Abstrict A flow meter, especially for measuring fluid flow passing through
large-diameter conduits, in which a rod-shaped vortex generating
body is built in a conduit section in a direction transverse to
the fluid stream passing therethrough and in which Karman vortices
detach themselves, the frequency of which, which is measured by
feeler elements, corresponds to the speed of the fluid passing through
the conduit. In order to assure that the aforementioned vortices
detach themselves uniformly over the whole length of the vortex
generating body even if the flow meter is built into a conduit of
large diameter, the tube section is divided by at least one thin
dividing wall into two vortex chambers. The vortex generating body
is arranged normal to the aforementioned dividing wall, and the
feeler elements for the sensing of the vortex frequency are arranged
in one of the vortex chambers.
Claims What is claimed as new and desired to be protected by Letters Patent
is set forth in the appended claims:
1. In a flow meter, especially for measuring fluid flow passing
through large-diameter tubular conduits, the tubular conduit having
a longitudinal axis and a central section plane extending through
said axis, a combination comprising a rod-shaped vortex generating
body from which Karman vortices detach when fluid flow passes through
the conduit, the frequency of vortices corresponding to the speed
of the fluid flow through the conduit, said body having a longitudinal
axis; a thin dividing wall extending through said central section
plane and dividing said conduit into at least two vortex chambers,
said dividing wall extending in said conduit normal to the longitudinal
axis of said body so that two substantially separated vortices are
respectively generated in said chambers, which vortices are detached
from said body without mutual interaction with each other; and feeler
means for measuring the frequency of said Karman vortices.
2. A combination as defined in claim 1 wherein said feeler means
are coordinated only with one of said vortex chambers.
3. A combination as defined in claim 1 wherein said at least one
dividing wall is constituted by a planar rectangular metal disk
fixedly connected at opposite edges to the inner surface of the
conduit, and wherein said vortex generating body extends to opposite
sides of said disk through the medium region of the latter.
4. A combination as defined in claim 1 wherein said rod-shaped
vortex generating body has a T-shaped cross section.
5. A combination as defined in claim 1 wherein said body extends
in said conduit substantially symmetrically relative to said dividing
wall.
6. In a flow meter, especially for measuring fluid flow passing
through large-diameter tubular conduits, the tubular conduit having
a longitudinal axis and a central section plane extending through
said axis, a combination comprising a rod-shaped vortex generating
body from which Karman vortices detach when fluid flow passes through
the conduit, the frequency of vortices corresponding to the speed
of the fluid flow through the conduit, said body having a longitudinal
axis; at least one thin dividing wall extending substantially in
the region of said central section plane and dividing said conduit
into at least two vortex chambers, said dividing wall extending
in said conduit normal to the longitudinal axis of said body so
that two substantially separated vortices are respectively generated
in said chambers, which vortices are detached from said body without
mutual interaction with each other, said dividing wall being constituted
by a planar rectangular metal disk having a height smaller than
the diameter of the conduit and connected at a middle region thereof
to said vortex generating body with the outer ends of the latter
fixed to the inner surface of the conduit; and feeler means for
measuring the frequency of said Karman vortices.
7. A combination as defined in claim 6 wherein a plurality of
substantially parallel transversely spaced dividing walls are provided
in the conduit section.
8. In a flow meter, especially for measuring fluid flow passing
through large-diameter tubular conduits, the tubular conduit having
a longitudinal axis and a central section plane extending through
said axis, a combination comprising a rod-shaped vortex generating
body from which Karman vortices detach when fluid flow passes through
the conduit, the frequency of vortices corresponding to the speed
of the fluid flow through the conduit, said body having a longitudinal
axis; at least one thin dividing wall extending substantially in
the region of said central section plane and dividing said conduit
into at least two vortex chambers, said dividing wall extending
in said conduit normal to the longitudinal axis of said body so
that two substantially separated vortices are respectively generated
in said chambers, which vortices are detached from said body without
mutual interaction with each other, said dividing wall being constituted
by a planar elliptical metal disk having a large axis extending
in axial direction of the conduit and a small axis of a length smaller
than the diameter of the conduit, said disk being connected at the
middle region thereof to said vortex generating body with the outer
ends of the latter fixed to the inner surface of the conduit; and
feeler means for measuring the frequency of said Karman vortices.
