Abstract:
A method of insulating a member, such as a cryogenic tank, pipe, or other cryogenic or extreme temperature element with multilayer insulation, and a packaged multilayer insulation blanket for use in the method. The packaged blanket includes (1) a multilayer insulation blanket including a plurality of alternating layers of aluminum or other heat-reflective foil and microfiberglass insulation spacer material, and (2) two layers of plastic sheeting sandwiching the multilayer insulation blanket therebetween. Each layer of plastic sheeting has at least one edge which is sealed to thus define an evacuated inside space containing the multilayer insulation. In the method, the edge of the packaged insulation is opened and an edge of the multilayer insulation blanket therein is attached to the cryogenic tank, container or other member to be insulated. The multilayer insulation is then guided onto or around the member, and out from between the plastic sheeting until edges of the multilayer insulation abut. Lastly, the abutting edges of the multilayer insulation blanket are attached with an appropriate means such as heat reflective tape in a manner to avoid “heat shorts”.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method of insulating a member, such as a cryogenic tank, pipe, or other cryogenic or extreme temperature member with multilayer insulation, and a packaged multilayer insulation blanket for use in the method. 
     BACKGROUND OF THE INVENTION 
     Multilayer insulation has been used for quite some time to insulate cryogenic tanks, cryogenic pipes, and other cryogenic or extreme temperature containers, members or elements such as superconducting magnet assemblies or power distribution devices, etc. Multilayer insulation for the above purposes is described, for example, in U.S. Pat. No. 5,590,054 to McIntosh. This patent describes a variable density multilayer insulation formed of alternating layers of separator materials such as glass fiber materials, and heat radiation barriers such as metal foil, such as copper or aluminum foil, or double aluminized Mylar (DAM). 
     It has also been known, prior to the above McIntosh patent, that thermal radiation heat transfer, as defined by the Stephan-Boltzmann law, that heat transfer between parallel surfaces is a function of the emissivities of the surfaces and the warm absolute temperature taken to the fourth power against the cold absolute temperature taken to the fourth power. Because of the powerful effect of raising the temperatures to the fourth power, the impact of radiation between radiation barriers near a cold wall of a cryogenic vessel drops dramatically from the impact of radiation between radiation barriers near the vessel&#39;s warm wall. Correspondingly, the temperature difference between the reflective barriers increases as the cold wall is approached. Thus, when cryogenic multilayer insulation is used to insulate between the inner and outer vessels of a Dewar vessel system, the heat reflective layers near the cold wall of the inner vessel are spaced further apart than the heat reflective layers closer to the warm wall. For this reason, prior methods of wrapping cryogenic containers using an orbital or wrapping method are not necessarily optimized for thermal performance, because these methods are unable to produce variable density multilayer insulation of the highest thermal efficiency. 
     Because the advantages of multilayer insulation have long been known, many methods have been proposed to simplify the installation of such multilayer insulation on large containers or tanks. 
     U.S. Pat. No. 4,104,783, to Schultz, et al., for example, discloses a method of installing multilayer insulation on the outside of a tank, by winding insulation and wire mesh around a cryogenic tank to form such a structure. A similar method is also disclosed in U.S. Pat. No. 3,241,702, to C. R. Navikas. By this latter method, alternating layers of glass fiber sheet material and perforated aluminum foil are wrapped around a cryogenic tank using a relatively complicated assembly of rollers, tensioners and apparatuses for holding and turning the containers or tank to be insulated. The multilayer insulation is wrapped around the container in a manner such that the ends of the insulation extend beyond the dimensions of the container and can be folded down and taped in place to insulate the entire container. An inner container thus wrapped is then inserted in an outer container to form a Dewar vessel construction. 
     More sophisticated methods of insulating cryogenic containers or vessels are disclosed in U.S. Pat. No. 4,741,456, to Faudou, et al., and U.S. Pat. No. 5,749,537, to Muzio, Jr., et al. The above Faudou., et al. patent discloses a method in which several insulating layers are helically wound around a tank which is supported and rotated about an axis by a shaft. 
