An experimental study of single-phase and two-phase flow pressure drop in annular helicoidal pipes

In this study, experimental investigations were conducted for single-phase and air/water two-phase flow in annular helicoidal pipes with vertical and horizontal orientations. Three test sections were investigated. The outer diameters of the inner tube were 12.7 mm, 9.525 mm, and 6.35 mm, and the inner diameters of the outer tube were 21.18 mm, 15.748 mm, and 10.21 mm, respectively. The experiments were performed for superficial water Reynolds numbers in the range of 210 to 23,000 and superficial air Reynolds numbers in the range of 30 to 30,000. The effects of coil geometry and the flow rates of air and water on single-phase and two-phase flow pressure drop were experimentally investigated for annular helicoidal pipes. The data were correlated as the relationship of the pressure drop multipliers versus Lockhart-Martinelli parameter for the two-phase flow. The average void fraction was also measured in the experiments by means of the quick acting valve method. Unlike two-phase flow in straight pipe, the pressure drop multipliers of two-phase flow in annular helicoidal pipes have been found to be dependent on the flow rate in addition to the Lockhart-Martinelli parameter for the annular helicoidal pipe with large diameter. Thus, the Lockhart-Martinelli correlation is not valid in the prediction. Correlations for two-phase flow in horizontal and vertical annular helicoidal pipes have been established for both single-phase and two-phase flow based on the present experimental data. (C) 1997 by Elsevier Science Inc.