Numerical study of the flow and heat transfer of bubbly flows in inclined channels

The effects of bubbles and inclination angle on the flow and heat transfer in a channel are examined by direct numerical simulations (DNS), where every continuum length and time scale are resolved using a front-tracking/finite volume method. Earlier simulations of bubbles in turbulent flows in vertical channels have shown that the presence of the bubbles increases the Nusselt number, compared to flow without bubbles. Here the flow and the enhancement of the heat transfer is described as a function of the angle of inclination of a channel where a constant heat flux is applied at the walls. The bubbles are nearly spherical and the void fraction is 3%. The results show that the temperature difference between the wall where the bubbles are concentrated and the fluid near to that wall is lower when the channel is inclined 30 degrees and 60 degrees than for vertical and horizontal channels, indicating that the heat transfer is more efficient in these cases. (C) 2015 Elsevier Inc. All rights reserved.