CA2051541A1 - Fluidic flowmeter - Google Patents
Fluidic flowmeterInfo
- Publication number
- CA2051541A1 CA2051541A1 CA 2051541 CA2051541A CA2051541A1 CA 2051541 A1 CA2051541 A1 CA 2051541A1 CA 2051541 CA2051541 CA 2051541 CA 2051541 A CA2051541 A CA 2051541A CA 2051541 A1 CA2051541 A1 CA 2051541A1
- Authority
- CA
- Canada
- Prior art keywords
- flowmeter
- target
- flowmeter body
- axis
- rear wall
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/05—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects
- G01F1/20—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by detection of dynamic effects of the flow
- G01F1/32—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by detection of dynamic effects of the flow using swirl flowmeters
- G01F1/3227—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by detection of dynamic effects of the flow using swirl flowmeters using fluidic oscillators
Landscapes
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Measuring Volume Flow (AREA)
Abstract
ABSTRACT
The present invention is directed to a flowmeter for measur-ing a flow rate comprising a flowmeter body having a hollow and rectangular cross-section and a center axis. The flowmeter body comprises a front wall and a rear wall for defining an expander section therebetween, an inlet nozzle formed at the -front wall, a target having a front surface and an axis, and a throttle portion formed at the rear wall. The front wall and the axis of the target are respectively perpendicular to the center axis of the flowmeter body. The inlet nozzle and the throttle portion have the same axis as the flowmeter body. The flowmeter body is formed so that, in a cross section perpendicular to the target, a circular arc defined by extending from one of the outlet edges of the inlet nozzle tangentially thereto, and passing on an edge of the target on the opposite side of the center axis to the outlet edge, further extends to cross the rear wall. According to the present invention, a fluidic oscillation of high frequency is caused by vortex flows generated behind the target occurs so that measurement of flow rate in a high accuracy is possible at a wide flow rate range.
The present invention is directed to a flowmeter for measur-ing a flow rate comprising a flowmeter body having a hollow and rectangular cross-section and a center axis. The flowmeter body comprises a front wall and a rear wall for defining an expander section therebetween, an inlet nozzle formed at the -front wall, a target having a front surface and an axis, and a throttle portion formed at the rear wall. The front wall and the axis of the target are respectively perpendicular to the center axis of the flowmeter body. The inlet nozzle and the throttle portion have the same axis as the flowmeter body. The flowmeter body is formed so that, in a cross section perpendicular to the target, a circular arc defined by extending from one of the outlet edges of the inlet nozzle tangentially thereto, and passing on an edge of the target on the opposite side of the center axis to the outlet edge, further extends to cross the rear wall. According to the present invention, a fluidic oscillation of high frequency is caused by vortex flows generated behind the target occurs so that measurement of flow rate in a high accuracy is possible at a wide flow rate range.
Description
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BACKGROUND OF THE INVEN'L'ION
FIELD OF THE I~VENTION
The present invention relates to a flowmeter of a hydrody-namic oscillator type, capable of measuring a wide range of flow rate with a high accuracy.
PRIOR ART
As a conventional device for measuring flow rate, a flowme-ter of a hydrodynamic type shown in Fig. 10 is known.
This flowmeter comprises a flowmeter body 1 generally being formed in a pipe of a rectangular cross-section, and is connected in a series to a pathway of a flow. The flowmeter body 1 com-prises an inlet nozzle 2 formed through a front wall 3, an expan-der section 4 surrounded by front wall 3, side walls 4a, 4b and rear wall 5a, 5b, and a throttle portion 6 arranged in an up-stream to downstream order. On the center axis C of the flowme-ter, a target 7 is arranged in the expander section 4 secured to the flowmeter body 1. The target 7 is for deflecting an entering flow Fe from the inlet nozzle 2. The flowmeter further comprises a sensor (not shown) at the expander section 4 for sensing pres-sure or velocity therein.
The flowmeter is used by connecting the flowmeter body 1 to a pathway of a flow, of which the flow rate is to be measured.
An entering flow Fe from the inlet nozzle 2 will be deflected by the target 7 as well as by "Coanda Effect" into one of the two sideways directions. The Coanda Effect is a function of the - .
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presence of a wall ad~acent to a free flow to deflect it in the vicinity of the wall. Thus the exhausted flow Fe is directed to run in the vicinity of the side wall 4a of the flowrneter body 1 as shown in Fig. 10. Subsequently, a portion of the entering flow Fe is directed to run upstream to generate a returning f]ow Fr~ The returning flow Fr propels the entering flow Fe from the inlet nozzle 2 to opposite direction (downwardly, in Fig. 10) so as to run along the side wall 4b. This process occurs repeatedly to make a fluidic oscillation.
