Patent Application
20140042355
This invention relates to a material for thermal insulation. More particularly, this invention provides an insulating material that exhibits high loft and efficient scattering of thermal radiation. Most particularly, this invention provides an insulating material composed of particulate units with (1) physical entanglements to maintain loft, (2) non-integer dimensionality to efficiently fill space, and (3) a material of construction that efficiently scatters thermal radiation.
Nature has provided its creatures a very diverse set of strategies to keep warm. While marine mammals depend solely on fat-based blubber, land-based mammals also use fat, but also rely on their fur (or hair). In contrast, winged creatures that are especially adapted to life in cold climates (e.g., geese and ducks), have developed a strategy based on very light weight down insulation.
The usual explanation of how down functions is based on its fluffiness, which is said to enable down to provide insulation by “trapping warm pockets of air”. The logic underlying this explanation is that the thermal conductivity of air is fairly low. Since thermal conductivity and thermal resistivity are inversely related, air can be equivalently viewed as a medium having a fairly high thermal resistance. In the building industry, thermal resistance is often quantified with the familiar “R-value” rating. The R-value of a material quantifies the thermal resistance of a 1-inch thick layer of the material. For air, the R-value is about 5.8° F.-ft2-Hr/Btu-inch. Table 1 shows a comparison of the R-value (per inch of thickness) of air with other common insulation materials used in the building industry. Table 1 shows that the R-value of air compares favorably to the leading commercial insulation materials.
Although a high R-value is desirable for good thermal insulation, the customary R-value characterizes only one of the three primary mechanisms of heat transfer: conduction. In addition to conduction, heat transfer can occur from a warm environment to a cold environment through the mechanisms of radiation and convection.
Convective heat transfer occurs upon physical motion or transport of warm material to colder surroundings. There are two classes of convection, often referred to as (i) forced, and (ii) natural. A common example of forced convective heat transfer is heat loss due to drafts through doors or windows of a house. Wind is another example that leads to the “wind chill factor”. This does not apply to our discussion of insulation because all insulation materials tend to be covered by some sort of wind barrier. For this, birds use their outer feathers, jackets use the outer cloth, and houses use their outer siding. Even in the absence of any wind, temperature differences can lead to natural convection. However, due to air's finite viscosity, convective motion is strongly suppressed by the presence of the insulation's support structure. Since convective transport requires transfer of mass and since the insulation materials of greatest commercial interest are primarily intended to fill the internal space of a mechanically intact volume (e.g. the space between walls or the interior of a garment), the mechanism of convection is insignificant relative to conduction and radiation in most insulation applications.
Radiative heat transfer, however, is often significant and occurs via the emission of thermal radiation from objects by virtue of their temperature. Since the intensity of thermal radiation increases strongly with increasing temperature, the radiative mechanism leads to a net transfer of heat from warm objects to cold objects without a transfer of mass, nor does it require a transfer medium. Indeed, the radiative mechanism even applies in vacuums (unlike either conduction or convection). For objects at room temperature, thermal radiation is primarily in the infrared (IR) portion of the electromagnetic spectrum, having its peak intensity at a wavelength near 10 microns. Detection of infrared radiation is the basis of most thermal imaging systems.
The significance of radiative heat transfer explains why air alone, despite its high conductive R-value, is a poor material for thermal insulation. It turns out that air is almost completely transparent to infrared radiation, which means that heat loss via radiative transport is highly efficient through air. Even though air is resistant to conductive heat transfer, the highly efficient radiative heat transport through air makes air an overall poor thermal insulator.
Mathematically, the total thermal resistance RTotal of an insulation material can be expressed
where Rconduction, Rradiation, and Rconvection correspond to the resistances of the insulation material to the conductive, radiative, and convective mechanisms of heat transfer, respectively.
In situations where convection is negligible, Eq. (1) simplifies to
In a medium like air, where the conductive resistance is much larger than the radiative resistance, Eq. (2) becomes
Eq. (3) indicates that the high conductive resistance of air provides little benefit to the overall performance of air as a thermal insulation material due to the high efficiency of radiative heat transport through air, where Rradiation would be small. Eq. (2) makes it evident that when considering an optimal insulation design, one simply cannot separate the loft's trapping of air with the loft's trapping of thermal radiation. Systems based on high thermal radiation trapping can have poor overall performance if the loft is not properly designed to trap air.
