Patent Application
20140263355
The present invention is related to insulation systems and devices to contain, insulate, and transport matter that is required to be kept at low temperatures, or otherwise thermally isolated, such as cold liquids, superfluids, and cryogens.
The most commonly used device to contain and insulate cryogens today is called a Dewar or vacuum flask. These devices are made by taking a single piece of metal, forming it into a cylinder and then with the same piece of metal forming a smaller cylinder inside the other cylinder. The purpose of this is to maximize the length thermal energy has to conduct through the curved piece of metal to get to the cryogen, with the only thermal conductivity being located around the lip of the container, usually the bottleneck. Some of these flasks use standoffs or metallic webs in a lower section of the cylinder away from the lip that provides for additional mechanical support of the smaller cylinder inside the larger one, instead of having the inner part of the flask being held solely by the lip. An example of such vacuum flasks is described in U.S. Pat. No. 872,795, issued in the year 1907.
This type of insulation system can be made very structurally sound, but only at the cost of severely increasing its thermal conductivity. Or, conversely, as is the case with most insulation systems, it can be made to better insulate but at a high cost to the structural integrity. The vacuum flask is the most common type of insulation system in use today. This is because it is a cheap way of insulating liquids in a design that can be easily manufactured, and is relied upon to store and transport most cryogens for relatively short periods of time. To allow for a cryogen to stay at the appropriate temperature for longer periods of time, active cooling systems are often used in addition to the Dewar insulation systems, in order to compensate for the quite significant heat leakages. Though this system is the most widely used, it is the standard minimum thermal insulator for most applications. It can often be used in conjunction with other systems.
Another common insulation system is multi-layered insulation (MU) system. MLI is composed of many layers of metal coated plastic sheets, all of very small thickness. Its operating mechanism is slowing down thermal transport by adding many different layers radiation must hit, before being reemitted. In order to be effective, MLI must as completely as possible cover what it is insulating, in order to shield it from radiation. This system is only of use when thermal transport through radiation dominates thermal transport through conduction or convection. For this reason, it is rarely used, as it is only needed in a few specialized circumstances, where conduction or convection is negligible. These could include uses in outer space such as satellites, other spacecraft, or inside or around vacuum flasks, to further insulate. However, the MLI systems are very fragile, giving next to no practical support to what it is insulating. It also has a comparable thermal conductivity to that of the above described vacuum flask.
A third less sophisticated in a sense, method of insulating a material is to simply surround it by another material that has a low thermal conductivity, such as plastics, Styrofoam™, Kevlar™, Mylar™, Kapton™, Aerogel, heat shield tiles, wood, other hot materials, other cryogens, pockets of air, and pockets of vacuum, carbon-carbon composites, glass, newspaper or other housing insulation, or asbestos. These other systems are often not comparable to the aforementioned solutions, neither structurally nor thermally, but occasionally offer very specific and desired combinations of thermal and structural properties. An example of such an insulation system is the tiles on the Space Shuttle. Furthermore, any number or combination of the above conventional devices can, and many have, been used together, or in combination. A few notable examples include, Layered Dewars (Dewars inside Dewars), Layered Dewar containing progressively colder cryogens, and Dewars layered with other insulation system such as MLI.
However, for many applications, the existing insulation systems designs are ineffective and insufficient for their requirements, because they are physically and structurally weak or would have a relatively high thermal conductivity, or both. For example, a physically and structurally weak system is undesirable and not suitable for application that are subjected to very high level of stress, forces, accelerations, very high vibrations and jerks, for example, in aerospace and aviation applications. Forces and stresses resulting from environmental conditions could damage or destroy the insulators of many existing systems. For many applications, very high thermal resistance is required so that the system is uncommonly insulative, especially if cryogenic liquids need to be transported and handled for longer time periods, at critical temperatures very near absolute zero. In such applications, any extra heat that reaches a storage tank can destroy the cryogen by evaporating it, and potentially damaging other devices. Even some of the best insulators that are currently available have severe limitations in many aspects, because the cryogen would heat up to fast and consequently phase change into a gas. Some existing insulation systems may provide for mechanical and structural strength, but are heavy and have poor thermal insulation. Also, due to poor insulation properties of cryogenic tanks for storage and transportation, a time period for using cryogen is so short that it entails significant impediments to the storage, use, supply, creation, and transport of cryogens.
