Vacuum insulation structures with multiple insulators

Abstract

A method for manufacturing a vacuum insulated structure includes positioning an inner liner within an external wrapper and defining a gap between the inner liner and the external wrapper, drawing a vacuum to seal the gap, and injecting a first insulator into the gap. The method further includes positioning a filter proximate to the first insulator within the gap and injecting a second insulator into the gap proximate to the filter.

Description

BACKGROUND

The efficiency of a refrigerator may, at least in part, rely on the refrigerator's ability to keep items within the refrigerator cool and prevent heat from entering the refrigerator. Accordingly, new methods and materials of insulating a refrigerator are sought.

BRIEF SUMMARY OF THE DISCLOSURE

According to one aspect of the present disclosure, a method for manufacturing a vacuum insulated structure includes positioning an inner liner within an external wrapper and defining a gap between the inner liner and the external wrapper, drawing a vacuum to seal the gap, and injecting a first insulator into the gap. The method further includes positioning a filter proximate to the first insulator within the gap and injecting a second insulator into the gap proximate to the filter.

According to another aspect of the present disclosure, a method for manufacturing a cabinet for a refrigerator includes positioning a liner within a wrapper to define a gap and dispensing a first insulator within the gap through a back aperture of the wrapper. The method further includes positioning a filter on the first insulator and dispensing a second insulator within the gap through the back aperture and proximate to the filter.

These and other features, advantages, and objects of the present disclosure will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of the disclosure, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the disclosure, there are shown in the drawings, certain embodiment(s). It should be understood, however, that the disclosure is not limited to the precise arrangements and instrumentalities shown. Drawings are not necessarily to scale. Certain features of the disclosure may be exaggerated in scale or shown in schematic form in the interest of clarity and conciseness.

FIG. 1A is a top perspective view of a refrigerator cabinet, according to one embodiment;

FIG. 1B is an exploded top perspective view of the refrigerator cabinet of FIG. 1A, according to one embodiment;

FIG. 1C is a cross-sectional view taken at line IC-1C of FIG. 1A, according to one embodiment;

FIG. 2A is a cross-sectional view taken at line II-11 of FIG. 1A, according to one embodiment;

FIG. 2B is a graph depicting the thermal conductivity of various insulator materials as a function of gas pressure;

FIG. 3A is a schematic depiction of a refrigerator cabinet insulator filling system, according to one embodiment;

FIG. 3B is a flow chart of a refrigerator cabinet insulator filling method, according to one embodiment;

FIG. 4A is a schematic depiction of a refrigerator cabinet insulator filling system, according to one embodiment; and

FIG. 4B is a flow chart of a refrigerator cabinet insulator filling method, according to one embodiment.

DETAILED DESCRIPTION

As required, detailed embodiments of the present disclosure are disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary of the disclosure that may be embodied in various and alternative forms. The figures are not necessarily to a detailed design and some schematics may be exaggerated or minimized to show function overview. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present disclosure.

As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

It is to be understood that the present disclosure is not limited to the particular embodiments described below, as variations of the particular embodiments may be made and still fall within the scope of the appended claims. It is also to be understood that the terminology employed is for the purpose of describing particular embodiments, and is not intended to be limiting. Instead, the scope of the present disclosure will be established by the appended claims.

For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the disclosure as oriented in FIG. 1A, unless stated otherwise. However, it is to be understood that the disclosure may assume various alternative orientations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.

Referring to FIGS. 1A-4B, a refrigerator 10 includes a cabinet 14 having an inner liner 18 and an external wrapper 22. The inner liner 18 is positioned within the external wrapper 22 such that a gap 26 is defined between the external wrapper 22 and internal liner 18. A first insulator 30 is positioned within the gap 26 and a second insulator 34 is positioned within the gap 26. A pressure within the gap 26 may be below about 1000 Pa.

