U.S. patent application number 12/013326 was filed with the patent office on 2008-10-09 for thin insulative material with gas-filled cellular structure.
Invention is credited to Nate Nathan Alder, Benjamin Maughan, Brady Woolford.
Application Number | 20080249276 12/013326 |
Document ID | / |
Family ID | 39827540 |
Filed Date | 2008-10-09 |
United States Patent
Application |
20080249276 |
Kind Code |
A1 |
Alder; Nate Nathan ; et
al. |
October 9, 2008 |
THIN INSULATIVE MATERIAL WITH GAS-FILLED CELLULAR STRUCTURE
Abstract
The present invention is directed to a lightweight, gas-filled,
highly insulative cellular structure and methods for manufacturing
the cellular structure. The cellular structure can be incorporated
into outdoor gear and apparel to make the outdoor gear or apparel
warm, while still maintaining a desired thinness and flexibility.
The insulative article takes advantage of the superior insulative
properties of dry gases and preferably highly insulative gases such
as argon. In addition, the size and shape of the cells in the
cellular structure are selected to minimize convection.
Inventors: |
Alder; Nate Nathan; (Provo,
UT) ; Woolford; Brady; (Spanish Fork, UT) ;
Maughan; Benjamin; (Provo, UT) |
Correspondence
Address: |
WORKMAN NYDEGGER
60 EAST SOUTH TEMPLE, 1000 EAGLE GATE TOWER
SALT LAKE CITY
UT
84111
US
|
Family ID: |
39827540 |
Appl. No.: |
12/013326 |
Filed: |
January 11, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60910485 |
Apr 6, 2007 |
|
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|
Current U.S.
Class: |
528/10 ; 156/60;
528/396; 528/44 |
Current CPC
Class: |
A41D 3/02 20130101; A41D
1/06 20130101; Y10T 156/10 20150115; A41D 2400/14 20130101; A41D
27/04 20130101; B32B 27/00 20130101; A41D 1/002 20130101; A41D 1/04
20130101; A41D 31/06 20190201; A63H 2027/1033 20130101; A41D 13/002
20130101 |
Class at
Publication: |
528/10 ; 528/44;
528/396; 156/60 |
International
Class: |
C08G 77/00 20060101
C08G077/00; C08G 77/04 20060101 C08G077/04; C08G 77/54 20060101
C08G077/54 |
Claims
1. A lightweight, gas-filled, highly insulative material,
comprising: a first sheet of a gas impermeable material and a
second sheet of a gas impermeable material joined together to form
a chamber having a cell structure, the cell structure comprising a
plurality cells that are in fluid communication; a dry insulating
gas disposed within the plurality of cells; and a dry gas reservoir
and a valve mechanism configured to allow the dry insulating gas to
be introduced and removed from the plurality of cells; wherein the
dimensions of the plurality of cells are such that free convective
mixing of the insulating gas is minimized within the cells by
selecting dimensions for the cells and the dry insulating gas so as
to yield a Rayleigh value of less than 300,000 for each cell.
2. An insulative material as in claim 1, wherein the insulative
material is incorporated into an article of outdoor apparel chosen
from the group consisting of coats, parkas, jackets, vests, pants,
gloves, mittens, hats, liners, waders, and snow boots, work boots,
ski boots, and snowboard boots.
3. An insulative material as in claim 1, wherein the insulative
material is incorporated into an article of outdoor gear chosen
from the group consisting of tents, sleeping bags, bivouac bags,
and sleeping pads.
4. An insulative article as recited in claim 1, wherein the gas
impermeable material for the first and second sheets comprises a
fabric bonded or laminated to a gas impermeable material.
5. An insulative article as recited in claim 4, wherein the gas
impermeable material is selected from the group consisting of
polyethylene, polypropylene, polyurethane, urethane, silicone
rubber, latex rubber, polytetrafluoroethylene (PTFE), expanded
PTFE, butyl rubber, and Mylar.
6. An insulative article as recited in claim 1, wherein the dry
insulating gas is dry atmospheric air having a moisture content
less than about 4 percent by weight.
7. An insulative article as recited in claim 1, wherein the dry
insulating gas is selected from the group consisting of argon,
krypton, xenon, carbon dioxide, sulfur hexafluoride, and
combinations thereof.
8. An insulative article as recited in claim 7, wherein the dry
insulating gas has a moisture content not greater than about 2
percent by weight.
9. An insulative article as recited in claim 7, wherein the dry
insulating gas has a moisture content not greater than about 1
percent by weight.
10. An insulative article as recited in claim 1, wherein a volume
and cell dimensions for each of the plurality of cells are selected
such that the Rayleigh value of the is less than about 300,000.
11. An insulative article as recited in claim 10, wherein the cell
volume is less than about 300 cm.sup.3 with dimensions of about 3
cm by about 14 cm by about 7 cm.
12. An insulative article as recited in claim 10, wherein the cell
volume is less than about 145 cm.sup.3 with dimensions of about 3
cm by about 12 cm by about 4 cm.
13. An insulative article as recited in claim 10, wherein the cell
volume is less than about 100 cm.sup.3 with dimensions of about 3
cm by about 8 cm by about 4 cm.
