U.S. patent application number 12/922022 was filed with the patent office on 2011-01-20 for device and method for chilling or deep-freezing food products by impacting jets.
This patent application is currently assigned to L'Air Liquide Societe Anonyme Pour L'Etude Et L'Ex ploitation Des Procedes Georges Claude. Invention is credited to Didier Alo, Antony Dallais, Thierry Dubreuil, Giuseppe Pigorini, Robert Taylor.
Application Number | 20110011097 12/922022 |
Document ID | / |
Family ID | 39769492 |
Filed Date | 2011-01-20 |
United States Patent
Application |
20110011097 |
Kind Code |
A1 |
Alo; Didier ; et
al. |
January 20, 2011 |
Device and Method for Chilling or Deep-Freezing Food Products by
Impacting Jets
Abstract
The invention proposes a device for chilling or deep-freezing by
impacting jets which consists of a tunnel comprising a moving belt,
at least one plate and preferably at least two plates located
parallel to each other on either side of said moving belt, at least
one plate, and preferably both plates, being provided with
through-holes, and at least one means for injecting a cold fluid,
said tunnel having a zone under pressure P1 and a zone under
pressure P2, the pressure P1 being greater than the pressure P2,
characterized in that it includes means for varying the pressure in
the zone under pressure P1 and/or means for cooling the plate or
plates down to a temperature below about -80 DEG C, preferably
below -90 DEG C and more preferably still below -100 DEG C and for
maintaining that temperature; and a method for chilling or
deep-freezing food products by impacting jets.
Inventors: |
Alo; Didier; (Criquetot
L'Esneval, FR) ; Dubreuil; Thierry; (Boissets,
FR) ; Dallais; Antony; (Palaiseau, FR) ;
Pigorini; Giuseppe; (Paris, FR) ; Taylor; Robert;
(Wavre, BE) |
Correspondence
Address: |
American Air Liquide, Inc.;Intellectual Property Dept.
2700 Post Oak Boulevard, Suite 1800
Houston
TX
77056
US
|
Assignee: |
L'Air Liquide Societe Anonyme Pour
L'Etude Et L'Ex ploitation Des Procedes Georges Claude
Paris
FR
|
Family ID: |
39769492 |
Appl. No.: |
12/922022 |
Filed: |
March 10, 2009 |
PCT Filed: |
March 10, 2009 |
PCT NO: |
PCT/FR09/50384 |
371 Date: |
September 10, 2010 |
Current U.S.
Class: |
62/1 |
Current CPC
Class: |
A23L 3/375 20130101;
F25D 3/11 20130101; F25D 13/067 20130101; A23L 3/361 20130101 |
Class at
Publication: |
62/1 |
International
Class: |
F25D 3/00 20060101
F25D003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2008 |
FR |
0851590 |
Claims
1-13. (canceled)
14. A device for chilling food products by impacting jets
comprising a tunnel comprising a moving belt, at least a first
plate located opposite, above or alternatively beneath, said moving
belt and provided with through-holes, said first plate being
provided with through-holes, at least one means for circulating a
cold fluid, wherein: said tunnel being adapted to maintain a zone
under pressure P1 above said first plate when said first plate is
located above said moving belt or and/or beneath said first plate
when said first plate is located below said moving belt; said
tunnel being adapted to maintain and a zone under pressure P2
between said first plate and the moving belt, P1 being greater than
P2; and a means for varying P1 and/or a means for cooling said at
least a first plate down to a temperature below about -80.degree.
C. and for maintaining that temperature.
15. The device of claim 14, wherein the cold fluid is a cryogenic
fluid is selected from the group consisting of nitrogen, carbon
dioxide, oxygen, air, and mixtures thereof.
16. The device of claim 14, wherein the chilling device is a
deep-freezing device.
17. The device of claim 14, wherein the means for cooling said at
least a first plate is selected from the group consisting of a
heat-exchange circuit attached to the plate, a plate/heat
exchanger, a cold fluid bath, and combinations thereof.
18. The device of claim 17, wherein the cryogenic fluid passing
through the heat exchanger is taken from the circuit for supplying
the chilling machinery.
19. The device of claim 14, wherein the means for varying the
pressure is selected from the group consisting of frequency
inverters and pressurized storage tanks.
20. The device of claim 14, wherein the circulation means is a
centrifugal fan driven by a motor.
21. The device of claim 14, wherein the means for cooling the fluid
is the means for cooling the plate.
