Abstrict A Karman vortex flow meter in which a main passage 1 and a bypass
passage 2 are adjacent to each other; a throttle portion 12 is formed
at the inlet of the bypass passage to continuously reduce the cross-sectional
surface area of the passage, and a flared portion 14 is formed in
the bypass passage 2 so that the cross-sectional surface area of
the passage is continuously enlarged from an intermediate portion
of the passage to the outlet of it. Further, the inlets and the
outlets of the main passage and the bypass passage are each arranged
in single planes perpendicular to the flow direction of the fluid
to be measured, and the boundary portions 16 17 between the main
passage and the bypass passage 2 are respectively formed to have
a smallest thickness.
Claims What is claimed is:
1. A Karman vortex flow meter, comprising: a main passage through
which a fluid to be measured is passed, at least one bypass passage
disposed closely adjacent and parallel to the main passage to pass
a part of the fluid therethrough, and vortex flow detecting means
disposed in the main passage, wherein the bypass passage comprises
a throttle portion for reducing gradually and continuously the cross-sectional
area of the bypass passage from an inlet thereof, and a flared portion
for enlarging gradually and continuously the cross-sectional area
of the bypass passage from an intermediate portion thereof to an
outlet thereof, and wherein an angle of convergence at the throttle
portion and an angle of divergence at the flared portion, relative
to an axis of the bypass passage, is about 3.degree..
2. A Karman vortex flow meter according to claim 1 wherein the
bypass passage comprises an outer shell portion and an inner flow
passage body detachably inserted in the outer shell portion.
3. A Karman vortex flow meter according to claim 1 wherein an
inlet of the main passage and the inlet of the bypass passage are
arranged in a single plane substantially perpendicular to the flow
direction of the fluid, and a boundary wall between the main passage
and the bypass passage has a small, knife edge-like thickness at
the inlets thereto.
4. A Karman vortex flow meter according to claim 1 wherein an
outlet of the main passage and the outlet of the bypass passage
are arranged in a single plane substantially perpendicular to the
flow direction of the fluid, and a boundary wall between the main
passage and the bypass passage has a small, knife edge-like thickness
at the outlets thereof.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Karman vortex flow meter. Particularly,
the present invention relates to a Karman vortex flow meter for
reducing a pressure loss in fluid passing through it by improving
the shape of its flow passage.
2. Discussion of Background
A Karman vortex flow meter is generally of such construction that
a detection device for detecting a quantity of a vortex flow is
disposed in a tubular main passage. In order to make the manufacturing
of the Karman vortex flow meter having different cross-sectional
surface areas easy, it has been proposed not to change the cross-sectional
surface area of the main passage but to provide separately a bypass
passage along the flowing direction of the main passage wherein
the cross-sectional area of the bypass passage is changed.
A Karman vortex flow meter having such a bypass passage is disclosed
in, for instance, Japanese Unexamined Utility Model Application
No. 53422/1980.
The Karman vortex flow meter disclosed in the Publication is shown
in FIGS. 1 through 3.
FIGS. 1 and 3 are respectively side views cross-sectioned and a
front view of a first embodiment of the Karman vortex flow meter
wherein a main passage 1 and bypass passages 2 are provided. The
main passage 1 is of a tubular form in which an inlet portion 1a
is enlarged; the cross-sectional surface area of the flow passage
of the main passage 1 is reduced at a throttle portion 1b, and a
reduced cross-sectional surface area portion is extended to an outlet
portion 1c. In the outlet portion 1c, a vortex flow generating means
3 and a vortex flow detecting means 4 which constitute a vortex
flow detecting device, are provided. The vortex flow detecting means
4 is constituted by an ultrasonic wave transmitter 4a and an ultrasonic
wave receiver 4b.
A rectifier 5 is disposed at the enlarged portion, i.e., the inlet
portion 1a. An ultrasonic wave absorbing material 6 made of, for
instance, non-woven cloth or the like is disposed in the entire
region or a necessary portion along the tubular inner wall of the
main passage 1 so that the function of the vortex flow detecting
means 4 can be improved. The ultrasonic wave transmitter 4a and
the ultrasonic wave receiver 4b are respectively covered with net-like
bodies 7. The bypass passages 2 are so arranged as to surround the
main passage 1 along the flow direction of fluid. The cross-sectional
surface area of each of the bypass passages 2 is reduced at an inlet
portion 2a and the cross-sectional surface area is enlarged at the
portion corresponding to the throttle portion 1b of the main passage
1 the enlarged portion being extended to an outlet portion 2b.
