U.S. patent number 3,870,082 [Application Number 05/370,895] was granted by the patent office on 1975-03-11 for venturi-type devices.
This patent grant is currently assigned to Micron Engineering Inc.. Invention is credited to Richard Adolf Holl.
United States Patent |
3,870,082 |
Holl |
March 11, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Venturi-type devices
Abstract
A venturi-type device comprises a fluid flow passage containing
in the direction of fluid flow, an upstream section of
progressively reducing cross-section, a venturi throat section, and
a downstream section of progressively increasing cross-section. The
necessary changes in cross-section are produced by a plurality of
physical barriers disposed in the passage and spaced from each
other transverse to the direction of flow of the fluid, the changes
in cross-section being caused by differences in length of the
barriers. The barriers may be substantially flat parallel plates
disposed longitudinally of the direction of the flow. The surfaces
of the barriers may be coated with liquid or solid material. In an
exchange device the barriers may be hollow to form other
passageways for the flow of a second fluid through the device in
exchange relation with the first fluid passing between the
barriers.
Inventors: |
Holl; Richard Adolf (Grimsby,
Ontario, CA) |
Assignee: |
Micron Engineering Inc. (St.
Catharines, Ontario, CA)
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Family
ID: |
26981206 |
Appl.
No.: |
05/370,895 |
Filed: |
June 18, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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317898 |
Dec 26, 1972 |
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Current U.S.
Class: |
138/40;
261/DIG.54; 55/482; 96/280 |
Current CPC
Class: |
B01D
47/10 (20130101); Y10S 261/54 (20130101) |
Current International
Class: |
B01D
47/00 (20060101); B01D 47/10 (20060101); F15d
001/02 () |
Field of
Search: |
;138/37,38,40,41,44
;73/211,213,25L ;261/DIG.54 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ruehl; Charles A.
Attorney, Agent or Firm: Rogers; Stanley J.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
The present application is a continuation-in-part of my application
Ser. No. 317,898, filed Dec. 26, 1972, now abandoned.
Claims
I claim:
1. A device of venturi type comprising a passage member providing a
passage for the flow of fluid therein in a predetermined direction,
the passage having in the direction of flow of fluid in the passage
and in the stated order an upstream section, a throat section and a
downstream section, the flow cross-sectional area of the passage in
the upstream section decreasing progressively toward the throat
section, and the flow cross-sectional area in the downstream
section increasing progressively away from the throat section,
wherein at least one of said upstream and downstream sections
comprises a plurality of physical barriers disposed in the passage,
which barriers are spaced from each other transverse to said
direction of flow and decrease the flow cross-sectional area of the
part of the passage in which they are located, the said change of
flow cross-sectional area being caused by differences in the said
direction of flow of the physical lengths of the barriers in the
corresponding section.
2. A device as claimed in claim 1, wherein both of the upstream and
downstream sections comprise parallel physical barriers of
different physical length.
3. A device as claimed in claim 2 wherein the physical barriers in
both of the upstream and downstream sections comprise a plurality
of spaced parallel plates.
4. A device as claimed in claim 3, and for passage of gas flow
having solid material entrained therein, wherein the minimum
spacing between immediately adjacent plates of said upstream and
downstream plates is from 5 to 15 times the size of the largest
particles of solid material to be handled by the device.
5. A device as claimed in claim 2, and for passage of gas flow
having solid material entrained therein, wherein the minimum
spacing between immediately adjacent physical barriers is from 5 to
15 times the size of the largest particles of solid material to be
handled by the device.
6. A device as claimed in claim 2, and comprising a fluid reaction
or contacting device, including means for supplying a liquid to the
physical barriers to coat the surfaces thereof.
7. A device as claimed in claim 2, and comprising a fluid reaction
or contacting device, wherein surfaces of the physical barriers are
coated with a solid material to be contacted by the fluid.
8. A device as claimed in claim 1, wherein the physical barriers in
either of the upstream or the downstream sections comprise a
plurality of spaced parallel plates.