9. In a flow meter, especially for measuring fluid flow passing
through large-diameter tubular conduits, the tubular conduit having
a longitudinal axis and a central section plane extending through
said axis, a combination comprising a rod-shaped vortex generating
body from which Karman vortices detach when fluid flow passes through
the conduit, the frequency of vortices corresponding to the speed
of the fluid flow through the conduit, said body having a longitudinal
axis; at least one thin dividing wall extending substantially in
the region of said central section plane and dividing said conduit
into at least two vortex chambers, said dividing wall extending
in said conduit normal to the longitudinal axis of said body so
that two substantially separated vortices are respectively generated
in said chambers, which vortices are detached from said body without
mutual interaction with each other, said dividing wall being constituted
by a planar circular metal disk having a diameter smaller than that
of the conduit and being arranged in a plane including the axis
of the latter, said disk being connected in a center region thereof
to said vortex generating body with the outer ends of the latter
fixed to the inner surface of the conduit; and feeler means for
measuring the frequency of said Karman vortices.
Description BACKGROUND OF THE INVENTION
The present invention relates to a flow meter, especially for measuring
fluid flow passing through large diameter conduits, in which, in
a conduit section through which the fluid stream passes, a rod-shaped
vortex generating body extending transverse to the direction of
fluid flow is arranged, from which Karman vortices detach themselves,
the frequency of which corresponds to the speed of the fluid passing
through the conduit, which speed is measured by a feeler element.
In such a flow meter, which is constructed as a vortex counter,
there exists between the frequency of the produced Karman vortices
and the fluid flow speed the relationship
in which f is the vortex detaching frequency, v the speed of the
fluid flow, b the characteristic width of the vortex generating
body, and S the Strouhal number. The Strouhal number S is determined
by the equation
wherein v is the speed of the fluid, f is the vortex frequency,
and b is the width of the vortex generating body. The cross section
of the vortex generating body determines the aforementioned Strouhal
number, which over a wide range of fluid speed is constant, so that
also the relationship between the frequency of the created Karman
vortices and of the fluid stream speed is correspondingly linear.
Optimum vortex signals with a high signal quality and a large linear
region can be obtained by corresponding selection of the cross section
of the vortex generating body in relationship to the cross section
of the conduit through which the fluid passes.
As will be clear from the first of the equations above, the vortex
detaching frequency drops with increasing width of the vortex generating
body. If one uses, to obtain a geometric similarity during mounting
of the vortex countar into conduit with increasingly larger diameter,
with the same or similar cross section of the vortex generating
body and the same ratio of the cross section of the body to the
cross section of the conduit, then the Strouhal number will remain
the same, but the frequency of the Karman vortices will drop with
increasing width of the body, so that the determination of the vortex
frequency will become more difficult with the increase of the diameter
of the conduit. Thus, for instance, at a conduit diameter of 250
mm a satisfactory vortex signal can still be obtained, whereas at
a conduit diameter of 600 mm the vortex frequency is so low that
the evaluation of the same in the connected electronic computing
device meets with great difficulty.
If the width b of the vortex generating body to be built into large-diameter
conduits would be reduced, then according to the above equation
the vortex frequency f could be increased; however, the stability
of the vortex path would be endangered, since the ratio of slenderness
of the vortex generating body which extends through the whole cross
section of the conduit would be too great. In this case, the vortices
would not detach themselves in the form of cylinders from the total
length of the vortex generating body, but due to the small coupling
of the fluid different detaching regions would occur in which the
detachment of the vortices would not be in phase, whereby disturbing
transverse streams would be formed, which would impair the quality
of the signals.
SUMMARY OF THE INVENTION
It is the object of the present invention to construct a vortex
counter in such a manner that during mounting of the same in conduits
of large diameter sufficiently high vortex frequencies are obtained,
without detrimentally affecting the ratio of slenderness of the
body and therewith the measured signal.
With these and other objects in view, the flow meter according
to the present invention, especially for measuring fluid flow passing
through large-diameter conduits mainly comprises at least one thin
dividing wall extending through a central plane of a section of
the conduit and dividing the conduit sections in at least two vortex
chambers, a rod-shaped vortex generating body from which Karman
vortices will detach, the frequency of which corresponds to the
speed of the fluid flow through the conduit, in which said body
has a longitudinal axis extending substantially normal to the aforementioned
dividing wall and feeler means for measuring the frequency of the
Karman vortices.
