U.S. patent application number 10/505719 was filed with the patent office on 2005-05-05 for method and apparatus for cooling and dehumidifying air.
Invention is credited to Paradis, Marc A..
Application Number | 20050091993 10/505719 |
Document ID | / |
Family ID | 27766177 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050091993 |
Kind Code |
A1 |
Paradis, Marc A. |
May 5, 2005 |
Method and apparatus for cooling and dehumidifying air
Abstract
A method and an apparatus for rapidly cooling and dehumidifying
air within a space. In this method, air to be cooled and
dehumidified is forced into a cooling zone including an evaporator
(101) having fins (103) forming air channels. The fins and the air
channels are preferably substantially vertical. Air is circulated
above method and apparatus for carrying out the same between the
space and the cooling zone in such a manner is that the evaporator
can be completely cleaned and sanitized in a few minutes. Since the
apparatus allows rapid shedding of any condensation off of the
evaporator, freeze-ups never occur. Defrosting is thus eliminated,
saving precious time and electrical energy. The above apparatus is
particularly adapted for rapidly cooling food.
Inventors: |
Paradis, Marc A.;
(Sainte-Foy, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
27766177 |
Appl. No.: |
10/505719 |
Filed: |
August 25, 2004 |
PCT Filed: |
February 26, 2003 |
PCT NO: |
PCT/CA03/00267 |
Current U.S.
Class: |
62/93 ; 62/285;
62/419 |
Current CPC
Class: |
F25D 17/067 20130101;
F25D 2317/0683 20130101; F25D 2317/0681 20130101; F25D 2400/28
20130101; F25D 17/062 20130101; F25D 2317/0411 20130101; F24F
3/1405 20130101; F25D 2400/22 20130101; B01D 53/265 20130101; F25D
17/06 20130101; F25D 21/14 20130101 |
Class at
Publication: |
062/093 ;
062/419; 062/285 |
International
Class: |
F25D 017/06; F25D
021/14 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2002 |
US |
60360015 |
Claims
1. A method for cooling and dehumidifying air within a space,
comprising the steps of: forcing said air to be dehumidified into a
cooling zone, said cooling zone including an evaporator plate
having a plurality of fins forming air channels; continuously
evacuating from said cooling zone droplets of condensed water
resulting from condensation; and circulating air within said
cooling zone in such a manner that said air circulates within said
air channels, said air being cooled and dehumidified by said
evaporator plate, the humidity within said air being condensed on
said evaporator plate.
2. A method according to claim 1, further comprising the following
step: preventing formation of a cold water layer on the surface of
said evaporator plate by rapidly removing said droplets of
condensed water from said surface of said evaporator plate.
3. A method according to claim 1, wherein said droplets of
condensed water are rapidly removed from said evaporator plate by
circulating said air along said air channels, and are evacuated
from said cooling zone before freezing.
4. A method according to claim 1, wherein said air channels are
being substantially vertical in such a manner that said air
circulates substantially vertically downward.
5. A method according to claim 1 wherein said fins are covered by a
hydrophobic coating.
6. An apparatus for cooling and dehumidifying air within a space,
comprising: a housing; at least one cooling zone located within
said housing, said at least one cooling zone having at least one
inlet in communication with said space, said at least one cooling
zone also having at least one outlet in communication with said
space; at least one fan for circulating air between said space and
said at least one cooling zone; and means located within said at
least one cooling zone for continuously evacuating droplets of
condensed water resulting from condensation, said at least one
cooling zone including at least one evaporator plate located
between said at least one inlet and outlet of said at least one
cooling zone, said at least one evaporator plate having a plurality
of fins forming air channels within which said air circulates.
7. An apparatus according to claim 6, wherein said air channels are
being substantially vertical in such a manner that said air
circulates substantially vertically downward.
8. An apparatus according to claim 6, wherein said fins are covered
by a hydrophobic coating.
9. An apparatus according to claim 6, wherein said fan is devised
to circulate air with enough velocity to remove said droplets of
condensed water from said at least one evaporator plate.
10. An apparatus according to claim 6, wherein said at least one
evaporator plate comprises an internal refrigerant circuit embedded
therein.
11. An apparatus according to claim 6, wherein each of said fins
has a base and a tip and said fins are thicker at the base than at
the tip.
12. An apparatus according to any one of claims claim 6 toll,
wherein said means for evacuating droplets of condensed water
comprises a drain.