9. A device as claimed in claim 1, wherein the said throat section
comprises a plurality of spaced parallel physical barriers all of
the same physical length in the said direction of flow.
10. A device as claimed in claim 9, wherein the throat section
comprises a plurality of spaced parallel plates.
11. A device as claimed in claim 10, and for passage of gas flow
having solid material entrained therein, wherein the minimum
spacing between immediately adjacent plates of said throat plates
is from 5 to 15 times the size of the largest particles of solid
material to be handled by the device.
12. A device as claimed in claim 9, wherein the throat section
comprises a plurality of section segments with the physical barrier
segments in each section segment all of the same physical
length.
13. A device as claimed in claim 9, and comprising a fluid reaction
or contacting device, including means for supplying a liquid to the
physical barriers to coat the surfaces thereof.
14. A device as claimed in claim 9, and comprising a fluid reaction
or contacting device, wherein surfaces of the physical barriers are
coated with a solid material to be contacted by the fluid.
15. A device as claimed in claim 9, wherein at least some of the
barriers of the throat section are hollow and constitute flow
passages for a second fluid to be in heat exchange relation with
the first-mentioned fluid passing between the barriers.
16. A device as claimed in claim 9, wherein the throat section
comprises a plurality of spaced parallel mesh plates.
17. A device as claimed in claim 1, wherein all of the said
sections comprise parallel physical barriers that extend in the
same direction of flow, the barriers of the upstream section being
of different physical length, the barriers of the throat section
being of the same physical length and the barriers of the
downstream section being of different physical length.
18. A device as claimed in claim 17, wherein the barriers of the
upstream and throat sections are constituted by flat parallel
plates extending between the two sections.
19. A device as claimed in claim 17, wherein the barriers of the
downstream and throat sections are constituted by flat parallel
plates extending between the two sections.
20. A device as claimed in claim 17, wherein the barriers of the
upstream, throat and downstream sections are constituted by flat
parallel plates extending between the three sections.
21. A device as claimed in claim 20, wherein the barriers of the
upstream, throat and downstream sections are constituted by spaced
parallel mesh plates extending between the three sections.
22. A device as claimed in claim 17, wherein all of said barriers
comprise spaced parallel plates.
23. A device as claimed in claim 19, and for passage of gas flow
having solid material entrained therein, wherein the minimum
spacing between immediately adjacent plates of all of said
upstream, downstream and throat plates is from 5 to 15 times the
size of the largest particles of solid material to be handled by
the device.
24. A device as claimed in claim 17, and comprising a fluid
reaction or contacting device, including means for supplying a
liquid to the physical barriers to coat the surfaces thereof.
25. A device as claimed in claim 17, and comprising a fluid
reaction or contacting device, wherein surfaces of the physical
barriers are coated with a solid material to be contacted by the
fluid.
26. A device as claimed in claim 1, wherein the upstream section
comprises a plurality of parallel barriers of different physical
lengths, said upstream section comprising a plurality of section
segments with the physical barrier segments in each section segment
all of the same physical length.
27. A device as claimed in claim 1, wherein the downstream section
comprises a plurality of parallel barriers of different physical
lengths, said downstream section comprising a plurality of section
segments with the physical barrier segments in each section segment
all of the same physical length.
28. A device as claimed in claim 1, wherein the upstream and
downstream sections each comprise a plurality of parallel barriers
of different physical lengths, each said upstream and downstream
section comprising a plurality of section segments with the
physical barrier segments in each section segment all of the same
physical length.
29. A device as claimed in claim 1, wherein the upstream and
downstream sections each comprise a plurality of parallel barriers
of different physical lengths, and the throat section comprises a
plurality of parallel barriers of the same physical length, each
section comprising a plurality of section segments with the
physical barrier segments in each section segment all of the same
physical length.
30. A device as claimed in claim 29, wherein each barrier of each
of the said section segments comprises a mesh plate.
