JP2000205903A - Combined flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make accurate flow measurements by performing very effectively the operation of straightening the flow of a fluid in a flow passage. SOLUTION: In this combined flowmeter A in which a flow sensor 2 is disposed in the flow passage 4 of a fluidic flowmeter 1, flow-straightening nets 6a-6c and a flow-straightening grid 7 are disposed in the flow passage 4. The flow of a fluid is thereby processed into a generally uniform distribution of flow velocities by the flow straightening nets 6a-6c and further into two-dimensional flow by the flow-straightening grid 7. Therefore the operation of straightening the flow of the fluid in the flow passage 4 is performed very effectively and accurate flow measurements can be made.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite flow meter including a flow sensor suitable for measuring a low flow rate region and a fluidic flow meter suitable for measuring a large flow rate region.

[0002]

2. Description of the Related Art Conventionally, there has been known a combined flow meter in which a flow sensor is incorporated in a fluidic flow meter in order to widen a measurement range of a fluid flow rate.

[0003] The principle of a fluidic flow meter is schematically shown in, for example, Japanese Patent Application Laid-Open No. 5-118888, in which a fluid flow meter flows from an upstream side to a downstream side in a flow path through which a fluid flows. Forming a narrowed portion having a narrowed flow path, a jet nozzle connected to the narrowed portion, and a flow channel enlarged portion extending from an outlet of the jet nozzle, and the flow channel expanded portion faces the outlet of the jet nozzle. Forming an exciter and an end block located downstream of the exciter, directing the fluid rectified by the jet nozzle to the exciter and distributing it to the left and right, expanding the fluid that alternately hits the left and right parts of the end block It returns to the jet nozzle side by the right and left wall of the part and hits the jet flow from the jet nozzle at right angles, and the frequency of the vibration (alternating pressure wave) generated by doing so is a pressure sensor More detection, it is intended to measure the flow rate of fluid by converting the output obtained by the detection into an electrical signal.

In a flow sensor, a thin film sensor portion is formed on a surface of a substrate via an insulating film, and when the energized thin film sensor portion is exposed to a flow of fluid, the thin film sensor portion changes in flow velocity. Since the temperature changes in response to the temperature change, a heat-sensitive flow sensor that measures the flow rate of the fluid based on the output (resistance value) of the thin film sensor corresponding to the temperature change is often used. In this case, it is necessary to thermally insulate the thin film sensor from the substrate. As the insulating structure, there are a microbridge type structure and a diaphragm type structure. The microbridge type has a structure in which a moat is formed in a portion of a substrate below a thin film sensor portion, and a bridge crossing the moat is formed by an insulating film and a thin film sensor portion. The diaphragm type structure is a structure in which an opening is formed below the thin film sensor portion and opens on the back surface of the substrate, and the thin film sensor portion is supported on a diaphragm formed by the remaining insulating film.

[0005] By the way, the heat-sensitive type flow sensor is arranged in a flow path having a circular or rectangular cross section. If there is a step or bend in the inner surface of the flow path, the flow of the fluid is disturbed, and the output of the flow sensor is disturbed. Flow measurement is difficult. For this reason, as described in Japanese Patent Publication No. 6-43907, a plurality of rectifying elements having a wire mesh structure or a honeycomb structure are provided at predetermined intervals in the flow direction of the fluid in the flow path of the fluidic flow meter. There has been proposed a flow meter which is provided with the opening. According to this, a wire mesh for rectification is relatively coarse, and it is said that there is an effect of reducing clogging and pressure loss due to dust in a flow, and suppressing turbulence and drift.

[0006]

SUMMARY OF THE INVENTION In the case of a composite type flow meter,
Since the heat-sensitive flow sensor is located at a position where the flow of the fluid is relatively stable, that is, upstream of the jet nozzle of the fluidic flow meter, if the flow condition upstream of the flow sensor is poor, The flow state before flowing into the jet nozzle is disturbed by the flow sensor in a form that develops three-dimensionally, and the Coander effect after the fluid ejected from the jet nozzle hits the inducer is weakened. It has been found that the stability of the vibration of is lost.

