U.S. patent application number 13/903315 was filed with the patent office on 2013-12-19 for oven for cooking foods.
The applicant listed for this patent is Electrolux Professional S.p.A.. Invention is credited to Paolo CESCOT, Riccardo FURLANETTO, Michele SIMONATO.
Application Number | 20130333684 13/903315 |
Document ID | / |
Family ID | 46168288 |
Filed Date | 2013-12-19 |
United States Patent
Application |
20130333684 |
Kind Code |
A1 |
CESCOT; Paolo ; et
al. |
December 19, 2013 |
OVEN FOR COOKING FOODS
Abstract
An oven (100) comprising an oven chamber (105) for the cooking
of foods, heating means (125) for heating the oven chamber, and a
vapor exhaust system (155) for treating vapors produced in the oven
chamber during a food cooking process. The vapor exhaust system
comprises: a first region (405) in fluid communication
(160,165,170) with the oven chamber so as to receive vapors exiting
the oven chamber and wherein the vapors are de-moisturized and
cooled down; and a second region (410) downstream the first region
and wherein the de-moisturized and cooled down vapors exiting the
first region are mixed to hot dry air (140) before being exhausted
to the outside ambient.
Inventors: |
CESCOT; Paolo; (Cordenons,
IT) ; FURLANETTO; Riccardo; (Musile di Piave, IT)
; SIMONATO; Michele; (Udine, IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Electrolux Professional S.p.A. |
Pordenone |
|
IT |
|
|
Family ID: |
46168288 |
Appl. No.: |
13/903315 |
Filed: |
May 28, 2013 |
Current U.S.
Class: |
126/21A |
Current CPC
Class: |
F24C 15/2007
20130101 |
Class at
Publication: |
126/21.A |
International
Class: |
F24C 15/20 20060101
F24C015/20 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2012 |
EP |
12169715.5 |
Claims
1. An oven (100) comprising an oven chamber (105) for the cooking
of foods, heating means (125) for heating the oven chamber, and a
vapor exhaust system (155) for treating vapors produced in the oven
chamber during a food cooking process, characterized in that the
vapor exhaust system comprises: a first region (405) in fluid
communication (160,165,170) with the oven chamber so as to receive
vapors exiting the oven chamber and wherein the vapors are
de-moisturized and cooled down; and a second region (410)
downstream the first region and wherein the de-moisturized and
cooled down vapors exiting the first region are mixed to hot dry
air (140) before being exhausted to the outside ambient.
2. The oven of claim 1, wherein said first region extends
vertically.
3. The oven of claim 1, wherein in the first region a tortuous path
for the vapors is formed.
4. The oven of claim 3, wherein said tortuous path is a duct
comprising a plurality of baffles (177;1077).
5. The oven of claim 4, wherein at least one of said baffles is
hollow and run through a heat-exchange fluid (1005).
6. The oven of claim 3, wherein a coolant liquid feeding device
(415,420) is associated with said first region, arranged for
feeding a coolant liquid into the first region for cooling down the
vapors.
7. The oven of claim 6, wherein said coolant liquid feeding device
comprises at least one liquid feeding nozzle (415) adapted to spray
coolant liquid into said first region in a nebulized form.
8. The oven of claim 6, wherein said coolant liquid feeding device
is arranged to cause the coolant liquid to enter into the first
region proximate to a top side thereof.
9. The oven of claim 6, wherein said coolant liquid feeding device
is connected to an activator adapted to selectively activate said
coolant liquid feeding device for selectively feeding the coolant
liquid.
10. The oven of claim 6, wherein at least a temperature sensor
(425) is associated with the first region, arranged for sensing the
temperature of the vapors entering into the vapors exhaust
system.
11. The oven of claim 10, wherein said coolant liquid feeding
device is selectively activated based on a sensed temperature of
the vapors sensed by said temperature sensor.
12. The oven of claim 1, comprising at least an air propeller (180)
associated with said vapor exhaust system and configured for
promoting the exit of vapors from the oven chamber and their flow
through the vapor exhaust system.
13. The oven of claim 12, wherein said air propeller comprises an
axial or radial fan arranged at the exit of the second region.
14. The oven of claim 12, wherein said air propeller is selectively
activatable.
15. The oven of claim 1, wherein said hot dry air comprises air
exploited to cool down at least one among a door (120) of the oven
and/or air exploited to cool down internal oven parts subjected to
heat up during the oven operation.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to cooking apparatuses for
cooking or baking foods, of the type having a cooking chamber, like
cooking ovens, both for domestic and for professional use. Within
this general scope, the present invention relates to improvements
in respect of the treatment of vapors produced in the cooking
chamber while cooking food. In the rest of the description, with
"cooking" it will be intended any kind of preparation of foods by
heat, including baking.