The above analysis reveals that the standard explanation of how insulation functions (i.e., by trapping warm air) is only half the story. The half that is typically ignored is the need to trap infrared photons to minimize the radiative contribution to heat loss. Down is an effective insulation material only in part because its structure creates loft, where the loft traps air to minimize conductive heat transfer. This structure also acts to highly impede convection. Equally important is the fact that the fibrous framework structure responsible for the loft of down performs yet another duty: namely it effectively scatters infrared radiation. As the radiation is scattered, its original outward path (from warm environment to cold surroundings) is severely disrupted and the radiation is substantially returned to the originating warm environment. The efficient scattering by the structure of down acts to trap infrared radiation and prevent its escape to the surroundings. Without a mechanism for trapping thermal radiation, down would be an ineffective thermal insulation material, despite its high loft, because of the high transparency of the air trapped in the structure of down to infrared radiation.
This scattering and trapping of infrared radiation is what allows Rradiation in Eq. (3) to markedly increase. The radiative resistance of down can be estimated to be Rradiative=8.8 using Eq. (2) with RTotal=3.5 and Rconductive=5.8. A remarkable feature of down is that the fibrous structure responsible for the efficient scattering of thermal radiation and high radiative resistance accounts for only about 1% of its volume. (Trapped air accounts for the remaining 99% of the volume and is the primary determinant of Rconductive.) This means that down has the further advantage of being a lightweight material. Down manifests the true optimization of thermal insulation by nature, i.e., optimal trapping of air, with high radiation trapping using a minimal amount of material.
Although down has many advantages as a thermal insulation material, it suffers from a few drawbacks. First, down is a natural material that is only available from living creatures. The special care and attention needed to harvest down tends to limit the supply of down and increase cost. Second, down has a tendency to irreversibly lose its loft when it gets wet and this greatly reduces its insulation capabilities. Third, down is difficult to launder and difficult to dry. Fourth, many people have allergies to down.
Because of the disadvantages of down, a number of synthetic alternatives have been developed. Synthetic insulation is commonly in the form of foam or fibers and has the advantage of being easy to manufacture and low in cost. Some synthetic insulation (e.g., those based on polymer fibers) can also be laundered easily and tends to retain some of its insulating qualities when it gets wet. The main disadvantage of synthetic insulation is that it tends to lose its loft when it gets compressed. Frequent compression tends to cause synthetic fibers to settle or break, resulting in a loss of loft and an accompanying contraction in the volume of air pockets. Loss of air pockets between fibers leads to a greater surface area of contact between fibers and an accompanying increase in heat loss due to conduction through the fibers (i.e., heat is transferred from fiber to fiber by direct contact of the fibers). Settling of fibers also creates a headspace filled with air that leads to efficient heat loss due to radiative transport where there is no longer any fiber material to act as infrared scattering centers. Foams tend to mechanically deform and lose loft over time when compressed repeatedly. The loss of loft is difficult to reverse and leads to a consistent degradation in the insulating power of synthetic foams and fibers over time. Synthetic insulation is also heavier than down and cannot match the performance of down in terms of its insulating performance per unit mass of the active material.
There is thus a need for a synthetic insulation material that is readily manufactured and possesses the attributes of down while maintaining the advantages of current synthetic fibers.
This invention provides a synthetic insulation material that rivals down in performance and even surpasses it without suffering degradation in insulating power over time. Moreover, it will not degrade when subjected to water, it will naturally resist mold growth, it will not damage human health or the environment with volatile organic compounds, and it will have excellent life cycle performance by being intrinsically recyclable. The new material includes an aggregate of particulate units that may have a fractal, fractal-like or related geometric configuration. The geometric configuration includes non-integer dimensionality that promotes physical entanglements of the particulate units. The physical entanglements impart a high frictional resistance to slippage of the particulate units and thus function to maintain the loft of the insulation material by inhibiting the settling of particulate units upon compression. Instead of slipping and settling, the geometric configuration insures that the instant particulate units become interlocked or entangled when compressed. The force of compression is stored as potential energy from bending of the particulate units from the point of entanglement or contact and this energy is available to restore loft when the force is removed.
The geometric configuration may further include aspects of self-similarity, in which geometric features on microscopic length scales mirror geometric features on macroscopic length scales. Self-similarity may aid in establishing entanglements between particulate units and may also lead to efficient filling of space to provide a lightweight insulation material.