14. An gas-filled, highly insulative article of outdoor gear or
outdoor apparel, comprising: a material sized and configured to be
worn by a person; a gas-filled insulative cell structure, the cell
structure having, a first sheet of a gas impermeable material and a
second sheet of gas impermeable material joined together to form a
cell; an insulative gas disposed with the cells and having a
moisture content of less than about 4 percent by weight; and
wherein the dimensions of the plurality of cells are such that free
convective mixing of the insulating gas is minimized within the
cells by selecting dimensions for the cells and the dry insulating
gas so as to yield a Rayleigh value of less than 300,000 for each
cell
15. An article of outdoor gear or outdoor apparel selected from the
group consisting of consisting of coats, parkas, jackets, vests,
pants, gloves, mittens, hats, liners, snow boots, work boots, ski
boots, snowboard boots, tents, sleeping bags, bivouac bags, and
sleeping pads.
16. An article of outdoor gear or outdoor apparel as recited in
claim 14, wherein the insulating gas is selected from the group
consisting of atmospheric air, argon, krypton, xenon, carbon
dioxide, sulfur hexafluoride, and combinations thereof.
17. An article of outdoor gear or outdoor apparel as recited in
claim 14, wherein the cell volume is less than about 300 cm.sup.3
with dimensions of about 3 cm by about 14 cm by about 7 cm.
18. An article of outdoor gear or outdoor apparel as recited in
claim 14, wherein the cell volume is less than about 145 cm.sup.3
with dimensions of about 3 cm by about 12 cm by about 4 cm.
19. An article of outdoor gear or outdoor apparel as recited in
claim 14, wherein the cell volume is less than about 100 cm.sup.3
with dimensions of about 3 cm by about 8 cm by about 4 cm.
20. An article of outdoor gear or outdoor apparel as recited in
claim 14, wherein a plurality of insulative cells are grouped
together to form an insulative article.
21. A method of manufacturing a lightweight, gas-filled, highly
insulative article, comprising: providing a first sheet of a gas
impermeable material and a second sheet of a gas impermeable
material; welding the first and seconds sheets of gas impermeable
material together to form a chamber having a cell structure
comprising a plurality cells that are in fluid communication,
wherein the volume and dimensions of the plurality of cells are
chosen such that free convective mixing of gas inside the cells is
minimized, the cell structure providing a valve mechanism
configured to allow an insulating gas to be introduced into and
removed from the plurality of cells; and filling the plurality of
cells with a dry insulating gas selected from the group consisting
of atmospheric air, argon, krypton, xenon, carbon dioxide, sulfur
hexafluoride, and combinations thereof, wherein the insulating gas
has a moisture content less than about 4 percent by weight.
22. A method as recited in claim 21, wherein the gas impermeable
material for the first and second sheets comprises a fabric bonded
or laminated to a gas impermeable material.
23. A method as recited in claim 21, wherein the gas impermeable
material is selected from the group consisting of polyethylene,
polypropylene, polyurethane, urethane, silicone rubber, latex
rubber, polytetrafluoroethylene (PTFE), expanded PTFE, butyl
rubber, and Mylar.
24. A method as recited in claim 21, wherein the further comprising
choosing a volume and cell dimensions for each of the plurality of
cells such that the Rayleigh value of each of the plurality of
cells is below 300,000.
25. A method as recited in claim 21, further comprising
incorporating the insulative articles into outdoor apparel and/or
gear chosen from the group consisting of coats, parkas, jackets,
vests, gloves, mittens, hats, liners, snow boots, work boots, ski
boots, snowboard boots, tents, sleeping bags, bivouac bags, and
sleeping pads.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/910,485, filed Apr. 6, 2007, which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. The Field of the Invention
[0003] The present invention is in the field of thermal insulation
materials. More particularly, embodiments of the present invention
relate to articles (e.g., ski jackets and other outdoor gear and
apparel) in which a dry gas is disposed in a cellular structure and
used as a thermal insulator.
[0004] 2. The Relevant Technology
[0005] Thermal insulators have long been important for human
survival and comfort in cold climates. The primary function of any
thermal insulator is to reduce heat loss (i.e., heat transfer) from
a heat source to a cold sink. There are three forms of heat
transfer: convection, conduction, and radiation.
[0006] Heat loss through convective mixing of gases is caused by
the tendency of a gas to form a rotational mixing pattern between a
warmed (i.e., less dense) region and a cooler (i.e., more dense)
region. In a convection cycle, warmed gas is constantly being
exchanged for cooler gas. One of the primary ways in which thermal
insulators work is through suppressing convection by trapping or
confining a volume of a gas within the insulative material. For
example, one of the reasons that a fiber-filled parka feels warm is
that the air near the wearer's skin is warmed by body heat and the
fibers act to prevent or at least slow convective mixing of the
warmed layer of the air with the cold air outside.
[0007] Conduction involves heat flow through a material from hot to
cold in the form of direct interaction of atoms and molecules. For
example, the phenomenon of conduction is one of the reasons why a
thin layer of insulation does not insulate as well as a thicker
layer.
[0008] Radiation involves direct net energy transfer between
surfaces at different temperatures in the form of infrared
radiation. Radiation is suppressed by using materials that reflect
infrared radiation. For example, the glass surface of a vacuum
flask is coated with silver to reflect radiation and prevent heat
loss through the vacuum region.
[0009] Different thermal insulators prevent heat loss through
convection, conduction, and radiation in different ways. For
example, fiber-based thermal insulators like polyester fiber fill
or fiberglass insulation utilize fairly low conductivity fibers in
a stack or batt with a volume of air trapped or confined amongst
the fibers. Furthermore, conduction is reduced by the random
orientation of the fibers across the stack or batt, and radiative
heat loss is somewhat reduced because the radiation is scattered as
it passes through the fibers.
