Note: Descriptions are shown in the official language in which they were submitted.
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PASSIVE REFRIGERATION SYSTEM FOR THE COLD CHAIN INDUSTRY
FIELD
The present technology is directed to a passive system for refrigerating
perishable products during
shipping and storage. More specifically, the technology is directed to a
system that uses carbon-dioxide
free cooling in the load chamber, and which has a high degree of temperature
regulation. The system is
designed both for pallet sized loads and trailer sized loads and stationary
cold storage facilities and is
therefore scalable.
BACKGROUND
The cold chain industry is responsible for shipping and storing refrigerated
temperature sensitive food
and pharmaceutical products. Losses can be incurred because of insufficient
refrigeration or improper
temperatures. Currently, companies involved in shipping perishable foods must
either have expensive
electro-mechanical refrigeration trucks with multiple refrigerated
compartments that can be set to
different temperatures, or place all items at a single temperature and hope
the frozen product does not
melt and spoil before delivery.
United States Patent 4,891,954 discloses a refrigeration system (10)
consisting of an insulated railcar (12)
that utilizes sublimated carbon dioxide to maintain the integrity of stored
products. The insulated railcar
(12) includes a divider (22) that partitions the insulated railcar (12) into a
lower storage area (26) and an
upper bunker (24). The bunker (24) contains a distribution manifold (28) for
forming carbon dioxide snow
and distributing the formed snow throughout the bunker (24). Sublimation ports
(30) along each sidewall
(18) and end wall (20) allow the sublimated carbon dioxide to pass to the
lower storage area (26) to
refrigerate the stored products during transit. A plenum (42) and emission
vent (44) is provided at each
end of the insulated railcar (12) to vent sublimated carbon dioxide to the
exterior atmosphere. The
insulated railcar (12) also includes pressure relief ports (32) located
substantially below the distribution
manifold (28) to vent flash gas generated during the snow forming process.
This technology does not
allow for temperature control over time, nor is there a consistent temperature
throughout the chamber.
Further, CO2 is added to the chamber.
United States Patent 5,460,013 discloses a refrigerated, thin-walled shipping
container (8) including a
horizontal dividing element (20) forming a compartment (22) for holding CO2
snow created by passing
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liquid CO2 through manifold (24) along at least one side of the compartment
and spraying the CO2 snow
against the opposite wall. The charging of the cooling compartment generates
gas pressure, and the
combination design of the charging manifold and pressure release vents allows
the operation to be
performed without excessive structural damaging pressure buildup. This
technology does not allow for
temperature control over time, or in different regions of the container.
Further, gaseous CO2 is added to
the chamber.
United States Patent 7,310,967 discloses a cryogenic shipping and storage
container, with an on-board
cooling unit in the form of a bunker for holding solid refrigerant. The unit
can be configured for different
sizes, and to refrigerate rather than freeze product. While this system allows
for better temperature
control in the chamber, it requires power and fans, and therefore is not a
passive system. Further, gaseous
CO2 is added to the chamber.
United States Patent 8,191,380 discloses a portable active cryo container for
maintaining product at
refrigerated and/or cryogenic temperatures. Said container comprising a
control system to monitor and
control the flow of cooling air from a bunker section to at least one material
storage section wherein
temperature sensitive product is contained. The control system is coupled to a
fan which enhances heat
transfer through forced convection when the system moves outside thermal
tolerance. The cryo container
is powered using battery packs or by being plugged into a vehicle's 12-volt
power supply. While this
system allows for better temperature control in the chamber, it requires power
and fans, and therefore
is not a passive system. Further, gaseous CO2 is added to the chamber. The
coolant, which is liquid
nitrogen, travels through a liquid vaporizing heat exchanger. Unlike a heat
pipe, it has an open end. The
open end discharges the coolant into the ambient environment in the chamber.
United States Patent 3714793 discloses a liquefied gas vaporizer in the bottom
portion of the freeze-
sensitive product storage chamber with thermal insulation around the liquid
vaporizing conduit and
thermally conductive metal floor means contiguously associated with and in
heat transfer relation to the
thermal insulation. The coolant, which is liquid nitrogen, travels through a
liquid vaporizing heat
exchanger. Unlike a heat pipe, it has an open end. The open end discharges the
coolant into the ambient
environment in the chamber.
