VELOCITY PROFILE MEASUREMENTS IN BUBBLY FLOW USING MULTI-WAVE ULTRASOUND TECHNIQUE

Abstract

Velocity profile measurements in bubbly flows have been performed by using the ultrasonic velocity profile technique, which can measure velocity distributions along a measuring line. To obtain the liquid and gas velocity distributions simultaneously, a new technique for separating liquid and gas velocity data is developed. The technique employs a unique ultrasonic transducer (TDX) referred to as a multi-wave transducer. The multi-wave TDX consists of two kinds of ultrasonic piezoelectric elements that are concentrically set and have different resonant frequencies. The central element of 3 mm diameter has a basic frequency of 8 MHz for liquid-phase measurements, and the outer element has a basic frequency of 2 MHz for bubble-phase measurements in two-phase bubbly flows. The multi-wave TDX can emit the two ultrasonic frequencies independently. First, the multi-wave TDX is used together with an ultrasonic velocity profiler (UVP) based on the ultrasonic pulse repetition method. The effects due to volume, liquid velocity, and bubble rising velocity measurements are obtained by the UVP in two-phase bubbly flows. However, the velocity distribution of bubbles measured by the UVP includes errors induced by tracer particles suspended in the liquid. The ultrasonic velocity profile technique requires tracer particles as ultrasonic reflectors. Then to improve the accuracy of the bubble rising velocity distribution, the ultrasound time domain correlation (UTDC) method is applied. Comparing the intensities of echo signals from 2 MHz and 8 MHz ultrasounds, bubble and liquid velocity distributions were obtained. The velocity distributions measured by the UTDC are in good agreement with those measured by the UVP. This technique can be utilized for many industrial applications.

Keywords:

• Bubbly flow
• Cross-correlation
• Two-phase flow
• Ultrasound
• UTDC
• UVP
• Velocity profile measurement

Acknowledgment

The authors gratefully acknowledge the support work given by Dr. Gentarao Yamanaka.