Measuring void fraction in vertical air–water bubbly flow using echo intensity and visualization techniques

In this study, we measured void fractions in vertical air–water bubbly flow using echo intensity and visualization techniques. To check the reliability of the echo intensity technique, void fractions obtained from the visualization technique was used. For echo intensity technique, ultrasonic wave amplitudes were acquired at different gas flow rates, and the amplitudes varied with gas flow rates. The averaged value of the amplitude kept decreasing with increasing gas flow rates. Images of bubbly flow were captured by a high-speed camera to evaluate void fractions. The images were processing to obtain area-averaged void fractions, then averaged over time to obtain time-averaged void fractions. The amplitudes obtained from the echo intensity and void fraction obtained from visualization can be correlated in the form of an exponential function: as the amplitude increases, the void fraction exponentially decreases.