Richard J.A.M. Stevens

Professor at the University of Twente

Wind energy · Turbulence · Environmental flows

Publication 4 · Thermal convection

Optimal Prandtl number for heat transfer in rotating Rayleigh-Bénard convection

R.J.A.M. Stevens, H.J.H. Clercx, D. Lohse, New J. Phys. 12, 075005 (2010).

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Main finding

Heat transport has an intermediate-Prandtl-number optimum at fixed rotation in the Ra = 10^8 simulations. The two limiting Ekman-pumping explanations are supported but not uniquely isolated or universally scaled.

Heat transport enhancement against Prandtl number at three rotation rates
How to read the figure. Nusselt number under rotation, normalised by its non-rotating value, against the Prandtl number at three Rossby numbers. Each curve peaks at intermediate Prandtl number, reaching about 1.3 at the strongest rotation shown - the roughly 30% enhancement the paper reports at Ra = 10^8 and Pr = 20. Neither very low nor very high Prandtl number is optimal. The two-limit Ekman pumping explanation fits this well but is not the only account it admits. Open the full-resolution figure. Figure 2. R.J.A.M. Stevens et al. (2010). No separate licence is stated here; consult the original publication and credited source before reuse.

Why this matters

Rotation helps heat transport most at an intermediate fluid-property ratio.

Research context

Earlier parameter maps establish the joint Rayleigh-, Prandtl-, and Rossby-number dependence and the rotation-induced transition. This study isolates the intermediate-Prandtl optimum at fixed rotation; later aspect-ratio and flow-state work tests the geometric and regime limits of the two-failure-mode Ekman-pumping explanation.

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