2003/07/31 by P.-E. Roche, P. -E. Roche, B. Castaing +3
Engineering · Physics and Astronomy · #Fluid Dynamics and Turbulent Flows #Fluid dynamics and aerodynamics studies #Quantum, superfluid, helium dynamics #cond-mat
paper · pdf · doi:10.1023/b:jolt.0000016727.23228.78
published as Journal of Low Temperature Physics 134 (2004) 1011 · submitted for publication to JLTP (august 2003)
arxiv created 2003/10/15 · openalex publication_date 2004/02/19 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
A Rayleigh-Bénard cell has been designed to explore the Prandtl (Pr) dependence of turbulent convection in the cross-over range 0.7<Pr<21 and for the full range of soft and hard turbulences, up to Rayleigh number Ra≃ 1011. The set-up benefits from the favourable characteristics of cryogenic helium-4 in fluid mechanics, in-situ fluid property measurements, and special care on thermometry and calorimetric instrumentation. The cell is cylindrical with diameter/height=0.5. The effective heat transfer Nu(Ra,Pr) has been measured with unprecedented accuracy for cryogenic turbulent convection experiments in this range of Rayleigh numbers. Spin-off of this study include improved fits of helium thermodynamics and viscosity properties. Three main results were found. First the Nu(Ra) dependence exhibits a bimodality of the flow with 4-7 % difference in Nu for given Ra and Pr. Second, a systematic study of the side-wall influence reveals a measurable effect on the heat transfer. Third, the Nu(Pr) dependence is very small or null : the absolute value of the average logarithmic slope (dlnNu/dlnPr)Ra is smaller than 0.03 in our range of Pr, which allows to disciminate between contradictory experiments [Ashkenazi et al., Phys. Rev.Lett. 83:3641 (1999)][Ahlers et al., Phys.Rev.Lett. 86:3320 (2001)].