Patent Application
20080249276
1. The Field of the Invention
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.
2. The Relevant Technology
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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° C.
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.
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.
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 cm3 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 cm3 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 cm3 with dimensions of less than about 3 cm by about 8 cm by about 4 cm.
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.
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.
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.
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.
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.
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.
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.
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:
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.
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.
For example, in a gas filled insulating cell 10 like the one depicted in
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.
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.
In equation 1, g represents gravity, B is the expansion coefficient for the gas, δ is the thickness of the cell structure when inflated with the gas, Pr is the Prandtl number, v is the kinematic viscosity of the gas, TB−T0 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° C. for TB and −40° C. for T0.
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
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=X·Y). 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.
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.
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.
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
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.
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
In one embodiment of the present invention, a plurality of insulative cells as depicted in
With reference to
In one embodiment, the cells 10 are in fluid communication with one another. In the cellular structure depicted in
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.
The insulative article 20 depicted in
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
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.
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.
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
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.
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.
In one embodiment, the insulative articles depicted in
In one embodiment, the insulative articles depicted in
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.
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.
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
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
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.
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.
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 60910485 | Apr 2007 | US |
