Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02876324 2014-12-31
TITLE OF THE INVENTION
HIGH RESISTANCE PANELS (HRP)
FIELD OF THE INVENTION
[0001] The present invention relates to high resistance panels (HRP) used for
thermal
insulation and a method of manufacturing the same.
BACKGROUND OF THE INVENTION
[0002] Heat transfers by three mechanisms: conduction, convection, and
radiation.
Conduction is the molecule to molecule transfer of kinetic energy. Convection
is the
transfer of heat by physically moving the molecules from one place to another.
Radiation is
the transfer of heat through a space between two objects via electromagnetic
waves.
[0003] The heat flow through solid materials is mainly by conduction. In
stable heat
transfer, the resistance to heat flow through solid materials can be described
by
Q = (Ti-T2)/R (1)
[0004] Where Q is heat flow per unit area, in w/m2 (Systeme International
Unit), T1 is the
higher temperature, in K, T2 is the lower temperature, in K, R is heat
resistance, R-Value,
in m2=K/w, defined as
R= ........ (2)
[0005] Where us the thickness of material which heat transfers through, in m,
and 2,, is
thermal conductivity of the material, in w/(m=K), which can be found in the
prior art.
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[0006] In SI unit, an R-Value such as 5.5 may be indicated as RSI5.5. In non-
SI unit, as
an imperial unit, R-Value uses ft2. F=hr/Btu. The conversion between non-SI
and SI is: 1
ft2. F=hr/Btu = 0.1762 m2=K/w. Thus, RSI5.5 = R31.2.
[0007] The higher the R-Value of a material, the better it is to resist heat
flow. R-Value
of a material is measured in test laboratories. Heat flow through the layer of
a material can
be determined by keeping one side of the material at a constant higher
temperature, for
example, 90 F (32 C), and measuring how much supplemental energy is required
to keep
the other side of the material at a constant lower temperature, for example,
50 F (10 C).
Then the R-Value can be obtained from Equation (1).
[0008] Heat transfers in liquids (air, gases, water, etc.) also by convection.
In stable
status, heat flux by convection can be expressed as
Q = h (Ti-T2) (3)
[0009] Where h is heat transfer coefficient of convection, in w/(m2.1().
[0010] Heat convection is a combination of diffusion and bulk motion of
molecules. Near
the surface the fluid velocity is low, and diffusion dominates. Away from the
surface, bulk
motion increases the influence and dominates. Heat convection may take the
form of either
forced convection or natural convection. Forced convection occurs when a fluid
flow is
induced by an external force, such as a pump, a fan or a mixer. Natural
convection is
caused by buoyancy forces due to density differences caused by temperature
variations in
the fluid. At heating the density change in the boundary layer will cause the
fluid to rise
and be replaced by cooler fluid that also will heat and rise. Boiling or
condensing
processes are also referred as heat convection.
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[0011] Heat transfer coefficient of convection h is dependent on the type of
fluids, the
flow properties such as velocity, viscosity and other flow and temperature
dependent
properties. Heat transfer coefficients of convection h can be found in the
prior art.
[0012] Heat flux by radiation via a space between two objects can be expressed
as
Q = z (Ti4 ¨ T24) (4)
[0013] Where c is the emissivity of the surface, and a is the Stefan-Boltzmann
constant,
5.67037 x 10-8 w/(m2.K4).
[0014] Thermal radiation is the emission of electromagnetic waves from all
matter that
has a temperature greater than absolute zero. It represents a conversion of
thermal energy
into electromagnetic energy. Thermal energy results in kinetic energy in the
random
movements of atoms and molecules in matter. All matter with a temperature by
definition
is composed of particles which have kinetic energy, and which interact with
each other.
These atoms and molecules are composed of charged particles, protons and
electrons, and
kinetic interactions among matter particles result in charge-acceleration and
dipole-
oscillation. This results in the electrodynamic generation of coupled electric
and magnetic
fields, resulting in the emission of photons, radiating energy away from the
body through
its surface boundary. Electromagnetic radiation does not require the presence
of matter to
propagate and travels in the vacuum of space infinitely far if unobstructed.
[0015] The characteristics of thermal radiation depend on various properties
of the
surface it is emanating from, including temperature, spectral absorptivity and
spectral
emissive power.
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[0016] Thermal radiation in a space within optical depth (for most insulation
materials) is
propagating via diffusion. A simple expression for conductivity of radiation
can be used as
follows
X, = c T3/E (5)
[0017] Where X,- is thermal conductivity of radiation, in w/(m=K), c is
constant related to
material, radiation energy, etc., in w/(m2.1(4), T is absolute temperature, in
K, and E is
extinction coefficient, in 1/m, can be expressed as
E = 1/d = p e (6)
[0018] Where d is the mean free path of the radiation photons, in m, p is
density of
material, in kg/m3, and e is mass specific extinction, in m2/kg.
