Note: Descriptions are shown in the official language in which they were submitted.
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CRYOGENIC CABINET FREEZER
This invention relates to cryogenic cooling
apparatus and more particularly to apparatus for using a
cryogen to cool a load within a specifically defined
chamber or compartment.
BACKGROUND OF THE INVENTION
Over the years, the advantages of cryogenic
cooling in being able to produce lower temperatures than
conventionally available mechanical freezing apparatus
has become apparent and has been found to be efficient
for commercial applications. Cryogenic fast-freezers
have proved to be of significant benefit to users
desiring relatively low-temperature environments, for
example, in the region of -30F. or -40F., and examples
of such cryogenic freezing units are set forth in U.S.
Patents Nos. 3,660,985, 3,672,181, 3,754,407 and
3,815,377. Various of the apparatus illustrated in
these patents were particularly designed for use with
car~on dioxide, which offers particular advantages when
cooling or freezing using temperatures in the
aforementioned range.
U.S. Patent No. 4,127,008, issued November 28,
1978 to Lewis Tyree, Jr., shows a variety of cryogenic
cooling apparatus including some which are designed to
employ a closed chamber in which a static or stationary
load can be placed, for example by rolling in a wheeled
cart or rack carrying the product disposed on vertically
spaced shelves. The cooling is accomplished in the
illustrated devices solely by the use of cryogen which
was expanded in a heat-exchanger and recovered,
requiring slightly more sophisticated equipment. It is
felt that there is a commercial market for somewhat
simpler devices which so efficiently utilize cryogen to
cool or freeze a load within a compartment that
35 expenditure of the cryogen can be permitted while ~,
remalning cost effective.
SUMMARY OF THE INVENTION
The invention provides a cabinet cooler or
freezer which efficiently utilizes cryogenic
refrigeration, with or without mechanical refrigeration,
to rapidly and efficiently lower the temperature of a
product load. As such, in one aspect, the invention
provides apparatus which is capable of intermittently
handling relatively large batches of product on an
efficient and economically attractive basis. In another
aspect, a spiral or helical conveyor is employed to
obtain the advantages of the invention in a dynamic load
environment. The invention utilizes the natural
expansion effect of cooling with a liquid cryogen that
is being vaporized, in combination with the mechanical
circulation of the gaseous atmosphere by blowers or
fans, to achieve an efficient circulation pattern that
establishes surface heat-exchange with the product being
cooled and the cold environment. A secondary
circulation and effect is induced, in a manner similar
to the operation of a jet pump, which amplifies the
circulation and is particularly efficient when the
blowers create a flow of vapor through the inducers even
when cryogen is not being expanded.
BRIEF DESCRIPTION OF THE DRAWINGS
- FIGURE 1 is a perspective view, with portions
broken away, of a single-door freezing apparatus
utilizing both cryogenic and mechanical refrigeration
and embodying various features of the invention;
FIGURE 2 is a top view with 2 major portion
broken away to show the interior of the apparatus of
FIGURE l;
FIGURE 3 is a front view with portions broken
away and with arrows provided to diagrammatically show
~ 35 the atmospheric flow patern achieved within the
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apparatus of FIGURE l;
FIGURE 4 is a view similar to FIGURE 3 of an
alternative version of a freezer cabinet using all
cryogenic refrigeration and embodying various features
: 5 of the invention;
FIGURE 5 is a top view with a large portion
broken away to show the interior of the cabinet of
FIGURE 4;
FIGURE 6 is a perspective view, similar to
FIGURE l, of a two-door all-cryogenic freezing cabinet
embodying various features of the invention;
FIGURE 7 is a top sectional view taken
generally along the line 7-7 of FIGURE 6;
FIGURE 8 is a front view, with portions broken
away, of the apparatus shown in FIGURE 6;
FIGURE 9 is a side sectional view taken
generally along the line 9-9 of FIGURE 8;
FIGURE 10 is a plan view of an alternative
version of a cabinet freezer which incorporates a
helical or spiral conveyor;
: FIGURE 11 is a vertical sectional view taken
generally along the line 11-11 of FIGURE 10; and
FIGURE 12 is a fragmentary perspective view
enlarged in size, illustrating one of the
refrigeration-generation devices employed in several of
the corners of the overall cabinet.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS
Illustrated in FIGURES 1=3 is a cabinet-type
refrigeration device which includes a cabinet ll formed
with insulated walls for maintaining a low-temperature
environment therewithin. A hinged door 13 is provided
to close an opening 15 through the front wall of the
cabinet, which door can be locked in closed position by
a latch 17. A short ramp l9 is preferably provided to
allow a wheeled cart to be easily moved into and out of
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the cooling enclosure or region 21 defined by the
cabinet 11 and closed by the door 13.
