US2966034A

US2966034A - Reciprocating flow gas expansion refrigeration apparatus and device embodying same

Info

Publication number: US2966034A
Application number: US820671A
Authority: US
Inventors: William E Gifford
Original assignee: Arthur D Little Inc
Current assignee: Arthur D Little Inc
Priority date: 1959-06-16
Filing date: 1959-06-16
Publication date: 1960-12-27
Anticipated expiration: 1977-12-27

Description

Dec. 27, 1960 w. E. GIFFORD 2,965,034

RECIPRQCATING FLOW GAS EXPANSION REFRIGERATION APPARATUS AND DEVICE EMBQDYING SAME: v

4 Sheets-Sheet 2 Filed June 16, 1959 INVENTOR. PVI'I/iam E. GzY'forJ Attorney Dec. 27, 1960 w. E. GIFFORD 2,965,034

RECIPROCATING FLOW GAS EXPANSION REFRIGERATION APPARATUS AND DEVICE EMBODYING SAME Filed June 16, 1959 4 Sheets-Sheet 3 I33 fi 1 VACUUM v 23 3s 44 '24 l 4| /A 1/ 4 Q3 -wao E v ;-|36 I32 ALKM l34 J, J x T REFRIGERATOR 13 cm.

INVENTOR.

I Vi/[iam E Gifford BY Afforney Dec. 27, 1960 w. E. GIFFORD 2,966,034 i RECIPROCATING FLOW GAS EXPANSION REFRIGERATION APPARATUS AND DEVICE EMBODYING SAME 4 Sheets-Sheet 4 Filed June 16, 1959 DISPLAGER R 2 4 m 4 m V. R E S E R 4 46 3 M 342 0 J1 N II R r L a W G F T 0AA Y m. as R N 0 E86 FS m E TM H N F EL EA M y E 1 m U. D ED RA A 8 M m a 0 A nu w E MH Fig. 12

Afforney United States Patent C) RECIPROCATING FLOW GAS EXPANSION RE- FRIGERATION APPARATUS AND DEVICE EM- BODYING SAME William E. Gifford, Lexington, Mass., assignor to Arthur D. Little, Inc., Cambridge, Mass., a corporation of Massachusetts Filed June 16, 1959, Ser. No. 820,671

18 Claims. (Cl. 62-6) refrigeration cycles.

There are, of course, in the prior artmany refrigeration devices including, for example, those described in U.S. Patents 2,764,877 and 2,458,894 for liquefying airand helium, respectively. These apparatus are in gen-; eral large and not adaptable to direct use in connection,

with other apparatus suchfor example as infrared detectors or for installations in storage tanks or-dewars where liquefied gases are to be kept. It is, therefore, necessary in these applications to transfer cold liquefied gases from the large refrigeration systems to suitable containers or heat exchange systems to make use of the refrigeration of the liquefied gases.

It would therefore be highly desirable to have available a small compact apparatus capable of producing refrigeration, down to about 50 K., which could be in corporated directly into other equipment.

It is therefore a primary object of this invention to pro-.

vide apparatus suitable for producing refrigeration down to about 50 K. which is simple and highly efiicient, and which at the same time may be incorporated into or directly attached to other equipment. It is another object of this invention to provide such refrigeration ap paratus which may be very small and compact. It is yet another object to provide a small compact system, including an infrared detector, which may be maintained as low as 50 K. with a minimum amount of work being supplied to the system.

These and other objects will become apparent in the following discussion.