The particulate units are formed from a material that efficiently scatters or reflects thermal radiation. The combination of high loft and efficient scattering or reflection of thermal radiation minimizes heat loss resulting from both conduction and radiation and leads to a superior material for thermal insulation.
The particulate units may be made from inorganic and/or organic materials that are natural and/or synthetic and that have been processed to a geometric configuration having non-integer dimensionality and/or self-similarity. Typical materials include natural or synthetic oxides, nitrides, minerals, carbons, plastics, metals or metal alloys, and high refractive index materials. The particulate units may be composites that include a base material and a surface coating, where the surface coating increases the efficiency of scattering or reflection of thermal or infrared radiation. In one embodiment, the surface coating is a metal and the base material is a plastic, a foam, a synthetic or natural fiber and may include down.
The invention further extends to mixtures of the instant particulate units with other insulation materials. The particulate units may be combined with down or other natural materials and/or with fiberglass or synthetic materials (including foams and fibers) to form a composite insulation material with controllable physical and thermal attributes.
The insulation material of this invention may be used as a fill material in buildings (e.g. insulation of walls, attics, ceilings, floors), in garments and other accessories (e.g. coats, footwear, hats, gloves, insulated curtains), and in outdoor gear (e.g. coolers, water bottles, tents, sleeping bags). The insulation material may also be used in sound-proofing or electrical insulation applications.
The insulation material may be formed by processes such as (physical or laser) cutting, scribing, grinding, stamping, and pulverizing to achieve particulate units that are dimensionally engineered to achieve non-integer dimensionality and advantageous loft characteristics.
The instant insulation material incorporates geometric and material features that provide loft to create air space to minimize heat losses due to conductive processes while simultaneously inhibiting radiative heat loss by insuring efficient scattering or reflection of thermal radiation. The instant material unites the advantages of down and existing synthetic insulation in a new material that provides one or more of the following advantages: high loft, durability of loft, high mechanical resilience, resistance to settling, water resistant, manufacturability, easy care, and biological inertness. This insulating material is designed to meet the most stringent performance metrics by the U.S. Environmental Protection Agency, especially in terms of its high R-value performance, its resistance to mold and to water damage, its lack of volatile organic content, and its very favorable life cycle performance in terms of its excellent long term impact on the environment due to its intrinsic ability to recycle and to reuse.
Although this invention will be described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art, including embodiments that do not provide all of the benefits and features set forth herein and including embodiments that provide positive benefits for high-volume manufacturing, are also within the scope of this invention. Accordingly, the scope of the invention is defined only by reference to the appended claims.
The instant insulation material is an aggregate of particulate units. As described more fully hereinbelow, the particulate units are dimensionally engineered to achieve a geometric configuration that restores loft when the insulation material is compressed or crushed. The geometric configuration may have non-integer dimensionality and may exhibit a high degree of self-similarity. The geometric configuration and/or material of construction of the particulate units may also facilitate scattering of thermal radiation to inhibit heat loss through radiative transport.
An important feature of an insulation material is loft. Loft refers to the capacity of an insulation material, or particulate units thereof, to adopt an expanded, porous configuration. The porous configuration provides a solid framework with internal cavities that can be occupied by another material. Preferably, the material that occupies the internal cavities has high resistance to heat transfer. Although condensed phases may occupy the internal cavities, gases are generally preferred because gases are lightweight and tend to have high resistance to conductive heat transfer. Air is a common gas used to occupy the internal cavities of a porous insulation material. As noted hereinabove, however, air is highly transparent to thermal radiation, so the framework structure that encapsulates the air must efficiently scatter thermal radiation to insure good insulation characteristics. In addition to providing loft, the geometric configuration of the framework structure of the instant materials inhibits heat loss through radiative processes by facilitating the scattering or reflection of thermal radiation.
The creation of loft in an insulation material ultimately requires forming a three-dimensional framework structure. The desired physical attributes of the framework structure include (1) the ability to efficiently fill three-dimensional space and (2) mechanical resilience. Efficient filling of three-dimensional space requires the framework structure to have high porosity (or void volume) and minimal material volume. Minimal material volume suppresses thermal conduction through the framework structure and provides the benefit of a lightweight insulation material. Mechanical resilience refers to the capacity of the framework structure to recover its original shape following compression or deformation. A common defect of prior art synthetic insulation materials is loss of loft due to settling or breaking of fibers or other particulate units over time due to compression or intrinsic weight. The framework structure of the particulate units of the instant insulation materials is geometrically configured to resist settling and promote an elastic response to compression to maintain the integrity of loft over time.
