Method and device for transmitting heating or cooling medium to a food product on a moving substrate

A device for transmitting a heating or cooling medium to a moving substrate which includes at least one continuous channel traversing at least a major portion of the width of the moving substrate for converting a multidirectional flow of the heating or cooling medium into a unidirectional flow, a device for removing and/or preventing the presence of foreign matter within the channel, and ovens and freezers employing the same.

TECHNICAL FIELD 
The present invention is generally directed to a device for transmitting a 
heating or cooling medium to a moving substrate and particularly to a 
device for transmitting a cool vapor such as air within an impingement 
freezer for freezing food in which frost buildup is substantially 
eliminated. 
BACKGROUND OF THE PRIOR ART 
Commercial ovens and freezers typically rely on the transmission of a 
heating or cooling medium such as air to the food product by a large fan 
or blower. The fan or blower is situated proximate to a conveyor which 
carries the food through the heater or freezer for a time sufficient to 
heat or freeze the food product. 
The food product entering the oven or freezer has a boundary layer composed 
primarily of stagnant air which insulates the food product from the 
surrounding atmosphere. In order to effect proper cooking or freezing, the 
boundary layer must be substantially reduced to expose the food product 
directly to the heating or cooling medium. 
Conventional fans or blowers generate a multidirectional flow of the 
heating or cooling vapor. Much of the vapor is scattered about the freezer 
and only a portion of this scattered vapor reaches the food product. At 
least a significant portion of the blown vapor, therefore, does not 
directly impinge on the food product in a perpendicular direction. Under 
these conditions, the vapor which does contact the food product often does 
not possess sufficient energy to substantially reduce the boundary layer. 
This results in inefficient heating or freezing or requires excessively 
long exposures of the food product to the heating or freezing operation. 
Efforts have been made to reduce the amount of heating or cooling vapor 
which is scattered about the freezer. This has been accomplished by 
employing a device within the oven or freezer which transforms the 
multidirectional air flow from the blower or fan into a unidirectional 
flow of air directly toward the food product which has sufficient energy 
to reduce the boundary layer. 
For example, Donald P. Smith, U.S. Pat. Nos. 3,884,213, 4,289,792 and 
4,338,911, disclose a cooking apparatus utilizing a series of spaced apart 
discrete jets of unidirectionally flowing air produced by appropriately 
spaced tubes. 
Donald P. Smith, U.S. Pat. No. 4,479,776, discloses a heating/cooling 
apparatus having a thermal treatment zone for supplying columnated jets of 
a gas to the exterior surface of a food product moving relative thereto in 
combination with at least one equilibration zone for promoting heat 
transfer into or out of the interior portions of the food product. A 
number of vertical spaced apart tubes are positioned in the 
heating/cooling section to direct a unidirectional air flow toward the 
food product. 
Mitchell C. Henke, U.S. Pat. No. 4,626,661, discloses the use of a 
plurality of nozzles spaced apart over the pathway of the food product for 
delivering discrete jets of unidirectional heating/cooling air. A 
plurality of high velocity air jets are also employed in Steven M. Shei, 
U.S. Pat. No. 4,757,800, in which impingement apertures direct heated air 
in a unidirectional manner to heat the food product passing on a conveyor. 
Another approach to providing unidirectional flow of air in an oven is 
disclosed in Virgil L. Archer, U.S. Pat. No. 4,873,107. Instead of 
employing tubes for directing the heated air toward the food product as 
discussed above, there is provided a spaced array of rectangular slots. 
The multidirectional air from the fan or blower is caused to enter the 
slots and thereby attain a more orderly and direct flow toward the food 
product. A similar arrangement of rectangular slots is disclosed in 
Clement J. Luebke et al., U.S. Pat. No. 4,972,824. 
Each of these heating/cooling devices provides an improvement over the use 
of fans and blowers alone because they generally produce a unidirectional 
flow of heating/cooling air having sufficient energy to reduce the 
boundary layer of the food product. However, such devices obtain these 
improvements by expending excessive energy to distribute the 
heating/cooling air to the food product. In addition, with respect to 
freezers, the tubes or slots used to form the unidirectional flow often 
become plugged with frost. The buildup of frost tends to degrade the 
freezing operation over a period of time. Frost reduces the amount of heat 
transferred from the food product and, therefore, as the time of the 
freezing operation increases, the efficiency of the transfer of heat from 
the food product to the atmosphere decreases. In order to remove the frost 
to keep the air passageway open, it has been necessary to shut down the 
freezer to melt the accumulated frost, resulting in delays and additional 
cost of the process. 