The apparatus of this invention will be further described below with reference to the accompanying drawings in which:

Fig. 1 is a front vertical view, partly in section, of the apparatus of this invention;

Fig. 2 is a side vertical view, partly in section, of the apparatus;

Fig. 3 is a cross-section of the apparatus taken along line 3-3 of Fig. 1;

Fig. 4 is a cross-section of a portion of the apparatus taken along line 44 of Fig. 1;

Figs. 5, 6 and 7 illustrate modifications of the bottom portion of the cylinder and displacer of this apparatus;

Fig. 8 is a section of the cylinder and displacer taken along line 8-8 of Fig. 7;

Fig. 9 is a diagrammatic representation of the extreme a preferred apparatus for practicing either of these novel Y 'ice positions taken by the displacer in the cylinder showing the spacing therebetween and the extent of displacer travel;

Fig. 10 is a plot showing the relation between the heat losses and the spacing which exists between the displacer and the cylinder walls;

Fig. 11 illustrates the adaptation of the refrigeration apparatus of this invention to the cooling of an infrared detector; and

Fig. 12 illustrates a modification of the cylinder equipped with a gas cell for maintaining predetermined temperatures.

The apparatus of this invention is illustrated in Figs. 1 and 2, which are side-plan views, partially in crosssection, and in Figs. 3 and 4 which are cross-sectional views.

In Figs. 1 and 2 the apparatus will be seen to consist of a head portion generally indicated as 20 which is maintained on a main support plate 21 through suitable connecting means such as screws 22. Depending from this head 20 is a cylinder 23 which is enclosed at the bottom by a plate 24. This cylindrical portion is enclosed in an evacuated housing 26 which may be of glass or transparent plastic if it is desired to observe the refrigeration system. The housing 26 is positioned with relation to the head portion 20 by means of the lower extension of the head portion 20 which functions as a :up the housing. A suitable line such as 27 leads into preferred embodiment.

pilot for housing 26. The housing 26, its bottom plate 28, head 20, cylinder 23, cap 24 and cylinder head adapter plate 25 define an evacuated space 29. O-n'ng seals such as 30 complete the sealing of these portions making evacuated area 29 and to an evacuation system 35. desired, means other than evacuation of the surrounding area around the cylinder may be used for insulation. The arrangement of Figs. 1 and 2 illustrate only a The housing 26 and its bottom plate 28 are held in relation to head 20 by means of three machine screws 32 (Fig. 2).

Within the cylinder 23 there is a movable displacer 36 spaced from the inside cylinder walls by an annular spacing 37 (see Fig.4). The displacer is attached at its top to a displacer rod 38 which passes through the top portion of the head and through an opening in the top plate 67. The displacer defines within cylinder 23 an upper annular chamber 40 and a lower refrigeration chamber 41. Suitable O-ring seals 42 are provided and the upper portion of displacer 36 remains at room temperature throughout.

Within displacer 36 there is a regenerator 44 having at its upper portion a regenerator head passage 43 through which the gas employed in the cycle passes into and out of the regenerator 44.

The regenerator 44 is preferably located within a circular passage in the displacer and is formed by stacking fine copper or brass wire screening cut in circular configurations to fit within the circular passage in the displacer. It is preferable that the screening material have a high heat capacity at the temperatures encountered. A preferred embodiment of the regenerator is shown in cross-section in Fig. 4. The screening 45 lies within the circular passage forming the regenerator 44 which in turn is defined by the displacer wall 36. This preferred embodiment of the regenerator, i.e., stacked copper or brass screening, results in a minimum amount of vertical heat transfer in the regenerator. This is necessary to realize maximum regenerator efiiciency, especialthe system through line 56 to enter a low-pressure reser'- voir 33.

Duplicate valvin-g means are also shown. Thus valve 58, valve spring 64) and valve rod 62, which operates within space 64, control the introduction of high-pressure gas. Valve rod 62 extends through seal 66 (equipped with O-rings 68) out above the top plate 67 of the head portion 26 to be actuated as described below. In a similar fashion valve 76', spring '72 and valve rod 74 (in spacing 76) provide for the control of the exhaust of lowpressure gas in the system. Likewise seal 78 and O-rings 80correspond to seal 66 and O-rings 68. Other types of valves which. permit programmed flow of high-pressure gas into the system and low-pressure gas out may, of course, be used.

