研究目的
To develop a new imaging method based on phase isolation technology for accurate measurement of void fraction in horizontal annular flow, addressing the challenges of complex flow patterns and phase interface instability.
研究成果
The developed imaging method with phase isolation effectively measures void fraction in horizontal annular flow, providing consistent results with natural annular flow at low gas volume fractions (errors <4%). The core-annular flow offers a smoother interface, enabling accurate parameter measurement. Centrifugal effects from phase isolation eliminate gravity-induced asymmetry in film thickness. Future work could optimize the method for other flow patterns and conditions.
研究不足
The method has a minimum detectable liquid film thickness of 39.5 μm due to total reflection effects in the circular tube. Uncertainty in void fraction measurement is estimated at 25.6%, influenced by image resolution and instrument precision. The phase isolation process may slightly reduce void fraction at high gas volume fractions compared to natural annular flow. Optical disturbances and long-term measurement stability (e.g., CCD sensor heating) could affect accuracy.
1：Experimental Design and Method Selection:
The study employs a phase isolation device to rectify gas-liquid two-phase flow into a core-annular flow with a clear interface, facilitating imaging-based measurement. Backlight collimated illumination and a high-resolution CCD camera are used for image capture, with detailed analysis of beam path and morphological characteristics.
2：Sample Selection and Data Sources:
Air and tap water are used as working fluids. Void fraction ranges from 0.736 to 0.978, with superficial gas velocities from 4.35 m/s to 39.12 m/s and superficial liquid velocities from 0.016 m/s to 0.504 m/s. Approximately 800 raw images are processed per condition.
3：736 to 978, with superficial gas velocities from 35 m/s to 12 m/s and superficial liquid velocities from 016 m/s to 504 m/s. Approximately 800 raw images are processed per condition.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Includes a flow loop with quartz glass test tube, phase isolation device (3D printed with corrosion-resistant resin), collimated backlight source, high-resolution CCD camera (MV-CA030-10GM), telecentric lens, pin gauges for calibration, electronic scale, vernier caliper, thermal mass flowmeter (Endress+Hauser), electromagnetic flowmeter (YOKOGAWA), and MATLAB software for image processing.
4：Experimental Procedures and Operational Workflow:
The flow loop mixes air and water, passes through the phase isolation device to form core-annular flow, and images are captured using the optical system. Calibration experiments with pin gauges and PLIF method are conducted to establish edge detection criteria. Image processing involves cropping, binarization, morphological filtering, edge recognition, correction, and calculation of void fraction and film thickness.
5：Data Analysis Methods:
Data is analyzed using MATLAB for image processing, including algorithms for binarization (OTSU thresholding), morphological operations, edge correction based on calibration curves, and statistical analysis of void fraction and uncertainties.
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