Accordingly, it would be desirable to employ a device for transmitting a 
heating or cooling medium such as air to a substrate such as a food 
product on a conveyor belt in a more energy efficient manner by providing 
for better distribution of the heating/cooling medium across the width of 
the conveyor belt. It would also be of benefit to provide better 
distribution of the heating/cooling medium from the source (e.g. the fan 
or the blower) to the food product. 
Furthermore, with respect to the freezing of food, it would be of 
significant benefit to prevent the buildup of frost in the freezer without 
having to terminate the freezing operation. 
SUMMARY OF THE INVENTION 
The present invention in its broadest aspects is generally directed to a 
device for transmitting a heating or cooling medium to a moving substrate 
such as a food product on a conveyor belt. The device comprises at least 
one continuous channel traversing at least a major portion of the width of 
the substrate for transforming a multidirectional flow of the heating or 
cooling medium into a unidirectional flow. 
The continuous channel has a first opening for receiving the heating or 
cooling medium and a second opening for discharging the medium in 
proximity to the substrate. As the medium passes through the channel from 
the first to the second opening it is transformed into a unidirectional 
flow having sufficient energy to at least reduce the boundary layer of the 
food product. In addition, the continuous channel enables a greater rate 
of heat transfer from the food product than conventional systems employing 
intermittent (non-continuous) slots or tubes. In a preferred form of the 
invention, the first opening of the channel has a greater cross-sectional 
area than the second opening. The larger entrance area enables a greater 
volume of the medium to enter the channel and facilitates the 
transformation of the medium into a unidirectional flow. 
In accordance with one aspect of the invention particularly related to the 
transmission of a cooling medium, means are provided for continuously 
cleaning the channel without having to terminate the freezing operation. 
The cleaning means is insertable into the channel and movable along at 
least a portion of the length thereof. The cleaning means comprises at 
least one projection, preferably in the form of a cleaning rod, extending 
into and along the height of each of the channels from the first to the 
second opening. The projections are movable within the channels along the 
length thereof and are adapted to loosely contact the walls of the 
channels as they move to remove and/or prevent the buildup of foreign 
matter including frost. The movement of the projections can be controlled 
in a manner which keeps the channels free of foreign matter while not 
interfering with the flow of the cooling medium through the channels. 
In a further embodiment of the invention, the cleaning rods can be provided 
with a pathway to allow a fluid to pass into the channel to assist in 
removing and/or preventing the buildup of frost and other foreign matter.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention shall be described with respect to a freezer for 
continuously freezing a food product by contacting the food product with a 
unidirectional flow of a cooling medium such as cold air, nitrogen or 
carbon dioxide vapor. It should be understood that the invention is also 
applicable to an oven for continuously heating a food product with a 
heating medium such as heated air. 
Referring to FIG. 1, there is shown a conventional belt-type commercial 
freezer customarily employed for freezing food products such as shrimp, 
chicken, chicken parts, scallops, vegetables, hamburger patties and the 
like. The freezer 2 includes a housing 4 having an entry port 6 for 
receiving the food product via a conveyor belt 8 driven by a motor 9. The 
entry port 6 leads to a freezer section 10 which is in the form of a 
tunnel 12 where the food product 14 is frozen prior to leaving the freezer 
2 via an exit port 15 at the opposite end of the freezer. 
A cooling medium is provided to the freezer section 10 in sufficient 
quantities so that the food product is frozen during passage through the 
tunnel 12. The cooling medium, such as air cooled by the presence of a 
liquid cryogen, is generated by a cooling section 16 comprised of a source 
of coolant 18, an exchange zone 20, and a fan or blower 22. 