A refrigeration-generation region 23 is
provided within the cabinet and is generally defined by
a partition 25 which extends for a major portion of the
height of the cabinet but which terminates slightly
below the upper edge. The rear wall of the cabinet and
the interior surface of the closed door 13 are parallel
and extend from the boundary with the region 23,
generally defining the cooling enclosure. Four circular
openings are provided in the partition 25l and four fans
or blowers 27, driven by electric motors, are mounted in
the openings in the partition. A rectangular opening 29
is also provided at the bottom of the partition 25.
Because the cabinet ll is provided with
refrigeration equipment designed for the creation of
temperatures well below the freezing point of water, it
- is generally referred to as a freezer. However, it
should be understood that this is simply dependent upon
the time that the load is allowed to remain in the
cabinet and/or the temperature at which the
refrigeration equipment is set to maintain the enclosure
21, and accordingly it could be used and referred to as
a cooler. The refrigeration-generation region 23 is
provided with a mechanical refrigeration system 31 and a
cryogenic refriqeration system 33 which can be both
operated at the same time or either can be operated to
the exclusion of the other. The fans 27 operate to
circulate the vapor in the same manner whether or not
the cryogenic system is operating. The cryogenic system
33 will usually be operated only in conjunction with the
operation of the mechanical refrigeration system 31.
By "mechanical refrigeration system" is meant
one which applies thermodynamics in a manner wherein a
cooling medium, or refrigerant, goes through a cycle so
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that it is recovered and reused. Generally, a
vapor-compression cycle is employed wherein the liquid
refrigerant is evaporated in low pressure region, i.e.
an evaporator, at a low pressure in an evaporator to
produce cooling, subsequently withdrawn ~o a compressor
where the pressure (and temperature) of the gaseous
refrigerant is raised, then transferred to a condenser
wherein its heat is discharged to the environment and
the refrigerant liquifies, and is thereafter stored in a
receiver until such time that it is to ~e recycled
through an expansion valve back into the evaporator. By
a "cryogenic refrigeration system" is meant one wherein
a liquified gas, usually carbon dioxide or nitrogen, is
allowed to expand and evaporate, often producing a
temperature of about -110F., or below. usually, the
cryogen is exp0nded e.g. by discharge to the atmosphere
after the desired use has been made of its capacity to
absorb heat in carrying out an attendant cooling or
freezing operation.
The mechanical refrigeration system 31 in the
illustrated embodiment includes an evaporator 35 wherein
a refrigerant, such as a Freon~ is allowed to evaporate
to a vapor or gas. The evaporator 35 is supplied from a
receiver which is part of a compressor-condenser
combination 37 located atop the cabinet 11. A control
valve 39 allows the flow of Freon~liquid from the higher
pressure receiver into the evaporator 35. The ca~inet
ll is provided with an overall control system 41 which
allows it to be set in different modes of operation and
which receives a signal from a sensor 43 that gives an
indication of the temperature at an upper location
within the refrigeration region 21. The valve 39 when
signalled by the control system allows the liquid Freon
to flow from the higher pressure region in the receiver
to the lower pressure region in the evaporator 35.