Proper design of the geometric configuration of the particulate units is needed to create and maintain loft. Geometric features at both macroscopic and microscopic length scales contribute to loft and its durability. By macroscopic length scale, we generally refer to geometric features that can be discerned with the unaided eye. Microscopic features are finer than macroscopic features. The geometric configuration of the instant particulate units has been designed to provide a “high friction” framework structure that resists translational relaxation when subject to an external compression force. Instead of causing motion of particulate units relative to each other, the application of compressive force to the particulate units establishes or strengthens entanglements between units. The aggregate framework structure does not relax appreciably through translation of particulate units past each other and instead responds to compressive force through the creation of interlocks between particulate units. The geometric configuration of the particulate units includes branching and features that impart roughness to the surface and edges. The roughness may include features that are jagged, hooked, barbed, branched, or otherwise irregular. As compressive force is applied and the particulate units shift position and impinge on each other, the branching and/or surface roughness causes the particulate units to interlock or entangle, thereby inhibiting relative translational motion (slippage) of the particulate units. Continued compression of interlocked particulate units bends, strains or otherwise deforms the units, but the entanglements between the units inhibit slippage and prevent settling. Instead of inducing slippage, an applied compressive force is stored in the bonds of interlocked particles and is manifested as an internal deformation or rearrangement of particulate units. Since the energy of the compressive force is stored as a form of internal energy, it becomes a form of potential energy that is available to restore the framework structure to its original, high loft configuration when the force is removed. The tendency of the instant particulate units to resist slippage and relative translation motion may be referred to herein as “friction”. The instant particulate units may be said to have high friction.
In prior art fiber-based insulation materials, in contrast, the surfaces of individual fibers are smooth and the fibers are prone to relative translational motion (slippage) upon application of a compressive force. As a result, the compressive force is dissipated as an irreversible settling of fibers instead of as a recoverable form of stored internal energy. Whereas the instant branched and surficially-rough particulate units have high friction (resistance to slippage), the smooth fibers of prior art materials have low friction and readily slide past each other upon application of a compressive force.
The settling of fibers leads to a loss of loft and a degradation of insulation performance Insulation performance suffers when fibers settle because (1) thermal conduction through the fibers becomes more efficient due to the increased area of contact between fibers that arises as fibers settle and (2) radiative heat loss increases as the overhead space vacated by settled fibers becomes occupied purely with infrared-transparent air.
The high frictional state of the particulate units prevents slippage of the units past one another and promotes dissipation of external compressive energy in the form of a configurational potential energy of the aggregate of particulate units that make up the insulation material. The configurational potential energy may be manifested as a bending, twisting, local compression, stretching or other deformation of individual particulate units or a plurality of particulate units. Inclusion of branching and/or surface or edge roughness promotes an interlocked arrangement of particulate units that prevents slippage and enables storage of compressive energy as a recoverable form of potential energy upon relaxation of the compressive force. The number of branches and the length of individual branches also influences the tendency of particulate units to form geometric entanglements that facilitate preservation of loft. Longer branches and greater branching numbers, in particular, promote greater entanglements. Recovery of the framework structure upon relaxation of the compressive force restores loft and preserves the insulation capacity of the material.
The geometric configurations of the instant particulate units include macroscopic and microscopic features. On the macroscopic level, five general types of particulate units can be identified. Illustrative examples of each type are presented in
The description of particulate units that follows makes reference to “branches”. As used herein, a single line defines one branch (see, for example, particulate units of Type (B)). Even if a particulate unit cannot be represented as a line, however, it may still consist of a single branch within the meaning of the definition used herein. The shape of particulate units of Type (A) or Type (E), for example, might be described as a square, rectangle, triangle, trapezoid, circle, or other shape and may nonetheless be regarded as having a single branch. A particulate unit having only one branch may be referred to as “unbranched”. Branching occurs when the shape of the particulate unit is notched or bifurcated in some manner. Branching is the feature that fundamentally defines the two non-linear types of particulate units (Types (C) and (D)). Type (C) units have two branches, while Type (D) units have an arbitrary number (n) of branches, where n is greater than two and has no upper limit.
