Effect of bubble diameter on modification of turbulence in an upward pipe flow

The experimental study in vertical upward driven bubbly pipe flow with void fractions of 0.5% and 1.0% is conducted to elucidate the effect of dispersed bubble size on turbulence modification. Liquid phase velocity is measured by particle image velocimetry with fluorescent tracer particles (PIV/LIF). Bubble size and velocity are estimated from the bubble image observed by a projected shadow image technique. Bubbles strongly accumulate near the wall which accelerate the liquid phase. The high concentration of bubbles in the vicinity of the wall induces a reduction of the fluctuation velocity intensity of the liquid. The effect of bubble-induced turbulence on the global pipe flow structure was investigated by the turbulence energy production and dissipation, estimated from the experiment data, and local vortical structure around the bubbles. (C) 2004 Elsevier Inc. All rights reserved.