31. A device as claimed in claim 1, and for passage of gas flow
having solid material entrained therein, wherein the minimum
spacing between immediately adjacent physical barriers is from 5 to
15 times the size of the largest particles of solid material to be
handled by the device.
32. A device as claimed in claim 31, wherein the said minimum
spacing is about 10 times the said size of the largest
particle.
33. A device as claimed in claim 1, and comprising a fluid reaction
or contacting device, including means for supplying a liquid to the
physical barriers to coat the surfaces thereof.
34. A device as claimed in claim 1, and comprising a fluid reaction
or contacting device, wherein surfaces of the physical barriers are
coated with a solid material to be contacted by the fluid.
35. A device as claimed in claim 1, wherein the said physical
barriers are constituted by spaced parallel mesh plates.
Description
FIELD OF THE INVENTION
The present invention is concerned with improvements in
venturi-type devices, and in apparatus incorporating such devices,
such as gas cleaners, dissolvers, reactors, and heat
exchangers.
REVIEW OF THE PRIOR ART
Venturi devices comprise a duct or pipe providing a fluid flow
passageway that decreases progressively in cross-sectional area in
an "upstream section" to a minimum at a "throat section," and then
increases progressively again in a "downstream section." Fluid
forced through the venturi device has its flow velocity increased
progressively in the upstream section to reach a maximum at the
throat, the velocity decreasing again in the downstream section,
usually accompanied by a considerable turbulence of the fluid in
the downstream section and in the duct- or pipe-work fed from the
device. The passage of fluid through the device is accompanied by a
pressure drop therein, the value of which is proportional to the
amount of energy or power required to pass the fluid therethrough.
It is usually one of the main endeavours of designers of these
devices to keep this pressure drop as low as possible, so that the
device and the apparatus in which it is incorporated will operate
at maximum efficiency and minimum external power requirements.
In a typical gas scrubbing device a gas cleaning liquid, usually
water, is injected into the gas stream at or very close the
entrance to the venturi throat, where it is immediately atomised by
the high-velocity gas stream into a mist or spray having a high
probability of physical contact with solid material to be cleaned
from the stream; this high probability results chiefly from the
difference in velocity between the slower moving mist droplets and
the faster moving gas-borne particles. This high contact
probability is also enhanced by the above-mentioned turbulence in
the gas downstream of the throat.
DEFINITION OF THE INVENTION
It is an object of the present invention to provide a new device
classifiable as being of venturi type.
In accordance with the present invention there is provided a device
of venturi type comprising a passage member providing a passage for
the flow of fluid therein in a predetermined direction, the passage
having in the direction of flow of fluid in the passage and in the
stated order an upstream section, a throat section and a downstream
section, the flow cross-sectional area of the passage in the
upstream section decreasing progressively toward the throat
section, and the flow cross-sectional area in the downstream
section increasing progressively away from the throat section,
wherein at least one of said upstream and downstream sections
comprises a plurality of physical barriers disposed in the passage,
which barriers are spaced from each other transverse to said
direction of flow and decrease the flow cross-sectional area of the
part of the passage in which they are located, the said change of
flow cross-sectional area being caused by differences in the said
direction of flow of the physical lengths of the barriers in the
corresponding section.