[0003] 2. Overview of the Relevant Known Art Related to the
Invention
[0004] Cooking apparatuses comprise a cooking chamber in which food
is cooked. During the cooking process, vapors forms in the cooking
chamber of the cooking apparatus. Vapors are predominantly in the
form of steam and consist of water vapor for the most part; in
addition, they also contain oils and fats, which are present in the
form of aerosols or else in liquid form. Other components may also
be contained therein.
[0005] Vapors are created during the cooking process through the
vaporization of water that is naturally contained in the foods
being cooked; in addition, however, vapor that is deliberately fed
into the cooking chamber of the apparatus (either by way of an
external steam generator or else by direct vaporization of water
inside of the hot cooking chamber) for some types of cooking also
contributes to the creation of vapors. This water vapor is
intentional and is important for certain aspects of the cooking
process.
[0006] When fat-containing foods or fat-containing cooking products
are cooked at high temperatures, the aforementioned oil and fat
aerosols are additionally created.
[0007] Vapors in excess must be exhausted to the outside, otherwise
an undesired vapor pressure would build up within the cooking
chamber. Some conventional cooking apparatuses have an exhaust air
opening from which steam or vapors can escape into the room air,
but this can lead to a strong accumulation of moisture and heat in
the room air in the surroundings of the cooking apparatus and in
the entire kitchen premises; moreover, the room is also dirtied by
the oil and fat aerosols contained in the escaped vapors. All this
is totally unsatisfying.
[0008] US 2011/072983 discloses a cooking apparatus having a
cooking chamber, wherein the vapors created in the cooking chamber
are removed with a vapor outlet channel. A vapor condensation
device brings the vapors into contact with a cooling liquid. The
vapor condensation device has a container, in which a liquid bath
is located. The vapor outlet channel carries the vapors out of the
cooking chamber into the container of the vapor condensation
device. There, the vapors are brought into contact with the liquid
from the liquid bath and thereby partially condensed. Furthermore,
a device drain is provided. The container of the vapor condensation
device has a vapor guide element, that guides the vapors through
one or more channels in the container; the vapor guide element is
configured such that one wall of the wall surfaces of the channel
or channels is formed by the surface of the liquid bath in the
container.
[0009] EP 691513 discloses an oven having a cooking interior
enclosed by a door and casing. There is a heater and floor drain
removing condensate. Above the oven, an extraction hood removes
water vapor, via a fan. Preferably, a suction duct connects the
extraction hood to drain. A hood intake is immediately above the
door opening and leads to a condenser integral with the hood; this
has vertical baffle surfaces defining a steam channel. The base
surfaces slant toward the extraction duct connection.
SUMMARY OF THE INVENTION
[0010] The Applicant has tackled the problem of devising a solution
for providing an oven with an improved treatment of vapors produced
in the cooking chamber while cooking or baking food.
[0011] According to an aspect of the present invention, there is
provided an oven comprising an oven chamber for the cooking of
foods, heating means for heating the oven chamber, and a vapor
exhaust system for treating vapors produced in the oven chamber
during a food cooking process.
[0012] The vapor exhaust system comprises:
[0013] a first region in fluid communication with the oven chamber
so as to receive vapors exiting the oven chamber and wherein the
vapors are de-moisturized and cooled down; and
[0014] a second region downstream the first region and wherein the
de-moisturized and cooled down vapors exiting the first region are
mixed to hot dry air before being exhausted to the outside
ambient.
[0015] Therefore, the oven has, associated with the first region,
means for de-moisturize and cool down vapors received from the oven
chamber, and, associated with the second region, means for mixing
hot dry air to the vapors exiting the first region.
[0016] Preferably, said first region extends vertically.
[0017] Advantageously, in the first region a tortuous path for the
vapors is formed.
[0018] Said tortuous path may be a duct comprising a plurality of
baffles.
[0019] In an embodiment, at least one of said baffles is hollow and
is run through a heat-exchange fluid.
[0020] Advantageously, a coolant liquid feeding device may be
associated with said first region, arranged for feeding a coolant
liquid into the first region for cooling down the vapors.
[0021] Said coolant liquid feeding device may comprise at least one
liquid feeding nozzle adapted to spray coolant liquid into said
first region in a nebulized form.
[0022] Said coolant liquid feeding device may for example be
arranged to cause the coolant liquid to enter into the first region
proximate to a top side thereof.
[0023] Said coolant liquid feeding device is preferably connected
to an activator adapted to selectively activate said coolant liquid
feeding device for selectively feeding the coolant liquid.
[0024] Preferably, at least a temperature sensor is associated with
the first region, arranged for sensing the temperature of the
vapors entering into the vapors exhaust system.
[0025] Said coolant liquid feeding device may be selectively
activated based on a sensed temperature of the vapors sensed by
said temperature sensor.
[0026] The oven may comprise at least an air propeller associated
with said vapor exhaust system and configured for promoting the
exit of vapors from the oven chamber and their flow through the
vapor exhaust system.
