JPH09280913A - Differential pressure flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable correct measurement of a fluid temperature, reduction in a piping cost and shorten a wire by a constitution that a temperature sensor is embedded in a throat or in the vicinity of the throat. SOLUTION: Since a temperature sensor 18 is provided on a cone pipe 5b at a downstream closely to a throat 4, it is not necessary to provide an attaching seat for the sensor on a side of a pipe 2 or lengthen a wire 19, so that a flow meter can be inexpensively manufactured and correct temperature measurement is possible. That is, a flow speed distribution of fluid 17 flowing in a conduit is such that it flows faster at the center of the conduit while it flows slower near a pipe wall, but the distribution is approximately uniform in the vicinity of the throat 4 since a throat diameter (d) is small. Thus influence of the pipe wall to temperature characteristics is small, exhibiting an approximately uniform temperature distribution, whereby a fluid temperature can be correctly measured even if the sensor 18 is not made to protrude into the conduit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential pressure flow meter which measures a flow rate from an upstream / downstream pressure difference by using a Venturi tube or a flow nozzle as a throttle mechanism, and more specifically, to correct the density of a fluid by temperature. It relates to the diaphragm mechanism.

[0002]

2. Description of the Related Art A differential pressure flow meter used for measuring the flow rate of various fluids such as liquid, gas, and steam flowing in a pipe line in a steady flow,
As a throttling mechanism, a venturi tube, a flow nozzle, an orifice or the like is usually used to generate a pressure difference, and the flow rate is measured from the pressure difference. That is, when a throttle mechanism for narrowing the cross-sectional area of the pipeline is provided in the middle of the pipeline, a pressure difference is generated before and after the throttle mechanism when the fluid flows therethrough. Since there is a certain relationship between this pressure difference and the flow rate, the differential pressure is introduced into a differential pressure gauge by a pressure guiding tube, converted into an electrical signal, and operated to calculate the flow rate of the fluid flowing in the pipeline. Can be calculated. Among such differential pressure flowmeters, in the differential pressure flowmeter using a Venturi tube, since the fluid is smoothly guided by the conical tube, the pressure loss is minimized (compared to the generated differential Pressure 10-20
%) And has the highest measurement accuracy among differential pressure flow meters.
In addition, the throat (throttle hole portion) is less worn, and the throat is less likely to be blocked by sedimentation. Assuming that the diameter of the Venturi tube is D and the throat diameter is d, the throttle diameter ratio (= d / D) is usually 0.25 to
It is set to about 0.5. Further, the upstream straight pipe portion requires at least 5D or more, but the length of the downstream straight pipe portion does not significantly affect the measurement.

[0003]

In such a differential pressure flowmeter, a measurement error occurs because the density of the fluid changes due to the temperature change of the fluid. Therefore, the temperature of the fluid is measured and the error due to the density change is corrected. In that case, since the fluid flowing in the pipeline has a high flow velocity at the center of the pipeline, a low flow velocity near the pipe wall, and a temperature gradient, the temperature sensor is installed so as to protrude into the pipeline. However, when the temperature sensor is projected into the pipe, a vortex is generated behind the temperature sensor to cause turbulence of the fluid flow and pressure reflection to change the pressure, so that 10 to 20 D upstream of the throat, or It was necessary to install the temperature sensor at a distance of 5D or more on the downstream side (according to JIS standard). Therefore, there is a problem that a mounting seat for a temperature sensor is provided on the pipe and the wiring becomes long. Also, 10 to 20D on the upstream side of the throat
If they are provided separately, the piping becomes longer, and the piping cost becomes higher.

Therefore, the inventors of the present invention have manufactured a flowmeter having a temperature sensor according to the JIS standard and a flowmeter having a different mounting position and mounting state of the temperature sensor. A comparative test was conducted to see how the measured temperature value was affected when the fluid was flowed under the conditions. As a result, if a vortex is generated behind the temperature sensor and the fluid flow is not disturbed or pressure reflection occurs, the temperature of the fluid can be measured faithfully even if the temperature sensor is installed close to or near the throat. It was confirmed that there was no problem in practical use. To prevent turbulence of the fluid flow or pressure reflection, make the temperature sensor not protrude into the pipe line and make it approximately flush with the inner wall surface of the throttle mechanism, or reach the outer wall up to the inner wall surface. A non-through hole may be formed and a temperature sensor may be arranged in this hole. It should be noted that, in such an experiment, since the temperature sensor is embedded in the throat or in the vicinity of the throat, it is difficult to apply it to the throttling mechanism using the orifice even though it can be applied to the Venturi tube or the flow nozzle. I understood.

The present invention has been made on the basis of the above-mentioned conventional problems and experimental results. The object of the present invention is to accurately measure the temperature of a fluid without disturbing the flow of the fluid or causing pressure reflection. Another object of the present invention is to provide a differential pressure flowmeter that can perform measurement, reduce piping cost, and shorten wiring.

