JP4280396B2 - Fluidic type flow rate detecting element and composite type flow meter using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fluidic type flow rate detecting element used for detecting a flow rate of a fluid such as a gas.
[0002]
[Prior art]
Conventionally, various types of flowmeters using fluidic type flow rate detection elements have been devised. As an example, FIG. 8 shows a flow meter using a fluidic type flow rate detecting element described in JP-A-8-210886.
[0003]
The fluidic flow rate detecting element 1 is formed by arranging a settling space 4, a nozzle 5, and a flow path expanding portion 6 in order from the upstream side on a path connecting the fluid inlet 2 and the fluid outlet 3. Yes. In the flow path expanding portion 6, an attractor 7 is provided on an extension of the center line of the nozzle 5, and the shape of the attractor 7 is formed between the attractor 7 and the fluid outlet 3. An end block 8 is provided.
[0004]
The flow path width from the fluid inlet 2 to the fluid outlet 3 is expanded from the fluid inlet 2 to the settling space 4, is reduced from the settling space 4 to the nozzle 5, and the nozzle 5 to the flow path expanding portion 6. And is reduced from the flow path expanding portion 6 to the fluid outlet 3. In the flow path from the fluid inlet 2 to the fluid outlet 3, the width of the fluid inlet 2 and the width of the fluid outlet 3 are substantially the same, and the width is narrowest at the nozzle 5.
[0005]
The attracting element 7 has a shape in which a concave surface 9 curved so as to draw an arc on a plane perpendicular to the axial direction of the cylindrical body is formed on the cylindrical body. The concave surface 9 faces the ejection port 10 of the nozzle 5.
[0006]
The fluid flowing in from the fluid inlet 2 is rectified into a two-dimensional flow in the settling space 4, and is ejected through the nozzle 5 into the flow path expanding portion 6. The jet flow, which is the flow of rectified fluid ejected from the nozzle 5, is divided into two directions sandwiching the attracting element 7 by hitting the attracting element 7, but when a certain flow rate is exceeded, a vortex formed behind the attracting element 7 Due to the instability, the current flows in one of the two directions sandwiching the above-described attractor 7. Therefore, the flow that hits the end block 8 reaches the jet port 10 of the nozzle 5 as a return flow that flows through the return flow path formed along the front surface shape of the end block 8 and the shape of the side wall 11 of the flow path expanding portion 6. It hits from the direction that goes almost straight to the jet. The return flow strikes the jet and biases the direction of the jet in a direction opposite to the initial bias direction.
[0007]
Such a change in the direction of deviation of the jet is regularly repeated (fluidic vibration), and an alternating pressure wave is generated. The frequency of the alternating pressure wave, that is, the number of changes in the jet bias direction per unit time increases linearly with increasing flow rate. That is, there is a linear relationship (linearity) between the flow rate and the frequency.
[0008]
Then, a pressure change generated in a pair of pressure detection holes 12 provided in the vicinity of the nozzle 10 of the nozzle 5 is detected by a pressure detection mechanism, and the frequency of the change in the jet bias direction is obtained from the period of the change. The flow rate is calculated based on this frequency.
[0009]
Currently, fluidic type flow rate detection elements are not suitable for flow rate measurement in a low flow rate region, and are therefore often combined with thermal flow rate detection elements to form a composite type flow meter. In the combined flow meter, the output of the thermal flow rate detection element is referred to when the flow rate is in the low flow rate region, and the output of the fluidic flow rate detection element is referred to when the flow rate is in the high flow rate region.
[0010]
[Problems to be solved by the invention]
The fluidic flow rate detecting element is desired to have a dynamic range in which the minimum vibration detection flow rate (the flow rate at which fluidic vibration starts) is low and the flow rate range is wide.
[0011]
If the flow rate can be measured with a fluidic type flow rate detecting element from a flow rate of 0, a flow meter using only the fluidic type flow rate detecting element can be realized.
