Experimental and numerical study of heat transfer enhancement in a turbulent bubbly flow in a sudden pipe expansion

Results of an experimental and numerical simulation of heat transfer in an upward bubbly flowin a sudden pipe expansion are presented. The experimental study of the heat transfer has been performed using infrared thermography. The measurements of the bubble size before the pipe expansion area were carried out by the shadow photographymethod. The numerical simulation of the bubbly flow structure in the sudden pipe expansion has been performed using the Eulerian approach in the presence of heat transfer between the two-phase flow and the wall surface. The model uses the system of Reynolds-averaged Navier–Stokes equations in an axisymmetric approximation, written with consideration of the back effect of bubbles on the averaged and pulsation characteristics of the flow. It has been experimentally and numerically shown that addition of air bubbles causes a significant (up to 3-fold) increase in the heat transfer intensity, these effects growing with bubble concentration. The largest rise in the heat transfer has been revealed in the region of flow relaxation downstream of the flow attachment point.