Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02538491 2006-03-01
Heat Transfer Device for Barbeaues
FIELD OF THE INVENTION
The invention relates generally to heat transfer devices for natural gas or
propane
barbeques. More particularly, the invention relates to the use of a knitted
wire mesh with an
open loop structure as a heat transfer device in barbeques.
BACKGROUND OF THE INVENTION
Barbeques have steadily evolved over the centuries from the earliest open
fires, to
simple grills placed over burning charcoal to the modern gas barbeque. While
the modem gas
barbeque is very convenient as compared to open fire or charcoal cooking, it
is often limited
by the quality of heat used to cook foods and by the flavour that may be
introduced into the
cooking foods. Moreover, the modem gas barbeque is often seriously affected by
grease fires
that may burn or otherwise impart undesirable flavours into cooking foods.
That is, as the modem gas barbeque does not combust wood or charcoal, smoke
flavours can generally only be introduced into cooking foods by burning
drippings from the
food. As such, the modern barbeque can incorporate a variety of heat transfer
devices such as
lava rocks, ceramic blocks or thin metal plates above the burner, that seek to
effectively cause
food drippings to burn to create flavour.
Furthermore, the gas flame of a modern gas barbeque does not provide an even
heat
source as the typical gas barbeque with a gas flame produces a significant
temperature
gradient between the hottest parts of the flame and those locations where
there is no flame.
Accordingly, in addition to providing an effective vaporizing surface for
juices, the heat
transfer devices also seek to effectively distribute heat in order to enable
the even cooking of
food.
A well known example of a heat transfer device that is limited in its
effectiveness is
lava rocks. Specifically, while lava rocks are intended to a) distribute the
heat from the
burners below, and b) collect and vaporize juices from the food within the
pores of the rocks,
over time, drippings of excess fat and other juices will clog the pores of the
lava rocks,
resulting in uneven heat distribution and increased flare-ups. As a result,
lava rocks require
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periodic cleaning and/or replacement. Moreover, the porosity of lava rocks
renders them
relatively poor conductors of thermal energy.
A review of the prior art reveals that while numerous systems have been
developed in
the past to address various limitations in barbeques, there remains a need for
heat transfer
devices that continue to improve the quality of barbeque cooking.
For example, US 4,403,597 attempts to improve upon the lava rock system by
using a
cast iron plate as a heat transfer device. The plate is placed above the
burner manifolds of the
barbecue and below the grill to radiate heat from the burner to the food
above. Food drippings
are vaporized or combusted atop the iron plate, the debris from which may be
scraped from
the surface upon cooling. However, over time, accumulation of charred debris
on the plate
reduces effective heat distribution to the food. Moreover, although cast iron
is a good
conductor of thermal energy, it is not a convenient heat transfer device for
use in barbecues as
it is heavy, cumbersome to manipulate, requires a significant length of time
to heat and cool
and therefore does not readily facilitate temperature adjustment during use.
US 6,114,666 teaches the use of a glass/ceramic-glass material as a heat
transfer
device. The glass/ceramic-glass material is placed above the barbecue burner
but below the
cooking grill which, when heated, acts as an infrared emitter. This material,
may however,
still collect a buildup of burnt food drippings leading to uneven heating and
flare-ups.
Other heat radiating devices are known in the art for distributing heat from a
various
types of burners. For example, US 1,614,746 teaches the use of wire gauze
between the
burner manifolds of a broiler to aid in the even distribution of heat to food
below. The wire
gauze is brought to a temperature at which it becomes luminous thus radiating
infrared heat.
In particular, there has been a need for a heat transfer device for barbecues
that evenly
distributes/radiates thermal energy from the heat source, will quickly respond
to changes in
heating temperature, while effectively vaporizing food drippings to impart
barbecue flavour to
food. It is further desired to have a heat transfer that can be readily
cleaned of carbon build-
up.
SUMMARY OF THE INVENTION
It is an object of the present invention to obviate or mitigate at least one
disadvantage
of previous heat transfer devices used in barbeques.