[0012]
Moreover, in the present combined flow meter, for example, in the case of a full scale of 4000 L / H, 200 L / H or more is measured with a fluidic type flow rate detection element in a high flow rate region, and the remaining 0 to 200 L / H is a low flow rate. The area is designed to be measured by a thermal flow rate detecting element. In other words, the thermal flow rate detecting element has a wide range, and the accuracy in the low flow rate region tends to be low. For this reason, strict specifications are required for the performance of the thermal flow rate detection element, and complicated signal processing and flow rate correction calculation are required.
[0013]
Therefore, even if the minimum vibration detection flow rate of the fluidic type flow rate detection element does not reach zero, the minimum vibration detection flow rate can be reduced by about 100 L / H from the current level, and only 80 to 90 L / H can be obtained. Since the range of the flow rate detecting element can be narrowed, the influence on the reliability of the signal processing and the manufacturing cost is great.
[0014]
An object of the present invention is to reduce the minimum vibration detection flow rate of a fluidic type flow rate detection element.
[0015]
An object of the present invention is to obtain a fluidic type flow rate detecting element capable of detecting a low flow rate.
[0016]
The present invention divides a full scale into a high flow rate region and a low flow rate region, and measures near the switching between the high flow rate region and the low flow rate region in a composite flow meter that uses a fluidic type flow rate detection element to measure the high flow rate region. The purpose is to improve accuracy.
[0017]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided an inducer having a concave surface disposed on the downstream side of a nozzle for ejecting fluid and facing the nozzle, and a part of the fluid ejected from the nozzle on the downstream side of the attractor. in is inverted and a wall to return fluid to a microfluidic type flow rate detecting element for generating fluidic vibrations by Coanda effect fluid and the feedback fluid ejected from the nozzle, the誘振child is The concave surface is formed on a cylindrical body having a diameter D and having a shaft center on the center line of the nozzle width, and both sides of the concave surface are rounded. The concave surface is formed in a sector shape having a center of curvature on the center line of the width of the nozzle and in contact with the axis, and the both side portions of the concave surface are Said invitation It is formed in a shape along an inscribed circle of radius R inscribed in the contour of the child, and the relationship between the diameter D of the cylindrical body and the radius R of the inscribed circle is such that R ≦ D / 60 It is characterized by satisfying.
[0018]
As a result, it is possible to obtain a fluidic type flow rate detecting element having a lower minimum vibration detection flow rate with a lower minimum vibration detection flow rate and a lower reproducibility .
[0025]
According to a second aspect of the invention, a microfluidic type flow rate detecting element according to claim 1, wherein誘振Ko is characterized in that the taper angle is conical below 3 °.
[0026]
Here, the taper angle refers to an angle between two buses of a cone in one axial section. If it is said range, even if it manufactures by the construction method with draft (taper), such as resin molding, the precision of a flow measurement is not impaired.
[0027]
The invention according to claim 3 is a composite flow meter that detects the full scale separately in a high flow rate region and a low flow rate region, and the fluid flow type according to claim 1 or 2 for the high flow rate region. It is detected by an output of a flow rate detecting element, and the low flow rate region is detected by a flow rate detecting means for detecting a flow rate by another method.
[0028]
Thereby, the low flow rate region can be narrowed.
[0029]
A fourth aspect of the present invention is the composite flow meter according to the third aspect of the present invention, wherein for detecting the flow rate in the low flow rate region, a heating resistor and a pair of temperature measuring elements disposed across the heating resistor are provided. A thermal type flow rate detecting element including an element and a flow path that passes from one of the temperature measuring element to the other of the temperature measuring element through the heating resistor is used.
[0030]
Therefore, the overlap of the measurement range between the fluidic type flow rate detection element and the thermal type flow rate detection element becomes large, and the flow rate correction near the switching between the high flow rate region and the low flow rate region becomes easy.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIGS. First, the structure of a composite flow meter including a fluidic flow rate detection element 21 and a flow sensor 22 that is a thermal flow rate detection element will be described with reference to the plan view of FIG.
