Refrigeration – Storage of solidified or liquified gas
Patent
1996-07-19
1998-06-16
Capossela, Ronald C.
Refrigeration
Storage of solidified or liquified gas
312401, 312406, F17C 100
Patent
active
057653798
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to thermally insulated units such as refrigerators, or to insulation elements such units. Conventionally, this type of units is made with an encapsulation made of a foam substance foamed with closed cells by the use of a blowing gas of a high molecular weight, whereby this gas by itself will be present in the closed cells and thus contribute to a high thermal insulation effect. As known, however, it has been found that there are some unlucky environmental effects of those gases, which are the best suited, and it has been found that acceptably applicable gases provide for a noticeably reduced insulation effect. It has already been proposed to go an entirely different way, viz. by evacuation of all gas in the insulation material, such that this may be present in a highly evacuated condition, whereby the insulation effect will be still better than with a heavy gas present in the material.
On this background it has been suggested to provide hermetically sealed, highly evacuated insulation panels, but these tend to be very expensive if they should be made such that their high insulation effect remains intact with the required duration. The hermetical sealing itself is expensive, and additionally it is required to use in the panels a fine cellular material, which is very expensive to produce when later development of gas in the material should be avoided; by the required very low pressure even a modest gas development will soon produce such a pressure rise that the super insulation gets lost.
DE-A-40 is 970 specifies the conditions for the establishing of the high insulation effect, given by a very low pressure and a small cell size in the insulation material. It is indicated that the high vacuum area in the pressure range below 0.001 mbar, but in the present connection this expression will also be used for pressures of about 1 mbar. Likewise it is indicated that it is hardly possible to produce insulation materials with a cell size below 1 mm, while by now it has been found that it is well possible to produce foam with cells of e.g. 0.1-0.5 mm. The results of the present invention seem to verify that there is not the best accordance between theory and practice with respect to the condition that the cell or pore size should be smaller than the moving distance of the relevant gas molecules at the actual pressure, inasfar as the invention has resulted in very attractive results for cell sizes of approximately 0.2 mm and pressures of about 1 mbar, i.e. a pressure much higher than the theoretically applicable pressure, corresponding to a much smaller pubpressure and thus to a vacuum far easier to establish.
FR 2,628,179 discloses a technique, which, on the detailed level, is less interesting, because it is based on the use of macro cavities and a relatively low vacuum of 50-100 mbar, this not conditioning any noticeably improved insulation effect, but which is nevertheless principally significant in suggesting that the insulation elements of a given unit such as a refrigerator may be connected to a vacuum pump mounted in the unit itself. It is mentioned that the insulation elements can hardly be sealed in any absolute sense, i.e. they are not presupposed to be sealed in any hermetical and diffusion tight manner; however, this is not required when it is possible to carry out an operational, current evacuation of the elements, this giving fundamentally changed and improved possibilities for the maintenance of the required low pressure throughout a long lifetime for the relevant units. The vacuum pump, which is now a machine part of the single unit, should have only a very small capacity, as in the long run it will only have to do away with air intruding from outside into the insulation elements.
Seen in the perspective of the invention such an arrangement will be advantageous also in that the operative evacuation of the gas in the insulation elements will apply even to the later developed gas in the foam held in the insulation elements.
It belongs to the theor
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Capossela Ronald C.
Elcold-Tectrade I/S
Safran David S.
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