Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
A THERMAL PROCESSING CHAMBER AND CONVEYOR BELT FOR USE THEREIN
AND METHOD OF PROCESSING PRODUCT
FIELD OF THE INVENTION
The present invention relates to a thermal processing chamber and a method for
thermal
to processing of products being conveyed through the chamber. The invention
further
relates to a conveyer belt for use in the thermal processing chamber for form
stabilizing
the products during the thermal process. More specifically, the invention
relates to a flat,
endless conveyor belt providing a level surface for placement of products for
thermal
processing in the processing chamber, the processing chamber being adapted for
the
quick-freezing or heating of food products such as fish filets, chicken
breasts or the like
through a combination of thermal convection and impingement thermal
conduction.
BACKGROUND OF THE INVENTION
As the global population grows, food processing becomes ever more important.
Pre-
cooked and frozen food products are a staple in the prepared food industry.
Freezing is
also readily used to allow food to be shipped around the world in a preserved
state and is
particularly used in the fish and poultry industries.
Thermal processing chambers and methods for heating or freezing food products
have
existed for years. At its most basic, a thermal processing chamber comprises a
conveyor
for conveying a food product through a heating or freezing process (or both).
3o An example of such a thermal processing chamber is taught in U.S. Patent
No. 3,708,995
issued to Berg. Berg teaches a chamber equipped with a series of conveyors for
conveying food to be frozen. Liquid CO2 is circulated in the chamber by a
plurality of
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circulating blowers (fans) in order to freeze the food products. The fans are
mounted in a
vertical orientation on the side of the conveyor such that the flow of air
from the fans is
from the side of the conveyors. Because the flow of air is from the side, it
does not
effectively remove the boundary layer that coats the food product resulting in
inefficient
cooling of the product and reduced quality of the frozen product. Slower
freezing will yield
a lower product as larger ice crystals form in the food product which causes
cell lysis.
When the food product is defrosted, the cells are destroyed and the
intracellular fluid is
lost. In addition, slower freezing results in greater dehydration which
therefore results in a
lower quantity of product by weight.
In order to overcome problems associated with the boundary layer, impingement
freezers
were developed. For example, U.S. Patent No. 5,551,251 issued to Ochs et al.
teaches a
tunnel freezing system having a plurality of high velocity refrigerated air
impingement jets
to quick freeze food products. The impingement jets are in blocks that are
located in air
ducts, the air ducts being located above and below a conveyor belt for
conveying the food
products through the freezer. The refrigerated air is forced through the
impingement jets
against the tops and bottoms of the food products, breaking apart the boundary
layer of
air on the food product surface. By breaking away the boundary layer, the
impingement
freezer increases the rate of convection heat transfer between the food
product and the
2o refrigerated air, thereby reducing dehydration of the food product as
compared to non-
impingement mechanical freezing methods.
The impingement freezers, however, do suffer from deficiencies. In order to
allow the
refrigerated air from the impingement jets to come into contact with the food
product, the
conveyors of the prior art impingement processors have an open structure. The
refrigerated air passes through the open structure of the conveyor and cools
the food
product. This open structure for the conveyor results in damage to the food
products prior
to freezing, such as unwanted markings on the food product, lost food material
trapped in
rough edges of the conveyor, deformation of the food product and the like;
such damage
3o resulting in a lowered value of the food product. In addition, this system
is not suitable for
freezing products having a liquid component, as the liquid would flow through
the
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conveyor openings. Furthermore, a purely impingement freezer would be more
expensive
as it would be a larger system.
Additional thermal processing designs have been developed in an effort to
further improve
the quality of the food product being processed. U.S. Patent No. 6,825,446
issued to
Arnarson et al. teaches a thermal processing chamber utilizing a combination
of thermal
convection from the surrounding air and thermal conduction from a conveyor
belt,
preferably made of aluminum with a Teflon coating. The thermal processing
chamber
has a form freezing endless conveyor belt made from a plurality of elongated
beams
io having a wing shaped cross-sectional shape. The beams have two orientations
- a first
orientation in the processing portion of the endless conveyor loop wherein the
trailing
edge of an elongated beam rests on the leading edge of the following elongated
beam
forming a continuous horizontal surface; and a second orientation in the
idling part of the
conveyor loop wherein each beam freely hangs vertically downwards. A thermally
charged stream of air is directed from the side of the conveyor belt, partly
over the belt
and partly below the belt. While the combination of conduction and convection
results in
improved thermal processing, because the thermally charged air is directed
from the side
it does not break the boundary layer around the food product. In addition,
after repeated
use, the Teflon coating will crack rendering the aluminum conveyor belt
unacceptable
for food processing (food products cannot be placed directly on aluminum),
requiring
replacement with consequent maintenance costs.