Supporting pieces 8 are provided in the bypass passages 2 in order
to reinforce the main passage 1 and the bypass passages 2.
FIG. 2 shows a second embodiment of the Karman vortex flow meter
disclosed in the above-mentioned Publication. In this embodiment,
the bypass passages 2 do not surround the main passage 1 but they
are formed separately from the main passage 1 so that the main passage
1 and the bypass passages 2 are joined in the radial direction.
The bypass passages 2 have respectively an enlarged inlet portion
2a in the same manner as the enlarged inlet portion 1a of the main
passage 1 and they are joined at the inlet portions 1a and 2a.
Numerals 9 designate flanges for connecting another passage, and
numerals 21 designate rod-like bodies which may have different cross-sectional
surface areas so that the flow rate of fluid flowing in the bypass
passages can be controlled. The other structural elements are the
same as those in the first embodiment.
In either case, the cross-sectional surface area of the main passage
1 is enlarged at the inlet portion 1a and a rectifier 5 is disposed
in the enlarged portion so that the detection of a vortex flow can
be effectively conducted, and the outlet portion 1c of the main
passage 1 in which the flow rate detecting device is disposed has
a reduced cross-sectional surface area.
In operation of the conventional vortex flow meters, fluid such
as air flowing through a suction pipe (not shown) is introduced
through the inlet portions 1a, 2a of the main passage 1 and the
bypass passages 2 of the Karman vortex flow meter. The fluid in
the main passage 1 is rectified by the rectifier 5 and then, the
fluid impinges the vortex generating means 3 in the outlet portion
1c to generate a vortex. The flow rate of the fluid is measured
by detecting a quantity of the vortex flow by means of the vortex
flow detecting means 4.
The conventional Karman vortex flow meter had the problems described
blow.
In the Karman vortex flow meter shown in FIGS. 1 and 3 since a
portion extended to the outlet portion 2b from the inlet portion
2a in the bypass passages was abruptly enlarged, there was a large
possibility of causing separation and disturbance in the fluid due
to a vortex flow at the abruptly enlarged portion. The separation
and the disturbance of the fluid resulted in that the kinetic energy
of the fluid was transformed into a heat energy, whereby the reduction
of the kinetic energy caused an increased pressure loss. When the
pressure loss increased, the density of the fluid is decreased.
When such a Karman vortex flow meter is disposed in an engine system,
the reduction of engine power is invited.
In the Karman vortex flow meter shown in FIG. 2 since the bypass
passages 2 were enlarged at each of the inlet portions 2a, the disturbance
of the fluid could be minimized at a portion extended to the outlet
portions 2b from the inlet portions 2a. However, the conventional
flow meter had such a construction that the main passage 1 was formed
separately from the bypass passages 2 and then, they were joined
later. Accordingly, the wall thickness at a joining portion was
fairly thick, so that there was a resistance to the fluid entering
into the Karman vortex flow meter, with the result that the disturbance
of the fluid was large, and there was an increased pressure loss
in the same manner as the flow meter as shown in FIG. 1 and 3.
Further, in the flow meter shown in FIG. 2 since the flow passage
of the bypass passages 2 was abruptly enlarged at the outlet portions,
the pressure loss was further increased.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a Karman vortex
flow meter of a type having a bypass passage which bypasses a part
of fluid from a main passage in which a vortex flow detecting means
is provided wherein a pressure loss due to disturbance of the fluid
can be reduced by minimizing the disturbance of the fluid in the
bypass passage or minimizing the disturbance of the fluid at an
inlet and outlet portions of the main passage.
In accordance with the first invention, there is provided a Karman
vortex flow meter which comprises a main passage through which fluid
to be measured is passed, a bypass passage disposed in parallel
to the main passage to pass a part of the fluid therethrough, and
a vortex flow detecting means provided in the main passage. The
bypass passage comprises a throttle portion for reducing continuously
the cross-sectional surface area of the bypass passage from an inlet
portion, and a flared portion for enlarging continuously the cross-sectional
surface area of the bypass passage from an intermediate portion
of the bypass passage to an outlet portion of the same.
In accordance with the second invention, there is provided a Karman
vortex flow meter which comprises a main passage through which fluid
to be measured is passed, a bypass passage disposed in parallel
to the main passage to pass a part of the fluid therethrough, and
a vortex flow detecting means provided in the main passage. An inlet
of the main passage and an inlet of the bypass passage are arranged
in a single plane which is substantially perpendicular to the flowing
direction of the fluid to be measured; the main passage and the
bypass passage are adjacent to each other, and the boundary portion
between the main passage and the bypass passage at their inlets
has the smallest thickness necessary for separating the main passage
from the bypass passage.