[0032]
The fluidic type flow rate detecting element 21 is arranged on the path connecting the fluid inlet 23 and the fluid outlet 24 in order from the upstream side to the first to third rectifier networks 25 to 27, the rectifier 28, the flow path reduction section 29, A nozzle 30 and a flow path enlarged portion 31 are disposed and formed. The flow sensor 22 is disposed immediately before the nozzle 30 in the flow path reduction section 29.
[0033]
In the flow path expanding portion 31, an attractor 32 is provided on an extension of the center line of the nozzle 30, and the shape is such that the attractor 32 is surrounded between the attractor 32 and the fluid outlet 24. An end block 33 is provided. The attracting element 32 is formed with a concave surface 35 that faces the ejection port 34 of the nozzle 30.
[0034]
The flow sensor 22 and the nozzle 30 are disposed on the same line. Since it is necessary to arrange the flow sensor 22 on the wall surface, the flow path is not a circular pipe, and the cross-sectional shape of the flow path is substantially rectangular.
[0035]
The fluid flowing in from the fluid inflow port 23 is first buffered by the first rectifying network 25 and mixed in the gap between the first rectifying network 25 and the second rectifying network 26, thereby mitigating periodic fluctuations. This fluid is made to have a substantially uniform flow velocity distribution by the second rectifier network 26 and the third rectifier network 27, and then is made into a two-dimensional flow by the lattice-like rectifier 28, so that it is an incompressible steady and uniform flow. Can do.
[0036]
Here, this flow has a very two-dimensional property because the flow path reduction section 29 is linearly restricted, and a stable output signal can be obtained depending on the flow sensor 22. It is done.
[0037]
In the vicinity of the jet port 34, both sides of the jet are occupied by a static fluid having a uniform pressure, so that the free streamline of the jet has an angle at first but finally becomes parallel. Since the pressure is constant on the free streamline, the flow rate is also constant. By arranging the attractor 32 at this position, fluidic vibration is obtained.
[0038]
The inventors of the present invention set the design parameters, and experimented and examined the linearity of the relationship between the flow rate at which fluidic vibration starts and the flow rate and the frequency of fluidic vibration. We found that shape is an important control factor.
[0039]
That is, when the fluid is ejected from the nozzle 30 having a certain width toward the attracting element 32, the “jet” ejected from the nozzle 30 that has a higher speed flow than the surrounding fluid, and the invitation placed in the flow. The relationship with the “wake”, which is the low-speed flow seen downstream of the pendulum 32, is important, and when considering the two-dimensional flow field, the shape of the attractor 32 is extremely important for the fluidic vibration characteristics. It means that
[0040]
This will be described in more detail. The “jet” is not ejected into a semi-infinite space, but is ejected into a space where there are obstacles such as the attracting element 32 and the wall surface 36 in the flow path expanding portion 31. It becomes impossible to maintain the direction of the initial speed of the hour. For this reason, it is considered that the two-dimensional jet becomes unstable, and this instability gives rise to the start of fluidic oscillation.
[0041]
On the other hand, a Karman vortex is generated downstream of the pendulum 32 arranged in the flow, and this vortex row becomes a meandering flow. Therefore, it is considered that the “wake flow” becomes an oscillating flow and cannot be stable.
[0042]
As described above, both the “jet flow” and the “wake flow” are affected by the shape of the attractor 32 and the wall surface 36 and become unstable, so that the “jet flow” and the “wake flow” can be effectively controlled. If the shape of 32 is selected, the fluidic type flow rate detecting element 21 in which the above problems are improved can be obtained.
[0043]
From the experiment, as shown in FIG. 2, the concave surface 35 of the attracting element 32 is formed in an arc shape having a center point on a line connecting the axis center of the cylinder and the center line of the width of the nozzle 30. By doing so, it is possible to control the two-dimensional jet when the jet collides with the attracting element 32, and by rounding both side portions 32a of the attracting element 32 with an inscribed circle inscribed in the outline of the attracting element 32, I knew that I could control it.