22. A method for chilling food products by impacting jets, in which
a fluid is cooled, a pressure P1 is applied to the fluid, the fluid
is forced to pass through holes in a plate and to impact the food
product to be chilled, wherein the temperature of the plate is
maintained at a temperature below about -80.degree. C. and/or P1 is
varied over time.
23. The method of claim 22, wherein the cold fluid is a cryogenic
fluid is selected from the group consisting of nitrogen, carbon
dioxide, oxygen, air, and mixtures thereof.
24. The method of claim 22, wherein the chilling method is a
deep-freezing method.
25. The method of claim 22, wherein the variation in pressure is a
notched sequence, the amplitude of which is a pressure difference
.DELTA.P between a normal operating value and a selected set value
that is lower or greater than the normal value, said pressure
difference .DELTA.P lying between 10 and 1000 Pa and the time for
which the variation in pressure is applied .DELTA.t lies between 1
and 60 s.
26. The device of claim 14, wherein: said at least a first plate
comprises first plate located above said moving belt and a second
plate located below said moving belt; each of said first and second
plates are provided with through-holes; the zone under pressure P1
is above said first plate or below said second plate; and the zone
under pressure P2 is between said first plate and said moving belt
or between said second plate and said moving belt.
27. The device of claim 14, wherein said means for cooling said at
least a first plate down to a temperature below about -80.degree.
C. is adapted to cool said at least a first plate down to a
temperature below -90.degree. C.
28. The device of claim 14, wherein said means for cooling said at
least a first plate down to a temperature below about -80.degree.
C. is adapted to cool said at least a first plate down to a
temperature below -100.degree. C.
29. The method of claim 22, wherein the temperature of the plate is
maintained at a temperature below about -90.degree. C.
30. The method of claim 22, wherein the temperature of the plate is
maintained at a temperature below about -100.degree. C.
31. The method of claim 25, wherein said pressure difference
.DELTA.P lies between 200 and 800 Pa.
32. The method of claim 25, wherein said pressure difference
.DELTA.P lies between 400 and 600 Pa.
33. The method of claim 25, wherein the time for which the
variation in pressure is applied .DELTA.t lies between 2 and 30
s.
34. The method of claim 25, wherein the time for which the
variation in pressure is applied .DELTA.t lies between 5 and 15 s.
Description
[0001] The present invention relates to industrial devices and
methods for chilling or deep-freezing food products.
[0002] The chilling of food products generally takes place by
convective exchange between a cold gas and the products. The use of
cryogenic fluids and fans is already known from manufacturers who
wish to deep-freeze foodstuffs.
[0003] Deep-freezing or chilling technology is based on the fact
that the products are chilled more quickly if they are subjected to
impacting jets of a cryogenic fluid.
[0004] These impacting jets are created by pressurizing the area
above a perforated plate, causing an increase in the speed of the
fluid at the holes of the plate. On the industrial scale, these
devices take the form of tunnels in which the pressurization above
a perforated plate is created by a means for circulating the gas,
for example a centrifugal fan, located above the belt on which the
food products to be chilled are arranged.
[0005] However, the presence of humidity in the enclosed space in
which the chilling takes place leads to the formation of frost and
to snow deposits when the temperature of the cold gas is below
0.degree. C. In cryogenic tunnels, the temperature can reach
-130.degree. C.
[0006] The humidity arises from the products which can become
partially dehydrated by the presence of humid air mixing with the
cold gas, in particular in the case of open-ended machinery such as
tunnels.
[0007] When the method of convection is based on the speeding up of
the cold gas when it passes through holes (which may be circular,
oblong, rectangular, etc.), the deposits of snow or ice crystals
tend to occur on the edges of these holes. Obstruction of the holes
to a greater or lesser degree results therefrom, and they can even
become completely blocked. Reducing the flow cross-section of the
holes modifies the flow-rate characteristics of the cold gas, which
adversely affects the chilling process and can even cause
malfunctions.
[0008] Patent application EP-1 621 830 discloses a means for
overcoming the frosting phenomenon by using mechanical vibrations
with the aid of a vibrator mounted on the plate that has the holes.
Other patent authors use heating systems to periodically defrost
frosted surfaces.
[0009] However, these means consume a lot of energy and are
difficult to implement.
[0010] The object of the present invention is a device and a method
for chilling food products, equipped with means for preventing the
clogging-up with frost of the holes forming the impacting jets,
without the use of mechanical vibration or heating.
