Experimental and numerical study of downward bubbly flow in a pipe

An experimental and numerical study of the local structure of downward gas–liquid flow in a vertical pipe with 20-mm inner diameter is reported. In the experiment, the electrodiffusion technique was used in combination with electrical conductivity measurements. To examine the effect of gas-phase dispersion on flow characteristics, two different gas–liquid mixers were used capable of producing large-diameter (>1 mm) and small-diameter (<1 mm) gas bubbles at identical rate characteristics of the flow. The unified heterogeneous-medium mechanics approach was used to develop, in the Eulerian two-velocity approximation, a calculation model for downward turbulent liquid/air bubble flows. It is shown that, as the volumetric gas flow rate of the mixture at the inlet to the pipe increases, local maxima of continuous phase velocity and bubble concentration emerge in the near-wall zone of the flow, with liquid turbulence suppressed in the wall zone and enhanced in the core of the flow.