Therefore, although there has been some advancements in the field of insulation systems, there is still a need for improved insulation systems having low weight, high mechanical strength, and excellent heat insulation capabilities.
According to a first aspect of the present invention, a storage system is provided. The storage system preferably includes an outer casing having an evacuated inner volume, and a vessel for storage located within the outer casing and having a plurality of protrusions distributed on an outer surface thereof. Moreover, the storage system also preferably includes a plurality of filamentary strands spanning the inner volume, wherein at least some of the plurality of protrusions are essentially tangentially contacted by a plurality of the filamentary strands to secure the vessel in six degrees of freedom relative to the outer casing.
According to another aspect of the present invention, a valve for a storage system is provided. The valve preferably includes a flexible, non-creasing tube, wherein a first end of the tube is in fluid communication with an interior of a storage vessel and a second of the tube is in fluid communication with atmosphere; and a lattice structure including an upper structure and a lower structure, wherein the upper structure and the lower structure move relative to each other to form an area contacting region therebetween. In addition, preferably the tube runs through the area contacting region of the lattice structure, and the relative motion of the upper structure and the lower structure controls an open-closed condition of the valve by contacting the tube with an area contact to bias a closed position and by removing the area contact to bias the open position.
Moreover, according to yet another aspect of the present invention, a thermal insulation device is provided. The thermal insulation device includes an outer shell exposed to an exterior area, a storage container located inside the outer shell, and a substantially vacuumized area between the outer shell and the storage container. Moreover, the thermal insulation device further preferably includes suspended filamentary strands located inside the vacuumized area, each filamentary strand having a first end and second end. In addition, preferably the first end and the second end of each filamentary strand is attached to an inner side of the outer shell to be suspended such that each filamentary strand holds the storage container at a fixed position.
These and other aspects and features of embodiments of the present invention will be better understood after a reading of the following detailed description, together with the attached drawings, wherein:
Similar reference characters denote corresponding features consistently throughout the attached drawings. The drawings are not intended to be depicted in scale, but are merely illustrative to show the embodiments of the present invention.
The present invention now is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
A first embodiment of the web insulation system is shown with respect to
The ends of the filamentary strands 60.1, 62.1, 64.1, 60.2, 62.2, 64.2 are attached to inner surface 24 of outer casing 20, at upper and lower sections of outer casing 20, respectively. As further depicted in
In another variant, it is also possible that four or more filamentary strands are used to support each protrusion 50.1, 50.2, also arranged in a rotational-symmetric fashion. Groups of filamentary strands 60.1, 62.1, 64.1, or 60.2, 62.2, 64.2 are arranged around each protrusion in the fashion as explained above, forming planes that are arranged in different angles to each other, preferably the planes also being arranged rotational-symmetric, when viewed from the z-direction. In the embodiment shown in
Also with respect to
Another aspect of the web insulation system used by container 10 is the strong reduction of thermal leakage paths and thermal leakage connections that have a very small cross sectional area and contact points by the use of a small number of Kevlar™ or Basalt fiber strands, or an equivalent material. For example, a surface of contact between the filamentary strands 60.1, 62.1, 64.1, or 60.2, 62.2, 64.2 with the respective protrusion 50.1 or 50.2 is as small as possible, preferably less than 10 mm2, to reduce the potential thermal leakage connection between strands 60.1, 62.1, 64.1, or 60.2, 62.2, 64.2 and protrusion 50.1, 50.2. Therefore, the protrusions preferably have a cylindrical shape to minimize the contact surface with corresponding strands, though other geometries can be used, for example a triangular cross-section with the edges of the triangle being in contact with the strands. Also, preferably exactly three strands 60.1, 62.1, 64.1, or 60.2, 62.2, 64.2 are used to have the minimal amount of strands that allows to restrict any movement of protrusion 50.1 and 50.2 in a direction of a plane formed by strands 60.1, 62.1, 64.1, or 60.2, 62.2, 64.2, so that the contact surface to protrusions are minimized.
