Prandtl-Number Dependence of Heat Transport in Turbulent Rayleigh-Bénard Convection

We present measurements of the Nusselt number N as a function of the Rayleigh number R and the Prandtl number in cylindrical cells with aspect ratios 0ex{0ex}=0ex{0ex}0. 5 and 1. 0. We used acetone, methanol, ethanol, and 2-propanol with Prandtl numbers 0ex{0ex}=0ex{0ex}4. 0, 6. 5, 14. 2, and 34. 1, respectively, in the range 310^710^11. At constant R, N (R, ) varies with by only about 2%. This result disagrees with the extrapolation of the Grossmann and Lohse theory beyond its range of validity, which implies a decrease by 20% over our range, but agrees with their recent extension of the theory to small Reynolds numbers.