US3397720A - Multiple layer insulation for a cryogenic structure - Google Patents

Description

P. JONES Aug. 20, 1968 MULTIPLE LAYER INSULATION FOR A CRYOGENIC STRUCTURE Filed OCt. 23, 1964 2 Sheets-Sheet 1 INVENTOR.

PE re-e J'o/vas P. JONES Aug. 20, 1968 MULTIPLE LAYER INSULATION FOR A CRYOGENIC STRUCTURE 2 Sheets-Sheet 2 Filed Oct. 23, 1964 INVENTOR.

P5 7222 J'o/vss BY I I United States Patent 3,397,720 MULTIPLE LAYER INSULATION FOR A CRYOGENIC STRUCTURE Peter Jones, Los Angeles, Calif., assignor, by mesne assignments to Hitco, Gardena, Califl, a corporation of California Filed Oct. 23, 1964, Ser. No. 405,929 7 Claims. (Cl. 138149) ABSTRACT OF THE DISCLOSURE A thermal insulation of alternating plain reflective plastic sheets and dimpled plastic sheets, the dimples being spaced apart along two directions substantially at right angles to each other. Support means at each end of an insulation pack are provided to prevent contact of the insulation with inner or outer walls of an insulated container.

This invention relates to a multiple layer insulation for a cryogenic pipe line, and particularly to the means to effectively prevent excessive heat transfer from the external atmosphere or room temperature to the cryogenic material which is flowing within a spaced inner pipe or conduit. The cryogenic material referred to in this application may be liquid hydrogen, nitrogen, oxygen, or the like, all of which have a very low temperature while in a liquid state.

My invention provides an effective means of insulating an inner conduit carrying cryogenic material from an outer pipe or jacket which surround-s the conduit to prevent heat from being transferred from the outside, or the atmosphere, to the cryogenic material whereby that material may be caused to vaporize. This means includes alternate layers of flat sunfaced reflective sheets, such as polyester film, separated by corrugated or dimpled sheets of the same reflective polyester film.

Another object of my invention is to provide a novel insulation means of the character stated, whereby a plurality of superposed sheets are supported at their ends by pads formed of glass fibers or other insulating material.

Another object of my invention is to provide an effective means to keep the flat reflector sheets separated, so that the reflector layers do not transmit heat by means of direct contact with each other.

Still another object of my invention is to provide a novel insulation means which is relatively inexpensive, and which requires a minimum of labor to install. Furthermore, my insulation means provides sufiicient strength and excellent resistance to external dynamic effects and damaging vibrations. The entire assembly of the reflector sheets is totally separated from contact with either cold or warm surfaces. This is accomplished by the end supports which are formed of strong material of low heat conductivity.

Other objects, advantages and features of invention may appear :from the accompanying drawings, the subjoined detailed description and the appended claims.

In the drawing:

FIGURE 1 is a perspective view of one pair of superposed insulation sheets.

FIGURE 2 is a fragmentary view of an insulated pipe line embodying my invention and with parts broken away to show interior construction.

FIGURE 3 is a transverse sectional view taken on line 3-3 of FIGURE 2.

FIGURE 4 is a fragmentary sectional view taken on line 4-4 of FIGURE 3.

FIGURE 5 is a fragmentary longitudinal sectional view taken on line 55 of FIGURE 3.

FIGURE 6 is an enlarged transverse sectional View of the insulation within the area indicated by 6 in FIG-URE 5.

FIGURE 7 is a fragmentary vertical sectional view of a modified form of insulation sheet support.

Referring more particularly to the. drawing, the numeral 1 indicates an inner conduit which will be termed the cryogenic conduit. This conduit carries the cryogenic material, such as liquid hydrogen, nitrogen, oxygen, or the like. An outer jacket 2 is spaced from the conduit 1 and is concentric with that conduit. The conduit 1 and the jacket 2 are both metallic pipes and of suflicient strength and thickness to carry the particular load which is required. Anannular space 3 is thus formed between the conduit 1 and the jacket 2 and this space is normally evacuated to assist in the heat insulation of the inner conduit 1. Evacuation of thespace 3 occurs after the insulation units (to be subsequently described) are in place and after all, or a substantial part, of the entire conduit has been layed.