The oscillation frequency does not depend on the physical properties of the flowing material but is proportional to the flow rate. The above-mentioned sensor produces an output signal whose frequency is proportional to the flow rate, therefore, the flow rate can be estimated from the output signal.
In the conventional flowmeter, it is ~nown that when the flow rate is constant, the frequency f is determined according to a size or a length of the returning flow Fr When the distance L
between the outlet of the inlet nozzle 2 and the throttle portion 6 is constant, and the distance H between the outlet of the inlet nozzle 2 and the target 7 is increased, the si.ze of the returning flow Fr will increase and the frequency f will decrease. When the width W is enlarged, the frequencY f will decrease in the same way.
For assuring the generation of returning flows Fr~ it is necessary to determine the distance H adequately small compared to the distance L as shown in Fig. 10, or to shape corners be-tween the side walls 4a, 4b and the rear wall 5a, 5b continuously curving as shown in Fig. 11.
This flowmeter is of a superior utility, since it does not : .
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include any mechanically moving portion, and is capable of meas-uring -flow rate without being lnfluenced by the physical proper-ties of the flowing material. flowever, the conventional flowme-ter still has the following disadvanta~es.
That is, as shown in Fig. 12, the frequency -f of the oscil-lation is rather small, which makes measuring results unstable especially in low flow rate ranges. Therefore, meter error becomes large in low flow rate range as shown in Fig. 13.
An object of the present invention i5, therefore, to present a flowmeter capable of measuring flow rate with a high accuracy over a wide flow rate range.
SUMMARY OF THE INVENTION
The present invention has been made to accomplish the object mentioned above, and is directed to a flowmeter for measuring a flow rate comprising a flowmeter body having a hollow and rectan-gular cross-section and a center axis, said flowmeter body com-prising:
a front wall and a rear wall defining a expander section therebetween;
an inlet nozzle formed at said front wall;
a target having a front surface and an axis, said front surface and axis being perpendicular to said center axis of said flowmeter body;
a throttle portion formed at said rear wall, said inlet nozzle and said throttle portion having the same axis as said center axis;
wherein said flowmeter body is formed so that, in a cross section perpendicular to said axis of said target, .
a circular arc defined by extending tangentia:L1~ f'rom one oY
the outlet edges o~ said inlet nozzle, and passing through a point defined on an edge of said targe-t on the opposite side of said center axis to said outle~ edge, fur-ther extends to cross said rear wall.
According to the present invention, vortex flows are gener-ated periodically at a downstream of the target which change direction of the entering flow alternatingly. This process generates an oscillation of high frequency 90 that a precise measurement is possible even when the flow rate is small.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a partial sectional view of the flowmeter body of the embodiment according to the present invention;
Fig. 2 is a schematic view of Fig. 1;
Fig. 3 is a gragh showing a relationship between H/t and frequency f;
Fig. 4 is a gragh showing a relationship between flow rate and meter error;
Fig. 5 is a gragh showing a relationship between W/t and frequency f;
Fig. 6 is a gragh showing a relationship between H/L and frequency f;
Fig. 7 is a gragh showing a relationship between T/t and frequency f;
Fig. 8 is a gragh showing a relationship between a/t and maximum meter error;
Fig. 9 is a gragh showing a relationship between a/b and maximum meter error;
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Fig. 10 is a schematic view of the conventional flowrneter body;
Fig. 11 is a schernatic view of another conventional flowme-ter body;
Fig. 12 is a gragh showing a relationship between H/t and frequency f measured by the conventional flowmeter body;
Fig. 13 is a gragh showing a relationship between flow rate and maximum meter error measured by the conventional flowmeter body.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the present invention will be described below.
In the Figs. 1 and 2, numeral 11 depicts a flowmeter body formed in a pipe of a rectangular cross section, which consists a flowmeter of a fluidic osci].lation type.
The -flowmeter body 11 has a center axis C, and comprises a front wall 12, a rear wall 13, side walls 14a, 14b and a top and bottom walls 15a, 15b. These 6 walls defines an expander section 16 therebetween. An inlet nozzle 17 of a rectangular cross section having a thickness t is formed through the front wall 12 so as divide it into two portions 12a, 12b. A throttle portion 18 is formed through the rear wall 13 so as divide it into two portions 17a, 17b. These inlet nozzle 17 and throttle portion 18 respectively have a rectangular cross sections parallel to the top, bottom and side walls 14a, 14b, 15a, 15b of the flowmeter body 11 and the same axis as the flowmeter body 11. A target 19 having a rectangular cross section is arranged in the expander section 16 by securing both ends thereof to the top and bottom ~ 0 ~
walls 15a, 15b. The target 19 is arranged in the flowmeter body 11 in a manner that the axis thereof is perpendicular to the center axis C of the flowmeter body, and the surfaces thereof are respectively parallel to the front, rear and side walls 12, 13, 14a, l~b. By such a construction, the cross section of the flowmeter body 11 perpendicular to the axis of the target 19 is the same, i.e., it has the uniform cross-sectional view along the direction perpendicular to the paper surface .in Fig. 1.