United States Patent 3421336 discloses a system for more uniform distribution
of refrigerant in long-haul
trailers and railcars by intermittently spraying cold fluid into the product
chamber and continuously
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expanding vaporised cold liquid into the same chamber with the production of
external work which is
recovered to circulate the sprayed cold fluid.
United States Patent 7891575 discloses a thermal storage and transfer system
that includes a cooling
system and method using ice or other frozen material with heat pipes to
produce a cool airstream.
Preferably, the ice is disposed in a container with the condensers and
evaporators of the heat pipes
respectively inside and outside the container. A fan blows air across the
evaporator sections through a
duct to circulate within an enclosed airspace to be cooled. A separate
refrigeration system which may be
used to independently cool the airspace also freezes water or another liquid
to produce the ice or other
frozen material in the container. The cooling system is broadly applicable,
including use on motor vehicles
to provide cooling for several hours when the vehicle engine is off. A heating
system includes an adsorbent
heat exchanger for extracting heat from exhaust gases of an engine and heating
an enclosed airspace.
This is not a passive system, as it requires fans.
United States Patent Application 20040226309 discloses a portable, temperature-
controlled container for
storing and transporting temperature-sensitive materials. The portable,
temperature-controlled
container includes a container having a bottom wall, four side walls, and a
top wall defining a cargo space.
The container includes a temperature regulating unit connected to the
container. The temperature
regulating unit comprising a refrigeration unit. The temperature regulating
unit being in communication
with the cargo space of the container. The container includes a temperature
controller connected to the
container. The temperature controller comprising a temperature control unit
and a temperature sensor
positioned in the cargo space of the container. The container also includes a
power supply. The
temperature regulating unit can include a heating unit. This is not a passive
system.
United States Patent 8,162,542 discloses a cargo container that includes a
cargo box affixed atop a hollow
base, with the base including forklift tunnels extending therethrough with
elongate bays disposed parallel
thereto. Each bay includes a removable tray for receiving electrical
batteries. And, a temperature control
system is disposed on a sidewall adjoining the base. The cargo container has
both an electrical heater and
vapor compression refrigeration. Onboard batteries provide power during
shipping. This is not a passive
system.
United States Patent Application 20130008188 discloses a cryogen heat
exchanger that includes a
container having a sidewall defining a chamber in the container for containing
a cryogen, and at least one
heat exchange assembly having a first portion disposed in the chamber and
extending through the
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sidewall to a second portion disposed in an atmosphere of a space external to
the chamber and at an
opposite side of the sidewall for providing heat transfer to the atmosphere.
The system uses heat pipes,
but also includes at least one fan, and therefore is not a passive system.
Temperature can be adjusted by
varying the pressure of the cryogen (liquid nitrogen or liquid carbon dioxide)
in the tank, presumably with
a pump or adjusting fan speed. Again, neither being passive. Other methods of
adjusting temperature
do not allow for temperature adjustment on the fly, but rather involve use of
a variable volume liquid
reservoir to the evaporator section of each heat pipe. The heat pipes are
stainless steel or copper.
A refrigerated container that can hold a pallet of product would be useful for
both shipping and storage
of perishable products. It would be preferably if carbon dioxide or other
coolant was not added to the
storage compartment, either directly or indirectly. Carbon dioxide displaces
oxygen and in high
concentrations will asphyxiate a person. Discharging carbon dioxide vapour
directly into the load space
compromises temperature control and because of its very rapid temperature
pulldown, compromises the
load unit's structural elements. Further, the expansion effect caused by phase
change requires significant
volumes of the cryogen vapour to vent the atmosphere, which increases
operating costs by increasing the
amount cryogen needed. It would be more preferably if it had a passive heat
transfer system with no
requirement for forced convention. It would be of further advantage if the
system allowed for delivery
and storage of cargo at various selected and controlled temperatures.
SUMMARY
The present technology provides a refrigerated container for both shipping and
storage of perishable
products. In one embodiment, it is sized to hold a pallet of product. Carbon
dioxide is not added or
released to the storage compartment, either directly or indirectly. The system
has a passive heat transfer
system with no requirement for forced convention. The system allows for
delivery and storage of cargo
at various selected and controlled temperatures.
