Note: Descriptions are shown in the official language in which they were submitted.
~ he present invention relates to vortex shedding flow
measuring devices.
In the prior art several patents have illustrated
the basic concept of providing an obstacle or body in a fluid
flow path which causes vortices to be formed, and which vortices
set up vibrations or oscillations in the obstacle. Measurement
of the vibrations has long been known to provide an indication
of the velocity of flow past the obstacle. Devices of the
general type are shown in United States Patent No. 3,972,232
wherein a piezoelectric pick-up is used for determining the
vibration of the obstacle, and wherein a particular shape of
obstacle is provided.
A single bar, flat plate assembly which can be
inserted into a conduit is shown in Japanese Utility Model
Publication No. 9015/1975. A vortex flowmeter which shows
a plurality of bodies arranged in a particular orientation in
relat~n to the direction of flow is shown in Japanese ~ent
Disclosure No. 20553~1973. Particular attention should be
given to Figure 7(h). The teaching is that a particular spacing
relationship is desired between two laterally spaced "pillars"
and a downstream pillar to obtain the desired action.
Another type o~ vortex flowmeter is shown in U.S.
Patent No. 3,796,096.
The use of a bluff body as the vortex shedding
obstacle or body is illus~rated in U.~. Patent No. 3,572,117,
and probe rods made of a polygonal cross section are disclosed
in U.~. Patent No. 2,813,42~. A flowmeter using rectangular
vortex shedding probes in one embodiment, wherein the wall of
the probe is intended to be the vorteæ shedding obstacle as
well as the moving or sensing element is shown in U.S. Patent
No. 3,927,566.
Patent No. 3,948,097 is of interest in that it
provides a plurality of slots in a vortex shedding obstacle
with the slots arranged to extend transverse to the flow direc-
tion, and these slots are alleged to assist in the production and
detection of vortices.
Another patent which illustrates three individual
flowmeters in a single pipe, is United ~tates Patent No.
3,979,954. Each of the meters generates a separate signal,
and the separate signals can be combined to provide an output
that is substantially proportional to the flow rate o~ the
fluid.
Investigations of the efects of multiple bars in flow
have been made for the purpose of predicting and minimizing
structural vibrations in devices such as boiler tubes.
The present invention relates to a vortex shedding
flowmeter having multiple bodies or bars forming flow obstruc-
tions in a single sensor assembly which provides a strong signal
and satisfactory ~nearity. The sensor comprises a generally
flat plate that is formed with slots that define spaced apart
bars which are spaced across the diameter of the flow pipe.
The sensor can be formed from a plate which will take about the
same space as an orifice plate. The width and spacing of the
bars is selected to provide a stable vortex pa~tern.
Because the device provides a frequency output which is
a higher frequency than conventional vortex meters using a
single larger bar, a simpler sensing circuit may be used and
faster response is possible. The vortex shedding bodies or bars,
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s~
when made in cooperation with other shsdding bodies ~rom a
single plate and have sufficient deflection so the movement of
the bars can be sensed as the indi~ation of vortex shedding.
The bars are aligned transversely o~ the flow direction but do
not operate in connection with any other bars positioned upstream
or downstream from the spaced bars.
Additionally, the construction provides ~o~ easily
inserted or removable sensors without dismantling the flow-
meter or the conduit carrying the fluid flow being sensed.
Because the sensor will fit in place of an ordinary
orifice plate in a flow line, the sensor can be used inter-
changeably with orifice plates that are now commonly used in
differential pressure sensing of flow in conduits.
In the Drawings:
Figure 1 is a typical sectional view of a portion of
a fluid carrying conduit having a vorteg shedding flowmeter
installed therein;
Figure 2 is a plan view of the vortex shedding
flowmeter of the present invention taken as on line 2--2
in Figure l;
Figure 3 is a sectional view taken as on line 3--3
in Figure 1, and illustrating the vortex generation in a ~irst
stage of operation;
Figure ~ is a sectional view taken on the same line
as Figure 3 with the showing of vortex generation in a second
stage;
Figure 5 is a vertical sectional view of a center one
of the vortex forming bars showing a signal pick-up installed
therein;
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52
Figure 6 is a vertical sectional view of a typical
vortex forming bar used in a vorte~ flowmeter having a capa-
citive type sensor installed therein;
Figure 7 is a sectional view taken as on line 7--7
in Figure 6;
Figure 8 is a plan view of a modified vor~ex flowmeter
made according to the present invention showing a modified
sensor also installed in such flowmeter; and
Figure 9 is a cross sectional view of a further
modified flowmeter taken generally along the same lines as
Figures 3 and 4 showing a flowmeter with four vortex forming
bars.
