GB2099116A

GB2099116A - Vacuum insulation spacer

Info

Publication number: GB2099116A
Application number: GB8116024A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-05-26
Filing date: 1982-05-26
Publication date: 1982-12-01
Also published as: GB2099116B

Abstract

A vacuum insulation spacer, in which support members formed by insulative lattice-type structures, are mounted at at least three levels and combined so that the upper and lower faces of the middle support member contact the adjacent support members at laterally displaced respective contact points, thereby to reduce heat conductance. <IMAGE>

Description

SPECIFICATION Vacuum insulation spacer The present invention relates to an insulation spacer to be used to infill the space between adjacent two walls of a vacuum insulated structure. It is widely known that vacuum insulation is undoubtedly an excellent means for maintaining a desired temperature.

Since heavy pressures are applied to a vacuum insulation structure due to the fact that the internal pressure is reduced when the interior is evacuated, the strength of the walls needs to be sufficiently high.

To achieve this the materials of the walls must have high mechanical strength and hence, comparatively thick walls must be used, and this limits the application for these structures.

Japanese Patent Application No: 1 979-63453 discloses vacuum insulation structures which withstand high outer pressures applied to the walls by the insertion of a honeycomb-shaped spacer made of an insulation material disposed between two walls. This is not entirely satisfactory.

By utilizing the honeycomb-shaped spacer, a double-walled interior does not coflapse under pressure when the interior is evacuated, and thus, deformation of the walls is prevented.

However, the difficulty is that the heat transfer by conduction arises through the honeycombshaped spacer composed of plate-shaped structures, and the effectiveness of the vacuum insulation is thus greatly reduced.

Additionally to reduce the pressure evenly when exhausting air through an air outlet during vacuum formation, each plate-shaped structure must suitably interconnect with the outlet and this is not easily achieved.

The present invention seeks to overcome these difficulties by providing according to the present invention a vacuum insulation spacer, said spacer having at least three supporting levels, each level comprising a lattice-like structure made from an insulating material, the members forming said lattice on each level being positioned so that contact points between said members at a first level and members at a second level adjacent thereto do not overlap contact points between any other level.

Embodiments of the present invention are now described, by way of illustration only, with reference to the accompanying drawings, wherein: Figure 1 is a perspective view illustrating a first embodiment of an insulation spacer of the present invention; Figure 2 is a cross-sectional diagram along the line 1-1 of Figure 1; heat flow being indicated by arrows; Figure 3 illustrates a second embodiment of the present invention, and shows a perspective view of an insulation spacer with a three-level structure; and Figure 4 illustrates a third embodiment of the present invention, and shows a perspective diagram of an insulation spacer with a four-level structure.

In a first embodiment of the spacer in the present invention as shown in Figure 1, crosspieces c1, c2 and c3 made of an insulative material with a rectangular cross section are aligned in parallel to form a first level support member. A second level support member, which is formed by crosspieces, ba, b2 and b3 aligned at right angles to those of the first level, is mounted on top of the support member at the first level.

Finally, a third level support member, formed by crosspieces a1, a2 and a3 aligned at right angles to those of the second level, is mounted on top of the second level support member.

The contact points between the support member at the second level and the support member at the third level are offset with respect to the contact points between the second and first levels, so that the upper and lower contact points of a supporter in the second level with those of other levels do not overlap.

Thus, the contact point 2 between crosspiece a2 of the support member at the third level and crosspiece b2 of the support member at the second level is placed half way between the contact point 6 and 7, where crosspiece b2 of the support member at the second level, and the crosspieces cr and c2 of the support member at the first level meet.

As illustrated in the-same figure, the other crosspieces b1 and b2 are also related in the same way, and this relation is also shown in Figure 2, which illustrates the sectional view of I-I in Figure 1.

Though not illustrated, heat transfer surfaces contact the upper faces of crosspieces a1, a2 and a3 at the third level, and the lower faces of crosspieces c, c2 and c3 at the first level.

When air in the space between two heat transfer surfaces is withdrawn so that a vacuum exists, heat is mainly transferred by conduction through the cross-pieces as well as by radiation through the evacuated space and by an element of convection, that is, by means of heat transference by the gas molecules remaining in the evacuated space. This occurs when the lower heat transfer surface has a lower temperature than the upper heat transfer surface..

