Refrigeration – Storage of solidified or liquified gas
Patent
1990-12-26
1993-07-13
Bennet, Henry A.
Refrigeration
Storage of solidified or liquified gas
62 483, 29890042, 165168, F17C 310, F28F 312
Patent
active
052262995
DESCRIPTION:
BRIEF SUMMARY
FIELD OF ART
The present invention relates to cryogenic engineering and, more particularly, it relates to the heat-insulating means of cryogenic objects, such as cryostats, Dewar flasks, cooled apparatus, and to the method for producing of a bank of radiation shields for the realization of such means.
PRIOR ART
Known in the prior art is a heat-insulating means of cryogenic objects, made in the form of a bank of passive shields arranged in line, one after another, on the path of heat radiation directed towards the cryogenic objects (DE, B, 2361360). The shields in this means have the form of coaxial cylinders arranged on the outside of a vessel with cryogenic fluid and secured to the filler throat of said vessel. The shields are cooled with cold gas discharged through the vessel throat from the cryogenic fluid.
However, the cooling efficiency of such means is low because each passive shield reduces the inflow of heat twice only and the heat exchange surface of the means is limited by the internal surface of the vessel filler throat.
There is another known heat-insulating means of cryogenic objects in the form of a cooled radiation shield provided with heat exchange channels for the flow of coolant, said channels being located between the shield layers (U.S. Pat. No. 4,492,088).
In this means the heat exchange is increased between the shield and cold gas since the latter is discharged not through the throat but through the heat exchange channels located between the shield layers. However, the cooling efficiency of this means is likewise low because the shield is made in the form of a single envelope to which the inlet and outlet pipes have to be soldered.
Finally, there is a known heat-insulating means for cryogenic objects in the form of a bank of six cooled radiation shields, said shields shaped like cylinders with flat end faces arranged coaxially one after another on the path of heat radiation, each provided with heat exchange channels for the flow of coolant, said channels communicating through connecting pipes (SU, A, 1180640). The heat exchange channels in the known means have the form of helical flattend pipes soldered to the face surface of each shield. The heat exchange channels intercommunicate through the connecting pipes also soldered to the ends of the spiral pipes. The cold vapours of cryogenic agent-liquid helium (coolant)-flow from the helium container into the system of heat exchange channels and cool the radiation shields. The advantages of this means include the rational utilization of enthalpy of the vapour released by the cryogenic agent-helium, and the relationship between the thermal load on the cryogenic agent and efficiency of heat insulation. The heavier the load, the more intensive is evaporation of helium and the better is the cooling of the shields which reduces the evaporation intensity of helium. The thermal contact of each shield with the structural connectors between the casing and the vessel reduces substantially the inflow of heat due to heat conductivity.
However, at the same time, the heat exchange between the coolant flowing through the channels and the surfaces of the shields is insufficiently effective because the coolant cools at first the channels proper, then the layer of solder and only afterwards it cools the surfaces of the shields which creates a thermal resistance. The coil-type heat exchanger made of a pipe with a constant passage area is not optimum from the view point of hydraulics and heat transfer because increasing the length of the heat exchanger in order to increase the cooled surface of the shields results in a higher hydraulic resistance of the cryogenic agent flowing through the pipe.
The limited area of the cooled end surfaces of the shields results in heating of the noncooled portion of the shields or in the necessity of making the shields from costly and heavy copper. An increase in the passage area of the pipe brings about a stronger heat inflow to the helium vessel due to heat conductivity along the pipe. On the other hand, the parameters o
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"Kriegennaya Tekhnika", E. I. Mikulin, 1969.
Bennet Henry A.
Kilner C.
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