The source of coolant 18, for example a liquid cryogen (e.g. liquid 
nitrogen or carbon dioxide) is placed in proximity to the warmed vapor 
which has given its cooling duty to the food product in the exchange zone 
20. The temperature of the warmed vapor is thereby reduced to well below 
32.degree. F. (0.degree. C.). The liquid cryogen is preferably sprayed 
into the exchange zone 20 through a nozzle or header (not shown) and 
thereby is brought into contact with the moving food product 14 by the 
downdraft generated by the fan or blower 22. Specifically, the cooling 
medium is blown by the fan 22 in the general direction of the food product 
14 as shown in FIG. 1 in the direction of the arrows. Upon eventual 
contact with the food product 14, the cooling medium gives off its cooling 
duty and is then drawn up into and reinserted into the exchange zone 20 by 
the fan 22 where it is again cooled by contact with the source of coolant 
18. 
The type of freezer shown in FIG. 1 is disadvantageous because the flow of 
the cooling medium is multidirectional. While the cooling medium is blown 
away from the fan 22 in the general direction of the food product, a 
significant portion of the cooling medium will scatter about the freezer 
section 10 before contacting the food product. As a result, the flow of 
the cooling medium loses some of its energy and, therefore, is not 
efficient in reducing the boundary layer associated with the unfrozen food 
product. To compensate for this inefficient flow of the cooling medium, it 
is often necessary to increase the horsepower of the fan or blower which 
adds significantly to the cost of the process. 
The present invention provides for a unidirectional flow of the cooling 
medium so as to more efficiently reduce the boundary layer. In addition, a 
cleaning device is provided which prevents the buildup of frost typically 
associated with prior freezers using conventional tubes and slots to form 
a unidirectional flow of the cooling medium. 
Referring to FIG. 2, the present invention includes a device 30 for 
generating a unidirectional flow of a cooling medium toward a conveyor 
belt having thereon a food product. The device 30 includes a plurality of 
parallel, spaced apart inverted U-shaped troughs 32. Each trough 32 has a 
wall 34 which lies proximate to, but spaced apart from, a corresponding 
wall 34 of an adjacent trough 32. The space between the walls 34 of 
adjacent troughs 32 defines a continuous, preferably parallelpiped shaped, 
channel 36 preferably having a first opening 38 for receiving a 
multi-directional flow of the cooling medium and a second opening 40 for 
discharging a unidirectional flow of the cooling medium to the food 
product. 
The unidirectional flow device 30 can be made of a variety of materials 
including metals such as stainless steel, aluminum and the like, as well 
as plastics such as polyethylene and polypropylene and the like. The 
dimensions of the channel 36 are sufficient to establish a straight or 
unidirectional flow of the cooling medium as it leaves the second opening 
40. For this purpose, the height of the channel 36 is generally greater 
than twice its width. For a typical size commercial freezer, the height of 
the channel 36 will be in the range of from about 1 inch (2.54 cm) to 12 
inches (30.48 cm) and the diameter or cross-sectional length of the 
channel 36 is typically from about 0.25 inch to 1.00 inch. The length of 
the channel 36 measured from the front 42 to the rear 44 of the trough 32 
is selected to run substantially the full width of the conveyor belt 8, 
typically about 36 inches (91.44 cm) for a commercial freezer. 
The second opening 40 is positioned at a distance from the food product 
typically in the range of from about 1 to 4 inches (2.54 to 10.16 cm). The 
distance is chosen so as to insure that the unidirectional flow of the 
cooling medium is of sufficient velocity to reduce the boundary layer of 
the food product, but does not move the food product as it passes on the 
conveyer belt 8. 
During continuous operation of the freezer some moisture from the 
atmosphere and the food product itself will enter the freezer section 
causing the buildup of condensation in the form of frost on the components 
of the freezer. In prior art devices, frost builds up on the interior 
surfaces of the tubes or slots used to produce unidirectional flow. If 
allowed to continue, the frost buildup will eventually retard and even 
prevent the flow of the cooling medium to the food product. The buildup of 
frost affects the rate of freezing by reducing the amount of heat which 
can be removed from the food product because less of the cooling medium is 
able to reach the food product. 
