Radio-frequency probe for bubble size and velocity measurements.

Area of Science:

• Fluid Dynamics
• Two-Phase Flow Measurement
• Instrumentation

Background:

• Gas-liquid two-phase flows are prevalent in various industrial processes.
• Accurate local measurements of void fraction and interface velocity are crucial for understanding and modeling these flows.
• Existing measurement techniques often have limitations in spatial resolution or applicability.

Purpose of the Study:

• To develop and validate a radio frequency (RF) probe for local void fraction and interface velocity measurements.
• To investigate the probe's response characteristics in controlled single-bubble experiments.
• To assess the probe's capability in determining bubble length and velocity.

Main Methods:

• Development of a novel RF probe with a sensitive tip length (2.75-3 mm).
• Controlled single-bubble experiments to analyze probe response.
• Independent measurement of bubble length and velocity using a dual light source and detector system.
• Analysis of RF probe output in relation to bubble characteristics and surrounding medium properties (dielectric constant, carrier frequency).

Main Results:

• The RF probe's response is dependent on the dielectric constant of the surrounding medium and the carrier signal frequency.
• The probe successfully provided sufficient information to determine bubble length (< 1 cm) and average bubble approach velocity (< 160 cm/s).
• Measurements obtained using the RF probe showed good agreement (+/-10%) with an independent optical method.

Conclusions:

• The developed RF probe is a viable tool for local void fraction and interface velocity measurements in gas-liquid two-phase flows.
• The probe's design and operational parameters allow for accurate determination of bubble dynamics.
• This technology offers a promising advancement for flow characterization in relevant industrial applications.