Liquid volumetric flow rate measurement in low gas volume fraction air–water flow using a Venturi tube and a swirler

Venturi flowmeter will over-read the liquid flow rate during measuring low gas volume fraction gas–liquid flow. This study developed a new liquid flow rate measurement method using a Venturi with a swirler. The test fluids are water and air, with gas volume fraction ranging from 0 to 30%. The inlet flow pattern is converted into a gas core-liquid annulus flow by means of a swirler. The subsequent variation characteristics of the Venturi differential pressure (ΔP_o) and swirler differential pressure (ΔP_s) are then investigated. When the gas flow rate is higher and the liquid flow rate is lower, the fluctuations in ΔP_s and ΔP_o are greater. The fluctuation amplitudes of ΔP_s and ΔP_o are less than 0.29 kPa and 0.22 kPa, respectively. For gas–liquid flow with low gas volume fraction, the Reynolds number has a relatively small effect on the swirler flow coefficient but a relatively large effect on the Venturi flow coefficient. Then, the correlations of ΔP_s and ΔP_o with the gas–liquid flow rates that consider the gas–liquid slip and gas–liquid phase interaction are established, respectively. Finally, by combining the correlations, a measurement model of the liquid volumetric flow rate is proposed, with a relative error maintained within ± 3.5%.