The flowmeter body 11 is formed so as to satisfy the follow-ing geometric conditions in a cross section shown in Fig. 1.
Firstly, circular arcs Ra or Rb is defined as follows. The circular arc Ra starts from the outlet 17a of the inlet nozzle 17 to extend in a direction tangential to the outlet 17a, i.e., the center of the circular arc Ra stays on the inner surface of the front wall 12. The circular arc Ra subsequently crosses the center axis C, and passes through a point defined on an edge l9b of the front surface l9c of the target 19 on the opposite side of the center axis C~ This circular arc Ra further e~tends to cross the rear wall 13b on the opposite side of the center axis C.
That is, such dimensions as width t of the inlet nozzle 17 12, distance H between the nozzle 17 and the target 19, distance L
between the front wall and the rear wall, width T of the throttle portion 18 and width W of the e~pander section 18, are chosen so that the circular arc Ra does not cross the side wall 14b before it crosses the rear wall 13b of the flowmeter body 11.
The arrangement is symmetrically the same with the circular arc Rb starting from the outlet 17b on the opposite side of the center axis C.
Secondly, the corner portions between the rear wall 13 and :: , :
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the side wall 14a. l~b are sharp, that is. the radius of curva-ture of the corner is negligibly small in comparison to the dimension of the elowrneter body 11. By such a construction, returning flows are not likely to occur when the entering flow Fe impacts to the rear wall 13. In the described embodiment, the rear wall portions 13a, 13b are arranged orthogonal to the center axis C. However, they may be in an inclined angular relation thereto. But the angle between side walls 14a, 14b and rear wall portions must be set obtuse in order to prevent the genera-tion of the returning flow.
Thirdly, the distance L and H, the former being defined between the outlet of the inlet nozzle 17 and the throttle por-tion 18 and the latter being defined between the outlet of the inlet nozzle 17 and the target 19. are chosen so as to satisfY
the following equation ~1);
H/L > 0.5 ---(1) Fourthly, width a of the target 19 and width T of the throt-tle portion 18 are chosen to satisfy the following equation (2);
a < T ---(2) Fifthly, width a of the target 19 and width t of the inlet nozzle 17 are chosen so as to satisfy the following equation (3);
1.0 < a/t < 1.4 ---(3) Sixthly, width a and thickness b of the target 19 are chosen so as to satisfy the following equation (4);
b/a < 0.6 ---(4) In Fig. 1, numeral 20 depicts a sensor for sensing pressure inside of the expander section 18 or velocity of the flow there-in. Numeral 21 depicts a microprocessor for receiving and proc-essing output signals of the sensor in order to compute the flow ::
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rate and to ~enerate it as output signals.
The flowmeter is used by connecting the f].owmeter body 11 in a series pathway of a flow, where the flow rate is to be meas-ured. An entering flow Fe wi].l be deflected by the target 19 to one direction at first, for example, toward a rear wall 13a.
Subsequently, a vortex flow Fv is generated behind the target 19, which further generates a circular flow Fc around the target 19 as shown in Fig. 2. The circular flow Fc will deflect the enter-ing flow Fe toward opposite side of the center axis C so that the direction of the entering flow Fe is switched toward the rear wall 13b. This process occurs alternatingly to produce a fluidic oscillation whose frequency is proportional to the flow rate.
This oscillation can be detected from the output signal of the sensor 20 in the same manner as the conventional flowmeter.
However, in the flowmeter of the present invention, since the oscillation is generated according to the vortex flow Fv and not to the returning flow, the fluidic oscillation is constantly presented especially even in small flow rate ranges. The reason is as follows. By the flowmeter, when the flow rate is constant, the frequency f is determined according to a size or a length of the vortex flow Fv. Therefore, when the distance H increases and the distance L is constant, the size of the vortex flow Fv be-comes small and frequency f increases, which is dif-f0rent from the conventional flowmeter. Fig. 3 is a gragh of the data show-ing the relationship between distance H and frequency f. The data are obtained at the same flow rate as the conventional flowmeter shown in Fig. 12. Fig. 3 shows that frequency f in-creases as distance H increases. Further, Fig. 3 shows that the frequency f of the invention is much higher than that of the .