[0006]

In order to achieve the above object, the present invention provides a differential pressure flowmeter for measuring a flow rate from a differential pressure between an upstream and a downstream of a venturi tube or a flow nozzle having a throat, and the throat or the vicinity of the throat. The temperature sensor is embedded in the section. Further, according to the present invention, a sensor loading portion that communicates with the inside of the conduit is provided in the throat or in the vicinity of the throat, and the temperature sensor in the sensor loading portion has an end surface on the temperature measuring portion side substantially the same as the inner wall surface of the throat or the vicinity of the throat. It is characterized in that it is loaded so as to form a surface. Furthermore, the present invention is characterized in that a non-penetrating hole reaching the vicinity of the inner wall surface is formed on the outer wall surface of the throat or a portion near the throat, and a temperature sensor is loaded in the non-penetrating hole.

In the present invention, since the temperature sensor is embedded in the throat or in the vicinity of the throat, the piping and wiring can be short. Further, the present invention, the temperature sensor is loaded in the sensor loading portion provided so as to communicate with the inside of the pipe in the throat or in the vicinity of the throat, and the temperature measuring portion side end surface thereof is used as an inner wall surface of the throat or in the vicinity of the throat. Since the same surface is used, or a non-through hole reaching the inner wall surface is formed in the outer wall surface of the throat or in the vicinity of the throat, and a temperature sensor is loaded in the non-through hole, so that the temperature sensor does not disturb the fluid. No pressure reflection occurs. The fluid flowing in the pipe has a flow velocity distribution in which the center of the pipe is fast and the velocity near the pipe wall is slow, but the throat diameter d is small in the throat portion, so that the flow velocity distribution becomes nearly uniform. Therefore, the temperature characteristic is less affected by the pipe wall, and the temperature can be accurately measured without protruding the temperature sensor into the pipe.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of a differential pressure flowmeter according to the present invention. In the present embodiment,
An example of application to a differential pressure flowmeter using a Venturi tube as a throttling mechanism is shown. In the figure, the differential pressure flowmeter 1 includes a Venturi pipe 3 provided in the middle of a straight pipe portion of the pipe 2. The Venturi tube 3 has a throat 4 with an inner diameter d.
And a tapered tapered conical tube 5a, 5b connected to both ends of the throat 4, and a straight tube 6 connected to the upstream conical tube 5a having an inner diameter D, and the downstream conical tube. 5
b and flanges 7 and 8 provided at the ends of the straight pipe 6 are connected to the flanges 9 and 10 of the pipe 2, respectively. Throat 4
Pressure outlets 11 and 12 are provided on the upper surfaces of the straight pipe 6 and the straight pipe 6, and these pressure outlets 11 and 12 are connected to the pressure guiding pipe 1
3, 14 are connected to the high pressure side and the low pressure side of the differential pressure gauge 15, respectively. On the outer wall surface of the conical tube 5b on the downstream side, a cylindrical sensor loading portion 16 having an inside communicating with the inside of the conduit is provided in a protruding manner. The sensor loading portion 16 is provided on the downstream side with an appropriate angle inclination, and a temperature sensor 18 for measuring the temperature of the fluid 17 is inserted and attached inside. When the sensor mounting part 16 is inclined to the downstream side, the inner opening end is directed to the upstream side, so that the fluid 17 can easily enter the sensor mounting part 16 and can be prevented from staying in the sensor mounting part 16. Temperature sensor 1
Reference numeral 8 is composed of a thermocouple, a resistance temperature detector, etc., and its end surface 18a on the temperature measuring portion side is positioned so as to be substantially flush with the inner wall surface 5a of the conical tube 5b and is in contact with the fluid 17. Further, an appropriate gap is formed between the temperature sensor 18 and the inner peripheral surface of the sensor loading portion 16. The temperature sensor 18 is connected to the differential pressure gauge 15 by a wiring 19.

In the differential pressure flowmeter 1 having such a structure, the upstream pressure P1 and the downstream pressure P2 are guided to the differential pressure gauge 15 through the pressure guiding pipes 13 and 14, and the differential pressure is detected. The flow rate Q of the fluid 17 flowing in the conduit of the pipe 2 can be calculated by converting it into an electric signal and performing arithmetic processing based on the following equation.

[0010]

[Equation 1]

Where F is a scale factor, T1 is the temperature of the designed fluid, P1 is the designed high pressure, and ΔP
Is a generated differential pressure, and ΔPSPAN is a differential pressure corresponding to a flow rate range of 100 Nm ³ / h.

When the temperature of the fluid 17 changes in the measurement, the density changes and a measurement error occurs. Therefore, fluid 1
The temperature of No. 7 is detected by the temperature sensor 18, and the flow rate is corrected by the following equation.

[0013]

[Equation 2]

However, Q'is the corrected flow rate, T1 'is the measured fluid temperature, and P1' is the measured upstream pressure.

In the present invention, since the temperature sensor 18 is provided in the conical pipe 5b on the downstream side in the vicinity of the throat 4, it is necessary to provide a mounting seat for the sensor on the pipe 2 side and lengthen the wiring 19. It can be manufactured inexpensively, and accurate temperature measurement can be performed. That is, the flow velocity distribution of the fluid 17 flowing in the pipe has a flow velocity distribution that the center of the pipe is fast and the velocity near the pipe wall is slow,
Since the throat diameter d is small in the portion close to the throat 4, the flow velocity distribution becomes almost uniform. Therefore, the temperature characteristics are less affected by the pipe wall and the temperature distribution is almost uniform.
The fluid temperature can be accurately measured without projecting the temperature sensor 18 into the conduit.