Figure 1 shows a fluid carrying conduit 10 which is
carrying fluid generally in the direction indicated by arrow
11 and which has a pair of flange type couplers 12, one on each
of two conduit sections, which are spaced apart to receive and
sandwich a vortex flowmeter plate assembly illustrated generally
at 13. The flanges are held together with suitable coupling
bolts 14, and they clamp and seal onto the vortex shedding flow-
meter plate 13.
The flowmeter plate 13 in this form of the inventionis made fro~ a circular plate with orifices or flow apertures
cut in the plate to define the cross bars. As can perhaps
best be seen in Figure 2, there is a perimeter or annular rim
15, and a center flow obstructing bar 16, a flow obstructing
bar 17 adjacent a first side thereof, and a flow obstructing
bar 18 adjacent a second side thereof. These bars or bodies
16, 17 and 18 are separated by suitable orifices or apertures
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gs~
(or slots) 21 and 22 on opposite sides of the ce~ter body 16
which are of equal size and shape, and orifices or apertures
(or slots) 23 and 24 to the outside of the bars 17 and 18, which
orifices 23 and 24 are also of equal shape and size. The outer
edges of each of the orifices or apertures indicated at 21a,
22A, 23A, and 24A are part circular and these edges define thè
effective flow diameter D of the flowmeter assembly.
The flowmeter plate 13 is relatively thin in direction
of the fluid stream 11, and the flow obstruction bodies or bars
16, 17 and 18 are formed to be substantially square (rectilinear)
in cross section as shown in Figures 3 and 4. The bars 16, 17
and 18 are made to cause flow separation, causing vortices to
be formed and shed from the bars along their side surfaces
(the surfaces parallel to the flow direction)a
The center bar 16 has a receptacle 25 defined therein,
leading from the exterior edge of the rim 15 and which is open
and accessible between the flanges 12. A piezoelectric sensor,
which is a motion sensor, indicated generally at 26, or some
other suitable motion sensor is placed into the receptacle
25 and can be held in the opening in a suitable manner. The
sensor 26 is utilized for sensing vibrations of the center
bar 16 caused by the formation and shedding of vortices as the
fluid in ~ conduit flows past the bars.
It has been found that preerably the sum of the widths
of the bars 16, 17 and 18 should be approximately .2 to O3 of
the diameter of the effective flow diameter of the plate. That
is, considering the width in diametral direction of each of the
members W, and the diameter of the effective opening in the plate
D, the sum of all of the widths of the plurality of bars or bodies
--5--
5;2
on the plate would e~ual .2D to .3D. This diameter D as shown
in Figure 2 is the effective 10w diameter defined by the edges
of the orifices or apertures in the meter assembly, rather than
the actual diameter of the conduit.
When a plurality of spaced obstruction bodies are
placed across the conduit and are commonly mounted to a rim
or ring as shown, the rim can be slipped into position in place
of a common orifice plate without modifying existing mounting
members.
The center bar 16 is centered on a diametral line
of the flow conduit, and the bars 17 and 18 are spaced an
equal distance from the center bar and ~rom the sides of the
conduit.
It has been found that when a plurality of the
obstruction bars or bodies such as 17, 18 and 19 which are
transversely aligned across the conduit are utilized, the forma-
tion of vortices will tend to shift across the diameter of the
conduit, so that primary or strong vortices are formed alter-
nately along the sides of the bars as shown in Figures 3 and 4.
Note that no upstream or downstream bars or obstructions are
used, but only the bars centered on a common plane perpendicular
; to the flow direction.
As a first step in explanation, previously formed
vortices indicated at 65 and 66 will be downstream from the flow
sensor, and the primary or strong vortices will be formed
along the sides of the bars 16 and 17 defining orifice or
opening 22. These vortices are shown at 67 and 68. Further
strong vortices will be formed along the side of the body
18 adjacent the conduit side by flow through the orifice or
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opening 23, and such a vortex is shown at 69 in Figure 3.
After the formation of these vortices 67, 68 and 69,
the primary vortices will next be formed along the sides of
the bars or flow obstruction bodies 16 and 18 defining orifice
or openin~ 21, as shown in Figure ~, and such vortices- are
shown at 70 and 71. The previous vortices 67, 68 and 69
are shown downstream slightly. Additional strong vortices
will be formed along one side of the body 17 by flow through
orifice or opening 24, as indicated at 72 in Figure 4. As
flow continues there is alternate "switching" or oscillation
of the place of formation of strong or primary vortices and
such alternation will cause a lateral vibration of the in-
dividual bars or bodies 16, 17 and 18. The vibration may be
picked up by the transducer 26, and the frequency output
will be recorded by suitable equipment well known in the prior
art for recording high frequency vibrations. It should be
noted that the end of the sensor shown in both Figures 2 and 5
is held snuggly at its outer end with a collar sleeve or other
member which is shown only schematically in Flgures 2 and 5.