Moreover, strands 60.1, 62.1, 64.1, or 60.2, 62.2, 64.2 are preferably arranged so that the outer surface 44 of vessel 40 is not in contact with strands 60, 62, 64, and the strands 60.1, 62.1, 64.1, or 60.2, 62.2, 64.2 are only in contact with inner surface 24 of outer casing 20 at the connection points 22 and protrusions 50.1-50.4. Due to the high tensile strength, preferably having a yield strength higher than 1000 MPa, of the filamentary strands, a cross section of the strands is also chosen to be as small as possible, to further reduce a thermal leakage path from inside vessel 40 and the exterior area of casing 20, preferably in the range of 0.01 mm2 to 10 mm2, but is dependent on the structural requirements of holding the vessel 40. Because of these small connection points and thin filamentary strands and the arrangement of the components as described above, the thermal leakage paths of these strands are the only conduit for thermal conduction, and therefore the insulation will be substantially improved as compared to conventional insulator. Therefore, filamentary strands 60.1, 62.1, 64.1, or 60.2, 62.2, 64.2, are chosen to have a high length-to-diameter ratio, preferably in a range of 10-1000:1.
Another feature of the first embodiment shown in
The reduced contact surface between strands 60.1, 62.1, 64.1, 60.2, 62.2, 64.2 and protrusions 50.1, 50.2, the reduced cross sectional area of strands 60, 62, 64, and their high length-to-diameter ratio lends to very low thermal conduction. Moreover, the use of Kevlar™ as a material for strands 60.1, 62.1, 64.1, 60.2, 62.2, 64.2 having a high tensile strength is sufficient to support a wide range of central cryogen tank designs without the need for thicker strands for more mechanical stability. In the embodiment shown in
With the above discussed features, container 10 exhibits excellent thermal insulation characteristics. Numerical estimations of the thermal conductivity have been made based on thermal conductivity values of Kevlar™ at about 0.04 W/(m*K) and of Basalt fiber at about 0.035 W/(m*K), and in which one-dimensional thermal conduction formulas were summed representing the thermal throughput of the container, having a vessel or tank 40 designed to hold one (1) liter of liquid nitrogen (LN2), having an upper bound of 4.36 mW, being container's total energy leak rate. This value appears to be about three (3) orders of magnitude smaller than average state of the art technology for cryogenic vacuum containers. One specific example are the cryogenic insulation systems from Sierra Lobo using multilayer insulation (MLI), these systems being designed for deep space missions where conserving cryogenic fuel is vital to satisfy mission parameters. The MLI-based system usually has a thermal throughput of about 4 W, about 1000 times greater than the estimates of the container 10 of the presented web insulation system suggests.
Also, container 10 proposes a design that is very sturdy, cost-effective, light-weight, and extremely thermally insulating. The filamentary strands can be made of very thin filaments of Kevlar that are light weight, and the multiple attachment points 22 and protrusions 50.1, 50.2 allow to have multiple mechanical support points spaced out equally around the vessel 40. This allows to reduce thicknesses of the materials used for vessel, and also the sturdiness of a neck or supply tube portion, as compared to a conventional design in which the only attachment point of vessel or tank to the outer casing 20 is via the neck or supply tube of tank. In addition, in light of the inherent flexibility of strands 60.1, 62.1, 64.1, 60.2, 62.2, 64.2, vibrations can be absorbed by the stands, and will avoid sudden or creeping breakage of the vessel 40 and supply tube 70.