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't'he control .sy~;~em 41 cau~e~ the four blower~ 27 to
run whenever -the door ~3 i~ la~ched ~hu~ ancl ~he ~reezer ls
actuated in any mode of operation, creating a primary circulation
of the cabinet atmosphere. The lowermost three fans 27 are
operated to suck the gaseous atmosphere from the lower regions of
the refrigeration region 21 and direct the atmosphere to the
right as depicted in FIGURE 3. The uppermost blower 27 is
operated to take suction from its right-hand side and discharge
to the left-hand side as indicated in FIGURE 3. This creates an
upward flow along the right-hand wall in the refrigeration-
generation region 23, and if desired, haffles can be provided to
assist this flow pattern. It also creates a natural flow of gas
through inducers 49 located near the top of the cabinet and
described hereinafter.
`~ Disposed at a level above the uppermost blower are a
pair of cryogen injection devices 45 in the form of injection
nozzles 47 connected to a source of high pressure cryogen.
~ Although nitrogen or some other suitable cryogen may be employed,
`~ liquid carbon dioxide is preferred, and the nozzles 47 are
`~ 20 preferably spring-loaded expansion nozzles desiyned to efficiently
produce a stream of CO2 snow and CO2 vapor, similar to those dis-
closed in U.S. Patent No. 3,815,377, issued June llt 1974.
Each of the nozzles 47 discharges at a location within
a surrounding inducer 49 which preferably has a flared entrance
`; and amplifies the circulation, thereby increasing efficiency.
The expansion of the liquid CO2 through an orifice at the end of
the nozzle 47 into the inducer and the discharge of this stream
out the open left-hand end creates a significant secondary
çirculation of gas within the interior of the cabinet.
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The action is similar to that of a jet pump and causes a
substantial volume of gas to be sucked into the
right-hand entrance of the inducer 49, which is
discharged at a high velocity along with the vapor and
snow being created at the nozzle orifice. Not only does
the effect of the pair of inducers 49, plus the
uppermost fan 27, balance the three lower fans operating
in the opposite direction to create a good flow pattern
throughout the entire refrigeration zone 21, but the
dispersion of the subliming CO2 snow within the
gaseous circulation pattern suspends the snow particles
and distributes them excellently throughout the zone so
that, even after operation for an extended period of
time, no accumulation of snow is created at the bottom
of the left-hand refrigeration zone 21.
The injection devices 45 are connected in
parallel downstream of a modulating valve 51 which
changes the pressure of the liquid cryogen flowing to
the injection devices 45 in response to a signal
received from the control system 41. To prevent
pressure from building-up within the cabinet, cryogen
vapor is vented from the cabinet whenever the cryogen
system is operating. When the cryogen is CO2, the
cold vapor is discharged through a heat-exchanger, which
may be mounted on the rear wall of the cabinet 11 and
which may exhaust through a check valve to a vent
conduit that preferably discharges to the atmosphere
exterior of the plant wherein the cabinet freezer is
being operated. The incoming stream of liquid CO2
from a suitable source, usually a standard high-pressure
liquid CO2 storage tank, passes through the
heat-exchanger 53 where the high-pressure liquid is
cooled by heat-exchange with the cold exiting vapor.
The combination of the modulating valve 51
which varies the rate at which liquid cryogen is
injected in combination with the secondary circulat1on
created by the inducers 49 results in an extrem01y
effective use of cryogen and is particularly
advantageous in its overall energy efficiency when it is
employed simultaneously with the mechanical
refrigeration system 31 that can effectively provide
cooling in upper temperature range. For example, the
cryogen refrigeration system 33 may be operated during
the time wherein product load is accepting more
refrigeration than the mechanical system 31 can supply
-- which is usually during the early part of a
refrigeration cycle.
As an example of the operation of the freezer
cabinet 11, a wheeled cart containing an open rack or
framework upon which are supported a plurality of layers
of shallow trays containing the products is pushed into
place through the opening 15. After the door 13 has
.
~een closed and latched, the control system 41 is set to
. ..
the desired mode of operation, for example,
rapid-freezing, and actuated to begin the cycle. The
~our blowers 27 are immediately started, and the valve
39 automatically supplies liquid Freon to the evaporator
through which the blowers are blowing the atmosphere
within the cabinet. There is gaseous flow through the
inducers even if Co2 is not being expanded.