[0007] As described in Japanese Patent Publication No. 6-43907, a structure in which a rectifying element having a wire mesh structure or a honeycomb structure is arranged upstream of a flow sensor rectifies a three-dimensional flow of fluid to two dimensions. I can't expect to do that.

[0008] For this reason, by arranging a grid-like rectifier upstream of the flow sensor, it is possible to suppress the generation of three-dimensional flow, stabilize the output of the flow sensor, and reduce the flow rate of the fluidic flow meter. Has proposed to reduce energy loss and obtain a stable vibration output.

However, it has been found that when the fluctuation of the flow velocity of the fluid is large, the flow is disturbed by the flow sensor and the influence on the fluidic flow meter is large. Also, if the flowing fluid is a flammable gas, and if this gas is burned violently downstream, pressure waves and sound waves of the fluid will be superimposed, resulting in a decrease in the performance of the flow sensor and a fluidic flow meter. It was found that the influence on the vibration was large.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a compound flow meter capable of extremely effectively rectifying a fluid in a flow path.

[0011]

According to the first aspect of the present invention,
Equipped with a fluidic flow meter that measures the flow rate of the fluid by converting the alternating pressure wave generated by the vibration phenomenon of the fluid ejected from the jet nozzle formed in the flow path into an electric signal, and the substrate on the surface of the substrate Is a composite type flow meter provided with a flow sensor for measuring the flow rate of a fluid based on the output of a thin film sensor portion that is thermally insulated and formed into a film, and the flow sensor is disposed upstream of the jet nozzle in the flow path. A rectifying net and a rectifying grid are provided. Therefore, the flow of the fluid can be processed into a substantially uniform flow velocity distribution by the flow rectifying net, and further processed into a two-dimensional flow by the flow rectifying grid.

According to a second aspect of the present invention, in the first aspect of the present invention, the flow path shape of the narrowed portion of the narrowed portion toward the jet nozzle is such that two opposed wall surfaces are parallel to each other. The two opposing wall surfaces have a rectangular cross section inclined in a direction in which the opposing interval becomes narrower toward the jet nozzle, and the maximum opposing interval on the most upstream side of the inclined two wall surfaces of the throttle portion is D, the minimum opposing interval on the most downstream side of the two inclined wall surfaces is d, and the effective length of the narrowed portion is L, the inclination angle θ of the two inclined wall surfaces in the narrowed portion is θ = arctan ((D−d) / 2L). Therefore, the flow of the fluid is hardly disrupted, and it is possible to eliminate losses other than energy loss due to friction with the wall surface of the throttle portion.

According to a third aspect of the present invention, in the first or second aspect of the invention, the center of the flow sensor is a boundary portion between the throttle section and the jet nozzle and is on a center line of the jet nozzle. It is located near the position. Therefore, the flow velocity of the fluid in the portion where the flow sensor is disposed is increased, and the output of the flow sensor increases.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, the rectifying net and the rectifying grid are arranged on the upstream side of the flow sensor. Therefore, pressure waves and sound waves of the fluid are superimposed as in the case where the fluctuation of the flow velocity of the fluid in the flow path is large, or the case where the flowing fluid is a flammable gas and the gas is burned violently on the downstream side. In this case, the influence of vibration on the flow sensor and the fluidic flow meter can be eliminated.

[0015] The invention according to claim 5 is based on claims 1, 2, 3
Alternatively, in the invention described in Item 4, the rectifying net and the rectifying grid are arranged in the flow passage having a substantially rectangular cross-sectional shape. Therefore, the rectifying net and the rectifying grid can be easily attached to the flow path.

The invention according to claim 6 is the invention according to claims 1, 2, 3,
In the invention described in 4 or 5, the rectifying net is disposed upstream of the rectifying grid. Therefore, it is effective to reduce the pressure waves and sound waves superimposed on the flow of the fluid by the rectifying net on the upstream side and process it into a uniform flow, and then to process the fluid flow into a two-dimensional flow by the rectifying grid. Done.