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conventional flowmeter. Therefore, a stab:Le -fluidic oscillation is obtained to reduce the meter error. Fig 4 is a gragh showing meter error according to the flowmeter of' the embodiment, wherein the meter error is smaller than the conventional flowrneter shown in Fig. 13 especi~lly in the small flow rate range. The meter error is measured by connecting the examined flowmeter to a standard flowmeter and calculating the deviation between measured flow rate values.
By the flowmeter of the invention, the fluidic oscillation is not generated from the returning flow, which flows in the vicinity of the side walls 14a, 14b. Therefore, the location of the side walls 14a, 14b or the quantity of width W of the expan-der section 16 does not influence the characteristics of the flowmeter. Fig. 13 is a gragh showing frequency f measured when the flow rate is constant while the width W is changed, which teaches that the frequency f is constant however wide W is.
The above-described fluidic oscillation of high frequency, which is caused by the vortex flow Fv behind the target 19, is generated at least when the first condition previously mentioned is satisfied. That is, the virtual circular arcs Ra or Rb reach the rear wall 13b, 13a. However, the first condition is neces-sary but not enough to create a stable fluidlc oscillation. By satisfying the second to sixth conditions in order as are previ-ously mentioned, the flowmeter of the embodiment becomes more and more capable of generating a stable vortex flow Fv to perform an excellent and constant function.
In the embodiment, the corner portion between the rear wall 13 and the side walls 14a, 14b are formed in a manner that straight walls 13 and 14a or 14b exist in a clearly distinguisha-. .
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ble manner from each other to intersect to each other with rightor obtuse ang]e. Moreover, the distance 1, and H are determined so as to satisfy the equation (1). By such ~eatures, the returning flow is positively prevented frorn occurringr, so tha~ the vortex flow Ft takes a major role in ge~eration of fluidic oscillation.
Fig. 6 is a gragh showing frequency f measured when H/L is varied while L/t is set as a parameter and flow rate is a low and con-stant value. The gragh shows a clear distinction respectively in the ranges divided by a line representing "H/L = 0.5". In the range where "H/L > 0.5", a characteristic feature caused by the vortex flow Fv is clearly shown.
Further, in the embodiment, dimensions "a", "b", "T" and "t"
are determined so as to satisfy the equations (2) to (4), so that the vortex flow Fv is generated in a stable condition. Experi-mental results are shown in Figs. 7 to 9 to prove the above men-tioned effect.
In Fig. 7, frequency f is plotted versus T/t within a range from "a/t" to "T/t" when flow rate is constant. The gragh shows that a higher frequency f is measured where "T" is larger than "a".
Another feature of the flowmeter of the embodiment is a relationship between width a of the target 19 and width T of the throttle portion 18. In Fig. 8, a maximum meter error is shown versus a/t when flow rate is constant. It clearly shows that maximum meter error is extremely small in the range where a/t is from 1.0 to 1.4.
Another feature of the flowmeter of the embodiment is a relationship between width a and thickness b of the target 19 described as the equation (4). In Fig. 9, maximum meter error is A
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plotted versus b/a when the -flow rate is kept Low and constant.
The gragh shows that maxirnlim meter error is extremely small when b/a is less than 0.6, which means that generation of the vortex flow Fv becomes unstab].e if thickr-ess of the tar~ret 19 is lar~e in comparison to the width thereof.
In the above embodiments, the rear wall 13 and the side walls 14a, 14b are formed to have straight sur-faces. However. it is possible to form them to have cylindrical surfaces of a large radius of curvature distinguishable from each other.
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BACKGROUND OF THE INVEN'L'ION
FIELD OF THE I~VENTION
The present invention relates to a flowmeter of a hydrody-namic oscillator type, capable of measuring a wide range of flow rate with a high accuracy.
PRIOR ART
As a conventional device for measuring flow rate, a flowme-ter of a hydrodynamic type shown in Fig. 10 is known.
This flowmeter comprises a flowmeter body 1 generally being formed in a pipe of a rectangular cross-section, and is connected in a series to a pathway of a flow. The flowmeter body 1 com-prises an inlet nozzle 2 formed through a front wall 3, an expan-der section 4 surrounded by front wall 3, side walls 4a, 4b and rear wall 5a, 5b, and a throttle portion 6 arranged in an up-stream to downstream order. On the center axis C of the flowme-ter, a target 7 is arranged in the expander section 4 secured to the flowmeter body 1. The target 7 is for deflecting an entering flow Fe from the inlet nozzle 2. The flowmeter further comprises a sensor (not shown) at the expander section 4 for sensing pres-sure or velocity therein.
