Experimental and numerical study of the hydrodynamics and heat transfer in a bubbly flow downstream of the axisymmetric sudden expansion

The results of experimental and numerical simulations of the flow and heat transfer in the polydispersed bubbly flows in a pipe with sudden expansion are presented. Mathematical model is based on the use of the Eulerian approach considering the effect of the bubbles on the mean characteristics and turbulence of the carrier phase. The turbulence of the carrier fluid phase is predicted using the model of Reynolds stress transport. The structure of the mean and fluctuating two-phase bubbly flow at small volumetric gas flow rate ratio, $\beta\leqslant 10\%$, is qualitatively similar to that of a single-phase fluid flow. The small bubbles are observed in almost the entire pipe section, whereas the large ones mostly move through the flow core and shear mixing layer. Addition of the air bubbles results in a significant increase in the heat transfer rate (up to $300\%$) in the flow relaxation region for the moderate Reynolds numbers. This effect enhances with an increase in the gas volumetric flow rate ratio. The largest heat transfer enhancement is observed in the flow relaxation zone downstream of the reattachment point.