[0017]

An embodiment of the present invention will be described with reference to the drawings. As shown in FIG.
Is composed of a fluidic flow meter 1 and a flow sensor 2. First, the configuration of the fluidic flow meter 1 will be described. The opening on the upper surface of the flow path main body 3 functioning as the main body of the fluidic flow meter 1 is closed by a cover (not shown). In the flow path main body 3, a flow path 4 having a rectangular cross section for flowing a fluid in the direction of the arrow is formed. In the flow path 4, an inlet portion 5, a plurality of rectifying nets 6 a, 6 b, 6 c and a rectifying grid 7 are arranged at predetermined intervals from the upstream side to the downstream side in the flow direction of the fluid. A flow path section 8, a flow sensor flow path section 9 as a throttle section, a jet nozzle 10, a flow path expansion section 11, and an outlet section 12 are formed. An exciter 13 facing the outlet of the jet nozzle 10 and an end block 14 arranged on the downstream side of the exciter 13 are formed in the flow path expanding portion 11. Pendulum 1
3 and the end block 14 are formed symmetrically with respect to a center line C passing through the center of the flow path 4. The flow sensor 2 is disposed in the flow sensor channel section 9, and the flow sensor channel section 9
The cross-section of a rectangular shape in which two opposite wall surfaces 15 in the vertical direction are parallel and two opposite wall surfaces 15 in the left and right direction are inclined in such a direction that the distance between the two opposite wall surfaces 15 decreases toward the jet nozzle 10. With.

The principle of fluid measurement of such a fluidic flow meter 1 is well known and will be briefly described.
The fluid flowing through the flow path 4 is jetted out of the jet nozzle 10, is directed to the right and left by the vibrator 13, and alternately hits the left and right portions of the end block 14. It is returned toward the jet nozzle 10 by the left and right wall surfaces and strikes the jet flow from the jet nozzle 10 at right angles. The frequency of the vibration (alternating pressure wave) generated in this manner is detected by a pressure sensor (not shown), and the detected output is converted into an electric signal to measure the flow rate of the fluid.

Next, the configuration of the flow sensor 2 will be described. In the flow sensor 2, an insulating film (not shown) is formed on a surface of a substrate 20 such as a silicon wafer, and a heating element 21 and a heating element temperature measuring element 22 as a thin film heater section, a fluid temperature, respectively. The temperature measuring element 23, the bonding pad 24 connected to the heating element 21, the bonding pad 25 connected to the heating element temperature measuring element 22, the bonding pad 26 connected to the fluid temperature measuring element 23, and the like are formed by etching. Heating element 21, heating element temperature measuring element 2
2. It is formed by covering the surface of the fluid temperature measuring element 23 with a protective film (not shown).

A moat 28 is formed on the substrate 20 so that a microbridge 27 is formed by the heating element 21, the heating element temperature measuring element 22, and a part of an insulating film formed thereunder.
Are formed by anisotropic etching. Thereby, the heating element 21 and the heating element temperature measuring element 22 are thermally insulated from the substrate 20. Bonding pad 24,
25 and 26 are connected to an external circuit (not shown).

In the flow sensor 2, the heating element 21, the fluid temperature measuring element 22, and the fluid temperature measuring element 23, which are exposed to the flow of the fluid to be measured, are energized to change according to the temperature of the fluid. The temperature of the fluid to be measured is obtained from the output of the fluid temperature measuring element 23 to be measured. Since the output that changes according to the temperature of the heating element temperature measuring element 22 itself changes according to the change in the flow velocity of the fluid at that time and the heat received from the heating element 21, the output of the heating element temperature measuring element 22 A current is applied to the heating element 21 so as to be equal to the output of the temperature measuring element 23, and the flow rate of the fluid is determined by determining the potential difference between both ends of the heating element 21 at this time.

The measurement principle of the fluidic flow meter 1 and the flow sensor 2 alone has been described above. According to the composite flow meter A of the present embodiment, the fluid flowing from the inlet 5 of the flow path 4 Flow is the rectification net 6 on the uppermost stream side.
a, the rectifying net 6a and the next rectifying net 6
b, and the periodic fluctuation is mitigated,
Processed into a substantially uniform flow velocity distribution by the next rectifying net 6c,
Subsequently, the flow is rectified to the initial two-dimensional flow by the rectifying grid 7 and a non-compressible stationary uniform flow almost hydrodynamically close to an ideal state is produced. Moreover, in this example, since the flow sensor channel section 9 in which the flow sensor 2 is disposed is narrowed linearly, the flow of the fluid has a more excellent two-dimensional property. Thereby, the output signal of the flow sensor 2 becomes stable.