Referring now to FIGS. 1A and 1B, the refrigerator 10 includes the cabinet 14. The refrigerator 10 may take a variety of configurations including French door, side-by-side, top freezer, bottom freezer, counter depth, compact, built-in, and other types of refrigerators. The cabinet 14 includes the inner liner 18, the external wrapper 22 and may optionally include a shell 42. In the depicted embodiment, the inner liner 18 has a generally rectangular box shape, but may take a variety of shapes including a cube, prism, parallelepiped, etc. and combinations thereof. The inner liner 18 may have a liner flange 46 disposed around the inner liner 18 and connected to a plurality of liner walls 50 which define the inner liner 18. The inner liner 18 may be formed from a polymeric material having high barrier properties (e.g., low gas permeation), metals and combinations thereof. The inner liner 18 may be formed via thermoforming, injection molding, bending and/or forming. The liner walls 50 of the inner liner 18 may have a thickness ranging from between about 0.1 mm to about 3.0 mm. In a specific embodiment, the liner walls 50 have a thickness of about 0.5 mm.

The inner liner 18 is shaped and configured to mate, couple or otherwise be positioned within the external wrapper 22. The external wrapper 22 includes a plurality of wrapper walls 58 to which a wrapper flange 62 is coupled. The wrapper flange 62 and the liner flange 46 are configured to be coupled when the cabinet 14 is in an assembled configuration. The coupling of the liner flange 46 and the wrapper flange 62 may be performed such that an airtight, or hermetic, seal is formed between the inner liner 18 and the external wrapper 22. The hermetic seal of the wrapper flange 62 and the liner flange 46 may be achieved through use of adhesives, welding, an elastomeric gasket under compression and/or crimping. The coupling of the liner flange 46 to the wrapper flange 62 may be performed proximate a front flange area 64 (FIG. 2A) of the cabinet 14. The front flange area 64 may be configured to couple with a door which permits access to an interior of the cabinet 14.

The external wrapper 22 may be formed of and by any of the materials and processes listed above in connection with the inner liner 18. The wrapper walls 58 of the external wrapper 22 may have a thickness ranging from between about 0.1 mm to about 3.0 mm. In a specific embodiment, the wrapper walls 58 have a thickness of about 0.5 mm. The wrapper walls 58 of the external wrapper 22 may define an injection port 66 and/or a vacuum port 70. The external wrapper 22 may include one or multiple injection ports 66 and/or vacuum ports 70. The injection ports 66 and/or vacuum ports 70 may be positioned as illustrated or in a variety of positions about the external wrapper 22. It will be understood that in alternative embodiments, the injection ports 66 and/or vacuum ports 70 may be disposed on both the external wrapper 22 and inner liner 18, or solely on the inner liner 18. The injection port 66 and the vacuum port 70 may be used to access (e.g., to inject an insulator, draw a vacuum and/or perform maintenance within) the gap 26 once the inner liner 18 and the external wrapper 22 are bonded. The injection port 66 and the vacuum port 70 may have a diameter of between about 10 mm and about 50 mm, or between about 12.5 mm and about 25 mm. In various embodiments, the injection port 66 and the vacuum port 70 may have different diameters than one another. Similarly, in embodiments utilizing more than one injection port 66 and vacuum port 70, the sizes of the injection ports 66 and the vacuum ports 70 may vary.

Referring now to FIG. 1C, the inner liner 18 and the external wrapper 22 may be joined via a trim breaker 72. The trim breaker 72 may be formed of a plastic, a metal, a composite and/or insulating materials. The trim breaker 72 may define a liner joint 72A configured to couple the inner liner 18 to the trim breaker 72. The trim breaker 72 may also define a wrapper joint 72B configured to couple the external wrapper 22 to the trim breaker 72. The liner joint 72A and the wrapper joint 72B may be vibration welded, crimped, thermally bonded, adhesively bonded or otherwise coupled to render the gap 26 airtight. The trim breaker 72 may be used to hold the inner liner 18 and the external wrapper 22 together and in place. Use of the trim breaker 72 may provide advantages of resisting thermal bridging between the inner liner 18 and the external wrapper 22 and easing manufacturing.