Generally, the container can be used to thermally isolate a substance located in vessel 40, or otherwise separate two or more substances in a way that minimizes the total energy transferred as heat between an inner area of vessel 40 and an outside area of outer casing 20. This system can be made in a way that is far physically stronger and more stable than many current insulation systems with superior thermal insulation properties, and at the same time has orders of magnitude better thermal insulation than the best state of the art. Kevlar is an ideal material for manufacturing the strands 60.1, 62.1, 64.1, 60.2, 62.2, 64.2, because of its light weight, very high tensile strength, and its very low thermal conductivity. Other materials having similar properties can also be used. The very high tensile strength is necessary for some important features of container 10, as next discussed.
First, the high tensile strength of Kevlar permits relatively thin strands 60.1, 62.1, 64.1, 60.2, 62.2, 64.2 to hold a heavy load with vessel or tank 40 if arranged as a web explained above. Second, the higher the tensile strength of the material used for the strands, like Kevlar, the less of it is needed to hold two objects, being vessel or tank 40 and outer casing 20 at a constant distance. Strands that can be made very thin due to its very high tensile strength allowing to reduce the cross sectional area as seen in a longitudinal direction, that at the same time allows to reduce the thermal conductance. Kevlar, having exceptional tensile strength of around 3000 MPa and light weight with a relative density as compared to water of 1.44, make it a preferred choice for manufacturing the strands. In this respect, even though Kevlar has a tensile strength higher than steel, it has an extremely low thermal conductivity, near the low end of the existing thermal conductivities of any known material at 0.04 W/m-K, whereas the thermal conductivity of steel ranges from approximately 10/m-K-60 W/m-K. Therefore, by holding vessel 40 inside outer casing 20 with strands 60.1, 62.1, 64.1, 60.2, 62.2, 64.2, and by evacuation the inner space 30 to create substantial vacuum therein, it creates an insulation system that has superior insulation characteristics, mechanical strength, and reduced weight as compared to conventional insulation system.
The proposed web insulation system with the special arrangement of strands 60.1, 62.1, 64.1, or 60.2, 62.2, 64.2 and the vacuumized space 30 in which strands are located has many advantages over the conventional systems. As explained above, the thermal insulation properties of the web insulation system are several orders of magnitude better than comparable conventional systems. The only solution that could be possibly compared in its performance having similar insulation properties would be a system that is substantially more expensive and more complex, and having a very low tolerance in its manufacture, such as the insulation system incorporated in the Gravity Probe B satellite experiment of 2004 of the National Aeronautics and Space Administration (NASA) and Stanford University. It can also be a replacement to the classic Dewar design in that it may present superior insulating properties having exceptional physical strength, light-weight, and simple design. Compared to the classic Dewar design, it has at least a comparable strength, but is a far superior insulator. The web insulation system also has a very low material cost, and a low cost of manufacture.
Widespread use of the web insulation system could also drastically increase the ease of handling for cryogenic materials, and the time limit for using cryogen after delivery and storage in tanks, currently very short, could be substantially increased. With the proposed web insulation system this time limit can be substantially increased and therefore will make most applications far easier and more efficient. It is known that the cooling to create and preserve the cryogen takes a large amount of energy, thus any cryogen lost is a large waste of energy and therefore cost. Similarly, actively cooling a cryogen to keep the cryogen at the critical temperature can be very energy intensive, and is necessary when insufficient insulation is used, or sufficient time has passed. Effectively removing this time limit severely lowers the cost of creating, storing, and using a cryogen because there is little lost due to poor insulation.
Therefore another advantage of the present web insulation system is substantial cost saving for cryogenic applications, because one of the most important factors in the price of liquid nitrogen are transportation costs associated to losses of liquid nitrogen during transportation from the distributor to the consumer. Also, substantial costs are spent by researchers and hospitals as their expensive cryogens succumb to ambient heating during storage. Currently, the price of liquid nitrogen is about $0.55/liter, and even in a relatively short transportation time, much liquid nitrogen can be lost that will result in a substantial price increase. These costs are substantially reduced when using the proposed container 10 for transporting liquid nitrogen, because the liquid nitrogen losses during transport are negligible. These savings on transport costs and storage costs would be even more obvious if more expensive liquids were transported, for example liquid helium at about $4/liter. Also, the weight of container 10 is more or less the same as the weight for conventional dewars, thereby not increasing transportation costs that are related to the weight of transported goods, for example for aerial or space transportation.