At intervals throughout the length of the conduit 1, I provide supporting annular rings 4, which are preferably formed of glass fibers or other similar somewhat porous material, but which has sufficient compressive strength to support the conduit 1 'within the pipe or jacket 2. The ring 4 is sufficiently porous so that air can readily pass through it when thespace 3 is being evacuated. Asleeve 5 is concentric with the ring 4 and is positioned on the outside of the ring, extending between the outer surface of the ring and the inner surface of the jacket 2. Thissleeve 5 is also formed of glass fibers or other suitable porous material which has sufficient compressive strength. Thesleeve 5 and the ring 4 are slightly spaced at their adjacent faces by aspacer ring 6. Thespacer 6 is shorter than the ring 4 andsleeve 5 to provide annular grooves to receive the ends ofannular insulation packs 7. Theinsulation packs 7 extend longitudinally between adjacent supporting rings 4, as shown, and these insulation packs are assembled in the following manner: A flat facedpolyester sheet 8 termed Mylar is coated by a reflecting material such as silver. Theflat sheets 8 are separated by corrugated or dimpled sheets 9, which sheets are also formed of a polyester coated material termed Mylar. The corrugated or dimpled sheets 9 have a permanent corrugation or dimple formed therein, and since the polyester sheet is so formed that the corrugation or dimpling of the sheet will not flatten or diminish, due to normal weight, vibration, or the like. The corrugated or dimpled separations, while contacting adjacentflat insulator sheet 8, will still not cause a heat flow or transfer through the insulating pack, due to the fact that the points of contact are small and, furthermore, the corrugated or dimpled sheets are also reflective structures, thus materially reducing the heat flow due to contact. The dimples of the separating sheet 9 are spaced along two directions which are disposed substantially at right angles to each other. A characteristic of the polyester sheet termed Mylar is such that no drying or baking cycle is required to dry moisture out of the insulation. The composition of the polyester film precludes the absorption of moisture or the entraprnent of gases. Also the dimpling or corrugation of the polyester sheets 9 provides convenient escape routes or passages for atmospheric air which might be trapped between theflat sheets 8 and the dimpled sheets 9 during the vacuum pump down. These qualities of the polyester sheets and their construction as described materially simplifies the maintenance of the required vacuum within the pipe line, and also materially simplifies this pump operation.

In FIGURE 7 I have illustrated a modified form of end support for the insulating bundles of polyester sheets, consisting of an outer annular supportingring 10 which is formed with an inner annular groove 11. A pair of inner annular sleeves 12-13 are spaced longitudinally of the conduit 1 to provide anannular space 14. The ends of theadjacent insulation packs 7 extend into the space between therings 10 and the spaced sleeves 1213 as shown. To hold thesepacks 7 in position, particularly as to their adjacent abutting ends, I provide a short length ofinsulation 14 which fits in the groove 11. The insulation 14- is constructed in the same manner as theinsulation pack 7 previously described. Asecond insulation pack 15 is positioned within thespace 14, and this insulation pack is also similar in construction to theinsulation pack 7 previously described. In this manner I provide additional depth of insulation between the inner conduit 1 and the outer pipe or jacket 2. In this construction also there is a continuous pack of insulation running longitudinally of the conduit and extending throughout the entire length of that conduit.

My method of suspending a dimpled polyester (Mylar) cryogenic insulation in pipe lines or in Dewars results in a stress-free system with a safety factor based on weight of the insulation of more than ten to one. The insulation qualities of metallized polyester sheets (Mylar) would never deteriorate in use, due to temperature, cycling or any other conditions to be found in cryogenic applications. This means that a dimpled sheet of Mylar, as disclosed in this application, will be maintenance free for the life of the equipment. There are also material advantages due to a savings in the cooled down process, due to a reduced mass in my insulation.

