US 3156100 A
Description (OCR text may contain errors)
Nov. 10, 1964 G. C. HAETTINGER 'ETAL APPARATUS FOR SUPPLYING LIQUEFIED GAS Filed May 19, 1961 2 Sheets-Sheet l INVENTORS GEORGE C. HAETTINGER STUART F. RAMSEY ATTORNEY Nov. 10, 1964 G. c. HAETTINGER ETAL 3,156,100
APPARATUS FOR SUPPLYING LIQUEFIED GAS Filed May 19, 1961 2 Sheets-Sheet 2 INVENTORS GEORGE C. HAETTINGER STUART P RAMSEY A TTORNE V United States Patent 3,156,100 APPARATUS FGR SUPPLYING LIQUEFIED GAS George C. Haettinger, Indianapolis, Ind., and Stuart P. Ramsey, Brighton, Mass., assignors to Union Carbide Corporation, a corporation of New York Filed May 19, 1961, Ser. No. 111,238 8 Claims. (Cl. 6251) This invention relates to an improved apparatus for supplying low-boiling liquefied gas, and more particularly to a double-walled container for storing liquefied gas and for discharging said gas in liquid form when the container is in any position or under any gravity condition, as for example, in an aircraft, space craft, or underseas.
Oxygen, nitrogen and air, for example, are widely used to provide breathing atmospheres or for pressurizing fuel systems and control mechanisms. These gases to be utilized most economically, are conveniently stored in the liquefied form to reduce the total storage volume and vessel weight required to supply a given volume of gas. Many such systems must be portable, as for example, where oxygen is to be supplied for high altitude and deepsea breathing purposes. This need for portable, lightweight equipment emphasizes the potential advantages of liquid storage as contrasted with containers for holding a pressurized gas. Low boiling liquefied gas containers are usually constructed with double walls, the space between the inner and outer walls being provided to insulate the liquid in the inner vessel from atmospheric heat. A thermal barrier is necessary because such liquefied gases are stored at very low temperatures, e.g., 183 C. for liquid oxygen, and without high quality insulation the liquid would vaporize very quickly.
Most prior art liquefied gas storage containers deliver the desired liquid flow only when properly positioned and under the influence of gravity. When these containers are inverted or when the gravitational force is eliminated as would be encountered in space flight, the liquid delivery either becomes sporadic or ceases completely. Conventional pressure building circuits in which the liquid phase of the container is connected to the gas phase through a vaporizer could not be used to pressurize the liquid in the prior art containers for this type of service since these circuits rely primarily on gravity as the pressuredriving force. Also, the gaseous phase in these previously proposed containers has the disadvantage of being in direct contact with the liquid phase. When a pressure-building circuit is used, a portion of the vaporized liquid is returned to the gas phase. Hence, when liquid air, for example, is stored, a portion of the oxygen will be condensed from the gas phase to achieve equilibrium within the container. This phenomenon will result in the gas phase always being nitrogen-rich and the liquid phase being oxygen-rich with respect to air. Since the container may be operated in various positions and delivery may occur from either gas phase or liquid phase, the desired composition of the output gas would not be obtained at any moment. This is a serious problem when the stored fluid is used to supply breathing atmospheres to divers 'or crew members in aircraft, since for optimum functioning the human body requires oxygen and nitrogen in a relatively narrow concentration range.
One prior art method which attempts to maintain liquefied gas flow from a storage container'in all positions .or under zero-gravity conditions involves positioning a flexible bladder inside the storage vessel. The bladder is inflated 0r collapsed with a gas having a lower boiling point than the stored liquid in order to pressurize the- Patented Nov. 10, 1964 "ice that will retain suflicient flexibility at the low operating temperatures of liquid gases.
Another previously proposed method of solving this diflicult' problem is to incorporate a separate energy source, such as a heat coil, within the storage container. Energy can thereby be added in large amounts to vaporize additional liquid within the container and thus provide sufficient pressure to force the liquid out as needed. Such an arrangement has the critical disadvantage of unsuitability for use with liquid air for breathing purposes since the heat energy input would cause a composition change by vaporizing primarily nitrogen.
