JP2892521B2 - Mass flow meter or density meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flowmeter or a density meter utilizing Coriolis force, and more particularly to a mass flowmeter or a density meter configured to allow a fluid to be measured to pass through a linear sensor tube.

[0002]

2. Description of the Related Art The flow rate of a fluid to be measured is desirably represented by a mass flow rate which is not affected by the type of fluid, physical properties (density, viscosity, etc.), and process conditions (temperature, pressure).

[0003] Therefore, various mass flow meters for measuring the mass flow rate of a fluid to be measured are being developed, and one of them is to utilize the Coriolis force generated when a fluid is caused to flow in a vibrating sensor tube. There are flow meters that measure the mass flow directly.

As an example of this type of conventional mass flow meter, there is a flow meter disclosed in Japanese Patent Application Laid-Open No. 63-158419. The mass flow meter disclosed in this publication oscillates a linearly extending sensor tube in the radial direction in order to reduce pressure loss when a fluid to be measured passes, and displaces the sensor tube due to Coriolis force proportional to the flow rate. It is configured to detect. Further, since the sensor tube thermally expands in the axial direction at the time of measuring the flow rate of the high-temperature fluid, its end is supported via a diaphragm.

However, in the configuration in which the end of the sensor tube is supported by the diaphragm as described above, when the amount of thermal expansion of the sensor tube is large due to a large temperature change,
There is a problem that the strain stress due to the thermal expansion of the sensor tube cannot be sufficiently absorbed, and the instrument difference level fluctuates.

In order to solve such a problem, for example, a flow meter as disclosed in Japanese Patent Application Laid-Open No. 63-30721 has been proposed. In the mass flow meter of this publication, a bellows for absorbing thermal expansion of a straight tubular sensor tube is provided in the middle of the pipe.

In a general bellows mounting structure of this kind, as shown in FIG. 8, for example, one end of a bellows 1 is connected and fixed to a manifold 3 holding a sensor tube 2, and the other end is connected to a mounting portion 4 a of a flange 4. Connection is fixed. The bellows 1 has a bellows shape in which arcuate valleys 1a and ridges 1b having a diameter larger than the valleys 1a are alternately and continuously formed. Therefore, the strain stress due to the thermal expansion of the sensor tube 2 due to the contraction of the plurality of valleys 1a and the ridges 1b is effectively absorbed.

[0008]

[SUMMARY OF THE INVENTION However, in the conventional mass flowmeter as described above, the total effective area is the inside diameter D _S of the sensor tube 2 of the effective diameter D _a of the bellows 1 as seen in FIG. 8 Unlike the sectional area, the effective sectional area of the bellows 1 is larger.

As described above, in order to reduce the pressure loss of the bellows 1 as much as possible, the effective cross-sectional area of the bellows 1 is larger than the total cross-sectional area of the inner diameter of the sensor tube 2. The tube 2 is pushed, and a compressive stress acts on the sensor tube 2 side.

In the vibration mode of the sensor tube 2 shown in FIG. 9, since the amplitudes of the two sensor portions 2b and 2c are theoretically the same phase changes, the sensor tube 2
In the case of two pieces, the phase change is offset and the sensing should not be affected, but in reality, there is a slight difference in welding conditions and a slight shift in the mounting position of various parts. When a compressive stress is applied to the sensor tube 2 due to the influence of the
b and 2c are different.

That is, a phase difference occurs between the sensor portions 2b and 2c due to the stress applied to the sensor tube 2.
As a result, the same phenomenon that the phase difference of the vibration of the sensor tube 2 occurs in the two sensor portions 2b and 2c due to the Coriolis force occurs in the sensor tube 2 and the accurate flow rate cannot be measured. there were.

Also, in a densitometer utilizing the natural frequency of the sensor tube, when a stress is applied to the sensor tube, the vibration mode of the sensor tube changes and the natural frequency (resonance frequency) changes, thereby affecting measurement accuracy. There was a problem that.

Accordingly, an object of the present invention is to provide a mass flowmeter or a density meter which has solved the above-mentioned problems.