[0011] To this end, the invention proposes a device for chilling
food products by impacting jets which consists of a tunnel
comprising [0012] a moving belt, [0013] at least one plate located
opposite (above or alternatively beneath) said moving belt and
provided with through-holes, and according to one of the preferred
embodiments at least two plates, an upper plate and a lower plate,
located parallel to each other on either side of said moving belt,
at least one plate, and preferably both plates, being provided with
through-holes, [0014] and at least one means for circulating a cold
fluid, said tunnel having [0015] a zone under pressure P1 above the
upper plate or plates and/or beneath the lower plate or plates,
[0016] and a zone under pressure P2 between the plate or plates and
the moving belt, [0017] the pressure P1 being greater than the
pressure P2, characterized in that it includes means that allow the
pressure to be varied in the zone under pressure P1 and/or means
for cooling the plate or plates down to a temperature below about
-80.degree. C., preferably below -90.degree. C., and more
preferably still below -100.degree. C., and for maintaining that
temperature.
[0018] The cold fluid can be cold air obtained by mechanical
refrigeration or alternatively a cryogenic fluid.
[0019] The cold fluid is preferably a cryogenic fluid chosen from
the group including, in particular, nitrogen, carbon dioxide,
oxygen, or air, and mixtures thereof.
[0020] The chilling device according to the invention is preferably
a device for deep-freezing food products. Deep-freezing is a means
of freezing food very quickly. This is the technique of choice on
the industrial scale when the foodstuffs are flat or small in size,
such as, for example, beefburgers, pizzas or diced bacon. The
heat-exchange surface area of these foodstuffs is large, and the
thickness small, which favors rapid freezing.
[0021] In the device according to the invention, the plate or
plates provided with through-holes are advantageously made from
food-grade stainless steel. These plates can be inclined and
disassembled to make it easier to clean them after operation.
[0022] Purely by way of example, the through-holes of the plate can
have different shapes and, in particular, can take the form of
cylinders, circles, elongated holes, trefoils or even cones with
beveled or rounded edges. The plates can be flat, V-shaped or even
corrugated.
[0023] In a conventional but non-restrictive manner, the means for
circulating the fluid is a centrifugal fan driven by a motor.
[0024] The means for varying the pressure in the zone under
pressure P1 and/or the means for cooling the plate or plates down
to a temperature below -80.degree. C. and for maintaining that
temperature make it possible to prevent the clogging-up with frost
of the holes in the plate without making the system more expensive
in terms of energy.
[0025] According to a particular embodiment of the invention, this
device is characterized in that the means for cooling the plate or
plates down to a temperature below -80.degree. C. and for
maintaining that temperature are chosen from the group including a
heat-exchange circuit attached to the plate, a plate that serves as
a heat exchanger (also referred to as a plate/heat exchanger), a
cold fluid bath on top of the plate or plates, and combinations
thereof.
[0026] Surprisingly and paradoxically, the inventors have found
that when the temperature of the plate is lowered to a temperature
below -80.degree. C., the ice crystals do not adhere to the edges
of the holes, thus preventing the holes from becoming clogged
up.
[0027] These cooling means are economical. Indeed, when the cooling
of the plates is effected by a heat exchanger, and according to a
preferred embodiment of the invention, the cryogenic fluid passing
through the heat exchanger is taken from the circuit for supplying
the chilling machinery. The cryogenic fluid contributes directly or
indirectly to the cooling of the fluid that is in contact with the
products.
[0028] These cooling means are easy to implement: the heat
exchanger attached to the plate can be a tube fixed to one or both
faces of the plate and within which a cold fluid circulates. The
heat exchangers preferably have a form that allows them to pass as
closely as possible to as many holes as possible, and thus to favor
the cooling of the plate around as many holes as possible.
[0029] According to a particular embodiment of the invention, the
heat exchanger attached to the plate has one or more passes
required for cooling as many through-holes as possible. Another
embodiment consists in using a material which is a good conductor
of heat for the plate, or which would be in contact with the plate
in order to cool the edge of the holes. This material would be
cooled locally by a cooling circuit.
[0030] Furthermore, this heat exchanger attached to the plate has a
form and a connection to the plate such that heat exchange is
favored. By way of example, the use may be envisaged either of a
weld of a form and made from materials that a person skilled in the
art will be capable of defining and/or of a thermal compound.
[0031] It is preferable that the plate is cooled optimally at the
through-holes and for as many holes as possible. The plate/heat
exchanger can thus be formed by two plates that may or may not have
baffles, for better distribution of the cold fluid. The use of
baffles makes it possible to prevent the fluid following preferred
channels, and thus promotes the cooling of as many holes as
possible.