Vertical movement of the displacer and operation of the two valve rods is accomplished through shaft 82 which is supported by shaft supports 81. Shaft 82 is coupled to a motor (not shown) through a suitable coupling 83. On shaft 82 there are located the cams which control the valve operations and the eccentric which controls the displacer.

Displacer eccentric 84-, operating a Scotch yoke 86 provides the vertical motion for displacer rod 38. Scotch yoke 86 is pivotally mountedto a support 88 through pin 90 and is joined to displacer rod 38 through a clevis 92 and clevis pin 94. Other means to accomplish displacer motion for other than a sinusoidal type may be employed.

For example, a cam in place of the eccentric with suitable follower arm configuration (cam follower, spring, adjusting screw) would give the desired programmed motion to the displacer 36.

Cam 96, alrixed on shaft 82 by means of a collar 98,

controls the operation of the high-pressure inlet valve 58. In connection with cam 96 there is provided cam follower 104i, cam follower mounting 102 and adjustable engaging plate 104 which contacts the top of valve rod 62 forcingthe valve to close, its normal position being open by virtue of the force of spring 64 Likewise, the

valve controlling'the exhaustof low-pressure gas is operated through cam 106 aflixed to shaft 82 by collar 108, cam follower 110 (in a mounting 112) and the adjustable engaging plate 114.

In the operation of the apparatus illustrated in Figs. 1 and 2 the cycle consists of four steps which may be briefly outlined. During the first step the displacer remains substantially in its lowermost position which means that the volume of chamber41 is substantially zero. Cam 96 is in a position permitting valve 58 to be open, thus permitting high-pressure gas to enter by way of

passages

48 and 46 into the upper regenerator passage 43. There remains Within these passages 46 and 43 a quantity of low-pressure gas, as described below in step 4, and the high-pressure gas entering compresses this low-pressure gas generating heat in the process.

During step 2 the compressed gas passes downwardly through the regenerator 44 giving up its heat to form a vertical temperature gradient within the regenerator. Simultaneously, the displacer during this step is gradually raised to its uppermost position. the pressure in the system fairly constant, valve 58 is permitted to remain open during the step to supply additional high-pressure gas to the system. This is necessary inasmuch as the gas, in passing through the regenerator' and during its subsequent expansion with-in chamber 41, is.

cooled and densified.

During step 3 the displacer 36 remains substantially'in its uppermost position; valve 58 is closed and valve 70 In order to maintain.

opened. Additional cooling is obtained in theexpansion of the gas, and as it returns through the regenerator 44 it is warmed to substantially the temperature at which the gas entered through the head passage 43.

Finally, during step 4 the displacer is moved to its lowermost position while valve 58 remains closed and valve 72 remainsopen. At the end of this step there remains in

passages

43, 46 and 52 a residual'amount of low-pressure gas which is subsequently compressed in step 1 of the cycle as described above. These four steps then make up the cycle by which the apparatus of this invention produces refrigeration. Once the end 24 of cylinder 23 reaches its lowest temperature, it is necessary to supply only suflicient refrigeration to make up for the heat leak into the system.

In Figs. 5, 6, 7 and 8 there are illustrated three modifications in the design of the bottom portion of the displacer and cylinder. In Fig. 5 there is shown a displacer having a regenerator 44 of equal diameter throughout.

In Fig. 6 'the displacer is so modified that the very bottom portion has an expanded diameter thus providing a much narrower annular spacing 122 between the expanded portion of the displacer 120 and the cylinder wall'23. Above this expanded portion 120 the spacing 37 is greater. In Fig. 6 the displacer is also modified to the extent that the bottom expanded portion 120 is preferably constructed of a material such as copper or brass which has a high heat capacity. Further, the expanded portion 120 may contain a small heat exchanger 124.

In Fig." 6 there are also shown two modifications in the bottom part of the cylinder itself. For example, this bottom portion designated as end cap 12.6 may also be constructed of amaterial' such as copper or brass having a-'very'high heat capacity and the bottom edge 128 may be serrated in order'to furnish a larger area of heat transfer surface.

