Effects of Prandtl number in quasi-two-dimensional Rayleigh-Bénard convection

We report an experimental study of the Prandtl-number effects in quasi-two-dimensional (quasi-2-D) Rayleigh-Bénard convection. The experiments were conducted in four rectangular convection cells over the Prandtl-number range of and over the Rayleigh-number range of. Flow visualization reveals that, as increases from 11.7 to 145.7, thermal plumes pass through the central region much less frequently and their self-organized large-scale motion is more confined along the periphery of the convection cell. The large-scale flow is found to break down for higher, resulting in a regime transition in the Reynolds number. For the range with a large-scale flow of system size, the number, Nusselt number and local temperature fluctuations were investigated systematically. It is found that scales as in the present geometry, which suggests that it is in line with the behaviour in the 2-D configuration. On the other hand, the measured relation tends to be compatible with the finding in a three-dimensional (3-D) system. For the temperature fluctuations in the cell centre and near the sidewall, they exhibit distinct-dependent scalings that could not be accounted for with existing theories, but their dependences for are in agreement with the predictions by Grossmann & Lohse (Phys. Fluids, vol. 16, 2004, pp. 4462-4472). These results enrich our understanding of quasi-2-D thermal convection, and its similarities and differences compared to 2-D and 3-D systems.