EXPERIMENTAL-STUDY OF HIGH-RAYLEIGH-NUMBER CONVECTION IN MERCURY AND WATER

Experimental results of Rayleigh-Benard convection in the strongly tur bulent regime are presented. The liquids tested are water (Pr approxim ate to 7) and mercury (Pr = 0.025), covering a range of Rayleigh numbe rs 4.6 x 10(6) < Ra < 6.3 x 10(9). The convective chamber consists of a cylindrical cell of aspect ratio Gamma = 1 (Gamma = diameter/depth). The heat flux, the temperature fluctuation spectra and the structure of the mean flow have been measured. For Ra > 2 x 10(9) a transition t o a new turbulent regime was observed with considerable increase of th e Nusselt number. A decrease in Nusselt number with decreasing Prandtl number is observed at given Ra.