     The Muzio, et al. patent discloses a number of prior art methods of wrapping cryogenic insulation around an inner tank of a Dewer vessel system in which alternating layers of cryogenic insulation paper and foil are wrapped around the tank in what is referred to as “serial wraps.” Each wrap consists of insulating paper spacer with metal foil centered thereon. An edge portion of the insulating paper abuts an edge portion of an adjacent layer or slightly overlaps the adjacent layer. While alternating layers of foil are slightly narrower in width than the insulated paper so that the edges do not contact one another. By this serial wrapping technique, it is ensured that alternating layers of insulating paper and foil are provided without significant “heat shorts” in which the cold side of one foil layer contacts the hot side of an adjacent foil layer. This method also requires considerably complicated and expensive machinery for holding the container to be insulated, for adjusting tension on the separately stored paper and foil layers and a frame suitable of supporting the entire apparatus. As can be appreciated by viewing the apparatus of Muzio, Jr., et al., a complicated and unwieldy drive means is provided including shafts, drives, translation devices, and tension devices, as well as a suitable braking system for providing adjustable tension control for the various rollers, and a frame for supporting the rollers, container, etc. Such large and complicated apparatuses are certainly not easily applicable to every situation in which a cryogenic container or other member needs to be wrapped with multilayer insulation. In addition, considerable skill and specialized training is required to operate the apparatus. Also, the Muzio, Jr. method, like other prior art methods can not easily be applied to thermally efficient, variable layer multilayer insulation. 
     It is therefore an object of the present invention to provide a method of insulating a cryogenic member such as a cryogenic container or tank, cryogenic pipe, or other cryogenic or extreme temperature member with multilayer insulation with a minimum of expense, in order to solve the problems of the prior art. 
     It is further object of the present invention to provide a method of insulating a cryogenic member such as a cryogenic container or tank, cryogenic pipe, or other cryogenic or extreme temperature member quickly, efficiently, and without the need for special equipment. 
     It is a particular object of the present invention to provide a method of insulating a cryogenic member such as a cryogenic container or tank, cryogenic pipe, or other cryogenic or extreme temperature member that is superior to the spiral or orbital wrapping technique conventionally used. The present invention strives for a method that avoids the labor- and time-intensive method of carefully rolling foil and spacer material onto the vessel without creating leaks or heat shorts. 
     It is a still further object of the invention to provide a method which can vary the thickness and/or quantity of spacer material between layers in any desired fashion. 
     It is also an object of the present invention to provide a packaged multilayer insulation and a method of packaging and producing fragile, multilayer insulation, particularly variable density multilayer insulation blankets or composites, which can be easily transported without damage and applied without special training and without significant time, labor, or complicated apparatuses. 
     It is also an object of the present invention to provide a method of packaging and a packaged insulation wherein the multilayer insulation is packaged and can be transported with low or no moisture content so that any subsequent evacuation required during the installation of the insulation is simplified. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, and in order to solve the above and other objects, the present invention provides a method of insulating a member, such as a cryogenic tank, pipe, or other cryogenic or extreme temperature element with multilayer insulation, and a packaged multilayer insulation blanket for use in the method. 
     According to the present invention, a method is provided of insulating a member with multilayer insulation, comprising the following steps. First, a packaged multilayer insulation blanket is provided. The packaged blanket includes (1) a multilayer insulation blanket including a plurality of alternating layers of heat-reflective foil and insulation spacer material, and (2) two layers of plastic sheeting sandwiching the multilayer insulation blanket therebetween, each layer having at least one edge, wherein the edge of the plastic sheeting is sealed to thus define an inside space containing the multilayer insulation. The inside space is preferably evacuated, partially evacuated, purged of air with an inert gas, or otherwise kept dry or in a low moisture state. Second, the edge of the packaged insulation is opened and an edge of the multilayer insulation blanket is attached to the member to be insulated. Third, the multilayer insulation is guided onto or around the member, and out from between the plastic sheeting until edges of the multilayer insulation abut. Lastly, the abutting edges of the multilayer insulation blanket are attached with any appropriate means such as heat reflective tape, or other fasteners. Preferably, reflective tape is used to ensure that no leaks or “heat shorts” result after the insulation is applied. The member to be insulated by the method according to the present invention can be a cryogenic container, such as the inner container of a Dewar structure having an inner container, an outer container, and evacuated space therebetween. The member can also be a cryogenic pipe, a heat shield for a spacecraft, superconducting power distribution equipment, such as superconducting magnets, or any one of a number of cryogenic or extreme temperature applications. 
     The heat reflective foil of the multilayer insulation is preferably aluminum foil, but can be any other suitable material such as double aluminized Mylar (DAM). The insulation spacer material is preferably microfiberglass insulation. 
     The method, in a preferred embodiment, comprises the further steps of providing a second packaged multilayer insulation blanket and installing it around the first multilayer insulation blanket so that the abutting edges of the second multilayer insulation blanket are offset from the abutting edges of the first multilayer insulation blanket. 