[0027] Said air propeller may comprise an axial or radial fan
arranged at the exit of the second region.
[0028] Said air propeller may be selectively activatable.
[0029] Advantageously, said hot dry air comprises air exploited to
cool down at least one among a door of the oven and/or air
exploited to cool down internal oven parts subjected to heat up
during the oven operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The following detailed description of exemplary and
non-limitative embodiments of the present invention will help to
render the above as well as other features and advantages of the
present invention clearer. For its better intelligibility, the
following description should be read while referring to the
attached drawings, wherein:
[0031] FIG. 1 schematically shows an oven according to an
embodiment of the present invention, in cross-section according to
a vertical plane orthogonal to a front of the oven;
[0032] FIG. 2 schematically shows the oven of FIG. 1 in cross
section according to a plane parallel to the front of the oven,
indicated in FIG. 1 as II-II;
[0033] FIG. 3 schematically shows the oven of FIG. 1 and FIG. 2 in
cross section according to a horizontal plane, indicated in FIG. 2
as III-III;
[0034] FIG. 4 is a schematization of a vapor exhaust tower of the
oven of FIG. 1 to FIG. 3, with indicated different vapor control
regions;
[0035] FIG. 5 is a schematization similar to FIG. 4, with notations
used in a mathematical analysis of the different vapor control
regions;
[0036] FIG. 6 is a simplified Carrier diagram or psychrometric
chart (specific humidity in ordinate versus temperature in
abscissa), of the humid air for a first control region of the vapor
exhaust tower;
[0037] FIG. 7 is a complete Carrier diagram of the humid air for a
first control region of the vapor exhaust tower;
[0038] FIG. 8 is a complete Carrier diagram of the humid air for a
second control region of the vapor exhaust tower;
[0039] FIG. 9 is a schematic flowchart of an exemplary way of
operation of the oven according to an embodiment of the present
invention, and
[0040] FIG. 10 shows, in a schematical view similar to that of FIG.
5, a vapor exhaust tower according to another embodiment of the
present invention.
DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION
[0041] Referring to FIG. 1, FIG. 2 and FIG. 3, an oven according to
an embodiment of the present invention is schematically depicted,
in three cross-sectional views (as explained in the Brief
description of the drawings).
[0042] The oven, denoted as a whole 100, comprises an oven chamber
105 (cooking chamber) wherein the foods to be cooked/backed are to
be introduced for being cooked.
[0043] The oven chamber 105 is a delimited region of space within
an oven cabinet 110 having a front opening 115 for
inserting/removing the foods, which is selectively closable by an
oven door 120, hinged to the oven cabinet 110 so as to be movable
by an oven user between a closed position (the one depicted in FIG.
1) adapted to close the front opening 115, and an open position
(not depicted in the drawings) in which the oven chamber 105 is
accessible through the front opening 115.
[0044] Inside the oven chamber 105, heating elements 125, for
example one or more resistive heaters, are provided, energizable
for heating up the oven chamber environment.
[0045] Preferably, an air propeller 130 is also provided inside the
oven chamber 105, operable (possibly in a selective way, depending
on a food cooking program selected by the oven user) to cause air
circulation within the oven chamber 105 so as to better distribute
the air heated up by the heating elements 125 and achieve a more
uniform temperature inside the oven chamber 105.
[0046] It is pointed out that although in FIG. 1 the heating
elements 125 are depicted as arranged at the periphery of the air
propeller 130, this is merely an example; the heating elements
might be arranged in different locations, and/or additional heating
elements might be arranged in different locations of the oven
chamber 105, e.g. at the top and/or at the bottom thereof.
[0047] The oven door 120 is designed so to have an air gap 135
formed therein, for the passage of cooling air 140 having the
function of cooling the external panel 145 (usually of glass or
other transparent material) of the oven door 120, in order to keep
such external panel at a temperature sufficiently low not to be
harmful for the oven user. The oven door cooling air 140 is for
example taken in from the outside ambient, e.g. through an opening
formed at the bottom of the door 120.
[0048] In a space formed between the oven chamber 105 and the walls
of the oven cabinet 110, thermally-insulating material 150 is
preferably provided, in order to avoid heat dissipation from inside
the oven chamber 105 to the outside ambient, and at the same time
reducing the temperature of the cabinet walls when the oven 100 is
operating.
[0049] Albeit not shown, it is intended that the oven 100 may
comprise several other components, like for example a steam and/or
microwaves generator(s) to be supplied to the oven chamber 105 for
performing some particular kinds of cooking processes.
[0050] According to the present invention, the oven 100 is equipped
with a system for exhausting vapors that are produced within the
oven chamber 105 when foods are cooked. Advantageously, the vapor
exhaust system is integrated, embedded in the structure of the oven
100.
