U.S. patent application number 12/735592 was filed with the patent office on 2011-01-13 for fluid microjet system.
This patent application is currently assigned to Novaltec Sarl. Invention is credited to Miroslaw Plata.
Application Number | 20110005737 12/735592 |
Document ID | / |
Family ID | 39523541 |
Filed Date | 2011-01-13 |
United States Patent
Application |
20110005737 |
Kind Code |
A1 |
Plata; Miroslaw |
January 13, 2011 |
FLUID MICROJET SYSTEM
Abstract
A device for generating fluid micro streams comprises a body
portion with a fluid supply cavity therein and a plurality of fluid
micro channels interconnecting the fluid supply cavity with an
external outlet face of the body portion, the body portion being
formed from a plurality of stacked plates, said micro channels
being formed at interfaces of at least certain of said stacked
plates. The micro channels have an oblong cross-sectional profile
over a certain section leading to the outlet face, with a major
width that is greater than two times a minor width thereof, where
the minor width is less than 200 um. The device can be used in
apparatus for freezing of food, cooling a gas or inducing a
chemical reaction between a liquid and a gas.
Inventors: |
Plata; Miroslaw; (Vetroz,
CH) |
Correspondence
Address: |
BAKER & DANIELS LLP
300 NORTH MERIDIAN STREET, SUITE 2700
INDIANAPOLIS
IN
46204
US
|
Assignee: |
Novaltec Sarl
Vetroz
CH
|
Family ID: |
39523541 |
Appl. No.: |
12/735592 |
Filed: |
February 2, 2009 |
PCT Filed: |
February 2, 2009 |
PCT NO: |
PCT/IB2009/050406 |
371 Date: |
July 30, 2010 |
Current U.S.
Class: |
165/166 ;
62/1 |
Current CPC
Class: |
F25D 3/11 20130101; B21B
45/0233 20130101; C21D 1/667 20130101; F28F 2260/00 20130101; F28F
13/06 20130101 |
Class at
Publication: |
165/166 ;
62/1 |
International
Class: |
F28F 3/08 20060101
F28F003/08; F25D 3/11 20060101 F25D003/11 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 2, 2008 |
EP |
08001981.3 |
Claims
1-21. (canceled)
22. A device for generating fluid micro streams comprising a body
portion with a fluid supply cavity therein and a plurality of fluid
micro channels interconnecting the fluid supply cavity with an
external outlet face of the body portion, the body portion being
formed from a plurality of stacked plates, said micro channels
being formed at interfaces of at least certain of said stacked
plates, characterised in that the stacked plates include a first
set of microchannel forming plates and a second set of spacer or
sealing plates interleaved between the first set of plates, and in
that said micro channels have an oblong cross-sectional profile
over a certain section leading to the outlet face, with a major
width that is greater than two times a minor width thereof, where
the minor width is less than 200 .mu.m.
23. Device according to claim 22, wherein the minor width of the
micro channels is less than 50 .mu.m.
24. Device according to claim 22, wherein the major width is
greater than three times the minor width.
25. Device according to claim 22, wherein the micro channels in
adjacent microchannel forming plates are offset in a direction
orthogonal to a plate stacking direction.
26. Device according to claim 22, wherein the density of micro
channels is greater than 10 micro channels per cm.sup.2.
27. Device according to claim 22, wherein the micro channels have a
non-constant width, the width being larger towards the input side
and narrower towards the outlet face.
28. Device according to claim 22, wherein the first set of plates
comprises slits entirely traversing the thickness of the plates,
the slits forming the microchannels.
29. Device according to claim 28, wherein the stacked plates
comprise a central cavity, whereby the central cavities of the
second set of plates are configured to overlap ends of the slits in
the first set of plates.
30. Device according to claim 22, wherein the first set of plates
are made of a material that is different to a material from which
the second set of plates are formed.
31. Device according to claim 22, wherein the thickness of the
plates of the first set is different to the thickness of the plates
of the second set.