[0014]

According to the present invention, there is provided a pipe having a straight pipe portion extending linearly between an inlet into which a fluid to be measured flows in and an outlet from which the fluid to be measured flows out; A vibrator for vibrating the straight pipe portion in the radial direction, a pickup for detecting a radial displacement of the straight pipe portion due to the vibration of the straight pipe portion, and an axial displacement of the straight pipe portion to be absorbed. In a mass flow meter or a density meter having a bellows formed in the middle of a pipe line and having a large-diameter peak portion and a small-diameter valley portion formed alternately and continuously,
The bellows is formed so that the effective sectional area is substantially equal to the total sectional area of the inner diameter of the straight pipe portion.

[0015]

By making the effective cross-sectional area of the bellows substantially equal to the total cross-sectional area of the inner diameter of the sensor tube (or the sum of the sensor tubes in the case of two or more sensor tubes), the pressure-receiving areas of both are made equal, and the bellows accompanying the pressure rise is increased. Of the bellows so that the stress caused by the displacement of the bellows does not act on the sensor tube.

[0016]

1 and 2 show an embodiment of a mass flow meter according to the present invention.

In both figures, a mass flow meter 11 includes a pipe 13 through which a fluid to be measured passes in a closed box-shaped casing 12,
And a bellows 14 for holding the conduit 13 so as to be displaceable in the axial direction. The pipe 13 has an inflow pipe 15 having an inflow port 15 a, an inflow side manifold 16, a pair of sensor tubes 17 and 18, an outflow side manifold 19, and an outflow port 2.
0a.

The inflow pipe 15 has a flange 15b connected to an upstream pipe (not shown) at the inflow end.
The other end of 5 extends through a side wall 12 a of the casing 12 to a chamber 12 b formed inside the casing 12.

The inflow side manifold 16 includes a bellows 14
Has an upstream connection port 16a to which the sensor tubes 17 and 18 are connected and fixed, and downstream connection ports 16b and 16c to which the upstream ends of the sensor tubes 17 and 18 are connected and fixed. The upstream connection port 16a and the downstream connection ports 16b, 16c communicate with each other via branch channels 16d, 16e.

The outlet manifold 19 has a pair of connection ports 19a and 19b to which the downstream ends of the sensor tubes 17 and 18 are connected and fixed, and a connection port 19c to which the upstream end of the outlet pipe 20 is connected. Have. The outlet side manifold 19 has a pair of connection ports 19a and 19b and a connection port 19c.
And flow paths 19d and 19e communicating therewith.

The pair of sensor tubes 17 and 18 are straight pipes extending linearly in the direction of fluid flow (X direction).
The inflow side manifold 16 and the outflow side manifold 19
And are provided in parallel between. The sensor tubes 17 and 18 formed of straight pipes are easy to manufacture because they have a small pressure loss when the fluid to be measured passes and do not need to be processed into a complicated shape.

The outflow pipe 20 has an upstream end connected and fixed to a connection port 19c of the outflow side manifold 19, and a downstream end protruding downstream (X direction) through the side wall 12c of the casing 12. An outlet 20a is opened at the downstream end of the outflow pipe 20, and a flange 20b connected to a downstream pipe (not shown) is provided on the outer periphery thereof.

The bellows 14 is provided in the middle of the pipe 13 so as to be interposed between the inflow pipe 15 and the inflow side manifold 16. That is, as shown in FIG. 2, the upstream end 21 of the bellows 14 is fixed to the attachment portion 15c of the inflow pipe 15 by welding or the like, and the downstream end 22 is fixed to the connection port 16a of the inflow manifold 16 by welding or the like. Have been.

The bellows 14 is, for example, a bellows-shaped stainless steel pipe, and has a plurality of arc-shaped valleys 1.
4a (14a ₁ ... 14a _n ) and crests 14b (14b ₁ .
14b _n ) are alternately and continuously formed. This valley 1
4a and the ridges 14b are, for example, sensor tubes 17, 18
When an axial force due to thermal expansion acts, it expands and contracts in the axial direction, absorbs stress due to thermal expansion, and also absorbs axial piping vibration transmitted.

The bellows 14 has an effective diameter D _a as described later.
So that the effective cross-sectional area of the valley 1 is substantially equal to the total cross-sectional area of the inner diameters of the sensor tubes 17 and 18.
4a and a peak 14b are formed.

Reference numeral 23 denotes a vibrator, which has substantially the same configuration as that of the electromagnetic solenoid, and is provided between substantially the middle portions of the pair of sensor tubes 17 and 18.

Reference numeral 24 denotes an upstream pickup, which is a vibrator 2
3 is provided between the sensor tubes 17 and 18 on the upstream side.