[0051] In the exemplary embodiment of the present invention here
presented, the vapor exhaust system comprises a vapor exhaust tower
155 which is accommodated at the rear of the oven 100, e.g.
approximately at the center or more or less proximate to a corner
of the oven cabinet 110, like the rear-left corner (looking the
oven 100 frontally), as shown in the drawings (it is intended that
the position of the vapor exhaust tower 155 is not at all
limitative for the present invention).
[0052] The vapor exhaust tower 155 according to an embodiment of
the present invention will be hereafter described with the help of
the principle schematic of FIG. 4.
[0053] The concept at the basis of the vapor exhaust tower 155
according to the present invention is the (selective) superposition
of three physical phenomena: a de-humidification, de-hydration,
moisture condensation of the vapors coming from the oven chamber
105 (phenomenon A); a cooling of the vapors (phenomenon B), and an
adiabatic intermixing of the vapors with relatively hot and dry air
(phenomenon C).
[0054] In an embodiment of the present invention, phenomena A and B
may take place concurrently, as depicted in the schema of FIG. 4,
in a bottom section 405 of the exhaust tower 155; phenomenon C
takes place in a top section 410 of the exhaust tower 155.
[0055] Referring back to FIG. 1 and FIG. 2, the exhaust tower 155
is, at a bottom thereof (i.e., at a bottom of the bottom section
405), fluidly connected to a vapor discharge duct 160 that, having
an inlet 165 preferably at the bottom of the oven chamber 105
(e.g., approximately in the central position), runs, preferably
declining, towards an outlet 170 opening approximately at the
bottom of the exhaust tower bottom section 405.
[0056] The bottom of the exhaust tower bottom section 405 is also
fluidly connected to a liquid drainage 175 (only part of which is
shown), which, when the oven is installed in a kitchen, is
connected to a kitchen water drainage spigot.
[0057] In the exhaust tower bottom section 405, a tortuous,
sinuous, serpentine, labyrinthic path is formed, for example, as in
the example depicted in the drawings, by means of properly offset
baffles 177.
[0058] In a vertical position along the exhaust tower bottom
section 405, vertical position that in the shown embodiment is
approximately at the top of the exhaust tower bottom section 405,
an inlet 415 for a cooling liquid is advantageously present, which
for example may comprise a nozzle for spraying cooling water that
is selectively fed, for example under control of a valve 420, e.g.
an electrovalve, controlled by an oven control unit (shown only
schematically in FIG. 4 and denoted 423). The nozzle preferably is
adapted to spray water in a nebulized form, i.e. as very small
droplets. The cooling water is for example fed via a piping that,
when the oven is installed, is coupled to a water outlet spigot of
the kitchen.
[0059] Preferably, a temperature sensor 425 may be provided in a
vertical position along the exhaust tower bottom section 405, for
example approximately at the bottom of the exhaust tower bottom
section 405, proximate to the outlet of the vapor discharge duct
160. When present, the temperature sensor 425 is in signal
connection with the oven control unit 423 to communicate thereto
the readings about the temperature of the vapors exiting the oven
chamber 105. The oven control unit 423 may for example be
programmed so as to activate the electrovalve 420 when the
temperature of the vapors exiting the oven chamber 105 (and
entering the vapor exhaust tower 155) reaches a pre-set
temperature, which may also depend on the specific cooking
programme selected by the oven user.
[0060] At a top thereof, the exhaust tower bottom section 405 has
an opening 430 leading into the exhaust tower top section 410,
which is for example more or less vertically aligned to the
underlying bottom section 405. The exhaust tower top section 410
has one or more inlets for relatively hot and dry air, which is
introduced so as to be intermixed to the de-moisturized vapor that,
after exiting the oven chamber 105, has passed through the exhaust
tower bottom section 405. The exhaust tower top section 410 may
include a first hot air inlet 433, in the shown example located
more or less midway the exhaust tower top section 410, for
admitting hot air that has been taken in from the outside ambient
for cooling oven parts like the motor for the air propeller 130,
among which there may be the exhaust tower bottom section 405, and
a second hot air inlet 435, in the shown example located more or
less at the top of the exhaust tower top section 410, for admitting
the oven door cooling air 140, that, after passing in the gap 135
formed in the oven door 120, passes in a gap between the oven
chamber 105 and a top panel of the oven cabinet 110.
[0061] A fan 180 is advantageously provided at the top of the
exhaust tower top section 410. The fan 180, that preferably is
selectively activatable by the oven control unit 423, creates a
depression inside the exhaust tower 155 and sucks the vapor and the
cooling fluxes inside it. Downstream the fan 180, i.e. on top of
it, the exhaust tower 155 opens into the external ambient or into a
discharge duct.
[0062] For the sake of explanation of its principle of operation,
the system for exhausting vapor according to an embodiment of the
present invention can advantageously be regarded as made up by two
so-called "control regions". A first control region is the exhaust
tower bottom section 405, where the phenomena A and B take place. A
second control region is the exhaust tower top section 410, where
the phenomenon C takes place.