13. An apparatus according to claim 6, wherein said means for
evacuating droplets of condensed water comprises a recipient for
collecting water.
14. A cooling apparatus for food comprising: an insulated housing;
at least one food zone located in said insulated housing for
receiving food to be cooled, said at least one food zone having at
least one inlet and at least one outlet; at least one cooling zone
located within said insulated housing, said at least one cooling
zone having at least one inlet in communication with said at least
one outlet of said at least one food zone, said at least one
cooling zone also having at least one outlet in communication with
said at least one inlet of said at least one food zone; at least
one fan for circulating air between said at least one food zone and
said at least one cooling zone; and means located within said at
least one cooling zone for continuously evacuating droplets of
condensed water resulting from condensation, said at least one
cooling zone including at least one evaporator plate located
between said at least one inlet and outlet of said at least one
cooling zone, said at least one evaporator plate having a plurality
of fins forming air channels within which said air circulates.
15. A cooling apparatus according to claim 14, wherein said air
channels are being substantially vertical in such a manner that
said air circulates substantially vertically downward.
16. A cooling apparatus according to claim 14, wherein said fins
are covered by a hydrophobic coating.
17. A cooling apparatus according to claim 14, wherein said fan is
devised to circulate air with enough velocity to remove said
droplets of condensed water from said at least one evaporator
plate.
18. A cooling apparatus according to claim 14, wherein said at
least one evaporator plate comprises an internal refrigerant
circuit embedded therein.
19. A cooling apparatus according to claim 14, wherein each of said
fins has a base and a tip and said fins are thicker at the base
than at the tip.
20. A cooling apparatus according to claim 14, wherein said means
for evacuating droplets of condensed water comprises a drain.
21. A cooling apparatus according to claim 14, wherein said means
for evacuating droplets of condensed water comprises a recipient
for collecting water.
22. A cooling apparatus according to claim 14, wherein the housing
comprises two sides opposite to each other, each of said sides
having one of said at least one food zone with said at least one
outlet of said one food zone located on top of it, each of said
sides also comprising one of said at least one cooling zone and at
least one opening located at a bottom of said at least one cooling
zone, said opening defining said inlet of said at least one food
zone and said outlet of said at least one cooling zone.
23. A cooling apparatus according to claim 22, wherein each of said
sides is provided with a plate defining a plenum located within
said at least one food zone, said plenum being in communication
with said at least one inlet of said food zone, each of said plates
being provided with a plurality of openings, the openings of each
of said plates at one end being offset with respect to the openings
of the same plate at the other end.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for rapidly
cooling and dehumidifying air. It also relates to an apparatus for
carrying out said method.
BACKGROUND OF THE INVENTION
[0002] The hospitality industry comprises over 300,000 hotels and 8
millions restaurants worldwide. It employs 60 millions people and
contributes to 950 billions US$ of the global economy. One of the
major challenges it now faces is a growing concern for health and
well-being. Indeed, a growing number of consumers want to be given
assurances about the quality of the food chain.
[0003] This concern is really not surprising, considering the high
rate of food-poisoning incidents occurring each year (33 millions
in the U.S.A., including 9,000 deaths).
[0004] Governments have thus stepped in and the food transformation
industry now finds itself with far more severe regulations for the
safe preparation, handling, cooking, conservation and distribution
of food. For example, in the United States, meat factories now have
to conform to severe standards imposed by HACCP (Hazard Analysis
Critical Control Points). The HACCP's regulations require that food
operators set-up a multi-step system designed to ensure food
safety. Rapidly cooling food immediately after the cooling process
is one of these essential steps in assuring proper food
quality.
[0005] The need for such rapid cooling systems results from the
fact that all food contains micro-organisms that are potentially
dangerous; Most of them are destroyed by the cooking process. But
those that survive (2% to 5%) can quickly regain their strength and
begin to proliferate if given favorable conditions, such as in the
critical temperature zone situated between 15.degree. C. and
45.degree. C. Some can even reproduce at the frantic speed of once
every 12 minutes this means that one surviving bacterium will
become one thousand bacteria after two hours, and one billion after
seven hours!
[0006] It is often recommended that two hours be the maximum
allowable cooling time. This way, food stays within the critical
zone for only a short period of time. Under such conditions, risks
of food poisoning are greatly reduced. The challenge is precisely
to cool down large quantities of food in less than two hours.