It is therefore a principal object of the invention to provide an improved liquefied gas storage container capable of dispensing a desired quantity of liquid from any container position and under any gravity condition.
Another object is to provide an improved liquefied gas storage container having the additional characteristics of being lightweight and having minimum heat inleak.
These and other objects and advantages of the invention will become apparent from the following description and the accompanying drawings in which:
FIG. 1 is a longitudinal view in cross-section of a double-walled, sliding piston container embodying the principles of the invention; the container is shown broken at the center portion in order to illustrate an alternate embodiment of the piston;
FIG. 2 is a segmentary view in cross-section and on an enlarged scale of a portion of the slideable piston shown in FIG. 1;
FIG. 3 is a segmentary view on an enlarged scale taken along line 3-3 of FIG. 1;
FIG. 4 is a segmentary view in cross-section and on an enlarged scale of a portion of the piston and container, and
FIG. 5 is another segmentary view in cross-section and on an enlarged scale of a portion of the container shown in FIG. 1.
In the drawings, similar elements in the several figures are designated by similar reference characters.
In accordance with one embodiment of the present invention, a portable container is provided for storing, and for dispensing from any container position, a pressurized liquefied gas having a boiling point below 233 K. The containerincludes an inner vessel for storing a. body of the pressurized liquefied gas, an outer shell enclosing and separating the inner vessel from the atmosphere, and an insulating spacet under a vacuum pressure definedby the inner vessel and the outer shell. A piston is transversely positioned across the cross-sectional area of the inner vessel $0133 to subtantially fill such area.
The piston is alo arranged and constructed to slideably move and be guided in a direction parallel to the container longitudinal axis, under the influence of an arti-,
ficial pressure applied against the external surface of said piston.
The piston peripheral edge is provided with suitable means for slidea-bly engaging the container inner wall while maintaining a substantially gas tight seal therewith. The piston also makes slideableycontac'twith a composite conduit extending longitudinally through the container and terminally positioned at the top and bottom respectively through which conduit both liquid and vaporized gas are conducted. The conduit comprises essentially an inner elongated tube surrounded by a second tube outwardly spaced therefrom to define an annular passage. The space intermediate the outer container shell and inner vessel is provided with a suitable insulation medium;
the space intermediate the piston upper surface and the vessel upper end wall, communicates with a source of prcssurizing gas whereby such gas may be delivered to said space to create an artificial gravity by bearing against said piston. The latter will then in turn exert pressure on the contained liquid body, thereby forcing a portion of the liquid from said container.
Before specifically describing the apparatus, we will explain that the term vacuum, as used hereinafter, is intended to refer to the vacuum pressure in the insulating space between the inner vessel and outer shell of the portable container of this invention. The term applies to subatmospheric pressure conditions not substantially greater than 1,000 microns of mercury, and preferably below 100 microns of mercury absolute.
In a preferred embodiment of the novel container, the insulating space contains an opacified insulating jacket, which is many times as efficient as the conventional powder-in-vacuum or highly polished reflective surfaces heretofore used in double-walled liquefied gas containers. The use of opacified insulation permits the fabrication of a liquefied gas container having a much narrower insulating space for a given rate of heat inleak, and consequently a smaller and lighter unit for a given liquid storage capacity. Alternatively, opacified insulation permits an increased liquid storage capacity for a given weight, as compared with a container insulated by conventional materials.