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In accordance with the invention, there is provided a heat transfer device for
use
within a barbeque comprising at least one layer of an open loop knitted wire
mesh. Preferably,
the heat transfer devices includes multiple layers of open loop wire mesh that
may be
assembled from at least one flattened cylinder or a length of open loop
knitted wire mesh.
The heat transfer device may be assembled with a frame. The wire mesh may be
manufactured using stainless steel wire or other materials and may comprise
single or
multiple strands of wire. The void space of the wire mesh may range from 50-
98.5%
In further embodiments, the invention comprises a kit for assembling a heat
transfer
device for a barbeque. In a first embodiment, the kit comprises: a length of a
flattened open
loop knitted wire cylinder, the open loop knitted wire cylinder having a
flexibility allowing
multiple layers of wire to be layered back and forth across one another. In a
second
embodiment, the kit comprises: a plurality of flattened open loop knitted wire
cylinders; and,
an end clamping system for clamping the plurality of open loop knitted wire
cylinders
together.
Other aspects and features of the present invention will become apparent to
those
ordinarily skilled in the art upon review of the following description of
specific embodiments
of the invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described, by way of example
only,
with reference to the attached Figures, wherein:
Figure 1 A is a perspective view of a heat transfer device in accordance with
one embodiment of the invention;
Figure 1 B is an exploded view of Figure 1 A showing detail of an open-loop
knitted mesh;
Figure 1 C is a schematic view of an open-loop knitted mesh having multiple
strands of wire;
Figure 2A is a schematic perspective view of a section of cylindrical knitted
wire mesh
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Figure 2B is a schematic perspective view of cylindrical knitted wire mesh
that
has been flattened into a dual layered mesh in accordance with one embodiment
of the
invention;
Figure 3 is a schematic side view of an open loop knitted mesh in which a
number of loops have been dropped during manufacture;
Figure 4A is schematic plan view showing a narrow diameter wire loop mesh
being assembled into a heat transfer device in accordance with one embodiment
of the
invention;
Figure 4B is a schematic side view of the heat transfer device of Figure 4A;
Figure 5A is a schematic diagram of a heat transfer device kit with a single
overlapped layered loop structure in accordance with one embodiment of the
invention;
Figure 5B is a schematic diagram of a heat transfer device kit with a multiple
overlapped layered loop cylinders in accordance with one embodiment of the
invention; and,
Figure 5C is a schematic diagram of a self-supporting heat transfer device kit
in accordance with one embodiment of the invention.
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DETAILED DESCRIPTION
With reference to the Figures, the invention provides a heat transfer device
10 for use
in barbeques. More specifically, the invention provides a wire mesh structure
having
characteristics favourable for use as a heat transfer device in barbecues. The
wire mesh
structure, when layered in a barbecue, conducts and radiates thermal energy to
the food being
cooked. The inherent flexibility of the wire mesh allows for simple cleaning
of carbon debris
from the mesh, and facilitates packaging for commercial purposes.
With reference to Figures lA and 1B, the wire mesh of the invention is knitted
from
metal wire I 1 such that each loop l0a of wire interlocks with adjacent loops
of wire at four
contact points. The interlocked knitted structure of the wire mesh therefore
readily facilitates
heat conduction between and along adjacent loops of wire during heating of the
mesh by a
localized heat source. Thus, when the mesh of the invention is placed above a
heat source
within a barbecue, the mesh can quickly be heated or cooled in response to
adjustment of the
burner temperature along the multiple tortuous paths defined by the knitted
wire structure. As
illustrated in Figure 1C, multiple strands of wire 30a, 30b can be knitted to
form the knitted
structure Wires 30a, 30b can be of a similar or dissimilar material.
