Cryocoolers and Space Cryogenics Laboratory (LCCS)

Adsorption Cryorefrigerators Adsorption is the physical mechanism by which a gas can be trapped on a surface. For a given material, the quantity of gas adsorbed is a function of the temperature and by the pressure, it increases when the temperature decreases and/or the pressure increases. Thus while varying the temperature it is possible to carry out a compression or a relaxation (pumping). This effect can then be used to design thermal compressors intended to feed, for example, a loop Joule Thomson, or to carry out a cryopompe making it possible to lower the pressure on a bath and thus to decrease its temperature. Moreover, this capacity to modify the pressure by varying the temperature makes it possible to design thermal switches with extremely effective gases of exchange. The principal interest of this technology is its total absence of parts moving. On the other hand, need for cycling components in temperature the reserve at the low even very low temperatures, where the low specific heats make it possible to obtain reasonable thermodynamic effectiveness. ECA-SBT however worked on systems functioning at the temperatures of liquid nitrogen or even at temperatures close to 150 K.

 

It is thus for the range of the temperatures relating to liquid helium (normal "4" or isotope "3" [ 0.2 K - 5 K ]) that this technique of cooling shows all its benefit and its capacities. The guiding principle consists in condensing gas, then to decrease its vapor pressure to lower its temperature. The management of gas is ensured by a pump adsorption and the control of the heat gradients by thermal switches (with adsorption). Multiple systems specific to the grounds applications were developed at ECA-SBT, monoétagé 3He or 4He, two-stage 4He/3He or 3He/3He, interruptory thermics, and except for specific achievements the majority were transferred to Air Liquide . Concerning space applications ECA-SBT developed and qualified with the European Space Agency of the thermal switches and cryorefrigerator 3He and 4He. Dans le cadre de la mission HERSCHEL CEA-SBT a la responsabilité de la fourniture des cryoréfrigérateurs à adsorption de vol de deux des trois instruments scientifiques, SPIRE (Spectral and Photometric Imaging Receiver) et PACS (Photo-conductor Array Camera & Spectrometer). En effet, les détecteurs bolométriques de ces instruments fonctionnent à des températures proches de 300 mK, et permettent d'effectuer des observations dans le domaine infrarouge submillimétrique. Les modèles structurels (STM) et les modèles de qualification (CQM) sont en cours d'assemblage et sont prévus pour une livraison aux projets à l'automne 2002.

 

Mechanical Cryorefrigerators The guiding principle of these refrigerating machines schematically consists in compressing gas, to then bring it in the cold part (which one generally calls the cold finger) then finally to slacken it to produce cold. The objective is to have the maximum of gas compressed with the cold end during the phase of relaxation. In other words, since the variations of pressures (compression, relaxation) and of gas mass in the machine are in general generated by piston machines (oscillator of pressure) and are thus quasi sinusoidal, one needs a null dephasing between flow masses and wave of pressure to the cold end. Two types of machines currently dispute the favours of the space market, Stirling and the pulsated gas-tube (TGP). Thermodynamically very effective, they differ by technology used to adjust dephasings débit/pression within the cold finger: mechanics with moving parts for Stirling, tire entirely static for the TGP. One guesses of course why this last, although more tardily developed, could in the long term supplant the Stirling machines. These two systems use similar oscillators of pressure primarily based on the technology of the membrane springs; although ECA-SBT developed at the beginning of the Nineties of the oscillators on stage gas, this work was arrétés with the profit of the use of these oscillators qualified available almost on rack near many industrialists of the space one. The research led to ECA-SBT currently concentrates on cold the finger part and we have for example two contracts in progress with the European Agency Space in collaboration with Astrium and Liquid air. These developments relate to miniature TGP; the most recent performances exceed refrigerating Watt of power for 25 Watts provided.

 

Last update : 02/20 2017 (264)

 

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