Confinement-Induced Enhancements of Heat-Transfer Efficiency and Thermal Plume Coherency in Turbulent Thermal Convection
Using the classical Rayleigh-Bénard convection model system, we show that a simple geometrical confinement can greatly increase the convective heat transfer efficiency, the Nusselt number Nu. It is found that when the aspect ratio (lateral dimension over height) of the system is decreased from 0.6 to 0.1, Nu is increased by 17% for the parameter range explored. Detailed experimental and numerical studies show that this enhancement is brought about by the changes in the dynamics and morphology of the thermal plumes in the boundary layers and in the large-scale flow structures in the bulk. It is found that the confined geometry produces more coherent and energetic hot and cold plume clusters that go up and down in random locations, resulting in more uniform and thinner thermal boundary layers. The study demonstrates how changes in turbulent bulk flow can influence the boundary layer dynamics. We expect the findings of this study to have potential applications in passive heat management.