A CO.sub.2 food freezer has an elongated enclosure through which material to be cooled is carried on an endless porous belt conveyor with an upper operating belt run vertically spaced from the lower return run to provide an intermediate region therebetween. Liquid CO.sub.2 injection means is located in an upper region to direct CO.sub.2 snow plus cold CO.sub.2 vapor downward onto material being conveyed. Blowers aimed at an angle of between about 5.degree. and about 35.degree. upward from the horizontal are located in the intermediate region, and fans in the upper region direct CO.sub.2 vapor downward onto material on the belt. The belt includes a plurality of longitudinally spaced transverse rods and a plurality of wire sections that respectively interconnect adjacent rods in pairs. The wire sections are bent so that all segments of wire extending generally between said rods lie in substantially the same plane which constitutes the upper surface of the upper run. The rods effectively deflect cold CO.sub.2 vapor from the blowers upward against the undersurface of material being carried along the belt and assure efficient freezing is accomplished.

This invention relates to cryogenic cooling of material being moved through 
an insulated enclosure, and more specifically to the freezing of 
relatively flat patties which are being carried through an insulated 
tunnel on an open mesh wire conveyor belt using a cryogen, such as carbon 
dioxide. 
BACKGROUND OF THE INVENTION 
Mechanical refrigerators, including those of the air-blast type, have long 
been used for cooling and freezing articles, such as food products. More 
recently, systems employing a cryogen, such as liquid nitrogen or liquid 
carbon dioxide, have become commercially important, particularly in the 
food market. Carbon dioxide is excellently suited for the cooling and/or 
freezing of food material because it exhibits the advantages of 
exceptional cooling efficiency at a temperature which is relatively close 
to the freezing point of water and thus does not cause fracturing problems 
in the surface of food products. 
Various systems have been developed to utilize the refrigeration advantages 
of carbon dioxide, and U.S. Pat. No. 3,815,377, issued June 11, 1974 to 
Lewis Tyree, Jr., discloses an insulated freezing tunnel designed for 
using carbon dioxide to freeze food articles being carried along an 
endless conveyor. The patent discloses a particularly efficient 
snow-making system wherein overhead nozzles are employed to direct a spray 
of carbon dioxide snow particles and cold vapor downward onto the food 
articles being transported therepast upon the endless conveyor. 
Improvements in cooling and/or freezing systems of this type which will 
perform more economically and/or efficiently are constantly being sought 
after. 
SUMMARY OF THE INVENTION 
The invention provides a food freezer having an endless wire mesh belt 
conveyor with its upper and lower runs vertically spaced apart to provide 
an intermediate region therebetween. CO.sub.2 injection means is located 
above the belt to direct snow and vapor downward thereupon, and fans are 
also located in the upper region of the enclosure. Blowers are located in 
the intermediate region and oriented at an angle of between 5.degree. and 
35.degree. upward from the horizonal. The conveyor belt is constructed of 
a plurality of transverse rods that are interconnected by wire sections 
which individually span a pair of rods; the wire sections are formed so 
that the bent segments of wire extending between the rods all lie in 
substantially the same plane constituting the upper surface of the belt 
upon which unpackaged food patties rest. The intermediate region blowers 
direct currents of cold vapor that impinge upon the transverse rods, which 
act as deflecting vanes and effectively direct the cold vapor currents 
upward against the undersurface of the food patties--surprisingly 
effecting freezing upward from the undersurface and resulting in the 
particularly efficient freezing of food patties.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Shown in FIG. 1 is an insulated elongated enclosure or tunnel 11 through 
which material to be frozen, such as unpackaged food patties 13, is 
transported on an endless conveyor 15 from an entrance end 17 to an exit 
end 19. The food patties 13 are placed upon the endless conveyor 15 at the 
entrance end and removed at the exit end by apparatus of a type well known 
in the art which forms no part of the present invention. The conveyor 15 
includes a wire open mesh belt 21 of a particular design and is driven in 
the customary manner in the direction shown by the arrows in FIG. 1 so 
that an upper run 23 of the conveyor moves from left to right and a lower 
or return run 25 moves from right to left. In order to best make 
economical use of the freezing system, the material to be frozen or 
cooled, preferably hamburger patties 13 or the like, are disposed in 
aligned transverse rows across the belt 21, which rows are closely spaced 
for most efficient overall operation. 