In one embodiment, a passive refrigeration box for controlled refrigeration of
a product is provided, the
refrigeration box comprising: an outer box, the outer box including an outer
insulation layer; an inner box,
the inner box including an inner insulation layer, and a thermal shield on an
outside of the inner insulation
layer, the inner box and the outer box defining a vapour channel therebetween;
and a thermal link, the
thermal link including an thermal layer and a plurality of heat pipes or
thermosyphons, the thermal layer
and a top section of the inner box defining a coolant chamber, the coolant
chamber including a coolant
chamber access, the thermal layer and a bottom section of the inner box
defining a load chamber, the
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load chamber including a load chamber access, each heat pipe or thermosyphon
having a condenser
section disposed in the coolant chamber and an evaporator section disposed in
the load chamber and
extending through the thermal layer.
The passive refrigeration box may further comprise a mesh header below the
heat pipes or
thermosyphons.
The passive refrigeration box may further comprise an outer skin on the outer
insulation and an inner
liner on the inner insulation.
In the passive refrigeration box the thermal shield may be an aluminum shield.
In the passive refrigeration box the coolant chamber access may include an
outer lid and an inner lid.
In the passive refrigeration box the inner lid may be seated on a step in the
inner box.
The passive refrigeration box may further comprise a gasket between the inner
lid and the step.
In the passive refrigeration box the heat pipes may be weld-free heat pipes.
In the passive refrigeration box the heat pipes may include a working fluid,
the working fluid being one of
pentane, propylene, acetone and methanol.
In the passive refrigeration box the thermal link may be a reconfigurable
thermal link.
The passive refrigeration box may further comprise a check valve in the outer
lid.
In another embodiment, a passive refrigeration system for the cold-chain
industry is provided, the system
including a box and a solid coolant, the box comprising: an outer box, the
outer box including an outer
insulation layer; an inner box, the inner box including an inner insulation
layer, and a thermal shield on an
outside of the inner insulation layer, the inner box and the outer box
defining a vapour channel
therebetween; and a thermal link, the thermal link including a thermal layer
and a plurality of heat pipes
or a plurality of thermosyphons, the thermal layer and a top of the inner box
defining a coolant chamber,
the coolant chamber including a coolant chamber access, the thermal layer and
a bottom of the inner box
defining a load chamber, the load chamber including a load chamber access,
each heat pipe or
thermosyphon having a condenser section disposed in the coolant chamber and an
evaporator section
disposed in the load chamber and extending through the thermal layer, and the
solid coolant is solid
carbon dioxide.
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In the system, the thermal link may be a reconfigurable thermal link.
In the system, the system includes the heat pipes.
In the system, the heat pipes may be weld-free heat pipes.
In the system, the heat pipes may include a working fluid, the working fluid
being one of pentane,
propylene, acetone and methanol.
In the system, the thermal shield may be an aluminum shield.
In another embodiment, a passive refrigeration box for controlled
refrigeration of a product is provided,
the refrigeration box comprising: a bottom, four side attached to the bottom,
an inner lid and an outer
lid, the sides including an outer insulation layer and an inner insulation
layer, the layers and the inner and
outer lids defining a vapour channel therebetween, an aluminum shield adjacent
the vapour channel and
abutting an outer side of the inner insulation layer and a top of the inner
lid, a thermal layer, the thermal
layer disposed below the inner lid and between the inner insulation layers to
define a coolant chamber,
the coolant chamber for retaining a coolant, a load chamber, the load chamber
defined by the inner
insulation, and the thermal layer, and a plurality of heat pipes or a
plurality of thermosyphons, each heat
pipe or thermosyphon having a condenser section disposed in the coolant
chamber and an evaporator
section disposed in the load chamber and extending through the thermal layer.
In another embodiment, a method of refrigerating a load passively is provided,
using the refrigeration box
described above, the method comprising loading the load into the load chamber
and charging the coolant
chamber with a solid coolant.
The method may further comprise configuring the thermal link to regulate the
temperature of the load.
