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Rugged Flexible cryogenic thermocouple
picture above : specially designed cryogenic thermocouple allowing measurement of sub-milliKelvin temperature differences without offset uncertainty

 

The ultimate regime of convection

 

 

Images

 

Images of convection apparatus (for animations / videos, click here)

 

 

Cells description

 

 

 

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LEFT : Aspect ratio G=1.14 short cell before it is hung in a cryogenic-vacuum chamber - RIGHT : Schematics of the Grenoble cells

 

 

Results

 

 

 

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(figure dating back to our NJP 2010 paper. For ref. to the cited dataset, see this paper) Compensated heat transfer Nu.Ra^{-1/3} versus Ra for very high Ra experiments in cylindrical cell of aspect ratio 0.5 <= G <= 1.14 and for 0.6 < Pr < 7. Datasets from Grenoble (green asterisks [Chavanne cell ; G=0.5], magenta pointing-up triangles [Vintage cell ; G=0.5], blue disks [Flange cell ; G=0.5], grey diamonds [Paper cell ; G=0.5] , orange diamonds [Short-cell ; G=1.14], Trieste [red stars ; G=1], Oregon [brown pointing-down triangles, ; G=0.5], Göttingen [purple stars ; G=0.5] and Chicago after correction (see paper) [black disks ; G=0.5]. The line corresponds to Delft T-RANS numerical simulations in an aspect ratio 8:8:1 cell.}

 

 

 

 

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LEFT : Parameter space for the datasets Short (orange diamonds), Vintage (magenta pointing-up triangles), Flange (blue discs), Paper (grey diamonds), ThickWall (green squares), Screen (brown diamonds) and Cigar (yellow squares) cells.


RIGHT : Local exponent of the Nu(Ra) law in various Rayleigh–Bénard cells for 0.6 < Pr < 7

 

 

 

For more information

 

On the triggering of the Ultimate Regime of convection.
Roche P.-E., Gauthier, F., Kaiser, R. and Salort, J.
NJP 12:085014 (2010)
download - Link to Publisher - hal-00499652 - arxiv:1202.0661

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VASE
Ph.R. Jan, 2012