Since refrigeration is to he delivered through end cap 126 it is desirable that an efiicient heat exchange is accomplished between the cold gas in refrigeration chamber 41 and the bottom of cap 126. In an arrangement such as that of Fig. 5, there is a limited amount of surface for heat transfer and as a result the temperature of the gas in chamber 41 is always appreciably below that of the end of the i displacer. The displacer and cylinder of Fig. 6 achieves more efiicient refrigeration through the use of a heat transfer path between the refrigerating gas and the point of refrigeration delivery. This path consistsof heat. exchanger 124, expanded displacer section 120, a portion of cylinder wall 23 and end cap 126.

In Figs. 7 and 8 another modification of the displacer and cylinder is shown. In this modification there is an extension 146 from the passage leading from the regenerator and extending almost to the bottom of the cylind'er when the displacer is at its lowermost position. The bottom wall of the cylinder is also modified in that it has in its central portion a small annular-shaped heat exchanger 149 made of stacked annular rings of screening 150 (see Fig. 8) which form a well 152. The annularshapedheat exchanger in turn is surrounded by an annular ring 148 made of a material having a high heat capacity, such as copper or brass. This secondannular ring 148. forms the bottom portion of the cylinder 23 and corresponds to the bottom plate of an unmodified cylinder (Fig. 1)., The annular heat exchanger 149 is so designed that the passage extension 146 of the main regenerator 4-4 in the displacer 36 extends thereinto when the displacer is in its lowermost position, thus forcing, the cold gas leaving the main regenerator 44 through the annular heat exchanger 149 which in turn is in thermal:

contact with the annular ring 148 and hence also with the bottom 151 ofthe cylinder.

. to pass through the annular heat exchanger 149 returning through the regenerator 44, the refrigeration available By forcing the cold gas fer path established through heat exchanger 149, ring 148 and bottom 151.

The significance of the spacing 37 (Figs. 5 and 6) and the spacing 122 (Fig. 6) may be further discussed with reference to Figs. 9 and 10. In Fig. 9 there is shown diagrammatically the bottom portion of the cylinder and

displacer

23 and 36, respectively, wherein Fig. 9a represents the displacer at its top-most position and Fig. 9b represents it at its lowermost position. The displacer in the course of the refrigeration cycle moves through distance at indicated by the arrow in Fig. 9a. This is the length of the stroke of the displacer, and this stroke is preferably limited to about one-fifth or less of the length of the temperature gradient of the cylinder, i.e., of the length of the cylinder from the top of the regenerator to the bottom plate 24 (Fig. 1) of the cylinder. This displacer stroke will, of course, vary from one unit size to another. For example, in very small units (i.e., where the cylinder is not much greater than one-fourth inch in diameter) if the stroke is more than about one-third of the temperature gradient length, the efficiency of the cycle is materially reduced.

The spacing 37 shown in Fig. 9 between the displacer and the inner wall of the cylinder has been found to be important. In cases where the displacer 36 is permitted to thermally contact the internal walls of the cylinder 23 there occurs what may be designated motional heat leak. This can be explained with reference to the simplified drawings in Fig. 9. When the displacer 36 is in its uppermost position (Fig. 9a), the bottom portion of the displacer is colder than the walls of the cylinder; while when the displacer is in its lowermost position (Fig. 9b) the opposite condition exists, that is, the'displacer is Warmer than the walls of the cylinder. As the displacer moves up and down, it will be seen that if good thermal contact exists between the displacer and the cylinder walls heat will be transferred depending upon the position of the displacer. This means that the ideal temperature gradient which should exist over distance a cannot be maintained.