[0010] Another example class of thermal insulators includes closed
cell structures, such as foams or microspheres. Closed cell
structures are generally comprised of a polymer matrix with many
small, mostly closed cavities. As with fiber-based insulations,
these insulators conserve heat by trapping a volume of air in and
amongst the cells. In fact, convection is effectively eliminated
inside the small, closed cells. Furthermore, conduction is reduced
by using low conductivity materials, and radiation is low because
the cells are typically very small and there is little temperature
difference between cavity walls and hence low driving force for
radiative heat transfer.
[0011] Essentially all thermal insulators present a tradeoff
between insulative value (i.e., prevention of convection,
conduction, and radiation), bulk, and cost. For example, because of
the bulkiness of fiber- or foam-based insulation, achieving a
sufficient degree of insulation for a given set of conditions can
be difficult without also making the article too bulky for
practical use. It should also be appreciated that adding additional
fiber- or foam-based insulation inevitably adds weight. Such
insulative materials are also static in that the amount of
insulative material cannot be changed or adjusted as the user's
needs change. For example, if a person is wearing a fiber filled
parka or sleeping in a fiber filled sleeping bag, the amount of
insulation cannot be increased or decreased as environmental or
activity conditions change.
[0012] In addition, many typical insulative materials produce toxic
and/or environmentally damaging byproducts in the process of
manufacture. For example, the manufacturing process for many
thermal insulators such as polyester fibers or foams produces CFCs
and/or greenhouse gases. Many typical thermal insulators also
continue to outgas toxic chemicals long after their manufacture.
For example, fiberglass insulation is typically manufactured with
formaldehyde compounds that continue to outgas long after the
insulation is placed in a wall or other structure. And many typical
insulators, such as fiberglass or polyester fiber fill, produce
loose fibers that can be harmful if they are inhaled.
BRIEF SUMMARY OF THE INVENTION
[0013] The present invention is directed to a lightweight,
gas-filled, highly insulative material and methods for
manufacturing the material. The insulative material has a cellular
structure that can be filled with an insulative gas (e.g., argon).
The insulative material can be incorporated into outdoor gear and
apparel to make the outdoor gear or apparel warm, while still
maintaining a desired thinness and flexibility. In one embodiment,
the volume of the insulative gas in the cellular structure can be
adjustable such that the insulation provided by the outdoor gear or
apparel can be selectable. Because the insulative component is a
gas, the insulation value of the article can be adjusted by
increasing or decreasing the amount of gas, without appreciably
affecting the weight of the article. The cellular structure can be
used to insulate a variety of outdoor clothing and gear.
[0014] The present invention includes a lightweight, gas-filled,
highly insulative material with a cellular structure. The cell
structure can be formed from a plurality of cells that are
configured to minimize thermal convection. In one embodiment, the
cell structure is formed from first and second sheets of a gas
impermeable material that are joined together to form a chamber
between the sheets. The chamber is subdivided into cells that are
in fluid communication with one another.
[0015] A dry insulating gas (e.g., argon) is disposed within the
plurality of cells. A reservoir of a dry gas is coupled to the
cells to allow the insulating gas to be introduced, and optionally
removed, from the cells. The volume and dimensions of the cells and
type of insulative gas are selected such that free convective
mixing of the insulating gas disposed within the cells is
minimized. In one embodiment the convective mixing of the
insulative gas in the cells has a Rayleigh value of less than
300,000 (based on a temperature difference of body temperature to
0.degree. C.
[0016] In one embodiment, the first and second sheets that form the
cellular structure comprise a fabric, such as nylon, polyester, or
spandex, that is bonded or laminated to a gas impermeable material.
Examples of suitable gas impermeable materials include, but are not
limited to, polyethylene, polypropylene, polyurethane, urethane,
silicone rubber, latex rubber, polytetrafluoroethylene (PTFE),
expanded PTFE, butyl rubber, and Mylar.
[0017] In one embodiment of the invention, the water content of the
insulative gas used in the cellular structure can be limited to
prevent accumulation of condensed water vapor. Preferably the water
content of the insulative gas in the cellular structure is less
than about 4 percent by weight, more preferably less than about 2
percent by weight and most preferably less than 1 percent by
weight. Examples of suitable gases that can be used with the
present invention include argon, krypton, xenon, carbon dioxide,
sulfur hexafluoride, and combinations thereof. In one embodiment,
atmospheric air can be used. However, atmospheric air is typically
less desirable if the water content is difficult to control since
excess water vapor has been found to lead to pooling of condensed
water vapor in the cellular structure, which substantially reduces
the insulative properties of the cellular structure and
substantially increases weight.
[0018] In one embodiment of the present invention, the cell volume
and cell dimension for the plurality of cells in the insulative
article are selected such that heat loss through convective mixing
is minimized. One way to minimize heat loss though convective
mixing is to select a cell volume and cell dimensions such that the
Rayleigh value of the cell is less than about 300,000. More
preferably, the Rayleigh value of the cell is in a range from about
50,000 to about 275,000. Most preferably, the Rayleigh value of the
cell is in a range from about 125,000 to about 250,000. A preferred
example of a cell configuration with a Rayleigh value below about
300,000 has a cell volume less than about 300 cm.sup.3 with
dimensions of about 3 cm by about 14 cm by about 7 cm. A more
preferred example of a cell configuration with a Rayleigh value
below about 300,000 has a cell volume less than about 145 cm.sup.3
with dimensions of about 3 cm by about 12 cm by about 4 cm. A most
preferred example of a cell configuration with a Rayleigh value
below about 300,000 has a cell volume less than about 100 cm.sup.3
with dimensions of less than about 3 cm by about 8 cm by about 4
cm.
