Enhancement of heat transport across a fluid layer is of fundamental interest as well as great technological importance. For decades, Rayleigh-Bénard convection has been a paradigm for the study of convective heat transport, and how to improve its overall heat-transfer efficiency is still an open question. Here, we report an experimental and numerical study that reveals a novel mechanism that leads to much enhanced heat transport. When vertical partitions are inserted into a convection cell with thin gaps left open between the partition walls and the cooling/heating plates, it is found that the convective flow becomes self-organized and more coherent, leading to an unprecedented heat-transport enhancement. In particular, our experiments show that with six partition walls inserted, the heat flux can be increased by approximately 30 %. Numerical simulations show a remarkable heat-flux enhancement of up to 2.3 times (with 28 partition walls) that without any partitions.

We report high-precision measurements of the Nusselt number Nu as a function of the Rayleigh number Ra in water-filled rectangular Rayleigh-Bénard convection cells. The horizontal length L and width W of the cells are 50.0 and 15.0 cm, respectively, and the heights H = 49.9, 25.0, 12.5, 6.9, 3.5, and 2.4 cm, corresponding to the aspect ratios (Γ x ≡ L/H, Γ y ≡ W/H) ). The measurements were carried out over the Rayleigh number range 6 × 10 5 Ra 10 11 and the Prandtl number range 5.2 Pr 7. Our results show that for rectangular geometry turbulent heat transport is independent of the cells' aspect ratios and hence is insensitive to the nature and structures of the large-scale mean flows of the system. This is slightly different from the observations in cylindrical cells where Nu is found to be in general a decreasing function of Γ , at least for Γ = 1 and larger. Such a difference is probably a manifestation of the finite plate conductivity effect. Corrections for the influence of the finite conductivity of the top and bottom plates are made to obtain the estimates of Nu ∞ for plates with perfect conductivity. The local scaling exponents β l of Nu ∞ ∼ Ra β l are calculated and found to increase from 0.243 at Ra 9 × 10 5 to 0.327 at Ra 4 × 10 10 .

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