Bubble velocity, diameter, and void fraction measurements in a multiphase flow using fiber optic reflectometer

Area of Science:

• Fluid Dynamics
• Optical Measurement Techniques
• Multiphase Flow

Background:

• Traditional probes for multiphase flow measurement face limitations like blinding and crawling.
• Accurate characterization of bubble dynamics (velocity, diameter, void fraction) is crucial for understanding multiphase systems.

Purpose of the Study:

• To investigate the feasibility of a single-probe fiber optic reflectometer (FOR) for measuring bubble velocity, diameter, and void fraction.
• To evaluate the FOR technique's accuracy and compare it with high-speed camera measurements.

Main Methods:

• Utilizing a fiber optic reflectometer with a single fiber probe based on signal interference.
• Analyzing reflected signals from bubble surfaces and fiber tips to determine bubble properties.
• Implementing corrections for void fraction measurements and analyzing coherent signals for velocity and chord length.

Main Results:

• The FOR technique accurately measures bubble velocity, preventing issues associated with dual-tip probes.
• Bubble diameters are directly obtained from signals containing velocity information, representing true diameters or minor axes.
• Observed deceleration of bubbles near the probe provides insights into probe-bubble interactions.

Conclusions:

• The single-probe FOR technique offers a feasible and accurate method for multiphase flow bubble characterization.
• This technique overcomes limitations of traditional probes, enabling reliable measurement of bubble velocity, diameter, and void fraction.
• FOR measurements show good agreement with high-speed camera data, validating its effectiveness.