It has been found that motional heat leak can be materially lessened if the fit between the displacer and the cylinder is such that a spacing 37 exists. However, the advantage which is to be gained from this in the form of decreased motional heat leak must be balanced against two disadvantages. The first of these disadvantages is that the spacing 37 requires, of course, that additional gas be supplied to fill this space and the thermal losses incurred through the use of this additional gas increases as spacing 37 becomes larger. The second disadvantage is that although this spacing 37 can in itself serve as a regenerator (and ideally it should so serve) certain losses are incurred due to the inefiiciencies of this spacing as a regenerator. The situation is sketched in the graph in Fig. 10 which shows that the spacing 37 between the displacer and the cylinder is important, varying in dimension for each size of cylinder and displacer combination. The optimum spacing can be determined experimentally for each size apparatus.

In Fig. 6 the expanded portion 120 of the bottom part of the displacer materially reduces the width of this annular space 37 (designated in that figure as spacing 122) and hence there exists a much closer fit between the displacer and the cylinder walls. By thus limiting a good thermal contact between these two surfaces to the very bottom portion of the displacer, good heat tranfer to the bottom portion of the cylinder, e.g., 128, is obtained and better refrigeration is the result. Thus, Fig. 6 essentially optimizes spacing 37 while increasing the performance of the refrigeration apparatus precisely at the point at which refrigeration is being delivered.

Figs. 11 and12 illustrate two modifications of the refrigeration apparatus of this invention to devices requiring refrigeration. It will be seen in these figures that the use of therefrigeration apparatus of this invention in this application'is not in the form of an aggregation of components but that the refrigeration apparatus is' coordinated and integrated with the devices illustrated.

In Fig. 11 the refrigeration apparatus of this inven-" tion is applied to the cooling of an infrared detector."

The use of infrared detection has increased to a very marked degree over the past few years. tions it has replaced radar and it may replace it in other applications. The sensitivity of an infrared detector is materially enhanced if it can be maintained at a low 1 permits the detector to operate under optimum condiportion of the refrigeration apparatus passes and by the tions. In Fig. 11 the infrared detector represented generally at 130, with leads 131, is attached directly to the refrigeration chamber wall, i.e., to the bottom portion 24 of the cylinder 23. Thus, the refrigeration available in chamber 41 is used directly to cool the infrared detector. This, of course, is a material improvement over previous systems which require continuously cycling very cold or liquefied gases into a receptacle in contact with the infrared detector.

Around the cylinder 23 and the detector is placed a vacuum tight housing 132 which may be continuously evacuated through line 133 or may be evacuated and sealed. The evacuated area 135 is defined by the housing 132, by a head plate 134 through which the cylindrical window 136, which may be sapphire or other material which transmits wave lengths in the infrared region. The refrigeration apparatus is generally represented at 137' and consists of the apparatus such as illustrated in Figs. 1 and 2. Suitable inlet and

exhaust lines

50 and 56,

respectively, and necessary auxiliary leads such as 138" are also provided.

In Fig. 12 a second modification of the refrigeration apparatus of this invention is shown. This device permits maintaining a constant temperature and consists of a small cell 140 thermally bonded to the bottom wall 24 of the cylinder. Reservoir 142 is provided to supply gas by way of conduit 144 to cell 140. For example, if the bottom plate 24, by virtue of the refrigeration achieved in chamber 41, is reduced to about 50 K., nitrogen may be supplied to cell 140 and liquefied therein, thus maintaining the bottom wall of the cell at a constant temperature, i.e., 77.3 K. which is the liquefaction point of nitrogen.

From the description given above of the refrigeration apparatus of this invention, it will be seen that there is provided an extremely compact refrigeration system which may be made in extremely small sizes and which may moreover be integrated with equipment requiring refrigeration. The resulting apparatus is compact and extremely efiicient.

The apparatus of this invention need not, of course be of a small size but it does make possible for the first time an extremely small refrigeration device. sign of the regenerator, displacer and cylinder, the proper control of the valves and displacers, and the control of the spacing between the displacer and the cylinder housing all combine to achieve a remarkably high dc gree of efiiciency in a very small apparatus.