[0044]
In FIG. 3, when the diameter of the inducer 32 is D, a concave surface 35 having a radius of curvature r = 0.35D, 0.5D, D is depicted. The attracting element 32 approaches a half-moon shape as the radius of curvature r of the concave surface 35 increases, and approaches a cylinder as the radius of curvature r decreases.
[0045]
Experimentally examining the allowable range of r / D, it has been found that r / D = 0.35 to 2.5, preferably r / D = 0.5 is good.
[0046]
Further, according to another experiment, it is known that the attracting element 32 does not have to be a vertical columnar shape, and if the taper angle is a cone shape of less than 3 °, the fluidic vibration performance is not adversely affected. The taper angle refers to the angle between the two buses of the cone in one axial section. That is, assuming that the attractor 32 is conical, and the cross section of the attractor 32 is taken on a plane including the axis of the attractor 32, the angle between the two buses of the attractor 32 in this cross section is If it is less than 3 °, the fluidic vibration performance is not adversely affected even if the attracting element 32 is not columnar. If the attracting element 32 satisfies the above range, the accuracy of flow rate measurement is not impaired even if it is manufactured by a method having a draft (taper) such as resin molding.
[0047]
FIG. 4 shows a typical cross-sectional shape of the pendulum 32 used in the experiment. D = 6 (mm), and the radius of curvature r of the concave surface 35 was set to 0.5D. Then, as shown in FIG. 5, both side portions 32a of the attractor 32 of FIG. 4 are rounded with three kinds of circles having radii R = 0.2, 0.5, and 0.8 (mm). Experiments were conducted for each case.
[0048]
FIG. 6 is a graph showing the instrumental difference of the No. 4 gas meter with respect to the flow rate obtained from the fluidic frequency of the composite flow meter using each attractor 32 of FIG. A flammable gas was used as the fluid. In the figure, the area indicated by the two-point difference line is instrumental difference for each flow rate determined by the measurement method. The instrumental error of the flow rate of 200 to 400 L / H is defined as within ± 3%, and the instrumental error of 400 to 4000 L / H is defined as within ± 1.5%.
[0049]
From this experimental result, it was found that there is no problem with R0.2 and R0.5, but the specified instrumental error is not satisfied with R0.8. Further, it was found that when R0.8, the instrumental difference was not satisfied both in the case of a relatively low flow rate of 1000 L / H or less and in the case of a relatively large flow rate of 3000 L / H or more. In this experiment, it was found that the vibration loss frequently occurs as the R of the both side portions 32a of the attractor 32 increases. This phenomenon of vibration loss hardly occurs at R0.5 or less when the diameter D of the attractor 32 is 6 (mm), and the lowest vibration detection flow rate is the smallest and stable at R0.2 or less. there were.
[0050]
FIG. 7 shows the relationship between the ratio R / D between the diameter D of the inducer 32 and the radius of curvature of the side portions 32a and the minimum vibration detection flow rate (L / H). According to the result of this experiment, the ratio R / D that satisfies the minimum vibration detection flow rate of 150 L / H is 1/12, and if it is 1/60, 100 L / H is satisfied.
[0051]
【The invention's effect】
In the invention described in claim 1 , both sides of the concave surface of the attractor are formed to be rounded, and the attractor is provided with a concave surface on a cylindrical body having a diameter D and having an axis on the center line of the nozzle width. The concave surface is formed in a sector shape having a center of curvature on the center line of the width of the nozzle and in contact with the axis when viewed in a cross section in a plane orthogonal to the axis. Since both sides of the concave surface are formed in a shape along an inscribed circle having a radius R inscribed in the contour of the attracting element, the minimum vibration detection flow rate can be reduced. Moreover, since the relationship between the diameter D of the cylindrical body and the radius R of the inscribed circle is R ≦ D / 60, a fluidic flow rate detection element having a lower minimum vibration detection flow rate can be obtained with good reproducibility. .