     The invention also relates to a packaged multilayer insulation blanket comprising (1) a multilayer insulation blanket including a plurality of alternating layers of heat-reflective foil and insulation spacer material, and (2) two layers of plastic sheeting sandwiching the multilayer insulation blanket therebetween, each layer having at least one edge, wherein the edge of the plastic sheeting is sealed to thus define an evacuated inside space containing the multilayer insulation. 
     Further objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments, when considered together with the attached figures of drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B show the construction of the packaged multilayer insulation according to the present invention. 
     FIGS. 2A and 2B show the first and second multilayer insulation blankets used in the exemplified preferred embodiment of the present invention. 
     FIG. 3 shows first and second multilayer insulation blankets installed on a container according to the present invention. 
     FIG. 4 shows a plan view of the multilayer insulation blanket according to the present invention. 
     FIG. 5 is a cross-sectional view through an insulated tank insulated with variable density multilayer insulation according to the method of the present invention. 
     FIG. 6 is a side view of a tank according to the present invention in which the first multilayer insulation blanket has been installed, but the top or second multilayer insulation blankets have not yet been installed. 
     FIGS. 7A and 7B show, by means of top views of the end of a tank, an alternative method of insulating the end of a tank with the method according to the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention will now be described with reference to a preferred embodiment, as shown in the Figures in which like reference numerals refer to like parts. 
     FIGS. 1A and 1B disclose the packaged multilayer insulation blanket according the present invention and a method of manufacturing the packaged blanket. The multilayer insulation blanket  1  is manufactured in a suitable, conventional manner, of multiple layers of heat-reflective foil  23  and low heat conductivity insulation spacer layers  22 , made of suitable material such as microfiberglass insulation. These layers  22 ,  23  and their construction will be discussed in more detail with respect to FIGS. 2A and 2B below. 
     According to the present method of manufacturing a packaged multilayer insulation, a top sheet  2  of plastic sheeting and a bottom sheet  3  of plastic sheeting are disposed on either side of the multilayer insulation blanket  1 . After the multilayer insulation is carefully disposed between the top and bottom sheets  2 ,  3 , the edges  11 ,  12  and  13  of the plastic sheeting, which extend beyond the dimensions of the multilayer insulation blanket  1 , are sealed in any appropriate manner, such as using adhesives or heat sealing. Heat sealing is preferable. Before the remaining edge  14  of plastic sheets  2 ,  3 , is completely sealed, the space between the sheets  2  and  3  is preferably evacuated. While any suitable vacuum can be used, the vacuum is preferably about 100 torr. The evacuation of the inside space serves, among other things, the purpose of keeping the multilayer insulation compact and moisture free. In addition to, or instead of evacuation, the inside space of the packaging can be purged of air with an inert gas. Also desiccants can be added to the package, in addition to or instead of evacuation, to keep the blanket dry and facilitate any subsequent evacuation required during installation of the multilayer insulation. 
     After evacuation, the remaining of edge  14  is sealed to form a packaged multilayer insulation  10  in which the multilayer insulation blanket  1  is enclosed in the evacuated space between sheets  2  and  3 . The package structure according to the invention allows the multilayer insulation blanket to be easily transported without damage, and without special containers or other treatment. It will be recognized that while FIGS. 1A and 1B disclose a rectangular multilayer insulation blanket  1 , multilayer insulation blankets of any desired configuration can be packaged according to the present invention. 
     FIGS. 2A and 2B disclose first and second multilayer insulation blankets  20  and  21 , respectively. Referring to FIG. 2A, spacer layers  22  are more numerous toward the top of FIG. 2A than toward the bottom of FIG.  2 A. This variable density construction is, as stated above, intended to take advantage of the effect that the impact of radiation between barriers near a Dewar vessel&#39;s cold wall drops dramatically from the impact of radiation between radiation barriers near the vessel&#39;s warm wall. Thus, by making the multilayer variable insulation as shown in FIG. 2A, fewer layers of insulation can provide equivalent heat loss, thus saving both materials and space by making the overall insulation more efficient. While blanket  20  comprises  19  spacer layers  22 , and  7  heat reflective foil layers  23 , other configurations may be desirable, depending on the use to which the blanket  20  is put and the temperature of the member to be insulated. 
     FIG. 2A also shows plastic sheeting  2 ,  3 , surrounding the multilayer insulation blanket  20  as it would appear in the packaged product. 