[0019] The development of insulation materials is to make efforts to reduce
heat transfer
by conduction, convection and radiation. Most insulation materials have been
developed
before 1950s, but the extensive application of thermal insulation started
after the oil crisis
in 1970s. Since the oil crisis, thermal insulation of buildings has become the
key issue to
prevent heat loss and to improve energy efficiency. The traditional thermal
insulation takes
air as the best insulator. The thermal conductivity of air of 0.024 w/(m=K)
sets the limit of
performance for such insulation materials. Presently, only vacuum technology
in
combination with microporous structures can achieve the thermal conductivity
of less than
0.024 w/(m-K), that is, Vacuum Insulation Panels (VIP).
[0020] In conventional insulation materials, such as fiberglass, foams, etc.,
three heat
transfer mechanisms are required to consider. Heat transfer in gases (or air)
by convection
and conduction may be taken as a combination, being a thermal conductivity kg.
The
overall thermal conductivity of an insulation material can be given as
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= kg ks + kr (7)
[0021] Where kg is thermal conductivity of gases (or air) in pores combining
heat
conduction and convection, in w/(m=K), ks is thermal conductivity of the
solid, in w/(m-K),
and kr is thermal conductivity by radiation, in w/(m=K).
[0022] Normal insulation materials have typical overall thermal conductivity
of 0.035 to
0.06 w/(m=K). To reduce overall thermal conductivity of insulation materials,
VIP has
been developed. VIP is to reduce kg and kr. VIP is a form of thermal
insulation consisting
of a nearly gas-tight enclosure surrounding a rigid core, from which the air
has been
evacuated. VIP consists of three main components:
[0023] (1) Walls: membrane walls or enclosures, used to prevent gases (or air)
from
entering the panel.
[0024] (2) Core: a panel of a rigid, highly-porous material, such as fumed
silica, aerogel,
perlite or fibres (glass fibres, mineral wool, etc.), to support the walls
against atmospheric
pressure once the air is evacuated.
[0025] (3) Getter: to collect gases (or air) leaked through the walls or
offgassed from the
core and wall materials.
[0026] Heat convection relies on the presence of gas molecules able to
transfer heat
energy by bulk movement through the insulator. Vacuum can reduce heat
convection.
Vacuum also greatly reduces heat conduction of gases (or air), as there are
far fewer
collisions between adjacent gas molecules, or between gas molecules and atoms
of the core
material.
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[0027] Since the core material in a VIP is similar in thermal characteristics
to materials
used in conventional insulation, VIP therefore achieves a much lower thermal
conductivity
than conventional insulation materials. VIP is claimed to achieve an overall
thermal
conductivity of 0.004 w/(m=K) across the centre of the VIP, or an overall
thermal
conductivity of 0.006-0.008 w/(m-K) after allowing for thermal bridging across
the VIP
edges.
[0028] Core materials used in VIP are normally polyurethane (PUR) foam,
expanded
polystyrene (EPS) foam, extruded polystyrene (XPS) foam, silica gels,
aerogels, fumed
silica, glass fibres, polymer beds, perlite, etc. which are believed to be
rigid to provide
strength to support the walls and have lower thermal conductivity ks. Under
fully
evacuated, in microporous structure, heat convection and radiation in VIP are
considered
to be negligible.
[0029] In practical application, it is difficult to maintain vacuum in a VIP.
A lot of efforts
have been made to improve structure of VIP in last decades. Improvement of VIP
is the
development of "maintenance of vacuum". Laminated plastic and aluminum sheets,
or
metal layer with a surface protection layer, can be used as wall materials for
VIP, for
example, in US Pat. No 4,444,821 to Young et al, in US Pat. No. 4,529,638 to
Yamamoto
et al, and in US Pat. No. 8,663,773 to Jang et al. To improve impermeability,
dual walls, or
two walls, or two bags are used as walls for VIP. For example, in US Pat. No.
4,726,974 to
Nowobilski et al, in US Pat. No. 7,449,227 B2 to Echigoya et al, in US Pat.
No. 7,517,576
82 to Echigoya et al, in US Pat. No. 7,968,159 B2 to Feinerman, in US Pat. No.
