Pressure drop has been measured for upward single- and two-phase gas–liquid flow across an orifice in a vertical pipe. A conductance probe provided average void fraction upstream of the orifice. Six orifices with different apertures/thickness were mounted in turn in a 34 mm diameter transparent acrylic resin pipe. Gas and liquid superficial velocities of 0–4 m/s and 0.3–0.91 m/s, respectively, were studied. For single-phase flow, pressure drop, expressed as an Euler number, was seen to be independent of Reynolds number in turbulent region. The Euler number increased with decreasing the open area ratio/orifice thickness and increasing velocity. The pressure drop was well predicted by the correlation of Idel'chik et al. (1994, Handbook of Hydraulic Resistances, 3rd ed., CRC Press, Boca, Raton, FL.), which uses a form of Euler number. The corresponding two-phase flow pressure drop depends on the flow pattern. Decreasing open area ratio/orifice thickness increased the pressure drop. For a given liquid superficial velocity, the pressure drop increases with gas superficial velocity except for low open area ratio where this increase is followed by a decrease beyond a critical superficial gas velocity for the high liquid superficial velocities. Relevant correlations were assessed using the present data via a systematic statistical approach. The two-phase multiplier equations of Morris (1985, “Two-Phase Pressure Drop Across Valves and Orifice Plates,” European Two Phase Flow Group Meeting, Marchwood Engineering Laboratories, Southampton, UK.) and Simpson et al. (1983, “Two-Phase Flow Through Gate Valves and Orifice Plates,” International Conference on Physical Modelling of Multiphase Flow, Coventry, UK.) are the most reliable ones.

An accurate two-phase flow rate measurement is essential in many applications and industries such as; oil/gas, chemical, pipeline transportation and nuclear industry. This paper presents the findings obtained from two-phase flow rate measurements using Venturi meters coupled with conductance probe sensors. The measurement system and presented methodology can be used to directly and continuously measure the mass flow rate of gas-liquid flows without any need for using a separator. Most of the available data in literature on mass flow rate using Venturis in gas-liquid two phase flows are limited/valid to a certain flow regime. However, the experimental data presented in this paper covered a wide range of flows (i.e. bubbly, slug and churn flows). Three Venturis with different diameter ratios, β = 0.40, β = 0.55 and β = 0.75 have been employed using an air-water vertical test section. The effect of the Venturi’s geometry on the flow behaviour was also evaluated. The average void fraction and void fraction time series have been measured along the test section by nine different conductance probe sensors covering the convergent, throat and divergent sections. In addition, the two-phase pressure drop across the Venturi was measured. Moreover, a new correlation for the gas-liquid slip ratio was proposed in this paper, which is necessary for calculating the two-phase mass flow rate. The proposed slip ratio correlation showed more accuracy than the ones available in literature. It was found that the correlation proposed by Chisholm to predict the two-phase mass flow rate in Venturis with a diameter ratio, β = 0.55, shows the best accuracy among others such as; Murdock, Lin, James and Zhang correlations.

An experimental investigation of the pressure drops measurements in a Venturi placed in a vertical pipe is achieved. Venturis with diameter ratios equal to 0.4, 0.55, and 0.75 were employed. Differential pressure transducers were used to measure the pressure drop between the Venturi inlet and the throat sections. The void fraction was measured upstream the Venturi using a conductance probe technique. Air and water superficial velocities ranges were chosen to cover single-phase flow and bubbly, slug, and churn flow regimes. The single-phase pressure drop increases with the liquid superficial velocity. The Venturi pressure drop coefficient increases with decreasing the Venturi area ratio. The discharge coefficient increases slightly with this ratio and approaches a value of unity at high Reynolds number. The two-phase flow pressure drop and the multiplier coefficient increase with the gas superficial velocity and with decreasing the area ratio. Dimensionless pressure drop decreases with increasing the liquid to gas superficial velocity ratio and approaches an asymptotic value at high ratio (greater than 10). This value matches the single-phase flow dimensionless pressure drop value at high Reynolds number. The Venturi with area ratio equal to 0.55 was shown to correlate well the two-phase multiplier and the liquid holdup.