Bubble size effect on low liquid input drift–flux parameters

Abstract

We investigated the effect of bubble size on the drift–flux parameters at low liquid flow conditions by measuring the radial profiles of void fraction and phase velocities in a vertical bubbly pipe flow of diameter D p=72 mm and height H=18 m . To study the effect of the bubble size we used two different types of bubble inlets. We measured the local bubble fraction and velocity U g by using single and four-point-optical fibre probes, and we used Laser Doppler Anemometry to determine the liquid velocity U l . The distribution parameter C 0 and the weighted mean drift velocity | U drift| were directly computed from the local measurements at a height h=5 m on our experimental set-up. Both parameters were influenced by the bubble size. Provided no liquid flow reversal occurred at the near wall region, the distribution parameter reached a below unity minimum plateau value of C 0=0.95 for wall peaking void fraction profiles. At low liquid input conditions both the liquid input and bubble size had an influence on the distribution parameter. Extreme values such as C 0>2 were measured. From these measurements we developed models for the drift–flux parameters to take into account the effect of bubble size and input-flow conditions for our intermediate pipe diameter value. These models were tested and validated with separately collected experimental data.