8,137,784
B2 to Veltkamp, and in US Pat. No. 8,475,893 B2 to Feinerman. Multi-layers of
structure
of VIP was described in US Pat. No. 8,383,225 B2 to Rotten Sealing of VIP is
important
to maintain vacuum, various sealing methods have been developed, for example,
in US
Pat. No. 8,281,558 B2 to Hiemeyer et al, and in US Pat. No.8,377,538 B2 to
Eberhardt et
al.
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[0030] Getters are used to absorb or adsorb gases (or air) leaked through the
walls or
offgassed from the core materials. Getter materials include zeolites,
activated carbon,
quicklime (CaO), for example, in US Pat. No. 7,838,098 B2 to Kim et al, and in
US Pat.
No. 8,663,773 to Jang et al, and a combination of them, as well as metal-
organic
frameworks (M0Fs), for example in US Pat. No. 5,648,508A to Yaghi, and in US
Pat. No.
8,647,417 B2 to Eisenhardt et al.
[0031] As described above, a lot of improvements for VIP have been obtained.
However,
some problems still exist in VIP as high thermal resistance panels for thermal
insulation,
which are: (1) It is difficult to maintain vacuum for long enough for serving
as
conventional insulation materials. (2) Materials for walls, core and getter of
VIP, and
sealing VIP are expensive. (3) It is not possible to cut to sizes to fit the
installations. (4)
Thermal bridging across the VIP edges increases heat transfer and reduces
overall heat
resistance. These problems limit the practical application of VIP.
[0032] Additional improved and modified structure and mechanism to combine
with the
improvements addressed above are required to overcome the disadvantages in VIP
to
develop high resistance panels (HRP).
[0033] The following Patents and References are cited:
[0034] US Patents:
4,444,821 04/1984 Young et al
4,529,638 07/1985 Yamamoto et al
8,663,773 03/2014 Jang et al
4,726,974 02/1988 Nowobilski et al
7,449,227 B2 11/2008 Echigoya et al
7,517,576 B2 04/2009 Echigoya et al
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7,968,159 B2 06/2011 Feinerman
8,137,784 B2 03/2012 Veltkamp
8,475,893 B2 07/2013 Feinerman
8,383,225 B2 02/2013 Rotter
8,281,558 B2 10/2012 Hiemeyer et al
8,377,538B2 02/2013 Eberhardt et al
7,838,098 B2 11/2010 Kim et al
5,648,508 A 07/1997 Yaghi
8,647,417 B2 02/2014 Eisenhardt et al
[0035] References:
[0036] Carslaw, H. S. and Jaeger, J. C., Conduction of Heat in Solids, Second
Edition,
1959, Oxford University Press, Reprinted 2000.
[0037] Tritt, Terry M., Thermal Conductivity: Theory, Properties, and
Applications,
Kluwer Academic/Plenum Publishers, New York, 2010.
SUMMARY OF THE INVENTION
[0038] The object of the present invention is to provide an improved and
modified
structure and mechanism to resolve the problems in conventional insulation
materials and
VIP described above. A newly developed mechanism in the present invention is
to reduce
total kinetic energy of air or gas molecules in voids in conventional
insulation materials
and VIP by spatial continuous infinite structures of phononic cocrystals, as
defined in the
present invention, in which continuous infinite and infinitesimal voids exist.
And the
elimination in heat radiation is reached by low emissivity of material
surfaces. This
constructs High Resistance Panels (HRP), which is comprised of low emissivity
of
surfaces, support materials in between the surfaces, and phononic cocrystals
which are
distributed on the low emissivity of surfaces, or mixed in support materials
or on surfaces
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of support materials. The structure of support materials is in a honeycomb
structure instead
of powders or fibres as in conventional insulation materials and VIP. Several
HRP can
stack together to meet the requirements of thickness and thermal resistance in
application.
HRP can reach a low overall thermal conductivity comparable to VIP.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 is a diagrammatic structure of HRP in the invention.
[0040] FIG. 2 is a diagrammatic sketch showing one of the structures
(hexagonal
honeycomb structure) for support materials of HRP in the invention.
[0041] FIG. 3 is a photograph of one of the structures (hexagonal honeycomb
structure)
for support materials of HRP in the invention.
[0042] FIG. 4 is a photograph of one of the structures (regular cubic
honeycomb
structure) for support materials of HRP in the invention.
[0043] FIG. 5 is a diagrammatic structure of two layers of HRP in the
invention.
[0044] FIG. 6 is a diagrammatic structure of three layers of HRP in the
invention.
[0045] The numbers in the FIGURES represent:
[0046] 1. Impermeable barrier and backing. 2. Surface of low emissivity coated
with
"phononic cocrystals" defined in the present invention. 3. Cell spaces in
support materials.
