Two-phase flow measurements at high void fraction by a Venturi meter

Abstract

An experimental investigation of a vertical upward annular two-phase flow across a Venturi flow meter has been performed for the measurement of two-phase flow parameters with reference to the experimental simulation of nuclear accidents, as LOCA, characterized by very high void fraction. The pressure drops between the inlet and throat section and between inlet and outlet (irreversible pressure losses) have been measured and analyzed. The Venturi flow meter is characterized by an inlet diameter of 80 mm and a throat diameter of 40 mm (β = 0.5), with equal convergent and divergent angles (θ = 21°). The instrument has been tested in a test section having an internal diameter (Di) of 80 mm and a total length (L) of about 4 m, with air–water two-phase flow at ambient pressure. The air superficial velocity ranged between 14 and 18 m/s while the water superficial velocity ranged between 0.0008 and 0.005 m/s, so that the flow pattern was annular and the corresponding flow quality ranged between 0.78 and 0.96. The dependence of the pressure drops on the phases velocities has been analyzed and modeled as a function of the superficial velocities of the phases, and the mass flow rate of the two phases has been derived from the present test data when the annular flow pattern does not change in a significant way. The flow quality can be evaluated with an accuracy of 5% and the mass flow rate of air and water can be estimated with an accuracy better than 2% and 30% respectively.