Referring now to FIG. 2A, once the inner liner 18 and the external wrapper 22 have been joined and the gap 26 defined, the first insulator 30 and the second insulator 34 may be dispensed into the gap 26. The gap 26 may have a thickness of between about 12 mm to about 30 mm. The gap 26 may have an air pressure of less than about 1 atm (101,325 Pa, 1013.25 mbar), less than about 0.5 atm (50,662.5 Pa, 506.63 mbar), less than about 0.1 atm (10,132.5 Pa, 101.33 mbar), less than about 0.001 atm (101.325 Pa, 1.0133 mbar) or less than about 0.00001 atm (1.01 Pa, 0.01 mbar). Over the service life of the refrigerator 10 (FIG. 1A), the air pressure within the gap 26 may rise more than about 0.001 atm (101 Pa, 1.01 mbar), greater than about 0.005 atm (506 Pa, 5.06 mbar) or greater than about 0.01 atm (1,013 Pa, 10.13 mbar) due to diffusion and/or permeation of gases into the gap 26 through the inner liner 18 and/or the external wrapper 22. The first and second insulators 30, 34 may be a material configured to have low thermal conductivity. For example, the first and second insulators 30, 34 may include precipitated silica, polyurethane foam, fumed silica, silica fume, beads (e.g., of glass, ceramic, and/or an insulative polymer), hollow organic micro/nano spheres, hollow inorganic micro/nano spheres, silica aerogel, nano-aerogel powder, rice husk ash, diatomaceous earth, cenospheres, perlite, glass fibers, polyisocyanurate, urea foam, rice hulls, polyethylene foam, vermiculite, fiberglass and combinations thereof. Optionally, an opacifier (e.g., TiO₂, SiC and/or carbon black) may be included in the first and/or second insulators 30, 34. Additionally or alternatively, materials configured to change the radiation conduction, flow properties and packing factor of the first and second insulators 30, 34 may be introduced. Further, one or more gas (e.g., oxygen, hydrogen, carbon dioxide) and/or moisture getters may be included in the first and second insulators 30, 34. The first and second insulators 30, 34 may include the same insulating material as one another, may be substantially the same material, or may be completely different materials.

In embodiments where the first and/or second insulators 30, 34 include organic spheres, the organic spheres may include polystyrene, polythiophenes, polyethylene, rubber and/or combinations thereof. In embodiments where the first and/or second insulators 30, 34 include inorganic spheres, the spheres may include glasses, ceramics and combinations thereof. In embodiments where the first and/or second insulators 30, 34 include beads or spheres, the beads or spheres may have an average outer diameter ranging from about 50 nm to about 300 μm, or from about 1 μm to about 300 μm, or from about 50 nm to about 1000 nm. In various embodiments, the diameter size distribution of the spheres is low. Sphere embodiments of the first and/or second insulators 30, 34 may be filled with a single gas (e.g., H₂, O₂, N₂, noble gases, volatile organic compounds, CO₂, SO, SO₂) or a mixture of gases (e.g., atmosphere, noble gases, O₂, SO₂, SO). The spheres may be sealed and have a gas pressure within the spheres of between about 0.1 atm and about 1.0 atm, or between about 0.2 atm and about 0.5 atm, or between about 0.25 atm and about 0.35 atm. The first and/or second insulators 30, 34 are positioned within the gap 26 and in contact with both the wrapper walls 58 and the liner walls 50. The packing factor of the first and/or second insulators 30, 34 within the gap 26 may be greater than about 60%, greater than about 62%, greater than about 65%, or greater than about 70%.

In embodiments where the first and/or second insulators 30, 34 include fumed silica, the fumed silica may be hydrophobic and/or hydrophilic. The fumed silica may have a particle size ranging from less than about 0.005μ to greater than about 1.0μ. The fumed silica may have a density of between about 32 kg/m³ to about 80 kg/m³. When positioned within the gap 26, the fumed silica may have a density between about 50 kg/m³ to about 300 kg/m³, or between about 80 kg/m³ to about 250 kg/m³ or between about 150 kg/m³ to about 200 kg/m³.