DESCRIPTION OF THE DRAWINGS
Particular preferred embodiments of the invention will now be
described, by way of example, with reference to the accompanying
diagrammatic drawings wherein:
FIG. 1 is a section through a gas cleaning apparatus in accordance
with the invention and incorporating venturi-type devices of the
invention wherein the said physical barriers are constituted by
longitudinally-disposed laminae,
FIG. 2 is a cross section taken on the line 2--2 of FIG. 1, and
drawn to a larger scale,
FIG. 3 is a longitudinal cross section through some laminae
constituting the physical barriers of the device of FIG. 1, drawn
to a larger scale, in order to show detail of construction
thereof,
FIG. 4 is a side elevation of a laminae to show another
constructional feature thereof,
FIG. 5 is a diagrammatic longitudinal cross section to a much
enlarged scale to explain the operation of the embodiment of the
invention illustrated by FIGS. 1 to 4,
FIG. 6 is a longitudinal cross section through another device in
accordance with the invention,
FIG. 7 is a section taken on the line 7--7 of FIG. 6,
FIG. 8 is a longitudinal cross section through a heat-exchange
device in accordance with the invention,
FIG. 9 is a longitudinal cross section through a further device in
accordance with the invention,
FIG. 10 is an exploded view of the device of FIG. 9 to show the
structure thereof,
FIG. 11 is a longitudinal cross section through a yet further
device in accordance with the invention, wherein the physical
barriers are constituted by transversely disposed perforated
sheets,
FIG. 12 is a longitudinal cross section through a still further
device in accordance with the invention, wherein the physical
barriers are constituted by a combination of
longitudinally-disposed laminae and transversely disposed
perforated sheets, and
FIG. 13 is a perspective view of some laminae constituting the
physical barriers of the device of FIG. 1, drawn to a larger scale,
to show the use of mesh sheets for this purpose.
In all of the figures of the drawings the relative scales of
different parts and their spacing etc. are changed and/or
exaggerated as necessary for clear illustration of the invention,
and they may not therefore be scaled in any way.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An air-cleaning apparatus as illustrated by FIG. 1 is especially
suited for the removal of particles such as dust and fume from
gases, e.g. furnace exhaust gases. It may also be employed for the
selective removal of one or more gases from other gases, e.g. by
selective solution, adsorption, absorption or chemical reaction.
The gas to be cleaned is drawn by a fan 10 through a primary coarse
venturi-type separator 11 and a secondary fine venturi-type
separator 12 before being discharged to atmosphere via an outlet
13. Both separators are disposed over a common water tank 14 which
is supplied with water from a pipe 15 via a level-control valve 16.
The level of the water in the tank is indicated by 17, and is
maintained above the lower edges of the partitions 18 and 19, so as
to isolate the separators from one another, and to force the air to
pass between them only via the connecting pipe 20. Water is drawn
from the tank by a pump 21 and passed by a pipe 22 to nozzles 23
and 24 which spray the water onto their respective separators. The
water draining from the separators is collected in the tank, the
suspended solid material settling to the bottom in the form of a
sludge and being removed therefrom as required via a valve 25.
Referring now especially to FIG. 2, in conjunction with FIG. 1, the
duct or pipe 26 of the primary separator is illustrated as of
square internal cross-section. A plurality of physical barriers
constituted by uniformly-spaced thin flat parallel plates are
disposed within the gas flow passageway formed by the pipe with
their larger faces parallel to the respective sides of the pipe,
forming a corresponding plurality of narrow, uniform-width,
parallel-sided straight passageways. As indicated above, the
spacing and number of plates shown in the drawing as constituting
the venturi-type device 11 is merely for clarity of illustration,
and does not necessarily correspond to the parameters for an actual
device, which will be discussed below.
Thus, the device is illustrated as comprising three parallel
longest plates 27 equally spaced from one another and from the
adjacent parallel walls of the pipe. Four shorter plates 28 are
each disposed between two immediately adjacent plates 27, or
between a plates 27 and the adjacent pipe wall, with its leading
and trailing edges substantially equally spaced from the respective
edges of the plates 27. Eight still shorter plates 29 are disposed
in the spaces between the plates 27 and 28 and the pipe walls. In
this embodiment the upper and lower edges of each plates are
equally spaced from the respective edges of the immediately
adjacent longer plates
It will be seen that the gas entering the device traverses a flow
passageway that decreases progressively in cross-sectional area in
an "upstream section" encompassing the leading ends of the plates
27 and 28 that extend beyond the shortest plates 29, until a
minimum is reached at the passageways bounded by the shortest
plates, constituting the "throat section" of the device. The
cross-sectional area of the passageway then increases progressively
in a "downstream section," encompassing the trailing ends of the
plates 27 and 28 that extend beyond the plates 29, until a maximum
is reached where the longest plates 27 terminate.
