Rayleigh-Bénard convection at very high Rayleigh numbers close to the 4He critical point

In this article we describe an experimental procedure to study Rayleigh-Bénard convection with He ⁴ close to its critical point (tabulated as T_c=5.1953 K in the EIT 90, P_c=2.275 bar) as the working fluid. The convention takes place in a closed cylindrical cell (20 cm height and 10 cm inner diameter). The experimental challenge lies in accurate temperature and density measurements. To test our system and our thermometry, an independent measurement of the critical temperature is performed and we found 5.1939 K±1.0 mK (EIT 90). Measurements of the Nusselt number versus the Rayleigh number, from the laminar regime (Ra∼10 ³) up to the highest Ra obtained in a laboratory experiment (2×10 ¹⁴) are reported, with Nu varying from 1 to more than 5000.