Difficulties have also been encountered in developing a suitable conveyor for
food
products. As discussed above, impingement thermal processors are most
efficient when
an open conveyor is used which allows the thermally charged air to pass
through the
conveyor and come into contact with the food product. However, open conveyors
cause
damage to the food product. Flat conveyors have also been designed, typically
in the
form of a plurality of horizontal slats forming a horizontal surface. However,
these flat
conveyors are not without their deficiencies: they can also cause damage to
food
products, usually as a result of gaps between adjacent slats, especially when
the slats
move around the sprockets at either end of the endless conveyor.
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One solution to limit the amount of separation between the top surfaces of
adjacent slats
has been to have the pivot point of the slats positioned to correspond to the
top outer
edge of the slats and to have the slats taper from top to bottom so that the
slats will not
come into contact with one another while rounding the sprocket. Two such slat
conveyors
are taught in U.S. Patent Nos. 4,326,626 issued April 27, 1982 to Brockwell
and
4,526,271 issued July 2, 1985 to Finnighan. One of the problems encountered
with the
slat conveyors has been with respect to bending of the slats. This is
particularly true with
larger conveyors. Finnighan attempts to overcome this problem by providing
each slat
with a supporting rod in the shape of a shallow V extending along the
underside of the
to plate of the slat. However, the thin slat of Finnighan is not suitable for
use in conducting
heat to a food product as it is not thick enough to be capable of storing
sufficient heat
energy. Another problem encountered by large conveyors that are subjected to
extreme
temperatures is the deformation of the slats and consequent problems with
maintaining
the alignment of adjacent slats
Accordingly, there remains a need for a flat conveyor belt that is suited for
conduction and
is adapted to maintain the alignment of adjacent slats and provide a
substantially flat
surface for the placement of product to be processed. There is also a
continuing need for
an improved thermal processing chamber utilizing both conduction and
convection in
order to process a product.
It is therefore an object of an embodiment of the invention to provide a
thermal processing
chamber using both impingement convection and conduction to thermally process
a food
product.
It is a further object of an embodiment of the invention to provide an
improved flat
conveyor belt.
SUMMARY OF THE INVENTION
The present invention comprises a thermal processing chamber having an endless
conveyor belt providing a level surface for placement of products for thermal
processing in
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the chamber. Thermal processing is completed through a combination of
convection from
impingement by a stream of thermally charged gas against the product and
conduction
between the conveyor belt and the product. The endless conveyor belt comprises
a
plurality of plates forming a flat, horizontal surface, each plate having a
set of male and
female linking elements for linking with an adjacent plate so as to prevent
misalignment of
the plates.
According to an embodiment of the invention there is provided a thermal
processing
chamber for thermally processing products comprising an insulated housing
defining an
io enclosure having an infeed area and an outfeed area. A conveyor is mounted
within said
enclosure for conveying the products from the infeed area through the chamber
to
eventually be discharged through said outfeed area. The processing chamber is
equipped with thermal processing means for thermally charging a gas and
delivering it
against the topside of the products and conveyor at a high velocity to impinge
the topside
of the products and conveyor. The conveyor is formed of a thermal energy
conducting
material, such that thermal processing of the products occurs as a result of
the
combination of thermal conduction between the conveyor and the products and by
convection between the thermally charged gas and the products.
2o The thermal processing means comprises charging means for thermally
charging the gas
within the housing enclosure, a fan for drawing gas through the charging means
into an
intake chamber, and an impingement compartment. The fan draws gas from the
intake
chamber, delivering it under pressure to the impingement compartment, which
directs the
pressurized gas towards the product and conveyor for impingement thereof.
