S0506-1-1 Drag reduction and heat transfer characteristics of micro-bubble pipe flows

Abstract

The effect of air micro-bubbles injected into water flowing through helical pipes with different curvature values (0.018, 0.027 and 0.045) on drug reduction and heat transfer performance were experimentally investigated. The mean diameter of the micro-bubbles generated was about 50μm with void fraction ranging from 0.09% to 0.25%. The effect of the Reynolds number is also presented in the range O(10^3)〜(10^5). The experimental results show that, the micro-bubbles have reduction effects in drag and heat transfer on the flows through helical pipes. However, the reduction in heat transfer was more significant than that in drag. It was found that both the heat transfer and drag reduction increase with the decrease of curvature and the increase of void fraction. The maximum value of drag reduction ratio obtained was about 17.6% in case of the lowest curvature coil, while the maximum heat transfer reduction for the same coil was 22.1%.