Similarly, the secondary venturi separator is illustrated as
comprising laminae all plates 27, 28 and 29, and in addition plates
30 which are shorter in length than the plates 29 and are disposed
with their leading and trailing edges equally spaced from the
corresponding edges of the plates 29. Because of the addition of
the plates 30 the final spacing between immediately adjacent plates
is smaller than in the primary separator, and the secondary
separator is effective with finer particles. It will be noted that
the shortest plates 30 of the secondary separator are considerably
longer than the shortest plates 29 of the primary separator to give
longer passages in which the scrubbing liquid from the nozzles 24
is effective.
It is found with a venturi-type device in accordance with the
invention that substantially less pressure drop is obtained across
the device compared to a conventional high energy venturi scrubber
of the same flow rate capacity, the particle collection efficiency
of the venturi-type device in accordance with the invention being
substantially higher.
In its most elementary form a venturi-type device of this aspect of
the invention can have the necessary physical barriers constituted
by a single set of plates disposed in the passageway, the plates
being of progressively different lengths with their leading and
trailing edges so disposed that the plates form the required
upstream, throat and downstream sections. In the embodiment
illustrated the progressive increase and decrease are of
substantially the same rate, but in other embodiments this need not
be the case, the different rates being achieved by corresponding
location of the leading and trailing edges of the plates.
It is possible also to profile the leading and/or the trailing
edges of the plates, for example, as illustrated by FIG. 4 for the
plates leading edges, so as to obtain a further decrease of
pressure drop by sharpening these edges.
In the case of a device such as that illustrated by FIGS. 1 to 4,
wherein a liquid is sprayed into the device, it is found that a
layer of the liquid adheres to the leading edges to effectively
"profile" those edges. These layers can also protect the edges
against erosion by mechanical particles entrained in the gas
stream, provided those particles are below a certain minimum size,
e.g. about 50 micrometers in the embodiment illustrated. In
applications in which the gas to be cleaned includes a substantial
guantity of particles above the corresponding preferred minimum
size, it may be preferred to provide a coarser scrubbing device
ahead of the device of the invention, e.g. a simple open chamber in
which the gas is passed through a liquid spray. Other forms of such
coarser scrubbing devices will be apparent to those skilled in the
particular art.
In the preferred embodiments illustrated herein the device is
formed by thin flat plates spaced accurately from one another to
provide passageways of corresponding width by narrow longitudinal
spacing elements 31, and the ease and simplicity of manufacturing
by such an arrangement will be apparent. It is also possible for
the device to be formed by spaced plates that are not flat, e.g.
curved in the directions transverse to the direction of gas flow
and/or curved in the directions parallel to the gas flow. An
extreme example of a device with plates curved transverse to the
gas flow consists of a plurality of spaced concentric cylinders, as
illustrated in FIGS. 6 and 7.
The apparatus illustrated by FIG. 8 is a heat exchange device where
one fluid may not come in contact with the other fluid. In such a
device at least the plates 29 immediately bounding the throat are
hollow and constitute a flow passage for the second fluid, these
hollow plates communicating with headers 33 provided with inlets
and outlets that are not shown. Other forms of exchange between two
fluids may also be effected by the device of the invention and, for
example, the walls of the hollow plates may be permeable.
Many of these devices will be fed with a spray of liquid as a gas
cleaning and/or cooling agent from the respective nozzle 23 or 24,
the nozzles being arranged to provide as uniform a spray as
possible over the cross-sectional area. The liquid runs down the
surfaces of the physical barriers to provide thin films 32 (FIG. 5)
thereon, which are contacted by the dust-laden air and wet and
remove the dust therefrom. The resulting dust-laden liquid drips
from the lower trailing edges of the barriers, and in the case of
laminae barriers these edges may be toothed or otherwise formed, as
illustrated for example by FIG. 4, to promote the formation of
large drops which fall into the reservoir. It is found however that
the devices of the invention are particularly efficient at
coalescing fine vapours of the spray into droplets of sufficient
size not to remain entrained in the gas stream.