[0007] The market has responded to the challenge with several types
of rapid-cooling processes, one of them being called "quick
chilling", sometimes called "blast chilling", in which food is
cooled by a high-velocity flow of very cold air. The air
temperature within the cooling zone can go as low as -15.degree. C.
Standard-sized pans (20".times.12") having depths of 1", 2.5" or 4"
are used to contain the food. The process, better adapted to
smaller operations, is widely used.
[0008] Existing blast chillers have in common two major flaws.
First, they simply cannot be properly cleaned. Cooling fans, fan
motors, evaporator fins, etc., are practically impossible to clean
and sanitize. After a short operating period, micro-organisms start
proliferating on the various surfaces and are circulated onto the
food itself by the air flow. The second major design defect is that
evaporators will catch most of the humidity given off by the food,
condense it in the form of droplets, and freeze it as soon as the
evaporator's surface temperature falls below 0.degree. C. Once the
water freezes up, the air flow is partially blocked, which
lengthens the food-cooling process. The end result is that quick
chillers often have to be defrosted after each cooling cycle. Most
user's manuals recommend at least one defrost cycle per day. In
some apparatus, the defrosting is done simply by leaving the door
of the cooled space open while fans are running. This takes
precious time. In most cases, an electrical resistance element is
used for defrosting. This takes time and uses a lot of electrical
energy.
[0009] Standard blast chillers also are quite noisy. Not
surprising, considering the fact that an 80 kg unit usually has
several large axial fans to move the air around.
[0010] Since fan motors are located within the cooled space, the
heat energy given off by the motors, due to internal
inefficiencies, heats up the air which then has to be cooled down
by the evaporator.
[0011] The cooling of food and the dehumidification of air are very
closely related. Indeed, in order to lower the food temperature,
the air within the closed space where the food is placed must be
dehumidified because of the heat and mass transfer process
occurring between the food and the closed-space air. During this
process, the air becomes more and more humid and reaches a
saturation level. Once this saturation level is reached, the air
will not absorb anymore heat from the food until it looses some of
its water vapor content. With that in mind, one can assume
correctly that some of the previously mentioned drawbacks which
characterize conventional food-cooling apparatus will also be found
in other dehumidifying systems such as air-conditioners,
dehumidifiers, freezers, cold rooms, etc.
SUMMARY OF THE INVENTION
[0012] A first object of the present invention is to provide a
method for cooling and dehumidifying air capable of overcoming the
above mentioned drawbacks.
[0013] The method for cooling and dehumidifying air within a space
comprises the following steps:
[0014] forcing the air to be cooled and dehumidified into a cooling
zone, the cooling zone including an evaporator, the evaporator
having a plurality of fins forming air channels;
[0015] circulating air within the cooling zone in such a manner
that the air circulates within the air channels, the air being
cooled and dehumidified by the evaporator, humidity within the air
being condensed on the evaporator; and
[0016] evacuating, from the cooling zone, the droplets of condensed
water resulting from condensation.
[0017] Another object of the invention is to provide an apparatus
for carrying out the method: The apparatus for cooling and
dehumidifying air within a space comprises a housing and at least
one cooling zone located in the housing. The at least one cooling
zone has at least one inlet in communication with the space. The at
least one cooling zone also has at least one outlet in
communication with the space. The at least one cooling zone
includes at least one evaporator located between the at least one
inlet and outlet of the at least one cooling zone. The at least one
evaporator has a plurality of fins forming air channels. The
apparatus also comprises at least one fan for circulating air
between the space and the at least one cooling zone, in such a
manner that the air circulates within the air channels. The
apparatus also comprises means located in the at least one cooling
zone for evacuating droplets of condensed water resulting from
condensation.
[0018] Another object of the invention is to provide an apparatus
for cooling food. The apparatus comprises an insulated housing and
at least one food zone located within the insulated housing for
receiving food to be cooled. The at least one food zone has at
least one inlet and at least one outlet. The apparatus also
comprises at least one cooling zone located in the insulated
housing. The at least one cooling zone has at least one inlet in
communication with the at least one outlet of the at least one food
zone. The at least one cooling zone also has at least one outlet in
communication with the at least one inlet of the at least one food
zone. The at least one cooling zone includes at least one
evaporator located between the at least one inlet and outlet of the
at least one cooling zone. The at least one evaporator has a
plurality of fins forming air channels. The apparatus also
comprises at least one fan for circulating air between the at least
one food zone and the at least one cooling zone. The apparatus also
comprises means located in the at least one cooling zone for
evacuating droplets of condensed water resulting from
condensation.