Numeral 25 is a pickup on the downstream side.
3 is provided between the sensor tubes 17 and 18 on the downstream side of the vibrator 23. The pickups 24 and 25 have the same configuration as the electromagnetic solenoid, respectively.
The displacement of 7, 18 is detected.

When measuring the flow rate, a pair of sensor tubes 17 and
Reference numeral 18 denotes a direction in which the vibrator 23 approaches and separates (Y direction).
Excited. The fluid to be measured supplied from the upstream pipe (not shown) flows into the bellows 14 from the inflow port 15a, and further flows into the vibrating sensor tubes 17, 18 through the flow paths 16d, 16e of the manifold 16. . The fluid that has passed through the sensor tubes 17 and 18 passes through the flow paths 19a and 19b of the manifold 19 and the outlet 20a.
It flows out to a downstream pipe (not shown).

Thus, the vibrating sensor tube 1
When the fluid flows through 7, 7, a Coriolis force corresponding to the flow rate is generated. Therefore, a straight tubular sensor tube 1
An operation delay occurs between the inflow side and the outflow side of the pickups 7 and 18, thereby causing a phase difference in the output signals of the pickups 24 and 25. Since this phase difference is proportional to the mass flow rate, the flow rate is obtained based on the phase difference between the output signals from the pickups 24 and 25.

The operation for measuring the flow rate of the high-temperature fluid will now be described. Inlet 1 as in the above flow rate measurement
When the high-temperature fluid is supplied from 5a, thermal expansion occurs due to the sensor tubes 17, 18 extending in the X direction. Up,
Since the downstream flanges 15b and 20b are connected and fixed to the upper and lower pipes, respectively, the sensor tubes 17 and 18 are provided.
The axial stress caused by thermal expansion of the bellows 14 is absorbed by the expansion and contraction of the bellows 14.

As a result, fluctuations in instrumental level due to thermal expansion of the sensor tubes 17 and 18 are prevented, and accurate flow rate measurement can be performed.

Next, the operation when the fluid pressure fluctuates during flow rate measurement will be described.

For example, when the pressure of the fluid increases during the flow rate measurement, the pressure of the high-pressure fluid acts on the inner wall of the bellows 14.

When an internal pressure acts on the inner wall of the bellows 14, the peak 14b of the bellows 14 slightly expands, and a force corresponding to an area corresponding to the pressure receiving area of the bellows 14 is generated in the axial direction. The pressure-receiving area is that of the effective cross-sectional area A _a of the bellows 14. The total cross-sectional area A _t (if sensor tube is one area that of the inner diameter of the effective cross-sectional area A _a is the sensor tube 17, 18 of the effective diameter D _a of the bellows 14 in the present invention, in the case of two or more each cross The bellows 14, which is equal to the sum of the areas, is attached to the sensor tubes 17, 1.
8 on the pipeline. If equal the total cross-sectional area A _t of the inner diameter of the effective cross-sectional area A _a and the sensor tube 17 in this manner the bellows 14, also act pipe pressure for reasons which will be described sensor tube 17
Is not subjected to axial stress by the bellows 14.

[0036] Here, the description of the effective sectional area A _a of the bellows 14.

As shown in FIG. 3, the effective diameter D of the bellows 14
_aIs the projected cross section of the inner surface side of the bellows 14 in the axial direction.
Of which, the part from the peak to the valley on the inner surface side of the bellows 14
The projected area in the axial direction of the hatched portion in FIG.
The inner shaded area I) and the mountain side (outer shaded area II in FIG. 3)
The effective diameter D of the bellows is the boundary where the areas are equal. _a
That.

[0038] Then, since the same area of the street view 3 hatched portions I and II of the seek effective radius gamma _a bellows 14 is given by the following equation (1).

[0039]

(Equation 1)

Here, r _{0 is} the radius from the ridge on the inner surface side of the bellows, and r _i is the radius from the valley on the inner surface side of the bellows.

[0041] Therefore, the effective sectional area A _a of the bellows 14 is represented by the following formula (2).

[0042]

(Equation 2)

[0043] Next, the operation principle will be described in accordance with the magnitude of the effective cross-sectional area A _a of the bellows 14.

First, the operation principle of the conventional case shown in FIG. 8 will be described with reference to FIG. 4 for comparison with the conventional case.
FIG. 4 is a principle diagram when the effective cross-sectional area of the bellows 1 disposed on the upstream side of the sensor tube 2 is larger than the total cross-sectional area of the inner diameter of the sensor tube 2.

