Heat transport by turbulent Rayleigh-Benard convection in cylindrical cells with aspect ratio one and less

We present high-precision measurements of the Nusselt number N as a function of the Rayleigh number R for cylindrical samples of water (Prandtl number sigma = 4.4) with a diameter D of 49.7 cm and heights L = 116.3, 74.6, and 50.6 cm, as well as for D = 24.8 cm and L = 90.2 cm. For each aspect ratio Gamma equivalent to D/L = 0.28, 0.43, 0.67, and 0.98 the data cover a range of a little over a decade of R. The maximum R similar or equal to 10(12) and Nusselt number N similar or equal to 600 were reached for Gamma = 0.43 and D = 49.7. The data were corrected for the influence of the finite conductivity of the top and bottom plates on the heat transport in the fluid to obtain estimates of N-infinity for plates with infinite conductivity. The results for N-infinity and Gamma > 0.43 are nearly independent of Gamma. For Gamma = 0.275 falls about 2.5% below the other data. For R less than or similar to 10(11), the effective exponent gamma(eff) of N-infinity = N0Rgammaeff is about 0.32, larger than those of the Grossmannft Lohse model with its current parameters by about 0.01. For the largest Rayleigh gamma(eff) saturates at the asymptotic value numbers covered for Gamma = 0.98, 0.67, and 0.43, gamma(eff) = 1/3 of the Grossmann-Lohse model. The data do not reveal any crossover to a Kraichnan regime with gamma(eff) > 1/3.