In Table 2, aspect ratio refers to the length:width ratio of a particulate unit. Although typical branch lengths are presented in Table 2 for each type of particulate unit, the length scales of the instant invention are not limited to any particular physical lengths. The extent (i.e., number) of branching, length of branches and the relative aspect ratio of particulate units contribute separately and in combination to the benefits afforded by the instant invention. Below we describe the applicability of the concept of non-integer (i.e., rational or irrational number) dimensionality to the description of the geometric configuration of the instant particulate units. Geometric descriptions based on non-integer dimensionality are largely equivalent to descriptions in terms of branching and aspect ratios and may provide a more convenient classification of the different types of particulate units.
Type (A) particulate units have one branch and may be referred to as “small” units. As seen in
Type (B) particulate units are depicted in
Type (C) particulate units have two branches and, as shown in
Particulate units of Type (D) are more complicated in geometric configuration and include multiple branches (
Type (E) particulate units (
An important feature of the instant particulate units on both macroscopic and microscopic levels is roughness or irregularity at edges and/or surfaces. Roughness or irregularity is a common feature of each of the five types of particulate units discussed hereinabove. The edges and surfaces of the instant particulate units are not necessarily flat, straight, or smooth, but may be “ragged”, uneven, or non-uniform instead. The edges and surfaces of the instant particulate units may include hooks, jags, protrusions, barbs, points, spikes, zigzags, indentations, depressions, teeth, and other shape irregularities that render the units non-smooth. While these are clearly evident on the macroscopic scale (
As noted hereinabove, the irregular edges and surfaces have important consequences in establishing loft and preserving or restoring loft upon removal of a compressive force. Restoration of the original volume of the insulation material from a compressed state can only proceed if there is a mechanism for mechanical resilience that provides a restoring force when an external compressive force is removed. The irregularities at the surfaces and edges cause the instant particulate units to interlock or bind when compressed to provide resistance to slippage and thereby create a mechanism for storing the force of compression as a recoverable form of potential energy that acts to restore loft when the compressive force is removed. As noted hereinabove, if the geometric configuration of particulate units is such that the units slide past each other upon compression, the units will settle into a low energy, relaxed state that lacks a mechanism for driving recovery of volume when the compressive force is removed. Inclusion of edge or surface irregularities in the instant particulate units overcomes this deficiency of prior art insulation materials. Branching also facilitates entanglements between particulate units that assist in restoring loft of the instant insulation materials upon removal of a compressive force.
Self-similarity is a further feature of some embodiments of the instant invention. Self-similarity generally refers to similarity of geometric features at the microscopic and macroscopic length scales. Self-similarity imparts fractal characteristics to the instant particulate units. An example of self-similarity may be seen in a comparison of
Embodiments of the instant insulation material have at least two distinct properties that reveal independent aspects of fractal behavior: (i) self-similarity on the microscopic and macroscopic length scales of surface and edge irregularities of the particulate units and (ii) complexity of branching on the macroscopic scale that approaches that of down.
We next determine the loft of representative samples of each type of particulate unit within the scope of the instant invention, describe the dimensionality of the instant particulate units and discuss the relationship between dimensionality and loft.
The loft of insulation is normally quantified as an inverse density and expressed as the volume of insulation material per unit mass. The insulation industry generally uses units of cubic inches per ounce of material (in3/oz). The following procedure was used to determine the loft of representative samples of each type of particulate unit: (1) a small cardboard box of known weight and volume was filled with a representative sample of each type of particulate unit (see
We observed a steady increase in loft from about 45 in3/oz for Type A (“small”) particulates units up to about 210 in3/oz for Type D (“non-linear n”) particulate units and with no further increase for Type E (“big”) particulate units. We believe that the apparently high loft of these Type E particulate units is an inaccurate account of their true loft and reflects their overall large physical sizes, which begin to approach the size of the measurement box. In other words, these “big” units do not homogeneously fill the measurement box.
Dimensionality is one way to characterize the loft of the instant insulation materials. Since the features of the individual particulate units that make up a given sample of material may vary, dimensionality is best understood as an average over the aggregate of particulate units contained in a sample. Down is known in the art to have a dimensionality (D) of about D=1.68. Linear particles (Type B particulate units) define a dimensionality D=1.0. Small particles (Type A particulate units) have D<1.0, where the dimensionality depends on the actual shape characteristics of the particles. True point objects have D=0. However, since the small Type A particulate units shown herein are not true point particle objects, D>0. Based on the features of Type A particulate units shown in
Because of the more pronounced structural irregularity of particulates units of Types C and D, estimation of dimensionality is more difficult. Instead, we resort to a mathematical approach based on loft to infer the dimensionality of Type C and Type D particulate units.