The knitted wire mesh is formed from wire having a composition and diameter
(typically 0.001" to 0.065" and preferably 0.01") suitable to provide
durability to the finished
product, while still possessing thermal conductive properties for rapid
dissipation of heat
between adjacent loops and thereby allowing an acceptable heating/cooling time
in response
to burner heat adjustments. Open loop knitted wire is further characterized by
having a high
surface area to weight ratio thus providing a high surface area for heating
and vaporizing food
juices while also providing a relatively high void space (typically in the
range of 50-98.5%).
In preferred embodiments, the average loop diameter is less than 0.25 inches.
In use, the heat
transfer device is preferably designed to provide a balance between the void
space and total
wire surface area such that food drippings passing through multiple layers of
mesh will
disperse as a film upon hitting the upper layers and vaporize before exiting
through the lower
layers.
Further still, open knitted wire provides improved stability over conventional
woven
wire meshes as the knitted wire has no bonded or welded surfaces that may
degrade after
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repeated heating and contraction during use. That is, any thermal expansion
and contraction of
the wire will not place thermal stress on any contact points between adjacent
wires. This
feature provides the further advantage of the heat transfer device being
compressible in each
of the directions shown as X, Y and Z (mainly X) in Figure 1 A.
In a preferred embodiment, the mesh is knitted from stainless steel wire such
as 304 L
or 316 L. The use of stainless steel wire improves the durability of the heat
transfer device by
minimizing the formation of rust, which can otherwise result from weathering.
Other
materials that withstand the heating and cooling cycle and are malleable for
forming can be
used.
In the embodiment shown in Figure lA, the heat transfer device includes one or
more
layers of wire mesh fixed within a frame or laying on top of a frame
corresponding to the
shape and size of a barbeque. In the embodiment shown, the frame includes
rigid frame ends
34, and may include flexible wire frame sides 33. Thus, the frame ends 34
provide structural
support in a first dimension Y, while the wire sides 33, if present, maintain
the flexibility of
the wire mesh in a second dimension X. This flexibility permits simple
mechanical removal
of carbon debris from the mesh as will be described below.
The heat transfer device can also be self supporting if it is fixed at either
end of the
barbecue or is formed from wires or layers of wires of sufficient structural
rigidity to self-
support the heat transfer device within a barbeque
Production of Wire Mesh Layers
Suitable wire mesh structures for use in accordance with the invention may be
produced by known wire knitting techniques and machinery. For example, and
with reference
to Figure 2A, it is preferred that cylinders produced on circular knitting
machines are used in
manufacturing the heat transfer device. A cylinder so produced may be
flattened to produce a
dual layer of mesh (as shown in Fig. 2B), which may be used alone or layered.
The flattened
cylinder(s) may be affixed within a frame sized to fit a particular type of
barbecue as
described above. Alternatively, cylinder layers may be fastened together by
other suitable
means such as stapling or crimping with stainless steel staples or wire to
prevent unravelling
and separation of the layers.
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Clearly, various sizes and shapes of mesh may be made in accordance with the
invention, which may be designed for use with certain makes and models of
barbecue. Such
shapes may be cut from a sheet or cylinder of wire mesh, with the loose ends
of each mesh
layer secured by welding or other means. However, it is preferable to form the
wire mesh
from an appropriately sized flattened cylinder as described above, as this
will prevent
unravelling of the sides of the wire mesh and therefore frame sides 33 will
not be required.
Although a single or dual layer of mesh may be used in accordance with the
invention,
it is preferable that several sheets of mesh be layered over the heat source
and beneath the
food grill. While each layer of mesh will have a large total void space,
multiple layers of mesh
will provide an increased surface area upon which to collect and vaporize
falling food
drippings. In various embodiments of the invention, up to 30 layers of wire
mesh may be
used, although the optimal number of layers will be determined based on the
particular
characteristics of specific barbeques.
In addition, once the wire mesh is formed by knitting, the wire loop can be
elongated
or stretched to form the appropriate dimensions for the barbecue and/or the
optimum densities
required to allow the cooking characteristics of vaporizing the drippings,
allowing quick
response to heat input and produce infrared radiant heat for cooking.