The first and second insulators 30, 34 are configured not only to thermally insulate the inner liner 18 from the external wrapper 22, but also to resist the inward directed force of the atmosphere on the lower than atmosphere pressure of the gap 26. Atmospheric pressure on the inner liner 18 and the external wrapper 22 may cause distortions which are unsightly and may lead to a rupture in either of the inner liner 18 or the external wrapper 22 thereby causing a loss of vacuum in the gap 26. Further, drawing the vacuum in the gap 26 may cause an impact or shock loading of the first and second insulators 30, 34 as the inner liner 18 and the external wrapper 22 contract around the first and second insulators 30, 34. Accordingly, the first and second insulators 30, 34 should have sufficient crush resistance to resist deformation of the inner liner 18 and the external wrapper 22 due to a pressure gradient between the atmosphere and an air pressure of the gap 26.

The first insulator 30 may be positioned within, and proximate to, the front flange area 64 of the cabinet 14 and the second insulator 34 may fill the rest of the gap 26. In the depicted embodiment, a filter 74 is positioned between the first insulator 30 and the second insulator 34. The filter 74 may be made of paper, a polymeric material, a ceramic and/or a metal. The filter 74 may be porous, solid and/or coupled to the inner liner 18 and/or the external wrapper 22. Use of the filter 74 may resist or prevent the migration and mixing of the first and second insulators 30, 34 such that the first and second insulators 30, 34 remain segregated. The front flange area 64, due to its thinner cross section and being surrounded by atmosphere on three sides, may suffer from a thermal, or heat, bridging effect. Such a thermal bridging across the front flange area 64 may result in an overall reduced efficiency of the refrigerator 10. Accordingly, in various embodiments the first insulator 30 may have a higher insulating property than the second insulator 34. In such an embodiment, the higher insulating property of the first insulator 30 may be sufficient to reduce, or eliminate any thermal bridging taking place through the front flange area 64.

Referring now to FIGS. 2A and 2B, as explained above, the gap 26 within the cabinet 14 may undergo a pressure increase over the service life of the refrigerator 10 due to permeation and/or diffusion of gases. As such, selection of the first and second insulators 30, 34 may account for the expected change in pressure within the gap 26. As can be seen in FIG. 2B, fumed silica undergoes the smallest increase in thermal conductivity over an expected pressure change range (e.g., between about 1 mbar and about 10 mbar), followed by precipitated silica. As such, use of fumed silica as the first insulator 30 and precipitated silica and/or combinations of insulators (e.g., precipitated silica and spheres) as the second insulator 34 may not only reduce thermal bridging across the front flange area 64 while the gap 26 is at manufactured pressure, but also over the service life of the refrigerator 10.

Referring now to FIGS. 3A and 3B, one embodiment of a first method 80 of inserting the first and second insulators 30, 34 within the gap 26 is depicted. The first method 80 includes step 84, step 88, step 92, step 94 and step 96. In step 84, the inner liner 18 is positioned within the external wrapper 22 as explained in greater detail above. The liner flange 46 and the wrapper flange 62 may be bonded so as to make the gap 26 airtight. Next, step 88 of drawing a vacuum may be performed. A vacuum, or negative pressure relative to atmospheric pressure, is generated within the gap 26. The vacuum is created by drawing the air out of the gap 26 through the at least one vacuum port 70. A pump or other suitable vacuum sources may be connected to the vacuum port 70 to facilitate drawing the vacuum. Additionally or alternatively, the first method 80, or any of its steps, may be performed within a vacuum chamber 98 to provide the vacuum to the gap 26.

Next, step 92 of injecting the first insulator 30 into the gap 26 is performed. Injection of the first insulator 30 into the gap 26 may be accomplished by feeding the first insulator 30 into a hopper 100 which in turn supplies the first insulator 30 to a transfer mechanism 104. The transfer mechanism 104 may be a powder pump, a vacuum transfer device, pneumatic pump, flexible screw conveyor, auger feeder and/or other devices capable of transferring or moving the first and second insulators 30, 34. The transfer mechanism 104 pumps or otherwise injects the first insulator 30 into the gap 26 of the cabinet 14 (FIG. 1A). The transfer mechanism 104 may utilize fluidization of the first insulator 30 to move the first insulator 30 into the gap 26. The transfer mechanism 104 may dispense the first insulator 30 into the cabinet 14 with or without pressure. Use of the transfer mechanism 104 allows the first insulator 30 to be inserted into the gap 26 without any densification or compaction, while also providing an easy and efficient means of inserting the first insulator 30. Once the first insulator 30 has sufficiently filled the front flange area 64 of the cabinet 14 and optionally been leveled off, the filter 74 may be placed on top of the first insulator 30 and optionally coupled to the inner liner 18 and external wrapper 22. Next, step 94 of injecting the second insulator 34 is performed. Injection of the second insulator 34 may be performed in substantially the same manner as injection of the first insulator 30 is carried out in step 92. In other embodiments, the second insulator 34 may be dispensed or injected under different conditions that produce a different packing factor or density of the second insulator 34 relative to the first insulator 30.