From the results, we observed that the dimensionality of a particulate unit is closely associated with its degree of branching. Loft systematically increases from particulate units of Types B, C, and D as the branching increases. The highest loft is observed for Type D, the particulate unit with the most extensive branching of the representative samples described herein. The trend in loft observed in the progression over particulate units of Types B, C, and D indicates that the complexity of branching is evolving toward that of down. Over the progression, the instant particulate units are increasingly developing the self-similarity and fractal-like features responsible for the superior performance of down as an insulation material.
The exponential fit used to model the relationship between loft and dimensionality has the form:
Loft=αeβD (4)
and includes two model parameters of interest, the pre-factor (α) and the exponential factor (β). To understand the significance of the parameters, we need to factor out physical effects from arbitrary effects associated with the choice of unit system. In
It is of interest that an exponential function should apparently well describe the relationship between loft and dimensionality. Exponential functions usually describe systems that self-reinforce. For example, the exponential rise in pressure with depth in the atmosphere arises because we must add the incremental weights of each elemental volume of air to all elements below. Analogously, each element of increasing dimensionality increases the total ability to fill three dimensional space. This is consistent with our description that higher dimensionality self-reinforces to produce greater entanglement, and this ultimately promotes greater volume filling efficiencies.
We define the volumetric dimensionality of a particulate unit to be a product of the exponential factor (β) and the dimensionality D.
The results show that down has the highest volumetric efficiency and that the volumetric efficiency of the particulate units of the instant invention increases as the degree of branching increases. Relative to the 100% volumetric efficiency of down, one-dimensional objects (Type B particulate units) are only 56% efficient. The low volumetric efficiency of one-dimensional objects explains why insulation materials based on elongated fibers (e.g. fiberglass) have limited insulation capabilities. By comparison, particulate units of Type D have a volumetric efficiency of 77% and are far more effective at filling three-dimensional space than conventional fiber-based insulation materials. The analysis shows not only that the loft of one-dimensional fibers is poor, but also shows that to achieve the same volumetric filling of three dimensional space as the instant Type D (non-linear n) particulate unit, 38% more of the fiber material would be needed. This difference in the mass of material needed to achieve comparable filling of three-dimensional space represents enormous inefficiency (in terms of both material and energy) in the production and use of fiberglass insulation.
As a nation, we must recognize that much of our insulation infrastructure is fundamentally flawed in that far more energy and material resources are needed to produce insulation than is necessary. The instant invention addresses this deficiency by providing a more intelligent design of insulation materials based on the principles of non-integer dimensionality. Biological survival necessarily entails reckoning with circumstances of limited resources and biological creatures have survived by achieving high levels of insulating performance at a minimum cost to the creature's resource and energy budget. Through many millions of years of evolution, nature has created down, which has the perfectly optimized dimensionality to fill three-dimensional space. Through particulate units of non-integer dimensionality, the instant invention effectively mimics down but does so in a way that is compatible with large scale manufacturing processes. Based on the principles elucidated herein, particulate units having non-integer dimensionality can be produced through ripping, tearing, cutting, grinding, stamping, scribing, and pulverizing processes and can be accomplished by physical or laser methods.
In one embodiment, particulate units of the instant invention have a dimensionality of less than or equal to 1.6. In another embodiment, particulate units of the instant invention have a dimensionality greater than 1.0 and less than 1.6. In still another embodiment, particulate units of the instant invention have a dimensionality of greater than 1.1 and less than 1.6. In yet another embodiment, particulate units of the instant invention have a dimensionality of greater than 1.2 and less than 1.6. In a further embodiment, particulate units of the instant invention have a dimensionality of greater than 1.3 and less than 1.6. In still a further embodiment, particulate units of the instant invention have a dimensionality of greater than 1.1 and less than 1.5. In still a further embodiment, particulate units of the instant invention have a dimensionality of greater than 1.2 and less than 1.5. Particulate units within the foregoing dimensionality ranges may have two or more branches. In another embodiment, particulate units within the foregoing dimensionality ranges may have three or more branches. In a further embodiment, particulate units within the foregoing dimensionality ranges may have four or more branches.