In accordance with one aspect of the present invention, there is provided a 
cleaning device which is adapted to continually remove foreign matter, 
including frost, from the channels which are employed for generating 
unidirectional flow. Referring to FIGS. 3, 4A and 4B, the cleaning device 
50 includes a support member, shown as a bar 52 attached at its opposed 
ends to a conveyor system 54 which is adapted to move the bar 52 along the 
length of the channels 36 as shown in FIG. 3 and as explained in detail 
hereinafter. 
Attached to the support bar 52 are a number of cleaning rods 56, preferably 
equally spaced apart, which are adapted to extend into each of the 
similarly positioned channels 36 along the substantial height thereof. The 
rods 56 are attached at one end to the bar 52 by a clamp 58 or other 
suitable attachment mechanism such as a collar (see FIG. 4A) and the like. 
The length of the rod is sufficient so that it extends substantially the 
full height of the channel 36 as shown best in FIG. 4B. The width of the 
rod is sufficient to enable the rod 56 to contact the walls 34 of the 
channel 36 as the rod is moved along the length of the channel 36 by the 
conveyor 54 so as to remove frost or other foreign matter contained 
therein. Accordingly, the width or diameter of the rods is slightly less 
than the width or diameter of the channels 36 [i.e. in the range of about 
0.25 to 1.00 inch (0.63 to 2.54 cm)]. 
In another embodiment of the invention, the rods 56 may be provided with a 
passageway for transmitting a fluid such as air from a source into the 
channels 36 to assist in preventing and/or removing frost and other 
foreign matter. Referring to FIG. 4B, the rods 56 are provided with a 
passageway 60 leading to a plurality of spaced apart openings 62 extending 
along the length of the rod 56. The fluid is fed into the passageway 60 of 
the rod 56 from a corresponding passageway 64 of the supporting bar 52 or 
in any other suitable manner. The pressure of the fluid supplied to the 
rod 56 should generate a flow of fluid out of the openings 62 sufficient 
to prevent and/or remove foreign matter which adheres to the interior of 
the walls 34 of the channel 36. 
The cleaning device 50 is adapted to clean the entire volume of the 
parallelpiped shaped channels 36. Accordingly, the rods 56 must be moved 
along substantially the entire length of the channel 36 which traverses 
the width of the conveyor belt 8. In one embodiment of the invention, as 
best shown in FIG. 3, a single bar 52 is provided for moving a single row 
of rods 56 along the entire length of the channel 36. As shown in FIG. 3, 
it is often desirable to cool the food product from above and below the 
conveyor belt 8 as shown by the arrows indicating the movement of the food 
product. Therefore, it is preferred to provide unidirectional flow devices 
30 and corresponding cleaning devices 50 both above and below the conveyor 
belt 8, with each single row of rods moving the entire length of the 
channel 36. 
Movement of the cleaning rods 56 along the length of the channels 36 is 
accomplished by a guidance system 66 for guiding the rods in a precise 
linear path and a system 68, either a pneumatic system or a hydraulic 
system, but preferably a pneumatic system, for supplying the force 
necessary to move the rods 56. Hereinafter, all reference to the system 68 
shall be limited to a pneumatic system. It shall be understood, however, 
that the force necessary to move the rods 56 can be supplied by a 
hydraulic system as well. Together the guidance system 66 and the 
pneumatic system 68 comprise the conveyor system 54. 
In the embodiment shown in FIG. 5A, the single support bar 52 must be moved 
along the entire length of the channels 36. Accordingly, the pneumatic 
system 68 must be of sufficient size to provide the appropriate movement 
for the support bar 52. Smaller pneumatic systems may be used by modifying 
the cleaning device to include more than one row of cleaning rods, with 
each row moving only a fraction of the length of the channels. In this 
way, the size and cost of the pneumatic system 68 can be minimized. 
Referring to FIGS. 5B and 6, there is shown an embodiment of the cleaning 
device in accordance with the present invention employing three rows of 
cleaning rods 36a-36c. 
Referring to FIG. 5A, the guidance system 66 comprises a guide rod 70 
positioned within the freezer section 10 by guide blocks 72 having an 
opening 74 allowing movement of the rod 70 therethrough. The guidance 
system 66 also includes a device 76 for attaching the guide rod 70 to the 
support bar 52. The device 76 includes a beam 78 which runs parallel to 
the guide rod 70 and is attached to the support bar 52 by a clamping 
device 80. The ends of the beam 78 extend at a right angle toward the 
guide rod 70 and are attached thereto by clamps 82a and 82b. 