The flowmeter is used by connecting the flowmeter body 1 to a pathway of a flow, of which the flow rate is to be measured.
An entering flow Fe from the inlet nozzle 2 will be deflected by the target 7 as well as by "Coanda Effect" into one of the two sideways directions. The Coanda Effect is a function of the - .
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presence of a wall ad~acent to a free flow to deflect it in the vicinity of the wall. Thus the exhausted flow Fe is directed to run in the vicinity of the side wall 4a of the flowrneter body 1 as shown in Fig. 10. Subsequently, a portion of the entering flow Fe is directed to run upstream to generate a returning f]ow Fr~ The returning flow Fr propels the entering flow Fe from the inlet nozzle 2 to opposite direction (downwardly, in Fig. 10) so as to run along the side wall 4b. This process occurs repeatedly to make a fluidic oscillation.
The oscillation frequency does not depend on the physical properties of the flowing material but is proportional to the flow rate. The above-mentioned sensor produces an output signal whose frequency is proportional to the flow rate, therefore, the flow rate can be estimated from the output signal.
In the conventional flowmeter, it is ~nown that when the flow rate is constant, the frequency f is determined according to a size or a length of the returning flow Fr When the distance L
between the outlet of the inlet nozzle 2 and the throttle portion 6 is constant, and the distance H between the outlet of the inlet nozzle 2 and the target 7 is increased, the si.ze of the returning flow Fr will increase and the frequency f will decrease. When the width W is enlarged, the frequencY f will decrease in the same way.
For assuring the generation of returning flows Fr~ it is necessary to determine the distance H adequately small compared to the distance L as shown in Fig. 10, or to shape corners be-tween the side walls 4a, 4b and the rear wall 5a, 5b continuously curving as shown in Fig. 11.
This flowmeter is of a superior utility, since it does not : .
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include any mechanically moving portion, and is capable of meas-uring -flow rate without being lnfluenced by the physical proper-ties of the flowing material. flowever, the conventional flowme-ter still has the following disadvanta~es.
That is, as shown in Fig. 12, the frequency -f of the oscil-lation is rather small, which makes measuring results unstable especially in low flow rate ranges. Therefore, meter error becomes large in low flow rate range as shown in Fig. 13.
An object of the present invention i5, therefore, to present a flowmeter capable of measuring flow rate with a high accuracy over a wide flow rate range.
SUMMARY OF THE INVENTION
The present invention has been made to accomplish the object mentioned above, and is directed to a flowmeter for measuring a flow rate comprising a flowmeter body having a hollow and rectan-gular cross-section and a center axis, said flowmeter body com-prising:
a front wall and a rear wall defining a expander section therebetween;
an inlet nozzle formed at said front wall;
a target having a front surface and an axis, said front surface and axis being perpendicular to said center axis of said flowmeter body;
a throttle portion formed at said rear wall, said inlet nozzle and said throttle portion having the same axis as said center axis;
wherein said flowmeter body is formed so that, in a cross section perpendicular to said axis of said target, .
a circular arc defined by extending tangentia:L1~ f'rom one oY
the outlet edges o~ said inlet nozzle, and passing through a point defined on an edge of said targe-t on the opposite side of said center axis to said outle~ edge, fur-ther extends to cross said rear wall.
According to the present invention, vortex flows are gener-ated periodically at a downstream of the target which change direction of the entering flow alternatingly. This process generates an oscillation of high frequency 90 that a precise measurement is possible even when the flow rate is small.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a partial sectional view of the flowmeter body of the embodiment according to the present invention;
Fig. 2 is a schematic view of Fig. 1;
Fig. 3 is a gragh showing a relationship between H/t and frequency f;
Fig. 4 is a gragh showing a relationship between flow rate and meter error;
Fig. 5 is a gragh showing a relationship between W/t and frequency f;
Fig. 6 is a gragh showing a relationship between H/L and frequency f;
Fig. 7 is a gragh showing a relationship between T/t and frequency f;
Fig. 8 is a gragh showing a relationship between a/t and maximum meter error;
Fig. 9 is a gragh showing a relationship between a/b and maximum meter error;
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Fig. 10 is a schematic view of the conventional flowrneter body;
Fig. 11 is a schernatic view of another conventional flowme-ter body;
Fig. 12 is a gragh showing a relationship between H/t and frequency f measured by the conventional flowmeter body;
Fig. 13 is a gragh showing a relationship between flow rate and maximum meter error measured by the conventional flowmeter body.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the present invention will be described below.
In the Figs. 1 and 2, numeral 11 depicts a flowmeter body formed in a pipe of a rectangular cross section, which consists a flowmeter of a fluidic osci].lation type.
