Abstract:
The present invention discloses multi-component gas mixtures adapted to provide condensed phase cryogenic refrigerants with normal boiling points below about 80° K. for cooling sensor device components. Exemplary gas mixtures generally include 19-40% Ar and 20.1-80.5% Ne. Open-loop Joule-Thomson systems in accordance with the present invention may be suitably adapted (with varying relative mass ratios of cryogenic gas mixtures) for cooling sensor devices to temperatures between 27° K. (100% Neon) and about 80° K. (0% Neon).

Description:
RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 11/374,806 filed on Mar. 13, 2006 by Lawrence D. Sobel in the United States Patent and Trademark Office. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention generally concerns refrigerant systems; and more particularly, representative and exemplary embodiments of the present invention generally relate to the cooling of sensor devices with mixed gas cooling systems.  
       BACKGROUND OF INVENTION  
       [0003]     Freon-type pure gases have been generally used in closed-cycle refrigeration systems operating within household and commercial refrigeration temperature regimes. More recently, mixed gases (frequently utilizing Freon as one of the constituent components) have also been employed. Such consumer-level refrigeration systems typically employ equipment that is suitably adapted to operate within desired pressure ratios and temperature ranges.  
         [0004]     When operating cooling systems in cryogenic temperature regimes, condensed phase refrigerants having normal boiling point temperatures below 120° K. (e.g., nitrogen, helium, methane, and the like) have been used. These cryogenic gases have ordinarily required the use of high pressure gas systems involving multi-stage compressors or high pressure oil-less compressors. Examples of these systems include pulse tube cryo-coolers and stirling cryo-coolers. These types of active refrigeration systems have become more expensive to manufacture and operate, and require frequent maintenance.  
         [0005]     In order to provide cryogenic systems which are less costly and more efficient, there have been mixed gas refrigerants proposed for use within cryogenic temperature ranges. Many such mixed gas systems have been proposed. These typically combine conventional and well-known cryogenic refrigerants with various hydrocarbons, including methane, ethane, propane, and isobutene, in various combinations.  
         [0006]     U.S. Pat. No. 5,441,658 to Boyarsky et al. discloses mixed gas refrigerants consisting of mixtures of 30-50% by molar weight of nitrogen combined with at least some, but less than 20% methane by mole fraction, at least 30% propane by mole fraction, and enough ethane or ethylene to balance the mixture. Russian Patent No. 627,154 suggests a mixed gas refrigerant combining nitrogen with various hydrocarbons (e.g., 25-40% nitrogen by molar weight, 20-35% methane by molar weight, 15-35% ethane by molar weight, and 25-45% propane by molar weight. Another reference which has suggested a combination of the same ingredients, but in different proportions, is U.K. Patent No. 1,336,892.  
         [0007]     There are numerous combinations of conventional cryogenic refrigerants. Existing systems, however, are generally only suitable for operation above about 80° K.  
         [0008]     Conventional cryogenic fluids with normal boiling points above about 80° K. generally include: N 2 , air, CO, F, Ar, O 2 , CH 4 , Kr, R14, O 3 , Xe, C 2 H 4 , BF 3 , N 2 O, C 2 H 6 , HCl, C 2 H 2 , CHF 3 , 1,1-C 2 H 2 F 2 , R13, CO 2 , Rn, C 3 H 8 , C 4 H 10 , and C 5 H 12 . Those with normal boiling points below about 27° K. generally include  3 He,  4 He, H 2 ,  2 H,  3 H, and Ne. For cryogenic applications between 27° K and 80° K, none of these pure compounds provide a suitable condensed phase normal boiling point temperature.  
         [0009]     Consequently, only active refrigeration systems, such as pulse tube cyro-coolers and stirling cryo-coolers, are currently in use for cryogenic applications below 80° K. Thus, there is a need for more reliable and less hardware-dependent systems for cryogenic applications below 80° K.  
       SUMMARY OF THE INVENTION  
       [0010]     In various representative aspects, the present invention discloses multi-component mixed gas systems suitably adapted to provide condensed phase cryogenic refrigerants with normal boiling points below 80° K. for cooling sensor devices. Exemplary gas mixture components generally include 19-40% argon and 20.1-80.5% neon. The disclosed multi-component gas mixture systems may be suitably adapted (with varying component mass ratios) for operation in sensor cooling systems between about 27° K. (100% Neon) and about 80° K. (0% Neon).  