Movement of the support bar 52 is accomplished by the pneumatic system 68 
which includes a pneumatic cylinder. The pneumatic cylinder 84 houses 
therein a piston 86 which is shorter than the cylinder and, therefore, the 
piston is movable within the cylinder. The cylinder has opposed openings 
88 and 90 for receiving and discharging air (or other gas) which is used 
to move the piston within the cylinder. The cylinder is attached at one 
end to the housing 4 of the freezer 2 by a bracket 92 and an extension 94 
attached to the piston 86, and at the opposed end to the support bar 52 by 
a bracket 96 and a corresponding extension 98 of the piston 86. The 
pneumatic system 68 operates by pumping air alternatively into the 
openings 88 and 90 to move the piston 86 forward and backward, 
respectively, within the cylinder 84 and, therefore, move the support bar 
52 in the same direction. More specifically, when air is pumped into the 
opening 90, it exerts a force on the piston 86 moving the piston forward. 
The piston 86 exerts pressure against the support bar 52 thereby moving 
the bar 52 in the same direction. 
As previously indicated, the support bar 52 is attached to the guidance 
system 66 via the beam 78 and clamps 80a and 80b. Accordingly, as the 
piston 86 moves forward, the guidance system 66 including the guide bar 70 
moves in the same direction as the piston 86. A precise linear path is 
maintained because the guide bar 70 is aligned during movement by the 
guide blocks 72. 
The guidance system 66 is moved in the opposite direction by reversing the 
flow of the air. If air is pumped into the opening 88, the piston 86 will 
move backwards causing like movement of the guidance system 66 as well as 
the support bar 52. 
Referring to FIG. 5B, three rows of cleaning rods 36a-36c are supported by 
three corresponding bars 52a-52c through collars 58. One end of the 
pneumatic system 68 is attached to the middle bar 52b. The bars 52a-52c 
are moved by the guidance system 66 and the pneumatic system 68 in the 
same manner as described in connection with the embodiment of FIG. 5A. 
However, each bar 52a-52c moves only about one-third the length of the 
channels 36, thereby reducing the size of the pneumatic system 68. 
Accordingly, the cleaning device 50 can be constructed so that each row of 
cleaning rods moves a designated fraction of the length of the channels 
36. Employing multiple rows of cleaning rods in this manner allows use of 
a smaller pneumatic system which is less costly than a single pneumatic 
system which must move the entire width of the conveyor belt. 
The unidirectional flow device 30 can be modified to provide an even more 
effective transition from multidirectional to unidirectional flow. 
Referring to FIG. 7, there is shown a unidirectional flow device 100 in 
accordance with a preferred aspect of the invention in which the entrance 
to the channels is expanded to accommodate a greater volume of the cooling 
medium and to better facilitate the transition from multidirectional to 
unidirectional flow. The device 100 has adjacent walls 102 forming a 
channel 104, preferably in the shape of a parallelpiped. The first opening 
106, unlike the unidirectional flow device shown in the embodiment of FIG. 
2, is formed by a pair of diverging walls 108a and 108b so that the 
cross-sectional area of the first opening 106 is greater than the second 
opening 110 which leads to the food product. 
Expanding the cross-sectional dimension of the first opening 106 
facilitates the manner in which the cooling medium is funneled into the 
channel 104. The larger opening permits a greater quantity of cooling 
medium to enter the channel 104 and, therefore, generates a more efficient 
stream of the cooling medium out of the second opening 110. In addition, 
the pressure drop through the channels 104 is reduced thereby reducing the 
horsepower needed to drive the cooling medium through the channels 104. 
Expanding the cross-sectional area of the opening 106 also reduces the 
likelihood of moisture buildup within the channel 104. This is because 
moisture buildup on the diverging wall 108a and 108b will not obstruct the 
flow of the cooling medium through the channel 104. 
In another embodiment of the invention as shown in FIG. 8, multiple 
unidirectional flow devices and corresponding cleaning devices may be 
housed in a single freezer. As shown specifically in FIG. 8, three pairs 
of such devices are positioned within a single freezer section 10. Each 
pair of devices occupies approximately 1/3 of the length of the freezer 
section 10 and functions as described previously in connection with the 
embodiments of FIGS. 2-7. 
