US 3593537 A
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Description (OCR text may contain errors)
United States Patent Robert W. Stuart Wakefield;
Walter H. Hogan, Wayland, both of, Mass. 813,959
Apr. 7, 1969 July 20, I971 Cryogenic Technology, Inc.
Inventors Appl. No. Filed Patented Assignee PROCESS AND APPARATUS FOR RAPIDLY COOLING A SMALL THERMAL LOAD 12 Claims, 2 Drawing Figs.
us. ca 62/62, 62/54, 62/259, 62/514 Int. Cl. 1 25b 19/00 Field of Search 62/514,
 References Cited UNITED STATES PATENTS 646,459 4 1900 Place 62/54 x 662,217 11/1900 Brady 62154 X 1,835,699 12/1931 Edmonds 62/54 X 3,025,680 3/1962 De Brosse et al. 62/514 X 3,203,477 8/1965 Collard 62/259 X 3,369,370 2/1968 Todd,.lr. et al 62/514X Primary Examiner-Albert W. Davis, Jr. Attorney-Bessie A. Lepper ABSTRACT: A small thermal load such as an infrared detector is exposed to a high-pressure inert fluid contained within a small high-pressure vessel. A valve-controlled vent tube extending through the wall of the vessel provides means for controllably bleeding off fluid from the vessel and hence for rapidly developing refrigeration. The fluid bled off may be circulated around the vessel surface to minimize loss of refrigeration in cooling the vessel wall.
PAIENIED JUL 20 1911 Robert W. S'ruorf Walter H Hogan INVENTORS Attorney PROCESS AND APPARATUS FOR RAPIDLY COOLING A SMALL THERMAL LOAD This invention relates to an apparatus and method for refrigerating a small load such as an infrared detector. For certain applications, particularly for infrared sensor cooling, there is a requirement for very rapid cooldown. Such cooling may be of relatively short duration and the apparatus used must often be expendable. Cooling of such devices is now normally accomplished through Joule-Thomson cooling. However, any Joule-Thomson cooling system must, of necessity, be relatively complicated in design and expensive to construct. Moreover, it requires a short but significant time to accomplish cooldown by any Joule-Thomson apparatus.
It would, therefore, be desirable to have a simple, inexpensive device capable of achieving very rapid cooldown and of delivering refrigeration to a small thermal load at such a rate and in such a manner as to make cooling of this device almost instantaneous.
It is, therefore, a primary object of this invention to provide a simple, easily constructed device of very rapidly cooling a relatively small load. It is another object of this invention to provide a device of the character described which is easily activated, inexpensive enough to be expendable after a single use, and flexible in its application to various types of refrigeration loads. It is yet another object of this invention to provide such a device which can be made in very small, lightweight units. It is yet another important object of this invention to provide a very rapidly cooled infrared detector. It is another important object of this invention to provide a method for rapidly cooling infrared detecting devices. Other objects of the invention will in part be obvious and will in part by apparent hereinafter.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps all as exemplified in the following detailed disclosure and the scope of the invention will be indicated in the claims.
For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawings in which FIG. 1 is a cross section of one embodiment of the apparatus in which the high-pressure vessel is spherical; and
FIG. 2 is a cross section of another embodiment in which the high-pressure vessel is a sphere with an elongated extension.
In the device of this invention, the thermal load to be refrigerated is mounted within a high-pressure vessel such that at least one surface of the load is exposed to high-pressure fluid contained within the vessel. A valve-controlled vent tube communicates between the interior and exterior of the vessel and preferably the vent tube inlet within the vessel is relatively close to the surface of the refrigeration load exposed to the fluid. The vessel is charged with high-pressure fluid and at the time refrigeration of the load is desired the valve in the vent tube is opened in a manner to bleed off some of the high-pressure fluid from within the vessel. By the process known as Simon expansion, the fluid in the vessel is very rapidly cooled and thus cools the refrigeration load. The fluid bled off from the interior of the vessel may be used to cool the outside wall of the vessel thus minimizing the amount of refrigeration lost to cooling the vessel which is constructed of a material having a low thermal conductivity at cryogenic temperatures.