32. Apparatus for rapid freezing of food stuffs and other
perishable goods, comprising a conveyor system, a cryogenic fluid
supply system, and one or more devices for generating cryogenic
fluid micro streams installed along the conveyor system, each fluid
micro stream device comprising a body portion with a fluid supply
cavity therein connected to the cryogenic fluid supply system and a
plurality of fluid micro channels interconnecting the fluid supply
cavity with an external outlet face of the body portion, the body
portion being formed from a plurality of stacked plates, said micro
channels having minor widths less than 200 .mu.m and being formed
at interfaces of at least certain of said stacked plates.
33. Apparatus according to claim 32, wherein the conveyor system
comprises a mesh conveyor belt and wherein devices for generating
cryogenic fluid micro streams are arranged on opposite sides of the
conveyor belt.
34. Apparatus according to claim 32, wherein the cryogenic fluid is
liquid nitrogen.
35. Apparatus according to claim 32, wherein the micro channels
have an oblong cross-sectional profile over a certain section
leading to the outlet face, a major width of the channel being
greater than two times a minor width thereof, where the minor width
is less than 200 .mu.m.
36. Apparatus according to claim 35, wherein the stacked plates
include a first set of microchannel forming plates and a second set
of spacer or sealing plates interleaved between the first set of
plates.
37. Apparatus for cooling a gas or inducing a chemical reaction
between a liquid and a gas, comprising: a chamber with a gas inlet
and a gas outlet configured for flow of said gas through the
chamber, and one or more fluid micro stream devices configured for
generating liquid micro streams in the chamber through the gas,
each fluid micro stream device comprising a body portion with a
fluid supply cavity therein connected to a fluid supply system and
a plurality of fluid micro channels interconnecting the fluid
supply cavity with an outlet face of the body portion, the body
portion being formed from a plurality of stacked plates, said micro
channels having minor widths less than 200 .mu.m and being formed
at interfaces of at least certain of said stacked plates.
38. Apparatus according to claim 37, wherein the stacked plates
include a first set of microchannel forming plates and a second set
of spacer or sealing plates interleaved between the first set of
plates, and in that said micro channels have an oblong
cross-sectional profile over a certain section leading to the
outlet face, with a major width that is greater than two times a
minor width thereof, where the minor width is less than 200
.mu.m.
39. Apparatus for chemical reactions on liquid metals comprising a
fluid micro stream device comprising a body portion with a fluid
supply cavity therein connected to a fluid supply system and a
plurality of fluid micro channels interconnecting the fluid supply
cavity with an outlet face of the body portion, the body portion
being formed from a plurality of stacked plates, said micro
channels having minor widths less than 200 .mu.m and being formed
at interfaces of at least certain of said stacked plates, wherein
the liquid metal is supplied as the fluid for generating fluid
micro streams and the device is immersed in a reaction medium, in
particular a reaction gas.
40. Apparatus according to claim 39, wherein the stacked plates
include a first set of microchannel forming plates and a second set
of spacer or sealing plates interleaved between the first set of
plates, and in that said micro channels have an oblong
cross-sectional profile over a certain section leading to the
outlet face, with a major width that is greater than two times a
minor width thereof, where the minor width is less than 200
.mu.m.
41. Apparatus for degassing liquid metals, comprising a fluid micro
stream device comprising a body portion with a fluid supply cavity
therein connected to a fluid supply system and a plurality of fluid
micro channels interconnecting the fluid supply cavity with an
external outlet face of the body portion, the body portion being
formed from a plurality of stacked plates, said micro channels
having minor widths less than 200 .mu.m and being formed at
interfaces of at least certain of said stacked plates, wherein the
fluid micro stream device is immersed in the liquid metal and a
degassing medium, such as an inert gas, is supplied as the fluid
for generating fluid micro streams.
42. Apparatus according to claim 41, wherein the stacked plates
include a first set of microchannel forming plates and a second set
of spacer or sealing plates interleaved between the first set of
plates, and in that said micro channels have an oblong
cross-sectional profile over a certain section leading to the
outlet face, with a major width that is greater than two times a
minor width thereof, where the minor width is less than 200 .mu.m.
Description
[0001] The present invention relates to a process and device for
generating a plurality of fluid microjets.
[0002] A device with multiple fluid microjets is described in U.S.