[0063] In the first control region 405, the labyrinthic path formed
by the baffles 177 allows compactizing the vapor exhaust tower 155,
thereby reducing its space occupation.
[0064] When the electrovalve 420 is open and the nozzle 415 sprays
cooling water, thanks to the presence of the baffles 177 a sort of
waterfall-type filter is formed, that at each fall condenses the
vapors exiting the oven chamber 105 and filters them by retaining
the particles of fat transported by the vapors.
[0065] The baffles 177 allows the cooling water, sprayed by the
nozzle 415, to have more time and surface area available for
enhancing heat exchange between the sprayed cooling water and the
vapors coming from the oven chamber 105. In addition, the presence
of the baffles 177 enables the sprayed cooling water to release at
least part of the heat absorbed by the vapors to the baffles 177
and the walls of the vapor exhaust tower 155 (this heat can then be
dispersed outside the vapor exhaust tower 155, and may
advantageously contribute to heating up the air that is then
introduced into the exhaust tower top section 410 through the first
air inlet 433). Concurrently, the injected cooling water cools down
the baffles 177, on which the moisture contained in the vapors can
condensate.
[0066] The injection of the cooling water by the nozzle 415 in the
form of nebulized droplets, creates a sort of fog inside the first
control region 405, that contributes to the increase of the thermal
exchange area and at the same time reduces the power and resources
(water) consumption and the generated noise.
[0067] In the second control region 410, the heat released by the
vapors passing through the first control region (exhaust tower
bottom section) 405 as well as by the operation of the oven (e.g.,
the motor of the air propeller 130) is caused to be absorbed by the
cooling air (that enters into the vapor exhaust tower 155 through
the first hot air inlet 433), thereby increasing the temperature
thereof. This allows to reduce the relative humidity of the cooling
air (at constant specific humidity), thereby increasing the
capacity of the cooling air of absorbing the residual humidity of
the vapors exiting the first control region 405, when they are
mixed with the cooling air: in fact, by increasing the temperature
of the cooling air, the specific humidity of the flow of intermixed
vapors and cooling air remains substantially the same, while the
relative humidity decreases; the capability of absorbing the
humidity contained in the flow of vapors is thus increased.
[0068] FIG. 5 schematizes again the vapor exhaust system according
to an embodiment of the present invention, and should be referred
to as an aid for the following analytical analysis of the energy
and mass balance. Hereafter, for the purpose of notation, it is
assumed that the normal to the control regions is directed as
exiting the surface delimiting the control regions. The mechanical
work is regarded as positive if exiting the control regions (i.e.,
when directed as the normal to the control regions) whereas the
heat is regarded as positive if entering into the control regions
(i.e., when opposite to the normal). The energy and mass flows are
regarded as positive if directed as the normal to the control
regions.
[0069] The vapor exhaust system according to an embodiment of the
present invention can be regarded as comprised of three "control
volumes" or "control regions": the first and second control regions
405 and 410 introduced in the foregoing, and a third control region
made up by the union of the first and second control regions 405
and 410.
[0070] For the purpose of notation, hereinafter the terms {dot over
(m)} denote mass flow rates of dry air; the subscript "steam"
denotes the flows containing a certain amount of vapor. In any
case, the term in is to be intended as referred to the fraction of
dry air present in a flow, whereas the fraction of humid air
present in a flow is denoted as {dot over (m)}x, with x denoting
the specific humidity. The terms with subscript "engine" or "door"
refer to the flux of cooling air of the engine of the air propeller
130 (entering into the vapor exhaust tower 155 through the inlet
opening 433) and, respectively, of the flux 140 of the cooling air
of the oven door (entering into the vapor exhaust tower 155 through
the opening 435).
[0071] Let: [0072] r.sub.0 be the water vaporization heat (water
vaporization enthalpy), and [0073] c.sub.p, c.sub.v constants.
[0074] Then:
x = m vapour m air , .phi. = m vapour m saturation ;
##EQU00001##
where x denotes the specific humidity and .phi. denotes the
relative humidity, and where the mass flows rates {dot over
(m)}.sub.steam and {dot over (m)}.sub.steam2 of dry air entering
and exiting the first control region 405 (equal to each other,
since as mentioned above the mass flow rates are referred to the
fraction of dry air) are defined as {dot over (m)}.sub.a:
{dot over (m)}.sub.a={dot over (m)}.sub.steam={dot over
(m)}.sub.steam2
[0075] The energy and mass balance equations for the first control
region 405 are:
Q.sub.1.sup.-={dot over (m)}.sub.a(h.sub.steam2-h.sub.steam)+{dot
over (m)}.sub.H2O.sub.outh.sub.H2O.sub.out-{dot over
(m)}.sub.H2Oh.sub.H2O Eq. (1)
{dot over (m)}.sub.H2O.sub.out={dot over (m)}.sub.H2O+{dot over
(m)}.sub.a(x.sub.steam-x.sub.steam2) Eq. (2)
where the first equation (Eq. (1)) relates to energy (the suffix
"-" for the heat Q.sub.1 means that the heat exits the control
region; the symbols h denote the enthalpy), and the second equation
(Eq. (2)) relates to the mass of water. The term
(x.sub.steam-x.sub.steam2) is due to the condensation of
moisture.
