Void fraction measurement using an imaging and phase isolation method in horizontal annular flow. (17th January 2019)

• Record Type: Journal Article
• Authors: Niu, Pengman; Wang, Dong; Yang, Yang; Wei, Pengkai; Pan, Yanzhi; Wang, Shuai; Yu, Xingang
• Is Part Of: Measurement science & technology. Volume 30:Number 2(2019:Feb.)
• Publication Date: 2019-01-17
• Subjects: phase isolation -- void fraction -- annular flow -- core-annular flow -- imaging; Physical measurements -- Periodicals; Scientific apparatus and instruments -- Periodicals; Equipment and Supplies -- Periodicals; Science -- instrumentation -- Periodicals; Technology -- instrumentation -- Periodicals; Mesures physiques -- Périodiques; Physical measurements; Scientific apparatus and instruments; Periodicals; 502.87
• DOI: 10.1088/1361-6501/aaf8ec
• Languages: English
• ISSNs: 0957-0233

Abstract

Abstract: A new imaging method was proposed to measure the void fraction of annular flow based on phase isolation technology in a horizontal circular tube. As the gas–liquid mixture passes through the phase isolation device, which is arranged upstream, a strong swirl flow is created due to centrifugal effect. The liquid phase is pushed to the tube wall and forms a uniform liquid film, while the gas phase is concentrated to the tube center and forms a gas core. This rectified core-annular flow has a more smooth and clear phase interface than that of natural annular flow, which makes the accurate measurement of some inherent flow parameters of gas–liquid two-phase flow possible and much easier to perform. A backlight-collimated illumination and high-resolution CCD camera were employed to capture the gas core and liquid film. A calibration experiment was conducted to acquire an accurate edge detection criterion for recognition of the phase interface. The morphological image characteristics of the core-annular flow and the beam path diagram of imaging procedure were analyzed in detail and a corresponding image processing algorithm was developed. The working fluids were air and water and the ranges of void fraction covered in the sexperiment were 0.736–0.978( U sg = 4.35 m s −1 –39.12 m s −1, U sl = 0.016 m s −1 –0.504 m s −1 ). For each experiment condition, about 800 raw images were processed to obtain an average result. Comparisons to a representative model of void fraction of natural annular flow showed that the void fraction of the core-annular flow rectified by the phase isolation device remains well consistent with that of natural annular flow in the range of low-gas volume fraction, while the void fraction of core-annular flow becomes a little lower than that of natural annular flow as the gas volume becomes very high.