The term opacified insulation, as used herein refers to a two-component insulating system comprising a low heat conductive, radiation-permeable material and a radiant heat impervious material which is capable of reducing the passage of infrared radiation rays without significantly increasing the thermal conductivity of the insulating system. Also, the tei'rn radiant heat barrier, as used herein, refers to radiationopaque or radiant heat energy impervious materials which reduce the penetration of infrared heat rays through the insulating system either by radiant heat reflection, radiant heat absorption or both. As defined, opacified insulation includes a mixture of finely-divided low-conductive particles which substantially impede heat inleak by conduction and yield to heat passage by radiation, and finely-divided radiant heat impervious bodies having a relatively high thermal conductivity. As more fully described and claimed in US. Patent 2,967,152 issued to L. C. Matsch and A. W. Francis, the low conductive particles may be selected from the group consisting of silica, perlite, alumina, magnesia and carbon black, and the radiant heat impervious bodies are preferably either aluminum or copper, although copper paint pigments, alumina paint pigments, magnesiurn oxide, zinc oxide, iron oxide, titanium dioxide, copper coated mica flakes, carbon black, and graphite either alone or in' combination with each other would give satisfactory results. Also, these bodies usually in the form of flakes or powder preferably constitute between 1% and 80% of the total weight of the insulation.
The opacified insulationmay also takethe form of the combination of a low'heat conductive material and a multiplicity of spaced radiation-impervious barriers. As more fully described and claimed in copending US. Serial No. 597,947 filed Iuly'l6, 1956 in the name of L. C. Matsch, now Patent No. 3,067,596, the low heat conductive material may be the previously listed powderous materials or alternatively a fiber insulation which may be produced in sheet form. Examples of the latter include a filamentary glass material such as glass wool, and fiber glass, preferably having fiber diameters of less than about 50 microns. Also such fibrous materials preferably have a fiber orientation substantially perpendicular to the direction of heat fiow across the insulation space. The spaced radiation-impervious barriers may comprise either a metal, metal oxide, or metal coated material, such as aluminum coated plastic film, or other radiation reflective or radiation adsorptive material or a suitable combination thereof. Radiation reflective materials comprising thin metal foils are particularly suited in the practice of the present invention, for example, reflective sheets of aluminum foil having a thickness between about 0.2 millimeter and 0.002 millimeter. Other radiation reflective materials which are susceptible of use in the practice of the invention are tin, silver, gold, copper, cadmium or other metals. When fiber sheets are used as the low-conductive material, they may additionally serve as a support means for relatively fragile radiation impervious sheets. For example, an aluminum foil-fiber sheet insulation may be spirally wrapped around the inner liquefied gas holding vessel with one end of the insulation wrapping in contact with the inner vessel, and the other end nearest the outer shell, or in actual contact therewith.
It would normally be concluded by one skilled in the art that the aforedescribed opacified insulation could not be economically used in portable liquefied gas containers because of the relatively heavy nature of such insulation. For example, a 50%-50% by weight mixture of silica powder with finely divided copper flakes has a bulk density of about 12 lbs. per cubic ft. However, it has been found that opacified insulation preferably in combination with light-weight aluminum or aluminum alloy construction provides an improved liquefied gas portable container which is substantially lighter than heretofore used containers having the same storage volume and the same insulating efiiciency. This remarkable result is attainable in part because the opacified insulations used in this invention have a relatively high insulating efficiency at vacuums poorer in quality than those required for vacuum-polished metal surface insulation. Because of this characteristic, aluminum, which is known to produce porous welds, can be used instead of relatively heavier stainless steel or copper which can produce relatively leak-proof metal joints.
The thermal insulating effectiveness of opacified insulation versus straight vacuum plus polished surfaces (no powder insulation) can be compared by using the example of two l-square foot metal plates spaced inch apart. When straight vacuum insulation was used, the inside surfaces of the plates were polished to an emmissivity of 0.04. The outer plate was at room temperature (70 F.) and the inner plate was at liquid oxygen temperature (297 F.). Under 50 microns pressure between the plates, an opacified insulation in this space consisting of 50%50% by weight mixture of silica powder and finely divided copper metal flakes had a heat transmission of about 1.85 Btu/hr. In order for straight vacuum insulation to have a comparable effectiveness, the pressure would have to be less than 0.01 micron. Under similar pressure conditions (50 microns) straight vacuum plus polished surfaces had a considerably higher heat transmission of about 43 B.t.u./hr. It can be seen that by using opacified insulation a highly efficient insulating system may be provided in aluminum liquefied gas portable containers even though the space between the inner vessel and the outercasing is maintained at a relatively poor vacuum because of the relatively porous nature of the ahnninum-containing joints. While a preferred embodiment of this invention includes the above-described opacified insulation as one of several interacting elements, it is to be understood that an alternate embodiment of the present portable container may utilize straight vacuumpolished surface insulation.