Pat. No. 5,902,543 for cooling an article. The device comprises a
plurality of micro channels with diameters from 30 to 100 .mu.m
formed as grooves in annular plates that are stacked one against
the other so as to form a plurality of micro channels between
adjacent plates, the cooling liquid being supplied through a
central opening of the circular plates. This allows a dense
arrangement of very fine jets of cooling liquid to be projected
onto the surface of the article to be cooled, resulting in a well
controlled and efficient cooling.
[0003] Although the above-mentioned microjet cooling system has a
high cooling efficiency compared to many other conventional
systems, the pressure drop through the micro channels for creating
the microjets is quite high and the desire to have essentially
laminar flow limits the velocity of the microjet. Manufacturing of
the stacked circular plates with grooves is also quite costly.
[0004] There is a continuous need for more efficient and effective
cooling systems.
[0005] In certain cooling applications, such as metal quenching, a
high degree of uniformity of cooling over or through the article is
desired to minimize the generation of internal stresses.
[0006] The use of fluid microjets may also be envisaged for
applications that are not limited to cooling alone, such as for
heating, degassing various liquids such as molten metals, cooling
of combustion gases, and chemical reactions between the microjets
and a medium onto which they are sprayed.
[0007] A fluid jet nozzle for blowing air with a wide target area,
for use in the textile field, is disclosed in US 2006/0186229. The
nozzles are formed by cut-outs in a pair of shims with the cut-outs
in the upper shim being offset with respect to the cut-outs in the
lower shim such that the nozzle head is provided with two layers of
rectangular shaped nozzles. Each nozzle layer requires a separate
gas inlet i.e. there are gas inlets into the nozzle head on opposed
outer sides of the pair of stacked shims. Such an arrangement
allows generation of a thin substantially planar wide air jet, but
is not appropriate for a nozzle jet system with a large surface
area or a plurality of nozzle layers greater than two since it is
not designed for stacking more than two shims. Such a nozzle system
is also not well adapted for generating high pressure liquid jets
in view of the pour sealing between the pair of stacked shims due
to leakage between the cut-outs and the interface between the two
shim plates. Such a nozzle arrangement would not be appropriate for
example for implementation in a liquid microjet system as described
in the above-mentioned document U.S. Pat. No. 5,902,543.
[0008] An object of this invention is to provide a device for
generating a plurality of fluid microjets that is compact, and that
has a high uniformity of treatment and a high efficiency in terms
of contact between the fluid and an article or medium to be
treated.
[0009] It would be advantageous to provide a fluid microjet device
that is compact and cost effective to manufacture.
[0010] It would be advantageous to provide a fluid microjet device
that minimizes pressure loss for generating the microjets.
[0011] It would be advantageous to provide a fluid microjet device
that is economical on fluid usage.
[0012] It would be advantageous to provide a fluid microjet device
that is able to generate a high density of very fine microjets of
essentially laminar flow, at high speed.
[0013] Other objects of this invention are to provide apparatus's
implementing fluid jets for: [0014] (i) cooling an article, liquid,
or gas very rapidly and with a high efficiency and uniformity;
[0015] (ii) for inducing an efficient chemical reaction between a
gas and a liquid; [0016] (iii) for efficient degassing of liquid
metals.
[0017] Another object of this invention is to provide a microjet
cooling device that enables rapid freezing of articles, for example
for cryogenic freezing of processed food.
[0018] Objects of this invention have been achieved by providing a
micro stream device according to claim 1.
[0019] Disclosed herein is a device for generating fluid micro
streams comprising a body portion with a fluid supply cavity
therein and a plurality of fluid micro channels interconnecting the
fluid supply cavity with an external outlet face or plurality of
external outlet faces of the body portion, the body portion being
formed from a plurality of stacked plates, said micro channels
being formed at interfaces of at least certain of said stacked
plates, wherein said micro channels have an oblong cross-sectional
profile over a certain section leading to the outlet face with a
major width that is greater than two times a minor width thereof,
where the minor width is in the range of 1 to 200 .mu.m.
[0020] The stacked plates include a first set of microchannel
forming plates and a second set of spacer or sealing plates
interleaved between the first set of plates. Advantageously, the
alternating first and second plates enable the stacked plates to
have excellent sealing of the microchannels as well as improving
the ease of manufacturing microchannels with low resistance (e.g.
polished) surfaces to reduce flow resistance and thus the pressure
required to generate a given number of fluid jets for a specified
surface area. The laminar flow properties and velocity of the jets
are thus also improved especially at critical subsonic or
supersonic velocities. The surface properties of the stacked plates
may be optimized not only by manufacturing techniques, but also by
the choice of materials, depending on the application.