[0076] In order to solve the first equation Eq. (1) for the energy,
let FIG. 6 be considered, showing a simplified Carrier diagram for
humid air. The transformation "1.fwdarw.2" marked on the diagram
can be decomposed into the two transformations "1.fwdarw.3" (latent
contribution) and "3.fwdarw.2" (sensible contribution).
[0077] Considering that:
m . ( h 2 - h 1 ) = m . [ ( .differential. h .differential. t ) x
.DELTA. t + ( .differential. h .differential. x ) t .DELTA. x ] Eq
. ( 3 ) ##EQU00002## h=h.sub.a+xh.sub.v Eq. (4)
where h.sub.a denotes the enthalpy of a dry air flow and h.sub.v
denotes the enthalpy of a flow of humid air, being:
h.sub.a=c.sub.pat
h.sub.v=r.sub.0+c.sub.pvt
it follows that Eq. (4) becomes:
h=c.sub.pat+x(r.sub.0+c.sub.pvt) Eq. (5)
and then, by derivation of Eq. (5):
( .differential. h .differential. t ) x = c pa + x c pv (
.differential. h .differential. x ) t = r 0 + c pv t
##EQU00003##
[0078] The energy balance equation (Eq. (1)) can thus be developed
as:
Q.sub.1.sup.-={dot over
(m)}.sub.a(c.sub.pa+x.sub.steam2c.sub.pv)(t.sub.steam2-t.sub.steam)+{dot
over
(m)}.sub.a(r.sub.0+c.sub.pvt.sub.steam)(x.sub.steam2-x.sub.steam)+{d-
ot over (m)}.sub.H2O.sub.outh.sub.H2O.sub.out-{dot over
(m)}.sub.H2Oh.sub.H2O Eq. (6)
[0079] By defining:
c pu = ( .differential. h .differential. t ) x = c pa + x c pv Eq .
( 7 ) and ##EQU00004## h v = r 0 + c pv t Eq . ( 8 )
##EQU00004.2##
the following developments are possible (introducing Eq, (2), Eq.
(7) and Eq. (8) in Eq. (6)):
Q.sub.1.sup.-={dot over
(m)}.sub.ac.sub.pu(t.sub.steam2-t.sub.steam)+{dot over
(m)}.sub.ah.sub.v(x.sub.steam2-x.sub.steam)+{dot over
(m)}.sub.H2O(h.sub.H2O.sub.out-h.sub.H2O)+{dot over
(m)}.sub.ah.sub.H2O.sub.out(x.sub.steam-x.sub.steam2)
Q.sub.1.sup.-={dot over (m)}.sub.a.DELTA.h.sub.sensible+{dot over
(m)}.sub.a.DELTA.h.sub.latent+{dot over
(m)}.sub.H2O(h.sub.H2O.sub.out-h.sub.H2O)+{dot over
(m)}.sub.ah.sub.H2O.sub.out(x.sub.steam-x.sub.steam2)
Q.sub.1.sup.-=Q.sub.s.sup.-+Q.sub..lamda..sup.-+{dot over
(m)}.sub.H2O(h.sub.H2O.sub.out-h.sub.H2O)+{dot over
(m)}.sub.ah.sub.H2O.sub.out(x.sub.steam-x.sub.steam2) Eq. (9)
where:
[0080] Q.sub.1.sup.- is the heat flow at the walls;
[0081] Q.sub.s.sup.-, Q.sub..lamda..sup.- are the fractions of
sensible and latent energies of the flow of humid air;
[0082] {dot over (m)}H2O(h.sub.H2O.sub.out-h.sub.H2O) is the Energy
fraction of the liquid;
[0083] {dot over
(m)}.sub.ah.sub.H2O.sub.out(x.sub.steam-x.sub.steam2) is the Energy
fraction of the condensed water.
[0084] FIG. 7 depicts the complete Carrier diagram of the humid air
for the first control region 405. The point on the diagram
indicated as 1 corresponds to the state of the flow of vapors upon
entering into the first control region; the point indicated as 2
corresponds to the state of the flow of vapors upon exiting the
first control region. As can be appreciated looking at the diagram,
the state of the flow of vapors exiting the first control region is
rather close to the state indicated as s on the diagram,
corresponding to the saturation condition (with relative humidity
.phi. equal to 100%): thus, by spraying cooling water into the
first control region, the temperature of the vapors decreases, and
the relative humidity .phi. increases, but the specific humidity x
decreases (because the flow of vapors exiting the first control
region has a lower content of humidity).