The low material cost, manufacturing costs, and severely reduced energy costs when operating the proposed web insulation system lead to a strongly reduced overall cost in using cryogens in any way. This should lower the cost of purchasing cryogenic material, and create an increased market niche for making insulation systems in general, with a significant portion of that niche relating directly to the present web insulation system.
A lattice or pressure structure having upper and lower frames 330, 340, with upper side walls 350, 352, lower sidewalls 360, 362, supporting plates 320, 322 for holding the flexible padding 324, 326, respectively, is arranged inside space 30. The pressure structure is configured such that upper and lower frames 330, 340 can be moved towards each other to compress the tube 310 for closing channel, and to release pressure on tube 310 to open channel 312, indicated by arrows F in
This mechanism of valve 80 is especially important to cope with cryogenic temperatures that are present in channel 312 of tube 310 and for the repeated opening and closing of a valve 80, and to prevent creasing that could create small cracks and holes in tube 310, allowing for leakage, reduction and even destruction of the vacuum of inner space 30. At cryogenic temperatures, many materials become brittle, and are more prone to wear and cracking with repeated and successive deformities of the structure. Therefore, creasing should be avoided because it can lead to leakages. This is especially important when dealing with superfluid cryogens, as they can easily leak through very small cracks on an atomic scale. Leaking cryogen into the inner space 30 would in turn lower the insulative properties of container 10 by compromising the vacuum. Frames 330, 340 and plates 320, 322 are preferably made of a stiff, lightweight material, that maintains its structural integrity at cryogenic temperatures for example aluminum, or a material having similar properties.
Next, supply tube 570 is arranged to protrude upwards in z-direction for providing and delivering stored content of storage container 510, and protrudes concentrically into neck 521 of outer casing. A valve system 580 is also arranged inside neck for opening and closing access. For lateral stabilization of inner volume 540 inside outer casing 520, another group of filamentary strands 560 are arranged around supply tube 570 on a horizontal x-y plane, also in a star configuration. Instead of having a protrusion associated with group 560 of strands, the strands are arranged to touch side walls of supply tube, and an upper surface of inner volume 530. Thereby, strands 560 are configured to stabilize volume 530 against lateral movements and accelerations, but also to hold inner volume 530 at its place along the z-direction. Also, while group of strands 561, 562, and 563 have the function of carrying the weight of volume 530, group of strands 560 are merely for stabilization purposes. Therefore, stands of group 560 can be made thinner than strands of groups 561, 562, and 563. Also, for additional weight and thermal insulation purposes, because the horizontal strand of the groups 561, 562, and 563 carries most of the weight, these three stands can be made thicker than the other two strands of the group.
The present invention has been described herein in terms of several preferred embodiments. However, modifications and additions to these embodiments will become apparent to those of ordinary skill in the art upon a reading of the foregoing description. It is intended that all such modifications and additions comprise a part of the present invention to the extent that they fall within the scope of the several claims appended hereto. Like numbers refer to like elements throughout. In the figures, the thickness of certain lines, layers, components, elements or features may be exaggerated for clarity.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and/or clarity.
As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, phrases such as “between X and Y” and “between about X and Y” should be interpreted to include X and Y. As used herein, phrases such as “between about X and Y” mean “between about X and about Y.” As used herein, phrases such as “from about X to Y” mean “from about X to about Y.”
It will be understood that when an element is referred to as being “on”, “attached” to, “connected” to, “coupled” with, “contacting”, etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, “directly on”, “directly attached” to, “directly connected” to, “directly coupled” with or “directly contacting” another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed “adjacent” another feature may have portions that overlap or underlie the adjacent feature.
Spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper”, “lateral”, “left”, “right” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is inverted, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the descriptors of relative spatial relationships used herein interpreted accordingly.
