Turbulent thermal convection of He gas at cryogenic temperatures

Srnka A, Hanzelka P, Musilova P, Urban P     (Institute of Scientific Instruments ASCR, Brno)
Skrbek L     (Faculty of  Mathematics and Physics, Charles University, Praha)

Turbulence: unsolved problem in physics, important in practice, difficulties with numerical simulations.
Experiments under stable laboratory conditions are of great importance.

Ubiquitous turbulent convection: in a horizontal layer of a fluid heated at the bottom and cooled at the top (Rayleigh-Benard convection).
Control parameters are Rayleigh number, Prandtl number, Nusselt number, cell aspect ratio.

Experiments: relations among Ra, Pr, Nu and aspect ratio are examined.
He gas near critical point: tuneable and well known properties, enables study over an unprecedented range of Ra


Helium cryostat for the study of turbulent thermal convection at cryogenic temperatures


Helium cryostat


Cylindrical convection cell

Ra = up to 1015 (for G = 1) variable aspect ratio G from 1 to 3

The design is focused on precise boundary conditions for the working fluid – helium gas: uniform temperature distribution over entire top and bottom plates and high insulation capability of the side wall.
The cell should withstand pressures from 100 Pa to 250kPa (350kPa) at T<8K for anticipated convection heat transfer of about 1W


Convection cell