I claim:

1. Apparatus for attaining temperatures downto about 50 K., comprising cylinder means, displacer means vertically movable within said cylinder means thereby tov define a refrigeration chamber in the'bottom portionv of said cylinder means when said displacer is raised above its lowermost position, means for imparting vertical mo-- tion to said displacer within said cylinder thereby to vary the volume of said refrigeration chamber, passage. means located within the upper portion of said displacer,

In some applica-' The de-' thermal storage means comprising stacked fine wire screening formed of a material exhibiting a high heat capacity at temperatures below about 50 located said cylinder meauswhen said displacer is raised above i 7 its lowermost position, head passage means'located within the upper portion of said displacer, thermal storage means comprising stackedfine wire screening formed of a material exhibiting a high heat capacity at temperatures. below about 50 K. located within said displacer means and connecting said passage means and said refrigeration chamber, high-pressure fluid reservoir'means and low-pressure fluid reservoir means, first and second passage means connecting said high-pressure and lowpressure reservoirs with said head passage means, valve meansassociated with said first and second passage means for alternately introducing high-pressure fluid into and for withdrawing low-pressure fluid from said passage means, and means for imparting vertical motion to said displacer within said cylinder.

3. Apparatus in accordance with claim 2 further characterized in that the bottom portion of said cylinder means is formed of metal having a high heat capacity at temperatures below about 80 K. V V

4. Apparatus in accordance with claim 2 further characterized in that the bottom portion of said cylinder means is constructed of a metal having a high heat capacity' at temperatures below about 80,? K. and the internal surfaceis serrated whereby the heat transferring area is .materially increased. a

5. Apparatus for attaining temperatures down to about 50 K., comprising cylinder means, displacer means vertically movable within said cylinder means thereby to define a refrigeration chamber inthe bottom portion of said cylinder means when said displacer is raised above its lowermost position, headpassage means located within the upper portion of said displacer, thermal storage means comprising stacked fine wire screening located within said displacer means and connecting said headv passage means andsaid refrigeration chamber, high-pressure fluid reservoir means and low-pressure fluid reservoir means, first and second passage means connecting said high-pressure and low-pressure reservoirs with said head passage means, valve means associated with said first and second passage means'for alternately introducing high-pressure fluid into and tfor 'withdrawing low-pressure fluid from said head passage means, means "for imparting vertical motion to said displacer within said cylinder, and insulation means surrounding at least that portion of said cylinder means corresponding to the position occupied by the upper part of said passage when'said displacer is in its lowermost position.

6. Apparatus for attaining temperatures down to about 50 .K., comprising cylinder means, displacer means vertically' movable within said cylinder means thereby to define a refrigeration chamber in the bottom portion of said cylinder means when said displacer is raised above its lowermost position, head passage means located within the upper portion of said displacer, thermal storage means comprising stacked fine wire screening located within said displacer means and connecting said passage means and said refrigeration chamber, high-pressure fluid reservoir means and low-pressure fluid reservoir means, first and second passage means connecting said high-pressure and low-pressure reservoirs with said head passage means, valve means associated with said first and second passage means for alternately introducing high-pressure fluid into and" for" withdrawing low-pressure fluid from said head passage means, means for imparting vertical motion to said displacer within said cylinder, gas-tight housing means surrounding a substantial portion of said cylinder means and means for evacuating' said gas-tight housing means. V

7. Apparatus for attaining temperatures down to about 50 K., comprising cylindermeans, displacer means vertically movable within said cylinder means thereby to define a refrigeration chamber in the bottom portion of said cylinder means when said displacer is raised above its lowermost position, the diameter of at least a portion of said displacer means being sufliciently smaller than the inside diameter of said cylinder means to define an annular spacing therebetween thereby substantially eliminating heat transfer betweensaid displacer and said cylinder and providing thermal storage means within saidannular spacing, head passage means located within the upper portion of said displacer, thermal storage means comprising stacked fine wire screens located within said displacer means and connectingsaid passage means and said refrigeration chamber, valve means for alternately introducing high-pressure fluid into and for withdrawing low-pressure fluid from said head passage means, and means for imparting vertical motion to said displacer within said cylinder.