Even though the previously described preferred opacified insulation is more effective than straight vacuum insulation at higher internal pressures (poorer vacuum), its effective thermal insulation life is extended if the pressure can be maintained at or below a desired level. A gas removing material such as an adsorbent, either in powder or pellet form, may be used in the insulation space to remove by adsorption the gas entering through the porous aluminum-containing joints. This is an extremely important feature since no provision is made in the relatively small portable container of the present invention for reevacuation of the insulating jacket. The adsorptive capacity of suitable adsorbents, such as natural and synthetic zeolites, silica gel and activated charcoal, generally rises with increased pressure. Therefore, these adsorbents are more effective for removal of insulation jacket air leakage when opacified insulation is used when straight vacuum is employed because of the higher vacuum space pressure involved. Furthermore, these adsorbents generally have higher adsorptive capacitives at relatively lower temperatures. Consequently, they are preferably mounted adjacent to the cold outer side of the inner vessel wall. Alternatively, the adsorbent may be randomly mixed in the opacified insulation. In particular, crystalline Zeolitic molecular sieves having pores of at least about 5 Angstrom units in size, as disclosed in copending U.S. Serial No. 557,477 filed January 5, 1956, now US. Patent No. 2,900,800 in the name of P. E. Loveday, are preferred as the adsorbent since they have extremely high adsorptive capacity at the temperature and pressure conditions existing in the insulating jacket and are chemically inert toward any gases which might leak into the insulating jacket. Such zeolites may be either natural or synthetic. This novel combination of opacified insulation and adsorbent thus facilitates construction of a liquefied gas portable container which is lighter in weight and has a longer effective life than the previously proposed containers. Such an adsorbent is also used advantageously in combination with straight vacuum-polished surface insulation.
Referring now more specifically to FIG. 1, the liquefied gas container indicated at includes a generally cylindrical liquid holding inner vessel 12. The inner vessel is completely surrounded and separated from the atmosphere by an outer shell 14, both vessel and shell being preferably fabricated from thin gauge stainless steel or aluminum alloy. The low density of aluminum especially allows a relatively thick outer casing to be used which has more resistance to handling abuse than would a relatively thin casing of equivalent weight fabricated from denser material.
An intermediate space 16, defined by the spaced vessel and shell, is preferably filled with the previously described opacified insulating material. The preferred form of the opacified insulation used with this invention comprises low heat conductive material such as glass wool or fiber glass having fiber diameters of less than about 50 microns, and a multiplicity of spaced radiation-impervious barriers, such as aluminum foil having a thickness between about 0.2 mm. and 0.002 mm. This layered insulation is conveniently assembled around the cylindrical inner vessels and tends to hold the inner vessel in spaced relation to the outer shell. Alternatively, the opacified insulation may be a mixture of finely divided low conductive particles and radiant heat impervious bodies having a relatively high thermal conductivity. For example, a 50%50% by weight mixture of finely divided silica powder having particle sizes below about 75 microns, and copper flakes smaller than about 50 microns with a flake thickness less than about 0.5 micron gives best results, although opacified insulation mixture having larger size particles have been tested with excellent results.
A blister or chamber 18 secured to, and in heat exchange relation with the bottom section of inner vessel 12, holds a gas-removing material 20 and preferably an adsorbent such as the previously described synthetic or natural zeolite to remove gas and vapors from the insulating jacket 16. The adsorbent material 20 communicates with the opacified insulating jacket through passages in the walls of chamber 18, the adsorbent material, for example, being retained in chamber 18 by glass cloth sheets extending across the passages and held against the chamber walls. It is to be understood that the glass cloth sheets do not interfere with vapor and gas communication between the opacified insulating jacket 16, and adsorbent material 20 although they serve to retain the latter.
