US2909908A - Miniature refrigeration device - Google Patents

Description

Oct. 27, 1959 A. PAsTUHov ET AL 2,909,908

MINIATURE REFRIGERATION DEVICE Filed Nov. 6, 1956 5 Sheets-Sheet 1 HRG/15 /N -l- Axas PAST Hov FRANK J. mMmf/mm; v

Oct. 27, 1959 A. PAsTuHov ETAL 2,909,908

MINIATURE REFRIGEEATION DEVICE Filed Nov. 6, 1956 5 Sheets-Sheet 2 I 2o l 4a 'l A2645 our 7/ IFI/'54 INVENTORS ALEXIS PAsTu H By FQAMK J. ZIMMEEM Oct. 27, 1959 A. PAsTuHov Erm.- 2,909,908

MINIATURE REFRIGERATION DEVICE Filed Nov. 6, 1956 5 Sheets-Sheet 3 HR GAS M/ /T i IWW nl; T. N

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INVENTORS `ALEXISv PAsTu Hav BY FQANK J. ZIMHEKMANN rlTl lll/ll l//l/l//ll/ 0d 27 1959 A. PIIssrul-iovv I-:TAL 2,909,908

MINIATURE REFRIGERAIION' DEVICE JNIGNTORS ALEXIS PASTUHOV FRANK J.ZIMMEMMI QM//Zm y A. 'PASTUHOV ET Al.

MINIATURE REFRIGERATION DEVICE oct. 27, 1959 5 Sheets-Sheet 5 Filed Nov. 6, 1956 FIG 6 JNVENTORS ALDUS, PASTUHOV 2,909,908 l MINIATURE REFRIGERATION DEVICE Application November 6, 1956, Serial No. 620,676 s Grams. (ci. ca -222) This invention relates to miniature refrigeration devices utilizing the Joule-Thomson effect, which are especially useful in providing intense cooling of small surfaces or areas such as those of small energy-detecting units.

The sensitivity of some types of energy-detecting units, such as those used for detecting infra-red or heat radiation, is increased considerably by cooling the detecting means to very low temperatures. The purpose of this invention is to provide a simple, compact device for cooling the detector means to very low temperatures, which device can be easily assembled, disassembled, and cleaned, can be simply manufactured, and occupies a minimum of space.

Briefly stated, the device of this invention comprises a tubular heat-exchanger having two concentric thermally f bonded spiral passageways, with lmeans at one end for admitting high-pressure gas into the inner passageway, an expansion valve at the other end for expanding the high pressure gas emerging from the inner passageway and directing it into the outer passageway, wherein it flows in out-of-contact counter-current heat exchange relation with the incoming high-pressure gas, and means at the inst-mentioned end for removing the outgoing lowpressure gas from the outer passageway. This low-pressure gas is compressed in a compressor, cooled in an aftercooler, passed through oil filters vand separators to whatever extent necessary, and Vreturned -to the highpressure side of the device. Thefaforesaid tubular heat exchanger is surrounded at its`cold end and throughout most of its length with a Dewar, in which is adetector such as an infrared detector lcell located adjacent the coldest end of the device. The Dewar is providedwith a window arranged to admit radiation to the detector cell, and leads are provided from the cell out through the walls of the Dewar to a conventional measuring device.

The tubular heat-exchanger described above may -also be made with more than one pair -of concentric spiral passageways, so that lower temperatures can be'attained by using two or more gases.

The device of this invention canbe used generallyfor providing low temperatures at desired points, for example in the cooling of units employed in the detection of infrared or heat radiation. Such units socooled provide a passive means for such detection-ie. no radiation is emittedand may be used for example 'in tire detection by placing one or more of'them in vlocations-wifiere fire might occur and connecting them through the aforesaid leads to an alarm associated with the measuring device.

United States Patent O fice This invention will now be described in moredetail in connection with the accompanying drawings, which are to be considered illustrative rathery than? limiting, and in which: f

Fig. 1 represents a cross-sectionalview of'afpreferred form of the heat-exchanger device; Figs. 2 and 3 represent cross-sectional viewsofmodilied forms of the device shown in Fig. 1;

body member 30 firmly iixed thereto;

" sageway formed by 2,909,908 Patented Oct. 27, 1959 Fig. 4 is a View, partly in section, of the heat-exchanger device associated with a Dewar and a detector cell;

Fig. 5 is a flow diagram showing the arrangement for providing the compressed refrigerating gas to the heatexchanger device; and

Fig. 6 represents a cross-sectional view of a modied form of the heat-exchanger device wherein a second pair of passageways is provided to increase the cooling effect.

