Pressure drop, void fraction and shear stress measurements in an adiabatic two-phase flow in a coiled tube

Abstract

Some tests have been carried out on a helically coiled tube (inside diameter, 19.8 mm; coil diameter, 1.17 m; helix angle, 7°27′) with a water-SF6 adiabatic mixture up-flow. Local pressure, wall shear stress and void fraction distributions as well as frictional pressure drop have been measured for total mass flow rates from 500 to 3000 kg s −1 m −2 gas mass fractions from 0.04 to 0.6. The working pressure from 1 to 13.5 bar allows a density ratio from 10 to 41. An analysis of the results was made to identify flow patterns and to propose some predictive relations. As reported in previous work on helically coiled tubes, the frictional pressure drop results obtained for single water flow are higher than those observed in straight tubes. As far as the two-phase flow pressure drop is concerned, the experimental values are quite different from those calculated with the Lockhart-Martinelli correlation and fairly good agreement is obtained with the Chisholm correlation. The mean cross-section void fraction results are overestimated by predictions made with 20 commonly used correlations; among these, the Stomma correlation gives the best agreement. The flow pattern seems to be bubbly or slug flow but no separated flow was observed. The shear stress and pressure distributions show a transition in single-phase flow for a Reynolds number between 26 000 and 50 000. Local parameters are of great interest to improve physical laws needed for numerical three-dimensional two-phase codes.