JPH08240463A - Flowmeter for liquid - Google Patents

Abstract

PURPOSE: To shorten the length of a straight pipe of a measuring part. CONSTITUTION: The flowmeter for liquid is provided with a pipe part 12 interposed, as its part, in the middle of piping 11a and 11b in which liquid flows and a flow rate sensor 13 to detect the flow rate of the liquid flowing in this pipe part 12. The pipe part 12 is provided with a connecting part 14 which is connected to the upstream side piping 11a and has a cross-sectional area smaller than the cross-sectional area of this upstream side piping 11a, a measuring part 15 having a straight pipe having the cross-sectional area corresponding to a measuring flow rate and an introducing part 16 to smoothly connect the connecting part 14 and the measuring part 15 to each other while gradually increasing the cross-sectional area over to the measuring part side from the connecting part side, and the flow rate sensor 13 outputs a signal according to its flow rate by coming into contact with liquid flowing in the measuring part 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid flow meter having a pipe part interposed as a part in the middle of a pipe through which a liquid flows, and a flow rate sensor for detecting the flow rate of the liquid flowing through the pipe part. Regarding

[0002]

2. Description of the Related Art Conventionally, as a main flow meter used for measuring the flow rate of a liquid flowing in a pipe, an electromagnetic flow meter, an ultrasonic flow meter, a vortex flow meter, a rotor type flow meter, a thermal type flow meter. Mass flowmeters and the like are known and are used depending on the purpose and accuracy. Among them, the vortex flowmeter and the rotor-type flowmeter have a drawback that they are not suitable for measuring a fluid mixed with foreign matter because the insertion portion and the movable portion are present in the pipe.
Further, the electromagnetic flowmeter has a drawback that it is difficult to downsize the device because it is necessary to connect a device such as a coil to the pipe.

When such a flow meter is used, it is generally necessary to provide a straight pipe part to some extent upstream of the measuring part in order to adjust the flow velocity distribution of the fluid to be measured, especially ultrasonic waves. In the case of a flow meter, there is a drawback that long straight pipe parts are required in the pipes before and after the measurement part in order to suppress the influence on ultrasonic waves.

On the other hand, the thermal mass flowmeter comprises a heating section which is heated to a constant temperature higher than the temperature of the fluid to be measured, and a temperature detecting section in which the value of the current flowing changes according to the change in temperature.
The temperature at which the heated heating section is cooled by the fluid flowing around it is detected as a change in the current flowing through the temperature detecting section. The higher the flow velocity of the fluid, the greater the degree of cooling of the heating unit. Therefore, the flow velocity of the fluid can be known by detecting the current flowing through the temperature detection unit.

A thermal type flow meter for liquids is shown in FIG.
Those having a structure as shown in are known. This flow meter includes a pipe portion 62 which is interposed as a part in the middle of a pipe through which the liquid flows in the direction of arrow 61, and a flow rate sensor 63 for detecting the flow amount of the liquid flowing through the pipe portion 62.
The flow rate sensor 63 is attached to the pipe portion 62 so as to come into contact with the fluid via the case 64.

Furthermore, in recent years, there has been proposed a miniaturized flow rate sensor by applying a thin film thermistor having a high-speed response as a temperature detecting section. The thermal mass flowmeter using this sensor has no insertion part or movable part in the pipe, and the size of the entire device can be easily reduced.

[0007]

However, when the flow rate of the liquid flowing through the pipe as shown in FIG. 6 is measured by a thermal type flow meter, a miniaturized flow rate sensor using a thin film thermistor is used. However, for the purpose of regulating the flow of the fluid to be measured, a straight pipe portion having a length of 5 times or more of the inner diameter of the pipe portion 62 is provided upstream of the measurement pipe portion 62 in which the flow rate sensor is arranged. It is necessary to provide. On the other hand, the pipe portion 62
The inner diameter of the is determined according to the range of the measured flow rate. Therefore, even if the flow rate sensor is downsized in the range corresponding to the measured flow rate, the size of the entire flowmeter including the straight pipe part needs to be the size that includes the length of the straight pipe part, so it is easy. There is a problem that it cannot be miniaturized.