The inner vessel 12 is supported'and stabilized against all relative movement (both vertical and lateral) by a suitable support system which may, for example, comprise a pair of end positioned suspension members 24 and 26 together with the layered insulation jacket 16 acting in combination. Said elements 24 and 26 are preferably formed from material such as stainless steel or a reinforced phenol formaldehyde plastic having the properties of relatively high compression and shear strengths, to maintain the rigid positioning of the liquid holding vessel. These support members also are possessed of low thermal conductivity properties in order to reduce the over-all heat leak by conduction.
Referring to FIGS. 1 and 3, the container inlet end is provided with a manifold cap 30 having lateral openings 32, 34 and 36 which communicate with passages for conducting fluid to and from the container interior. As illustrated in FIG. 4, one end of the tubular support member 26 is peripherally engaged in a fluid tight seal to an opening formed in the top wall of vessel 12. The other end of said tubular member 26 is sealably joined to the manifold cap 30 thereby forming a gas tight fluid passage through the insulated wall of the container. A closure plate 40 positioned in the said one end of member 26 provides a closure to the gas tight chamber 42.
Again with reference to FIGS. 1 and 4, an elongated conduit 44 longitudinally transverses the container and is end positioned to the top and bottom walls thereof. The conduit 44 according to the invention serves two important functions. Primarily said member provides a passage for fluids entering and leaving the container, in which respect the outlet or upper end thereof registers with and is joined by welding or other suitable means to an opening in the end closure 40 thereby communicating said conduit with chamber 42. A second function of the conduit resides in serving as a guide for the slideable piston 46 which will be herein described in greater detail. The conduit lower end as shown in FIG. 1 is positioned to the vessel lower wall by means of a hub 47 with which said conduit is engaged.
As shown in FIGS. 1 and 4, an elongated duct 48, positioned within conduit 44, extends for the length thereof defining an annular passage 49. Said duct is sealably engaged with a central hollow chamber 50 at the hub 47 and in turn is communicated by a short nipple52 with the lower interior section of vessel 12 thereby providing a passage for the contained fluid. The upper end of duct 48 is Welded or soldered into a recessed passage 54 to which the threaded outlet 34 is communicated, which out let may then be coupled either to a supply of fluid to be pumped into the vessel or to a conduit into which the stored material is to be fed.
Duct 48, to be suitably accommodated within conduit 44, is of a smaller diameter than the surrounding member, and is preferably of metallic construction such as copper or stainless steel. As noted above, this tube provides a passageway for introducing fluid-to the interior vessel, liquid holding compartment, or conversely, it provides a means of egress for the same fluid, to the point of use.
, The slideable piston assembly indicated generally by numeral 46 in FIG. 1, comprises essentially a relatively thin metallic cup or disc 56 having a circular periphery, and a center opening. The center opening is'en gaged with a slideable collar 58 to form a gas tight joint about conduit 44. The collar 58 consists of an elongated cylindrical member 60 having an axial passage in which the conduit 44 registers. A threaded portion at each opposed end of said member engages metallic retainer caps 62 and 63 to compressively retain resilient ring packings 64 and 65 respectively in slideable sealing contact with the outer surface of conduit 44. The packing means here employedmust of course be capable of maintaining a sufliwith. It has been found that satisfactory sealing may be' i! realized at temperatures as low as 196' C. without cracking or embrittlement of the seal medium, when the packing rings 64 and 65 are fabricated of a material such as trifiuorochloroethylene polymers, tetrafluoroethylene polymers or a polyethylene terephthalate resin. These materials are found to readily resist low temperature embrittlement at the working temperature of liquid oxygen or liquid nitrogen, and are therefore highly preferred for the sliding seal.