The device shown in Fig. l is made up of a central rod 10 provided with spiral threads 12 throughout its length, a cylindrical tube 14 of heat-conductive metal tting against the apexes of threads 12 and provided with a spirally-wound strip 16 of heat-conductive metal thermally bonded to tube 14, and an outside cylindrical tube 18 surrounding this assembly and close to strip 16. The tube 14 is made so as to t tightly against threads 12 when the device is in operation; hence the gases pass along the spiral channels provided by threads 12 and strip 16, and do not by-pass them. When the device is warmed to about room temperature, the tit is suiiiciently loose to permit ready assembly and disassembly.

Tube 14 is supported by entrance conduit 2d attached to one end thereof, and is provided at the other end with a small block 22 having therethrough an oriiice 24. Cooperating with orifice 24 is needle 26 mounted on end 23 of tube 18, thereby providing an expansion valve, in the form of a needle valve. At the other end of tube 1S is this member and conduit 20 are provided with cooperating threads 32. Gases emerging from travel around spiral strip 16 escape into space 34. Skirt 36 is attached in gas-tight relation to `conduit 20; O-ring seal 38 positioned in body member 30 provides a gas-tight seal between member 30 and skirt 36. The emerging Vgases pass from space 34 out through exit 40, which is in gas-tight relation with skirt 36, whiletheihigh-pressure gases enter the device through opening 42 in conduit 20.

The device of Fig. l is assembled by inserting threaded rod 10 into finned tube 14. Insertion of removal of this rod can be facilitated by using a wrench inserted in hole 44 in the top of rod 10, which is conveniently inserted and removed with a turning or threading motion'rather than straight in or out. vMember 301is then screwedV into conduit 20 via threads 32, thereby moving skirt 36 down tightlyover O-ring seal 38. The distance to which member 30 is screwed onto conduit 20 determines the distance to which needle 26 moves into orifice 24, and hence the needle valve setting.

12. The expanded gas then passes into space 34 and thence out of the device through pipe 40.

In operation, there is sometimes a tendency for deposits nfrom the incoming highpressure gaseous stream to form in, and plug, the threads 12, particularly in the coldest part of the length of the threads. To assist in correcting this ditliculty, the lower threads on rod 10 may be made deeper and'further apart, thus providing channels ofA larger cross-sectional area in the spiral pasthe threads on rod`10. Such an arrangement is indicated in Fig. 2, where the deeper and -further-apart threads are indicated bythe numeral 1 3,

other' `parts being the same aslike-numbered parts in The arrangement shown in Fig. 3 is functionally like that in Fig. 1, except that the Fig. 3 arrangement provides a needle valve setting which is less affected by thermal contraction than that in Fig. 1. However, the Fig. 1 arrangement is satisfactory for most operations, whereas in the Fig. 3 arrangement the amount of metal `at the cold end is larger than is sometimes desired.

The device shown in Fig. 3 is provided Vwith rod 10, threads 12 thereon, tube 14, spiral strip 16, and tube 18, as in Fig. 1. At the cold end of tube V14 is attached block 50, having openings 52, orifice 53 communicating therewith, and threads 54 which fit like threads on needle 56 which is mounted on end 28 of tube 18. Collars 55 prevent needle 56 from jamming in orifice 53. At the warm end of the device is head block 58 having inlet port 60 and outlet 62 leading from chamber 64 into which the low-pressure gas moving along the spirals 16 discharges. O-ring 66, positioned in annular channel member 67 which is fixed to tube 18, provides a fiuidtight seal for chamber 64. The warm end of tube 14 is fixed to head block 58.

The device of Fig. 3 is assembled by first placing rod in tube 14, as described for Fig. 1. Then tube 18 is slipped over the spirals of tube 14 (from the cold end) until threads 54 meet; then tube 18 is screwed on a sufficient distance to give the proper needle-valve setting, i.e. until needle 56 projects far enough into orifice 53. In the assembly, tube 14 is pushed a suitable distance into annular space 59 and may then be soldered or otherwise fixed in position relative to block 58, as indicated above.