The operation of the present invention can be best explained by reference 
to FIGS. 2, 3, 7-0. FIG. 9 shows an embodiment of the invention with one 
unidirectional flow device and cleaning device contained within the 
freezer section. Unfrozen food product 14 enters the freezer 2 on a 
conveyor belt 8 through the opening 6 where it is transported to the 
freezer section 10 through the tunnel 12. Positioned above and/or below 
(see FIGS. 8 and 9) the conveyor belt 8 is at least one unidirectional 
flow device 30, preferably operatively associated with a cleaning device 
50 of the present invention. The freezer section 10 receives a 
multidirectional flow of the cooling medium from the exchange zone 20 via 
the fan 22 as shown best in FIG. 9 which enters the first opening 38 of 
the flow device as shown best in FIG. 8. The cooling medium which enters 
the channel 36 is transformed into a unidirectional flow as it passes 
through the channel 36 and out the second opening 40 (see FIGS. 2 and 7). 
Upon leaving the second opening 40, the cooling medium comes into immediate 
contact with the food product and gives off its cooling duty while being 
deflected into the trough 32 where it is drawn back to the exchange zone 
20 and is provided with additional coolant to lower the temperature 
thereof. 
During operation of the freezer 2, moisture can enter the freezer from a 
number of locations, principally through the opening 6 for receiving the 
unfrozen food product and from the food product 14 itself. The moisture 
condenses on various components of the freezer causing the buildup of 
frost. The channels 36 of unidirectional flow device 30 are particularly 
susceptible to the buildup of frost and must therefore be cleaned. 
Prevention of frost buildup is accomplished by the cleaning device 50. As 
the food product 14 moves on the conveyor 8, the cleaning rods 56 are 
guided along the length of the channels 36 by the guidance system 66 
through the power provided by the pneumatic system 68. 
In the embodiment shown best in FIG. 8, each channel 36 is cleaned by three 
cleaning rods, each adapted to travel about one-third of the total length 
of the channel. This configuration reduces the size of the pneumatic 
requirements and, therefore, lowers the cost of the freezing operation. 
The rods 56 are supported on three supporting bars 52a-52c, respectively. 
The bars move in unison with each other and thereby clean the entire 
channel while each rod travels only one-third the length of each channel. 
The speed of the bars, and therefore of the rods, is sufficient to prevent 
the buildup of frost while not interfering with the flow of the cooling 
medium through the channel. Preferably, the bars move at the rate of about 
0.5 to 10 ft/min. Movement of the bars need not be continuous. For 
example, the bars may be moved intermittently during their travel along 
the length of the channel or may be discontinued for a period of time. The 
selection of a suitable mode of operation and travel speed will be 
dependant on the rate of frost buildup in the freezer. 
EXAMPLE 
A standard belt-type freezer of the type shown in FIG. 1 was employed to 
generate data for determining the amount of time needed to freeze a 
hamburger patty measuring 4.5 inches (11.43 cm) in diameter, 0.5 inch 
(1.27 cm) thick and weighing 4 ounces (113 grams). The heat transfer 
coefficient for this type of freezer was determined to be 7 
BTUs/lb-ft.sup.2 -.degree. F. [40 W.div.(m.sup.2 -.degree. C.)]. 
The food product enters the freezer at 30.degree. F. (-1.degree. C) and 
must exit the freezer at 0.degree. F. (-18.degree. C). As a result 28 BTUs 
(29.5 Kjoules) of heat must be removed from the hamburger patty. The 
freezer section is operated at -80.degree. F. (-62.degree. C.) and it will 
take approximately 11.5 minutes to freeze the hamburger patty to 0.degree. 
F. (-18.degree. C). 
The impingement type freezer of the present invention was determined to 
have a heat transfer coefficient of 17 BTUs/lb-ft.sup.2 -.degree. F. [96.5 
W.div.(m.sup.2 -.degree. C.0]. Operating under the same conditions as 
described for the standard belt-type freezer, the same hamburger patty 
will freeze to 0.degree. F. (-18.degree. C.) in only 4.7 minutes.