A plurality of cryogen injection devices 27 are provided in the regions 
above the conveyor belt which are supported from the top wall of the 
enclosure or tunnel and are connected to one or more cryogen headers 29. 
As indicated, the preferred cryogen is liquid carbon dioxide, and the 
injection devices 27 are preferably spring-loaded to the closed position 
as described in detail in U.S. Pat. No. 3,815,377, the disclosure of which 
is incorporated herein by reference. These devices 27 each have a variable 
nozzle, the orifice area of which varies as a result of the liquid 
CO.sub.2 pressure at the device, which is determined by a modulating valve 
31 located upstream of the header 29 that is regulated by a main control 
system 33. Accordingly, as the pressure of liquid CO.sub.2 applied to the 
headers 29 is increased, the flow rate of cryogen through the injection 
devices 27 not only increases because of the higher fluid pressure, but 
also because of the increasing orifice areas. As also described in the 
aforesaid patent, other controls may be used to obtain desired liquid 
CO.sub.2 injection. 
Also preferably disposed in the upper region of the tunnel are a plurality 
of fans 37, each of which is connected by a shaft that extends through the 
insulated top wall to an electric motor 39 disposed exterior of the 
tunnel. As depicted in FIG. 1, some of the fans 37a and 37c circulate the 
cold vapor downward against the upper surface of the articles 13 being 
carried along the conveyor while other of the fans 37b draw the cold vapor 
upward within the tunnel. In order to obtain a uniform pattern of CO.sub.2 
snow across the entire width of the conveyor belt 21, a plurality of 
injection devices 27 will normally be provided at each longitudinal 
station so as to obtain the desired coverage, e.g., 3-5 or more devices 
may be connected to transverse or equivalent subheaders. Similarly, a 
plurality of fans 37 could be provided at each longitudinal station; 
however, by appropriately sizing the fan blade, it has been found that a 
single fan at each location will usually suffice to create the desired 
vapor movement for conveyor belts of the usual width. 
The combination of impinging some CO.sub.2 snow on the upper surface of the 
patties 13, plus the direct downward impingement of the cold vapor within 
the tunnel 11, effectively removes the heat from the patties and freezes 
the upper portion of the patties as they are transported through a tunnel 
of some reasonable length at a fairly substantial rate of speed. It is, 
however, somewhat more difficult and thus takes longer to remove the heat 
from and freeze the lower portions of the food patties, and the present 
improvement is primarily directed to accomplishing this objective. 
As best seen in FIGS. 3 and 4, the endless conveyor belt 21 is made using a 
plurality of transverse rods 41 of circular cross section which link 
together a plurality of wire units or sections 43 formed from metal wire 
of circular cross section. Inasmuch as some heat is removed from the 
unpackaged food patties via conductive heat-transfer through the metal 
wire, a metal having a heat-conductivity at least about as great as that 
of stainless steel is preferably used for both the wire units 43 and the 
transverse rods 41. Viewed oppositely, the patties 13 sufficiently warm 
the low mass wire units 43 to prevent CO.sub.2 snow from collecting 
thereabout. The wire units are formed in an unusual configuration as 
described in detail hereinafter. 
As illustrated in FIG. 1, the upper or working run 23 of the endless 
conveyor belt 21 is vertically separated a substantial distance from the 
lower or return run 25 of the conveyor belt so as to create an 
intermediate region 45 therebetween. The vertical dimension of this region 
45 is preferably equal to at least about one-third of the vertical 
interior height of the insulated tunnel 11. Disposed in this region are a 
plurality of blowers 47 which are individually oriented to discharge cold 
vapor upwardly at an angle between 5.degree. and 35.degree. above the 
horizontal as depicted in FIG. 1. Each of the blowers 47 includes a rotary 
blade that is powered by an electric motor and disposed within a 
surrounding sleeve. The discharge of each blower is past the motor casing 
so as to quickly dissipate the heat of the electric motor. As shown in 
FIG. 1, the blowers 47 are arranged to create fairly high velocity 
currents of cold vapor which move generally in both directions from about 
the center of the tunnel and which are oriented toward the underside of 
the upper run 23 of the conveyor belt. Because of the particular design of 
the conveyor belt, the transverse rods 41 serve as effective deflecting 
vanes. 