In another aspect, the impingement compartment comprises a plurality of
alternating
impingement ducts and pressure release channels, each of the impingement ducts
having
a removable tray. The tray has a plurality of holes defined therein, which the
pressurized
gas pass through at a high velocity..
In another aspect, the conveyor comprises a plurality of thermal energy
conducting slats
mounted about a pair of sprockets, each slat bounded at each end by a chain
link, the
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chain links being pivotally connected one to another at a pivot point thereby
joining the
slats.
Each of said slats comprises an elongated plate having a top planar surface
and sides
tapering to a lower surface. The edges of the top surfaces of adjacent slats
are in
abutment. The edges of the top surface of each slat are located at the pivot
points
between adjacent chain links.
In another aspect, each of the slats further comprises a set of linking
elements. The
io linking elements comprise a longitudinally extending bar and a slot, the
bar being sized to
fit within the slot of an adjacent slat and to move within the slot when
adjacent slats travel
about the sprockets. The bar is mounted on a pair of spaced non-tapered
portions and
the slot extends into a corresponding single non-tapered portion. The single
non-tapered
portion is sized to fit between the spaced non-tapered portions.
In another aspect, the thermal processor further comprises a secondary
conveyor
positioned below said conveyor and a slide, said product traveling from the
conveyor
down the slide to the secondary conveyor for further thermal processing by way
of
convection before exiting the thermal processor at the outfeed area.
According to an alternative embodiment of the invention there is provided a
conveyor for
use in a thermal processing chamber for thermally processing a product. The
conveyor
comprises a plurality of thermal energy conducting slats, each slat bounded at
each end
by a chain link, chain links on adjacent slats being pivotally connected one
to another
thereby joining the slats. A pair of drive sprockets is mounted on a frame,
the chain links
being mounted about the sprockets such that the slats form an endless loop.
Each of the
slats has a set of linking elements comprising a male element insertable
within a female
element.
3o Each of said slats of the conveyor comprises an elongated plate having a
top planar
surface and sides tapering to a lower surface. The slats are connected to the
chain links
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such that the edges of the top surface of each slat are located at the pivot
points between
adjacent chain links. The edges of the top surfaces of the slats are in
abutment.
In another aspect of the conveyor, the linking elements comprise a
longitudinally
extending bar and a corresponding slot, the bar being sized to fit within the
slot of an
adjacent slat and to move within the slot when adjacent slats travel about the
sprockets.
The bar is mounted on a pair of spaced non-tapered portions and the slot
extends into a
corresponding single non-tapered portion, the single non-tapered portion sized
to fit
between the spaced non-tapered portions.
According to a further altemative embodiment of the invention there is
provided a method
of thermally processing a product using the thermal processing chamber
described above
comprising the steps of placing a product on the conveyor and conveying the
product
within the processing chamber, the product being subjected to thermal
conduction with
is the conveyor and to thermal convection from the thermally charged air, the
thermally
charged air impinging the product
The foregoing was intended as a broad summary only and of only some of the
aspects of
the invention. It was not intended to define the limits or requirements of the
invention.
Other aspects of the invention will be appreciated by reference to the
detailed description
of the preferred embodiment and to the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the invention will become more apparent from the
following
description in which reference is made to the appended drawings and wherein:
Figure 1 is a sectional view from the right,side of the preferred embodiment
of a
thermal processing chamber according to the invention;
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Figure 2 is a sectional view from the front of a thermal processing chamber
taken
along line 2-2 shown in Fig. 1;
Figure 3 is a sectional view from the top of a thermal processing chamber
taken
along line 3-3 shown in Fig. 2 with the access doors in an open position;
Figure 4 is a sectional view from the top of a thermal processing chamber
taken
along line 4-4 shown in Fig. 2 with the access doors in an open position;
Figure 5 is a sectional view of a portion of an impingement chamber and an
upper
conveyor belt having food product placed thereon;
Figure 6 is a perspective view of a portion of the impingement chambers of the
thermal processor;
Figure 7A is a sectional view of a portion of the upper conveyor traveling
about a
sprocket;
Figure 7B is a perspective view of a portion of the endless conveyor with a
portion
magnified to show the linking elements between slats of the conveyor;
Figure 8A is top view of a slat of the conveyor for use in the thermal
processor
shown in Fig. 1;
Figure 8B is a bottom view of the slat shown in Fig. 8A;
Figure 9 is a cross-sectional view of the slat shown in Fig. 8A taken along
line 9-9;
Figure 10 is a perspective view of two conveyor slats taken from the bottom
left;
and
Figure 11 is a perspective view of two conveyor slats taken from the bottom
right.
