Prandtl-, Rayleigh-, and Rossby-number dependence of heat transport in   turbulent rotating Rayleigh-Benard convection
  Experimental and numerical data for the heat transfer as a function of the Rayleigh-, Prandtl-, and Rossby numbers in turbulent rotating Rayleigh-Benard convection are presented. For relatively small $Ra ~ 10^8$ and large Pr modest rotation can enhance the heat transfer by up to 30%. At larger Ra there is less heat-transfer enhancement, and at small Pr = 0.7. there is no heat-transfer enhancement at all. We suggest that the small-Pr behavior is due to the breakdown of the heat-transfer-enhancing Ekman pumping because of larger thermal diffusion. 
Jin-Qiang Zhong (1), Richard J.A.M. Stevens (2), Herman J.H. Clercx   (2,3), Roberto Verzicco (4), Detlef Lohse (2), Guenter...