4. Support materials. 5. Impermeable barrier.
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DETAILED DESCRIPTION OF THE INVENTION
[0047] VIP can provide low thermal conductivity for insulation. The keys in
VIP are
vacuum technology and microporous structure. Vacuum is a space that is devoid
of
matters, or a region with a gaseous pressure less than atmospheric pressure.
In practice, the
vacuum is partial vacuum. Less air molecules in voids of core materials of VIP
eliminates
heat conduction and convection by reduction in total kinetic energy of air
molecules, or
increase in the mean free path of air molecules (more space for molecules),
therefore less
collisions between air molecules. Heat transfer by radiation can be eliminated
by micro
scale of voids in VIP with microporous structure, provided that the sizes of
voids are less
than the mean free path of photons.
[0048] In the present invention, the reduction in total kinetic energy of air
or gas
molecules is obtained by spatial continuous infinite structures of "phononic
cocrystals", as
defined in the present invention, in which continuous infinite and
infinitesimal voids exist.
And the elimination in heat radiation is reached by low emissivity of material
surfaces.
[0049] Cocrystal is a crystalline structure made up of two or more components,
where
each component is defined as either an ion, an atom, or a molecule to form a
joint super
lattice, by a definite stoichiometric ratio between the components as each
pure component
has its own distinct bulk lattice arrangement. This includes many types of
compounds,
such as hydrates, solvates, clathrates, and eutectics, which represent the
basic principle of
host-guest chemistry. Spatial continuous infinite different structures of
cocrystals are a
mixture comprised of infinite different structures of cocrystals. The spatial
continuity is
defined to be as in an atomic or molecular level in stoichiometric ratio
between different
pure cocrystals. The "different structures" means that contiguous cocrystals
are completely
different in structures. In spatial continuous infinite structures of
cocrystals there are very
small voids between super lattices. The sizes of the voids are less than the
mean free path
of phonons. For convenient description, the cocrystals are named as "phononic
cocrystals"
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or "phononic eutectics", or "photonic cocrystals". "Phononic cocrystals"
represents all the
names used in the context. It is shown from theory of thermal conductivity of
matters that
phonons can be scattered by crystal defects which reduce the thermal
conductivity of
crystals because the defects produce local variations of sound velocity
through change in
density or elastic constants. The defects in the phononic cocrystals provided
by the voids
greatly reduce the thermal conductivity to a very low level. The charge-
acceleration and
dipole oscillation by kinetic interactions among particles in the phononic
cocrystals result
in the electrodynamic generation of coupled electric and magnetic fields,
which propagate
as waves around the space surrounding the phononic cocrystals, and interfere
with the
matters (air or gases) in the space, reducing their total kinetic energy, and
then resulting in
a reduction in heat transfer.
[0050] Heat radiation from a material through a space larger than optical
depth is greatly
related to the emissivity of material surfaces. A low emissivity of surface
can eliminate
heat transfer by radiation. Surface of foils of aluminum or its alloys has
emissivity of 0.03
which is much less than most materials used for insulation. Surface of silver
has a lower
emissivity of 0.02-0.03 but silver is much more expensive.
[0051] HRP in the invention overcomes the disadvantages of conventional
insulation
materials and VIP. HRP mainly includes the following improvements and
modifications:
(1) Phononic cocrystals provide a low thermal conductivity. (2) Reduction in
kinetic
energy of air or gas molecules in the spaces of support materials by the
phononic
cocrystals results in reduction in heat transfer. (3) Low emissivity of
surfaces reduces heat
transfer by radiation. (4) HRP can be cut to any sizes to meet requirements of
installation.
(4) No thermal bridging on edges. (5) HRP can stack or pile up to a thickness
to meet
requirements of installation and heat resistance.
[0052] One embodiment of the present invention is shown in FIG. 1. A HRP
consists of
two impermeable barriers and backings 1, two surfaces 2 with a low emissivity
facing each
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other in direction of heat transfer and coated with phononic cocrystals,
support materials 4
for a structure and cell spaces 3.
[0053] The materials for impermeable barrier and backing can be aluminum
foils,
metallised films which are polymer films coated with a thin layer of metal
usually
aluminum, metal plates, plastics laminated with metal films or by a means of
deposition or
coating, having very high impermeability and sufficient strength. Low
emissivity of
surfaces can be provided by aluminum foils or metallised films. The phononic
cocrystals
are mixed with a clear and transparent adhesive and coated on the surfaces.