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DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENTS
The preferred embodiment of a thermal processing chamber according to the
invention
generally referred to as reference numeral 30 is shown in Fig. 1. Referring to
Fig. 1, it can
be seen that the thermal processing chamber 30 generally comprises a housing
2,
preferably formed of stainless steel with polyurethane insulation, defining a
chamber or
tunnel within which food products are thermally processed while traveling
along an upper
conveyor 4 through a combination of convection and conduction.
Referring to Figs. 1-4, the processing chamber is also preferably equipped
with a lower
conveyor 6, both conveyors mounted on a conveyor frame 72 and powered by a
power
source. Processing chamber 30 has an infeed area 12 and an outfeed 14. The
size of
the openings of the infeed area 12 and the outfeed 14 is minimized so as to
ensure the
temperature within the interior of the processing chamber 30 is not affected.
As shown in
the preferred embodiment of the processing chamber 30, the upper conveyor is
preferably
contained within the confines of the processing chamber. Products to be
thermally
processed are fed onto the upper conveyor 4 by way of an infeed conveyor 16.
Alternatively, the upper conveyor could extend out of the processing chamber a
small
2o amount to allow placement of product directly on it.
The upper conveyor 4 is formed of a relatively thick heat conducting material,
preferably
stainless steel, which acts as a thermal battery as described in more detail
below. When
a product comes into contact with the upper conveyor, heat energy is absorbed
by the 25 conveyor belt by way of conduction. Thermally charged air is also
blasted onto the
product cooling it via convection as discussed in greater detail below.
Products placed on
the upper conveyor are quickly cooled through the combination of conduction
and
impingement convection cooling eventually developing a form stable partly
frozen shell.
While the time to achieve the form stable state varies by product, it
typically takes
3o approximately 1-3 minutes at a temperature of minus forty (-40) degrees
Celsius. The
speed of the upper conveyor 4 is altered to provide the food products
sufficient time to
achieve the form stable state before reaching the end of the upper conveyor 4.
At the
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end, products drop onto a slide 18 leading to lower conveyor 6. The products
travel along
lower conveyor 6 for a sufficient period of time to finish freezing. On the
lower conveyor
6, the food can be stacked or in contact with other products and cooled to the
required
equilibrated temperature, the amount of time to do so again varying by
product. Full
freezing can range from 6 minutes to 60 minutes depending on the thickness of
the
product and its moisture content. The full frozen food products leave the
chamber
through the outfeed area 14, sliding down a chute 15 to another conveyor (not
shown)
where it is transported away for further processing or packaging.
io Cooling of the processing chamber is accomplished by way of a pair of
evaporators 8
mounted atop an impingement compartment 10. The evaporators comprise a network
of
metal tubes 20 and aluminum fins 22. The evaporators 8 cool the chamber 30 by
evaporation of CFC gases or by ammonia compressed by a compressor, or like
method.
Preferably, cooling is accomplished by way of an ammonia system. Ammonia gas
is
is compressed at high pressures to a liquid state. The compressed ammonia is a
hot gas
which is cooled externally by a condenser (not shown) until it changes state
into a high
pressure liquid. A throttling device decreases the pressure of the liquid
ammonia entering
the evaporator. The ammonia entering the evaporator is at a low temperature
and is
converted from liquid to gaseous state as it picks up heat from the
surrounding
zo environment. The gaseous ammonia is retumed to the compressor to repeat the
cycle.
Referring to Fig,2, ammonia enters the evaporator through infeed tube 24 and
exits via
outfeed tube 26.
