Experimental investigation of turbulent Rayleigh-Benard convection of water in a cylindrical cell: The Prandtl number effects for Pr > 1

We report an experimental study of turbulent Rayleigh-Benard convection in a cylindrical cell of aspect ratio unity, focusing on the effects of the Prandtl number (Pr). Purified water was used as the convecting fluid. Five different Pr between 3.58 and 9.40 were achieved by changing the mean temperature of water, and the measurements were carried out over the Rayleigh number range 2.63 x 10(8) <= Ra <= 3.89 x 10(10). Over the present parameter range, the measured Nusselt number Nu is found to scale as Nu similar to Ra-beta with beta = 0.30 and to be independent of Pr. Based on the oscillation period of the measured temperature, the Reynolds number Re scales as Re similar to (RaPr-0.72)-Pr-0.47. The local temperature fluctuations at the cell center and near the cell's sidewall were measured, and their relations with Ra and Pr were studied. Our results further reveal that the non-Oberbeck-Boussinesq effects of water have a relatively small influence on the measured scaling relation Nu similar to Ra-beta.