An object of the present invention is to reduce the size of a thermal type flow meter for liquid in view of the problems of the prior art.

[0009]

In order to achieve this object, in the present invention, a pipe portion interposed as a part in the middle of a pipe through which a liquid flows, and a flow rate for detecting the flow rate of the liquid flowing through this pipe portion. In a liquid flowmeter equipped with a sensor, the pipe part is connected to an upstream pipe, and a connecting part having a cross-sectional area smaller than the cross-sectional area of the upstream pipe and a straight pipe having a cross-sectional area corresponding to the measured flow rate. And a lead-in portion that connects the connecting portion and the measuring portion smoothly from the connecting portion side to the measuring portion side while gradually increasing the cross-sectional area, and the flow rate sensor flows in the measuring portion. It is characterized by being in contact with a liquid and outputting a signal according to the flow rate thereof.

Still further, the introduction portion has a conical shape that spreads from the connection portion side toward the measurement portion side, and the spread angle is less than 15 °. It is preferable to use a thin film thermistor as the flow sensor.

[0011]

In this structure, the flow velocity distribution of the liquid flow may be disturbed in the upstream side pipe due to the bending or the insertion thereof. However, such turbulence is corrected when the liquid flow passes through the connection because the cross-sectional area of the connection is smaller than that of the upstream pipe. Then, the introduction portion that smoothly and gradually spreads from the connection portion acts like a straight pipe to further regulate the flow velocity distribution, and guide the liquid flow in which the turbulence is corrected to the measurement portion without disturbance.

The inner diameter of the straight pipe constituting the measuring section is set so as to have a cross-sectional area corresponding to the measured flow rate, that is, a cross-sectional area which provides a flow velocity suitable for the measurement range of the flow rate sensor. This setting is the same as in the conventional case of a straight pipe type in which the upstream side of the flow rate sensor is entirely constituted by a straight pipe in order to adjust the flow velocity distribution. Therefore, if the same flow rate sensor is used, the inner diameter of the measurement portion provided with the flow rate sensor is the same as that of the conventional straight pipe type.
However, in the case of the conventional straight pipe type, the straight pipe on the upstream side of the flow sensor needs to have a length of 5 times or more of the inner diameter of the measurement portion, whereas in the present invention, the connection portion, the introduction portion, and the Even if the total length of the measurement portions is less than 5 times the inner diameter of the measurement portion, the flow rate is stably measured by the action of the connection portion and the introduction portion. Therefore, the length of the straight pipe portion required for measuring the flow rate is shortened as compared with the conventional straight pipe type. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013]

FIG. 1 is a sectional view showing a liquid flowmeter according to an embodiment of the present invention. As shown in the figure, this flowmeter includes a pipe portion 12 which is interposed as a part in the middle of the pipes 11a and 11b through which the liquid flows, and a flow rate sensor 13 for detecting the flow amount of the liquid flowing through the pipe portion 12. Prepare The pipe portion 12 is connected to the upstream pipe 11a and has a connecting portion 14 having an inner diameter D2 smaller than the inner diameter D3 of the pipe 11a, a measuring portion 15 having a straight pipe having a cross-sectional area corresponding to the measured flow rate, and the connecting portion 14 and the measurement. Introducing part 1 for smoothly connecting the part 15 to the measuring part side from the connecting part side while gradually increasing the inner diameter.
6 and a lead-out section 18 that connects the measuring section 15 and the downstream pipe 11b. The flow rate sensor 13 is in contact with the liquid flowing in the direction of the arrow 17 in the measuring unit 15 and outputs a signal corresponding to the flow rate. Each of the connecting portion 14, the measuring portion 15, and the lead-out portion 18 has a cylindrical tubular shape, and the introducing portion 16 has a conical tubular shape. And these are located on a common cylindrical axis. The spread angle θ of the introduction part 16 is less than 15 °. Further, the total length of the connecting portion 14 and the introducing portion 16 is 5 of the inner diameter D1 of the measuring portion 15.
Less than double. The inner diameters D1 and D2 are
Considering the flow rate of the liquid flow flowing through 11b and the measurement range of the flow rate sensor 13, the flow rate suitable for the measurement is set to be obtained at the connection portion 14. The inner diameter of the lead-out portion 18 is adapted to the cases where the pipe 11b has various inner diameters.

