Void fraction measurement using an imaging and phase isolation method in horizontal annular flow
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....
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Veröffentlicht in: | Measurement science & technology 2019-02, Vol.30 (2), p.25301 |
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Sprache: | eng |
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Zusammenfassung: | 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(Usg = 4.35 m s−1-39.12 m s−1, Usl = 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. |
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ISSN: | 0957-0233 1361-6501 |
DOI: | 10.1088/1361-6501/aaf8ec |