Two-phase flow behaviour in a smooth hairpin tube: analysis of the disturbance using capacitive measurements

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

Two-phase refrigerant flow up-and downstream of a sharp return bend is studied. The capacitance of the flow is logged at several locations up-and downstream of the return bend. Analysis of the capacitance time traces is performed to evaluate the presence of a flow disturbance due to the bend. A vertically oriented bend is studied with an inner diameter of 8 mm and a radius of 11 mm. Smooth straight tubes with an internal diameter of 8 mm are connected to the in- and outlet of the return bend. Upward as well as downward directed flows are studied. The refrigerant R134a is used and the mass flux G and vapour quality x are varied between 200 and 400 kg/m²s and 0-1, respectively. A downstream disturbance up to 21.5D is observed for both up-and downward flow.