In FIG. 4, the axial force generated by the internal pressure is indicated by arrows

[0046]

(Equation 3)

Are shown. Both ends of the flow meter are casing 12
Has been fixed by. Bellows 1 when internal pressure acts
In the area of, the power of and is generated. However,,
Is generated very close to the fixed casing 12, this force is the reaction force of the fixed casing 12,

[0048]

(Equation 4)

Is canceled by

When the internal pressure is applied to the manifold 3, the following forces are generated, but these forces cancel each other because they have the same magnitude and opposite directions. Further, the manifold 3 is usually composed of the bellows 1 and the sensor tube 2.
And the axial length is much shorter than that of the sensor tube 2, so that
It is not necessary to consider that the manifold 3 extends in the axial direction due to the above force.

Here, the force generated in the bellows 1 pushes the sensor tube 2. That is, when the effective cross-sectional area of the bellows 1 is not equal to the total cross-sectional area of the inner diameter of the sensor tube 2, tension or compression is applied to the sensor tube 2 by the force generated by receiving the internal pressure on the surface of the difference between the two. Stress acts.

That is, in the case shown in FIG. 4, since the effective cross-sectional area of the bellows 1 is larger than the total cross-sectional area of the inner diameter of the sensor tube 2, the sensor tube 2 is compressed by the internal pressure of the bellows 1. Become.

Next, as shown in FIG.
For when the total cross-sectional area A _t of the inner diameter of the effective cross-sectional area of 4 A _a and the sensor tube 17, 18 are equal it will be explained with reference to FIG.

FIG. 5 is a principle diagram for explaining the operation principle of the mass flow meter 11 shown in FIG.

In FIG. 5, when an internal pressure is applied, a force is generated at the bellows 14 portion. However, since this force is generated near the fixed casing 12, this force is canceled by the reaction force of the fixed casing 12.

Further, in the manifolds 16 and 19, when an internal pressure is applied, the following forces are generated. However, the forces of and are equal in magnitude and opposite in direction and cancel each other out. Further, the force generated by the upstream manifold 16 and the force generated by the bellows 14 have the same magnitude and are opposite to each other because the directions are opposite to each other.

Further, since the force generated in the downstream manifold 19 is generated near the fixed casing 12, this force is the reaction force of the fixed casing 12.

[0058]

(Equation 5)

Is canceled by

Therefore, the forces generated by the action of the internal pressure cancel each other out, and the sensor tubes 17 and 18 cancel each other.
No stress is applied. However, the pipe section A and the manifold section B between the manifold 16 and the bellows 14 inside the casing 12 are connected to the sensor tube 1.
Rigidity is much higher than 7, 18 or bellows 14,
Further, since the length in the axial direction is extremely shorter than that of the sensor tubes 17 and 18, expansion and contraction caused by receiving a force at this portion does not need to be considered.

[0061] As mentioned above, the effective cross-sectional area A _a and the sensor tube 1 of the bellows 14 in a mass flow meter 11 of the present invention
Sensor tube 17 and 18 also act internal pressure being equal total cross-sectional area A _t of the inner diameter of 7, 18 is not subjected to axial stress.

Accordingly, the sensor tubes 17 and 18 can stably vibrate without receiving an axial force due to the pressure fluctuation, and the fluctuation of the instrumental difference level due to the pressure fluctuation is prevented, and more accurate flow rate measurement can be performed. Becomes

As a result, the bellows 14 can absorb the strain stress of the sensor tubes 17 and 18 due to the temperature change without being affected by the fluctuation of the fluid pressure. Even when the pulsation is severe, the flow rate can be measured without being affected by these.

Further, even if axial vibration is generated due to axial piping vibration or impact on the casing 12, it is absorbed by the bellows 14 as described above.

FIG. 6 shows a modification of the present invention.

FIG. 6 is a diagram showing a mass flow meter 31 having the bellows 14 provided above and downstream of the sensor tubes 17 and 18. In the figure, also in this mass flow meter 31, the effective sectional area A _a of the bellows 14, 14 'provided on the upstream and downstream side, so that substantially equal to the total cross-sectional area A _t of the inner diameter of the sensor tube 17, 18 Is formed.

