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United States Patent [1113,59U,597 Inventor David Neil Campbell [56] References {Cited} Redditch, England UNITED STATES PATENTS [21 1 Appl No

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United States Patent [1113,59U,597 Inventor David Neil Campbell [56] References {Cited} Redditch, England UNITED STATES PATENTS [21 1 Appl No United States Patent [1113,59U,597 Inventor David Neil Campbell [56] References {Cited} Redditch, England UNITED STATES PATENTS [21 1 Appl No. 847,917 [22] Filed Aug. 6, 1969 3,431,750 3/1969 Lefranc ..................... .. 62/514 [451 Patented July/.6, 1971 Primary Examiner—-Meyer Perlin [73] Assignee The Hymatic Engineering Company Attorney—-Watson, Cole, Grindle & Watson Limited Redditch, England (32] Priority Aug. 6, 1968 ABSTRACT: The second stage in a miniature cryogenic two [33] Great Britain stage cooler, working on the Joule-Thomson principle, is sup [31] 37477/68 plied with gaseous refrigerant which passes from a supply under pressure through one path of a tubular heat exchanger, _ to an expansion nozzle, after which the expanded gas returns [541 COOLING APPARATUS EMPLOYING THE J OULE through‘the other path‘of the heat exchanger to cool the in THOMSON EFFECT ‘ coming second stage gas. In the ?rst stage, a precooling 6 Claims, 1 Drawing Fig. refrigerant in liquid form is supplied to a metering nozzle which, havingno heat exchanger, is accommodated within the [52] US. Cl. ..................................................... .. 62/514 heat exchanger of the second stage, and this refrigerant [51] Int. Cl ........... .. .. F25b 19/00 evaporates to precool the second stage refrigerant. The nozzle [50] Field of Search . .. 62/222 of each stage is automatically controlled to vary the flow of 5 14, 467 refrigerant in accordance with the demand for cooling. \ O 0 Q 59 ‘ Q 54 Q ‘ o 62 72‘ s1 , I o 76- ,. ‘ 53 - 7 7 _ Q 9 75 O 10 O O O 13 0 11 9 25 Q Q Q I 0 Q . 72 ‘9 o O , 74 O 24 O Q Q C) Q 0 ~ 0 32 g 7 O " 6 33 - l 29 35 '_ 34 s ‘ 30 22 , 23 t 5 26 , "27 . ‘ ,39 j 37 ‘=——"_~ i PATENTEU JUL-6 {9n 3,590,597 // 090UQQQQQOQ / .i?gw:, 8 29 @QQOQQQQQQQQQ. 30 37 IN VE NTOR DAxnb NEH. CAMPBELL BY 424m ATTORNEY 3,590,597 ll 2 generally at atmospheric pressure, and in this case there can COOLING APPARATUS EMPLOYING THE JOlUlLlE not be any variation of temperature so long as the liquid is in THOMSON iElFh‘lElCT equilibrium with its vapor. Thus in the preferred arrangements This invention relates to cooling apparatus of the type em~ described, the control is not directly in accordance with the ploying the Joule-Thomson effect, that is to say in which cool temperature of the refrigerant but in accordance with the level ing is produced by expansion, through a nozzle, of a of the liquid refrigerant which comes into contact with a sen refrigerant in gaseous form under pressure, which before ex sor as the level rises, and controls the temperature of the sen pansion at the nozzle is at a temperature below its inversion temperature. ’ sor. Other arrangements may be employed in which the con The invention is particularly, though not exclusively, con trol is in accordance with some other or intermediate function cerned with such coolers which are of miniature size, for ex~ depending upon the supply and demand for cooling, for exam ample for cooling infrared detectors to the temperature of ple the sensor may have an extended tail affording a path for liquid nitrogen. In a typical construction the complete cooler the ?ow of heat to the liquid refrigerant, the length of which is largely situated within a cylindrical heat exchanger having a path varies with the level of refrigerant. Again the sensor may length of between 2 and 3 inches and a diameter of about a be in heat exchange relationship with parts of the apparatus third of an inch and wound with a helical coil of ?nned tubing above the pool of liquid refrigerant so that its temperature will of which the diameter over the fins is less than one-twentieth depend partly upon the level of liquid refrigerant and partly on of an inch. In general it is a requirement not only that the the temperature of the vapor escaping from the nozzle. cooler itself should be of extremely small size, but in addition In one arrangement in accordance with the present inven that the supply of compressed refrigerant required should also 20 tion the second stage expansion nozzle is arranged and con be as small and light as possible. trolled as described above and includes a needle valve con It is known that each refrigerant has a temperature, known trolled by a bellows the pressure upon which is determined by as its inversion temperature, at which no cooling is produced a sensor comprising a vapor bulb with an extended tail extend ing down to the pool of liquefied refrigerant. The ?rst stage is by the Joule-Thomson e?ect, that is to say by expanding the 25 refrigerant gas through