Air is thermally charged (in this case cooled) by being drawn through the
evaporators 8
25 into an intake chamber 34 by a pair of centrifugal fans 28 driven by
electric motors 32.
Intake chamber 34 is defined by a wall 36 shown best in Fig. 2 bordered at
either end and
at the top by housing 2 and at the bottom by the top 38 of impingement
compartment 10
and by wall 40 located adjacent the evaporators on the side proximal to the
fans 28
(shown best by reference to Figs. 2-4) and the evaporators 8 themselves.
Openings in
30 wall 40 correspond to the location of the evaporators 8 allowing air to
travel through the
evaporators 8 into the intake chamber 34.
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The cold air in the intake chamber 34 is drawn into the fans 28 and blown into
the
impingement compartment 10. Impingement compartment 10 has a plurality of
impingement ducts 42 having holes 44 through which cold air from the fans is
blown.
Preferably, each impingement duct 42 is equipped with a removable tray 44
having holes
44 as shown best in Figs 5 and 6. A tab 52 connected to the tray can be
grasped in order
to lift the tray from its position in impingement duct 42. The trays are
removable for
cleaning purposes, and also so that different sized trays can be inserted in
order to vary
the distance between food products 50 and the holes 44 thereby optimizing the
freezer for
different products. Preferably the holes 44 are staggered such that each hole
is
io equidistant from all adjacent holes, as this formation permits the closest
distance between
adjacent holes.
Between each impingement duct 42 is a pressure release channel 43. These
release
channels have open bottoms which provide space for the high pressure air from
the
impingement ducts to escape after being blown through holes 44.
As shown in Fig. 5, cold, pressurized air, represented by arrows 54 is forced
through the
small holes at high velocities, impacting perpendicularly against the top of
the food
product 50 and the top of the conveyor 4, thereby breaking the boundary layer
and
increasing the rate of cooling via convection. At the same time, heat energy
is conducted
from the food to the slats 56 of the upper conveyor 4, the conveyor having
been cooled by
convection through contact with the air. Referring again to Figs. 1 and 2, a
series of side
covering plates 60, 62, 64, 66, 68 and 70 are visible. Upper side covering
plates 60 and
64 are shown in the open position providing access to the upper conveyor 4 and
the
impingement channels 42. Upper side covering plate 62 is shown in the closed
position.
When in the closed position, the upper side covering plates 60, 62 and 64 act
to seal the
end of the impingement channels 42, preventing cold air from escaping. After
striking the
food product 50 and the slats upon which the food product 50 rests, the cold
air flows into
the pressure release channels 43 and around the lateral sides of the upper
conveyor 4
3o down to the lower conveyor 6.
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In Fig. 1, lower side covering plates 66 and 70 are shown in the open
position, while lower
side covering plate 68 is shown in the closed position. When in the open
position, lower
side covering plates 66, 68 and 70 provide access to the lower conveyor 6,
while in the
closed position they act to keep the cold air from the impingement compartment
in the
area of the conveyors. The upper side covering plates are hingedly connected
to the
conveyor frame 72 at their bottom end such that the tops of the plates pivot
outward and
downward. Conversely, the lower side covering plates are hingedly connected to
the
conveyor frame 72 at their top end such that the bottoms of the plates pivot
outward and
upward.
The processing chamber is equipped with a plurality of access doors 74,
providing access
to different parts of the chamber in order to allow it to be cleaned,
inspected and
maintained.
Referring to Figs. 1 and 7, upper conveyor 4 is preferably formed of a
plurality of metal
slats 56 connected pivotally in a closed loop about a pair of sprockets 58.
Preferably the
slats are made from a material with a good thermal conductivity and approved
for hygienic
treatment such as stainless steel.
2o As shown in Figs. 7-11, each of the slats 56 is an elongated plate having a
top planar
surface 76 and sides 84 tapering to a lower surface 78. Chain links 82 are
welded to the
ends of the slats and adjacent chain links pivotally connected to one another
at a pivot
point thereby connecting adjacent plates. The chain links are mounted about
drive
sprockets 58 for driving the conveyor, with the connected slats forming an
endless loop.
