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.