Structure of air-water two-phase flow in helically coiled tubes

Murai, Yuichi*; Yoshikawa, Shinji ; Toda, Shinichi*; Ishikawa, Masaaki*; Yamamoto, Fujio*

Air-water two-phase flow in helicallly coiled tube of 20mm in the internal diameter is investigated ezperimentally to elucidate the effect of centrifugal acceleration on the flow regime map and the local instantaneous flow structure. Three kinds of test tubes including a straight tube are used to compare the flow structure under turbulent flow condition. The superficial velocity up to 6 m/s is tested so that centrifugal Froude number covers a range from 0 to 3. The inter facial structure is visualized from two directions by a high-speed video system with a synchronized measurement of local pressure fluctuation. The results reveral that the flow transition line alters due to centrifugal force acting on liquid phase in the tube. Especially the bubbly fow regime is narrwed significantly. The pressure fluctuation amplitude gets large relatively to the average presure loww as void fraction increases. The Frequency spectra of the pressure fluctuation have plural peaks in the case of strong curvature, implying that the periodicity of slugging two-phase flow is collapsed by internal secondary flow actibated inside liquid phase. Moreover, the substantial velocity of gas phase is slower than the total superficial velocity in case of large Froude number because of biased distribution to the inner surface allowing liquid flow passing outside as like a radial stratified flow.