[0019] In one embodiment, the insulative cell structure of the
present invention may be used to insulate outdoor apparel.
Exemplary outdoor apparel items include, but are not limited to,
coats, parkas, jackets, vests, gloves, mittens, hats, liners,
waders, snow boots, work boots, ski boots, and snowboard boots.
[0020] In another embodiment, the cell structure of the present
invention may be used to insulate outdoor gear. Exemplary outdoor
gear items include, but are not limited to, tents, sleeping bags,
bivouac bags, and sleeping pads.
[0021] The present invention includes a method for manufacturing a
lightweight, gas-filled, highly insulative material. The method
comprises steps of (1) providing a first sheet of a gas impermeable
material and a second sheet of a gas impermeable material; (2)
welding the first and seconds sheets of gas impermeable material
together to form a chamber having a cell structure comprising a
plurality cells that are in fluid communication; (3) filling the
plurality of cells with a dry insulating gas selected from the
group consisting of argon, krypton, xenon, carbon dioxide, sulfur
hexafluoride, and combinations thereof, wherein the insulating gas
has a moisture content less than about 4 percent by weight. In
addition, the insulative material can then be incorporated into an
article of outdoor apparel or outdoor gear.
[0022] In one embodiment, the first and second sheets that form the
cellular structure comprise a fabric, such as nylon, polyester, or
spandex, bonded or laminated to a gas impermeable material.
Preferably the materials used to form the insulative material are
flexible such that the insulative material can be wearable or
useable next to a person's body. Examples of suitable gas
impermeable materials include, but are not limited to,
polyethylene, polypropylene, polyurethane, urethane, silicone
rubber, latex rubber, polytetrafluoroethylene (PTFE), expanded
PTFE, butyl rubber, and Mylar.
[0023] Heat loss through the insulative material is lessened if
convective mixing of the gas in the plurality of cells is
minimized. In turn convective mixing of the gas in the plurality of
cells is minimized if the dimensions are such that the Rayleigh
value is below about 300,000. In one embodiment of the present
invention, the method further comprises choosing a volume and cell
dimensions for each of the plurality of cells such that the
Rayleigh value of each of the plurality of cells is less than about
300,000.
[0024] As mentioned above, the insulative material can be
incorporated into an article of outdoor apparel and/or outdoor
gear. Examples of suitable articles of outdoor apparel and/or
outdoor gear include, but are not limited to, coats, parkas,
jackets, vests, gloves, mittens, hats, liners, snow boots, work
boots, ski boots, snowboard boots, tents, sleeping bags, bivouac
bags, and sleeping pads. The use of a selectable volume of gas to
control the insulative value of the article is particularly
beneficial for use with outdoor gear and outdoor apparel since it
allows a person to dynamically control heating adjacent the body,
thereby ensuring greater likelihood that a desired comfort level
can be achieved.
[0025] These and other objects and features of the present
invention will become more fully apparent from the following
description and appended claims, or may be learned by the practice
of the invention as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] To further clarify the above and other advantages and
features of the present invention, a more particular description of
the invention will be rendered by reference to specific embodiments
thereof which are illustrated in the appended drawings. It is
appreciated that these drawings depict only typical embodiments of
the invention and are therefore not to be considered limiting of
its scope. The invention will be described and explained with
additional specificity and detail through the use of the
accompanying drawings in which:
[0027] FIG. 1 illustrates a schematic of single insulating gas cell
having X, Y, and Z dimensions, a gas reservoir, and a valve;
[0028] FIG. 2 illustrates an arrangement of a plurality of
insulating gas cells as in FIG. 1 that are in fluid connection with
one another and with a gas reservoir;
[0029] FIG. 3 illustrates an alternate arrangement of a plurality
of insulating gas cells that are in fluid connection with one
another;
[0030] FIG. 4 illustrates yet another alternate arrangement of a
plurality of insulating gas cells that are in fluid connection with
one another;
[0031] FIG. 5 illustrates even yet another alternate arrangement of
a plurality of insulating gas cells that are in fluid connection
with one another.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] The present invention is directed to a lightweight,
gas-filled, highly insulative material having a cellular structure
and methods for manufacturing the material. The cellular structure
can be incorporated into outdoor gear and apparel to make the
outdoor gear or apparel warm, while still maintaining a desired
thinness and flexibility. The insulative material takes advantage
of the superior insulative properties of dry gases and preferably
highly insulative gases such as argon. In one embodiment, the
volume of the insulative gas in the insulative material can be
adjustable such that the insulation provided by the outdoor gear or
apparel can be selectable. Because the insulative component is a
gas, the insulation value of the article can be adjusted by
increasing or decreasing the amount of gas, without appreciably
affecting the weight of the article. The cellular structure can be
used to insulate a variety of outdoor clothing and gear.
I. Design of an Insulative Gas Cell
[0033] FIG. 1 illustrates a schematic of single insulating gas cell
10 having X, Y, and Z dimensions. In a lightweight, gas-filled,
highly insulative article that depends on the insulating properties
of dry gases, the selection of X, Y, and Z dimensions are selected
to reduce heat transfer by means of convection.