[0032] According to an embodiment of the device according to the
invention where a bath of cold fluid is used as the means for
cooling the plate down to a temperature below -80.degree. C. and
for maintaining that temperature, the plate is equipped with edges
that are sufficiently high, with tubular holes and with a means for
regulating the level of the bath. Such a device can make it
possible to prevent the cold fluid from overflowing through the
through-holes and over the edges of the plate.
[0033] According to a particular embodiment, and with the aim of
further reducing the energy costs, the device can be designed in
such a way that the fluid which is stirred within the zone under
pressure P1 is cooled only in contact with the cold plate. In this
embodiment, the fluid arrives in the zone under pressure P1 at an
ambient temperature T1 and cools to a temperature T2 when it passes
through the through-holes of the plate which is at a temperature T3
below -80.degree. C., T2 lying between T1 and T3. The means for
cooling the fluid can thus be the means for cooling the plate.
[0034] The means for cooling the plate down to a temperature below
-80.degree. C. and for maintaining that temperature have the
advantage that they are easy to implement, in particular on
existing and inexpensive cooling devices, as a person skilled in
the art can simply swap conventional perforated plates with
perforated plates provided with heat exchangers.
[0035] According to another aspect of the invention, the device is
characterized in that the means for varying the pressure are chosen
from the group including frequency inverters and pressurized
storage tanks.
[0036] Varying the pressure in the zone under pressure P1 can be
effected, in a particular embodiment of the invention, by varying
the circulation rate of the centrifugal fan. If the circulation
rate of the centrifugal fan increases, the pressure in the zone
under pressure P1 increases. In this case, to obtain a variation in
the pressure in the zone under pressure P1, the speed of the motor
driving the centrifugal fan is varied according to controlled
proportions.
[0037] Another way of generating a variation in the pressure in the
zone under pressure P1 is to intermittently supply an additional
quantity of pressurized fluid to the zone under pressure P1. This
fluid can come from a pressurized tank connected to the zone under
pressure P1 by means for releasing the pressure of the tank which
are, for example, valves. The opening and closing of these
releasing means are activated so as to generate the desired
variation in pressure in the zone under pressure P1.
[0038] These two means for varying the pressure in the zone under
pressure have the advantage of being able to be used on existing
machinery for chilling foodstuffs.
[0039] The present invention also proposes a method for chilling
food products by impacting jets, in which [0040] a fluid is cooled,
[0041] a pressure P1 is applied to the fluid, [0042] the fluid is
forced to pass through holes in a plate and to impact the food
product to be chilled, characterized in that the temperature of the
plate is maintained at a temperature below about -80.degree. C.,
preferably below -90.degree. C. and more preferably still below
-100.degree. C., and/or in that the pressure P1 of said fluid is
varied over time.
[0043] According to a preferred embodiment of this method, the cold
fluid is a cryogenic fluid chosen from the group including, in
particular, nitrogen, carbon dioxide, oxygen, air, and mixtures
thereof.
[0044] The chilling method according to the invention is
advantageously a deep-freezing method.
[0045] The variation in the pressure P1 is preferably short and
with a small amplitude, which has the advantage of being
inexpensive in terms of energy and not requiring any significant
modification to the chilling device.
[0046] The variation in pressure is preferably a notched sequence,
the amplitude of which is a pressure difference .DELTA.P between a
normal operating value and a selected set value that is lower or
greater than the normal value, said pressure difference .DELTA.P
lies between 10 and 1000 Pa, in particular between 200 and 800 Pa
and preferably between 400 and 600 Pa, and the time for which the
variation in pressure is applied .DELTA.t lies between 1 and 60 s,
in particular between 2 and 30 s and preferably between 5 and 15
s.
[0047] The method of the invention is preferably implemented with
the device described above.
[0048] This variation in pressure can be achieved by varying the
rate at which the cold fluid is circulated in the zone P1 of the
device.
[0049] This variation in pressure can thus be caused by the brief
and sudden release of pressure coming from a pressurized tank
connected to the zone under pressure P1. This release of pressure
takes place when a release means such as, for example, a valve is
opened. The opening and closing of this pressure release means can
be automated.
[0050] The method according to the invention has the advantageous
feature of being able to be applied to existing chilling or
deep-freezing devices.