[0019] One of the main advantages of the above apparatus for
carrying out the same is that the evaporator can be completely
cleaned and sanitized in a few minutes. Such substantially reduces
the risk of contamination normally present in conventional quick
chillers. The result is a longer period of safe food storage.
[0020] Moreover, since the previous apparatus allows rapid shedding
of any condensation off of the evaporator, freeze-ups never occur.
The icing and defrosting processes are thus eliminated, which saves
precious time and electrical energy.
[0021] In addition, the absence of ice improves the heat transfer
process between the air and the refrigerant, so that a smaller
compressor can be used.
[0022] The objects, advantages and other features of the present
invention will become more apparent upon reading of the following
non-restrictive description of a preferred embodiment thereof,
given for the purpose of exemplification only with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a front view of a cooling apparatus for food
according to the preferred embodiment of the invention, showing the
insulated housing.
[0024] FIG. 2 is a side view of the apparatus shown in FIG. 1.
[0025] FIG. 3 is a exploded perspective view of the apparatus shown
in FIG. 1.
[0026] FIG. 4 is a perspective view of the apparatus shown in FIG.
1, which shows features within the apparatus.
[0027] FIG. 5 is a front view of the cooling zones diametrically
opposed to each others.
[0028] FIG. 6 is a perspective view of the cooling zones
diametrically opposed to each others.
[0029] FIG. 7 is a top view of one of the cooling zones, showing
the fins and the air channels.
[0030] FIG. 8 is a front view of one the cooling zones shown in
FIG. 7.
[0031] FIG. 9 is a side view of one of the cooling zones shown in
FIGS. 7 and 8.
[0032] FIG. 10 is a front, cross-sectional view of one side of the
above apparatus showing the air flow within the cooling zone and
the food zone.
[0033] FIG. 11 is a front, cross-sectional view of the same
apparatus showing the opposite cooling zones and food zone.
[0034] FIG. 12 is a top plan view of the insulated ceiling.
[0035] FIG. 13 is a front elevational view of the insulated
ceiling.
[0036] FIG. 14 is a cross-sectional view taken along lines B-B of
the insulated ceiling shown in FIG. 12.
[0037] FIG. 15 is a cross-sectional view taken along lines A-A of
the insulated ceiling shown in FIG. 13.
[0038] FIG. 16 is a top perspective view of the insulated ceiling
shown in FIGS. 12 to 15.
[0039] FIG. 17 is a top plan view of the plate incorporating the
fan inlet.
[0040] FIG. 18 is a perspective view of the vertical plate
separating the cooling zone from the food zone.
[0041] FIG. 19 is a perspective view of a variant of the vertical
plate shown in FIG. 18, which contains a plurality of openings.
[0042] FIG. 20 is a side elevational view of the plate
incorporating the fan inlet shown in FIG. 17.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
[0043] FIGS. 1 and 2 are front and side elevational views of an
apparatus 1 according to a preferred embodiment of the invention,
which comprises an insulated housing 3, in which food may be
stored. FIG. 3 is an exploded view of the apparatus 1. Most of the
components of said apparatus are preferably made of stainless
steel, but plastic and aluminum could also be used.
[0044] As illustrated in FIGS. 4, 5 and 6, the apparatus according
to the preferred embodiment of the invention has two cooling zones
102, 104 each comprising one evaporator 101. Except where mentioned
otherwise, both sides of the unit are symmetrical. Evaporator size
may be approximately 74 cm wide, 56 cm high and 8 cm thick. Its
fins 103 may be 5 cm deep and are distant from one another by about
2.2 cm.
[0045] FIGS. 7 to 9 are showing evaporators 101 design featuring a
large plate having long, deep, thick and smooth fins 103, with
enough distance between them to create air channels 111 and permit
the circulation of large volume of air flow. Such a large distance
between fins 103 also provides easy cleaning. The air flow travels
along the evaporator 101, in between and along the fins 103. In
standard evaporators, the air normally flows perpendicular to a
bank of finned tube. While circulating within the air channels 111,
the air looses its humidity and heat contents.
[0046] Plates having fins are common in computers and the like, but
in such cases, it is used for heat dissipation, not for heat
absorption. The dissipation occurs through natural convection or
via a forced, perpendicular air flow generated by an axial fan
close to the plate. Moreover, in such cases, the fins do not serve
as air channels.