[0021] Advantageously, the oblong cross-sectional profile of the
micro stream improves efficiency of treatment of an article or
medium with respect to the conventional microjets that have a
cross-section approximately square or circular, the oblong microjet
having a greater surface area for a given laminar or turbulent flow
rate.
[0022] The micro channels may advantageously be arranged such that
their long axes are essentially parallel and essentially orthogonal
to a direction of relative movement of an article or medium to be
treated with respect to the device.
[0023] In a preferred embodiment, cross-section of micro channels
at the outlet have a major width greater than three times the minor
width, where the minor width is preferably less than 100 .mu.m,
more preferably less than 50 .mu.m. In a preferred embodiment, the
distance between adjacent micro channels in a direction of stacking
of the plates is preferably less than 10 mm. Preferably the
distance between adjacent micro channels in the same plane is 0,5
to 10 mm. Advantageously the density of micro channels in the
device according to this invention may be greater than 4 micro
channels per cm.sup.2, preferably more than 10 micro channels per
cm.sup.2 up to as many as 1000 micro channels per cm.sup.2.
[0024] The position of micro channels in adjacent plates may
advantageously be offset in a direction orthogonal to the plate
stacking direction thus giving a better surface coverage by the
micro streams of the article to be treated.
[0025] The micro channels may advantageously have a non-constant
major width, the major width being larger towards the input side
and narrower towards the outlet face. This advantageously allows
the body portion to have the necessary mechanical integrity and
good sealing between stacked plates, while reducing flow resistance
and therefore the pressure drop across the micro channels. In an
embodiment, the micro channels may advantageously be formed as
slits in a first set of plates sandwiched between plates of a
second set, central cavities of the second set of plates configured
such that they overlap ends of the slits opposite the outlet end of
the micro channel. The first set of plates also comprise a central
cavity for passage of the supply fluid therethrough, the cavity
however being separated from ends of the slits by a certain width
of material ensuring structural integrity of the first set of
sheets. The minor width of the micro channels may thus be
determined by the thickness of plates of the first set, the width
of the slits that are cut through the plate determining the major
width of the micro channels, at least over a longer section
thereof.
[0026] The slits through the plates of the first set may be cut by
various known cutting techniques, such as by laser cutting, by
means of a die, high-pressure water jet cutting, electro-erosion
and other known manufacturing techniques for cutting through thin
plates as well as etching. The first set of plates may be made of
the same material as the second set of plates, or of a different
material whereby the combination of materials may be optimized for
sealing effectiveness between the stacked faces, ease of cutting
and forming the slits, and for cost reasons. The plates of the
first set may for example be made of a ceramic, metal or plastics
material, depending on the application and the environmental
temperatures whereas the plates of the second set could be made of
steel or plastic or ceramics depending on the application and
operating temperature range.
[0027] Plates of the second set may have smooth surfaces, for
example polished surfaces with a low roughness thus reducing flow
resistance in a fairly economical manner. Advantageously, the
density of micro streams can also be easily varied by varying the
thickness of the plates of the second set, without affecting the
micro channel geometry or the manufacturing process for the micro
channels.
[0028] A fluid micro stream device according to an embodiment of
this invention may advantageously be used in an apparatus for rapid
freezing of food stuffs and other perishable goods, the fluid micro
stream device being installed in an apparatus having a supply of
cryogenic liquid, in particular liquid nitrogen, that is injected
by the micro streams onto the article to be frozen. The articles to
be frozen may advantageously be transported on a mesh conveyor
belt, fluid micro stream devices being positioned either side of
the conveyor belt such that jets of the cooling liquid are
projected upon opposing sides of the article. The extremely rapid
and efficient cooling resulting from the micro stream geometry and
arrangement according to this invention enables particularly rapid
cooling with minimal use of the cryogenic liquid thus reducing
freezing cycle time, and use of cooling liquid, thus reducing
overall costs as well as improving product quality. Very rapid
freezing of food stuffs reduces dehydration of the product during
the freezing process, among other advantages.
