1mm
A room temperature operating cryogenic cell for in vivo monitoring of dry snow metamorphism by X-ray microtomography
Context
Snow sampling
Description of the cell
Neige Calonne1, 2, F. Flin1, B. Lesaffre1, A. Dufour1, J. Roulle1, P. Puglièse1, A. Philip1, F. Lahoucine3, J. M. Panel1, S. Rolland du Roscoat2 and C. Geindreau2.
neige.calonne@meteo.fr
1Centre d'Etudes de la Neige, CNRM-GAME UMR 3589, Météo-France CNRS, St Martin d'Hères, France.
2Laboratoire 3S-R UMR 5521, CNRS UJF G-INP, Grenoble, France.
3Concept Soudure, Echirolles, France.
Conclusion et perspectives
Three-dimensional (3D) images of snow offer the possibility of studying snowmetamorphism at the grain scale by analysing the time evolution of its complex microstructure. Such images are also particularly useful for providing physical effective properties of snow arising in macroscopic models. Up to now, two different approaches have been used to obtain 3D images:
Time evolution: tomography of the same snow sample at several time intervals Time evolution: tomography of
different snow samples collected at several time intervals
Temperature conditions at the boundaries of the sample are controlled
to drive the metamorphism Temperature conditions at the
boundary conditions are fixed to avoid melting of the impregnation product
(T~- 30°C)
In a cold-room At ambiant temperature
Non-impregnated snow samples:
microstructure still evolves Impregnated snow samples:
microstructure is fixed
The in vivoapproach The static approach
Isothermal metamorphism (-2°C), Flin et al. 2004
513 hours 561 hours 609 hours Temperature gradient metamorphism (55°K m-1, -7.6°C),
Pinzer et al. 2012
Examples of 3D images obtained
19 days 84 days 0 day
OUR WORK: We developed a new in vivo cryogenic cell which:
allows to follow the evolution of the same snow samplewith time precisely controls the temperature conditions at the boundaries of the sample (choice of conditions for the snow metamorphism)
can be used with a large panel of tomographic scannersprovided with large cabin size: advantages in terms of speed, resolutions, imaging techniques…
Sampling a cylindrical core into a snow slab
Diameter = 1 cm Length = 1 cm
Inserting into the aluminium sample holder
Placing the sample holder into the cell
Cold production and conduction
Precision of Pt100 about +/- 0.03°C (between 0 and –10°C)
Regulation of Peltier modules about +/- 0.01°C
Main requirements for the development of the cell:
- size of the cell linked to the desired resolution (source to sample distance) - X-ray absorption properties of the materials used
- size of the snow sample large enough to be representative
- 360° rotation of the whole apparatus during the tomographic aquisitions
Insulation from the outside
Pressure of about 0.1 Pa, leading to a thermal conductivity of air ~ 0.0015 Wm-1K-1(reduced by 28 compared to that at atmospheric pressure).
Cryogenic cell in the tomographic cabin
Hot exchanger Peltier module Cold exchanger Copper column
Plexiglass cylinder Aluminium sample holder Snow sample Vacuum chamber
Vacuum gauge
Turbomolecular pump
Water circulation for Peltier cooling
Components of the cell (symmetrical with respect to the sample)
RX source
RX detector
Radiography
Membrane pump
Sealing cap Insulating box
Preliminary results – Vertical cross sections and 3D images of snow Equi-temperature metamorphism at –7°C Temperature gradient (TG) metamorphism of 18°C/m at -2°C
t = 0 hour t = 28 hours
Slow evolution Grain rounding
References:
• Flin, F., J. B. Brzoska, B. Lesaffre, C.
Coléou, and R. A. Pieritz, 2004, Annals of Glaciology, 38(1), 39-44.
• Pinzer, B. R., M. Schneebeli and T. U.
Kaempfer, 2012, The Cryosphere, 6, 1141-1155.
Acknowledgement:
• 3SR lab for the tomography and machining operations
• F. Dominé for the pumping system
• ANR DigitalSnow (ANR-11-BS02-009- 03) for funding
Temperature probe (Pt100) Ambiant T ~25°C
0 h 28 h
1 mm
-38 mm-1 +38 mm-1
t = 0 h t = 31 h t = 93 h t = 105 h
1mm
Rounding at the top of grains Facetting at the base of grains
Fast evolution from RG to DH General growth of structures
0 h 31 h
93 h 105 h
The cell can be very useful to improve our understanding of dry snow metamorphism:
- numerical computations of properties on the obtained 3D images - study of the physical mechanisms involved at the grain scale
- development of metamorphism models at microscale by using the obtained 3D images as a guideline and validation tool.
Other experiments could be carried out under different conditions (temperature, TG, snow type…) and the cell could be adapted to the study wet snow metamorphism.
Settlement
Growth/decay of bonds
1 mm
1mm
T = -6.921°C
T = -6.922°C Simulated temperature field for a regulation of Peltier modules at –7°C
Maximum TG = 0.2°C/m
Snow sample
-38 mm-1 +38 mm-1
red arrow oriented toward the base of the physical sample
1vox = 7.8 µm
1vox = 7.8 µm
Poster Number: C13B-0667
