Helium cryostat for experimental study of natural turbulent convection

Abstract

Published experiments on natural turbulent convection in cryogenic (4)He gas show contradictory results in the values of Rayleigh number (Ra) higher than 10(11). This paper describes a new helium cryostat with a cylindrical cell designed for the study of the dependence of the Nusselt number (Nu) on the Rayleigh number (up to Ra approximately 10(15)) in order to help resolve the existing controversy among published experimental results. The main part of the cryostat is a cylindrical convection cell of 300 mm in diameter and up to 300 mm in height. The cell is designed for measurement of heat transfer by natural convection at pressures ranging from 100 Pa to 250 kPa and at temperatures between 4.2 and 12 K. Parasitic heat fluxes into the convection medium are minimized by using thin sidewalls of the bottom and top parts of the cell. The exchangeable central part of the cell enables one to modify the cell geometry.

Comments on heat transfer efficiency in cryogenic helium turbulent Rayleigh-Bénard convection

“…1 to study turbulent RBC in a cylindrical cell of height 0.3 m, diameter 2R = 300 mm; for a detailed technical description see Urban, Hanzelka, Kralik, Musilova, Skrbek & Srnka (2010). It is designed to minimize the influence of its structure on the convective flow of cryogenic 4 He gas of Prandtl number P r ≈ 1, with the aim of resolving existing contradictions in N u(Ra) scaling.…”

Weather and anomalous heat flow occurring near absolute zero

“…Such corrections are reviewed in ref. 5, and the design of the recently built apparatus of Urban et al (1) specifically addressed this particular issue (7).…”

Anomalous heat transport and condensation in convection of cryogenic helium

“…1. The cylindrical RB cell, 300 mm in both diameter and height, is designed to minimize the influence of its structure on the convective flow (1) and is capable of running at very high Rayleigh numbers up to 10 15 (2,3). These studies used cryogenic helium gas as the working fluid and have been performed under nearly Oberbeck-Boussinesq conditions (all physical properties of working fluid assumed constant except its density varying linearly with temperature) (2), as well as for the case when non-OberbeckBoussinesq conditions cause asymmetry between the top and bottom boundary layers (3).…”