Because the temperature being sensed initially
is quite high, likely close to ambient, the control
system 41 generally operates the cryogen injection
~ devices 45 at a high rate. Assuming that liquid CO2
; 30 is being expanded, the modulating valve 51 opens
relatively wide and may apply nearly full pressure of
liquid cryogen to the snow-making nozzles 47. This
results in an immediate discharge of C02 snow and
vapor from the left-hand end of the two inducers 49
whlch creates the des1red Hecond~ry ciraulation by
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sucking gaseous atmosphere through the flared
entrances. AS a result, the flow of cold vapor and
finely dispersed particles of snow is outward across the
upper layexs of the load on the car~ being refrigerated
and then downward along the left-hand wall of the
refrigeration zone 21 whence it is drawn across the
lower layers o~ product, from left to right, by the flow
patterns set up by the lowermost three blowers 27.
As the temperature within the refrigeration
zone 21 begins to drop to mean the preselected
temperature and is detected by the sensor 43, the main
control system 41 causes the modulating valve 51 to
begin to close slightly, thus lowering the pressure of
the liquid CO2 and reducing the rate of CO2 flowing
to the cryogen injection devices 45 and the rate at
which CO2 snow and vapor are injected via the
nozzles. When a certain predetermined temperature is
reached within the cabinet, for example, -80F., the
control system 41 may close the modulating valve 51
entirely thus discontinuing operation of the cryogen
re~rigeration system 33 until such time as the
temperature might again rise above this predetermined
temperature. Of course, different predetermined
temperatures may be set for different products and when
different cryogens are used.
The cryogen refrigeration system 33 may be set
to operate for a total "freeze time" duration.
- Thereafter, the mechanical refrigeration system 31
continues to operate and may operate intermittently when
the cabinet temperature begins to stabilize. The
mechanical refrigeration system 31 maintains the
atmosphere within the refrigeration zone a desired
holding temperature range, typically, about -10F. to
0F. Once an overall set time expires, the control
system 41 may be programmed to light an indicator light
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and/or cause an audlble signal to be sounded to alert
personnel in the plant that the cycle has been completed
Shown in FIGURE 4 is a cabinet reezer 61 which
is similar in outward appearance to the cabinet freezer
11 but which is provided with an all-cryogenic
refrigeration-generation system. The cabinet includes a
single door 63 which provides access to a refrigeration
zone 65 which is substantially the same as that
previously described. A refrigeration-generation zone
67 on the right-hand side of the refrigeration zone 65
- in FIGURE 5 is of su~stantially the same size as the
zone 23; however, the refrigeration-generation equipment
is different. In the illustrated embodiment, three
blowers 69 are employed in combination with four cryogen
injection units 71a, b, c & d, each of which includes
the combination of an injection nozzle 73 and an inducer
75 of the same type as hereinbefore described with
$~ regard to the FI~UR~ 1 embodiment. Instead of employing
~; a baffle to separate the two zones, porous screen
material 77 is employed which extends vertically from
; top to bottom and which merely provides protection
against the possibility of inadvertent contact with the
; blades of the blowers while allowing free-flow of
gaseous atmosphere back and forth be~ween the two zones.
The three blowers 69 are mounted in a main
baffle 79 which extends from the right-hand wall
- generally diagonally across the region to a point
~ ; generally adjacent the screen 77. The blowers 69 are
$ mounted in three apertures in the baffle main 79 and are
of a design wherein ~he gaseous stream discharged by the
blower passes over the motor housing, as ~est seen in
~ FIGURE 5. Disposed in generally converging relationship
!, ` to the main baffle is a row of curved vanes or thin
baffles 81 which extend substantially from the floor of
the cabinet to the ceiling. The vanes 81 are uniformly
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spaced apart and serve to smoothly turn the vapor
discharge from the blowers into a flow pattern across
the refrigeration zone 6S from right to left, as shown
by the pattern of arrows in FIGURE 5. The vanes 81
serve a dual purpose, as described hereinafter in more
detail, of creating a relatively high-pressure region 83
between the main baffle 79 and the row of vanes.