The arrangement of the above-described refrigerator unit with a Dewar and a detector cell is shown in Fig. 4. Specifically illustrated is the device of Fig. 1, with outside tube 18, entrance conduit 20, skirt 36, pipe 40, and end 28 of tube 18. A Dewar 70 is provided, surrounding the cold end of tube 18 and the major part of the length thereof. This Dewar has outer wall 71, inner wall 73, and evacuated space 75 therebetween, and is provided with a fluid-tight seal 72 against tube 18, and evacuated. A detector cell 74 is positioned adjacent the outer face of end 28 with the end of inner Dewar wall 73 therebetween, and joined by leads 76 passing through seals 78 in the Dewar wall to a suitable detecting, measuring, or other identifying device 80 which receives the signal from cell 74. Opposite cell 74 is a window 82 in the Dewar wall, made of special glass or other material which permits passage of the radiation to be detected by cell 74.

The assembly shown in Fig. 4 is mounted in any desired fashion, so that the detector cell and its window will face the radiation to be detected. Device 80 may be located at a relatively remote distance and may receive leads from several of these assemblies. Thus, in a fire detecting system, several of the units shown in Fig. 4

.may be mounted in several places with windows 82 facing various strategic spots, and all these units may feed into one detecting device 80 which may be equipped with signal lights, alarm means, or otherwise, including indicia corresponding to the location of each detecting unit.

Any suitable arrangement for providing a supply of compressed gas to the refrigerating device of Figs. 1-'3 may be employed, such as that shown in Fig. 5. As there shown, compressor 90 compresses the gas (e.g. air or nitrogen) which is used for refrigeration; the heat of compression is largely removed from the gas in an aftercooler associated with the compressor 90, in conventional fashion, and the cooled compressed gas is then passed through appropriate purifying means such as oil separator 94 and oil fume filter 96, to remove vas far as possible oils, hydrocarbons, and like impurities which if not thus removed would condense in and block the passageways in the refrigerating device. The compressed purified gas then passes to the refrigerating device, here represented by the numeral 98, wherein its course is as described in connection with Fig. 1. and after expansion therein passes through line 99 back to compressor 90.

Gas holder 100, or other source of gas for refrigeration, is provided, with line 102 controlled by valve 104 leading into the system through line 105. Original and make-up gas is supplied to the system by opening valve 104. To avoid excessive pressure build-up in the system, e.g., when the refrigeration requirements of unit 98 are relatively low, a relief valve 106 is provided leading from a point in the system, e.g. from separator 94, through line 108 back to compressor 90, connecting also through line with surge tank 110.

' The devices hereinabove described are suitable for providing for example liquid air or liquid nitrogen temperatures at the Vcold end of the refrigerating device. These are very effective for most detecting purposes. However, even lower temperatures, such as those of liquid hydrogen, or even liquid helium, can be produced by providing a plurality of sets of channels for refrigerant gases.. A typical arrangement for such purpose is shown in Fig. 6.

Four concentric channels, 110, 112, 114 and 116, are shown in Fig. 6. Channels 110, 112, and 116 are in the form of spiral threads, like threads 12 of Fig. l, while channel 114 is formed with a spirally-wound strip like strip 16 of Fig. l. At the inner end of each pair of channels is a needle valve or equivalent expansion valve 118, 120. High pressure nitrogen or other refrigerant gas is admitted through a suitable opening 122, Hows spirally-along the threads of channel 110, expands and cools at needle valve 118, and returns through the threads of channel 112, in counter-current heat-exchange relation with inowing gas in channel 110, thereby cooling the latter. This expanded gas is then exhausted through opening 124. High pressure hydrogen or other lowerboiling-point gas is admitted through opening 126, flows spirally along the turns of passage 114, expands and cools at needle valve 120, and returns through the threads of channel 116, in counter-current heat-exchange relation with incoming gas in channel 114, thereby cooling the latter. The combined cooling effect of the gas expansion in the outer channels 110 and 112 with that in the inner channels 114 and 116 provides ultra-low temperatures of the device at the coldest region, i.e. around needle valve 120.V Inasmuch as the temperature reached by the expanding nitrogen is higher than that of the other lowerboiling-point gas, the nitrogen passage does not extend the full length of the passage of the other gas, but stops short of the end thereof.

The arrangement of Fig. 6 may be modified if desired to provide that the nitrogen channels 110, 112 are on the inside and the longer channels 114, 116 for the lowerboiling-point gas are on the outside.