[0029] Fluid micro stream devices may advantageously be used in
many other cooling applications, such as for cooling of metal
articles in material treatment processes (high precision extrusion
quenching, sheet and plate uniform quenching, roll cooling, cooling
of polymer extrusions), or for cooling hot gases, such as
combustion gases.
[0030] Inventors have further realised, surprisingly, that fluid
micro stream devices may also be advantageously implemented in
applications for: inducing a chemical reaction between a liquid and
a gas; for chemical reactions on liquid metals; and for degassing
liquid metals.
[0031] Also disclosed herein is an apparatus for cooling a gas or
inducing a chemical reaction between a liquid and a gas, comprising
a chamber with a gas inlet and a gas outlet configured for flow of
said gas through the chamber, and one or more fluid micro stream
devices configure for generating liquid micro streams in the
chamber through the gas. The micro stream device comprises a body
portion with a fluid supply cavity therein connected to a liquid
supply system and a plurality of fluid micro channels
interconnecting the fluid supply cavity with an external outlet
face of the body portion, the body portion being formed from a
plurality of stacked plates. The micro stream device used in this
application may advantageously comprise the features of the micro
stream device according to the embodiments described above.
[0032] Also disclosed herein is an apparatus for chemical reactions
on liquid metals comprising a fluid micro stream device comprising
a body portion with a fluid supply cavity therein connected to a
fluid supply system and a plurality of fluid micro channels
interconnecting the fluid supply cavity with an external outlet
face of the body portion, the body portion being formed from a
plurality of stacked plates, said micro channels having minor
widths less than 200 .mu.m and being formed at interfaces of at
least certain of said stacked plates, wherein the liquid metal is
supplied as the fluid for generating fluid micro streams and the
device is immersed in a reaction medium, in particular a reaction
gas. The device for generating fluid micro streams may
advantageously further comprise features of the micro stream
described above.
[0033] Also disclosed herein is an apparatus for degassing liquid
metals, comprising a fluid micro stream device comprising a body
portion with a fluid supply cavity therein connected to a fluid
supply system and a plurality of fluid micro channels
interconnecting the fluid supply cavity with an external outlet
face of the body portion, the body portion being formed from a
plurality of stacked plates, said micro channels having minor
widths less than 200 .mu.m and being formed at interfaces of at
least certain of said stacked plates, wherein the device is
immersed in the liquid metal and a degassing medium, such as an
inert gas, is supplied as the fluid for generating fluid micro
streams. The device for generating fluid micro streams may
advantageously further comprise features of the micro stream
described above.
[0034] Further objects and advantageous features of the invention
will be apparent from the claims and the following description and
drawings in which:
[0035] FIG. 1a is a perspective view of a portion of a fluid micro
stream device formed of a stack of plates according to this
invention;
[0036] FIG. 1b is an exploded perspective view of a portion of a
fluid micro stream device formed of a stack of plates according to
this invention;
[0037] FIG. 2a is a view of a plate of a second set of plates of an
embodiment of the invention;
[0038] FIG. 2b is a view of a plate with micro channels of a first
set of plates of the device according to this invention;
[0039] FIG. 2c is a view of the stacked assembly of the plates of
FIGS. 2a and 2b;
[0040] FIG. 3a is a perspective view of a section of an embodiment
of the device according to this invention;
[0041] FIG. 3b is a perspective representation of fluid micro
streams according to this invention;
[0042] FIG. 3c is a partial view of a configuration of fluid
microchannels according to an embodiment of this invention;
[0043] FIG. 4a is partial detailed view of first and second plates
of a device according to another embodiment of this invention,
showing microchannels according to a second embodiment;
[0044] FIG. 4b is a view similar to FIG. 2a, of a third
embodiment;
[0045] FIG. 5 is a perspective schematic view of part of an
apparatus for cryogenic freezing of processed food products
according to this invention;
[0046] FIG. 6 is a schematic cross-sectional view of an apparatus
suitable for cooling heated gas, or for reacting a gaseous medium
with a liquid, according to this invention.