In accordance with the third invention, there is provided a Karman
vortex flow meter which comprises a main passage through which fluid
to be measured is passed, a bypass passage disposed in parallel
to the main passage to pass a part of the fluid therethrough, and
a vortex flow detecting means provided in the main passage. An outlet
of the main passage and an outlet of the bypass passage are arranged
in a single plane which is substantially perpendicular to the flow
direction of the fluid to be measured; the main passage and the
bypass passage are adjacent to each other, and the boundary portion
between the main passage and the bypass passage at their outlets
has the smallest thickness necessary for separating the main passage
from the bypass passage.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the attendant
advantages thereof will be readily obtained as the same becomes
better understood by reference to the following detailed description
when considered in connection with the accompanying drawings, wherein:
FIG. 1 is a cross-sectional view viewed from the top of a conventional
Karman vortex flow meter;
FIG. 2 is a cross-sectional view viewed from the top of another
conventional Karman vortex flow meter;
FIG. 3 is a front view of the flow meter shown in FIG. 1;
FIG. 4 is a cross-sectional view viewed from the top of a Karman
vortex flow meter according to a first embodiment of the present
invention;
FIG. 5 is a cross-sectional view taken along a line A--A in FIG.
4;
FIG. 6 is a front view of the Karman vortex flow meter according
to the first embodiment of the present invention;
FIG. 7 is a cross-sectional view viewed from a side of a Karman
vortex flow meter according to a second embodiment of the present
invention;
FIG. 8 is a front view of the flow meter according to the second
embodiment of the present invention; and
FIG. 9 is a cross-sectional view viewed from a side of a Karman
vortex flow meter according to a third embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings wherein the same reference numerals designate
the same or corresponding parts, FIGS. 4 through 6 designate the
first embodiment of the present invention.
A Karman vortex flow meter comprises a main passage 1 and a bypass
passage 2. The main passage 1 has an inlet portion 1a, a throttle
portion 1b and an outlet portion 1c in the same manner as the conventional
flow meter. The fluid flow area of the inlet portion 1a is enlarged
in comparison with that of the outlet portion 1c, and a rectifier
5 is disposed in the inlet portion 1a. A vortex generating pillar
10 and vortex detecting pillar 11 are provided in an intermediate
portion of the main passage 1.
The operation of the detection of a flow rate of fluid passing
through the main passage 1 is the same as that described with respect
to the conventional technique, and accordingly, description is omitted.
The bypass passage 2 is formed of a tubular body 20 as shown in
FIG. 5 wherein the cross-sectional surface area of the flow passage
is continuously or gently reduced from the inlet portion, and the
portion where the cross-sectional surface area of the bypass passage
2 is continuously or gradually reduced constitutes a throttle portion
12.
A reduced portion 13 where the cross-sectional surface area of
the flow passage is minimum, is formed around the middle portion
of the flow passage of the bypass passage 2. A flared portion 14
is formed from the reduced portion 13 to the outlet of the bypass
passage 2 so that the cross-sectional surface area of the flared
portion is continuously or gently increased. The throttle portion
12 the reduced portion 13 and the flared portion 14 are formed
by thickening or thinning the inner wall thickness of the tubular
body which constitutes the bypass passage 2.
An angle formed between the throttle portion 12 or the flared portion
14 and the flow passage or the flow direction of fluid (i.g. .theta..sub.1
+.theta..sub.2 or .theta. in FIG. 5) is about 6.degree..
The edge of the inlet portion of the main passage 1 and the edge
of the inlet portion of the bypass passage 2 are arranged in a single
and same plane which is substantially perpendicular to the flowing
direction of the fluid to be measured. Further, as shown in FIG.
5 the main passage 1 and the bypass passage 2 are adjacent to each
other in the direction traversing their flow passages by interposing
a partition wall 15 which constitutes a part of tubular bodies.
Further, a boundary portion 16 (a part of the partition wall 15)
between the main passage 1 and the bypass passage 2 at the inlet
portion of the Karman vortex flow meter has the smallest thickness
necessary for separating the main passage 1 from the bypass passage
2. The thickness of the boundary portion 16 can be to the extent
that it is difficult to cause disturbance of the fluid even when
the fluid introduced into the vortex flow meter impinges the boundary
portion 16.