The ends of the slats are chamfered 57 in order to accommodate the chain links
82, which
are composed of two repeated segments, on segment fitting into the other. The
chamfered ends 57 are required so that there is clearance for the larger link.
In addition,
there is a bolt (not shown) connecting the links that extends beyond the edges
of the link.
The slats are connected such that the edges 80 of the adjacent upper surfaces
are in
abutment to one another so as to form a single solid surface along the top of
the
conveyor, with edges 80 located at the pivot point of the chain links 82 as
shown in Fig.
7A. As the slats round the sprocket, the flat surface between adjacent slats
is broken,
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resulting in release of items of food from the conveyor. Because the edges 80
are located
at the pivot point between adjacent slats, there is minimal separation between
the edges
of adjacent slats ensuring minimal damage to product placed on the conveyor.
Each slat is equipped with linking elements to prevent misalignment of
adjacent slats.
The slats are produced with sides 84 tapering at a forty-five degree (45 )
angle from the
top planar surface 76 down to the lower surface 78 except at the locations of
the linking
elements, where the non-tapered portions form part of the linking elements.
The linking
elements are comprised of a male element and female element, the male element
io insertable within the female element as described in more detail bellow.
Preferably the linking elements comprise a reinforced longitudinally extending
bar 86
connected to a pair of non-tapered portions 90 on one side and a corresponding
slot 88
extending through a single non-tapered portion 92 and into the slat on the
opposing side
of each slat, the bar 86 and slot 88 being sized such that the bar fits in the
slot and the
single non-tapered portion 92 being sized to fit between the pair of non-
tapered portions
90. When adjacent slats are attached to one another by way of the chain links
82, the bar
86 on one slat is inserted into the slot 88 of the adjacent slat. The slot is
angled such that
when the slats rotate around a drive sprocket 58 at either end of the
conveyor, the bar 86
can slide in and out of the slot 88 so that alignment is maintained between
slats.
Preferably the slot is formed by machining of the metal slat as shown in Figs.
9 and 11.
The bar 86 is preferably connected to the pair of non-tapered portions 90 by
welding as
best shown in Fig. 10. Preferably the slot is angled such that the rod is able
to enter the
slot without binding when adjacent slats pivot relative to one another. The
actual angle
will vary depending on the size of the sprockets, chain links, slats and
linking elements.
The linking elements do not need to be overly large in order to have the
desired effect in
maintaining alignment of adjacent slats. For example, with a slat that is two
inches wide,
five feet long and 0.375 inches thick, only two sets of linking elements set
equidistant
3o apart along the length of the slat are required to maintain alignment, the
bar having a
diameter of 0.125 inches and length of 1.375 inches and the slot being 1.375
inches.
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With a slat having these dimensions, the slot should be set at an
approximately 22.5
degree angle relative to the top surface. Preferably there are at least 2 sets
of linking
elements per slat for slats equal or greater than five feet in length, with at
least one set of
linking elements for slats that are shorter than 5 feet.
Because food product 50 is in a form stable shape when it is transferred from
the upper
conveyor 4 to the lower conveyor 6, the lower conveyor need not be of the same
type as
the upper conveyor 4. Instead, any prior art belt having openings therein is
suitable. Use
of such a belt allows air arriving from above to flow through the belt,
enveloping the food
io product as it is conveyed along the lower conveyor 6.
The conveyors are driven by frequency controlled electrical gear motors which
work
independently so that each of the conveyors can be run at different speeds.
Variable
Frequency Drives are used to control the speed of each gear motor.
For the purposes of this description, the thermal processing chamber described
above
was one designed for freezing food products such as raw chicken breast or fish
fillets or
the like through a combination of impingement convection cooling and cooling
by
conduction. It will be understood that the system could be reversed such that
the
processing chamber is equally adapted for heating food products with suitable
modification (having a heater system rather than a cooling evaporator,
injecting heated air
rather than cooled air and installing a suitable grease disposal and cleaning
system). It is
also contemplated that other gases than air could be used.
It will be appreciated by those skilled in the art that the preferred and
alternative
embodiments have been described in some detail but that certain modifications
may be
practiced without departing from the principles of the invention.
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