The cup 56, as shown in FIG. 4 is provided with a center opening having an in-turned lip 70 which may be welded or otherwise sealably engaged with the outer surface of cylindrical member 60. The peripheral edge of cup 56 is adapted to slideably contact the inner wall of vessel 12 which may be ground or otherwise sufficiently smoothed to prevent the fiow of fluid through the peripheral sliding joint and which will permit the piston assembly to readily move along said wall. As shown in FIGS. 1 and 5, the cup outer edge may be provided with a circumferentially disposed spring member 72 having outwardly turned flanges 73 and 74 which bear laterally against the vessel wall to form a substantially gas tight seal therein as the piston 46 moves longitudinally through the vessel to separably define a liquid chamber and a gaseous chamber.
A preferred embodiment of the sliding seal for the piston outer edge is shown in detail in FIG. 2 and comprises the metallic cup 56 which has an outer diameter slightly less than the inner diameter of vessel 12. A step formed at said outer edge accommodates a series of thin, layered members including a metallic back-up strip 78 and a series of circumferentially positioned spring members 80 which are preferably formed of a plurality of short strips of a resilient metal such as Phosphor bronze. Said spring member 80 is of suliicient length to exert a lateral force against a circumferential plastic seal 82, to maintain the latter in rubbing contact with the vessel inner Wall. This seal member 82 according to the invention consists of a continuous ring of a material which will be resilient at temperatures as low as 196' C. As pre' viously mentioned it has been found that a suitable material for operation at such temperatures may be trifluorochloroethylene polymers, trifluoroethylene polymers, or polyethylene terephthalate resin.
Because of the low temperature atmosphere in which the piston must ordinarily operate, the seal member 82 will tend to assume a permanent set although retaining some degree ofresilience. To assure a gas tight seal between the curved edge of member 82 and the adjacent vessel wall, the circumferentially disposed spring strips, 80, are positioned to urge said curved edge of the sealing member outwardly against said wall. To adjust the spring force exerted against the seal, these respective strips may be radially positioned relative to the piston cup.
The fluid sealing assembly including seal member 82, springs and backing strips are maintained fixedly in place by a pair of adjacently positioned shrink rings 84 and 85. Said rings are preferably fabricated of brass or other metal having a coefiicient of expansion greater than the stainless steel piston cup in order that the normally low operating temperatures will cause the rings to contract inwardly against shoulder 36 and thereby compress the respective spring and seal members to a relatively firm relationship. This type of construction is found to result in a more uniform compression of the respective springs and seal member. As seen in FIG. 2, the step 86 may consist of a circular member or series of circularly positioned members which are adjustably mounted against disc 56 by circularly disposed series of bolts 87 or similar fastening members.
In normal operation the disclosed container is employed when it is desired to maintain a flow of liquid gas as, for instance, a refrigerant material, under zero gravity conditions such as experienced in high flying aircraft. For example, when the velocity and trajectory of a high speed aircraft with respect to the earth are such that there will be little or no gravity force acting on the container liquid, the necessary flow of refrigerant for the purpose of cooling the aircraft heated portions, will be maintained by use of the instant apparatus.
To prepare the apparatus for actual use by filling with a low boiling point refrigerant gas, the container is positioned uprightly with the manifold 30 at the top, thereby permitting the piston 46 to fall by its own weight to the lower end of the vessel. A fluid carrying hose communicating with a source of the refrigerant gas is coupled with the opening 34 at cap 30, to introduce a flow of the liquid through conduit 48 and into said lower portion of vessel 12. Unless the vessel interior is maintained at a sufficiently low temperature approximately the boiling point of the incoming gas, entering liquid will, on contacting the warm walls, immediately vaporize and expand thereby forcing the piston toward the top position.
To permit free upward passage of the piston, the space intermediate the piston top surface and the vessel upper wall is vented to the atmosphere. This is accomplished as shown in FIG. 4 by provision of a plurality of openings 92 extending through the wall of conduit 44 which communicate annular passage 49 with the vessel storage area, only when the piston is positioned above said openings.
Prior to the piston reaching the vessel top position, exiting air or gas being compressed above the rising piston will pass through said openings 92, into the annular passage 49 and thence to chamber 42. The latter, while not here shown in the figures, is communicated through the manifold cap 36 to outlet 36 which is provided with a suitable valve for controlling the flow of fluid therethrough, thereby passing the discharged air to the surrounding atmosphere. In such manner, the vessel may be filled with liquid substantially to the full capacity of the storage area.
