Void fraction measurement using NIR technology for horizontal wet-gas annular flow

It is difficult to measure the void fraction of wet-gas annular flow due to the low water holdup. The near infrared (NIR) spectrum has characteristic absorption band for water, which can increase the sensibility to water in the void fraction measurement of wet-gas annular flow. This paper presents a void fraction measurement method based on NIR spectrum. A non-invasive sensor was designed in this paper. According to characteristic O-H absorption band of H2O, 970 nm was selected as the emission wavelength of NIR light source. Considering absorption of liquid film, scattering of entrained droplets and interface reflection of two-phase, a void fraction model base NIR transmittance was constructed and further simplified. Utilizing the simplified model and designed sensor, void fraction measurements had been obtained for 48 horizontal wet-gas annular flow conditions in the pipeline pressure of 0.4 MPa and 0.5 MPa. Laboratory results indicate that the relative deviations of the measurement model range from −5.53% to 7.34%, but the 93.75% of relative deviations are within ±5%.