An Experimental and Numerical Study of Turbulent Bubbly Flow and Heat Transfer in a Vertical Pipe with Sudden Expansion

The flow patterns and heat transfer in a bubbly flow downstream of a sudden pipe expansion are
experimentally and numerically studied. Measurements of the bubble size were performed using
shadow photography. Fluid phase velocities were measured using a PIV system. The numerical
model was employed the Eulerian approach. The set of RANS equations was used for modelling twophase
bubbly flows. The turbulence of the carrier liquid phase was predicted using the Reynolds
stress model. A significant growth (up to 30%) in wall friction in bubbly flow downstream of pipe with
abrupt expansion is obtained. The mean and fluctuating flow structures in bubbly flow with small
values of β ≤ 10% is similar to that of a one-phase fluid flow. The peak of axial and radial fluctuations
of the carrier fluid (liquid) velocity in the bubbly flow is observed in the shear layer. The addition of air
bubbles resulted in a significant increase in the heat transfer rate (up to 300%). The main
enhancement in heat transfer is observed after the point of flow reattachment. The main enhancement
in heat transfer is observed after the point of flow reattachment. In general, the Nusselt number
distributions in the bubbly flow have qualitatively similar character as that one for single-phase fluid
turbulent separated flows.