Deep Submergence Ambient Pressure Cryogenic Storage Apparatus

Abstract

The cryogenic storage vessel comprises a liquid storage volume, a conduit ading from that volume, a large flowable mass of solid spherical insulators within that conduit and a diaphragm at the end of the conduit opposite the liquid storage volume. The ambient pressure of the seawater surrounding the apparatus is transmitted to the cryogenic liquid by means of displacement of the diaphragm which is in contact with the ambient seawater and the corresponding change in the internal volume of the liquid storage apparatus. The mass of insulating spheres are allowed to flow within the conduit and partially into the liquid storage area upon displacement of the diaphragm. The insulators allow vapor of the liquid within their interstices but maintain a thermal gradient between the liquid and the diaphragm sufficient to protect the diaphragm from the extremely low temperatures of the cryogenic liquid by substantially preventing convection and conduction.

Description

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

The use of cryogenic liquids as fuels is desirable because of the high energy/density ratio of cryogenic fuels and oxidizers. To achieve the high energy/density ratio the fuels are stored as liquids and used as gasses. Such fuels as hydrogen and oxygen are used to power thermal engines, fuel cells, rocket engines, etc. In order to take advantage of the high energy/density ratio of the cryogenic fuels, they must be stored and maintained as cryogenic liquids. Further, it is necessary to store them in vessels which themselves are not so heavy as to substantially decrease the energy/density ratio of the system (fuel and liquid storage mechanism) to below a desirable level. A heavy storage mechanism would obviate the advantage of using cryogenic liquids as fuels.

One traditional storage technique requires that the liquids be stored in a vacuum environment. This necessitates the use of a heavy steel shell to support the vacuum and in the case of a deep submergence vessel an even heavier steel shell to also support the great hydrostatic pressure loads at deep submergence. Another traditional technique is the use of a non-vacuum container which allows considerable heating of the liquid due to an inability to sufficiently insulate the liquid. This results in a corresponding liquid boil off which increases the internal pressure of the vessel. Therefore, a high strength and heavy container is also necessary to withstand the maximum pressure of the cryogenic vapor at equilibrium temperatures. Each of these traditional approaches require high strength containers whose weight diminishes the high energy/density ratio of the system. This results in the loss of the desirable high energy/density ratio advantage of cryogenic liquids as fuels.

OBJECTS OF THE INVENTION

An object of this invention is to provide a lightweight pressure equalizing container for the underwater storage of fluids which have normal boiling points very much lower than seawater temperatures.

Another object of the invention is to provide a means of protecting a flexible diaphragm from severely cold cryogenic temperatures so that it will be able to maintain its flexibility and strength.

Another object of the invention is to store cryogenic fluids in a lightweight leak tight container in which the internal pressure is equalized with the ambient sea pressure and which is adequately insulated both internally and externally for maintaining the temperature of the stored cryogenic liquid at or below the equilibrium temperature corresponding to its storage pressure and density.

Another object of the invention is to provide a means for establishing high temperature gradient through a media which is itself able to maintain its physical structural integrity and insulating characteristics while being maintained at cryogenic temperatures and at the same time able to flow in response to the displacement of an adjacent element which must be maintained at ambient seawater temperatures.

Another object is the storage of substances at changing ambient pressures while maintaining a high thermal gradient between the ambient temperature and the temperature of the stored substance.