In FIG. 7, when the internal pressure is applied, the bellows 14, 14 'on the upper side and the downstream side are turned on.

[0068]

(Equation 6)

The following force is generated. But with

[0070]

(Equation 7)

Since this force is generated near the fixed casing 12, this force is the reaction force of the fixed casing 12,

[0072]

(Equation 8)

Is canceled by

When an internal pressure is applied to the manifolds 16 and 19, the following forces are generated. However, the forces of and are equal in magnitude and opposite in direction and cancel each other out. Also, manifold 1
6,19, and the bellows 14,14 '

[0075]

(Equation 9)

Since the forces are the same in magnitude and opposite in direction, they cancel each other out.

Therefore, all the forces generated by the application of the internal pressure cancel each other out, so that no stress is applied to the sensor tubes 17 and 18.

Therefore, even when the bellows 14 and 14 'are provided on the upstream and downstream sides of the sensor tubes 17 and 18, respectively,
By the effective sectional area A _a of the bellows 14, 14 'is equal to the total cross-sectional area A _t of the inner diameter of the sensor tube 17, the sensor tube 17 and 18 without being subjected to axial forces caused by the pressure fluctuation Vibration can be stably performed, and fluctuation of the instrumental difference level due to pressure fluctuation is prevented, and more accurate flow measurement can be performed.

In the above embodiment, the flow rate was measured.
The technical idea of the present invention may be applied to a density meter that measures the density by using the fact that the natural frequency of the sensor tubes 17 and 18 changes according to the density of the fluid.

[0080]

As described above, in the mass flow meter or the density meter according to the present invention, the inner diameter of the peaks and valleys of the bellows is substantially equal to the total cross-sectional area of the inner diameter of the straight pipe portion. With such a configuration, the forces generated by the internal pressure are balanced, so that the bellows can absorb the axial strain stress of the straight pipe portion due to the temperature fluctuation without being affected by the fluctuation of the fluid pressure. It is possible to prevent the application of strain stress in the direction. Therefore, it is possible to set the operating temperature range and the operating pressure range for flow rate measurement and density measurement in a wide range.

Therefore, even when the temperature of the fluid changes drastically or when the fluid pressure pulsates violently, the mass flow rate / density can be accurately measured without being affected by these. In addition, even if an axial vibration is generated by applying an impact to a pipe vibration in the axial direction or a flow meter or the like, these disturbance vibrations can be absorbed by the bellows to measure accurately.

[Brief description of the drawings]

FIG. 1 is a plan sectional view of one embodiment of a mass flow meter according to the present invention.

FIG. 2 is an enlarged cross-sectional view of a main part of the present invention, showing the main part in a side view.

FIG. 3 is a diagram for explaining an effective sectional area of a bellows.

FIG. 4 is a principle diagram for explaining the action of the internal pressure of a conventional mass flow meter.

FIG. 5 is a principle diagram for explaining the action of the internal pressure of the mass flow meter shown in FIG. 1;

FIG. 6 is a longitudinal sectional view for explaining a modification of the present invention.

FIG. 7 is a principle diagram for explaining the action of the internal pressure of the mass flow meter shown in FIG. 6;

FIG. 8 is an enlarged sectional view of a main part for describing a conventional mass flow meter.

FIG. 9 is a principle diagram for explaining a vibration mode of the sensor tube.

DESCRIPTION OF SYMBOLS 11 Mass flow meter 14 Bellows 14a Valley 14b Crest 15 Inflow pipe 16 Inflow side manifold 17, 18 Sensor tube 19 Outflow side manifold 20 Outflow pipe 21 Upstream end 22 Downstream end 23 Exciter 24, 25 pickup

Claims (1)

(57) [Claims] 1. A conduit having a straight pipe portion extending linearly between an inlet into which a fluid to be measured flows in and an outlet from which the fluid to be measured flows out, and the straight pipe portion is arranged in a radial direction thereof. A vibrator for vibrating, a pickup for detecting a radial displacement of the straight pipe portion due to the vibration of the straight pipe portion, and a large-size sensor provided in the middle of the pipe so as to absorb the axial displacement of the straight pipe portion. In a mass flowmeter or a density meter having a bellows in which a diameter peak portion and a small diameter valley portion are formed alternately and continuously, an effective sectional area of the bellows is substantially equal to a total sectional area of an inner diameter of the straight pipe portion. A mass flowmeter or a density meter characterized by being formed as follows.