The adhesive
can be glues made from polyvinyl acetate, hot melt adhesives, or pressure-
sensitive
adhesives. The adhesive also performs as a binder to glue the support
materials to the
surfaces. The support materials are natural fibres, glass fibres, rock wool,
plastics, and
other inorganic materials, and their mixtures, and made to form sheets, for
example, paper
sheets and the like, and then from sheets to form a honeycomb structure using
the methods
in the prior art. After sufficient strength has been considered, the thinner
the sheets, the less
heat transfer through the sheets.
[0054] Honeycomb structures allow the minimization of the amount of support
materials
to reach minimal weight and maximum strength. A hexagonal honeycomb structure
for
support materials of HRP in the invention is shown in FIG. 2 and FIG. 3. A
regular cubic
honeycomb structure is shown in FIG. 4.
[0055] The phononic cocrystals by the definition in the invention are a
mixture of spatial
continuous infinite different structures of cocrystals.
[0056] The phononic cocrystals can be constituted from salt hydrates and
fusion
(melting) temperature-depressing salts that are generally non-hydrated salts
in a high
viscosity of polymer solution. A simple method and process are described as
follows: (1)
Mixing a salt hydrate with a fusion (melting) temperature-depressing salt at a
ratio in a
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polymer solution. (2) Heating the solution to a temperature at which the salt
hydrate and
the fusion (melting) temperature-depressing salt melt completely. (3) Then
gradually
cooling the mixture without agitation to form the cocrystals. The high
viscosity in the
solution plays an important role in the process. The formation of phononic
cocrystals in the
process is induced by the spatial difference of ion concentrations in the
solution with high
viscosity. When the mixture is being cooled, a eutectic in a space is formed
and the ions in
the surrounding are being consumed. A different eutectic will be formed in the
adjacent
space, because the high viscosity reduces the ions to migrate to the space.
[0057] The phononic cocrystals can also be formed from molten salts with
different
melting temperatures. The low melting point of salt provides high viscosity
when heated to
a molten status. The other salts with high melting points as powders are
distributed in the
molten salt. The mixture is heated to melt, then is gradually cooled without
agitation to
form phononic cocrystals.
[0058] Furthermore, the phononic cocrystals can be formed from metal oxides
during
oxidation and water soluble salts where water acts as a catalyst. A simple
example is that
iron oxides from the oxidation of iron and sodium chloride constitute phononic
cocrystals.
Saturated solution of sodium chloride is mixed with iron powders and exposed
to air or
oxygen for oxidation while it is being cooled. The iron oxides formed absorb
water, and
sodium chloride crystals are seeded out with iron oxides to form eutectics.
Due to the
concentration gradients of sodium chloride spatially in the mixture, different
eutectics are
formed. In this process, the oxidation consumes oxygen in air. If the closed
cells are
formed by support materials, the absence of oxygen in air can produce partial
vacuum in
the cells, resulting in a reduction in total kinetic energy of air.
[0059] The phononic cocrystals formed from the processes described above are
not
perfect because they are greatly dependent on the control of formation
conditions. The
perfect phononic cocrystals can be made by modern nano technology.
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[0060] The quantity of phononic cocrystals in HRP, coated on surfaces or mixed
with
support materials, depends on the structure and volume of honeycomb cells by
the support
materials. The thickness of HRP depends on the sizes of honeycomb structures,
thickness
and strength of sheets made from support materials, and strength requirement
for the
application. It is suggested that 0.2 mg to 2 mg of phononic cocrystals per
cubic centimeter
of total volume of HRP be appropriate for the purpose, preferably 0.5 mg to
1.5 mg. The
thickness of HRP (in heat transfer direction) can be 1 mm to 60 mm, preferably
3 to 15
mm. The thickness of sheets made from support materials can be in a range of
0.02 mm to
2 mm, preferably 0.05 mm to 1 mm. The area of each honeycomb cell,
perpendicular to
heat transfer direction, can be in a range of 0.1 mm2 to 1 x 106 mm2,
preferably 1 mm2 to 1
x 103 mm2. The volume of a cell in honeycomb structure made from support
materials can
be 0.1 mm3 to 106 mm3, preferably 0.5 mm3 to1 x 105 mm3.
[0061] Two or more HRP can be stacked or piled up to form a thickness to meet
requirements for installation and heat resistance. FIG. 5 shows two layers of
HRP stack,
and FIG. 6 shows three layers of HRP stack. The impermeable barrier 5 between
two HRP
can serve the both.
[0062] HRP in the present invention performs a low thermal conductivity that
is in the
order of 10-3 w/(m=K), thus providing high thermal resistance for insulation.
HRP
overcomes the disadvantages in VIP and conventional insulation materials, and
can be
made easily and at a low cost. HRP has a low density of 20-100 kg/m3, and can
be cut to
any sizes to meet requirements for installation.
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