[0085] Coming to the second control region 410, FIG. 8 depicts the
respective humid air Carrier diagram. The point 2 on the diagram
represents the starting state of the flow of vapors upon entering
into the second control region (it corresponds to the point 2 on
the Carrier diagram of FIG. 7).
[0086] The balance equations are:
m . door h door + m . engine h engine + m . steam 2 h steam 2 = m .
final h final == ( m . door + m . engine + m . steam 2 ) h final Eq
. ( 10 ) m . door x door + m . engine x engine + m . steam 2 x
steam 2 = m . final x final == ( m . door + m . engine + m . steam
2 ) x final Eq . ( 11 ) ##EQU00005##
where Eq. (10) is the energy balance equation and Eq. (11) is the
mass balance equation.
[0087] Dividing the two equations above for {dot over
(m)}.sub.final it follows:
h final = m . door m . final h door + m . engine m . final h engine
+ m . steam 2 m . final h steam 2 ##EQU00006## x final = m . door m
. final x door + m . engine m . final x engine + m . steam 2 m .
final x steam 2 ##EQU00006.2##
[0088] The state of the flow of vapors, in the second control
region, moves from point 2 to point 4, which represents the state
of the flow of vapors exiting the second control region. Points 5
and 6 represent the states of the flows of hot and dry air entering
into the second control region and that are mixed with the flow of
vapors: both are characterized by a low relative humidity
.phi.).
[0089] The third control region is the union of the first and
second control regions 405 and 410. The energy and mass balance for
the third control region can thus be obtained from the above
equations. The result is that the variables related to the common
surfaces to the first and second control regions are eliminated,
i.e. {dot over (m)}.sub.steam2h.sub.steam2, and {dot over
(m)}.sub.steam2x.sub.steam2 ({dot over (m)}.sub.steam2={dot over
(m)}.sub.a).
[0090] At the end, the flow of vapors exiting the second control
region has a relatively low content of humidity.
[0091] FIG. 9 is a simplified flowchart illustrating a possible way
of operation of the oven 100 according to an embodiment of the
present invention.
[0092] When the oven 100 is started, the oven control unit 423
reads the operation selected by the oven user (block 905). The oven
control unit 423 then decides whether or not the oven user has
selected and started a cooking operation (decision block 910). If
the oven user has not decided to start a cooking operation (exit
branch N of decision block 910), the operation flow jumps back to
block 905. If instead the oven user has selected and started a
cooking operation (exit branch Y of decision block 910), the oven
control unit 423 obtains information about the type of cooking
selected by the oven user (block 915).
[0093] Then, depending on the type of cooking selected by the oven
user, the oven control unit 423 decides whether or not the air
propeller 180 is to be activated (block 920). If yes, the air
propeller 180 is activated, if not, the air propeller 180 is kept
off.
[0094] Still based on the type of cooking selected by the oven
user, the oven control unit 423 determines (block 921) at which
pre-set temperature of the vapors entering the vapor exhaust tower
155, the electrovalve 420 is to be activated to enable the intake
of cooling water; such determination made by the control unit 423
may be carried out exploiting a database of parameters database,
from which the oven control units 423 picks at which pre-set
temperature of the vapors entering the vapor exhaust tower 155.
Then, by exploiting the readings of the temperature sensor 425, the
oven control unit 423 monitors the temperature of the vapors
leaving the oven chamber 105 (block 923). In particular, the oven
control unit 423 checks if such temperature is over the pre-set
intervention temperature (block 925).
[0095] Until the temperature of the vapors leaving the oven chamber
105 and entering into the vapor exhaust tower 155 remains below the
pre-set intervention temperature (exit branch N of decision block
925), the oven control unit 423 checks whether the cooking process
is terminated (decision block 930): if the oven control unit 423
determines that the cooking process is terminated (exit branch Y of
decision block 930), the oven control unit 423 checks (decision
block 931) if the electrovalve 420 is currently open: in the
affirmative case (exit branch Y of decision block 931) the
electrovalve 420 is closed (block 933); after closing the
electrovalve 420 (or leaving it closed, if it was already
closed--exit branch N of decision block 931), the oven control unit
423 checks (decision block 935) whether the fan 180 is running in
the affirmative case (exit branch Y of decision block 935), the fan
180 is left running for a predetermined time after the end of the
cooking process, whereas if the fan 180 is not running (exit branch
N of decision block 935) the oven control unit 423 activates the
fan 180 (block 940) for a predetermined time. The operation flow
then jumps back to block 905. If the oven control unit 423
determines that the cooking process has not terminated yet (exit
branch N of decision block 930), the oven control unit 423 checks
whether the electrovalve 420 is activated (decision block 943): in
the negative case (exit branch N of decision block 943), the
operation flow returns to block 923, where the oven control unit
423 obtains a new reading of the temperature sensor 425; if instead
the oven control unit 423 assesses that the electrovalve 420 is
activated (exit branch Y of decision block 943), the oven control
unit 423 de-activates the electrovalve 420 (block 945) and then the
operation flow returns to block 923.