     FIG. 2B shows the second multilayer blanket  21  of the present invention. The second blanket has a similar variable density structure to the first blanket  20 , in that the spacer layers  22  closer to the top of the figure are more numerous than at the bottom of the figure. The second blanket  21  comprises  11  spacer layers and  8  heat reflective foil layers  23 , but other configurations can be used as required by a particular application. Generally, the heat reflective foil layers of blanket  21  are closer together and more numerous than the heat reflective foil layers of blanket  20 . This structure is advantageous, because, in the illustrated embodiment, the first blanket  20  is intended to be closer to the cold wall of a Dewar container structure, and the second blanket  21  is intended to be closer to the warm wall of such a structure. 
     The low heat conduction insulation spacer layers  22  are preferably made of a paper of microfiberglass, ceramic paper or other suitable material. While there is some latitude in the fibers which make up the paper, the layers must be flexible so as to be accurately wrapped onto the container  30  (See FIG. 3) or other member. The fibers must retain the felting properties of the insulation at cryogenic temperatures. These requirements mean that the fibers are usually chosen from a limited group of fibrous materials. Natural inorganic fibrous material, such as asbestos, has been used in the past, and byproduct inorganic fibrous material, such as spun slag, has also been used. However, neither of these materials, or other like inorganic materials, are preferred in the method of the present invention. Organic materials are also not preferred for many uses because the spacer material must be oxygen compatible and many organic materials are flammable, oxidizable, or otherwise not oxygen compatible. Nonetheless, because the spacer layers are not subjected to the same kind of mechanical stress applied in the prior art orbital wrapping method, the variety of materials capable of being used in the present invention is greater than in the prior art. 
     In the present invention, while the spacer layer  22  is made of fibrous material, as in the prior art, that fibrous material, in combination with the heat-reflective foil, must be capable of retaining the feltlike structure of insulation even at very low temperatures, such as, for example, the temperature of liquid helium (4.2° K.), hydrogen (20.4° K.) or oxygen (90.2° K.). However, the method according to the present invention can also be used to insulate hot members up to about 660° C. 
     The spacer layer  22  should have a thickness of about 0.0025 in. to about 0.0035 in. to ensure both sufficient strength to allow the constructed multilayer insulation blanket to have sufficient flexibility for wrapping onto the container and to ensure the above-noted functionalities at cryogenic temperatures. 
     It is preferred that the fibrous material is a microfiberglass, and it is most preferred that the microfiberglass is borosilicate glass. While there is some latitude in the diameter of the glass, especially when the microfiberglass is borosilicate glass, it is preferred that the microfiberglass has an average diameter range of between about 0.3 to 10 microns, especially about 0.5 to 4 microns, for example, about 0.75 to 1.5 microns. 
     The fiber length should also be short, for example, less than about 2 mm, especially less than 1 mm, for example, between 0.1 and 1 mm. One particularly suitable material for the heat spacer layer  22  is comprised of unbonded glass fibers and manufactured by the Lydall Manning Company in Troy, NY, and sold under the CRYOTHERM trademark. One especially preferred material is CRYOTHERM  243 . Another particularly preferred material is ceramic fiber paper material manufactured, such as the ceramic fiber paper of high-purity alumina-silica paper manufactured by the Lydall Manning Company in Troy, N.Y., and sold under the LYTHERM trademark. 
     While certain organic fibers, for example, polyester fibers, can function in cryogenic applications, as stated above, it is preferred that combustible organic fibers not be used in cryogenic applications, since cryogenic tanks often contain combustible or oxidizing liquefied gases. 
     Likewise, there is some latitude for the heat reflective foil  23  of the multilayer insulation blankets  20 ,  22  according to the present invention. The most satisfactory materials for the heat reflective foil are metal foil, such as copper stainless steel or aluminum foil, or double aluminized Mylar (DAM). When the aluminum foil or other suitable material has a thickness of about 0.00025 to about 0.0015 in., the foil has both the strength and flexibility to be applied in the manner according to the method of the present invention without breaking, tearing, wrinkling, or the like, and to function properly at cryogenic temperatures. Because the multilayer insulation of the present invention uses a prefabricated structure, much thinner aluminum foil layers having thicknesses as small as 0.000285” can be used without tearing. If aluminum foil is used, the aluminum foil preferably has a “0” temper. 
     FIG. 4 illustrates a plan view of the multilayer insulation blanket  1  in which cut out portions  40  are provided to allow the multilayer insulation to be folded over the edge of the top of a container to be insulated. It will be recognized by one of ordinary skill in the art that cutouts  40  could be provided on both edges of the blanket to allow the blanket to be folded over at either end of a container, or to be cut out in any other desirable way to compensate for the geometry of the container or other member to be insulated. 