[0051] Other features and advantages of the invention will become
apparent on reading the following description. This description is
purely illustrative and must be read in conjunction with the
attached drawings, in which:
[0052] FIG. 1 is a cross-sectional view of a chilling tunnel,
[0053] FIG. 2 is a photograph of the underside of a lower plate
after the chilling device according to Example 1 has been
operating,
[0054] FIG. 3 is a drawing of part of the chilling device, of the
plate used in Example 2,
[0055] FIG. 4 is a photograph of the top side of the lower plate
after the device according to Example 2 has been operating,
[0056] FIG. 5 is a diagrammatic drawing of the operating mode used
in Example 3,
[0057] FIG. 6 is a photograph of the top side of the upper plate
after the device according to Example 3 has been operating,
[0058] FIGS. 7a, 7b, 8, 9a and 9b are drawings of means for cooling
the plate according to particular embodiments of the invention.
[0059] FIG. 1 is a cross-sectional view of a device for chilling by
impacting jets according to the prior art. This device consists of
a tunnel 1 within which is arranged a moving belt 2 which makes it
possible to move the foodstuffs to be deep-frozen or to be chilled,
which are arranged on said belt, from one end to the other of said
tunnel 1. Plates 3 are present parallel to each other on either
side of said moving belt. These plates 3 are provided with
through-holes 4 that allow a fluid to pass through. Two zones can
be distinguished within the tunnel 1. The first zone 5, termed the
zone under pressure P1, is defined by the walls of the tunnel 1,
the top side of the upper plate 3a, the underside of the lower
plate 3b and pressure zone separating elements 6. The second zone 7
is termed the zone under pressure P2 and is defined by the walls of
the tunnel 1, the underside of the upper plate 3a, the top side of
the lower plate 3b and the separating elements 6. A centrifugal fan
8 is placed in the upper part of the tunnel 1 and within the zone 5
under pressure P1. Its role is to circulate the fluid within the
zone 5 under pressure P1. The centrifugal fan is driven by a motor
9 preferably positioned outside the tunnel 1. Furthermore, a cold
fluid feed 10 is provided in the zone 5 under pressure P1.
[0060] When the device in FIG. 1 is operating, the cold fluid that
is supplied by the cold fluid feed 10 is stirred by the circulation
means (centrifugal fan 8 and motor 9). This circulation generates a
pressure P1 in the zone 5 under pressure P1 which subsequently
forces the cold fluid to pass through the through-holes 4 of the
plates 3 at a relatively high speed. At the outlet of the
through-holes 4 the fluid takes the form of impacting jets that
subsequently impact the foodstuffs arranged on the moving belt 2.
Once it has impacted the foodstuffs present on the moving belt, the
cold fluid then escapes via the zone 7 under pressure P2 which is
open to the outside. Of course P1 is greater than P2 during the
operation of the device, and P1 is equal to P2 when the device is
not running. If the tunnel 1 is located in a room at atmospheric
pressure, then P2 is also atmospheric pressure.
[0061] When the above-described device is operated in the presence
of humidity supplied by a vapor generator such as that described in
Example 1 below, it is observed, as can be seen in FIG. 2, that the
through-holes 4 of the plates 3 are clogged up by the formation of
frost. This phenomenon is representative of the actual phenomenon
that occurs when food products are chilled or deep-frozen on an
industrial scale. The residual humidity present in the tunnel and
the humidity from the foodstuffs cause the holes to become clogged
up, which means that the operators have to halt the device and
clean the plates and holes.
[0062] The invention proposes to attach means for preventing such
clogging-up to the known device for chilling foodstuffs.
[0063] In a first embodiment of the invention, such means can take
the form of means for cooling the plate down to a temperature below
-80.degree. C. and for maintaining that temperature, as illustrated
in FIG. 3 and in Example 2 below. FIG. 3 shows a drawing of a heat
exchanger 11 attached to a plate 3 with the aim of maintaining the
temperature at the through-holes 4 below -80.degree. C. This heat
exchanger 11 is provided with a cold fluid inlet 12 and a cold
fluid outlet 13. The heat exchanger has several passes 14 in order
to optimize heat exchange.
[0064] FIGS. 7a and 7b show other drawings of heat-exchange devices
attached to a plate. The cold fluid is caused to circulate in
proximity to the through-holes 4 of the plate 3 in a cold fluid
circuit 15. In these figures it can be clearly seen that the pipe
is fixed on the plate very closely to the edge of the holes and
that its cross-section is such that it allows maximum heat exchange
with the plate.