The state in which the flow sensor channel section 9 is narrowed linearly will be described in detail with reference to FIG. The flow path shape of the flow sensor flow path portion 9 in a portion where the flow path 4 is narrowed toward the jet nozzle 10 is such that two vertically opposed two wall surfaces are parallel, and two left and right opposed wall surfaces 15 are jet nozzles. 10, has a rectangular cross section that is inclined in a direction in which the opposing interval becomes narrower, and as shown in FIG. 4, the maximum opposing interval on the most upstream side of the two inclined wall surfaces 15 is D, Assuming that the minimum opposing interval on the most downstream side of the wall surface 15 is d, and the effective length of the narrowed portion in the flow sensor channel portion 9 is L, the inclination angle θ of the inclined two wall surfaces 15 is θ = arctan ((D −d) / 2L).

Therefore, the flow of the fluid is hardly disrupted, and the loss other than the energy loss due to the friction with the wall surface 15 of the flow sensor channel section 9 can be eliminated.
Since the width of the jet nozzle 10 is kept constant from the linearly constricted inlet section, a two-dimensional jet stream of incompressible perfect fluid is formed. Since both sides of the jet stream near the outlet side of the jet nozzle 10 will be occupied by a stationary fluid of uniform and symmetric pressure, the free stream lines of the jet stream will be initially angled but eventually parallel. Become. Since the pressure is constant on the free stream line of the jet flow, the flow velocity is also constant. By arranging the U-shaped vibrator 13 at this position, a good co-under effect occurs on the left and right wall surfaces of the end block 14, and ideal fluidic vibration can be obtained.

FIG. 3 shows this state. FIG. 3 is a graph showing the relationship between the fluidic frequency and the flow rate. FIG. 3A shows the measurement results in the configuration shown in FIG. 1 with the rectification grids 7 removed while leaving the rectification nets 6a to 6c, and FIG. FIG. 1 shows the measurement results in a state where the rectifying nets 6a to 6c and the rectifying grid 7 are provided as shown in FIG.

In FIG. 3A, a plurality of rectifying nets 6a to 6
The fluid is mixed during the period c, and the periodic fluctuation of the fluid (the phenomenon in which the fluid is distorted by the flow velocity distortion, the rotational motion, or the expansion and contraction of the fluid moving on the flow due to the superposition of the pressure wave or the sound wave on the fluid) is reduced. However, the development of three-dimensional flow cannot be suppressed. Thereby, a kink is seen in a region where the number of Reynolds changes from laminar flow to turbulent flow (critical Reynolds number region). The critical Reynolds number region in the present embodiment is around 2500 liter / H. However, 4000
Fluctuations above 1 liter / H are expected to cause the fluidic oscillations to begin to saturate.

On the other hand, FIG.
In (b), the fluid is mixed by the rectifying nets 6a to 6c to mitigate the periodic fluctuation, and the rectifying grid 7 is disposed further downstream, so that the development of the three-dimensional flow is suppressed and the initial flow is reduced. Following the two-dimensional flow, an incompressible, steady, uniform flow is obtained which is very close to the ideal state hydrodynamically. This shows that the pressure is constant on the free stream line of the jet flow after passing through the jet nozzle 10, so that the flow velocity is also constant, and a good Coneard effect is generated and ideal fluidic vibration is obtained. You can see that there is.

Further, as shown in FIG. 4, the center of the flow sensor 2 is the boundary portion (on the straight line Y) between the narrowed portion of the flow sensor flow path portion 9 and the jet nozzle 10 and the center of the jet nozzle 10 By mounting the flow sensor 2 near the position on the line C, the flow velocity of the fluid in the portion where the flow sensor 2 is arranged can be increased, so that the output of the flow sensor 2 can be increased. (See FIG. 5A.) On the other hand, in the flow sensor channel section 9, a center line C passing through the center of the jet nozzle 10 is formed.
When the center of the flow sensor 2 is located at an arbitrary position, the output of the flow sensor 2 becomes slightly lower (FIG. 5B).
reference). Note that the vertical axis in FIG. 5 is the output of the heating element 21 of the flow sensor 2.