[0047] Referring to the figures, a device for generating fluid
micro streams 7 comprises a body portion 4 comprising an outlet
face 6 through which micro streams of fluid 7 are projected, a
fluid supply cavity 8 within the body portion connected to fluid
supply system (not shown), and a plurality of micro channels 10 in
fluid communication between the fluid supply cavity 8 and the
outlet face 6.
[0048] In a preferred embodiment, the body portion 4 comprises a
stack of plates 12, 14 between which the micro channels 10 are
formed.
[0049] In a preferred embodiment, the micro channels 10 are formed
in plates 12 of a first set as slits that are cut through the
entire thickness of said plates of the first set and plates 14 of a
second set without slits are interposed therebetween. The micro
channels 10 are thus formed by the slits in the first set of plates
12 sandwiched between the plates 14 of the second set in an
alternating manner. The first plates 12 have openings 16 that form
part of the boundary of the fluid supply cavity 8 in the body, the
slits 10 extending from an outlet edge 18 that forms part of the
body portion outlet face 6 to a closed end 20 that is separated at
a certain distance R from an edge 22 of the opening 16, the
distance between the end of the slit 20 and the edge 22 being
sufficient to ensure mechanical integrity of the first plate 12
during handling and assembly between the second plates 14.
[0050] The second plates 14 also have openings 24 that form part of
the fluid supply cavity 8, an edge 26 of the opening adjacent the
outlet face 6 overlapping a portion 10a of the slits such that the
closed ends 20 of the slits are in fluid communication with the
cavity 8 as best seen in FIGS. 2c, 4a and 4b. The second plates 14
may be of a simple planar construction with smooth surfaces thus
lowering flow resistance in the micro channels 10.
[0051] The slits 10 may be produced by various conventional
techniques, such as laser cutting, water jet cutting,
electro-erosion, die stamping, etching, or by means of circular
saws, depending on the material of the first plate 12 and the
channel dimensions. The slit manufacturing method may also be
chosen as a function of the surface smoothness of the micro channel
and manufacturing costs. The alternate sandwich construction of
first and second plates with the micro channels formed by slits in
one of the two plates provides a large versatility in the choices
of materials and manufacturing techniques for the plates to
optimize the performance and cost for various applications. For
high temperature applications, the plates 14 may for example be
made of a high temperature stainless steel whereas the first plates
12 could also be made of steel, or a thin ceramic such as mica. For
low temperature applications the first plates with slits 12 could
be made out of a sheet of thin polymer or composite material.
Depending on the desired density of micro streams, the second
plates 14 may be from various thicknesses, without affecting the
manufacturing of the micro channels. The flexibility in material
choice and the separate alternate first and second plates also
enable the surface properties of the microchannels to be optimized,
in particular to reduce flow resistance and improve laminar flow,
and also to provide excellent sealing between plates and around the
microchannels.
[0052] The stack of plates forming the body portion 4 may be held
together sealingly by means of compression bolts 11 extending
through bolt holes 13 in the body portion, clamping the stack of
plates together. Other clamping means may however be used. It is
also possible, within the scope of the invention, to weld, glue, or
otherwise bond the stacked plates together.
[0053] Referring to FIG. 4a, the micro channels 10 may
advantageously have non-constant width, with a large width W.sub.1
towards the closed end 20 in order to increase the channel
cross-section at the fluid inlet, the channel width reducing to a
narrow section W.sub.2 corresponding essentially to the desired
micro stream cross-sectional profile at the outlet face 6. The
latter configuration reduces flow resistance and pressure drop
through the micro channels without compromising on the structural
integrity of the device and the sealing between adjacent plates.
The enlarged closed ends of the slits may be easily manufactured,
for example by a die stamping etching or electro-erosion
process.
[0054] As shown in FIG. 4b, the micro channels may have
non-constant profiles 27 also at the outlet end for example to
create a oval shaped channel for the creation of supersonic fluid
jets.
[0055] The micro channels could alternatively be formed as grooves
on the surface of plates that are stacked one on the other where a
side of the plate opposite the grooves is stacked against the side
with grooves of the adjacent plate. Such plates could
advantageously be made by injection moulding of a polymer or other
injectable materials such as certain metal alloys, whereby the die
imprinting the micro channels could be made by photo lithography
and etching. For example the injection moulding die with the micro
channel profiles could be made out of silicon in a standard etching
process. This would allow micro channels of particularly small and
well controlled dimensions to be produced. The injected micro
channels could have non-constant profiles as discussed in relation
to FIGS. 4a and 4b above.