In my method and structure as disclosed, no Mylar layers will touch either a cold or warm surface of the evacuated space, thereby permitting only a small temperature difference across theinsulation packs 7 or the layers thereof. This means according to the Stefan- Boltzmann law that the undesirable heat leak is brought to a minimum and is under a controlled design environment.

tMy improved multiple layer insulation is applicable to cryogenic installations other than a pipe line, for example, this construction can be used on cryogenic Dewar vessels, spaced chambers, as might be employed in outer space, as 'well as vessels, containers, and the like, which either contain or house a cryogenic material, or with which to exclude an outer low temperature from the space within the vessel. My insulation construction can be employed in any vessel or pipe line with vacuum jacketin g.

Having described my invention, I claim:

1. A multiple layer insulation in combination with a cryogenic pipe line comprising,

an inner pipe conveying a cryogenic material,

an outer jacket surrounding the inner pipe and radially spaced therefrom,

an insulation pack in said space comprising superimposed sheets of reflective plastic material formed as cylinders surrounding the inner pipe,

said insulation pack comprising alternate plain surfaced sheets of reflective plastic material separated by a dimpled sheet of reflective plastic material which dimples make small points of contact with a 4 said plain surfaced sheets and wherein said dimples are spaced apart along two directions disposed substantially at right angles to each other,

and annular insulative and porous supporting rings surrounding the inner pipe and longitudinally spaced thereon,

said annular supporting ring having means thereon to receive one end of an insulation pack to support said insulation pack in spaced relation to both said inner pipe and said outer jacket.

2. A multiple layer insulation in combination with a cryogenic pipe line comprising,

an inner pipe conveying a cryogenic material,

an outer jacket surrounding the inner pipe and radially spaced therefrom,

an insulation pack in said space comprising superimposed sheets of reflective plastic material formed as cylinders surrounding the inner pipe,

said insulation pack comprising alternate plain surfaced sheets of reflective plastic material separated by a dimpled sheet of reflective plastic material which dimples make small points of contact with said plain surfaced sheets and wherein said dimples are spaced apart along two directions disposed substantially at right angles to each other,

and annular insulative and porous supporting rings surrounding the inner pipe and longitudinally spaced thereon,

said annular supporting ring having means thereon to receive one end of an insulation pack to support said insulation pack in spaced relation to both said inner pipe and said outer jacket,

said means comprising an annular groove in the end of the supporting ring into which the end of the insulation pack fits.

3. An assembly comprising:

(a) a container having spaced inner and outer walls;

and

(b) thermal insulation packs extending between said walls and being spaced therefrom;

(c) each of said packs including opposed and spaced essentially planar, radiation-reflecting sheets; and (d) a separator sheet intermediate each pair of said reflecting sheets,

(c) said separator sheet being formed to provide dimples facing each pair of said reflecting sheets which dimples make small points of contact with said reflecting sheets,

(f) said dimples being spaced apart along two directions of said separator sheet disposed substantially at right angles to each other; and

(g) thermal insulative support means interfitting edge portions of said packs for holding said packs in spaced relation to said walls.

4. The assembly defined inclaim 3 in which said support means comprises porous material, the space between said walls being at a pressure substantially below atmospheric pressure.

5. The assembly defined inclaim 3 in which each of said sheets consists of plastic film having a radiationreflecting metallic coating on the outer film surfaces.

6. A thermal insulation packing comprising:

(a) opposed and spaced essentially planar, radiationreflecting sheets; and

(b) a separator sheet disposed intermediate each pair of said reflecting sheets,

(c) said separator sheet being formed to provide dimplies facing each pair of said reflecting sheets which dimples make small points of contact with said reflecting sheets, and said dimples being spaced apart along two directions of said separator sheet disposed substantially at right angles to each other, and

(d) porous, thermal insulative support means interlitting edge portions of: the packing for holding the packing between and in spaced relation to inner and outer walls of a container.

7. The packing defined inclaim 6 in which each of said sheets consists of plastic film with a metallic, radiation-reflecting coating on the outer surfaces of said film.

References Cited UNITED STATES PATENTS 683,514 10/1901 Stephens 138-448 1,987,798 1/1935 Ruppricht 161137 X 2,179,057 11/1-939 Schuetz 138148X 10 LAVERNE D. GEIGER, Primary Examiner.

C. L. HOUCK, Assistant Examiner.

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