATO In a previous study, the heat transfer enhancement of a drag-reducing surfactant solution flow mixed with fine bubbles was considered. The diameter of the fine bubbles was 100 μm or more. However, the flow characteristics of a flow mixed with even finer bubbles like microbubbles are unclear. This paper describes the flow and heat transfer characteristics of a drag-reducing surfactant solution–microbubble two-phase virtical flow. Microbubbles were generated in two ways for air injection in this experiment: mixing air through a porous metal and using a high-speed swirling flow-type generator. The volumetric flow rates of the microbubbles were 0.3% and 0.5%. In the experimental results, the diameter of the microbubbles generated with the swirling flow-type generator was about 70 μm regardless of the Reynolds number. With the surfactant solution–microbubble two-phase flow, the pipe friction factor was increased and the heat transfer coefficient was enhanced compared with the single-phase flow. The heat transfer enhancement of the drag reducing flow increased with the smaller microbubble diameter. The experimental results indicate that microbubble injection into the surfactant solution affects the micelle structure in the solution.