Openings 122, 124, 126 and 128 of Fig. 6 are shown merely diagrammatically; they may be connected in any suitable manner with lines leading to and from the compressors for the refrigerant gases. A separate compressor system, such as that shown in Fig. 5, is used for each separate gas.

The Dewar 70 (Fig. 4) is fitted around the refrigerating unit shown in Fig. 6 in the same way as illustrated in Fig. 4. The detector cell 74 is attached to the refrigerating Vunit adjacent the coldest region thereof, i.e. adjacent needle valve (Fig. 6).

In a typical arrangement as shown in Fig. 1, we may for example introduce high-pressure gas at a rate of under 1.0 s.c.f.m. (say 0.4 to 0.8 s.c.f.m.), and achievea cooling of the cold end to about 300 F. in about 10 minutes. The system will run for several hours without plugging of'thechannels, provided that an effective purification system for the gas isused. Plugging occurs 'more slowly as the rate of 'gas introduction is lowered; thus, we have successfully operated the device for over 8 hours` with a fow rate of about 0.2 s.c.f.m. and an eflicient purification system. When pluggingoccurs, the obstruction may be removed by bringing the heat exchanger Vunit up Yto room temperature and passing clean dry gas through it, preferably after opening the needle valve as by screwing entrance conduit 20 part way out of body member 30 (Fig. 1).

Various modifications in the apparatus of this invention, within the scope of the appended claims, will be evident to those skilled in this art. For example, the various channels for high and low pressure gas may be made either in screw-thread form (e.g. threads 12, Fig. l), or of spirally edge-wound ribbon (eg. spirals 16, Fig. 1). The arrangements shown in Figs. 1, 2, 3, and 6 are, however, the most convenient ones from the point of view of ease of manufacture and of assembly and disassembly. Also, if it should be desired to use spiral strips instead of screw threads for the inner channel of Fig. 2, the spirals would be wound further apart throughout the area there shown to be occupied by threads 13.

We claim:

1. A refrigerating device comprising a heat exchanger including means forming two concentric paths in heat exchange relation with each other along substantially their entire lengths, each of said paths being in the form of a spiral passageway, entrance means at one end of said heat exchanger for introducing a gas at high pressure into the inner of said two paths, exit means at said end for removing said gas, after the expansion thereof, from the outer of said two paths, passage means at the other end of said heat exchanger for leading said gas from said inner path to said outer path, said passage means including an expansion valve for expanding said gas, the spiral passageway of one of said paths being movable longitudinally with respect to the spiral passageway of the other of said paths, and means cooperating with said pathforming means to elect such relative movement and thereby to regulate the setting of said expansion valve.

2. A refrigerating device according to claim 1, further characterized in that the spiral passageway of the inner of said two paths is of larger cross-sectional area in its coldest region.

3. A refrigeration device having a heat exchanger assembly comprising a centrally disposed, externally spirally threaded rod, an inner cylindrical heat-conductive tube tting against the apexes of the threads of said rod and with said threads defining a first channel, a heat-conductive metallic strip spirally wound around and thermally bonded to said tube, an outer cylindrical tube closely surrounding said strip and with said strip defining a second channel; gas inlet means and gas outlet means positioned at one end of said heat exchanger assembly and separated from each other by said inner tube, an expansion valve positioned at the other end of said heat exchanger assembly and comprising an orifice and a needle, said expansion valve providing an adjustable passageway between said channels whereby the flow of gas between said channels is controlled, said orifice communicating with, and in xed position with respect to, said iirst channel, said needle being in xed position with respect to said second channel, and means for effecting relative movement between said lneedle and said orifice whereby to open or close the latter, said last-named means comprising a threaded member attached in xed position with respect to said outer tube.

4. A refrigeration device according to claim 3, further characterized in that said threaded member cooperates with a second threaded member which is in xed position with respect to said gas outlet means.

5. A refrigeration device according to claim 3, further characterized in that said rst channel is of larger crosssectional area adjacent said other end of said heat exchanger.

6. A refrigeration device according to claim 3. further characterized in that said heat exchanger assembly is in heat exchange relation throughout a substantial portion of its length with a second heat exchanger, said latter exchanger comprising two spiral passageways arranged for countercurrent ow of a gaseous fluid and an expansion valve providing a passage for and arranged to expand, and thereby cool, said gaseous uid in passing from one of said spiral passageways to the other.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Article: Attenuated Superconductors, by Andrews et al., published in Review of Scientific Instruments, vol. 13, July 1942, pages 281-292.

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