In the present embodiment, the rectifying nets 6a to 6a
6c and the rectifying grid 7 are arranged on the upstream side of the flow sensor 2, so that when the flow velocity of the fluid in the flow path 4 fluctuates greatly, or when the flowing fluid is a flammable gas, Even when pressure waves or sound waves of a fluid are superimposed as in the case of intense combustion on the side, the influence of vibration on the fluidic flow meter 1 and the flow sensor 2 can be eliminated.

Further, in the present embodiment, the rectifying net 6a
6c and the rectifying grid 7 are arranged in the flow path 4 having a substantially rectangular cross-sectional shape.
a to 6c and the rectifying grid 7 can be easily attached.

Further, in the present embodiment, the rectifying net 6a
6c are arranged on the upstream side of the rectifying grid 7, so that the pressure waves and sound waves superimposed on the flow of the fluid can be rectified by the rectifying mesh 6 on the upstream side.
It is effective to process the fluid flow into a two-dimensional flow by relaxing the flow by a through 6c and then processing the fluid flow into a two-dimensional flow by the rectifying grid 7.

Next, a specific example of the structure of the rectifying grating 7 is shown in FIG.
A description will be given based on (a) and (b). Any rectifying grid 7
Also, the vertical plate 61 and the horizontal plate 62 are combined in a lattice shape, and a common feature is that the vertical plate 61 does not pass through the center of the rectifying lattice 7. More specifically, in FIGS. 7A and 7B, the number of vertical plates 61 is different, but one horizontal plate 62 passes through the center of the rectifying grid 7. Figure (c)
(D), the number of vertical plates 61 is different, but a plurality of horizontal plates 62 are provided.
Are arranged with the center of the rectifying grating 7 removed.

However, the vertical plate 61 and the horizontal plate 62 of the rectifying grid 7 are provided.
Are not limited to the above example. Further, the number of rectifying gratings 7 may be singular or plural. In the case of a plurality, the same or different numbers and combinations of the vertical plate 61 and the horizontal plate 62 may be used.

Although three rectifying nets 6a to 6c are used in the above-described embodiment, the number of rectifying nets may be one, two, or four or more with some difference in function. However, since the pressure loss increases as the number of rectifying nets increases, it is desirable to select the roughness of the mesh.

[0035]

According to the first aspect of the present invention, there is provided a screen for measuring a flow rate of a fluid by converting an alternating pressure wave generated by a vibration phenomenon of a fluid ejected from a jet nozzle formed in a flow path into an electric signal. A flow sensor for measuring the flow rate of the fluid based on the output of the thin film sensor unit formed on the surface of the substrate and thermally insulated from the substrate is provided on the upstream side of the jet nozzle in the flow path. In the combined flow meter provided, a rectifying net and a rectifying grid are disposed in the flow path, so that the flow of the fluid is processed into a substantially uniform flow velocity distribution by the rectifying net, and a two-dimensional flow is further formed by the rectifying grid. Can be processed into a stream. Thereby, the output signal of the flow sensor becomes stable.

According to a second aspect of the present invention, in the first aspect of the present invention, the shape of the flow path of the narrowed portion of the flow path toward the jet nozzle is such that two opposed wall surfaces are parallel to each other. The two opposing wall surfaces have a rectangular cross section inclined in a direction in which the opposing interval becomes narrower toward the jet nozzle, and the maximum opposing interval on the most upstream side of the inclined two wall surfaces of the throttle portion is D, the minimum opposing interval on the most downstream side of the two inclined wall surfaces is d, and the effective length of the narrowed portion is L, the inclination angle θ of the two inclined wall surfaces in the narrowed portion is θ = arctan ((D−d) / 2L), the flow of the fluid is hardly disrupted, and losses other than energy loss due to friction with the wall surface of the throttle portion can be eliminated.

