  In this work we study the heat transport in inhomogeneous bubbly flow. 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 close to the cold
wall). 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 characterised
using Laser Doppler Anemometry (LDA), different flow regimes occur with
increasing gas flow rates. In the generated inhomogeneous bubbly flow there are
three main contributions to the mixing: (\textit{i}) transport by the buoyancy
driven recirculation, (\textit{ii}) bubble induced turbulence (BIT) and
(\textit{iii}) shear-induced turbulence (SIT). The strength of these
contributions and their interplay depends on the gas volume fraction which is
reflected in the measured heat transport enhancement. We compare our results
with the findings for heat transport in homogeneous bubbly flow from
Gvozdi{\'c} \emph{et al.} (2018). We find that for the lower gas volume
fractions ($\alpha<4\%$), inhomogeneous bubbly injection results in better heat
transport due to induced large-scale circulation. In contrast, for
$\alpha>4\%$, when the contribution of SIT becomes stronger, but so does the
competition between all three contributions, the homogeneous injection is more
efficient.
