Simultaneous measurement of local liquid velocity and void fraction in bubbly flows using a laser doppler velocimeter

A new technique using a gas laser is developed to measure the local values of void fraction, liquid velocity and its turbulence intensity in two-phase dispersed flows, especially in bubbly flow. A laser beam is modulated in frequency and attenuated in light intensity during it passes through the bubbly flow. The modulation rate in frequency gives the local liquid velocity and the attenuation rate in light intensity gives the line void fraction. This study was carried out in the following steps: (1). The developed laser Doppler velocimeter was confirmed to give accurately the local liquid velocity and its turbulence intensity in bubbly flows. (2). An equation giving the relation between the beam transmission rate and the void fraction was deduced theoretically and confirmed experimentally on the assumption that the bubble size distribution is given. (3). Combining the above techniques, the profiles of above-mentioned parameters across ducts were simultaneously measured in vertical air-water bubbly flows, which characterized the flow pattern of the vertical bubbly flow. (auth.)