In the method, the solid coolant is solid carbon dioxide.
FIGURES
Figure 1 is a longitudinal sectional view of a heat pipe of the present
technology.
Figure 2 is a longitudinal sectional view of an end cap and tube end of the
heat pipe of Figure 1.
Figure 3 is a perspective sectional view of the passive refrigeration box of
the present technology.
Figure 4 is a longitudinal sectional view of Figure 3.
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Figure 5 is a longitudinal sectional view an alternative embodiment of Figure
3.
Figure 6 is a longitudinal sectional view of an alternative embodiment of
Figure 3.
DESCRIPTION
Except as otherwise expressly provided, the following rules of interpretation
apply to this specification
(written description, claims and drawings): (a) all words used herein shall be
construed to be of such
gender or number (singular or plural) as the circumstances require; (b) the
singular terms "a", "an", and
"the", as used in the specification and the appended claims include plural
references unless the context
clearly dictates otherwise; (c) the antecedent term "about" applied to a
recited range or value denotes an
approximation within the deviation in the range or value known or expected in
the art from the
measurements method; (d) the words "herein", "hereby", "hereof", "hereto",
"hereinbefore", and
"hereinafter", and words of similar import, refer to this specification in its
entirety and not to any
particular paragraph, claim or other subdivision, unless otherwise specified;
(e) descriptive headings are
for convenience only and shall not control or affect the meaning or
construction of any part of the
specification; and (f) "or" and "any" are not exclusive and "include" and
"including" are not limiting.
Further, the terms "comprising," "having," "including," and "containing" are
to be construed as open
ended terms (i.e., meaning "including, but not limited to,") unless otherwise
noted.
To the extent necessary to provide descriptive support, the subject matter
and/or text of the appended
claims is incorporated herein by reference in their entirety.
Recitation of ranges of values herein are merely intended to serve as a
shorthand method of referring
individually to each separate value falling within the range, unless otherwise
indicated herein, and each
separate value is incorporated into the specification as if it were
individually recited herein. Where a
specific range of values is provided, it is understood that each intervening
value, to the tenth of the unit
of the lower limit unless the context clearly dictates otherwise, between the
upper and lower limit of that
range and any other stated or intervening value in that stated range, is
included therein. All smaller sub
ranges are also included. The upper and lower limits of these smaller ranges
are also included therein,
subject to any specifically excluded limit in the stated range.
Unless defined otherwise, all technical and scientific terms used herein have
the same meaning as
commonly understood by one of ordinary skill in the relevant art. Although any
methods and materials
similar or equivalent to those described herein can also be used, the
acceptable methods and materials
are now described.
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DEFINITIONS
Heat pipe ¨ in the context of the present technology, a heat pipe consists of
a sealed pipe that
unreleasably retains a working fluid. A wick is present in the bore of the
pipe.
Thernnosyphon ¨ in the context of the present technology, a thermosyphon is
similar in components and
construction to a heat pipe, except it contains a larger amount of working
fluid and it does not contain a
wick structure. It unreleasably retains a working fluid.
Weld-free heat pipe ¨ in the context of the present technology, a weld-free
heat pipe is one that has
barbed end caps and barbs on the inside of the tube of the heat pipe proximate
the ends. The end caps
and tube are press fit together.
Weld-free, soldered heat pipe ¨ in the context of the present technology, a
copper heat pipe will be
soldered to close the end caps to the tube.
Weld-free soldered thermosyphon ¨ in the context of the present technology, a
thermosyphon will be
soldered to close the end caps to the tube.
Working fluid ¨ in the context of the present technology, a working fluid is
one that is present as both a
saturated liquid phase and a vapour phase in the heat pipe. The liquid is
evaporated to a vapour at the
evaporator region of the heat pipe, and the vapour is condensed to a liquid at
the condenser region of
the heat pipe.
Wick ¨ in the context of the present technology, a wick is a material that
lines the bore of the heat pipe
and exerts a capillary action on the liquid phase of the working fluid.
Thermal link ¨ in the context of the present technology, a thermal link is an
interface for the management
of heat flow (thermal energy flow). The design and the material used
determines the thermal conduction
of the thermal linkage. The thermal linkage includes the heat pipes and an
insulating or conducting layer
(the thermal layer).