         [0011]     Advantages of the present invention will be set forth in the Detailed Description which follows and may be apparent from the Detailed Description or may be learned by practice of exemplary embodiments of the invention. Still other advantages of the invention may be realized by means of any of the instrumentalities, methods or combinations particularly pointed out in the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Representative elements, operational features, applications and/or advantages of the present invention reside inter alia in the details of construction and operation as more fully hereafter depicted, described and claimed—reference being made to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. Other elements, operational features, applications and/or advantages will become apparent in light of certain exemplary embodiments recited in the detailed description, wherein:  
         [0013]      FIG. 1  representatively illustrates a schematic of an open-loop Joule-Thomson cooling system in accordance with an exemplary embodiment of the present invention; and  
         [0014]      FIG. 2  representatively illustrates a temperature/entropy diagram for an open-loop Joule-Thomson cooling system in accordance with an exemplary embodiment of the present invention. 
     
    
       [0015]     Elements in the Figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the Figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention. Furthermore, the terms “first”, “second”, and the like herein, if any, are used inter alia for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. Moreover, the terms “front”, “back”, “top”, “bottom”, “over”, “under”, “forward”, “aft”, and the like in the Description and/or in the claims, if any, are generally employed for descriptive purposes and not necessarily for comprehensively describing exclusive relative position. Any of the preceding terms so used may be interchanged under appropriate circumstances such that various embodiments of the invention described herein, for example, may be capable of operation in other configurations and/or orientations than those explicitly illustrated or otherwise described.  
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0016]     The following representative descriptions of the present invention generally relate to exemplary embodiments and the inventor&#39;s conception of the best mode, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description is intended to provide convenient illustrations for implementing various embodiments of the invention. As will become apparent, changes may be made in the function and/or arrangement of any of the elements described in the disclosed exemplary embodiments without departing from the spirit and scope of the invention.  
         [0017]     A detailed description of a representative mixed gas refrigerant cooling system is provided as a specific enabling disclosure that may be generalized to any operational embodiment of the disclosed invention.  
         [0018]     The present invention may be described herein in terms of multi-component gas mixtures and Joule-Thomson systems. Multi-component gas mixtures, according to various aspects of the present invention, generally comprise Argon (Ar) and Neon (Ne). It should be appreciated that in accordance with various aspects of the present invention, Ar and Ne comprise inversion temperatures suitable for operation in Joule-Thomson systems. In accordance with various aspects of the present invention, Ar may comprise an inversion temperature of approximately 723° K., and Ne may comprise an inversion temperature of approximately 231° K.  
         [0019]     In a representative embodiment, approximately 19% Ar by molar weight may be combined and/or balanced with Ne. The resulting multi-component mixture demonstrates a normal boiling point temperature of approximately 49° K.  
         [0020]     In another representative embodiment, approximately 40% by molar weight Ar may be combined and/or balanced with Ne. The resulting multi-component mixture demonstrates a normal boiling point temperature of approximately 60° K.  
         [0021]     Multi-component gas mixtures in accordance with various aspects of the present invention may be implemented as refrigerants in sensor cooling systems. It should be appreciated that when implemented in sensor cooling systems, multi-component gas mixtures may generally be employed as refrigerants at temperatures below the inversion temperatures of the discrete gaseous components taken by themselves.  
         [0022]     Sensor cooling systems in accordance with various aspects of the present invention may include Joule-Thomson cooling systems, adiabatic expansion systems and/or the like. Referring now to  FIG. 1 , it will be appreciated that a representative sensor cooling system  100 , in accordance with various aspects of the present invention, may comprise conventional gas vessel  105 , counter-flow heat exchanger  110 , isenthalpic expansion valve  115  and reservoir  120 .  
         [0023]     It will be appreciated that gas vessel  105 , in accordance with various aspects of the present invention, may comprise any suitable material for housing the multi-component mixture. Suitable materials may include, for example: glass, metal, polymers, plastics, ceramics and/or the like. In a representative embodiment of the present invention, gas vessel  105  may comprise an insulated vessel. In another representative embodiment, gas vessel  105  houses a multi-component gas mixture in accordance with representative embodiments of the present invention, and may be connected to counter-flow heat exchanger  110 .  
         [0024]     It will be appreciated that counter-flow heat exchanger  110 , in accordance with various representative aspects of the present invention, may comprise any heat exchange system or sub-system, whether now known or hereafter discovered, or otherwise described. The counter-flow heat exchanger  110 , in accordance with various aspects of the present invention, may comprise any suitable mechanism for heat transfer from one fluid to another, where the fluid flow fields are configured roughly perpendicular to each other. Counter-flow heat exchanger  110  may include shell and/or tube heat exchangers, plate heat exchangers, plate heat exchangers, regenerative heat exchangers, adiabatic wheel heat exchangers, fluid heat exchangers, dynamic scraped surface heat exchangers, and/or the like.  