The -flowmeter body 11 has a center axis C, and comprises a front wall 12, a rear wall 13, side walls 14a, 14b and a top and bottom walls 15a, 15b. These 6 walls defines an expander section 16 therebetween. An inlet nozzle 17 of a rectangular cross section having a thickness t is formed through the front wall 12 so as divide it into two portions 12a, 12b. A throttle portion 18 is formed through the rear wall 13 so as divide it into two portions 17a, 17b. These inlet nozzle 17 and throttle portion 18 respectively have a rectangular cross sections parallel to the top, bottom and side walls 14a, 14b, 15a, 15b of the flowmeter body 11 and the same axis as the flowmeter body 11. A target 19 having a rectangular cross section is arranged in the expander section 16 by securing both ends thereof to the top and bottom ~ 0 ~
walls 15a, 15b. The target 19 is arranged in the flowmeter body 11 in a manner that the axis thereof is perpendicular to the center axis C of the flowmeter body, and the surfaces thereof are respectively parallel to the front, rear and side walls 12, 13, 14a, l~b. By such a construction, the cross section of the flowmeter body 11 perpendicular to the axis of the target 19 is the same, i.e., it has the uniform cross-sectional view along the direction perpendicular to the paper surface .in Fig. 1.
The flowmeter body 11 is formed so as to satisfy the follow-ing geometric conditions in a cross section shown in Fig. 1.
Firstly, circular arcs Ra or Rb is defined as follows. The circular arc Ra starts from the outlet 17a of the inlet nozzle 17 to extend in a direction tangential to the outlet 17a, i.e., the center of the circular arc Ra stays on the inner surface of the front wall 12. The circular arc Ra subsequently crosses the center axis C, and passes through a point defined on an edge l9b of the front surface l9c of the target 19 on the opposite side of the center axis C~ This circular arc Ra further e~tends to cross the rear wall 13b on the opposite side of the center axis C.
That is, such dimensions as width t of the inlet nozzle 17 12, distance H between the nozzle 17 and the target 19, distance L
between the front wall and the rear wall, width T of the throttle portion 18 and width W of the e~pander section 18, are chosen so that the circular arc Ra does not cross the side wall 14b before it crosses the rear wall 13b of the flowmeter body 11.
The arrangement is symmetrically the same with the circular arc Rb starting from the outlet 17b on the opposite side of the center axis C.
Secondly, the corner portions between the rear wall 13 and :: , :
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the side wall 14a. l~b are sharp, that is. the radius of curva-ture of the corner is negligibly small in comparison to the dimension of the elowrneter body 11. By such a construction, returning flows are not likely to occur when the entering flow Fe impacts to the rear wall 13. In the described embodiment, the rear wall portions 13a, 13b are arranged orthogonal to the center axis C. However, they may be in an inclined angular relation thereto. But the angle between side walls 14a, 14b and rear wall portions must be set obtuse in order to prevent the genera-tion of the returning flow.
Thirdly, the distance L and H, the former being defined between the outlet of the inlet nozzle 17 and the throttle por-tion 18 and the latter being defined between the outlet of the inlet nozzle 17 and the target 19. are chosen so as to satisfY
the following equation ~1);
H/L > 0.5 ---(1) Fourthly, width a of the target 19 and width T of the throt-tle portion 18 are chosen to satisfy the following equation (2);
a < T ---(2) Fifthly, width a of the target 19 and width t of the inlet nozzle 17 are chosen so as to satisfy the following equation (3);
1.0 < a/t < 1.4 ---(3) Sixthly, width a and thickness b of the target 19 are chosen so as to satisfy the following equation (4);
b/a < 0.6 ---(4) In Fig. 1, numeral 20 depicts a sensor for sensing pressure inside of the expander section 18 or velocity of the flow there-in. Numeral 21 depicts a microprocessor for receiving and proc-essing output signals of the sensor in order to compute the flow ::
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rate and to ~enerate it as output signals.
The flowmeter is used by connecting the f].owmeter body 11 in a series pathway of a flow, where the flow rate is to be meas-ured. An entering flow Fe wi].l be deflected by the target 19 to one direction at first, for example, toward a rear wall 13a.
Subsequently, a vortex flow Fv is generated behind the target 19, which further generates a circular flow Fc around the target 19 as shown in Fig. 2. The circular flow Fc will deflect the enter-ing flow Fe toward opposite side of the center axis C so that the direction of the entering flow Fe is switched toward the rear wall 13b. This process occurs alternatingly to produce a fluidic oscillation whose frequency is proportional to the flow rate.
This oscillation can be detected from the output signal of the sensor 20 in the same manner as the conventional flowmeter.