FIG. 2 is a sectional view showing the structure of the flow rate sensor 13. As shown in the figure, the flow rate sensor 13 is a flow rate sensor using a thin film thermistor, and includes a case 21,
A substrate 22 mounted in the case 21, a thin film heating element 23 provided on the substrate 22, and an insulating film 2 covering the heating element 23.
4, a thin film thermistor 25 provided on the insulating film 24, a lead-out electrode 26 connected to the heating element 23 and the thin film thermistor 25, respectively, and a lead wire 27 connected to these lead-out electrodes 26.

The flow sensor 13 is attached to the opening of the measuring unit 15 so as to come into contact with the liquid flowing through the measuring unit 15 via the case 21. Then, when an electric current is passed through the heating element 23 to generate heat, the heat is released from the bottom surface side of the heating element 23 into the liquid flow flowing through the measuring unit 15, so that the temperature near the heating element 23 exhibits a constant temperature. But
The temperature is measured as the resistance value of the thin film thermistor 25. The flow rate of the liquid flow is obtained based on the difference between this temperature and the temperature of the liquid flow measured by another thermistor or the like.

In this structure, the liquid flow flowing into the pipe portion 12 via the pipe 11a may have a disturbance in the flow velocity distribution of the liquid flow due to the bending of the pipe 11a or an insert therein. . But such disturbances
Since the inner diameter D2 of the connecting portion 14 is smaller than the inner diameter D3 of the pipe 11a, the liquid flow is corrected when passing through the connecting portion 14. Then, the liquid flow whose turbulence is corrected is connected to the connecting portion 1
4 is guided to the measuring section 15 through the introducing section 16, but the introducing section 16 has a conical shape that smoothly and gradually expands from the connecting section 14 and its divergence angle θ is less than 15 °. It acts in the same manner as a pipe, its flow velocity distribution is further adjusted, and it is guided to the measuring unit 14 without being disturbed.
Then, the temperature corresponding to the flow rate of the liquid flow having the adjusted flow velocity distribution is detected via the thermistor 25, and the flow rate is measured.

FIG. 4 is a graph showing the results of measuring the flow rate of water at 42 ° C. in this way. However, the introduction section 16
Has a divergence angle θ of 10 °, the combined length of the connecting portion 14 and the introducing portion 16 is 3.5 times the inner diameter D1 of the measuring portion 15, and the connecting portion 1
The inner diameter D2 of 4 is 0.8 times the inner diameter D3 of the pipe 11a. In this graph, the horizontal axis is the flow rate, the vertical axis is the resistance value R of the thermistor 25, and the results are shown by ●.
Further, for comparison, only the spread angle θ of the introduction portion 16 is set to 18
The measurement results in each case of changing to 0 °, 40 °, and 20 ° are also shown by ▲, ◆, and ■ marks, respectively. Also, for comparison, instead of the pipe portion 12, a straight pipe having the same inner diameter as the inner diameter D1 of the measurement unit 15 and having a length 12 times the inner diameter D1 upstream of the flow sensor is used. The measurement results when the flow rate sensor 13 is attached are also shown by cross marks. From these results, the introduction part 16 is
It can be seen that when the spread angle θ is less than 15 °, the resistance value of the thermistor 25 largely changes with respect to the change in the flow rate, as compared with the case where the spread angle θ is 15 ° or more.
Further, in the case of the present embodiment, the magnitude of the change in the resistance value of the thermistor 25 with respect to the change in the flow rate is comparable to that in the case where the straight pipe is used instead of the pipe portion 12. That is, according to the present embodiment, the flow velocity can be measured accurately as in the case where the flow velocity distribution is adjusted using a long straight pipe.

