Two-Phase Flow through Corrugated U-Tube

New measurements of the frictional pressure drop of air—water two-phase flow in a flexible corrugated U-tube have been carried out. Experiments were performed under the following conditions of two-phase parameters: mass flux of 300—800 kg/m² s, gas quality of 1—60 per cent, and system pressure of 3—7 bar. The inner diameter of the U-tubes tested was 40 mm, with a ratio of curvature radius to inner diameter varying from 3 to 7.5. The results demonstrate that the two-phase flow resistance, energy dissipation, friction losses, and interaction of the two phases in flexible corrugated U-tubes are perceptible about two to five times greater than those in smooth U-tubes. Hence, the two-phase friction factor of such tubes increases from 0.65 to 1.4, depending on the influencing flow and geometrical parameters. The available correlations in the open literature present a similar trend and behaviour. However, they predict the data presented poorly because of the complex geometry of the flexible corrugated U-tube. Based on the energy balance and the presented experimental results, a new model has been developed to calculate the frictional two-phase pressure drop and hence the friction factor of the flexible U-tube. The model includes the relevant primary parameter, fits the experimental data well, and is sufficiently accurate for engineering purposes. The standard deviation of the data is less than 7 per cent. The reported results enable a practical design with standard products and optimization of the geometry of the flexible corrugated U-tube for specific conditions.