[0034] Convective heat transfer consists of both forced and natural
convection. Forced convection is due to the induced movement of the
gas in the gas-filled cell. For example, in the case of a
gas-filled cell that is incorporated into a garment, forced
convection can be caused by movement of the wearer. Natural
convection is a rotational flow pattern of gas caused by the
temperature differential between warm and cool regions of the cell
and gas buoyancy.
[0035] For example, in a gas filled insulating cell 10 like the one
depicted in FIG. 1, the gas adjacent to the cell 10 surface nearest
to a source of heat is typically at a higher temperature and lower
density than the gas at the surface of the cell closest to
atmospheric conditions. The hotter gas will rise and the cooler gas
will replace the hotter gas thus setting off convective mixing of
the gas within the cell 10. This will increase the heat transfer
through the cell 10, which is undesirable for insulation. For both
natural and forced convection, heat transfer is enhanced as the
length of the free flowing path of the gas is increased. This is
because convective mixing of the gas is allowed to more fully
develop in these free flowing paths and thus heat transfer by
convection is increased. This means that increasing the XYZ
dimensions of the cell 10 depicted in FIG. 1 will tend to increase
the tendency of convection coils to form inside the cell 10, which
increases heat loss.
[0036] In one embodiment of the present invention, the cell 10
structure is specifically designed to reduce both free and forced
convection of the gas inside the cell 10. Free and forced
convection are minimized by choosing cell volume and dimensions
that break up the free flow path of the gas inside the cell 10 and
thus reduce convective mixing or rotational motion of the gas in
the cell 10. In one embodiment of the present invention, a heat
transfer model was developed that allows one to predict preferred
cell dimensions (i.e., X, Y, and Z dimensions) in order to minimize
natural convection and increase the insulating capabilities of the
cell 10. These preferred cell dimensions for natural convection
will also reduce heat transfer due to forced convection.
[0037] The model is developed by using both the Rayleigh value and
the Nusselt number to predict the convective coefficient for the
cell 10 under static conditions (i.e., natural convection and no
forced convection). The Rayleigh value is a correlation between the
buoyancy and viscous forces of the gas inside the cell 10. Large
Rayleigh values are indicative of very buoyant flows leading to
increased convection in the cell. Large Rayleigh values would be
typical of convective mixing or rotational motion of the gas in
large free flowing paths. The Rayleigh value can be expressed as
the following for the geometry used for the cell structure.
Ra L = gB ( T B - T 0 ) .delta. 3 v 2 Pr ( 1 ) ##EQU00001##
[0038] In equation 1, g represents gravity, B is the expansion
coefficient for the gas, .delta. is the thickness of the cell
structure when inflated with the gas, P.sub.r is the Prandtl
number, v is the kinematic viscosity of the gas, T.sub.B-T.sub.0 is
the temperature difference between the inner and outer wall of the
cell 10. For purposes of this invention, the Rayleigh value is
calculated using a value of 37.degree. C. for T.sub.B and
-40.degree. C. for T.sub.0.
[0039] The Rayleigh value is used in turn to predict the Nusselt
number, which quantifies convective heat transfer from the surfaces
of the cell 10. The Nusselt number is then used to calculate the
total heat transfer through the cell 10. Empirical correlations for
the average Nusselt number for natural convection in enclosures
were used to determine the Nusselt number based on the Rayleigh
value and cell geometry. The Rayleigh value is significantly
influenced by the thickness (i.e., the Z dimension depicted in FIG.
1) of the cell 10 and also the temperature difference between the
inner and outer wall of the cell 10. Increasing the thickness will
increases the free flowing path of the gas. When either the cell
thickness or the temperature difference is increased than the
Rayleigh value is increased which also causes the Nusselt number to
increase. Equation 2 shows that as the Nusselt number is increased
the total heat transfer in the cell is also increased.
Q = kNuA ( T B - T 0 ) .delta. ( 2 ) ##EQU00002##
[0040] Equation 2 also shows that the heat transfer through the
cell 10 is also dependent on the facial area of the cell 10 (i.e.,
A=XY). As the facial area is increased, the heat transfer through
the cell 10 is also increased. The equation for heat transfer also
shows the importance of the thermal conductivity value, k of the
gas used in the cell structure. The smaller the thermal
conductivity of the gas the lower the total heat transfer through
the cell structure. Thermal conductivity of the gas is a function
of the gas type (i.e., some gases are better insulators than other
gases), the moisture content of the gas (i.e., increased water
content increases the thermal conductivity of the gas), and on the
temperature.
[0041] One will appreciate from the above discussion that there is
an interplay between heat loss through convection, as primarily
influenced by cell thickness, and heat loss through conduction, as
primarily influenced by the facial area of the cell, along with the
thickness of the cell. In one embodiment, this interplay is
balanced leading to a preferred range for dimensions of the cell
10. That is, as the cell 10 thickness is increased heat transfer
through conduction is decreased. Nevertheless, there is a point of
diminishing returns due to the fact that convective mixing or
rotational motion increases as the cell 10 thickness is increased.
Increased convective mixing and loss of insulation value is seen as
an increase in the Rayleigh value for the cell 10. That is, as the
thickness of the cell 10 is increased, there is a point where the
increase in heat transfer due to convection is greater than the
decrease in heat transfer due to conduction. After this point there
is no longer a need to increase the thickness because no benefit in
reducing heat transfer can be obtained.
