X. Chavanne et al., HIGH RAYLEIGH NUMBER CONVECTION WITH GASEOUS HELIUM AT LOW-TEMPERATURE, Journal of low temperature physics, 104(1-2), 1996, pp. 109-129
This article presents an experimental set-up to study the turbulent re
gime of free thermal convection in a Rayleigh-Benard cell. Helium gas
around 4 K is confirmed in a cell of aspect ratio 0.5. With a thermoco
uple technique we can measure temperature differences across the cell
as low as 0.2 mK, which allows to test the adiabatic gradient effect.
Covering a large range of Rayleigh numbers (10(3) to 5 x 10(12)), Nuss
elt numbers from 1 to 10(3) are obtained. The results are compared wit
h previous works. They show a departure from the 2/7 power law above R
a = 3 x 10(10).