Three of the cryogenic injection devices 71 a,
b ~ c and their associated inducers 75 are mounted
horizontally at a vertical level just slightly higher
than the three blowers 69, as shown in FIGURE 4. The
fourth cryogen injection device 71d is mounted
vertically near the bottom of the cabinet. With respect
to the three horizontal devices, the inducers 75 are
mounted in passageways cut out from the vanes 81 so that
`~ their entrances lie on the right-hand side of the row of
vanes, in the high-pressure region 83, and each exit is
on the left-hand side of the vanes. As a result of this
design and location, the high-pressure gas region at the
entrance of the inducers 75 not only assures the flow of
gas through the inducers when CO2 is not being
expanded but also has the effect of supercharging the
inducers and creating an even more effective secondary
circulation of vapor throughout the refrigeration zone
65 when CO2 is being expanded.
The fourth vertically oriented inducer 71d is
located generally adjacent the vertex of the region
- defined by baffle 79 and the row of vanes 81, as seen in
FIGURE 5, and is directed upward. The two vanes 81
nearest the door are shortened to allow the inducer unit
to be accomodated~ In the all-cryogenic cabinet freezer
61, the cryogen is employed to provide refrigeration
throughout the entire temperature range wherein cooling
or freezing is being accomplished. For efficient
performance when only a low rate of refrigeration need
~ ti~
be supplied, the modulating function referred to
hereinbefore is important, and the vertical disposition
of the fourth injection unit and its location near the
bottom are also important, particularly when the cryogen
-5 is carbon dioxide. As can be seen from FIGURE 4, the
flow pattern purposely established in the refrigeration
zone 65 is generally stratified, as typified by the
pattern of arrows. This arrangement assures the desired
flow through relatively narrow horizontal passageways
between layers of trays on a wheeled cart or rack. The
vertically disposed injection unit 71d not only assures
effective mixing of vapor between these stratified
`~layers when its discharge intersects with the discharges
from the three blowers 69, but it also assures that a
;15 significantly colder region is not created near the
bottom of the refrigeration zone 65 wherein snow might
possibly accumulate.
Although the supply of liquid cryogen to the
injection units 71 can be in the same manner as
-~20 hereinbefore described with respect to the freezer 11,
preferably a piping arrangement is employed which
directs a stream of cryogen of relatively higher vapor
content to the vertical injection unit as compared to
~the streams which are supplied to three horizontal
-~25 injection units. In this respect, a heat-exchanger 85
is located at the vapor vent outlet, and a modulating
valve 87 is located in the supply line for the incoming
C2 stream which is the same as previously described.
However, the cryogen from the valve 87 flows to a
horizontal manifold 89 in the refrigeration-generation
zone 67 from which the four inducer units are supplied.
The liquid in the top region of the manifold will tend
to have a greater vapor content than the liquid in the
lower region.
The three horizontal injection units 71a, b ~ b
-13-
are supplied by piping 91 which connects to th~ bottom
of the manifold 89, and the vertical injection unit 71d
is supplied through piping 93 which connects to the top
of the manifold. Accordingly, the liquid cryogen
flowing in the manifold having the higher vapor content
is preferentially directed to the lower injector 71d.
This has the advantage of creating a somewhat lesser
percentage of C~2 snow at the lower injector and a
greater percentage of vapor, thus achieving an even
greater upward secondary circulation to accomplish the
desired mixing. Likewise, the relatively greater
percentage of snow e~iting from the three horizontal
injection units places ~he snow in the vicinity of the
product being cooled and/or frozen where it is most
effective. The secondary circulation created by the
inducers 75, together with the blowers 69, creates a
cyclonic effect about a vertical axis which very
~- efficiently cools material even when disposed in layers
` of closely spaced shallow trays.
The overall function of the freezer cabinet 61
is generally the same as that earlier described except
that, of course, all of the refrigeration results from
the initial injection of cryogen. ~he three blowers 69
are set to run continuously, with the injection units 71
~ 25 being operated in response to the temperature sensed by
a sensor 95 and the particular program which has been
set into the main control system 97.