[0047] In standard evaporators, the air normally flows
perpendicularly to a finned tube, the fins themselves being very
thin, fragile and very close to one another. Humidity contained in
the air condenses on the tube itself. The water droplets resulting
from condensation freeze between the fins. This freezing process
takes up precious cooling energy, which reduces system efficiency.
The accumulated ice also reduces the available fin-to-air heat
transfer surface, which further reduces system efficiency. The
water freezing process continues until the passageway between fins
is completely blocked. The refrigeration system then has to be shut
down and a defrosting process has to be initiated, which takes up
precious time and requires electrical energy.
[0048] In FIG. 10, together with a vertical plate 115, said fins
103 form a large number of air channels 111 for the air to
circulate and be cooled. Each of said fins 103 has a base and a tip
and said fins 103 are thicker at the base than at the tip,
providing good heat-transfer efficiency. Because of their size,
shape and smooth surface, fins 103 are easy to hand clean and
sanitize, either with a rag, a special brush or even with a hot
water hose. This prevents bacterial growth. Preferably, the
distance between the fins is large enough to prevent droplets from
touching at the same time to both sides of the channel formed by
the fins, which would tend to improve adherence to surfaces and
subsequent freezing of the condensed water droplets. A distance
between fins of, say 6 mm or more, is recommended. Larger
distances, say 15 mm and up, may also be provided for easier
cleaning.
[0049] The evaporator can also provide some energy storage. Indeed,
after an initial pre cooling of the system, there is a
<<hold>> period during which the evaporator is kept at
about 0.degree. C. During this period, the mass of the evaporator
helps reducing the number of On-Off cycles of the refrigeration
system, improving its durability.
[0050] FIG. 10 shows the path of air flow in and out of a food zone
201, on the left-hand side of the unit. When cooled air leaves
evaporator 101 and arrives at the bottom of channel 123, droplets
of condensed water are separated from the air flow by making said
air flow turn 90.degree. and pass through an outlet 121 of the
cooling zone 102 punched in the lower part of said plate 115. The
heavy droplets, being unable to follow the same path because of the
gravitational force, end up in a transversal cavity 125 and into a
drain hole 141. Then, water is eventually drained outside of the
apparatus 1 through an opening 143. A recipient for collecting
water could also be used instead of a drain.
[0051] After passing through the outlet 121 of the cooling zone
102, the cold dry air is forced to turn upwards through another
90.degree. because of the presence of vertical plate 207. Said
plates 115, 207 form a plenum 209 inside which said air can go up
and be distributed into the food zone 201 via a plurality of
openings 205. Inside said food zone 201, the resulting horizontal
jets 203 of cold dry air are mixed (because of the well-known
entrainment effect) with the warmer, humid air above the pans 501.
The colder air flow circulating around the pans of hot food thus
picks up heat energy and humidity. The result is a gradual cooling
of the food through convection.
[0052] Each side of the unit has its own evaporator 101 and plenum
chamber 209, and both sides have symmetrical air flow paths, except
that the left-hand side openings 205 are offset with respect to the
openings 205 of the same plate at the other side. Said offsets are
chosen in such a way that the jets 203 directions alternate: for
example, below the bottom pan 501, there is a left-hand-side jet
203 direction, while above said bottom pan 501, there is a
horizontal, right-hand-side jet 203 direction.
[0053] The heated air is eventually pulled out from the food zone
201 by an outlet 211 of the food zone 201 by fan 401, pushed inside
plenum 129 and then through a horizontal passageway 127 located
above the food zone 201. Then, said air turns 90.degree. and goes
through a short, vertical passageway formed by plates 115 and 117,
before arriving at the evaporator 101 and down between vertical
fins 103 and plate 115, where a new cooling cycle begins.
[0054] The fan 401 is preferably of the radial or mixed flow type.
Both types of fans can be efficient and very silent. Both also
produce a greater pressure rise than the usual axial fans, which
results in a higher speed flow of air along the fins 103. This also
helps in providing a uniform air distribution inside the apparatus
1. One large radial fan rotating at a relatively low speed (may be
1125 RPM) is normally preferable: noise will be reduced and energy
saved.
[0055] In FIG. 7 to 10, the finned evaporators 101 are preferably
made of cast aluminum. They are cooled by an internal refrigerant
circuit, consisting of a coil 113 embedded in the evaporators 101
during the casting operation. Said evaporators 101 are part of a
common vapor-compression refrigeration system.