an expansion nozzle. Above the inver generally similar but in this case the sensor bulb is secured to a sion temperature such expansion actually produces a rise of curved plate ?tting within the body of the heat exchanger at temperature, and it is only below it that it produces a cooling about the level of the metering nozzle so as to respond effect. Moreover at temperatures only slightly below the in primarily to the temperature of the heat exchanger at that part version temperature the cooling effect is correspondingly of the apparatus. Just below the metering nozzle a cup is slight and if a substantial cooling effect is required the expan secured to the inside of the body of the heat exchanger to col sion must be carried out from a temperature substantially lect liquid refrigerant formed by the first stage refrigerant, and below the inversion temperature. at the corresponding part of the length of the heat exchanger Thus in the case of Joule-Thomson coolers employing the helical finned tube is not finned but is soldered to the outer refrigerants with an inversion temperature below atmospheric 35 surface of the heat exchanger tube so‘ as to transmit heat from temperature it is essential to employ more than one stage, so the second stage refrigerant within it to the liqui?ed first stage as to precool the refrigerant before expansion, but even in the refrigerant inpthe cup within the body. case of refrigerants, such as air or nitrogen, having an inver The invention may be put into practice in various ways but sion temperature substantially above atmospheric tempera one specific embodiment will be described by way of example tures, the efficiency can be considerably improved by employ 40 with reference to the accompanying drawing which shows a ing a precooling stage. This, however, has generally not been two-stage cooling device. done in coolers of the type with which the invention is con In this embodiment the invention is applied to a two-stage cerned since the space available has not been suf?cient to ac cooler of miniature size, perhaps 3 inches in length and one commodate a precooling stage. third inch in diameter comprising two stages. The ?rst, According to the present invention cooling apparatus in 45 precooling, stage is supplied with Freon which is stored in cludes two stages in the second of which a second stage liquid form, under pressure but at atmospheric temperature, refrigerant from a supply in gaseous form is passed through and is admitted past a metering ori?ce to a space where it can one path of a heat exchanger, expanded through an expansion expand to atmospheric pressure, thereby effecting precooling. nozzle and passed back through the other path of the heat It operates with nitrogen in gaseous form under pressure exchanger to cool the incoming second stage refrigerant, and which is fed through the inner path of a helical tube heat a precooling ?rst stage in which a precooling refrigerant is exchanger to an expansion nozzle where it expands and cools supplied in liquid form under pressure through a metering due to the Joule-Thomson effect, producing a pool of liquid nozzle to a space at reduced pressure where it evaporates to nitrogen, while the remaining gas escapes by the outer path of cool the second stage refrigerant before the latter passes the heat exchanger, i.e. past the outside of the helical ?nned through the heat exchanger, the effective area of the nozzle of 55 tube, cooling the incoming nitrogen. each stage being automatically controlled in accordance with The cooling apparatus is of elongated form, and for pur a parameter depending upon the relationship between cooling poses of description it will be assumed that it is placed verti_ supplied and cooling demanded at that stage. cally with its cold end at the bottom. The apparatus includes In one form of the invention the apparatus is generally of tu an annular heat exchanger Mi comprising a tubular body 11 bular form, the heat exchanger comprising a ?nned tube around which is helically wound a ?nned coiled tube 12. An wound to helical form with the second stage refrigerant ?ow external coaxial tube 13, which may be the inner wall of a ing through it in one direction and past its outside in the op Dewar ?ask, is located around the ?nned coil and the space 14 posite direction, the second stage expansion nozzle being at between the body and the external tube provides a path for ex the cold end of the heat exchanger while the ?rst stage meter 65 haust gas ?owing past the fins to cool the incoming high-pres ing nozzle is enclosed within its warm end. sure working fluid within the helical ‘tube. The lower end of In the above-noted cooling apparatus designed, for exam~ the external tube is closed to provide a reservoir (not shown) ple, for cooling infrared detectors to the temperature of liquid in which the liquid working ?uid can accumulate.
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