For discharging the gas to the point of use entirely in the liquid phase, the following procedure is utilized.
Assume for the purpose of illustration that the previously mentioned aircraft is provided with a cooling system adapted to receive a flow of the liquid refrigerant, which liquid will then vaporize, and cool the parts desired. The container outlet 34 is communicated with said system to provide a flow of the liquid at all times. Under normal conditions and with the container disposed in an upright position the weight of the piston itself bearing on the stored gas will tend to provide a continuous flow of the liquid. When however, the position or altitude of the aircraft is such as to put the container in a condition of zero gravity, the flow of liquid gas will cease. According to the preferred method of the invention, the downward movement of the piston is now maintained by introducing a pressurized flow of a gas such as helium or nitrogen to the pressurizing area or gaseous chamber defined between the piston top surface and the inner surface of the vessel. The pressurizing gas is furnished to the container through opening 32 in cap 30 and thence conducted to the pressurized area through tube 99.
As pressurizing gas is introduced, the piston 46 will force the remaining refrigerant confined beneath the piston against the liquid refrigerant. This compressing action will destroy the equilibrium between said refrigerant vapor and the liquid thereby condensing the remaining vapor. It is readily seen that under normal operations there will at no time be any substantial amount of vapor in the liquid storage area.
In accordance with the invention, the pressure of the gas in the pressurized space must be sufficiently great to prevent the formation of refrigerant vapors within the storage area which would eventually flow from the container. So long as said pressure is maintained, the piston will be urged toward the container bottom wall thereby forcing liquid out of the storage area and through conduit 48 to the refrigerating system. To assure a steady outflow of liquid refrigerant with no intermixed vapors,
the pressurizing gas should preferably have a sufiiciently low boiling point to maintain a pressure at least greater than the vaporization pressure of the refrigerant.
While the foregoing discussion has been limited mainly to the use of helium and nitrogen gas as the pressurizing medium, it is understood that other gases such as argon or hydrogen might also be employed. Further, it is possible under certain conditions and by the use of supplementary equipment, to utilize excessive refrigerant vapors from the main storage area as the source of pressurizing gas.
As the contained liquid is discharged and the piston approaches the lower portion of the vessel indicating the maximum downward travel point, a small amount of residual refrigerant will remain in the vessel. This liquid may be forced out by provision of means for communicating the gaseous and liquid portions of the storage area. As shown in FIG. 1, such a provision may consist of a vent tube 96 which engages the slider collar assembly to communicate the storage area with the wall of conduit 44. While normally there will be no fluid leakage past the piston where it contacts the conduit, 44, the lower end of said conduit may be provided with a longitudinal groove thereby destroying the gas tight seal as the piston slider collar passes over said groove. With the upper and lower storage areas so communicated, the pressurizing gas entering the longitudinal groove will be conducted through the vent 96 to thereby apply a direct pressure against the residual refrigerant liquid.
It should be noted that this method of utilizing the residual refrigerant is particularly adaptable to conditions when the container will not be at zero gravity. For example, when an aircraft or missile is on its return flight. Or when a diver is returning to the surface. When such conditions are not known, however, another method of utilizing the residual refrigerant would be to use a flatheaded piston in conjunction with a fiat-bottomed container. The use of a fiat-bottomed container is, however, limited to containers of low pressures, for example, 100 psi. or less.
It is readily seen that by maintaining the pressurizing gas at a relatively constant pressure, it is possible to realize a uniform rate of fiow of liquid refrigerant from the containers. The uniformity is highly desirable and a vast improvement over the use of mechanical resilient means such as springs for obtaining a forced feed from the container is realized. Also, while it has not been explained in great detail, it is understood that contingent with the use of the present containers as with most liquefied gas vessels it is necessary to provide automatic pressure venting means so that if the vapor pressure rises above thecontainer design strength, it will be relieved.
