Numerical studies of combined free and forced convection through a seven-rod bundle in a circular shell in the horizontal configuration are reported in the paper. Each of the six peripheral circular rods has been modelled by an equivalent curved trapezium. The model has been verified to corroborate experimentally measured transport rate values. Buoyancy induces secondary motions in the transverse direction over the forced axial flow. The secondary velocities reduce the through-flow rate at a given impressed pressure gradient. The friction factor is consequently increased. The change in fRe is perceptible for Cu defined on the rod radius more than approximately 10(3), whereas Nu increases monotonically with Gr.