SUMMARY OF THE INVENTION

The purpose of the present invention is to store cryogenic liquids in a lightweight container which allows the pressure of the ambient seawater to be transmitted to the internal section of the liquid storage means. The pressure of the internal section of the liquid storage means changes by allowing the volume of the entire storage container to change in response to pressure. This is done by means of a flexible displaceable diaphragm which makes up one of the walls separating the seawater from the internal liquid storage section of the container. Since most flexible materials lose their flexibility and become brittle at cryogenic temperatures, it is necessary to thermally insulate the diaphragm from the extremely cold cryogenic temperatures of the liquid stored within the container. To do this, a conduit is placed between the diaphragm and the liquid storage area which is filled with the plurality of small solid spheres made up of an insulating material such as glass, ceramic material, polycarbonate, chlorotrifluroethylene, tetrafluoroethylene, as examples. The mass or plurality of small spheres insulates for two reasons. First, the thermal resistivity and the minimal mutual surface contact of the spheres have an insulating effect. Second, the interstitial vapor acts as a thermal insulator since vapor convection is severely retarded by the spheres. Though the insulating effect of the mass of solid spheres would be diminished, materials with a low thermal resistivity (which are not normally considered insulators) could also be used, for example, aluminum and stainless steel. These spheres will tend to separate themselves from the liquid by either being displaced by the liquid or displacing the liquid. The spheres will be selected to be more dense or less dense than the stored liquid depending upon the choice of the embodiment of the invention. If the spheres are of a less density than the liquid and are therefore displaced by the liquid, the conduit leading to the diaphragm will be placed above the liquid storage volume. This will cause the gravitational attraction of the liquid to displace the spheres and maintain them in a conduit and adjacent the diaphragm. Of course, the vapor of the liquid will also be displaced and thereby fill the interstices within the mass of the spheres located in the conduit. Alternatively the spheres could be denser than the liquid and the conduit placed below the liquid storage container. The spheres would displace the liquid and the vapor from the boiled liquid in the conduit would insulate the stored liquid. Whichever density of the spheres and vertical orientation of the conduit is chosen, the mass of spheres shall be maintained primarily in the conduit and in contact with the partitions or diaphragm. The spheres are free to move with respect to each other and therefore are able to flow as a mass and shift position within the conduit and partially move into the liquid storage volume upon displacement of the diaphragm. These spheres, as a mass, along with vapor of cryogenic liquid in their interstices insulate the diaphragm from the cryogenic temperature of the liquid by substantially preventing thermal convection and conduction through the mass of spheres. The diaphragm is maintained at the ambient temperature, e.g., seawater temperature. The flowability allows the diaphragm to displace freely in response to the high hydrostatic loading of the storage system upon deep submergence. The diaphragm and the liquid storage volume are at opposite ends of a conduit which allows free movement of the spheres between the diaphragm and the liquid storage volume. Alternatively the diaphragm may be replaced by a free piston which will move within a cylinder in response to changes in the ambient pressure.

The surface of the lightweight storage container except for the area made up by the diaphragm is a thin wall metal rigid structure which is covered by a solid pressure resistant insulation. For example, a thermo-plastic coating material, syntactic foam or a low density ceramic could be used to rigidly insulate the rigid surfaces of the liquid storage volume and the connecting conduit.

The storage container includes a tube leading from the liquid storage volume which allows the cryogenic fluid to be introduced into the system or to be extracted from the system. A porous filter is used at the beginning of the tube to prevent any of the solid spheres from entering the tube. This porous filter allows only liquid and gas flow through the tube.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross section of a cryogenic liquid storage means which shows a flexible diaphragm attached to the end of a conduit, a large mass of flowable solid spherical insulating elements within the conduit, and a liquid storage volume attached to the conduit at the end opposite the flexible diaphragm. In this FIGURE, the conduit and diaphragm are located above the liquid storage volume and the mass of solid spherical insulating elements is displaced from the liquid and forced into the conduit and up against the diaphragm.

FIG. 2 is a cross section of a free piston used alternatively in place of the diaphram 11 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the FIGURES wherein like reference numerals designate corresponding parts throughout the several views, there is shown an ambient pressure lightweight cryogenic liquid storage system 10. A liquid storage volume 16 has a conduit 19 leading away from it. At the opposite end of the conduit a flexible diaphragm 11 is allowed to move in response to changes in the ambient pressure of the seawater. Within the conduit and adjacent the internal side of the diaphragm, there is a large mass of independent spherical solid insulating spheres 13. These spheres 13, as a mass, rest against the flexible diaphragm 11 but do not restrict its freedom of movement within the conduit 19. A continuous thin lightweight metal wall 12 makes up the internal wall of both the conduit 19 and the liquid storage volume 16. Externally, both the rigid conduit and rigid liquid storage volume are insulated by a rigidly attached pressure resistant insulation 15. Optionally, a lightweight external wall 14 may be used to protect the pressure resistant insulation 15. The cryogenic liquid 20 is allowed to occupy the internal space of the liquid storage volume 16. The liquid storage volume 16 also includes an insulated extraction tube 17 and a porous material 18 which prevents any solid insulating material from exiting the system through the tube 17.