[0056] According to the invention, the micro channels
advantageously have an oblong profile at or proximate the outlet
face 6, defined by a minor width W.sub.min and a major width
W.sub.maj where the major width is advantageously more than two
times the value of the minor width. The micro channels are
configured preferably such that the major width W.sub.maj is
defined by the narrow width W.sub.2 of the slit 11 and the minor
width is defined by the thickness of the first sheet 12. It is
however possible to have a first plate thickness superior to the
slit width W.sub.2 such that the micro channel major width
W.sub.maj is defined by the plate thickness and the slit width
W.sub.2 defines the minor width W.sub.min.
[0057] The micro channels in a first plane may be offset in a
direction orthogonal to the stacking direction of the plates, which
may advantageously correspond to a direction of relative movement
between the fluid micro stream device and an article to be treated
such that the oblong micro streams have a better impact coverage
across the surface to be treated.
[0058] The oblong shape of the micro streams, and in addition the
offset arrangement of adjacent micro streams provides more uniform
and more efficient cooling of the surface to be treated than the
conventional microjets. As shown in FIG. 3c, a plurality of
successive micro stream layers may be offset by a distance Os with
respect to a first layer depending on the major width and spacing S
(see FIG. 3) between micro streams and the cooling efficiency
required.
[0059] Referring to FIG. 5, an apparatus for cryogenic freezing of
articles, for example food stuffs, comprises a conveyor system 30
for conveying the articles through the apparatus, and one or more
fluid micro stream devices 2 arranged along the conveyor system and
configured to project micro streams on the articles as they are
transported along the conveyor system. The conveyor system may
comprise a conveyor belt that is preferably in the form of a mesh
or grill in order to allow projection of micro streams from above
and below the articles for more efficient and rapid all round
cooling of the articles. Other conveyor systems may however be
used, depending also on the articles to be cooled.
[0060] In the embodiment shown, fluid micro stream devices are
placed on opposite sides of the conveyor belt 32, across the width
of the conveyor belt and project micro streams of fluid on top and
bottom sides of the articles 34 to be cooled.
[0061] Depending on the amount cooling required, a plurality of
fluid micro stream devices can be arranged along the conveyor belt
as shown in FIG. 3. For cryogenic freezing of articles, the cooling
fluid supplied to the devices is advantageously liquid nitrogen
although other very low temperature cooling liquids could be used,
such as liquid helium. In view of the relatively high cost of
liquid nitrogen and other cryogenic cooling liquids, the very rapid
and efficient cooling provided by the micro streams enables minimum
use of cooling fluid and moreover the velocity of micro streams may
be easily varied with a direct effect on the rate of cooling. For
example, the micro streams velocity may be reduced, by reducing
pressure in the supply cavity towards the end of the cooling cycle.
In the arrangement of FIG. 5, the most downstream fluid micro
stream device 2c may for instance have a lower supply pressure of
cooling liquid than the most upstream device 2a.
[0062] The invention may advantageously be used in various
applications not limited to cooling, such as for heating, degassing
various liquids such as molten metals, cooling of combustion gases,
and chemical reactions between the micro streams and a medium onto
which they are sprayed.
[0063] Referring to FIG. 6, an apparatus for cooling combustion gas
comprises one or more fluid micro stream devices 2 mounted in a
cooling chamber 38 having an inlet 40 for the inflow of hot
combustion gas at one end of the cooling chamber, and an outlet 42
for exit of the cooled combustion gas at the other end of the
chamber. A cooling liquid source 43 connected to the fluid micro
stream device 2 preferably supplies de-ionised or distilled water.
The fluid micro stream device used in this application may
advantageously be provided with features of the fluid micro stream
device described hereinabove in relation to FIGS. 1 to 5.