         [0025]     It should be appreciated that in accordance with various aspects of the present invention, cooling may be generally achieved by expansion of a gas (or mixture of gases) thru expansion valve  115 . Any materials suitable for regulating the flow of gas and/or isenthalpic expansion of gas thru expansion valve  115  may be alternatively, conjunctively or sequentially employed to achieve cooling. In a representative embodiment of the present invention, expansion valve  115  may be insulated to substantially prevent heat transfer to and/or from the gas.  
         [0026]     It should be appreciated that in accordance with various representative aspects of the present invention, evaporator-reservoir  120  may comprise any mechanism suitable for boiling-off the multi-component gas mixture of the present invention. In a representative embodiment of the present invention, evaporator-reservoir  120  may substantially maintain a relatively constant temperature of the multi-component gas mixture.  
         [0027]     The cryogenic gas mixture is initially contained in vessel  105 . After release from vessel  105 , the gas proceeds via path  102  to heat exchanger  110 . The gas absorbs heat in heat exchanger  110  then proceeds via path  112  to expansion valve  115 , where the gas undergoes isenthalpic expansion to cool the gas mixture before proceeding via path  117  to reservoir  120 . Cryogenic gas in reservoir  120  is collected and boiled-off where the gas then proceeds via path  122  to heat exchanger  110  prior to discharge as exhaust via path  127 . Heat exchanger  110  may be placed in contact with sensor device components to provide cooling thereof.  
         [0028]     Referring now to  FIG. 2 , in a representative embodiment of the present invention, changes in temperature as a function of entropy may be observed as the cryogenic gas mixture moves through the open-loop Joule-Thomson cooling system. As the gas mixture passes through heat exchanger  110 , the pressure remains relatively constant over this path  205 - 210  as the temperature decreases. As the gas mixture expands through expansion valve  115 , the heat remains relatively constant (i.e., isenthalpic expansion) over this path  210 - 215  as the temperature decreases further. As the gas mixture passes through reservoir  120 , the gas is collected and boiled-off at relatively constant temperature with entropy generally increasing over this path  215 - 220 . As the gas passes through the counter-flow circuit of heat exchanger  110 , the pressure remains relatively constant over this path  220 - 225  as the temperature increases. Through this process of isenthalpic expansion, no extra work (mechanical or otherwise) is necessary to affect a lowering in temperature and/or a cooling of the system  100 .  
         [0029]     Sensor cooling systems in accordance with representative aspects of the present invention may be implemented to provide cooling of, for example, long wave infrared sensors. Sensor cooling systems in accordance with representative embodiments of the present invention may generally provide safer alternatives, inasmuch as no highly reactive and/or dangerous fluids are employed. In yet a further embodiment of the present invention, representative sensor cooling systems provide customizable refrigeration solutions which may be suitably adapted for a variety of sensors, electronics, sensor systems, and/or the like. In yet a further representative aspect of the present invention, sensor cooling systems in accordance with the present invention generally provide the ability to vary refrigeration temperature regimes without hardware (e.g., device-level or system-level) modifications.  
         [0030]     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments; however, it will be appreciated that various modifications and changes may be made without departing from the scope of the present invention as set forth in the claims below. The specification is to be regarded in an illustrative manner, rather than a restrictive one and all such modifications are intended to be included within the scope of the present invention. Accordingly, the scope of the invention should be determined by the claims appended hereto and their legal equivalents rather than by merely the examples described above.  
         [0031]     For example, the components and/or elements recited in any apparatus claims may be assembled or otherwise operationally configured in a variety of permutations to produce substantially the same result as the present invention and are accordingly not limited to the specific configuration recited in the claims.  
         [0032]     Benefits, other advantages and solutions to problems have been described above with regard to particular embodiments; however, any benefit, advantage, solution to problem or any element that may cause any particular benefit, advantage or solution to occur or to become more pronounced are not to be construed as critical, required or essential features or components of any or all the claims.  
         [0033]     As used herein, the terms “comprising”, “having”, “including” or any contextual variant thereof, are intended to reference a non-exclusive inclusion, such that a process, method, article, composition or apparatus that comprises a list of elements does not include only those elements recited, but may also include other elements not expressly listed or inherent to such process, method, article, composition or apparatus. Other combinations and/or modifications of the above-described structures, arrangements, applications, proportions, elements, materials or components used in the practice of the present invention, in addition to those not specifically recited, may be varied or otherwise particularly adapted to specific environments, manufacturing specifications, design parameters or other operating requirements without departing from the general principles of the same.