In still further embodiments, the wire mesh can be crimped at appropriate
angles and
then layered upon each other to give a variety of densities for specific
barbecues. The
crimped layers can also be used in conjunction with uncrimped layers or other
crimped layers
having similar or differing crimping angles.
In still further embodiments, a "window strip" as shown in Figure 3 can be
knitted into
the mesh to allow a better visual picture of the ignition state of the burner
or to accommodate
the particular design of a barbeque or the particular combustion functionality
of the burner of
a barbeque. The window strip can be produced by dropping stitches during
knitting.
Further still, the wire mesh can be knitted in a narrower strip 40 (typically
'/4"- 2"
wide) and then formed to the final structure by placing the mesh on its side
in either a crimped
form or a flat form and layering it back and forth as shown in Figures 4A and
4B. In this
embodiment, the layers of flattened wire mesh are oriented perpendicularly to
the vertical. A
frame 42 may be utilized to secure the layers of wire mesh.
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In yet another embodiment, void spaces may be incorporated between different
layers
of the wire mesh.
Use of the Heat Transfer Device
In use, a heat transfer device in accordance with the invention is placed
above the
burner of a barbecue and below the food grill. When the barbecue is lit, the
burner will heat a
portion of the heat transfer device. Under most heating conditions, the layers
of wire loop in
closest contact to the burner flame will be heated to a red hot temperature,
thus becoming an
infrared heating source for cooking the food. Due to the looped nature of the
wire mesh, the
heat from within the wire will be quickly dissipated throughout the heat
transfer device thus
providing an evenly heated surface. Similarly any adjustments to the heating
temperature will
result in a rapid change in the heating temperature.
For those foods with any of fats, juices, marinades or sauces, as the food
cooks, these
substances will drip from the food and contact the wire mesh and will either
be burnt or
vaporized to impart a barbecue/smoked flavour to the meat. During use, a
certain amount of
carbon debris will become lodged within the mesh layers of the heat transfer
device. The user
may remove this debris by simple mechanical manipulation of the mesh structure
such as by
shaking or banging the heat transfer device against a surface.
As noted above, the open wire loop structure of the heat transfer device
provides
flexibility in the X and Y and Z dimensions such that repeated expansion and
compression of
the void space between the knitted loops readily displaces any residual burnt
carbon debris.
Alternatively, repeated physical vibrations caused by forceful contact with
any surface would
similarly dislodge any residual burnt carbon debris. In comparison to a woven
wire structure,
the knitted loop structure will prevent holes forming within the mesh by the
displacement of
overlapping wires with respect to one another as may occur with woven meshes.
Still further,
the knitted structure allows the void space area to change for cleaning which
will then return
to the original shape. In comparison, a mesh with overlapping wires will have
a fixed hole
size and result in clogging of the mesh.
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Heat Transfer Device Kit
The present device may be provided to users as a kit. As shown in Figure 5A, a
kit can
be as simple as a long length of knitted material 50 that can be folded to the
recommended
size (width and depth) for a particular barbecue. The folded structure can be
held together by
either permanent or removable staples or a frame 52. In such an embodiment, a
user could
form multiple layers of wire mesh over an existing lava rock layer or directly
on top of the
barbeque burners or lay directly on top of the metal plates found in present
barbecues.
In another embodiment as shown in Figure 5B, a kit for making a custom heat
transfer
device may include pre-cut cylinders 54 of wire mesh and an appropriate end
crimping or
clamping system 54 for allowing a user to assemble a desired number of layers
of wire mesh
for their particular barbeque.
In another embodiment as shown in Figure 5C, a kit may comprise pre-formed
layers
of wire mesh 58 and a support system 60 (or equivalent) for supporting the
wire mesh on the
lower surface of the barbeque above the barbeque burner such that a supporting
grid is not
required.
The above-described embodiments of the present invention are intended to be
examples only. Alterations, modifications and variations may be effected to
the particular
embodiments by those of skill in the art without departing from the scope of
the invention,
which is defined solely by the claims appended hereto.
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