Heat transfer through the crosspieces is conducted through the whole supporting system at a third level. However, heat has to be transferred through reduced areas at the contact points with the support member at the second level, and heat transferred through the contact points, must then move laterally to heat transfer surface beneath through adjacent contact points with the support member at the first level.

Thus, as shown in Figure 2, heat is transferred to crosspiece b2 in the second support member from crosspiece a2 in the third support member via contact point 2, and is diffused to right and left.

The heat is then transferred to crosspieces c1 and c2 at the third level via contact points 6 and 7.

In the case of conventional one-level spacers, such as honeycomb-shaped spacers, the areas of heat transfer of both upper and lower sides of the surface are the areas where a lattice contacts both sides of heat transfer surface and the distance of heat transfer is the length of the straight line connecting both surfaces.

In the case of an insulation spacer, as shown in Figure 1 wherein contact points do not overlap heat transfer is considerably reduced due to the minimized heat transfer areas at the contact points of supporters in each level, and the extended distance which the conducted heat must travel.

Materials which may be used for the support members of the present invention, (ie: as an insulation spacer) may be any poor heat conductor such as, for instance, thermosetting resins eg: epoxy resin, bakelite and urea resin; thermoplastic resins eg: polypropylene, high density polyethylene, polyester and ABS resin, or impregnated paper or pulp reinforced with resin.

Naturally, to select a desirable material, the temperature of a vacuum insulation structure in use has to be measured, and heat durability of material has to be taken into consideration.

Ceramics are especially recommended when the vacuum insulation structure is to be used under high temperature conditions.

It is preferred that the contact points at each level are placed in abutting relationship and glued, or morticed into each other, to make them solid and structurally stable. Another preferred method of fabrication is an integral molding.

The density of the materials used for the support members decides how wide or how narrow the intervals between adjacent crosspieces need to be.

When intervals between adjacent crosspieces are reduced, the volume of heat transfer through spacers increases considerably; the thinner the crosspieces, the less the volume of heat transfer.

However, mechanical strength required for a spacer is a factor in deciding the thickness of crosspieces. When a spacer is made of a synthetic resin, it is usually adequate to provide an average cross piece thickness of 1-2 mm, with 10~50 mm intervals therebetween.

Figure 3 also illustrates another example of a three-level insulation spacer of the present invention. Both support members A and C in the third and first levels respectively are formed with insulative crosspieces with a rectangular cross section in the shape of lattice. Lattice-shaped support members of the third and first levels support walls of an insulation structure, and reinforce them against external pressures. Support member B at the second level is formed by aligning insulative crosspieces Ba, B2 and B3 each with a rectangular cross-section, in spaced parallel relation.

Figure 4 shows an example of a four-level insulation spacer of the present invention. In this Figure both support members D and A in the first and fourth levels respectively, face walls of an insulation structure, and are constructed in the shape of a lattice.

Both support members C and B (in the second and third levels respectively) are formed by aligning cross-pieces in spaced parallel relation without allowing the contact points to overlap at each level. To construct this four level structure, for instance, the first and second levels can be integrally molded by using a thermoplastic resin.

These integrally molded support members can be reversely utilized at the third and fourth levels.

They can simply be placed one on the other, or preferably glued together to form a four-level insulation spacer.

The insulation spacers of the present invention may be inserted between adjacent walls of a vacuum insulation structure to support and reinforce both walls. Since each space in the support member is not blocked, evacuation is easily effected, and perlite or aerogel powder, which is commonly used for vacuum insulation, can also be added with ease.

The mean free path of gas molecules remaining in the space is reduced by adding perlite to the vacuum area and this reduces direct heat transfer by means of the gas molecules, and results in improved effectiveness in vacuum insulation.

Aluminium foils which reflect heat can also be inserted between levels of a spacer constructed with three levels or more, thus reducing heat transfer by radiation.

An insulation spacer of the present invention can be used not only for insulation of flat structures, but also for cylindrical or spherical insulation structures; in which case the support member has to be adjusted to fit a curved surface.

The support member need not be applied to a whole area of an insulation structure. Instead, it can be partially applied to a part of the structure where an additional reinforcement is required. An.

example of the above case is where a spacer is used at the bottom a vacuum bottle to support the weight of an inside container, thus resulting in the effective reinforcement thereof without reducing the effectiveness of the insulation.