One embodiment of the apparatus of this invention is illustrated in FIG. 1 which illustrates the use of a spherical vessel. In this embodiment there is provided a thick-walled, highpressure vessel formed of a low thermal conductivity material, such as glass fiber-reinforced resins, to prevent consuming the available refrigeration in cooling the vessel wall. Into the wall of vessel 10 and forming a part thereof is sealed a window 11 to which is attached an infrared detector 12, or other device to be cooled, in such a way that it is exposed to high-pressure fluid of volume 14 defined by the vessel wall. In the case where an infrared detector is the load, lead wires 13 are provided through the wall to the external atmosphere. The vessel 10 is conveniently charged with high-pressure fluid through a charging line 15 which may be sealed off once the pressure has been built up to a desired level within the vessel. If desired, the inlet charge line 15 may be so formed as to be reusable.
A vent tube 16 communicates between the interior volume 14 of the vessel and the area external of the vessel wall. Preferably this vent tube is so positioned within the vessel as to be very close to the surface of the detector as indicated by the small gap 17. By positioning vent tube 16 in a manner to be closely associated with the surface of the load 12, and by placing the vent tube so that its inlet end is aligned with the surface to be cooled, it is possible to effectively concentrate the refrigeration at that surface. Vent tube 16 has an external valve 18 which, when opened,permits the high-pressure fluid to bleed out of the volume 14 into conduit 16. Cooling is accomplished through a process which isgenerally known as Simon expansion. Thus, the gas that remains in volume 15 thermodynamically pushes some of the gas out of the vessel and therefore the gas that remains experiences an isentropic expansion. For example, if the fluid contained within volume 14 is nitrogen under a pressure of about 1,200 atmospheres and the bleedofi is continued until the nitrogen has reached atmospheric pressure, it should be theoretically possible to obtain a fluid within volume 14 at 77 K., 35 percent of which would be liquid. This calculation assumes no heat leak to the surrounding atmosphere.
There is, of course, some refrigeration lost to cooling the walls of the vessel 10. This may be minimized in two ways. First, the vessel 10 is constructed of a material which has very low heat conductivity at the cryogenic temperatures involved. Such a material is preferably a glass fiber-filled resin. A second way of minimizing heat transfer and hence heat loss to the walls of the vessel 10 is to provide means for'defining a fluid passage around the vessel walls and discharging the cold low-pressure gas which exits through vent tube 16 through valve 18 into the passage. Thus, in FIG. 1 it will be seen that there is provided around substantially the entire exterior wall of the vessel 10 an outer spherical wall 20 formed of a material such as a'resin or plastic. This outer wall defines with the outer surface of the vessel 10 a fluid passage 21 having a plurality of small gas release ports 22. The passage 21 is in communication with vent tube 16 through a connecting piece 25 ,which may have associated with it a valve 26. A branch conduit 27, having valve 28, communicates with joining member'25 so that it is possible, if desired, to discharge either all or aportion of the cold low-pressure fluid into the atmosphere rather than into fluid passage 21.
In the embodiment of FIG. 2, in which like reference numerals refer to like components in FIG. 1, there is added an elongated extension or neck so that the pressure vessel has in essence a spherical body 30 with an integral extension 31. This configuration may be more convenient to build into some systems. The extension is sealed with a window 32 and ring 33. As in FIG. 1, the load is affixed to the inside surface of the window 32 and leads 13 are provided for external connection where necessary. The vent tube 16 extends through the extension passage 34 and terminatesnear the surface of load 12. In the embodiment of FIG. 2 all of the fluid bled from the vessel is discharged into fluid passage 21, which could if desired be also extended to enclose, at least partially, the extension 31.