Although the cabinet 61 illustrated and
described is designed to accept and freeze a stationary
batch of product disposed in shallow trays and supported
upon a transportable cart having multiple shelves, the
cooling principles embodied in the apparatus design can
be used effectively to cool throughout a defined chamber
on compartment. For example, a spiral endless conveyor
may be located within a relatively large cabinet having
a lower entrance and an upper exit upon which products
can be continuously transported while they are being
cooled and frozen by the cyclonic circulation effect
that is created about a central axis, that may
substantially concide with the axis of the spiral
conveyor.
Depicted in FIGURES 6 ~hrough 9 is a freezer
101 which resembles the freezer 61 insofar as it
con~ains an all cryogenic refrigeration system; however,
it is designed to have substantially twice the capacity
by being provided with two separate refrigeration zones
103a and b to which access is provided by separate doors
105. A refrigeration generation zone 107 is located
centrally between the two refrigeration zones. Although
the freezer 101 can be operated with a load in only one
of the two zones 103, by eliminating the operation of
certain of the cryogen injection units directed toward
the zone not being used, it is far more economical and
efficient to load both of the zones simultaneously and
- 20 carry out concurrent cooling and/or freezing operations
in both zones at the same time. A representative
wheeled cart 109 is shown in the right hand compartment
in FIGURE 6 which has a plurality of horizontal racks or
shelves that may be spaced closer together depending
upon the particular product being frozen.
The equipment in the refrigeration generation
zone 107 includes six blowers 111 of the type described
with respect to the freezer 61, which discharge the
vapor stream over their electric motor housings, being
aligned in two side-by-side vertical rows. As best seen
in FIGURE 7, the three blowers 111 in the front row
nearest the doors 105 take suction from the left-hand
zone 103a and discharge into the right-hand
refrigeration zone 103b, whereas the three blowers 111
in the rear row operate vice-versa. Accordingly, as
-15-
generally depicted by the arrow pattern in FIGURE 8, the
blowers tend to create a relatively stratified, cyclonic
circulation throughout both refrigeration zones. This
circulation is extremely effective in achieving contact
between the cold vapor and the layers of food product
- being cooled which are supported on the many-tiered
wheeled carts 109, and it greatly adds to the overall
efficiency of the freezer.
~ The actual refrigeration is achieved by cryogen
-~ 10 injection units 113 which are substantially the same as
those described with respect to the freezer 61, but
twice in number. In this respect, a horizontal
injection unit 113 is assoclated with and positioned
just slightly above each of the blowers 111 (as best
seen in FIGURE 9) which unit discharges in the same
direction as the blower, and these six injection units
thus reinforce the cyclonic movement of the gaseous
atmosphere within the cabinet which achieves the
extremely efficient cooling and/or freezing of the
product disposed in relatively shallow layers. Flow
diffusing baffles 115 are preferably located in the
regions of discharge to spread the discharge stream from
each of the blowers 111 so that intermingling and mixing
occurs between it and the adjacent secondary circulation
streams emanating from the inducers 117 of the injection
units 113.
In addition, a single vertically oriented
injection unit 113 is located in association with each
vertical row of blowers. As in the case of the freezer
61, each of the two vertically oriented injection
devices 113 is directed to discharge into a region where
it will intersect with the discharge streams from the
three blowers 111 disposed thereabove it. This
arrangement eliminates the possibility of stratification
occurring on one vertical level which might create a
-16-
different temperature there than at other levels and
also assures that a particularly cold region is not
created near the bottom of the zone as a result of the
tendency of cold, more dense vapor to gravitate downward.
A temperature sensor 121 may ~e located in tne
rear of the refrigeration-generation region 107 that is
connected to a main control unit 123. Alternatively, a
pair of sensors may be located one in each of the
. refrigeration regions with the control system being
designed to simply average the temperatures which it
interprets from the signals received. A single
modulating valve 125 can be employed to control the rate
at which cryogen is simultaneously injected from all of
the units 113. Alternatively, one modulating valve can
be wsed to control the front four injector units and
another to control the rear four units, in which case
four of the units can be removed from operation in the
case when only a single load is being frozen in one
refrigeration zone 103 -- ~y simply having the control
system 123 shut down one modulating valve.