[0056] Now referring to FIG. 11, while fan 401 is located inside a
cold, insulated zone, its motor 405 is located outside of said
cooling zones 102, 104 above the insulated ceiling 301, its driving
shaft 403 going through a hole in the ceiling 301. The ceiling is
fabricated out of two vacuum/heat formed plastic plates, separated
by about 6 cm of urethane foam. Ceiling 301 and plate 303 provide
the walls for plenum 129. Also shown in FIG. 17 to 20, said plate
303 incorporates the fan inlet ring 305 and is hinged 133 to the
internal back wall of the apparatus 1.
[0057] The boundaries of said cooling zones 102, 104, appearing in
FIG. 11, are the insulated ceiling 301, the insulated vertical
walls 119 and the insulated floor 145. FIGS. 12 to 16 show the,
insulated ceiling 301.
[0058] FIGS. 17 to 20 show plates 115, 207, which form the
left-hand-side and the right-hand-side plenums 209, are hinged 131
to the internal back wall of the apparatus 1. This way, they can be
opened and closed like ordinary doors, for cleaning purposes, or
removed for repairs.
[0059] As mentioned earlier, in this apparatus 1, freeze ups cannot
occur since condensed humidity cannot accumulate on the evaporators
101. Indeed, getting rid of the condensed water droplets can be
facilitated in a number of ways: the evaporators 101 are installed
vertically; air channels 111 between fins 103 are also vertical;
air flows between fins 103, vertically from top to bottom; the air
velocity is high between fins 103 (may be 10 m/s.+-.5); the fins
103 are smooth; the fins 103 feature a hydrophobic coating such as
Teflon.
[0060] Because of these characteristics, gravity helps water
droplets to travel vertically down along the fins 103 and the air
flow also helps water droplets to travel vertically down along the
fins 103. The smoothing and hydrophobic coating of the fins 103
make the droplets slide down more easily along the fins 103.
[0061] Three plenums are built into the apparatus described above.
The first plenum 129 is located above food zone 201. Its function
is to ensure a uniform horizontal air distribution through the
evaporator fins 103, and thus a uniform cooling of the air. The
other two plenums 209 are located between vertical plates 115 and
117, on each side of the food zone 201. Their function is to ensure
a uniform horizontal and vertical distribution of cooled air in the
food zone 201. This, in turn, produces a uniform cooling of the
food everywhere inside the food zone 201.
[0062] Plenums always have to be as large as possible. But again, a
compromise has to be reached between plenum efficiency and global
unit size.
[0063] Even though plenums are a common tool in heating and cooling
systems, they are used here in a novel way, since they are
installed in cascade, i.e. air goes through two plenums on its trip
between the fan 401 and the food zone 201. Moreover, this is the
only unit where the air flow is split in two before going to the
evaporators. Finally, all three plenums can easily be opened and/or
dismantled for cleaning purposes, which is a first.
[0064] It has been found experimentally that most of the
water-vapor condensation occurs during the first part of the
food-cooling cycle, while the food surface temperature is
approximately above 10.degree. C. Consequently, if the evaporator
101 temperature is kept at, say, 1.degree. C. during that period,
no icing will occur on the evaporator 101 surface; the water
droplets will simply slide along said fins 103 and accumulate at
the bottom of the cooling zone where they will be collected by a
transversal cavity 125, and will be drained 143 to the outside of
the unit.
[0065] Control strategy also contributes to the elimination of
defrosting cycles, which is an important time and energy-saving
feature. Control of the evaporator 101 temperature can be obtained
in a number of ways. The most usual technique being the use of the
hot-gas-bypass technique, in which part of the flow of hot gases
from a compressor outlet are sent directly to the evaporator 101
without first going through a condenser. By regulating, via a
hot-gas-bypass valve (or HGBV), the quantity of gases going through
the bypass, one can control the evaporator 101 temperature.
[0066] It has also been found, however, that even when the
evaporator temperature is not kept under control during the cooling
process, very good results are still obtained, hardly any freezing
will occur on the plate. Most of the humidity has' already
condensed when the plate temperature gets below 0.degree. C. This
provides for much simpler controls.
[0067] As soon as the food surface temperature has dropped
approximately below 10.degree. C. (and/or the air temperature
within the food zone has dropped to 4.degree. C. approximately),
the evaporator 101 surface temperature can be allowed to drop to a
second set-point temperature of approximately -20.degree. C., with
no fear of evaporator-surface icing, since very little humidity is
then circulated.