[0042] Through use of this theoretical model, it was determined the
preferred dimensions for minimal heat transfer through the cell 10
occur at a preferred Rayleigh value less than 300,000. More
preferably, the Rayleigh value of the cell is in a range from about
50,000 to about 275,000. Most preferably, the Rayleigh value of the
cell is in a range from about 125,000 to about 250,000. Rayleigh
values greater than 300,000 will cause the insulative cell to
perform less optimally due to convective heat transfer. This will
reduce the effectiveness of the gas cell 10 as an insulator.
[0043] In one embodiment, the present invention includes a
gas-filled, highly insulative cell 10. The cell 10 includes a first
sheet of a gas impermeable material and a second sheet of a gas
impermeable material joined together to form a cell 10. In one
embodiment of the present invention, the cell 10 depicted in FIG. 1
is attached to a dry gas reservoir 12 and a valve mechanism 16
configured to allow the dry insulating gas to the introduced into
and removed from the cell 10. Additionally, the cell 10, the gas
reservoir 12, and the valve mechanism are connected to the cell 10
by means of a gas line 14. As was explained more fully in the
preceding paragraphs, the volume and XYZ dimensions of the cell are
chosen such that free and forced convective mixing of gas inside
the cell is minimized.
[0044] In one embodiment, the cell 10 includes a dry insulative gas
disposed within the cell 10. The identity of the insulating gas is
an important factor is determining the insulative properties of the
cell 10. In general, dry gases insulate better than moist gases,
monatomic gases insulate better than diatomic or polyatomic gases,
and heavy, viscous gases insulate better than lighter, less viscous
gases. Preferably, the gas disposed within the cell 10 has a
moisture content less than about 4 percent by weight. More
preferably, the gas disposed within the cell 10 has a moisture
content less than about 2 percent by weight. Most preferably, the
gas disposed within the cell 10 has a moisture content less than
about 1 percent by weight. The insulating gas can be selected from
the group consisting of atmospheric air, argon, krypton, xenon,
carbon dioxide, sulfur hexafluoride, and combinations thereof.
[0045] In one embodiment, the preferred Rayleigh value for the cell
10 is less than 300,000. More preferably, the Rayleigh value of the
cell is in a range from about 50,000 to about 275,000. Most
preferably, the Rayleigh value of the cell is in a range from about
125,000 to about 250,000. Based on a preferred Rayleigh value of
less than 300,000, preferred X, Y, and Z dimensions for the cell 10
depicted in FIG. 1 were determined. Preferably, the cell volume is
less than about 300 cm.sup.3 with XYZ dimensions of less than about
7 cm by about 14 cm by about 3 cm. More preferably, the cell volume
is less than about 145 cm.sup.3 with XYZ dimensions of less than
about 4 cm by about 12 cm by about 3 cm. Most preferably, the cell
volume is less than about 100 cm.sup.3 with XYZ dimensions of less
than about 4 cm by about 8 cm by about 3 cm. These dimensions
minimize heat transfer due to both forced and natural
convection.
II. Insulative Material Having Cellular Structure
[0046] In one embodiment of the present invention, a plurality of
insulative cells as depicted in FIG. 1 are grouped together to form
an insulative cell structure. FIGS. 2-5 depict various arrangements
of the plurality of cells 10 that form a cell structure.
[0047] With reference to FIG. 2, the cell structure 20 comprises a
first sheet of a gas impermeable material and a second sheet of a
gas impermeable material that are joined together to form a chamber
there between. The chamber is subdivided into a cellular structure
comprising a plurality cells 10. The first and second sheets are
bonded together such that there are open sections that form the
cells 10. In between the cells, there are regions 29 where the
first and second sheets are bonded together leaving essentially no
open space between the first and second sheets.
[0048] In one embodiment, the cells 10 are in fluid communication
with one another. In the cellular structure depicted in FIG. 2, the
cells 10 are in fluid connection with one another via short
connector tubes 26 and 28 that allow gas to flow between cells 10.
It should be mentioned, however, that the connector tubes 26 and 28
do not enhance convection within the cells 10. That is, the
connector tubes 26 and 28 are sufficiently small and they are
placed such that convection currents do not form between adjacent
cells 10.
[0049] In one embodiment, a dry insulating gas is disposed within
the plurality of cells 10. The identity of the insulating gas is an
important factor is determining the insulative properties of the
insulative article 20. In general, dry gases insulate better than
moist gases, monatomic gases insulate better than diatomic or
polyatomic gases, and heavy, viscous gases insulate better than
lighter, less viscous gases. Preferably, the gas disposed within
the cells 10 has a moisture content less than about 4 percent by
weight. More preferably, the gas disposed within the cells 10 has a
moisture content less than about 2 percent by weight. Most
preferably, the gas disposed within the cells 10 has a moisture
content less than about 1 percent by weight. The insulating gas is
selected from the group consisting of atmospheric air, argon,
krypton, xenon, carbon dioxide, sulfur hexafluoride, and
combinations thereof.
[0050] The insulative article 20 depicted in FIG. 2 is depicted as
it may be attached to a dry gas reservoir 12 and a valve mechanism
16 configured to allow the dry insulating gas to be introduced into
and removed from the cells 10 comprising the insulative article 20.