However, in the flowmeter of the present invention, since the oscillation is generated according to the vortex flow Fv and not to the returning flow, the fluidic oscillation is constantly presented especially even in small flow rate ranges. The reason is as follows. By the flowmeter, when the flow rate is constant, the frequency f is determined according to a size or a length of the vortex flow Fv. Therefore, when the distance H increases and the distance L is constant, the size of the vortex flow Fv be-comes small and frequency f increases, which is dif-f0rent from the conventional flowmeter. Fig. 3 is a gragh of the data show-ing the relationship between distance H and frequency f. The data are obtained at the same flow rate as the conventional flowmeter shown in Fig. 12. Fig. 3 shows that frequency f in-creases as distance H increases. Further, Fig. 3 shows that the frequency f of the invention is much higher than that of the .
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conventional flowmeter. Therefore, a stab:Le -fluidic oscillation is obtained to reduce the meter error. Fig 4 is a gragh showing meter error according to the flowmeter of' the embodiment, wherein the meter error is smaller than the conventional flowrneter shown in Fig. 13 especi~lly in the small flow rate range. The meter error is measured by connecting the examined flowmeter to a standard flowmeter and calculating the deviation between measured flow rate values.
By the flowmeter of the invention, the fluidic oscillation is not generated from the returning flow, which flows in the vicinity of the side walls 14a, 14b. Therefore, the location of the side walls 14a, 14b or the quantity of width W of the expan-der section 16 does not influence the characteristics of the flowmeter. Fig. 13 is a gragh showing frequency f measured when the flow rate is constant while the width W is changed, which teaches that the frequency f is constant however wide W is.
The above-described fluidic oscillation of high frequency, which is caused by the vortex flow Fv behind the target 19, is generated at least when the first condition previously mentioned is satisfied. That is, the virtual circular arcs Ra or Rb reach the rear wall 13b, 13a. However, the first condition is neces-sary but not enough to create a stable fluidlc oscillation. By satisfying the second to sixth conditions in order as are previ-ously mentioned, the flowmeter of the embodiment becomes more and more capable of generating a stable vortex flow Fv to perform an excellent and constant function.
In the embodiment, the corner portion between the rear wall 13 and the side walls 14a, 14b are formed in a manner that straight walls 13 and 14a or 14b exist in a clearly distinguisha-. .
2 ~
ble manner from each other to intersect to each other with rightor obtuse ang]e. Moreover, the distance 1, and H are determined so as to satisfy the equation (1). By such ~eatures, the returning flow is positively prevented frorn occurringr, so tha~ the vortex flow Ft takes a major role in ge~eration of fluidic oscillation.
Fig. 6 is a gragh showing frequency f measured when H/L is varied while L/t is set as a parameter and flow rate is a low and con-stant value. The gragh shows a clear distinction respectively in the ranges divided by a line representing "H/L = 0.5". In the range where "H/L > 0.5", a characteristic feature caused by the vortex flow Fv is clearly shown.
Further, in the embodiment, dimensions "a", "b", "T" and "t"
are determined so as to satisfy the equations (2) to (4), so that the vortex flow Fv is generated in a stable condition. Experi-mental results are shown in Figs. 7 to 9 to prove the above men-tioned effect.
In Fig. 7, frequency f is plotted versus T/t within a range from "a/t" to "T/t" when flow rate is constant. The gragh shows that a higher frequency f is measured where "T" is larger than "a".
Another feature of the flowmeter of the embodiment is a relationship between width a of the target 19 and width T of the throttle portion 18. In Fig. 8, a maximum meter error is shown versus a/t when flow rate is constant. It clearly shows that maximum meter error is extremely small in the range where a/t is from 1.0 to 1.4.
Another feature of the flowmeter of the embodiment is a relationship between width a and thickness b of the target 19 described as the equation (4). In Fig. 9, maximum meter error is A
-:, .' ' :
2 ~
plotted versus b/a when the -flow rate is kept Low and constant.
The gragh shows that maxirnlim meter error is extremely small when b/a is less than 0.6, which means that generation of the vortex flow Fv becomes unstab].e if thickr-ess of the tar~ret 19 is lar~e in comparison to the width thereof.
In the above embodiments, the rear wall 13 and the side walls 14a, 14b are formed to have straight sur-faces. However. it is possible to form them to have cylindrical surfaces of a large radius of curvature distinguishable from each other.
,, , ~ ~ , ,, ; ! . ~ . ~ ~ . . , , :
'' '' " ',.'1' , ' ' ~ ' ~ ~ ' ' . . ' .
