Light extinction technique for void fraction measurements in bubbly flow

The analysis of the scattering induced by a dispersion of gas bubbles in a liquid medium on a collimated, monochromatic light beam, traversing the two -phase flow, allows for the direct measurement of the 2-D distribution of t he line-average of the interfacial area density. The 2-D distribution of th e line-average of the void fraction is deduced from that of the interfacial area density through an image processing algorithm. To demonstrate the tec hnique, experiments are performed in a pool of water injected with air and illuminated with a CW argon ion laser. Since the bubble diameters range fro m a fraction of a millimeter to a few millimeters, the scattering processes are entirely in the Mie range. The limits of applicability of the techniqu e and the measurement uncertainty are discussed. The results compare favora bly with level-swell based measurements used as a reference.