8. Apparatus for attaining temperatures down to about 50 K., comprising cylinder means, displacer means vertically movable within said cylinder means thereby to define a refrigeration chamberin the bottom portion of said cylinder .means. when. said displacer is raised above its lowermost positionfhead passage means located within the upper portion of said displacer, thermal storage means comprising stacked fine wire screens of a material having high heat capacity at below about 80 K. located within said displacer means and connecting said passage means and said refrigeration chamben gas-tight sealing means between the wall of said displacer means and the inside wall of said cylinder located inv a position above the connection between said head passage and said thermal storage means, said displacer and said cylinder means forming an annular space for at least'a portion of the length of said displacer below said sealing means, valve means for alternately introducing high-pressure fluid into and Withdrawing low-pressure fluid from said head passage means, and means for imparting vertical motion to said displacer within said cylinder.

9. Apparatus for attainingtemperatures down to about 50 K., comprising cylinder means, displacer means vertically movable within said'cylinder means thereby to define a refrigeration chamber in the bottom portion of said cylinder means when said displacer is raised above its lowermost position, head passage means located within the upper portion of said displacer, gas-tight sealing means between the wall of said displacer means and the inside wall of said cylinder located in the position corresponding to that occupied by said head passage means, thermal storage means located within said displacer and connecting. said head passage means and said refrigeration chamber, valve means for alternately introducing highpressure fluid into and for withdrawing said low-pressure fluid from said head passage means, and means for imparting vertical motion to said. displacer Within said cylinder, the diameter of a portion of said displacer directly below said sealing means being sufliciently smaller than the internal diameter of said cylinder means .to define therebetween an annular spacing of suflicient width to prevent heat transfer between said displacer and said cylinder, the diameter of the remaining portion of said displacer being enlarged to form an expanded displacer section whereby heat may be transferred between said cylinder walls and said expanded displacer section.

.10. Apparatus in accordance with claim 9 further characterized in that said expanded displacer section is constructed of a material exhibiting. high heat capacity-at temperatures" below about K.

11. Apparatus in accordance with claim 9 further characterized in that said expanded displacer section contains therein a heat exchanger comprising stacked fine wire screening of a material having a high heat capacity at temperatures below about 80 K.

12. Apparatus in accordance with claim 9 further characterized in that said expanded displacer section is constructed of a material exhibiting high heat capacity at temperatures below about 80 K. and contains therein a heat exchanger of stacked fine wire screens.

13. Apparatus for attaining temperatures down to about 50 K., comprising cylinder means, displacer means vertically movable within said cylinder means thereby to define a refrigeration chamber in the bottom portion of said cylinder means when said displacer is raised above its lowermost position, head passage means located within the upper portion of said displacer, gastight sealing means between the wall of said displacer means and the inside wall of said cylinder located in the position corresponding to that occupied by said head passage means, thermal storage means located within said displacer and connecting said head passage means and said refrigeration chamber, valve means for alternately introducing high-pressure fluid into and for withdrawing said low-pressure fluid from said head passage means, means for imparting vertical motion to said displacer within said cyilnder, gas-tight housing means surrounding a substantial portion of said cylinder, and means for evacuating said gas-tight housing means, the diameter of a portion of said displacer directly below said sealing means being sufliciently smaller than the internal diameter of said cylinder means to define therebetween an annular spacing of sufiicient width to prevent heat transfer between said displacer and said cylinder, the diameter of the remaining portion of said displacer being enlarged to form an expanded displacer section whereby heat may be transferred between said cylinder walls and said expanded displacer section.