It is found that for efficient operation as a gas cleaner or the
like the transverse spacing between each immediately adjacent pair
of plates in the throat section should be closely correlated with
the maximum size of particle that is to be removed by the device.
In particular this spacing preferably is from 5 to 15 times the
said maximum size, and more specifically is about 10 times.
The length of the throat section also is correlated with the
particle size and should increase with decrease of particle size,
owing to the greater difficulty usually experienced in separation
with decrease of particle size. It is also preferred that in the
upstream and downstream sections the ratio of length thereof to
width perpendicular to the plane of the plates should be not less
than about 3:1 in order to give a sufficiently uniform distribution
of velocity and flow.
It is believed that with these preferred spacings the gas flow
between the plates is in the form of two back-to-back turbulent
boundary layers, as illustrated by FIG. 5, between the two
immediately-adjacent liquid films, giving a very high probability
that the particles will be trapped by the liquid films and removed
from the air stream. The liquid can be provided with a surface
tension reducing agent to increase its capture efficiency.
As indicated above, the spacing between the plates is correlated
with the maximum size of particle to be handled by the device, and
will therefore decrease for smaller particles. As illustrated by
FIG. 3, the surface of each Plates, at least adjacent the leading
edge thereof, may be provided with transverse ridges or
corrugations to promote the capture of the particles, although this
will result in an increase in pressure drop through the device.
As a specific example of the results obtained a device in
accordance with this aspect of the invention was constructed with a
minimum spacing of about 0.016 inch between the laminae of the
throat section to give a velocity ratio of 2:1. The longest laminae
were 30 inches in length, while the shortest laminae were 6 inches
long. The air velocity at the intake was 1600 feet per minute, and
the pressure drop measured across the device by a manometer was 8.5
inches water gauge. This device was able to remove cigar smoke fume
(comprising particles in the sub-micron to colloidal size range)
from an air stream to the extent that the exhaust from the device
was not visible. A conventional known venturi scrubber to operate
with particles of this size cannot give the same efficiency of
particle removal, since the air velocities become excessive. For
example, it has been reported that to give a comparable cleaning
efficiency of non-visible exhaust with sub-micron fume particles
requires an air velocity of over 30,000 feet per minute in the
throat, such a device operating with a pressure drop of over 60
inches water gauge. Moreover, the device of the invention does not
require a centrifugally-operated mist-removal chamber that may
always be provided for such known venturi scrubbers in order to
deposit the water with its entrained solid material.
The construction of a device using plates physical barriers
involves the assembly of a large number of thin sheets of different
sizes in correct order and such an operation is very susceptible to
error, even with a careful assembler, resulting in a device plates
incorrect characteristics and reduced efficiency. The assembly
operation can be simplified and such errors avoided by means of the
construction illustrated by FIGS. 9 and 10. The pipe constituting
the fluid flow passage is subdivided into a plurality of units,
each of which is pre-assembled with plates portions all of the same
length. Thus the throat portion is constituted by a corresponding
pipe segment 26d containing all of the plates 30 together with the
central portions of the longer plates 29, 28 and 27. At each end of
the throat section there are mounted respective pipe segments 26c
and 26e in registry with the segment 26a and containing the end
parts of the plates 29 together with the corresponding parts of the
plate 27 and 28. Similarly, pipe segments 26b and 26f contain the
end sections of plates 28 and corresponding parts of the plates 27,
while pipe segments 26a and 26g contain only the end sections of
the laminae 27. In constructions in which very close spacing is
required between the plates the segments may be disposed, as
illustrated, so that the plates segments in successive pipe
segments are transverse to one another, preferably at right angles
to one another.
It is not essential for the laminae to be continuous surfaces, and
instead perforated plates can be employed provided the size of the
perforations is made such that the surface performs with the liquid
used as if it were a continuous surface. Thus, the surface energy
of the liquid will ensure that it will form a continuous film over
a perforated surface when the perforations are of sufficiently
small size. The perforated plates can for example be formed of wire
or plastic mesh, preferably a woven mesh, as illustrated by FIG.