As best seen in FIGS. 3 and 4, each of the wire units 43 is made up of a 
plurality of alternating straight wire segments 51 and a plurality of 
parallel wire segments 53 of generally inverted U-shape. These alternating 
segments are interconnected by curved interconnections 55 which constitute 
the bend of the wire around the rod 41 and which respectively join one 
straight segment 51 to the next inverted U-shape segment 53. The 
interconnections 55 are proportioned to fit loosely about the surface of 
the cylindrical rods 41. As best seen in FIG. 3, the straight segments 51 
are arranged so as to lie atop against pairs of rods 41 in the upper run 
of the conveyor, and the inverted U-shape segments 53 extend upward 
between the rods. Accordingly, the major fraction of the wire which forms 
the wire sections 43 lies generally in the upper plane that constitutes 
the surface upon which the food patties 13 rest. As a result, the 
longitudinal length of the wire required to form the individual units 43 
is less than was employed in the prior art type of wire mesh conveyor 
belts 21A (illustrated in FIG. 5) because the major portion of the length 
of the inverted U-shape segments 53 constitutes a part of the upper 
support surface and thus fills what would otherwise be a gap between the 
parallel, straight wire segments 51, allowing the spacing between adjacent 
parallel straight wire segments in each wire unit 43 to be increased. In 
this respect, the substantially straight central portion of each inverted 
U-shape segment 53 is equal to at least about 50 percent of the length of 
the straight segment. Moreover, the acute angle A (FIG. 3) which each of 
the straight segments forms with each of the transverse rods 41 is 
determinative of the spacing between adjacent segments, and it is 
preferably between about 60.degree. and about 75.degree.. 
In addition to using less metal wire than was employed in the prior art 
wire mesh belts 21A (because of this gap-filling function of the 
alternating inverted U-segments 53), this arrangement eliminates the 
build-up of snow and food particles in the regions of the open links which 
was a substantial problem with respect to prior art belts. As depicted in 
FIG. 5, the prior art wire mesh belt 21A was symmetrical, with its upper 
and lower surfaces 59,61 being substantially the same, thus defining 
essentially a pair of planar surfaces. The lower surface 61 of the wire 
links never came in contact with the material being frozen and thus 
remained quite cold, and the middle region 63 between these upper and 
lower surfaces in the prior art belt of the open wire mesh type tended to 
accumulate food particles and carbon dioxide snow throughout the day as 
the freezer was in continuous use. As a result, vapor flow through the 
belt 21A would slowly decrease, and more importantly, the use of such a 
belt would prevent achievement of the bottom cooling effect that is an 
important feature of the present invention. The build-up of snow in the 
interstices 63 between the upper and lower surfaces of prior art wire mesh 
belts 21A would tend to block the flow of vapor currents of the type 
created by blowers 47 disposed in the intermediate region 45, thus 
negating the vane-effect of the transverse rods which is utilized to 
obtain the increased cooling effect. Particularly for food items of large 
size, belts of slightly different design utilizing transverse rods and/or 
other equivalent deflecting devices might be employed. 
To obtain this bottom cooling effect without blowing a large amount of 
vapor out one end of the tunnel freezer 11 and possibly unbalancing the 
overall cooling operation, an even number of blowers 47 are preferably 
provided in the intermediate region 45, with half of them being directed 
toward each longitudinal end. Preferably, a pair of the blowers 47 are 
provided at about the longitudinal center of the tunnel, as depicted in 
FIG. 2, on opposite sides of a central vertical baffle 67. In flanking 
relationship to these blowers are a pair of overhead fans 37a which are 
directed downwardly. Flanking the fans 37a is another pair of blowers 47 
which take suction generally from the region below the downwardly directed 
fans 37a. There may be additional downwardly directed fans 37c included; 
however, somewhere between the ends of the tunnel and the outermost pair 
of blowers 47 there preferably are a pair of upwardly directed fans 37b, 
particularly when the tunnel is greater than about 35 feet long. 