As flow continues, the vortices will alternately
switch back and forth in a stable pattern. The maximum output
will be achieved when the previously recited preferred relation-
ship between the sum of the widths tW) of the flow obstruction
bars and the overall diameter (D) of the opening is maintained.
It should be noted that there will be a Iocal re-
striction at the flowmeter plate because the diameter "D", which
is the effective diameter in which the bars are placed is less
than the diameter of the conduit itself. The diameter D should
be no less than ahout 90~ of the internal diameter of the conduit
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,~
~ S 2
or pipe itself. If the open~ng diameter at the flowmeter plate
is substantially less than 90% of the diameter of the pipe,
turbulence will adversely affect the vortex generationO
The spacing between the individual bars is sufficiently
close so that any vortex formed along the side of one bar which
is adjacent another bar enhances, th ~ ugh a reinforcing action,
the vortex formation along the next adjacent bar. Signal
magnitudes on the order of 10 times the magnitudes obtained
with a single bar can be obtained by addition of e~tra bars
to obtain the desired coaction between the vortices formedO
The spacing between adjacent bars is preferably substantially
twice the width (W) of the bars.
If the bars are too close, the vorte~ shedding is
adversely effected and the vortex pattern described does not
occur resulting in a very erratic low level signal. For
example if the spacing = W the signal is not useful.
With the plurali~y of bars, it has been found that
the vortices will be shed uniformly along the length of the
individual bars, and each of the bars affects positively the
shedding of the vortices ~rom the adjacent bars.
It has also been ~ound that while three bars are
useful, two bars can also be used providing a single orifice or
opening between them and openings on the outer sides of the bars
(between the sides of the conduit and ~he individual bars).
Four bars can also be used if desired as will be shown. The
plate from which the bars are formed is sufficiently thin so that
it can be used in place of an orifice plate.
In the present device the bars are square tha~ is,
L = W. While L should not be substantially greater than W
--8--
for best results, the bars can be t'~inner than they are wide. L
should not be less than .6W for strong vortex formation, how-
ever.
In Figure 6, a center bar 30 of a typical vortex flow-
meter, such as that shown in Figures 1 tllrough 7, is shown with
a different type sensing unit. The bar 30 has an interior
passagewa~T 31, and a ceralnic rod 32 is installed in this opening
31. It can be seen that the inner end 32A of the rod tightly
fits into the opening 31, and the upper end 32B also tightly
10 f its in this opening. ~ center portion 33 of th e rod, which is
of a reduced diameter carries capacitor plate members com-
prising spaced, oppositely facing metal film layers irldicated
at 34 and 35.
Suitable leads can be run from the respective capaci-
tor plate members 34 and 35 up through the upper portion 32B
of the ceramic rod, and then out through the opening in the
center bar 30, as with the previous sensors.
In Figure 7, a cross sectional view of the sensor
is shown, and it can be seen that the side to side motion
20 of the bar 30 indicated by the double arrows 36 will cause
changes in capacitance as the bar 30 vibrates back and forth.
The capacitance changes occur between the respective surfaces
34 and 35 and the surface portions on the interior of the opening
which are adjacent to and aligned with these active capacitor
portions. The spacing will change during vibration, and this
spacing change causes capacitance changes that can be detected
with suitable capacitance detection equipment. The bar, as
shown is a circular cross section cylindrical member, rather than
triangular or rect ilinear.
_g_
5;~
In Figure 8, a ~urther modified form of the invention
is shown. In this ~orm, an orifice plate 40 is provided
with a peripheral rim 40A, and a pair of square cross section
center bars 41 and 42, respectively. The bars 41 and 42 are
de~ined by apertures or openings 43 and 44 which are part
circular in their outer periphery, and are to the outside
of the respective bars 41 and 42. A center aperture or opening
45~is defined between the two bars 41 and 42.
It can be seen that a ~irst hole 46 is drilled ~rom
the edge surface of the rim 40A into the center of the bar
41, a second hole 47 is drilled from the edge surface of the
rim 40A into the second bar 42. The upper portions of these
holes are of larger diameter ~han the lower portions, and it
can be seen that a ceramic rod 48 is inserted in the hole 46
and is securely held near its lower end 48A by reduced portion
of the hole 46, and likewise a second ceramic rod 49 is insert-
ed in the hole 47, and is held snuggly and securely adjacent
its lower portion 49A as shown in Figure 8. The rods 47 and 48
are moved back and forth as the bars 41 and 42 flex. Vibration
of the bars 41 and 42 is caused by the formation of vortices
along the side edges. It should be noted t~ at the clearance
of the holes 46 and 47 is selected to provide sufficient room
for vibration.
