Investigation on Venturi and nozzle devices as volume flow meters for two-phase, water-very-viscous oil flows

Evaluation of total volume flow rate for multiphase flows is still a great challenge in spite of the numerous efforts documented in the last fifty years. This works presents the results of an experimental characterization of two-phase, water-very viscous oil flows through Venturi and Nozzles flow meters. The fluids under consideration are tap water (density = 998 kg/m^3, dynamic viscosity = 1.026×10-3 Pa∙s at 20°C) and Milpar 220 oil (density = 910 kg/m^3, dynamic viscosity = 0.9 Pa∙s at 20°C) flowing in standard devices with inlet and throat diameters of 40 and 30 mm, respectively. The investigated range of inlet superficial velocities is 0.45 ≤ Jw ≤ 1.33 [m/s] for water, and 0.25 ≤ Jo ≤ 0.72 [m/s] for oil, including the range between annular and dispersed flow patterns. Experiments have shown that the two-phase mixture through the variable area devices behaves like a homogeneous flow, thus enabling the measurement of the total volume flow rate with average deviations lower than 5%. Furthermore, the detection of the pressure gradient upstream of the device can be used with a suitably developed two-fluid model, in order to determine the water and oil volume fractions, and hence the volume flow rates of the single phases.