Preferably, a horlzontal manifold (not shown)
is also used so that the two vertically oriented
injection units 113 are supplied ~y connections coming
from the upper region of the manifold and the six
horizontally directed injection units 113 are supplied
with cryogen from the lower region of the manifold.
This arrangement achieves the effect described
hereinbefore with respect to the
refrigeration-generation system for the cabinet 61
depicted in FIGURES 4 and 5,l namely the discharge of a
larger percentage of CO2 snow from horizontally
oriented injectors 113.
The double-row, oppositely-facing arrangement
of blowers and injectors creates a cyclonic movement of
the atmosphere within the cabinet that i~ extremely
-17-
effective in cooling produc~ on multiple-tiered carts
109 of the type shown. Moreover, precise regulation of
the cryogen injection rates by the modulating valve
allows accurate control of temperature as low as about
-80F. without the accumulation of snow on the cabinet
` f loor.
Illustrated in FIGURES 10 through 12 is a
cabinet refrigeration device 130 which includes a large
insulated cabinet 131 having four vertical insulated
walls 133 for maintaining a low-temperature environment
therewithin. Several doors 135 provide physical access
to the interior of the cabinet wherein an endless
conveyor 137 is located.
The conveyor 137 is of the type illustrated in
U.S. Patent No. 4,078,655, issued March 14, 1978. The
conveyor 137 includes an endless belt preferably made of
stainless steel which i5 arranged to have a short
straight entrance section 139 disposed near the bottom
of the cabinet that preferably protrudes through a lower
entrance opening 141 in the insulated wall of the
cabinet and a short straight exit section 143 that
similarly preferably extends just through an upper exit
opening 145. In between the straight entrance and exit
sections, the main section 147 of the endless belt is
arranged to travel along a spiral or helical path about
a central cage-type driving drum 149. Although the path
is circular in plan view (FIG. 10), it might also be
oval or the like, in which case a modified drive
arrangement would be employed. A main motor 151 drives
the drum through a gear arrangement and preferably also
drives a sprocket drive which meshes with the belt near
its exit location so as to suitably provide a low
tension in the belt sufficient to frictionally engage
the central drum 149 which provides the primary motive
power for the conveyor, all as taught in the
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just-mentioned U.S. Patent.
Refrigeration genera~ion equipment is disposed
in three of the four corners within the cabinet, as best
seen in FIGURE 10, and could additionally be located in
the center region by utilizing a suitably open drum. A
primary circulation of the atmosphere within the cabinet
is achieved by blowers or fans 153 which are arranged in
vertical array. Each of the fans is powered by an
individual electric motor 155 and is surrounded by a
sleeve 157 that contributes to eficient flow and serves
a protective func~ion. ~ssociated with most of the fans
1~3 are a plurality of cryogen injection units 159 of
the type earlier described, each including the
combination of a spring-loaded injection nozzle plus a
surrounding inducer. As a result of the location of the
injection units 159 just downstream from a fan 153,
there will be a significant flow of vapor through the
inducers even when cryogen is not being expanded, and a
supercharging effect is created with respect to vapor
flow through the inducer when cryogen is being
expanded. Thus, an even more effective secondary
circulation of vapor is created by the action of the
injection units.
As best seen in FIGURE 10, the fan arrays are
directed at the helical section 147 of the endless
conveyor and are oriented to discharge in a generally
concurrent direction to the articles carried on it so
~` that they are moving away from the fans and rising
whereby the vapor currents tend to force the articles
onto the belt, which has been found to surprisingly
provide more efficient heat transfer than if the
discharge is directed either directly radially inward
toward the center or in countercurrent direction. The
arrangement of the refrigeration units creates a
swirling flow of cryogen vapor, and minute particle6 of
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C2 snow if carbon dioxide is used as the cryogen,
which follows the helical path of movement within the
cabinet. As best seen in FIGURE 12, the lowermost fan
153, which is directing the vapor circulation past the
lower strata of the conveyor helix containing the
material, usually food, that has most recently entered
the cabinet, need not necessarily be provided with
a6sociated cryogen injection units. Because the cold
cryogen is more dense than the cryogen vapor that has
been warmed by heat transfer with the material being
carried on the conveyor, it has a tendency to gravitate
towards the bottom of the cabinet, and thus efficient
operation is achieved if the cryogen injection units 159
are located in the vertical central region and above.