DESCRIPTION OF THE SYSTEM IN OPERATION

As shown in the FIGURE, the liquid storage volume 16 is filled with a cryogenic liquid 20 which displace the solid spherical insulating elements 13 and cause it to occupy the conduit 19 and lie in contact with the diaphragm 11. The ambient environment may be made up of seawater. The seawater would completely surround and be in contact with all the external surfaces of the system including the external surface of the diaphragm 11. If the system is attached to a submarine diving to deeper ocean depth, the hydrostatic load on the system will be increasing. As this external pressure increases, the diaphragm 11 will be displaced within the conduit 13 to decrease the total volume of the system and thereby allow the internal and external pressure to equalize. The mass of insulating materials 13 is allowed to flow through the conduit and into the liquid storage volume and it is displaced by the movement of the diaphragm. Throughout this operation, the diaphragm is maintained at seawater temperature by the insulating action of the mass of solid insulating spheres which establish a thermal gradient between the diaphragm 11 and the stored cryogenic liquid 20. Vapor from the stored cryogenic liquid 20 is allowed to fill the instertices of the spherical insulating elements which make up the mass 13 but substantial heat loss due to convection and conduction is prevented by the mass 13. As the ambient pressure is increased and the flexible diaphragm 11 moves within the conduit some of the solid insulating spheres 13 will flow into the liquid storage volume and partially heat the stored liquid 20. This will cause some of the cryogenic liquid to boil off and form vapor and thereby increase internal pressure of the system to assist in maintaining the internal pressure at the pressure of the ambient seawater and in maintaining a stored cryogenic liquid at equilibrium temperature. When the stored cryogenic liquid is needed as a fuel it may be extracted through the insulated withdrawal tube 17. The filter 18 prevents any of the solid particles from flowing into the tube 17. The rigid insulation 15 prevents the conduction of heat from the seawater in contact with the rigid external surfaces of the system from being introduced to a stored cryogenic liquid 20.

Of course, it will be recognized that the embodiments described above are illustrative only and that many variations may be made by those of skill in the art of storing cryogenic liquids. For example, this system could be used to maintain a high temperature gradient between an internal liquid and an external environment while maintaining them at an equalized pressure. In that vein, it may be desired to maintain a liquid at a high temperature but at the same pressure as a relatively low temperature ambient environment. In many such applications, this invention would be useful and appropriate with little or no modification. It is therefore understood that the invention may be practiced otherwise than as specifically described.

Claims

What is claimed is:

1. An apparatus for storing a liquid in a high ambient pressure environment while maintaining said liquid at a high temperature differential with respect to the ambient temperature comprising:

a means for storing liquid;

a partition means in contact with the ambient environment and separating the ambient environment from the internal volume of the apparatus and which is displaced in response to a change in the differential pressure between the internal and the ambient pressure, thereby causing a change in the volume of the entire apparatus;

a means connecting said means for storing liquid and said partition means for allowing free transmission of the ambient pressure into the liquid storing means and restricted transmission of some of the liquid in the vapor state from the means for storing liquid to said partition means while substantially preventing heat transfer by conduction and vapor convection and establishes a high temperature gradient between the ambient temperature and the temperature of the stored liquid.

2. An apparatus for storing a liquid as in claim 1, wherein said means connecting said means for storing liquid and said partititon means comprises:

a conduit means;

a flowable means within said conduit means and in contact with said partition means, which flowable means has interstices which may be permeated with the vapor of the stored liquid wherein said flowable means both occupies the conduit means and partially flows into and out of the means for storing liquid in response to changes in the volume of the apparatus.

3. An apparatus as in claim 1, wherein:

said partitition means is a flexible diaphragm.

4. An apparatus as in claim 1, wherein:

said partition means is a movable piston.

5. An apparatus as in claim 1, including:

a means connected to said means for storing liquid, for extracting liquid from said means for storing liquid.

6. An apparatus for storing a liquid in a high ambient pressure environment while maintaining said liquid at a high temperature differential with respect to the ambient temperature, comprising:

a means for storing liquid;

a partition means in contact with the ambient environment and separating the ambient environment from the internal volume of the apparatus and which is displaced in response to a change in the differential pressure between the internal and the ambient pressure, thereby causing a change in the volume of the entire apparatus;

a conduit means;

a flowable means within said conduit means and in contact with said partition means, which flowable means has interstices which may be permeated with the vapor of the stored liquid wherein said flowable means both occupies the conduit means and partially flows into and out of the means for storing liquid in response to changes in the volume of the apparatus.

7. An apparatus as in claim 6, wherein:

said means for storing liquid and said conduit means comprise;

a thin metal inner wall; and

a thermal insulation covering said walls.

8. An apparatus as in claim 6, wherein:

said partition means and said means for storing liquid are attached to opposite ends of said conduit means.

9. An apparatus as in claim 6, wherein said means within said conduit means is a mass of small solid particles.

10. An apparatus as in claim 8, wherein:

said small solid particles are spherical in shape and made of a material from the group of materials consisting of glass, ceramics, polycarbonate, chlorotrifluroethylene, tetrafluoroethylene, aluminum, and stainless steel.

11. An apparatus as in claim 9, wherein said small solid particles are spherical in shape and thermal insulators.