It is further understood that while the container, as here disclosed, constitutes a preferred embodiment of the apparatus, changes and modifications in the device may be made by one skilled in the art without exceeding the scope of the invention.
What is claimed is:
1. Apparatus which comprises: a double-walled vacuum-insulated container having a storage space therein with liquid portion and gaseous portion ends, a piston positioned transversely within the container defining separable liquid and gaseous portions in the container storage space, means for engaging said piston with the inner surface of said container storage space to provide a fluid tight seal therewith a conduit assembly fixedly positioned in substantial co-axial relationship with the container longitudinal axis and adapted to longitudinally guide said piston and maintain a fluid-tight seal therebetween, said conduit assembly comprising an inner duct and a conduit surrounding such duct and outwardly spaced therecontainer storage space for introducing liquid in and discharging liquid from such portion, and said conduit having perforations therein for communication between said annular passage and the container storage space liquid portion when the slidable piston is disposed adjacent the gaseous end portion of said container storage space for venting such liquid portion during the filling of such liquid portion.
2. Apparatus according to claim 1 including a resilient member at said piston peripheral edge engaging the adjacent container storage space inner surface to provide a fluid tight seal therewith during longitudinal movement of said piston along the storage area.
3. In a container substantially as described in claim 1 wherein the piston comprises a disc having the peripheral edge thereof disposed adjacent the cylindrical wall, a low temperature resistant flexible seal ring positioned at said piston outer edge, said ring being outwardly urged by resilient means into contact with said wall to form a fluid tight slideable seal therewith.
4. In a container substantially as described in claim 1 wherein the piston comprises a metallic disc having a peripheral edge, a low temperature resistant seal ring positioned at said edge, a resilient member also positioned at said edge in supporting relation to said ring, said ring being outwardly urged by said resilient member toward the cylindrical wall whereby said ring may fluid tightly engage the Wall and maintain a circumferential seal therewith during relative longitudinal movement of said piston with said wall.
5. A container substantially as described in claim 4 wherein the seal ring is made from trifluorochloroethylene.
6. A container substantially as described in claim 4 wherein the seal ring is made from a polymer of tetrofluoroethylene.
7. A container substantially as described in claim 4 wherein the seal ring is made from polyethyleneterephthalate.
8. A container for storing low temperature vaporizable gas having a boiling point at atmospheric pressure less than about 183 C., and for dispensing said gas from said apparatus at a substantially constant pressure which apparatus comprises: an elongated vessel having a cylindrical wall and opposed upper and lower end walls defining a low temperature storage area, a shell, outwardly positioned from the vessel defining an insulating space therebetween, a piston disposed transversely of the crosssectional area of the vessel providing fluid tightly separable liquid and gaseous portions in the said storage area, a manifold at the upper end of the vessel affording access to said storage area, aplurality of openings in said manifold, a conduit assembly positioned in substantial co-axial relationship with the cylindrical walled storage area and terminally fixed to said vessel upper and lower end walls respectively, said conduit assembly comprising, an inner duct, a conduit surrounding said duct and outwardly spaced therefrom to define an annular passage therebetween, said duct communicated with the storage area at a point adjacent said lower Wall and engaging an opening in said manifold, the annular passage communicated at the upper end thereof with a second of said manifold openings, said piston slideably engaging said conduit to be guided thereby in a direction longitudinally of the vessel to define the storage area gaseous portion intermediate the piston and the vessel upper wall, means communicating said gaseous portion with athird outlet at said manifold to provide a flow of pressurizpassage with the liquid portion of said storage area when the slideable piston is disposed adjacent the vessel upper wall.
(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Goddard Oct' 17, 1950 Payne July 22, 1952 5 Mueller Dec. 17, 1957 Beckman et al Feb. 7, 1961 12 Gardner July 31, 1962 OTHER REFERENCES Advances in Cryogenic Engineering (Timmerhaus), published by Plenum Press, Incorporated, (New York), 1960. Proceedings of the 1959 Cryogenic Engineering Conference (pages 100 and 101 relied on).