However, depending upon the particular product, it may
be desired to provide a very cold environment at the
entrance level.
A control system is provided which includes a
control panel 161 for monitoring and controlling the
overall operation and maintaining the desired
temperatures throughout the cabinet. One or more
temperature sensors 163 are provided within the cabinet
to read the temperature and supply a signal to the
control system. The overall control system preferably
employs a modulating valve arrangement, such as that
earlier described, so that the pressure of the liquid
cryogen being fed to the spring-loaded nozzles can be
varied to achieve precise temperature control without
wasting cryogen.
The cold, more dense cryogen vapor gravitates
to the bottom of the cabinet and has a tendency to flow
out the lower entrance 141 through which the material
being cooled is entering the cabinet on the straight
conveyor section 139. To retard outflow of cryogen
vapor at this location, a series of chambers 167 are
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provided just interior of the entrance to serve as a
labyrinth-type seal, which reduces convection currents
in the immediate region interior of the entrance. Its
effect i5 increased by the provision of a blower 169
which is directed upwards and which takes suction from
the entrance chamber system.
More specifically, a compartment is provided
which surrounds and extends upward from the conveyor
belt and which includes two depending baffles 171 which
effectively separate it into three chambers 167.
Located adjacent the entrance chamber is a small chamber
173 that serves as a plenum, and the blower 169 is
supported atop the plenum and takes its suction
therefrom. The blower 169 is powered by an electric
motor and discharges vertically upward past its drive
motor. There is an opening in the wall of the plenum
between it and the entrance chamber, and an opening in
the opposite wall of the plenum communicates with the
main portion of the cabinet. The opening between the
two chambers is par~ially closed by a slidable gate 175,
and a similar slidable gate 177 is provided on the
opposite wall to partially close that openingO
Positioning of the slidable gates 175,177 effects
adjustment of the intake of cold cryogen to the plenum
173 and permits the careful balancing of the suction so
as to retard any substantial outflow of cold cryogen
through the conveyor entrance 141 while preventing the
ingress of humidity-bearing ambient air.
A generally similar but smaller chamber 181
having one or more depending baffles 183 is optionally
provided just interior of the exit opening where the
problem of cryogen outflow is less critical because of
the higher density of the colder cryogen -- particularly
when carbon dioxide is being used as a cryogen.
Especially when carbon dioxide is being employed as the
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cryogen, spill-over exhaust blowers (not shown), of a
type well-known in the art, are preferably associated
with side ducts 185 and 187 to remove the outflowing
cold cryogen vapor from the vicinity of the cabinet and
discharge it to the atmosphere exterior of the plant.
The spiral conveyor cabinet refrigeration
device 130 is extremely efficient and can be used to
freeze a wide variety of products because the speed of
the conveyor can be varied within a fairly wide range so
as to provide a cooling time of from less than ten
minutes to well over one hour. The spring-loaded
injection nozzles plus the inducers, in combination with
the strategically located fans, provide excellent
circulation of vapor along the entire length of the
conveyor in the cabinet. The provision of multi-chamber
vapor locks adjacent the entrance and the exit virtually
eliminates air infiltration into the operating
refrigeration cabinet and produces increased freezing
rates while minimizing cryogen consumption.
Although the invention has been described with
regard to certain preferred embodiments, it should be
understood that various changes and modifications as
would be obvious to one having the ordinary skill in
this art may be made without departing from the scope of
the invention which is defined in the appended claims.
For example, automatically operated defrosters can be
incorporated in associa~ion with the evaporators in the
cabinets 11~