Next, step 96 of vibrating at least one of the inner liner 18 and the external wrapper 22 is performed. Vibration of the inner liner 18 and/or the external wrapper 22 may cause the first insulator 30 to increase its packing factor. During steps 84, 88, 92, 94 and/or 96 the inner liner 18 and/or external wrapper 22 may be supported by one or more supports 106 such that relative motion between the inner liner 18 and the external wrapper 22 is minimized or prevented. The supports 106 may allow the thickness of the gap 26 to remain constant through filling and vibration. It will be understood that although method 80 was described in a specific order, the steps may be performed in any order or simultaneously without departing from the spirit of this disclosure.

Referring now to FIGS. 4A and 4B, depicted is a second method 108 of dispensing the insulator 30 within the gap 26 between the inner liner 18 and the external wrapper 22. The second method 108 includes step 112, step 116, step 118, step 120 and step 124. The second method 108 begins with step 112 of positioning the inner liner 18 within the external wrapper 22 and sealing the gap 26, as disclosed above. Next step 116 of dispensing the first insulator 30 within the gap 26 is performed. In the second method 108, dispensing of the first insulator 30 into the gap 26 may be accomplished through a back aperture 132. The back aperture 132 may take a variety of shapes (e.g., square, rectangular, circular, oblong, and combinations thereof) and sizes which are configured to allow the first insulator 30 to be poured or otherwise dispensed into the gap 26. The first insulator 30 may be dispensed into the gap 26 between the inner liner 18 and the external wrapper 22 via the transfer mechanism 104 (FIG. 3A), pouring the first insulator 30, or manual application. In embodiments of the cabinet 14 (FIG. 1A) where the external wrapper 22 includes the back aperture 132, the external wrapper 22 may not include the injection port 66 (FIG. 3A). Optionally, step 116 may be performed while at least one of the inner liner 18 and the external wrapper 22 are vibrated. Vibration of the inner liner 18 and/or the external wrapper 22 may facilitate in shaking or vibrating the first insulator 30 into its maximum packing factor and facilitate a more complete filling of the gap 26. Optionally, once the front flange area 64 is sufficiently filled with the first insulator 30 and optionally the first insulator 30 has been leveled off, the filter 74 may be placed on the first insulator 30 as described above.

Once the front flange area 64 of the gap 26 between the inner liner 18 and the external wrapper 22 is filled with the insulator 30 and sufficiently packed with the first insulator 30, step 118 of dispensing the second insulator 34 is performed. Dispensing of the second insulator 34 may be accomplished in a substantially similar manner to that described in connection with the first insulator 30 in step 116. Next, step 120 of positioning a back plate 142 over the back aperture 132 is performed. The back plate 142 may be constructed of the same or similar material as the external wrapper 22, or a different material. Once the back plate 142 is positioned over the back aperture 132, the back plate 142 is sealed to the external wrapper 22 to form an airtight, or hermetic, seal. After step 120 is completed, step 124 of drawing a vacuum within the gap 26 is performed. The vacuum may be drawn through the vacuum port 70 (FIG. 3A) of the external wrapper 22. Additionally or alternatively, method 108, or individual steps thereof, may be performed within the vacuum chamber 98 such that drawing a vacuum may not be necessary, or less vacuum can be drawn. Further, the second method 108 may utilize the supports 106 to resist relative motion of the inner liner 18 and the external wrapper 22. It will be understood that steps of the first and second methods 80, 108 may be omitted, combined, mixed and matched, or otherwise reordered without departing from the spirit of this disclosure.