The arrangement preferably comprises a single thin dividing wall
arranged in a plane including the axis of the conduit and the thus
resulting division of the conduit section carrying the vortex generating
body into two vortex chambers, will produce in each vortex chamber
a separate vortex path respectively detaching itself from each half
of the vortex generating body. The ratio of slenderness which results
from the length of the vortex generating body in relationship to
its width, will thereby be reduced by half, so that the vortices
will now detach themselves from the vortex generating body uniformly
and without any phase shifting while forming stable rotation cylinders.
With vortex counters for use with conduits of large diameters,
it is therefore possible to reduce the width of the vortex generating
body to a half, so that the vortex detaching frequency is doubled
and now sufficiently great to assure its evaluation in the electronic
computer device connected thereto. A deterioration of the measuring
signal, due to non-uniform vortex detachment and detrimental cross
streams in the vortex paths, is avoided due to the division of the
vortex generating body. The thin dividing wall creates practically
no additional flow resistance; in fact, the pressure loss in the
conduit section can be considerably reduced due to the attainable
reduction of the width of the vortex generating body.
If instead one dividing wall extending along the axis of the conduit,
a plurality of parallel dividing walls is provided in the conduit
section having the vortex generating body, then it is possible to
reduce the width of the vortex generating body still further, so
that if the flow meter according to the present invention is used
in conduits with very large diameters, a still perfect vortex detaching
action with sufficiently high frequency can be obtained.
The feeler elements for the determination of the vortex frequency
need only be built into one of the vortex chambers, whereas the
vortex generating body extends over the whole cross section of the
conduit, so that a symmetrical fluid flow in the conduit will be
maintained.
The single dividing wall which extends along the axis of the conduit
may be constituted by a thin rectangular plate of sheel metal, which
extend over the whole height of the conduit and which divides the
cross section of the conduit in the actuating region of the vortex
generating body into halves. Such a sheet metal disk can be easily
built into the conduit section. By arranging the vortex generating
body in the middle region of the sheet metal disk, the latter is
arranged in the region of the vortex detachment, so that a reciprocal
action between the adjacent vortex chambers is avoided.
Since the detachment region of the vortices extends upwardly and
downwardly up to the inner surface of the conduit, it is possible
to use also rectangular, circular or an elliptically shaped sheet
metal disk as the dividing wall, which in its height or in its diameter
is smaller than the diameter of the conduit section and which is
in its middle region connected to the vortex generating body. Since
the sheet metal disk which is arranged in the center of the conduit,
is carried by the vortex generating body, a separate connection
for the disk to the wall of the conduit is not necessary.
The novel features which are considered as characteristic for the
invention are set forth in particular in the appended claims. The
invention itself, however, both as to its construction and its method
of operation, together with additional objects and advantages thereof,
will be best understood from the following description of specific
embodiments when read in connection with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a vertical cross section through one modification of
the present invention with a single dividing wall and a vortex generating
body attached thereto;
FIG. 2 is a cross section taken along the line II--II of FIG. 1;
FIG. 3 is a longitudinal cross section similar to FIG. 1 but showing
a circular separating wall carried by the vortex generating body
attached thereto;
FIG. 4 is the cross section taken along the line IV--IV of FIG.
3;
FIG. 5 is a further modification in accordance with the present
invention, in which two parallel transversely spaced dividing walls
are provided in the conduit section;
FIG. 6 is a cross section taken along the line VI--VI of FIG. 5;
FIG. 7 is a longitudinal cross section of an additional modification
according to the present invention, which includes a rectangular
dividing wall having a height smaller than the diameter of the conduit
section and being carried by the vortex generating body, the opposite
ends being fixed to the conduit section;
FIG. 8 is a cross section taken along the line VIII--VIII of FIG.
7;
FIG. 9 is a longitudinal cross section through yet a further embodiment
according to the present invention, in which the dividing wall is
an elliptically shaped dividing wall having a small axis smaller
than the diameter of the conduit section and being carried by the
vortex generating body; and
FIG. 10 is a cross section taken along the line X--X of FIG. 9.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the conduit section 1 illustrated in FIGS. 1 and 2 a dividing
wall in the form of a thin rectangular sheet metal disk 2 is arranged
extending in the longitudinal center plane of the conduit section
1 and having a height equal to the diameter of the conduit section
1 and connected at opposite longitudinal end edges by weld seams
4 or the like to the inner surface 3 of the conduit section 1. The
vortex generating body 5 extends with its longitudinal axis normal
to the dividing wall 2 and to opposite sides of the latter over
the whole width of the conduit section 1. The conduit section 1
is divided by the dividing wall 2 into two vortex chambers 6 and
7 in which the same flow characteristics will occur, since the vortex
generating body extends symmetrically to the dividing wall 2 through
both vortex chambers 6 and 7.