Reconfigurable thermal link ¨ in the context of the present technology, a
reconfigurable thermal link refers
to a thermal link that can be altered to change or optimize the thermal
conductivity for a given application
(temperature requirement).
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Solid coolant ¨ in the context of the present technology, charging the coolant
chamber with a solid coolant
means that a solid coolant is added, or a liquid coolant is injected which
then changes phase from a liquid
to a solid coolant.
DETAILED DESCRIPTION
A heat pipe, generally referred to as 8 is shown in Figure 1. It is a tube 10
that has a first end 12, with a
first end cap 14, and a second end 16, with a second end cap 18. The second
end cap 18 has a fill tube 20
extending therefrom. A bore 22 extends from the first end cap 14 to the second
end cap 18. The fill tube
20 has a crimping end 24 distal to the second end cap 18 and a fill tube bore
26. The second end cap 18
has a central aperture 28. The wall 30 of the central aperture 28 has a step
32 upon which the proximal
end 32 of the fill tube 20 is seated (Figure 2). A solder bead 34 attaches the
fill tube 20 to the second end
cap 18. In Figure 1, the crimping end 24 is crimped, after the working fluid
has been added to the pipe. A
bead of solder 40 seals the crimped end 24. The heat pipe 8 has a wick 42 in
the bore 22.
As shown in Figure 2, and using the second end cap as an example, the first
end 12 and the second end
16 and the end caps 14, 18 are barbed 50, with the end cap 14, 18 preferably
being the male mating
member 52 and the ends 12, 16 being the female mating member 54 and also
having barbs 56. An 0-ring
60 is seated in the mating pair. This provides a weld-free heat pipe.
As noted above, the thermosyphon is weld-free and is soldered closed.
A passive refrigeration box, generally referred to as 80 is shown in Figure 3.
The refrigeration box 80
provides passive cooling through the use of heat pipes 8 and with no release
of coolant into the load
chamber 82. The outer box 81 includes a bottom 84 attached to four walls 86,
and an outer lid 88. The
box is preferably constructed to provide sufficient strength and support for
the load and to be moved
using a fork lift. An outer skin 90 of aluminum or steel or plastic is
optionally supported by a metal frame
92 in the bottom 84 and four walls 86. A layer of outer insulation 94 lines
the inside 96 of the skin 90 and
frame 92. The outer insulation 94 is preferably closed cell, extruded or
expanded polystyrene or the like.
The bottom 84 includes slots 97 for accepting forks of a forklift.
An inner box 98 includes four inner walls 100, an inner bottom 102, and an
inner lid 104. A layer of inner
insulation 110 lines the inner liner 112 of the walls 100 and the skin 114 of
the inner lid 104. The inner
insulation 110 is preferably closed cell, extruded or expanded polystyrene or
the like. The inner liner 112
and skin 114 are aluminum or plastic. The inner liner 112 includes stand-offs
116 that extend a short
distance into the load chamber 150 to ensure that an air gap 116 is maintained
between the inner liner
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112 and the load. The outer lid 88 is similarly constructed of a skin which is
aluminum or plastic and
insulation that is preferably closed cell, extruded or expanded polystyrene or
the like.
Abutting the upper surface 118 of the insulation 110 of the inner lid 104 and
the outer surface 120 of the
inner insulation 100 is a thermal shield 122 which in the preferred embodiment
is an aluminum shield
122. The aluminum shield 122 and both the layer of outer insulation 94 on the
walls 86 and the outer lid
88 define a space referred to as vapour channel 124. The thermal shield 122
helps to manage heat leaks
and maintain the temperature of the cold space. It also decreases the time to
cool a load from its initial
higher temperature to steady-state while consuming less dry-ice.
