Measurement of two-phase velocities in bubble flows using laser Doppler velocimetry

The measurement of two-phase velocities in bubble flows using laser Doppler velocimetry (LDV) is studied. The key to the problem is to differentiate the LDV signals from bubbles and tracers, based on which the two-phase velocities can be characterized. In this study, two experiments are carried out. Firstly, the bubble-chain experiment is performed to investigate the optical response of bubble surface and the corresponding LDV signal. The optical response shows that the light received by the LDV detector is dominated by the reflection component, which is similar to specular reflection to some extent. There are three typical patterns of signals of large bubbles passing through the measurement volume, all of which are with high amplitude and saturated. Then, the upward-flow experiment is conducted to study the statistical characteristics of large bubbles as well as micro tracers and micro bubbles. The results show that the amplitude of signal of millimeter bubbles is about an order of magnitude larger than that of tracers or micro bubbles. Based on this significant difference of the amplitude, we propose a phase discrimination method to distinguish two-phase signals. The capability of the proposed method is tested in a complex bubble flow, and its reliability is verified by bubble tracking velocimetry (BTV) technology.

Automated summary

The measurement of two-phase velocities in bubble flows using laser Doppler velocimetry (LDV) is investigated. The study proposes a phase discrimination method based on the significant difference in signal amplitude between large bubbles and tracers/micro bubbles. The method is tested in a complex bubble flow and verified by bubble tracking velocimetry (BTV) technology.