An ultrasonic sound measuring device comprising an ultrasonic transmitter
8 and an ultrasonic sound receiver 9 as feeler element is arranged
downstream of the vortex generating body 5 as considered in direction
of flow of fluid passing through the conduit section 1 in the vortex
chamber 6 for the scanning of the Karman vortices. A conductor 10
leading from the ultrasonic sound transmitter to a non-illustrated
sound producer is connected to the feeler element 8 and a corresponding
conductor 11 is connected to the element 9 and leading to the non-illustrated
electronic computing device known per se in the art. The ultrasonic
beam emanating from the ultrasound transmitter 8 is modulated by
the vortices which detach themselves from the vortex generating
body 5 and this change of the beam is received by the ultrasonic
receiver 9 and a signal for the presence of a vortex is transmitted.
Different feeler elements known in the art may also be used instead
of the ultrasonic sound measuring device mentioned above. Such devices
are for instance disclosed in the U.S. Pat. Nos. 3680375; 3756078;
and 3788141.
The vortex generating body 5 is arranged in about the middle region
of the dividing wall 2 so that the vortices produced in the vortex
chambers 6 and 7 can detach themselves from the body 5 without mutual
interaction. Thereby the vortex detachment is stabilized, so that
the width b of the body 5 of for instance T-shaped cross section
can be reduced at the same ratio of slenderness to a half, and therewith
the frequency of the detaching vortices be doubled. In conduits
of large diameter, a vortex frequency sufficiently high for the
electronic evaluation circuitry will be obtained.
In the embodiment illustrated in FIGS. 3 and 4 there is instead
a rectangular sheet metal disk 2 which extends through the whole
height of the tube section 1 a circular thin sheet metal disk 12
provided, the diameter of which is smaller than the inner diameter
of the conduit section 1 so that the conduit cross section is not
entirely divided into halves. The diameter of the circular disk
12 is, however, large enough so that, in the region of detachment
of the vortices forming in the vortex chambers 6 and 7 and in the
adjacent marginal zones, the vortices are sufficiently separated
from each other, so that no interaction of the vortices produced
in the vortex chambers 6 and 7 will result. The circular metal sheet
disk 12 can be produced in a simple manner, and this disk 12 is
fixedly connected with the vortex generating body 5 the opposite
ends of which are fixed in any desired manner to the inner surface
of the conduit section 1.
In the embodiment shown in FIGS. 5 and 6 two parallel dividing
walls 13 and 14 are built in the conduit section 1 so that this
conduit section 1 is, in the region of the vortex generating body
5 divided into three vortex chambers 15 16 and 17. The ultrasonic-sound-measuring
ultrasonic sound transmitter 8 and ultrasonic sound receiver 9 are
in this case connected to the middle vortex chamber 16.
In the embodiment shown in FIGS. 7 and 8 a dividing wall 12a of
rectangular configuration is used, the height of which is slightly
smaller than the diameter of the conduit section 1.
A further embodiment is shown in FIGS. 9 and 10 in which the dividing
wall 12b is of elliptical configuration, the large axis of which
extends in the direction of the axis of the tube section 1 and
the length of the small axis of which is smaller than the diameter
of the tube section 1. In the embodiments illustrated in FIGS. 5-10
the dividing walls 12a or 12b are carried by the respective vortex
generating body 5 which is fixedly connected at opposite ends to
the inner surface of the respective tube section 1.
It will be understood that each of the elements described above,
or two or more together, may also find a useful application in other
types of flow meters in which a rod-shaped vortex generating body
extends through a tube section through which the fluid stream to
be measured passes in a direction transverse to the direction of
the fluid stream, differing from the types described above.
While the invention has been illustrated and described as embodied
in a flow meter of the aforementioned kind, especially for use in
conduits of large diameter in which the conduit section in which
the vortex generating body is provided is divided by at least one
dividing wall into at least two vortex chambers through which the
vortex generating body extends, it is not intended to be limited
to the details shown, since various modifications and structural
changes may be made without departing in any way from the spirit
of the present invention.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can, by applying current
knowledge, readily adapt it for various applications without omitting
features that, from the standpoint of prior art, fairly constitute
essential characteristics of the generic or specific aspects of
this invention. |