[0068] As the food core temperature reaches the desired final set
point temperature, two methods can be used for ending the
rapid-cooling process to avoid the freezing of the food. One method
is to stop the compressor and let the evaporator 101 temperature
come back to the first set-point temperature of 1.degree. C., the
fan 401 still circulating the air. The other method is to keep the
compressor running, but use the HGBV to send hot refrigerant gas
into the evaporator 101 until it warm up to approximately 3.degree.
C. Then, after closing the HGBV, the system would let the system
run and come back to the first set-point temperature of 1.degree.
C.
[0069] From then on, the control system acts as a thermostat trying
to keep the air temperature at about 3.degree. C., just like in a
standard refrigerator. The core temperature will then slowly come
down from 10.degree. C. to 3.degree. C. Of course, all these set
points are adjustable.
Alternative Embodiments
[0070] Although the present invention has been explained
hereinabove by way of a preferred embodiment thereof, it should be
pointed out that any modifications to this preferred embodiment
within the scope of the appended claims is not deemed to alter or
change the nature and scope of the present invention.
[0071] Several alternative embodiments of the present invention can
be created. For example, a prototype unit according to the present
invention has been build. The unit has a nominal capacity of 40 kg
of solid food (e.g. meat, vegetables, pastry, etc.) and
accommodates up to 10 standard-size pans. The unit has two
evaporators. A refrigeration compressor has 1.5 hp, or about 25%
less hp than a refrigeration compressor in a conventional
chiller.
[0072] Another apparatus for cooling food according to the present
invention having a 16 kg food capacity has been designed, built and
tested, featuring a single vertical evaporator located vertically
on a right-hand side of a food zone. The evaporator, including its
fins, was 40 cm long, 50 cm high and 9 cm thick. The air flow was
generated by a single centrifugal or radial fan also located
vertically on the right-hand side of the food zone. In this
apparatus, air to be cooled is pushed by the fan through a thin,
wide passageway, through the top of the evaporator, and then down
along the evaporator, between its vertical fins. When cooled air
leaves the evaporator droplets of condensed water are separated
from the air flow by making said air flow turn 90.degree.. The
heavy droplets; being unable to follow the same path because of the
gravitational force, end up in a transversal cavity and into a
drain hole. The air flow then travel horizontally to the left
through a passageway and then up through a plenum, from which the
air is distributed into the food zone through openings for cooling
the food. The colder air flow circulating around the pans of hot
food thus picks up heat energy and humidity. The result is a
gradual cooling of the food through convection.
[0073] The preferred embodiment of the invention features a single
radial fan. However, provided some modifications are made to the
design of the unit, other types of fans could be used. Furthermore,
two or more fans could be used. There are advantages to using a
single, large fan, rotating at low speed, instead of two or more
smaller fans. Firstly, there is an significant cost reduction.
Secondly, a single fan results in an important noise level
reduction and in energy efficiency.
[0074] The apparatus for cooling food according to the present
invention has a fan, which motor is located outside of the cooling
zone, i.e. outside of the insulated housing. Several advantages are
thus provided. Firstly, the cooling zone can be completely washed
and sanitized using a water hose, without fear of electrical
shocks. Secondly, heat loss from the motor of the fan is not
transferred to the cooling zone, thus reducing the heat to be
removed from said cooling zone.
[0075] One or more evaporators can be used within the apparatus,
but in practice, one or two evaporators are preferred. Those
evaporators can be flat or curved. Even cylindrical ones are an
interesting possibility.
[0076] Tests have also been successfully performed with a vertical
evaporator having horizontal fins, the air then circulating
horizontally between the fins. In such a case, the air velocity
between fins had to be increased somewhat to between 5 and 15 m/s
approximately, in order for the droplets to be dragged towards the
drain.
[0077] Although long fins are preferred, shorter will do fine.
Also, the fin pitch (distance between fins) can be varied at will,
but there will always be a compromise to be reached between ease of
cleaning and heat transfer efficiency.
[0078] Instead of being cast, the evaporator can be made from
extruded aluminum profiles. In such a case, the front of the
evaporator featured the deep longitudinal fins while its back
featured a plurality of longitudinal grooves. The grooves featured
have, say a 4.5 mm radius and a circular shaped bottom. The coil,
fabricated using a plurality of straight copper tubes having, say a
7.8 mm-diameter, is designed to fit into the grooves. Proper
thermal contact between the copper coil and the wall of the groove
is first established by pouring hot liquid zinc into the groove.