The upper ends of the two bars 48 and 49 are connected
by metal force bars 5~ and 51, respectively, which in turn are
attached to capac:itor plates 52A and 52B. Leads 53A and 53B
as shown lead from the plates 52A and 52B respectively. The
motion of the ceramic rods moves these capacitor plates alter-
nately toward and away from each other as vortices are shed
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from bars ~1 and 42. Thus ~he capacitance as measured on leads
53A and 53~ varies at the same frequency as the ~requency of
vortex shedding.
This arrangement has the advantage o~ cancelling
in-phase vibration of the plates 52A and 52B induced by pipe
or conduit vibration not related to vortex shedding since these
vibrations will not cause relative motion of the two capacitor
plates.
The mounting portions 48A and ~9A are near the
inflection point of the vibrating bars in order to get maximum
motion transmitted externally to the sensing uni~ at the
exterior of the plate. The motion of the bars at their inflection
includes a rotating component which causes large angular
rotation in the rods 47 and 48. ~his angular rota~ion causes
a large deflection at the end of the rods andi~fectively amplifies
the motion of the bars.
In Figure 9, a cross sectional view of a typical
orifice plate utilizing four bars, as opposed to the three
bars and two bars shown previously, is illustrated. A vibration
~0 or motion sensor would be used in at least one of the bars and
would be generally the same type as before. At least one of
the bars in Figure 9 would have an opening for receiving a sen-
sor.
The plate 55 as shown has bars 56, 57, 58 and 59
defined therein. The opening in the plate would be circular
as previously shown, in that the outer edges of the openings
between each of the bars would be rounded to define an internal
diameter D as shown in Figure 2.
It has been found that in certain applications, cer-
q~
tain combinations of bars in the sensor worlc better than others.For example, where water is flowing through a four inch diameter
pipe at rates between one and 15 feet per second, a four bar
configuration shown in Figure 9 is found to provide high out-
puts. The bars shown are quarter inch square, that is, the
plate itself is a quarter inch thick and the bars are a quarter
inch wide. The spacing between ~e bars at the center plane
of the plate (along a diametral line) is one half inch, or
double the length of the bars in direction of the flow. Using
a frequency to voltage analogue type output having a two
second time constant, the analogue output variations are within
one percent for the specific orifice plate 55 that is shown
in Figure 9.
In other configurations, up to a five percent analogue
output variation is found. This variation (which may be called
a fluctuation or ripple in the signal) is undesirable and a low-
er value gives more reliable information as to the flow rates.
Thus, in all forms of the combination the plurality
of bars are utilized to enhance the output when vortices are
formed along the side surfaces of the bars. It should be noted
that when round bars are utilized, the facing surface portions
actually are substantially half cylinders, but even with round
bars, as well as with rectilinear or triangular bars, there
are facing surface portions between adjacent bars. In a
triangular cross section bar, one surface of the triangle could
be normal to the flow direction.
In summary, the obstruction bars are formed on a plate
so that they have an equal length dimens~ni (L) in direction
of flow, and are spaced side by side on a common bisecting
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~'r~ j2
plane transverse to the flow stream, and they are spaced suffi-
ciently close laterally so that each reinforces the vortices
formed at adjacent bars.
The flowmeter has bars that are centered in direction
of the flow on a plane perpendicular to the flow direction
and are spaced in direction transverse to the flow direction
to cause the lateral alternation of primary vortex formation
for strong signal output. There axe no additional posts or
obstructions either upstream or downstream of -the trans-
versely aligned bars that might dampen or destroy the vortexformation along alternate side surfaces of the transversely
aligned bars.
Hollow or tubular square bars can be used to minimize
mass and sensitivity to pipe vibrations. Triangular, round or
other cross sections can also be used. Although the bars are
shown as uniform in cross section along their length they could
vary in cross section. The width of each bar could vary to
correspond to the velocity profile along its length to enhance
vortex shedding simultaneously along the entire length of each
bar.
In addition, although the bars in a given flowmeter
are shown to be the same width, the width of the various bars
could also be individually proportioned to correspond to the
velocity profile across the pipe to enhance simultaneous vortex
shedding from all of the bars.
Piezoelectric and capacitive motion sensing have been
described. However, other motion sensors could be employed,
such as electromagnetic or optical for example.
While motion sensing of individual bars only has been
described as the preferred design, where space permits, other
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`~
means o~ sensing vortices could be employed, such as acoustic
or thermal conduction probes posi~ioned downstream (or upstream)
of the vortex generating assembly.
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