[0064] The fluid micro stream devices 2 are preferably mounted at
or near the end of the combustion chamber proximate the inlet 40
and configured to generate a large plurality of densely distributed
and very fine micro streams 7 towards the outlet end 42 of the
chamber 38. The density of micro streams, the dimensions of each
jet, the velocity of the jet and flow rate may be optimized
empirically for optimal cooling of the combustion gas, depending on
the combustion gas temperature and flow rate through the cooling
chamber. The configuration of the micro streams may advantageously
be configured to ensure complete or almost complete evaporation of
the injected cooling water to avoid accumulation of cooling liquid
in the cooling chamber or outlets of the cooling chamber. The
region near the outlet end of the cooling chamber 38 thus
represents an evaporation zone 46 of the micro stream cooling
liquid. The cooling chamber may however also be provided with a
collector for collecting cooling liquid and circulating it to a
waste water treatment installation.
[0065] The above-described cooling system may be applied to other
hot gases, not just combustion gases, and the cooling liquid used
for the micro streams may be a liquid other than water.
[0066] The apparatus illustrated in FIG. 6 and described above may
however also be configured for use in an application for inducing a
chemical reaction between the micro streams and a gaseous medium.
In this case the apparatus in FIG. 6 would represent a reaction
chamber 38 in lieu of the cooling chamber and the reaction gas
would replace the heated combustion gas. Such a configuration would
be particularly advantageous with the micro stream device 2
according to the invention in view of the high density, high
velocity and very fine fluid streams that can be generated over a
large surface.
[0067] In applications for chemical reactions on liquid metals, the
device for generating fluid micro streams is supplied with liquid
metal as the fluid for generating fluid micro streams, and the
device is immersed in a reaction medium, in particular a reaction
gas.
[0068] In applications for degassing liquid metals, the device for
generating fluid micro streams is immersed in the liquid metal and
a degassing medium, such as an inert gas such as Argon, is supplied
as the fluid for generating fluid micro streams and injected into
the liquid metal.
[0069] In apparatuses of the above applications, the stacked plates
of the micro stream devices may be made from high temperature
materials, or chemically inert materials, such as ceramics. In such
applications, the intermediate plates with slits could be omitted,
and the micro channels provided as grooves directly on one side of
each of the stacked plates. The micro stream devices in these
applications could however advantageously be provided with any of
the advantageous features of the preferred embodiments of the micro
stream devices described herein, provided high temperature
resistant, respectively chemically inert materials are used,
depending on the application.
EXAMPLES
Example 1
Quenching Aluminium Alloy
[0070] Cooling of Aluminium alloy strip, thickness of 0.5 to 5 mm,
typical specific flow 20 liter/m.sup.2/s. A typical set of values
for micro streams for this application are: W.sub.maj=120 .mu.m,
W.sub.min=50 .mu.m, S=3 mm, H=3 mm.
[0071] Advantages compared to conventional cooling technology: More
homogeneity in cooling, and consequently high mechanical properties
homogeneously distributed, less residual stresses.
Example 2
Freezing Food
[0072] For cryo-freezing of foodstuffs such as meat, fish, fruits
Typical specific flow 0.5 liter/m.sup.2/s. A typical set of values
for micro streams for this application are: W.sub.maj=150 .mu.m,
W.sub.min=20 .mu.m, S=5 mm, H=5 mm.
[0073] Advantages compared to conventional freezing technology:
economy of cryogenic fluid (which is expensive). The quantity of
cryo-coolant needed is minimal, since the freezing is optimally
conducted and the heat-transfer is optimal. Rapidity of freezing
and small jet impingement forces preserves also the integrity of
the products as they are being frozen.
Example 3
Heating, Degassing and Chemical Reactions on Liquid Metals
[0074] In this example, liquid metal, for example aluminium, is
sprayed as micro streams. The ambient gas around the streams
interacts with the liquid metal micro streams. The gas may be used
to heat the liquid metal, or to interact with it chemically, or for
degassing. The liquid metal is thus supplied as the fluid for
generating fluid micro streams and the device immersed in a
reaction medium, in particular a reaction gas. Typical specific
flow 5 liter/m.sup.2/s. A typical set of values for micro streams
for this application are: W.sub.maj=1000 .mu.m, W.sub.min=180
.mu.m, S=6 mm, H=4 mm.
[0075] Advantages compared to conventional technology: The surface
of interaction and of contact between gas and liquid is maximal.
Therefore the chemical reaction as well as the heat transfer is
highly efficient.
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