Claims (9)
1. A flowmeter for measuring a flow rate comprising a flowmeter body having a hollow and rectangular cross-section and a center axis, said flowmeter body comprising:
a front wall and a rear wall defining a expander section therebetween;
an inlet nozzle formed at said front wall;
a target having a front surface and an axis, said front surface and said axis being perpendicular to said center axis of said flowmeter body;
a throttle portion formed at said rear wall, said inlet nozzle and said throttle portion having the same axis as said center axis;
wherein said flowmeter body is formed so that, in a cross section perpendicular to said axis of said target, a circular arc defined by extending tangentially from one of the outlet edges of said inlet nozzle, and passing through a point defined on an edge of said target on the opposite side of said center axis to said outlet edge, further extends to cross said rear wall.
a front wall and a rear wall defining a expander section therebetween;
an inlet nozzle formed at said front wall;
a target having a front surface and an axis, said front surface and said axis being perpendicular to said center axis of said flowmeter body;
a throttle portion formed at said rear wall, said inlet nozzle and said throttle portion having the same axis as said center axis;
wherein said flowmeter body is formed so that, in a cross section perpendicular to said axis of said target, a circular arc defined by extending tangentially from one of the outlet edges of said inlet nozzle, and passing through a point defined on an edge of said target on the opposite side of said center axis to said outlet edge, further extends to cross said rear wall.
2. A flowmeter according to claim 1, wherein said target is erected between a couple of walls of said flowmeter body, said couple of walls facing to each other and being perpendicular to said axis of said target.
3. A flowmeter according to claim 1, wherein said rear wall and said side wall of said flowmeter body are formed so as to prevent a returning flow, said side walls being parallel to said axis of said target.
4. A flowmeter according to claim 3, wherein said rear wall and said side wall of said flowmeter body are formed to have straight surfaces distinguishable from each other.
5. A flowmeter according to claim 3, wherein said rear wall and said side wall of said flowmeter body are formed to have cylindri-cal surfaces distinguishable from each other.
6. A flowmeter according to claim 1, wherein said flowmeter body is formed to satisfy the following equation;
H/L ? 0.5 whereby, the distance L is between said outlet of said inlet nozzle and said throttle portion, and the distance H is between said outlet of said inlet nozzle and said front surface of said target.
H/L ? 0.5 whereby, the distance L is between said outlet of said inlet nozzle and said throttle portion, and the distance H is between said outlet of said inlet nozzle and said front surface of said target.
7. A flowmeter according to claim 1, wherein said flowmeter body is formed to satisfy the following equation;
a ? T
whereby, "a" is width of said front surface of said target, "T" is width of said throttle portion.
a ? T
whereby, "a" is width of said front surface of said target, "T" is width of said throttle portion.
8. A flowmeter according to claim 1, wherein said flowmeter body is formed to satisfy the following equation;
1.0 ? a/t ? 1.4 whereby "a" is width of said front surface o-f said target and "t" is width of said inlet nozzle.
1.0 ? a/t ? 1.4 whereby "a" is width of said front surface o-f said target and "t" is width of said inlet nozzle.
9. A flowmeter according to claim 1, wherein said flowmeter body is formed to satisfy the following equation;
b/a ? 0.6 (4) whereby "a" is width of said front surface of said target and "b" is thickness of said target.
b/a ? 0.6 (4) whereby "a" is width of said front surface of said target and "b" is thickness of said target.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24954190A JP2865839B2 (en) | 1990-09-19 | 1990-09-19 | Fluid vibration type flow meter |
| JP02-249541 | 1990-09-19 | ||
| JP3108765A JP3025046B2 (en) | 1991-04-12 | 1991-04-12 | Fluid vibration type flow meter |
| JP03-108765 | 1991-04-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2051541A1 true CA2051541A1 (en) | 1992-03-20 |
Family
ID=26448590
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2051541 Abandoned CA2051541A1 (en) | 1990-09-19 | 1991-09-17 | Fluidic flowmeter |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA2051541A1 (en) |
| FR (1) | FR2667146A1 (en) |
| GB (1) | GB2248300A (en) |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE408094B (en) * | 1977-09-26 | 1979-05-14 | Fluid Inventor Ab | A FLOWING MEDIUM METHODING DEVICE |
-
1991
- 1991-09-17 CA CA 2051541 patent/CA2051541A1/en not_active Abandoned
- 1991-09-17 GB GB9119861A patent/GB2248300A/en not_active Withdrawn
- 1991-09-19 FR FR9111563A patent/FR2667146A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| GB2248300A (en) | 1992-04-01 |
| GB9119861D0 (en) | 1991-10-30 |
| FR2667146A1 (en) | 1992-03-27 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Dead |