Experimental investigation of heat transport in inhomogeneous bubbly flow

In this study the heat transport in inhomogeneous bubbly flow is experimentally investigated. The experiments were performed in a rectangular bubble column heated from one side wall and cooled from the other, with millimetric bubbles introduced through one half of the injection section (close to the hot wall or the cold wall). We characterise the global heat transport while varying two parameters: the gas volume fraction α =0.4%−5.1%, and the Rayleigh number Ra_H =4×10^9 − 2.2×10^10. Different flow regimes occur with increasing gas flow rates. In the generated inhomogeneous bubbly flow there are three main contributions to the mixing: (i) transport by the buoyancy driven recirculation, (ii) bubble induced turbulence and (iii) shear-induced turbulence (SIT). The strength of these contributions and their interplay depends on α which is reflected in the measured heat transport enhancement. Comparing with the case of homogeneous bubbly flow, for α<4%, inhomogeneous bubbly injection results in better heat transport due to induced large-scale circulation. In contrast, for α>4%, when the contribution of SIT becomes stronger, but so does the competition between all three contributions, the homogeneous injection is more efficient.