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In this work we study the heat transport in inhomogeneous bubbly flow. Theexperiments were performed in a rectangular bubble column heated from one sidewall and cooled from the other, with millimetric bubbles introduced through onehalf of the injection section (close to the hot wall or close to the coldwall). We characterise the global heat transport while varying two parameters:the gas volume fraction $\alpha = 0.4\% - 5.1 \%$, and the Rayleigh number$Ra_H=4\times10^9-2.2\times10^{10}$. As captured by imaging and characterisedusing Laser Doppler Anemometry (LDA), different flow regimes occur withincreasing gas flow rates. In the generated inhomogeneous bubbly flow there arethree main contributions to the mixing: (\textit{i}) transport by the buoyancydriven recirculation, (\textit{ii}) bubble induced turbulence (BIT) and(\textit{iii}) shear-induced turbulence (SIT). The strength of thesecontributions and their interplay depends on the gas volume fraction which isreflected in the measured heat transport enhancement. We compare our resultswith the findings for heat transport in homogeneous bubbly flow fromGvozdi{\'c} \emph{et al.} (2018). We find that for the lower gas volumefractions ($\alpha<4\%$), inhomogeneous bubbly injection results in better heattransport due to induced large-scale circulation. In contrast, for$\alpha>4\%$, when the contribution of SIT becomes stronger, but so does thecompetition between all three contributions, the homogeneous injection is moreefficient.

Experimental investigation of heat transport in inhomogeneous bubbly flow