[0065] FIG. 8 shows another embodiment of the means for cooling the
plate down to a temperature below -80.degree. C. and for
maintaining that temperature. In this figure, a plate 3 with high
edges 16 and whose holes 4 are preferably tubular is arranged so as
to create a cold fluid bath 17. The cold fluid is thus unable to
pass through the through-holes 4.
[0066] A third embodiment of the means for cooling the plate down
to a temperature below -80.degree. C. and for maintaining that
temperature is illustrated in FIGS. 9a and 9b. These figures are
drawings of a heat exchanger incorporated into the plate. This heat
exchanger can be formed by two plates joined together at the
through-holes 4. A space between the two plates 15 permits the
circulation of the cold fluid that enters through a feed end 12 and
that leaves through an end 13 for extracting the cold fluid.
EXAMPLES
Example 1 (for Comparison)
Trial of the Deep-Freezing Device with No Anti-Clogging Means
According to the Invention
[0067] A device such as that described in FIG. 1 is used, which
has: [0068] a moving belt, [0069] two perforated plates, an upper
one and a lower one, that have circular through-holes with an 18 mm
diameter and spaced 104 mm apart, [0070] a distance of 7 cm between
the plate and the moving belt, [0071] a centrifugal fan driven by a
motor, [0072] gaseous nitrogen at -70.degree. C. as the cryogenic
fluid, supplied by a ramp located in the zone under pressure P1,
[0073] a water vapor generator equipped with a pipe, one end of
which is fixed to the center of the belt and directed toward the
gas recovery zone in order to artificially generate frost.
[0074] The vapor generator runs for about 4 hours from the
beginning of the operating cycle.
[0075] The temperature of the tunnel is maintained at -80.degree.
C. During operation, the pressure in the zone under pressure P1 is
measured by means of a manometer or pressure sensor placed in the
zone under pressure P1 of the lower plate and variations in the
pressure curve are observed, indicating partial blocking of the
holes. After 4 hours of operating, the plates are photographed
(lower plate seen from below in FIG. 2) and it is observed that the
plates are completely blocked by snow and that there is ice in the
center of the holes.
Example 2
Trial of the Deep-Freezing Device with the Cooling of the Plate as
an Anti-Clogging Means
[0076] The device in Example 1 is used, modified by fixing a heat
exchanger to the underside of the lower plate, which makes it
possible to maintain the temperature of the latter in the region of
-100.degree. C., a few centimeters away from the heat-exchange tube
during operation.
[0077] This heat exchanger, which is shown in FIG. 3, consists of
two copper tubes with a 14 mm diameter which are mounted in hairpin
fashion over two sets of 5 holes and welded to two copper plates
that are themselves fixed to the underside of the lower perforated
plate. Thermal compound ensures a better contact.
[0078] Liquid nitrogen at approximately -187.degree. C. is passed
through the heat exchanger, allowing the plate to be cooled
down.
[0079] The holes cooled by the heat exchanger are the holes in the
rows 4 and 5 and the lines 2 to 6 indicated in FIGS. 3 and 4.
[0080] The vapor generator is run throughout the operating cycle,
i.e. for 4 hours.
[0081] The pressure P1 is maintained at 550 Pa and the temperature
in the tunnel at -60.degree. C.
[0082] After 4 hours of operating, the top side of the lower plate
is photographed. The resulting photograph is shown in FIG. 4. In
this photograph it can be observed that the holes of the lower
plate closest to the heat exchanger are not blocked. These are the
holes in the rows 4 and 5 and the lines 2 to 6, i.e. the holes
whose edges are cooled by the heat exchanger.
Example 3
Trial of the Deep-Freezing Device with Pressure Variation as an
Anti-Clogging Means
[0083] The device in Example 1 is used and the pressure is varied
over time in the sequence shown in FIG. 5. The variation applied is
in the form of notches, the amplitude .DELTA.P of which between a
normal pressure value PN and a high pressure value PH is 500 Pa.
The time for which the zone under pressure P1 is subjected to the
pressure PH is .DELTA.t which corresponds to 10 s. The time between
two notches is 5 minutes in FIG. 5.
[0084] PN is chosen to be equal to 550 Pa and PH to be equal to
1330 Pa.
[0085] The temperature of the tunnel is maintained at -60.degree.
C. The vapor generator is run throughout the trial, i.e. for 4
hours.
[0086] After 4 hours of operating, the top side of the upper plate
is photographed (FIG. 6) and it is observed that a considerable
amount of snow has accumulated on the plate but that all the holes
have remained free.
* * * * *