[0055]
In the invention according to claim 2 , in the invention according to claim 1 , the attractor has a conical shape with a taper angle of less than 3 °, and therefore can be manufactured by a method having a draft (taper) such as resin molding. Therefore, the manufacturing cost can be suppressed without impairing the accuracy of the flow rate measurement.
[0056]
According to a third aspect of the present invention, a flow rate detecting means for detecting the high flow rate region by the output of the fluidic type flow rate detecting element according to claim 1 or 2 and detecting the flow rate by another method for the low flow rate region. Since the low flow rate region can be narrowed, the measurement accuracy of the flow rate detection means responsible for the measurement in the low flow rate region can be increased.
[0057]
According to a fourth aspect of the present invention, in the third aspect of the invention, for detecting the flow rate in the low flow rate region, a heating resistor and one of a pair of temperature measuring elements and a temperature measuring element disposed across the heating resistor are provided. Since a thermal flow rate detection element with a flow path that passes through a heating resistor to the other of the temperature measurement element is used, the overlap of the measurement range of the fluidic type flow rate detection element and the thermal flow rate detection element increases, It becomes easy to perform flow rate correction in the vicinity of switching between the high flow rate region and the low flow rate region.
[Brief description of the drawings]
FIG. 1 is a plan view schematically showing a structure of a fluidic type flow rate detecting element according to an embodiment of the present invention.
FIG. 2 is a plan view of an attractor.
FIG. 3 is a plan view showing the shape of a concave surface formed on the attractor.
FIG. 4 is a plan view showing the shape of the concave surface of the attracting element used in the experiment for changing the shape of both ends.
FIG. 5 is a plan view of a pendulum showing a method of changing the shape of both side ends.
FIG. 6 is a graph showing the instrumental difference at each flow rate of a fluidic flow rate detection element including an attractor having different shapes at both ends.
FIG. 7 is a graph showing the relationship between the shape of both ends and the minimum vibration detection flow rate.
FIG. 8 is a plan view showing an example of a flow meter using a conventional fluidic type flow rate detecting element.
[Explanation of symbols]
21 Fluidic type flow rate detecting element 22 Thermal type flow rate detecting element 30 Nozzle 32 Inductor 32a Both ends 35 Concave surface 36 Wall surface

Claims (4)

An attractor having a concave surface that is disposed downstream of a nozzle that ejects fluid and faces the nozzle, and a part of the fluid ejected from the nozzle is inverted downstream of the attractor to provide a return fluid. and a wall surface, a fluidic type flow rate detecting element for generating fluidic vibrations by the Coanda effect and fluid ejected by said feedback fluid from said nozzle, said誘振child is both side portions of the concave rounded The concave surface is provided on a cylindrical body having a diameter D and having a shaft center on the center line of the width of the nozzle, and the attractor is seen in a cross section in a plane orthogonal to the shaft center. The concave surface is formed in a sector shape having a center of curvature on the center line of the width of the nozzle and in contact with the axis, and the both side portions of the concave surface are inscribed in the contour of the attractor Half It is formed in a shape along the inscribed circle of R, and the relationship between the diameter D of the cylindrical body and the radius R of the inscribed circle satisfies the condition R ≦ D / 60. Fluidic type flow rate detection element . The fluidic flow rate detecting element according to claim 1, wherein the attracting element has a conical shape with a taper angle of less than 3 °. A combined flow meter that detects a full scale separately in a high flow rate region and a low flow rate region, wherein the high flow rate region is detected by an output of a fluidic flow rate detection element according to claim 1 or 2 , The composite flow meter is characterized in that the low flow rate region is detected by a flow rate detecting means for detecting a flow rate by another method. For detecting the flow rate in the low flow rate region, a heating resistor, a pair of temperature measuring elements arranged across the heating resistor, and one of the temperature measuring elements pass through the heating resistor to the other of the temperature measuring elements. The composite flow meter according to claim 3 , wherein a thermal flow rate detection element including a flow path is used.

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