According to a third aspect of the present invention, in the first or second aspect of the invention, the center of the flow sensor is a boundary portion between the throttle portion and the jet nozzle and is on a center line of the jet nozzle. Since it is arranged near the position, the flow velocity of the fluid at the portion where the flow sensor is arranged can be increased, so that the output of the flow sensor can be increased.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, the rectifying net and the rectifying grid are arranged on the upstream side of the flow sensor.
Fluid pressure waves and sound waves are superimposed, such as when the flow velocity of the fluid in the flow path fluctuates greatly, or when the flowing fluid is a flammable gas and the gas is burned violently downstream. In addition, the influence of vibration on the flow sensor and the fluidic flow meter can be eliminated.

The fifth aspect of the present invention provides the first, second, and third aspects.
Alternatively, in the invention described in Item 4, the rectifying net and the rectifying grid are arranged in the flow passage having a substantially rectangular cross-sectional shape. Therefore, the rectifying net and the rectifying grid can be easily attached to the flow path.

The invention according to claim 6 is the invention according to claims 1, 2, 3,
In the invention described in 4 or 5, since the rectifying net is arranged on the upstream side of the rectifying grid, the pressure waves and the sound waves superimposed on the flow of the fluid are alleviated by the rectifying net on the upstream side to be uniform. It is effective to process the fluid into a flow, and then to process the fluid flow into a two-dimensional flow by the flow rectifying grid.

[Brief description of the drawings]

FIG. 1 is a plan view showing the internal structure of a compound flow meter according to an embodiment of the present invention.

FIG. 2 is a plan view of the flow sensor.

3A and 3B are graphs showing a relationship between a fluidic frequency and a flow rate. FIG. 3A is a measurement result when only a rectifying net is arranged in a flow path, and FIG. It is a measurement result in the state where the grid was arranged.

FIG. 4 is an enlarged plan view showing a flow sensor channel section.

FIG. 5 is a graph showing a result obtained by experimentally measuring a relationship between an output of a flow sensor and a flow rate.

FIG. 6 is a schematic diagram illustrating a configuration example of a rectifying grating.

[Explanation of symbols]

 A Combined flow meter 1 Fluidic flow meter 2 Flow sensor 4 Flow path 6a to 6c Rectifying net 7 Rectifying grid 9 Restricted portion 10 Jet nozzle 15 Inclined two wall surfaces 20 Substrate 21, 22 Thin film sensor portion C Center line

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Toshiyuki Takamiya 2-2-13 Nishikicho, Naka-ku, Nagoya-shi, Aichi F-term in Ricoh Elemex Corporation (reference) 2F030 CA10 CD13 CF01

Claims (6)

[Claims] 1. A fluid flow meter for measuring a flow rate of a fluid by converting an alternating pressure wave generated by a vibration phenomenon of a fluid ejected from a jet nozzle formed in a flow path into an electric signal, comprising: In a composite type flow meter, a flow sensor for measuring a flow rate of a fluid by an output of a thin film sensor portion formed on a surface thereof and thermally insulated from the substrate is disposed on the upstream side of the jet nozzle in the flow path. A rectifying net and a rectifying grid are provided in the flow passage, wherein the flow meter is a composite flow meter. 2. A flow path shape of a throttle portion in a portion where the flow path is narrowed toward the jet nozzle is such that two opposing wall surfaces are parallel and the other opposing two wall surfaces are opposed to each other toward the jet nozzle. It has a rectangular cross section inclined in the direction in which the interval becomes narrower, and the maximum opposing interval on the most upstream side of the inclined two wall surfaces of the throttle unit is D, and the minimum opposing interval on the most downstream side of the inclined two wall surfaces is D. Where d is an opposing interval and L is an effective length of the narrowed portion, the inclination angle θ of the two inclined wall surfaces in the narrowed portion is defined as θ = arctan ((D−d) / 2L). 2. The composite flow meter according to 1. 3. The composite according to claim 1, wherein the center of the flow sensor is located near a position on a boundary between the throttle section and the jet nozzle and on a center line of the jet nozzle. Type flow meter. 4. The composite flow meter according to claim 1, wherein said rectifying net and said rectifying grid are arranged upstream of said flow sensor. 5. The composite flow meter according to claim 1, wherein said rectifying net and said rectifying grid are arranged in said flow passage having a substantially rectangular cross section. 6. The combined flow meter according to claim 1, wherein said rectifying net is disposed upstream of said rectifying grid.