The test results of an insulation spacer in the present invention are shown below in Example 1.

EXAMPLE 1 A test was conducted using a vacuum insulation container in which an inner tank (300 mm x 300 mm x 400 mm) and outer tank (340 mm x 340 mm x 440 mm), both made of 1 mm thick stainless steel were coaxially interengaged.

A 20 mm thick spacer to be used for a test was inserted in the entire space between the inner tank and outer tank, and the space was evacuated to 6 x 10-7 torr, thereby to provide vacuum insulation of the inner tank. A thermocouple was arranged to monitor temperature of water in the inner tank. The top of the container comprised an opening of 63.5 mm diameter.

For the test, a phenolic-resin insulation spacer with four-level support members was used; the material had a cross sectional area of 2 mm x 5 mm, as shown in Figure 4.

Intervals between the lattice of support members in the first and fourth levels of an insulation spacer used for this test were 30 mm; while intervals between crosspieces in parallel in the second and third levels were also 30 mm.

Furthermore, an aluminium foil was inserted between the third and fourth supporters.

18 litres of boiling water, which half filled the inner tank was poured thereinto, and temperature changes of water were read with the thermocouple installed in the inner tank. It was found that 6 hours were required for temperature to drop from 800 to 600.

EXAMPLE 2 The test was repeated using the same container equipped with a 20 mm thick honeycomb insulating spacer (made of phenolic resin, with 2 mm thick plates at intervals of approximately 30 mm) was used, it took 4.5 hours for water temperature to drop from 800C to 600C.

As the results indicate, the insulation spacer of the present invention has better insulative qualities.

EXAMPLE 3 When the same container equipped with an insulation material consisting of 20 mm thick rigid foamed urethane was used it took 2 hours for the water temperature to drop from 800C to 600C.

Thus, a vacuum insulation spacer in the present invention is much superior in insulation characteristics to rigid foam.

Claims

1. A vacuum insulation spacer, said spacer having at least three supporting levels, each level comprising a lattice-like structure made from an insulating material, the members forming said lattice at each level being positioned so that contact points between said members at a first level and members at a second level adjacent thereto do not overlap contact points between any other level.

2. The vacuum insulation spacer of claim 1, wherein at least at said first level said lattice-like structure comprises a plurality of insulative crosspieces in spaced relation, each having a rectangular cross-section.

3. The vacuum insulation spacer of claim 2, wherein at least at one other level said lattice-like structure comprises a plurality of insulative crosspieces in spaced relation, each a rectangular cross-section.

4. The vacuum insulation spacer of claim 2 or claim 3 wherein at said first level the plurality of crosspieces are parallel to one another, and wherein said second level adjacent to said first level comprises a plurality of crosspieces each perpendicular to the crosspieces of said first level.

5. The vacuum insulation spacer of any preceding claim wherein adjacent levels on each side of said first level comprise crosspieces having a rectangular cross-section and made from an insulating material, said crosspieces in said adjacent levels being aligned in the shape of a lattice.

6. The vacuum insulation spacer of claim 5, wherein a third and fourth level of said structure comprises crosspieces aligned in the shape of a lattice, said first and said second levels of said spacer being sandwiched together between said third and said fourth levels so that said third and said fourth levels contact opposing surfaces of said vacuum insulation structure.

7. The vacuum insulation spacer of any one of claims 1 to 6 wherein at least one other level of said spacer comprises a plurality of parallel crosspieces having rectangular cross-section and made from an insulating material.

8. The vacuum insulation spacer of any one preceding claim wherein the spaces in each level between said members are filled with perlite.

9. The vacuum insulation spacer of any one of claims 1 to 7 wherein the spaces in each level between said members are filled with aerogel powder.

10. The vacuum insulation spacer of any one preceding claim, wherein one or more sheets of metallic film are inserted between adjacent levels.

1 A vacuum insulation spacer substantially as hereinbefore set forth.

12. A vacuum insulation spacer substantially as hereinbefore set forth with reference to, and as illustrated in any one of Figures 1 to 4 of the accompanying drawings.

13. A method of reducing heat conductance in a lattice like heat insulative structure which comprises utilizing a spacer as claimed in any one of claims 1 to 12.