Use of the present disclosure may offer several advantages. For example, use of the present disclosure allows for the formation of vacuum insulated cabinets 14, panels, and structures without noticeable deformation of the inner liner 18 and the external wrapper 22. By filling the gap 26, deformation of the inner liner 18 and the external wrapper 22 from the pressure differential between the atmosphere and the gap 26 is resisted by the first and second insulators 30, 34. Vacuum insulated cabinets 14, panels and structures may provide enhanced insulative properties as compared to traditional foam filled insulating structures in addition to a reduced size (e.g., thickness decrease of greater than about 55%, 60% or 70%). Additionally, use of the disclosure may allow for the construction of a less dense cabinet 14 while also providing increased rigidity due to the use of the first and second insulators 30, 34. Further strategic use of the first insulator 30 in more critical insulation areas (e.g., in the front flange area 64, in corners and/or thin locations) and the second insulator 34 in the rest of the cabinet 14 may allow for a cost savings in embodiments where the first insulator 30 is more expensive (e.g., fumed silica) than the second insulator 34 (e.g., precipitated silica). Even further, in embodiments where the first insulator 30 has a lower increase in thermal conductivity per unit pressure increase than the second insulator 34, use of the first insulator 30 proximate the front flange area 64 allows for a greater resistance to thermal bridging as the pressure within the gap 26 increases over the service life of the refrigerator 10. It will be understood that although the disclosure was described in terms of a refrigerator, the disclosure may equally be applied to coolers, ovens, dishwashers, laundry applications, water heaters, household insulation systems, ductwork, piping insulation, acoustical insulation and other thermal and acoustical insulation applications.

In this specification and the appended claims, the singular forms “a,” “an” and “the” include plural reference unless the context clearly dictates otherwise. For the purposes of describing and defining the present teachings, it is noted that the terms “substantially” and “approximately” are utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The terms “substantially” and “approximately” are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

It is to be understood that variations and modifications can be made on the aforementioned structure without departing from the concepts of the present disclosure, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise.

Claims

1. A method for manufacturing a vacuum insulated structure, comprising: positioning an inner liner within an external wrapper and defining a gap between the inner liner and the external wrapper;drawing a vacuum to seal the gap;injecting a first insulator into the gap;positioning a filter proximate to the first insulator within the gap; andinjecting a second insulator into the gap proximate to the filter.

2. The method of claim 1, further comprising the step of: vibrating at least one of the inner liner and the external wrapper.

3. The method of claim 2, further comprising the step of: using supports to maintain a thickness of the gap during the vibration of at least one of the inner liner and the external wrapper.

4. The method of claim 1, wherein the step of positioning a filter proximate to the first insulator further comprises the step of: coupling the filter to the inner liner and the external wrapper.

5. The method of claim 1, wherein the step of injecting a first insulator into the gap further comprises the step of: dispensing the first insulator into the gap via a transfer mechanism.

6. The method of claim 5, further comprising the step of: utilizing fluidization of the first insulator to dispense to the first insulator with the transfer mechanism.

7. The method of claim 1, further comprising the step of: leveling the first insulator within the gap.

8. The method of claim 1, wherein the step of injecting a first insulator further comprises the step of: injecting the first insulator proximate to a front flange area defined by the inner liner and the external wrapper.

9. A method for manufacturing a cabinet for a refrigerator, comprising: positioning a liner within a wrapper to define a gap;dispensing a first insulator within the gap through a back aperture of the wrapper;positioning a filter on the first insulator; anddispensing a second insulator within the gap through the back aperture and proximate to the filter.

10. The method of claim 9, further comprising the step of: bracing the liner and the wrapper with supports.

11. The method of claim 9, further comprising the steps of: vibrating the liner and the wrapper; andleveling the first insulator within the gap.

12. The method of claim 9, further comprising the step of: positioning the liner and the wrapper within a vacuum chamber to define a vacuum in the gap.

13. The method of claim 9, further comprising the step of: coupling a back plate to the wrapper to define a hermetic seal.

14. The method of claim 13, further comprising the step of: drawing a vacuum via a vacuum port defined by the wrapper.

15. The method of claim 9, wherein the step of dispensing the first insulator further comprises the step of: dispensing the first insulator proximate to a front flange area defined by the wrapper and the liner.