The edges of the outlet portions of the main passage 1 and the
bypass passage 2 are arranged in a single and the same plane in
the same manner as the edges of the inlet portions of the main passage
1 and the bypass passage 2 and the thickness of a boundary portion
17 can be the smallest thickness in the same manner as described
with respect to the boundary portion 16.
In the Karman vortex flow meter according to the first embodiment
of the present invention, the behavior of the fluid passing through
the bypass passage 2 is as follows. In FIG. 5 the fluid is introduced
from the direction of the flow arrows. Then, at the upstream side
22 of the partition wall, a part of the fluid impinges on the boundary
portion 16. However, since the boundary portion 16 is formed to
have the smallest thickness, the fluid does scarcely impinge on
the boundary portion 16 and accordingly, it flows into the Karman
vortex flow meter without causing disturbance.
Then, the fluid flows into the throttle portion 12 having a continuously
reduced flow passage in the bypass passage 2. The fluid, then, flows
through the flared portion 14 having a continuously enlarged flow
passage. Thus, the fluid dose not flow through portions where the
cross-sectional surface area of the flow passage is abruptly changed.
Accordingly, there is no possibility of separation and disturbance
of the fluid in the bypass passage 2 and the fluid flows smoothly.
Further, since the thickness of the boundary portion 17 at the
outlet of the bypass passage 2 is also formed to have the smallest
thickness necessary for separating the main passage from the bypass
passage, disturbance of the fluid in a portion where streams of
the fluid are joined at the downstream end 23 of the partition wall
15 which separates the main passage 1 from the the bypass passage
2 can be minimized. Further, since the angle formed between the
flared portion 14 and the direction of the flow passage is about
6.degree., a pressure loss which is caused when the fluid flows
out the bypass passage 2 can be reduced.
FIGS. 7 and 8 show the second embodiment of the present invention
wherein FIG. 7 is a cross-sectional side view from a side of the
vortex flow meter and FIG. 8 is a front view of it.
In the second embodiment, four bypass passages 2 are provided so
as to surround four sides of the main passage 1. The inlet portion
1a of the main passage 1 is enlarged and the outlet portion 1c is
throttled so that the cross-sectional surface area of the main passage
is reduced in comparison with that of the inlet portion 1a.
The construction of each of the bypass passages 2 is the same as
that of the first embodiment. Namely, the bypass passage 2 has a
throttle portion 12 where the cross-sectional surface area of the
flow passage is continuously reduced from the inlet portion to the
downstream side of it, and a flared portion 14 having a continuously
enlarged portion which is formed from an intermediate portion of
the flow passage to the outlet portion. Further, boundary portions
16 17 which separate the main passage 1 from the bypass passages
2 at the inlet and outlet portions are so formed as to have the
smallest thickness. Further, an angle formed between the slant surface
of the throttle portion 12 or the flared portion 14 and the flow
direction of the fluid (.theta..sub.1 +.theta..sub.2) is about 6.degree..
The operation of the second embodiment is the same as that of the
first embodiment, and accordingly description is omitted.
FIG. 9 shows a third embodiment of the present invention.
The construction of the Karman vortex flow meter of the third embodiment
is substantially the same as that of the first embodiment except
that the bypass passage is constituted by an outer shell portion
18 and a passage main body 19 wherein the passage main body 19 is
detachably fitted to the inner wall of the outer shell portion 18.
The third embodiment allows to easily form bypass passages having
different cross-sectional surface areas.
In accordance with the first embodiment of the present invention,
the bypass passage has no portion where the cross-sectional surface
area of the flow passage is abruptly changed, whereby fluid can
be smoothly passed without causing separation and disturbance. Further,
a pressure loss of the fluid in the flow passage can be prevented,
and the reduction of the kinetic energy of the fluid is avoidable.
In accordance with the second embodiment of the present invention,
there is no risk that the fluid introduced into the bypass passage
impinges on the boundary portion thereby resulting disturbance flow,
and a pressure loss of the fluid can be prevented.
In accordance with the third embodiment of the present invention,
there is no risk that two streams of fluid flowing in the main passage
and the bypass passage impinge on each other at a junction to thereby
cause a disturbance flow, and a pressure loss of the fluid can be
prevented.
Further, in accordance with the above-mentioned embodiments, the
cross-sectional surface area of the bypass passage can be easily
changed.
Obviously, numerous modifications and variations of the present
invention are possible in light of the above teachings. It is therefore
to be understood that within the scope of the appended claims, the
invention may be practiced otherwise than as specifically described
herein.
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