Experiments on rapidly rotating convection: The role of the Prandtl number

We measure the efficiency of convective heat transfer (Nusselt number) by turbulent convection in a rapidly rotating Rayleigh-B\'enard convection experiment. Series of measurements are done at two constant values of the Rayleigh number. Using water at different mean temperatures, we change the Prandtl number. Raising the Prandtl number leads to a reduction of the Nusselt number with a significantly stronger dependence than without rotation. We hypothesize that this dependence is caused by the changing ratio of the thermal and kinetic boundary layer thicknesses.