The insulative article 20 is connected to the gas reservoir 12, and
the valve mechanism 16 via a gas line 14. The connector tubes 26
and 28 depicted in FIG. 2 allow gas introduced into one cell 10 to
fill all cells 10 in the insulative article 20.
[0051] As was explained more fully in the preceding section, the
volume and X dimension 22, Y dimension 24, and Z dimension (not
shown) of the cells 10 are chosen such that free and forced
convective mixing of gas inside the cell is minimized. Minimizing
free and forced convection of the gas inside the plurality of cells
10 increases the insulative efficiency of the insulative article
20. In one embodiment, the preferred Rayleigh value for the each of
the plurality of cells 10 is less than about 300,000. More
preferably, the Rayleigh value of the cell is in a range from about
50,000 to about 275,000. Most preferably, the Rayleigh value of the
cell is in a range from about 125,000 to about 250,000. Based on a
preferred Rayleigh value of less than about 300,000, preferred
dimensions for each of the plurality of cells 10 depicted in FIG. 2
were determined. Preferably, the cell volume is less than about 300
cm.sup.3 with XYZ dimensions of about 7 cm by about 14 cm by about
3 cm. More preferably, the cell volume is less than about 145
cm.sup.3 with XYZ dimensions of about 4 cm by about 12 cm by about
3 cm. Most preferably, the cell volume is less than about 100
cm.sup.3 with XYZ dimensions of about 4 cm by about 8 cm by about 3
cm. These dimensions minimize heat transfer due to both forced and
natural convection.
[0052] In one embodiment, the first and second sheets of material
that form the plurality of cells 10 that comprise the insulative
article 20 are comprised of a fabric, such as nylon, polyester, or
spandex, bonded to a gas impermeable material. Examples of suitable
gas impermeable materials include, but are not limited to,
polyethylene, polypropylene, polyurethane, urethane, silicone
rubber, latex rubber, polytetrafluoroethylene (PTFE), expanded
PTFE, butyl rubber, and Mylar.
[0053] FIG. 3 depicts an alternate arrangement of a plurality of
cells 10 to form an insulative article 30. The cells 10 are formed
as open space between two sheets of gas impermeable material that
are bonded together to form a plurality of cells 10. Bonded regions
36 are formed between the cells 10. The cells 10 are arranged in a
zigzag fashion with adjacent cells 10 arranged at substantially
right angles relative to one another. Each cell 10 has an X
dimension 32, a Y dimension 34, and a Z dimension (not shown). The
Y dimension 34 is depicted in part by an imaginary line that
extends into the adjacent cell. The cell is bounded by the dotted
lines because gas atoms traveling through the center of the cell
have a free motion that is essentially bounded by these dimensions
since most the gas atoms bouncing off the walls will stay within
this space.
[0054] As in the previous examples, the dimensions of each of the
cells 10 are chosen such that heat loss through convection is
minimized. Even though the cells are connected, the formation of
convection currents that lead to heat loss are minimized because
the right angles break up the free flow path of any convection
currents that may form. That is, rotational convection currents
generally cannot form around right angles.
[0055] Heat loss through convection is minimized if the Rayleigh
value for the each of the plurality of cells 10 is preferably less
than about 300,000. More preferably, the Rayleigh value of the cell
is in a range from about 50,000 to about 275,000. Most preferably,
the Rayleigh value of the cell is in a range from about 125,000 to
about 250,000. Based on a preferred Rayleigh value of less than
about 300,000, preferred dimensions for each of the plurality of
cells 10 depicted in FIG. 3 were determined. Preferably, the cell
volume is less than about 300 cm.sup.3 with XYZ dimensions of about
7 cm by about 14 cm by about 3 cm. More preferably, the cell volume
is less than about 145 cm.sup.3 with XYZ dimensions of about 4 cm
by about 12 cm by about 3 cm. Most preferably, the cell volume is
less than about 100 cm.sup.3 with XYZ dimensions of about 4 cm by
about 8 cm by about 3 cm. These dimensions minimize heat transfer
due to both forced and natural convection.
[0056] FIG. 4 depicts another alternate arrangement of a plurality
of cells 10 to form an insulative article 40. The arrangement is
similar to the arrangement depicted in FIG. 2. The cells 10 are
formed as open space between two sheets of gas impermeable material
that are bonded together to form a plurality of cells 10. Bonded
regions 49 are formed between the cells 10. The cells are in fluid
connection with one another via connector tubes (46 and 48) between
the cells.
[0057] As in previous examples, each of the plurality of cells 10
have an X dimension 42, a Y dimension 44, and a Z dimension (not
shown). The XYZ dimensions are chosen according to the preferred
Rayleigh value of less than 300,000 so as to minimize heat loss
through convection of the gas within the cells 10.
[0058] FIG. 5 depicts another alternate arrangement of a plurality
of cells 10 to form an insulative article 50. The arrangement is
similar to the arrangement depicted in FIG. 3. The cells 10 are
formed as open space between two sheets of gas impermeable material
that are bonded together to form a plurality of cells 10. Bonded
regions 58 are formed between the cells 10. The cells are in fluid
connection with one another via connector tubes 56 between the
cells.
[0059] As in previous examples, each of the plurality of cells 10
have an X dimension 52, a Y dimension 54, and a Z dimension (not
shown). The XYZ dimensions are chosen according to the preferred
Rayleigh value of less than 300,000 so as to minimize heat loss
through convection of the gas within the cells 10.