As shown in Figure 4, the inner lid 104 sits on a step 126 in the inner liner
112. A gasket 128 fits between
the inner lid 104 and the step 126 in the inner liner 112. The vapour channel
124 is sealed from the
ambient and from the coolant chamber 140. However, there is a check valve 125
mounted in the outer
lid 88 so that a small over pressure can be maintained inside the vapour
channel 124. This prevents the
ingress of external moist air when the dry ice charge is depleted. A coolant
142 which is preferably solid
carbon dioxide, is loaded and retained in the coolant chamber 140. Once
closed, the coolant chamber
140 does not communicate with the ambient environment. The coolant chamber 140
has a plurality of
heat pipes 8 extending into the chamber through a base 143 of the coolant
chamber 140. The base 143
and the heat pipes 8 form a reconfigurable thermal link 144. The
reconfigurable thermal link 144 allows
for customization and optimization of thermal energy transfer between the
coolant 142 in the coolant
chamber 140 and the load chamber 150. The coolant chamber 140 is in a top
section 146 of the inner box
98. The load chamber 150 is in a bottom section 148 of the inner box 98.
The construction of the heat pipes 8 assist in providing this customization.
The portion of the heat pipes
8 extending into the coolant chamber 140 includes the condenser section 152.
Below the base 143 and
the inner liner 112 is the load chamber 150. The portion of the heat pipes 8
extending into the load
chamber 150 includes the evaporator section 156. A mesh header 160 protects
the heat pipes 8 from
damage in case the load in the load chamber 150 shifts. The mesh is aluminum,
steel or plastic and
additionally functions to ensure sufficient space for air circulation. It
extends across the load chamber
150 in the vicinity of the top 162 of the load chamber 150. The load chamber
150 is an enclosed space.
An inner door 170 and an outer door 172 are constructed in the same manner and
with the same materials
as the lids 88, 104. These doors do not impede the vapour channel 124. At
least one temperature sensor
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176 is located in the load chamber 150 and is in electronic communication with
a display 178 that is
remote to the refrigerator box 80 or is on an outer surface 178 of the
refrigerator box 80.
In one embodiment, the refrigeration box 80 is sized to accept a pallet load
of product. The load is placed
in the refrigeration box and then the refrigeration box can be moved into and
out of a storage facility or
a truck for transport. Different refrigeration boxes operating at different
temperatures can be placed side
by side and can be delivered together or independently of other refrigeration
boxes in the truck. This
increases the flexibility in the truck load to be delivered, allows for
optimization of storage conditions for
product, and reduces energy consumption and the associated pollution caused by
running a generator to
cool a truck load.
In an alternative embodiment, a side access allows the coolant chamber 140
either to be slid out and
charged with solid coolant 142, or simply accessed on the side and charged.
In another embodiment, shown in Figure 5, the passive refrigeration box 80 of
Figures 3 and 4 further
includes a liquid injection port 180 and a distribution manifold 182 in the
coolant chamber 140 for the
addition of liquid carbon dioxide. This liquid carbon dioxide flashes into
solid carbon dioxide snow (solid
coolant 142), hence charging the coolant chamber with solid coolant 142.
In another embodiment, shown in Figure 6, the refrigeration box is sized to
fit as a single unit in an ISO
container 200, hence it is slightly smaller than the inside dimensions of an
150 container 200. The load
chamber 150 has a load chamber access 202 that is an inner 204 and an outer
door 206. The coolant
chamber access 208 may be through lids or an access 208 on the side, as shown
in Figure 5. The
construction and relationship between the doors is the same as the lids ¨
there is a thermal shield 206 on
the outer side 208 of the inner door 202 and the vapour channel 210 has an
unimpeded path between
the doors 202, 204.
In another embodiment, the refrigeration box is a container for transport on a
trailer or a flat bed. It again
has doors and is as described and shown in Figure 5.
In another embodiment, the refrigeration box 80 is a trailer. It again has
doors and is as described and
shown in Figure 5.
In another embodiment, the heat pipes are replaced with thermosyphons.
While example embodiments have been described in connection with what is
presently considered to be
an example of a possible most practical and/or suitable embodiment, it is to
be understood that the
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descriptions are not to be limited to the disclosed embodiments, but on the
contrary, is intended to cover
various modifications and equivalent arrangements included within the spirit
and scope of the example
embodiment. Those skilled in the art will recognize, or be able to ascertain
using no more than routine
experimentation, many equivalents to the specific example embodiments
specifically described herein.
Such equivalents are intended to be encompassed in the scope of the claims, if
appended hereto or
subsequently filed.
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