Measurement of pseudoturbulence intensity in monodispersed bubbly liquids for 10<Re<500

Experiments were performed to measure the velocities of both phases in a monodispersed bubbly flow in a vertical column. Using water and water-glycerin mixtures, measurements were obtained for a range of Reynolds numbers from 10 to 500. For all cases, the Weber number was below 2. To generate a uniform stream of bubbles, an array of identical capillaries was used. To avoid coalescence, a small amount of salt was added to the interstitial fluid, which did not affect the fluid properties significantly. Measurements of the bubble phase velocity were obtained using a dual impedance probe and through high-speed digital video processing. A measurement of the vertical component of the fluctuating liquid velocity was obtained using a flying hotwire technique, which resolved the deficiency of this technique for flows with zero-mean velocity. To the best of our knowledge, this technique has not been used to study bubbly liquids in the past. It was found that for all cases, the bubble velocity decreases as the mean gas volume fraction increases. For vanishing gas volume fraction, the mean bubble velocity was found to be smaller than that calculated for an isolated bubble. The flow agitation, characterized by the velocity variance both in the liquid and the bubble phases, increases with bubble concentration. The bubble velocity variance was found to rapidly increase with gas volume fraction but to reach a nearly constant value for concentrations higher than 1.5% for all cases. The liquid velocity variance was found to increase linearly with gas concentration for large Re; for low Re the increase was at a smaller rate. The variance, normalized with the mean bubble velocity squared, increased as the Reynolds number decreased. Direct comparisons are performed with recent theoretical and computational studies for the same range of conditions.