[0060] In one embodiment, the insulative articles depicted in FIGS.
2-5 may be used to insulate outdoor apparel. Exemplary outdoor
apparel items include, but are not limited to, coats, parkas,
jackets, vests, gloves, mittens, hats, liners, and boots.
[0061] In one embodiment, the insulative articles depicted in FIGS.
2-5 may be used to insulate outdoor gear. Exemplary outdoor gear
items include, but are not limited to, tents, sleeping bags,
bivouac bags, and sleeping pads.
III. A Method of Making an Insulative Article
[0062] In one embodiment, the present invention includes a method
for manufacturing a lightweight, gas-filled, highly insulative
material. The method comprises steps of (1) providing a first sheet
of a gas impermeable material and a second sheet of a gas
impermeable material; (2) welding the first and seconds sheets of
gas impermeable material together to form a chamber having a cell
structure comprising a plurality cells that are in fluid
communication; (3) providing a valve mechanism configured to allow
an insulating gas to be introduced into and removed from the
plurality of cells; and (4) filling the plurality of cells with a
dry insulating gas selected from the group consisting of argon,
krypton, xenon, carbon dioxide, sulfur hexafluoride, and
combinations thereof. In an alternative embodiment, dry atmospheric
air can also be used, although the foregoing dry gases are
preferred. Preferably, the insulating gas used to fill the
plurality of cells has a moisture content less than about 4 percent
by weight. More preferably, the insulating gas used to fill the
plurality of cells has a moisture content less than about 2 percent
by weight. Most preferably, the insulating gas used to fill the
plurality of cells has a moisture content less than about 1 percent
by weight.
[0063] In one embodiment, the first and second sheets that form the
cellular structure comprise a fabric, such as nylon, polyester, or
spandex, bonded or laminated to a gas impermeable material.
Preferably the materials used to form the insulative material are
flexible such that the insulative material can be wearable or
useable next to a person's body. Examples of suitable gas
impermeable materials include, but are not limited to,
polyethylene, polypropylene, polyurethane, urethane, silicone
rubber, latex rubber, polytetrafluoroethylene (PTFE), expanded
PTFE, butyl rubber, and Mylar.
[0064] Exemplary techniques to welding the first and seconds sheets
of gas impermeable material together to form a chamber having a
cell structure comprising a plurality cells that are in fluid
communication include, but are not limited to, ultrasonic welding,
laser welding, stamp heat welding, hot plate welding, gluing,
taping, sewing, and other fabric joining techniques known by those
having skill in the art. For example, the repeating patterns of
cells, examples of which are depicted in FIGS. 2-5, can be formed
by welding two sheets if gas impermeable fabric together with an
ultrasonic welding drum or a hot plate welding drum that is
machined to impress the pattern into the sheets of fabric.
[0065] Heat loss through the article is lessened if convective
mixing of the gas in the plurality of cells is minimized. In turn
convective mixing of the gas in the plurality of cells is minimized
if the dimensions are such that the Rayleigh value, which is a
function of the cell dimensions, is below about 300,000. In one
embodiment of the present invention, the method further comprises
choosing a volume and cell dimensions for each of the plurality of
cells such that the Rayleigh value of each of the plurality of
cells is less than about 300,000. Based on a preferred Rayleigh
value of less than about 300,000, preferred dimensions for each of
the plurality of cells 10 depicted in FIG. 3 were determined.
Preferably, the cell volume is less than about 300 cm.sup.3 with
XYZ dimensions of about 7 cm by about 14 cm by about 3 cm. More
preferably, the cell volume is less than about 145 cm.sup.3 with
XYZ dimensions of about 4 cm by about 12 cm by about 3 cm. Most
preferably, the cell volume is less than about 100 cm.sup.3 with
XYZ dimensions of about 4 cm by about 8 cm by about 3 cm. These
dimensions minimize heat transfer due to both forced and natural
convection.
[0066] In one embodiment, the method disclosed herein further
comprises incorporating the insulative material into an article of
outdoor apparel and/or outdoor gear. Exemplary articles of outdoor
apparel and/or outdoor gear include, but are not limited to, coats,
parkas, jackets, vests, pants, gloves, mittens, hats, liners, snow
boots, work boots, ski boots, snowboard boots, tents, sleeping
bags, bivouac bags, and sleeping pads. The insulative material can
be an integral component of the article of outdoor gear or apparel.
For example, the insulative material can form part of the wall of a
jacket or ski pant. The insulative material can be used to make a
hat where all or part of the hat is the insulative material with a
cellular structure. The insulative material can be used as a liner
in a sleeping bag or it can be sewn such that the insulative
material is a permanent component of the sleeping bag. The liner
can be used as the fabric portion of the wall of a tent. The
insulative material can be used in the floor of the tent to provide
a barrier between a person and the ground. In addition, the
insulative material can be used as a sleeping pad to provide
insulated separation between a person and the ground.
[0067] Alternatively, the insulative material can be overlaid or
attached as a liner to the article of outdoor gear or apparel. In
this case, the insulative material can be attached using a zipper,
snaps, hook and loop fastener (i.e., Velcro), or any other suitable
connection means. In one embodiment, the insulative material can be
incorporated into a vest or jacket that can zip into the shell of a
coat. This mechanism allows the insulative material to be
selectively used or removed depending on weather condition.
[0068] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. The described embodiments are to be considered in
all respects only as illustrative and not restrictive. The scope of
the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
* * * * *