As an example of the operation of this apparatus, the vessel 10 or 30/31, may be filled with high-pressure nitrogen between about 10,000 and 20,000 psi. By bleeding off the high-pressure fluid from volume 14 through vent tube 16 at such a rate that only a fraction of a second is required to reduce the fluid to a low pressure, i.e., close to atmospheric pressure within'volume 14, it is possible to reach temperatures as low as 77 K. and to effect a cooldown of the load, i.e., infrareddetector 12, in as short a time as one-tenth ofa second. Inasmuch as in the refrigeration developed there will probably be formed within the volume 14 (or 14/34) a small quantity of liquid nitrogen, refrigeration will be supplied to the load within the volume over a period of time until such liquid has evaporated and the volume within the vessel reaches a temperature above the cryogenic level.
The entire apparatus may be constructed in a relatively small size, i.e., about two inches in diameter, and the valve 18 to effect refrigeration may be of any type which can be automatically actuated upon a given signal. Thus, the entire device is adaptable to installation on a missile and is capable of cooling the infrared detector down to about 80 K. by the time the missile requires guidance from the infrared detector. It is, of course, within the scope of this invention to form the apparatus in any desired size and to use any load within the volume 14. It is, however, particularly adaptable to small devices and to small refrigeration loads.
It will thus be seen that the objects set forth above among those made apparent from the preceding description are efficiently attained, and since certain changes may be made in carrying out the above method and in the construction set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
1. A rapid cooldown refrigeration device comprising in combination a. a high-pressure vessel adapted to contain fluid under high pressure and formed of a material having low thermal conductivity at cryogenic temperatures;
b. high-pressure fluid within said vessel,
c. a load to be refrigerated having at least a portion of its surface within said vessel directly exposed to said highpressure fluid;and
d. a valve-controlled fluid conduit extending within said vessel and positioned to be directed at and close to said load, said fluid conduct providing communication between the interior and exterior of said vessel, whereby when highpressure fluid is rapidly discharged from said vessel said fluid undergoes rapid cooling and refrigerate said load.
2. A refrigeration device in accordance with claim 1 wherein said vessel is spherical in shape.
3. A refrigeration device in accordance with claim 1 wherein said vessel is spherical with an integral elongated neck.
4. A refrigeration device in accordance with claim 1 wherein said load is an infrared detector mounted on a window forming a portion of the wall of said vessel.
5. A refrigeration device in accordance with claim 1 wherein said vessel is formed of a glass fiber-reinforced synthetic resin.
6. A refrigeration device in accordance with claim I including means to define a fluid passage around at least a portion of the outer surface of said vessel and connecting means to connect said conduit means with said fluid passage.
7. A refrigeration device in accordance with claim 6 wherein said connecting means has fluid flow control means associated therewith.
8. An infrared detector adapted for very rapid cooldown, comprising in combination a. a high-pressure vessel adapted to contain fluid under high pressure and formed of a material having low thermal conductivity at cryogenic temperatures;
b. a window transparent to infrared radiation sealed into the wall of said vessel and forming a part thereof;
c. infrared-detecting means internal of said vessel and mounted on the surface of said window;
d. high-pressure fluid within said vessel; and
e. a valve-controlled fluid conduit communicating between the interior and exterior of said vessel, said conduit being directed at and close to said infrared-detecting means. 9. An infrared detector in accordance with claim 8 including means to define a fluid passage around at least a portion of the outer surface of said vessel and connecting means to connect said conduit means with said fluid passage.
10. A method of rapidly cooling a small refrigeration load comprising the steps of a. exposing a load to be refrigerated to a volume of highpressure fluid contained within a high-pressure vessel; and
b. discharging said fluid from said volume from a point adjaeent said load in said volume at a sufficiently rapid rate to effect isentropic expansion of said fluid, whereby said load is cooled through direct contact with the insentropically expanded fluid.
11. A method in accordance with claim 10 in which the discharged fluid is circulated around at least a portion of the external wall of said high-pressure vessel.
12. A method in accordance with claim H0 wherein said load is an infrared detector affixed to a window forming a part of the wall of said vessel.