Further, since the temperature sensor 18 is not projected into the pipe, the fluid 1 can be provided even if it is provided on the upper end side of the pressure extracting portion.
The flow of 7 is not disturbed, and pressure reflection does not occur even if it is provided on the downstream side. Furthermore, if a gap is provided between the temperature sensor 18 and the sensor loading portion 16, the temperature sensor 18
Since the fluid 17 enters the surrounding area of the temperature sensor 18 and the contact area of the temperature sensor 18 can be increased, the influence of the temperature of the tube wall can be reduced.

In the above-described embodiment, the example in which the thermometer 18 is provided in the conical tube 5b on the downstream side has been shown, but the present invention is not limited to this, and the throat 4 as shown in FIG. 2 or 3, for example.
May be provided. That is, FIG. 2 shows that the sensor loading portion 16 is provided on the pipe wall of the throat 4 so as to incline toward the downstream side and integrally project.
An example in which the temperature sensor 18 is loaded in the sensor loading unit 16 is shown. The sensor loading portion 16 is formed in communication with the inside of the throat 4. Temperature measurement side end surface 18a of the temperature sensor 18
Like the above-described embodiment, forms a substantially same surface as the inner wall surface of the throat 4 and does not project into the throat 4.

On the other hand, FIG. 3 shows the outer surface of the throat 4 on the tube wall.
An example is shown in which the sensor loading 28 made of a non-through hole is formed so as to be orthogonal to the axis of the throat 4 and the temperature sensor 18 is loaded in the sensor loading portion 28. Therefore, the temperature sensor 1
8 does not project into the throat 4 and does not come into direct contact with the fluid 17. The sensor loading portion 28 is deeply formed so as to reach as close as possible to the inner surface of the throat 4 on the tube wall. In such a structure, the temperature sensor 18
Is not in direct contact with the fluid 17, but the wall thickness of the sensor loading portion 28 of the throat 4 is set to be extremely thin, so that heat transfer is good, the temperature gradient is small, and there is no problem in practical use. It was

In each of the above-described embodiments, an example in which the present invention is applied to a differential pressure flow meter using a Venturi tube as a throttle mechanism having a throat has been shown, but the present invention is not limited to this and uses a flow nozzle. It can also be applied to differential pressure flowmeters. Further, in the present invention, an example in which the sensor loading portions 16 and 28 are provided in the downstream conical tube 5b and the throat 4 is shown, but they may be provided in the upstream conical tube 5a.

[0020]

As described above, the differential pressure flow meter according to the present invention is a differential pressure flow meter for measuring a flow rate from a differential pressure upstream and downstream of a venturi pipe having a throat or a flow nozzle. Since the temperature sensor is embedded in the section, there is no need to lengthen the pipe, provide a sensor mounting seat, or lengthen the wiring, and can be manufactured at low cost. Further, since the throat or the portion close to the throat has a small throat diameter, the flow velocity distribution is nearly uniform, and therefore the temperature characteristics are less affected by the pipe wall, so that accurate temperature measurement can be performed. Further, the present invention is such that the end surface of the temperature sensor on the temperature measuring portion side is substantially flush with the inner wall surface of the throat or the portion near the throat, or the outer wall surface of the throat or the portion near the throat reaches the inner wall surface in the vicinity of the inner wall surface. Since the temperature sensor is mounted in this non-penetrating hole, the fluid flow is not disturbed and pressure reflection is not caused.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment in which the present invention is applied to a differential pressure flowmeter using a Venturi tube.

FIG. 2 is a sectional view showing another embodiment of the present invention.

FIG. 3 is a sectional view showing still another embodiment of the present invention.

[Explanation of symbols]

1 ... Differential pressure flow meter, 2 ... Piping, 3 ... Venturi tube, 4 ...
Throat, 5a, 5b ... Conical tube, 6,7 ... Straight tube, 11,
12 ... Pressure outlet, 16 ... Sensor loading part, 18 ... Temperature sensor, 28 ... Sensor loading part.

Claims (3)

[Claims] 1. A differential pressure flowmeter for measuring a flow rate from a differential pressure between an upstream and a downstream of a venturi tube or a flow nozzle having a throat, wherein a temperature sensor is embedded in the throat or a portion near the throat. Total. 2. The differential pressure flowmeter according to claim 1, wherein a sensor loading part communicating with the inside of the pipe is provided at or near the throat, and the temperature sensor has an end face on the temperature measuring part side in the sensor loading part. Alternatively, the differential pressure flowmeter is characterized in that the differential pressure flowmeter is mounted so as to form a surface that is substantially flush with the inner wall surface in the vicinity of the throat. 3. The differential pressure flowmeter according to claim 1, wherein a non-penetrating hole reaching an inner wall surface is formed on an outer wall surface of the throat or a portion near the throat, and a temperature sensor is loaded in the non-penetrating hole. A differential pressure flow meter.