In one embodiment, the particulate units of the instant invention have an aspect ratio of 2:1 or greater. In another embodiment, the particulate units of the instant invention have an aspect ratio of 2:1 or greater and two or more branches. In another embodiment, the particulate units of the instant invention have an aspect ratio of 2:1 or greater and three or more branches. In another embodiment, the particulate units of the instant invention have an aspect ratio of 2:1 or greater and four or more branches. In another embodiment, the particulate units of the instant invention have an aspect ratio of 2:1 or less. In another embodiment, the particulate units of the instant invention have an aspect ratio of 2:1 or less and two or more branches. In another embodiment, the particulate units of the instant invention have an aspect ratio of 2:1 or less and three or more branches. In another embodiment, the particulate units of the instant invention have an aspect ratio of 2:1 or less and four or more branches.
In one embodiment, the particulate units of the instant invention have an aspect ratio of 4:1 or greater. In another embodiment, the particulate units of the instant invention have an aspect ratio of 4:1 or greater and two or more branches. In another embodiment, the particulate units of the instant invention have an aspect ratio of 4:1 or greater and three or more branches. In another embodiment, the particulate units of the instant invention have an aspect ratio of 4:1 or greater and four or more branches. In another embodiment, the particulate units of the instant invention have an aspect ratio of 4:1 or less. In another embodiment, the particulate units of the instant invention have an aspect ratio of 4:1 or less and two or more branches. In another embodiment, the particulate units of the instant invention have an aspect ratio of 4:1 or less and three or more branches. In another embodiment, the particulate units of the instant invention have an aspect ratio of 4:1 or less and four or more branches.
In one embodiment, branches of the instant particulate units have a length of at least 0.25 inch. In a further embodiment, the branches of the instant particulate units have a length of at least 0.5 inch. In another embodiment, the branches of the instant particulate units have a length of at least 1.0 inches. In still another embodiment, the branches of the instant particulate units have a length of at least 2.0 inches. In yet another embodiment the branches of the instant particulate units have a length of at least 4.0 inches. In yet another embodiment the branches of the instant particulate units have a length of at least 6.0 inches.
In one embodiment, branches of the instant particulate units have a uniform cross-section. In another embodiment, branches of the instant particulate units have a non-uniform cross-section. In still another embodiment, the non-uniform branches include tapered regions.
In one embodiment, the particulate units of the instant invention have a volumetric efficiency of at least 60%. In another embodiment, the particulate units of the instant invention have a volumetric efficiency of at least 70%.
The materials selected to form particulate units in accordance with the instant invention are designed to efficiently scatter and/or reflect infrared radiation to minimize heat loss through radiative transport mechanism. In one embodiment, the material is typically an inorganic material, such as SiO2, metal oxide or other oxide, transparent conductive oxide, nitride, carbide, boride or mineral. These materials typically possess heteropolar bonds that exhibit strong resonant interactions with infrared radiation to provide efficient scattering of infrared radiation. In another embodiment, the material may also be a metal or metal alloy. Metals and metal alloys possess free carriers that strongly interact with and scatter or reflect infrared radiation. In one embodiment, the metal or metal alloy is resistant to oxidation. Suitable metals include Al, Pt, Au, Ag, and Cu. In a further embodiment, the material is a high refractive index material such as diamond or a semiconductor (e.g. column IV semiconductor or a III-V semiconductor).
Materials in accordance with the instant invention also include composite materials. Composite materials include layered materials that include a substrate material and a coating material. The substrate material is a base material and may be a plastic or organic material. Substrate materials include, but are not limited to, polycarbonate (PC), polyurethanes, polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), and polyethyleneterephthalate (PET). The coating material is on one or more of the exposed surfaces of the substrate material and is the portion of the composite material that receives infrared radiation and efficiently scatters or reflects it. The coating material may be one of the single materials mentioned hereinabove. In one embodiment, the composite material includes an aluminum coating on a plastic substrate.
The plurality of particulate units that are combined to produce an insulation material according to the instant invention may include particulate units that differ in material of construction and/or dimensionality. Particulate units formed from composite and non-composite materials, for example, may be combined to produce an insulation material. Particulate units with low and high dimensionality may also be combined. The invention further extends to insulation materials formed from a combination of particulate units in accordance with the instant invention and other materials. The materials combined with the instant particulate units may be natural or synthetic, organic or inorganic, and may have integer or non-integer dimensionality. Representative natural or synthetic materials that may be combined with the instant particulate units include other forms of insulation, foams, fibers, down, plastics, polycarbonate, polypropylene, polyethylene, polystyrene, polyethyleneterephthalate, cellulose, polyisocyanurate, wool, rock wool, fiberglass, polymer fibers, cotton, down, fur, hair and silk
The infrared blocking capability of the particulate units described hereinabove in connection with
R
Total=1−T (5)
where T is the transmitted fraction of thermal radiation and RTotal is the thermal infrared blocking power. RTotal includes the combined fraction of scattered and reflected thermal radiation. In this description, we assume that that the absorption of infrared energy is minimal.