13, and a useful reduction in weight of material achieved by such
use. A woven mesh has the additional advantage that it will provide
what is effectively a ridged or undulated surface transverse to the
direction of fluid flow and the advantage of such a construction
was explained above in relation to FIG. 3. By way of illustration
in the embodiment of FIG. 10 only the laminae of the segments 26a
are shown as perforated, but it will be understood that any or all
of the other segments can be similarly constructed.
With such a construction the segments can be preassembled with no
chance of error since all laminae segments in each pipe segment are
of the same length. Moreover each segment can itself be formed of
one or more units or modules each of standard length in the
direction of flow. For example, if each unit is of length n inches
then a throat section of any length xn can easily be assembled by
aligning and fastening end to end x number of pre-assembled units.
The lengths of the upstream and downstream portions can also be
determined in the same manner. It may also be necessary to dispose
each unit transverse to the immediately preceding and succeeding
unit to avoid obstruction of the channels in the units.
The device illustrated by FIG. 11 employs a different form of
physical barrier to provide the upstream throat and downstream
sections, namely a plurality of perforated screens disposed
transverse to the direction of flow of the fluid in the passageway.
Thus, the pipe segments 26a and 26g contain a number of transverse
perforated sheets juxtaposed closely against one another, the
spacing of immediately successive barriers in the direction of flow
being such that substantially continuous films of liquid can form
parallel to the direction of fluid flow under the action of the
liquid surface energy, as explained above in connection with the
use of perforated laminae. These sheets of the segments 26a and 26g
are the most coarsely perforated, so that they provide the least
reduction in flow cross-sectional area of the passage. The pipe
segments 26b and 26f contain another two groups of juxtaposed
sheets that are more finely perforated than the sheets 26a and 26g
so that they provide a greater reduction of flow cross-sectional
area. Similarly, the sheets of segments 26c and 26e are more finely
perforated than those of 26b and 26f respectively, while the pipe
segment 26d contains sheets of the finest perforation and greatest
flow cross-sectional area reduction to constitute the throat
section.
As with the other described embodiments fewer or more segments may
be employed ahead of and after the throat section to provide the
required progressive changes effective in flow cross-sectional
area, each segment containing a sheet or sheets of a different
degree of perforation. The number of segments in the upstream and
downstream sections can be quite different from one another.
Preferably the size of perforation in the throat section is about
twice the maximum particle size to be handled by the device. In a
specific embodiment of a device intended to operate with particle
size 20 .mu.m and smaller the sheets of section 26d comprise wire
mesh screens of openings 40 .mu.m square, those of sections 26c and
26e are of mesh screens of 80 .mu.m openings, those of sections 26b
and 26f are mesh screens of 160 .mu.m openings, and those of
sections 26a and 26g are mesh screens of openings 320 .mu.m.
In the embodiment of FIG. 12 both types of physical barrier are
employed, the throat section being constituted by transverse
perforated sheets, while the upstream and downstream sections are
constituted by longitudinally disposed flat parallel plates.
The invention has been particularly described as applied to a gas
cleaning device, but is applicable to all cases in which a
venturi-type device must be provided. Other specific examples of
uses for the device of the invention are as follows:
a. A gas reaction device in which the gas passing through the
apparatus is brought into intimate contact with a chemical flowing
over the surfaces of the physical barriers.
b. A gas reaction device in which the gas is brought into intimate
contact with a solid material, such as a catalytic material, coated
on the surfaces of the physical barriers.
c. A gas reaction device in which two or more separate gases are
fed simultaneously to the device and are mixed therein, either
alone or in combination with a solid or liquid material on the
surfaces of the physical barriers.
d. A gas velocity and/or flow measuring device in which a low-ratio
throat is employed and a suitable pressure detecting meter is
located in the throat, such a device operating with a low overall
pressure drop.
e. A heat exchange device as illustrated in FIG. 8.
* * * * *