As an example of one commercial embodiment of the freezer 11 designed for 
freezing hamburger patties 13 of the general type served in fast-food 
restaurants, an endless wire mesh conveyor belt 21 is provided about 26 
inches in width. The belt 21 is fabricated as shown in FIGS. 3 and 4 with 
the transverse rods 41 being about 1/4 inch in diameter and being disposed 
on about one inch centers and with the parallel segments 53 being spaced 
about 3/4" from one another. The freezer conveyor has a variable speed 
drive, but when operating at design speed in a 60-foot long tunnel will 
run at a velocity of about 30 feet per minute. The hamburger patties 13 
are placed three, four or five abreast (depending on size) in transverse 
rows, which rows are separated by a distance of only about 1/4 inch. They 
are transported through the freezer, entering at an average temperature of 
about 35.degree. F. and exiting substantially completely frozen at a 
temperature below 20.degree. F. 
An insulated tunnel 11 between about 40 and 60 feet long may contain four 
blowers 47, arranged as depicted in FIG. 1 in the intermediate region 45. 
Each of the blowers 47 discharges cold CO.sub.2 vapor at a rate of about 
10 feet per second. Banks of CO.sub.2 injection devices 27 are spaced 
longitudinally along the length of the tunnel, usually with 4 injection 
units in each bank so as to provide a snow pattern generally uniformly 
across the entire width of the endless conveyor belt 21. In the tunnel of 
this length, there may be such banks of CO.sub.2 injection devices 27. All 
of the banks of devices may be fed from a single supply header 29 of 
liquid CO.sub.2 controlled by a single modulating valve 31, or two or more 
separate headers may be employed with additional modulating valves so as 
to allow for varying of the rate at which CO.sub.2 snow is created in the 
various longitudinal regions of the tunnel. A pair of downwardly directed 
fans 37a are provided in flanking location to the two side-by-side blowers 
47, and additional fans are provided along the length of the tunnel with 
some fans 37c directed downward and some fans 37b directed upward so as to 
assure that continuous movement of the cold vapor is achieved within the 
tunnel. Additionally, an exhaust system is located adjacent each end of 
the tunnel to remove the CO.sub.2 vapor and vent it to a location exterior 
of the plant. Such exhaust systems are well known in the art. 
In order to control the overall operation and assure that efficient 
freezing is effected, an overall control system 33 is provided which 
operates using at least one temperature sensor 69 located in the insulated 
tunnel at a location generally near the exit end, downstream from the last 
blower 47. The general means of control is by varying the pressure of 
fluid supplied to the CO.sub.2 header 29 which has a dual effect upon the 
CO.sub.2 injection devices 27. The spring-loaded devices 27 when subjected 
to a higher pressure, enlarge the orifice area of the nozzle through which 
the liquid CO.sub.2 is being ejected which, coupled with the higher fluid 
pressure head, increases the amount of CO.sub.2 being expanded per 
increment of time. Although variable speed motors could be provided for 
the fans and/or the blowers, so as to even more precisely adapt the 
freezer to varying rates of product throughput, generally adequate control 
is achieved simply by the employment of one or more modulating valves in 
the supply lines for the liquid CO.sub.2. 
Although the apparatus has generally been described as a food freezer, it 
should be understood that a temperature below 32.degree. F. need not be 
achieved in the material carried along the conveyor and that the apparatus 
can be also efficiently employed to effect the cooling of material to a 
temperature above freezing. Likewise, although the greatest commercial use 
presently forseen is in the freezing of food patties or the like, it could 
also be efficiently used to cool or freeze other articles, including 
non-food articles. 
Although the invention has been described with regard to a preferred 
embodiment, it should be understood that changes and modifications as 
would be obvious to one having the ordinary skill in this art may be made 
without deviating from the scope of the invention which is defined solely 
by the claims appended hereto. Particular features of the invention are 
emphasized in the claims that follow.