The IR detector of the infrared camera integrates the signal over a wide cross-section of the insulation material and determines an average result over a plurality of particulate units. The infrared camera receives the thermal IR energy transmitted through the plastic window film and the insulation material and processes it to produce an equivalent temperature. In order to determine transmittance from the temperature output, we performed a calibration of the infrared camera to develop a correlation between changes in output temperature and changes in transmitted thermal IR energy. The principle underlying the calibration is that the IR camera interprets a reduction in infrared energy reaching it as a reduction in the temperature. The extent to which the temperature determined by the camera is reduced correlates with the reflection/scattering efficiency of the insulating material placed between the thermal IR source (hot plate) and the camera. If the insulating material scatters thermal IR radiation, less radiation is received at the camera and the temperature recorded by the camera is less than the temperature recorded in the absence of the insulating material. The more effectively the insulating material scatters or reflects, the greater the reduction in radiation received by the camera is and the greater the decrease in temperature output is.
The calibration procedure is summarized in
We continued by repeating the calibration after inserting a plastic window film between the hot place and infrared camera. As indicated hereinabove, a clear plastic window film was used to support samples of the instant insulation materials that were tested for IR transmittance. In order to properly determine the transmittance of the samples, it is necessary to account for the effect of the supporting plastic window film on the temperature recorded by the IR camera. The temperature measured for the plastic window film (without any insulation material on top) is shown in
Since the insulation materials selected for testing were placed on the plastic window film, the open beam calibration (solid line) shown in
Measurements of infrared transmittance were conducted by applying a layer of each particulate unit on the plastic film in separate trials, reading the output of the infrared camera and converting it to a transmittance using the calibration. To properly compare particulate units of a different type, the same mass was used for the layer of each type of particulate unit. The mass selected for the layers was determined from particulate units of Type A. Since particulate units of Type A have the lowest dimensionality, they have the lowest loft of the samples described herein. To establish a mass for the trials, particulate units of Type A were applied to the plastic window film in the minimum amount needed to completely cover the plastic film and just block out light visible to the eye. The particulate units of Type A were arranged to prevent overlap and to avoid stacking so that single-layer coverage of the plastic film was achieved. This level of coverage may also be referred to herein as “monolayer” coverage of the plastic film. The mass of particulate units of Type A needed to achieve monolayer coverage was 3.3 g and this mass was defined as the reference mass for all samples of the experiment and was used to define monolayer coverage of particulate units of each type.
The results of the IR transmittance measurements are shown in
Although differences in the IR transmittance of the different types of particulate units were observed, these differences were small. To appreciate the insignificance of the difference,
The extremely low loss of thermal IR energy through the radiative transport mechanism means that its radiative resistance (i.e., Rradiation, see Eq. (2)) of the instant insulation materials will be very large in comparison to Rconductive of air. The insulating performance of the instant insulation materials will therefore be limited primarily by the thermal conduction of the air occupying the pores and openings established by the loft of the material. The instant non-integer dimensionality particulate units provide both high loft and excellent IR blocking efficiency and exhibit insulating characteristics limited not by IR transmittance, but by thermal conduction through the medium occupying the open spaces in the surrounding solid framework. At the same time, the high dimensionality of the particulate units enables us to construct the solid framework with the minimal amount of material. As a result, the instant insulation materials are extremely light in weight and exhibit minimal conduction through the solid framework. As described more fully hereinabove, the high dimensionality of the instant particulate units provides the further benefit of mechanical resiliency, which prevents deterioration of insulating power by preventing the settling of particulate units upon compression.
Those skilled in the art will appreciate that the methods and designs described above have additional applications and that the relevant applications are not limited to the illustrative examples described herein. The present invention may be embodied in other specific forms without departing from the essential characteristics or principles as described herein. The embodiments described above are to be considered in all respects as illustrative only and not restrictive in any manner upon the scope and practice of the invention. It is the following claims, including all equivalents, which define the true scope of the instant invention.