14. Apparatus for attaining temperatures down to about 50 K., comprising cylinder means, annular heat exchange means bounded on the outside and bottom by a block of high heat capacity metal, said block forming the bottom of said cylinder means and said annular heat exchanger means defining a centrally located well within said cylinder means displacer means vertically movable within said cylinder means thereby to define a refrigeration chamber in the bottom portion of said cylinder means and integral with said well when said displacer is raised above its lowermost position, head passage means located within the upper portion of said displacer, thermal storage means comprising stacked fine wire screens located within said displacer means lower passage means leading from said thermal storage means and extending beyond said displacer and adapted to move vertically within said well, high-pressure fluid reservoir means and low-pressure fluid reservoir means, first and second passage means connecting said high-pressure and low-pressure reservoirs with said head passage means, valve means associated with said first and second passage means for alternately introducing high-pressure fluid into and for withdrawing low-pressure fluid from said passage means, and means for imparting vertical motion to said displacer within said cylinder.

15. Apparatus for attaining temperatures down to about 50 K. comprising cylinder means, displacer means vertically movable within said cylinder means thereby to define a refrigeration chamber in the bottom portion of said cylinder means when said displacer is raised above its lowermost position, head passage means located within the upper portion of said displacer, thermal storage means comprising stacked fine wire screens located within said displacer means and connecting said passage means and said refrigeration chamber, high-pressure fluid reservoir means and low-pressure fluid reservoir means, first and second passage means connecting said highpressure and low-pressure reservoirs with said heat passage means, valve means associated with said first and second passage means for alternately introducing highpressure fluid into and for withdrawing low-pressure fluid from said passage means, means for imparting vertical motion to said displacer within said cylinder, and a gas cell having a portion of its surface thermally bonded to said refrigeration chamber and adapted to contain a liquefied gas therein providing constant temperature refrigeration over the remaining unbonded surface of said gas cell.

16. Improved infrared detecting system, comprising an infrared detector thermally bonded to a refrigeration system capable of producing refrigeration down to about 50 K. at the point of thermal binding, said refrigeration system comprising cylinder means, displacer means vertically movable within said cylinder means thereby to define a refrigeration chamber and the bottom portion of said cylinder means when said displacer is raised above its lowermost position, passage means located within the upper portion of said displacer, thermal storage means located within said displacer means and connecting said passage means and said refrigeration chamber, valve means for alternately introducing high-pressure fluid into and for withdrawing low-pressure fluid from said passage means and means for imparting a vertical motion to said displacer within said cylinder.

17. An improved infrared detecting system, comprising cylinder means, displacer means vertically movable within said cylinder means thereby to define a refrigeration chamber in the bottom portion of said cylinder means when said displacer is raised above its lowermost position, head passage means located within the upper portion of said displacer, thermal storage means comprising stacked fine wire screen located within said displacer means and connecting said passage means and said refrigeration chamber, high-pressure fluid reservoir means and low-pressure fluid reservoir means, first and second passage means connecting said high-pressure and low-pressure reservoir means to said head passage, valve means associated with said first and second passage means for alternately introducing high-pressure fluid into and for withdrawing low-pressure fluid from said passage means by way of said first and second passage means, means for imparting vertical motion to said displacer within said cylinder, infrared detector means thermally bonded to said refrigeration chamber and gas-tight housing means surrounding a substantial portion of said cylinder means and equipped with a window transparent to infrared radiation located to permit radiation to strike said infrared detector, and means for evacuating said housing means.

18. Apparatus for attaining temperatures down to about 50 K., comprising cylinder means, displacer means of shorter length than said cylinder means and movable within said cylinder means thereby to define a refrigeration chamber at one end and a fluid inlet chamber at the other end of said cylinder means, means for imparting motion to said displacer within said cylinder thereby to vary the volumes of said refrigeration chamber and said fluid inlet chamber, thermal storage means comprising stacked fine wire screening formed of a material exhibiting a high heat capacity at temperatures below about 50 K. located within the central portion of said displacer and connecting said fluid inlet chamber and said refrigeration chamber, and valve means for alternately introducing high-pressure fluid into and for withdrawing low-pressure fluid from said fluid inlet chamber.

Kohler Oct. 21, 1958 Newton Oct. 6, 1959