Results were excellent.
[0079] A simpler and cheaper method is also possible: the diameter
of the straight copper tubes is chosen so that it closely fit into
the circular grooves. After being positioned into the grooves, the
tubes are partly flattened out using a press brake to establish a
very good mechanical and thermal contact between tubes and the
aluminum extrusion.
[0080] Evaporators can be made from any suitable material, using
any known fabrication process. They can be cooled by any suitable
primary or secondary refrigerant. For example, such finned
evaporators could be cooled using a circulating solution of glycol.
Even pure water can be used in some of the applications mentioned
below.
[0081] The cooling of the food is more efficient by controlling
parameters such as the food-core temperature, the evaporator
temperature and the air temperature within the insulated housing.
It should be mentioned, however, that even when controlled solely
with a food-core probe and an on/off thermostat, the system will
give very acceptable results. It will also work quite well with a
simple timer.
[0082] The present invention has several other applications. It
will be particularly useful in applications in which the circulated
air must both be cooled and dehumidified, which is the case in air
conditioners, air dehumidifiers, freezers, refrigerating rooms,
etc.
[0083] Another application of the invention concerns air
conditioners. In order for air conditioners to be efficient, they
have to cool the air quickly and remove humidity efficiently. To
ensure safety, they should also be very easy to clean. Otherwise,
users will neglect the cleaning task and micro-organisms will start
proliferating within the air circuit, especially in between the
closely-spaced fins of the evaporator, which are most of the time
filled with condensed water. These problems are very similar to
those facing the quick chiller designer. The present invention can
provide a solution to these efficiency and safety problems by
providing an apparatus that can be cleaned in a few minutes, while
conventional air conditioners simply cannot be cleaned
properly.
[0084] Moreover, since condensed-water droplets are quickly
eliminated from the evaporator surface, the heat transfer between
the air and the evaporator is much improved. This permitted a
slightly higher evaporating temperature of the refrigerant and thus
a better operating coefficient of performance (COP) and a larger
capacity of the system. Also, the quantity of water removed from
the air in time unit is appreciably higher. The use of a
centrifugal fan instead of the usual axial fan also gives an
important reduction in noise level of the unit.
[0085] Another application of the invention concerns air
dehumidifiers. In order for air dehumidifiers to be efficient, they
should remove as much humidity as possible from the air. To ensure
safety, they should also be vely easy to clean. Theses are problems
that can be solved by the present invention.
[0086] The present invention may also be used to condense water
vapour generated, for example, by the action of the sun on salty or
polluted water. The end product will then be potable water. After
minor modifications and the addition of components for storing the
condensed water, the invention will thus become an efficient
desalination plant or a water purification system. People in
regions around oceans or on tropical islands would welcome such a
technology.
[0087] Such a desalination plant (or water purification system)
could even be made very cheaply by eliminating the mechanical
refrigeration system altogether, replacing it with a continuous
salt water (or polluted water) circulation. This would work as long
as the available water is about 10.degree. C. (or more) colder than
the atmosphere. Moreover, the plates having a plurality of fins
forming air channels could be made out of formed thin sheet metal
or even out of thin thermoformed plastic sheets. One possible
design for the finned plates would be assembling two of the formed
sheets back to back, the cold water circulating between the two
finned sheets, preferably from bottom to top, while the flow of air
on the outside, between fins, would preferably be vertically
downward. The flow of air would be generated by a fan of any
available type.
[0088] In all the preferred and alternative embodiments, it could
be interesting to monitor operational parameters such as the
evaporator temperature, the air temperature once it leaves the
evaporator, the cooled-space air temperature. However, tests have
shown that not monitoring these parameters did not have an
important effect on the efficiency of the apparatus. Monitoring the
various parameters is however recommended for security reasons or
to improve the durability of the components of the apparatus.
[0089] Of course, in the case of the blast chiller, the food-core
temperature becomes an important parameter that can be monitored in
order to indicate to the refrigeration system when to stop the
rapid-cooling process. The evaporation and condensation pressures
also are important parameters that one might like to monitor, in
order to avoid operating conditions that would decrease the life of
the costly compressor.
[0090] In the above mentioned simplified desalination plant, there
would be no real need for monitoring any of the operating
parameters, except maybe the salt water flow.
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