ELECTRICAL CAPACITANCE PROBE CHARACTERISATION FOR VERTICAL ANNULAR AIR-WATER FLOW INVESTIGATION

The experimental analysis and the qualification of an Electrical Capacitance Probe (ECP), for the void fraction measurement, is presented. The ECP, developed at the SIET, is used to investigate a vertical air/water flow, characterized by high void fraction. Mass flow rates have been analyzed between 0.094 and 0.15 kg/s for air and between 0.002 and 0.021 kg/s for water, corresponding to void fraction up to 90 % and to annular and wavy-annular flow patterns. The ECP signals are used to obtain the geometrical shape functions (signals as a function of electrode distances) in single and two phase flows. The dependence of the signal by the void fraction is derived and other flow characteristics as the liquid film thickness and the phase velocities are evaluated by means of rather simple models. The experimental analysis allows to characterize the ECP, showing the advantages and the drawbacks of this technique for the two-phase flow characterization at high void fraction, and it provides a reliable tool for the selection of the instrumentation for the SIET Company SPES3 facility