     FIG. 3 is a schematic view showing first multilayer insulation blanket  20  and second multilayer insulation blanket  21  installed around container  30 . It should be noted that the seam  31  at which the edges of multilayer blanket  20  abut is offset from the seam  32  of multilayer insulation blanket  21  in order to prevent heat leakage. The installation of multilayer insulation blanket  20  and  21  around a container  30  will now be described with reference to FIGS. 5 and 6. 
     A packaged insulation layer blanket  10  containing multilayer insulation blanket  20  is transported to the site of a container  30  to be insulated. An edge  14  of the packaged insulation  10  is opened and one edge  61  of multilayer insulation blanket  20  is attached to container  30  by tape, adhesive, or other suitable means. Multilayer insulation blanket  20  is then carefully guided out from between plastic sheets  2  and  3  and onto or around container  30 . After the multilayer insulation blanket  20  has been completely guided around tank  30  and edges  61  and  62  abut, the edges are fastened in any suitable manner such as adhesive or heat-reflective tape  60 . The installation is completed so that adjacent heat reflective foil layers  23  do not touch so as to create “heat shorts.” It will be appreciated that the present method is superior to prior art orbital or spiral wrapping methods because of its ease and quickness. A container or other member can be insulated according to the method of the present invention with a 75% savings in time by persons not having any specialized skill or training. 
     FIG. 5 shows container  30  after it has been completely insulated by multilayer blankets  20  and  21 . It will be noted that a top circular plug  50  of multilayer insulation equivalent in construction and thickness to multilayer insulation blanket  20  is installed on the top of container  30  and attached in a suitable manner, such as with reflective tape. 
     Thereafter, multilayer insulation blanket  21  is installed around multilayer insulation blanket  20  in the manner described and shown in FIG.  3 . After installation of multilayer insulation blanket  21 , a second top plug  51  is installed on top of plug  50  and attached to top edges of blanket  21  with suitable means such as reflective tape  55 . In this embodiment, the bottom edge of blanket  20  is folded underneath the bottom of tank  30  until it abuts outlet structure  52 . A circular plug  53  is provided for the bottom of the tank having a configuration suited to surround outlet structure  52  and abut the bottom edges of blanket  21 . 
     FIGS. 7A and 7B show an alternative embodiment of the method of the present invention in which the end of a container  30  is insulated by folding over an excess of multilayer insulation blanket  20  (or  21 , or both) is folded over to cover the end of container  30  and abut in seam  70 . The resulting pointed, folded ends  71 ,  72  are then folded over as shown in FIG.  7 B. The method of this embodiment also ensures that the container  30  is insulated with any resulting “heat shorts” in the blanket  20  or  21 . 
     According to the present invention, the method can be used to insulate container  30 , or to insulate a Dewar structure in which container  30 , as insulated by blankets  20  and  21  is disposed inside a further container (not shown). One of skill in the art will also appreciate that the method according to the present invention can be used to insulate any other cryogenic or extreme temperature member such as a cryogenic pipe, a cryogenic superconducting electricity distribution element or superconducting magnet, etc. As stated above, the method can also be used to insulate high temperature vessels or members. 
     As discussed above, the present invention has a number of significant advantages over the prior art. The method greatly reduces the installation time of insulation, particularly oxygen compatible, variable density, multilayer insulation for cryogenic purposes. The method allows prefabrication of oxygen compatible multilayer insulation blankets in any desired configuration. The method of the present invention, particularly the packaged multilayer insulation blanket, prevents the individual layers of the multilayer insulation from shifting during handling and installation. The packaging protects the multilayer insulation from possible contamination and damage during shipping, storage, and installation. The method using the packaged multilayer insulation according to the present invention eliminates thermal shorting due to mechanical fastening, for example, tag pins or stitching. Lastly, the packaged multilayer insulation blanket according to the present invention allows the prefabrication and easy application of multilayer insulation with variable layer density, a result which is not easily achieved with the standard spiral or orbital vessel wrapping process. As is known in the art, variable layer density multilayer insulation is more efficient and allows fewer layers of insulation for equivalent heat loss. 
     While the present invention has been illustrated by means of a preferred embodiment, one of ordinary skill in the art will recognize that modifications, amendments, additions, and substitutes and deletions can be made while remaining within the scope and spirit of the present invention as defined by the appended claims.