Capacitance signal analysis of horizontal two-phase flow in a small diameter tube

Two-phase flow modelling strongly depends on flow patterns. For the purpose of objective flow pattern identification, a capacitance sensor is developed for horizontal two-phase flow in small diameter tubes. The influences of the electrical properties of water and refrigerants upon the measurements are discussed, as well as the effect of temperature variations. The charge/discharge frequency of the transducer has to be matched with the electrical resistance and capacitance of the fluids.A test rig is constructed and a series of experiments is done with horizontal air–water flow in a 9 mm tube. Experimental results with tap water and demineralised water are compared. The sensor is able to characterise all main flow regimes described in the literature. Differences in sub-regimes were distinguished and described. Time-averaged sensor signal values, combined with the variances and a high frequency contribution factor, are studied to quantify the differences in flow pattern, in comparison to the visual discrimination. These parameters of the sensor signals are suitable for more objective flow regime discrimination.