[0096] Let now be supposed that the temperature of the vapors
leaving the oven chamber exceeds the pre-set temperature (decision
block 925, exit branch Y): the oven control unit 423 activates the
electrovalve 420 (block 950); cooling water thus starts to be
sprayed by the nozzle 415 into the exhaust tower bottom section
405, to cool the vapors exiting the oven chamber 105.
[0097] The oven control unit 423 then determines whether the
cooking process has terminated (decision block 955): if not (exit
branch N of decision block 955), the operation flow jumps back to
block 923 (where the oven control unit 423 obtains a new reading of
the temperature sensor 425; if instead the oven control unit 423
determines that the cooking process has terminated (exit branch Y
of decision block 955), the oven control unit 423 obtains (through
the temperature sensor 425) the temperature of the vapors entering
into the vapor exhaust tower 155 (block 960), and then the oven
control unit 423 checks whether the temperature of the vapors
exceeds the pre-set intervention temperature (decision block 965):
until the vapors temperature stays above the pre-set intervention
temperature (exit branch Y of decision block 965), the electrovalve
420 is kept open, and the oven control unit 423 continues to
monitor the vapor temperature. When the vapor temperature falls
below the pre-set intervention temperature (exit branch N of
decision block 965) the electrovalve 420 is closed (block 933) and
the same operations described above (blocks 935 and 940) are
performed. The operation flow returns to block 905.
[0098] In other words, the injection of cooling water into the
exhaust tower bottom section 405 (i.e., into the first control
region of the vapor exhaust system) is selectively enabled based on
an assessment of the temperature of the vapors that leaves the oven
chamber 105 and enters into the vapor exhaust tower. Also the
activation of the fan 180 is selective, depending on the cooking
process.
[0099] The vapor exhaust system according to the described
embodiment of the present invention comprises a sinuous, tortuous,
labyrinthic vapors conduit arranged vertically, into which cooling
water can (selectively) be injected. The tortuous shape of the
conduit, thanks to the depression generated by a fan downstream the
first control region (in the shown example, the fan 180) allows
exploiting the inertia of the particles of vapor/fat, pushing them
against the baffles 177 (in particular, against the first ones,
proximate to the bottom of the exhaust tower bottom section 405).
The spray of nebulized cooling water allows capturing the finest
particulate (and this effect is also promoted by the baffles 177
proximate to the top of the exhaust tower bottom section 405, which
are cooled down by the water spray).
[0100] Experimental trials carried out by the Applicant have shown
that the temperature of the vapor flow exiting the vapor exhaust
system according to the described embodiment of the present
invention, also in critical operating conditions (oven chamber
temperature set to 250.degree. C. and 100% of humidity), did not
exceed 30.degree. C. at a relative humidity of 25% (with 19.degree.
C. of ambient air temperature).
[0101] In FIG. 10 there is depicted, schematically as in FIG. 4, a
vapor exhaust tower according to a slightly different embodiment of
the present invention; components, parts and elements that are
identical, similar or equivalent to those described in connection
with the previous embodiment are denoted with same reference
numerals. A difference of the embodiment of FIG. 10 compared to the
previous embodiment resides in that at least part (one, more than
one, possibly all) of the baffles 177, like the baffles 1077
visible in the figure, are hollow at their interior and arranged to
be run through by a relatively cold heat-exchange fluid 1005 (e.g.,
liquid, like water), which receives heat released from the vapors
passing through the first control volume 405. In this way, the heat
released by the vapors leaving the oven chamber can be at least
partly collected by the heat-exchange fluid, instead of being only
dissipated.
[0102] Another difference in the embodiment of FIG. 10 compared to
the previous embodiment is the different position of the nozzle 415
(which in this embodiment is not at the top of the first control
region) and of the temperature sensor 425 (which in this embodiment
is not at the bottom of the first control region). In particular,
differently from the previous embodiment, in this embodiment the
nozzle 415 is associated to a lower portion of the bottom section
405 with respect to the temperature sensor 425.
[0103] In FIG. 10 just one opening in the exhaust tower top section
410 is shown; this single opening may schematize the two openings
433 and 435 of the previous embodiment, but it might also be
possible that through such single opening both of the two cooling
air fluxes enter into the vapor exhaust tower. In still other
embodiments, one of the two cooling air fluxes might be absent.
[0104] Also with the vapor exhaust tower of the embodiment of FIG.
10, the oven 100 may operate as described in connection with the
previous embodiment (flowchart of FIG. 9).
[0105] In the foregoing, exemplary embodiments of the present
invention have been presented and described in detail. Several
modifications to the described embodiments, as well as alternative
ways of practicing the invention are conceivable, without departing
from the protection scope defined by the appended claims.
* * * * *