Modeling of the flow patterns and heat transfer in a turbulent bubbly polydispersed flow downstream of a sudden pipe expansion

Abstract

Results from the numerical simulation of the structure and heat transfer in polydispersed bubbly turbulent flow, downstream of a sudden pipe expansion, are presented. The structure of the mean and fluctuating two-phase bubbly flow at small values of volumetric gas flow rate ratio, β⩽10%, is qualitatively similar to that of a single-phase fluid flow. Small bubbles are present in almost the entire pipe section, whereas large ones mostly move just through the flow core and shear mixing layer. An increase in the dispersed phase size causes the production of extra turbulence in the liquid phase (up to 30%). The addition of air bubbles results in a significant reduction in the length of the separation region (up to 50%) and a significant increase in the heat transfer rate (up to 100%). These effects are augmented by increasing bubble size and concentration.