FIG. 3 shows a case where the upstream pipe is a pipe 31a bent 90 ° immediately before the pipe portion 12. Figure 5
Is a graph showing the results of flow rate measurement in this case. The results are indicated by ●. The measurement conditions are the same as in the case of this embodiment described above. In addition, for comparison, the results of the same measurement performed when the upstream pipe is a straight pipe that is not bent are also shown by X marks. From this result, it can be seen that even if the pipe on the upstream side of the flowmeter is bent just before the flowmeter, the measured value hardly changes.

In this embodiment, the cross section of the pipe portion is all circular, but other shapes such as square or a combination thereof may be used. For example, the cross section of the upstream side connecting part is square, the cross section of the introducing part is square on the upstream side, and the cross section is circular on the downstream side, so that the cross section after the measuring part is It may be circular. However, in any case, the flow velocity distribution is adjusted, and in order to prevent turbulence, there is a connecting part and an introducing part having a cross-sectional area smaller than the cross-sectional area of the upstream side pipe, and the cross-sectional area of the introducing part is to be measured. It must gradually increase over time and smoothly connect the measuring part and the upstream connecting part.

[0020]

As described above, according to the present invention, the measurement pipe through which the fluid to be measured passes has a connecting portion having a cross-sectional area smaller than the cross-sectional area of the upstream pipe and a cross-sectional area corresponding to the measured flow rate. Having a measuring unit which is a straight pipe to which the flow sensor is attached, smoothly connects the connecting unit and the measuring unit,
It is preferable that the flowmeter is provided with the introduction portion having a divergence angle of 15 ° or less, so that the length of the entire flowmeter including the portion for adjusting the flow velocity distribution can be shortened. In other words, even if the upstream pipe is bent and the flow is disturbed, the flow rate can be accurately measured by directly connecting to the turbulent flow portion without providing a long straight pipe portion. Moreover, since the cross-sectional area of the connecting portion is smaller than the cross-sectional area of the upstream pipe, it can be relatively easily adapted to the upstream pipe having various inner diameters.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a liquid flowmeter according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a flow sensor attached to the flow meter of FIG.

FIG. 3 is a cross-sectional view showing a case where the flowmeter of FIG. 1 is connected to a bent upstream side pipe.

FIG. 4 is a graph showing the measurement results obtained by the flowmeter of FIG.

5 is a graph showing another measurement result by the flow meter of FIG. 1. FIG.

FIG. 6 is a cross-sectional view showing a conventional thermal type flow meter for liquid.

[Explanation of symbols]

11a and 31a: upstream piping, 11b: downstream piping, 13: flow rate sensor, 14: connection part, 15: measuring part,
16: introduction part, 17: arrow, 18: derivation part, 12: case, 22: substrate, 23: heating element, 24: insulating film, 25:
Thin film thermistor, 26: electrode, 27: lead wire.

Claims (3)

[Claims] 1. A flowmeter for liquid, comprising: a pipe part interposed as a part in the middle of a pipe through which a liquid flows, and a flow rate sensor for detecting a flow rate of the liquid flowing through the pipe part, wherein the pipe part is A connecting portion connected to the upstream side pipe and having a sectional area smaller than the sectional area of the upstream side pipe, a measuring portion having a straight pipe having a sectional area corresponding to the measured flow rate, and connecting the connecting portion and the measuring portion. An inlet part that gradually connects to the measuring part side while gradually increasing the cross-sectional area and smoothly connects, and the flow rate sensor contacts a liquid flowing in the measuring part and outputs a signal corresponding to the flow rate. A flow meter for liquid, characterized in that 2. The liquid flowmeter according to claim 1, wherein the introduction portion has a conical shape that expands from the connection portion side toward the measurement portion side, and the spread angle is less than 15 °. A liquid flowmeter characterized by. 3. The fluid flow meter according to claim 1, wherein the flow sensor is a flow sensor using a thin film thermistor.