JPS6129658B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a density meter that determines the density of a flowing fluid based on the static pressure difference between two points upstream and downstream of the fluid flowing in a vertical pipe.

This type of density meter is installed in the vertical piping of the equipment to be measured and measures the density of the flowing fluid. When determining fluid density, pressure loss within the pipe due to fluid flow must be taken into account. In order to eliminate the need for compensation due to such pressure loss, the applicant provides a different diameter section such as a restriction or an enlarged diameter section in the vertical pipe, and
Select a pressure measuring part that has a pressure loss equal to the pressure drop or pressure rise of this different diameter part, and measure the density based on the static pressure difference between this pressure measuring part and the pressure measuring part provided in the different diameter part. A density meter has already been proposed. (Tokuko Akira
(See Publication No. 52-30867).

However, such conventional density meters were designed focusing only on the pressure loss caused by internal friction between the two pressure measuring sections installed in the vertical tube. If a bent pipe is connected just before the inlet side of the vertical pipe section to change the flow direction of the fluid, the fluid will create a swirling flow within the bent pipe, and this swirling will cause the inner wall of the vertical pipe section to have a swirling flow. The pressure caused by the centrifugal force acts, causing a partial pressure rise, or pressure fluctuation, until it subsides. This pressure fluctuation affects the static pressure of each measuring section, resulting in a problem that causes measurement errors.

Therefore, in such a density meter, in order to avoid pressure fluctuations in the vertical pipe section caused by connecting the above-mentioned curved pipes, as shown in Fig. 1,
A length l is provided on the upstream side of the vertical pipe section 2 constituting the density meter 1.
It is common practice to connect an extended straight pipe 3 to a bent pipe 4 through the extended straight pipe 3.
That is, the vertical pipe section 2 of the density meter 1 is installed vertically between the horizontal pipes 5 and 6 of the device to be measured, and the fluid is directed from below to above within this vertical pipe section 2 as shown by arrow A in the figure. It flows. In the pressure measuring section 7 on the upstream side of the vertical pipe section 2, a throttle (not shown) is formed and a pressure measuring opening 8 is provided. is fixed. Further, a measuring opening 12 is provided in the downstream pressure measuring part 11 which is a distance H from the upstream pressure measuring part 7 of the vertical pipe part 2, and this opening 12 is also connected to a pressure measuring part 9 connected to a differential pressure gauge 9. The portion 13 is fixed. The differential pressure gauge 9 measures the density of the fluid based on the pressure difference between the two pressure detectors 10 and 13.

In this case, an extended straight pipe 3 is connected to the upstream side of the vertical pipe section 2 to avoid pressure fluctuations caused by the bent pipe 4.
The fluid from the inlet horizontal pipe 5 extending approximately horizontally is guided to the vertical pipe section 2 via the curved pipe 4, and a curved pipe 14 is connected to the downstream side of the vertical pipe section 22. The fluid is guided to the horizontal pipe 6 on the outflow side via the curved pipe 14.

FIG. 2 is a graph showing the effect when the curved pipe 4 is connected via the straight extension pipe 3 mentioned above.
The pressure rise h is shown in each case. Here, curve A represents the case where l=0, that is, the curved pipe 4 is directly connected without connecting the straight extension pipe 3, and curve B represents the case where l is
= 5D (D is the inner diameter of the straight extension pipe 3), that is, when the curved pipe 4 is connected through the straight extension pipe 3 having a length 5 times the inner diameter D of the straight extension pipe 3, and the curve C is l. =
A case is shown in which a bent pipe 4 is connected via a 10D straight extension pipe 3. As is clear from this graph, the pressure increase h due to the curved pipe 4 increases almost geometrically with respect to the flow velocity v, but if the curved pipe 4 is By connecting it, the size can be reduced to an almost negligible level.

Therefore, by using a straight extension pipe 3 having a length of l = 10D or more, it is possible to compensate for the influence of the curved pipe 4. When connected, the vertical pipe length (H _MA
(U ) is too long, making it extremely difficult to install in places where height is restricted, such as inside tunnels or indoors, and is also problematic when the pump output pressure is low. Ta.

In view of these points, the present invention provides a pressure measuring part in each of the horizontal pipe part and the vertical pipe part on the downstream side of the substantially L-shaped pipe body, and makes the inner diameter of each pressure measuring part different. At the same time, the downstream pressure measuring section is
In order to equalize the pressure loss in the upstream pressure measuring section, take into account pressure fluctuations in the different diameter sections of each pressure measuring section and pressure fluctuations in the curved pipe section of the pipe body, and install it at a position away from this curved pipe section. This makes it suitable for use in narrow spaces such as tunnels due to its low height.
The present invention also provides a density meter with good measurement accuracy.

Hereinafter, the present invention will be explained in detail using embodiments shown in the drawings.

3 and 4 show an embodiment of the density meter according to the present invention, with FIG. 3 being a side view showing its installed state, and FIG. 4 being a side view thereof. In these figures, the density meter, which is generally designated by the reference numeral 20, includes a vertical pipe section 21 and a horizontal pipe section 23 provided upstream of the vertical pipe section 21 via a bent pipe section 22. The tube body 24 has a substantially L-shaped tube body 24, and the fluid flowing inside the tube body 24 flows from the horizontal tube portion 23 toward the vertical tube portion 21 as shown by arrow B in the figure. are doing. Pipe body 24
An upstream pressure measuring section 26 having an aperture 25 is provided in the horizontal pipe section 23, and a pressure measuring opening 27 is formed in the tube wall of this pressure measuring section 26. A pressure detection section 28 is fixed to this opening 27, and the pressure detected by this pressure detection section 28 is transmitted to a differential pressure gauge 30 through a capillary reach tube 29.
In addition, the vertical pipe portion 21 of the pipe body 24 and the curved pipe portion 2
2, a downstream pressure measuring section 31 having the same inner diameter as the pipe body 24 is provided at a position separated by a straight pipe distance L, which will be explained based on the principle described later.
A pressure measuring opening 32 is also provided in the pipe wall of the pipe, similar to the upstream side pressure measuring section 26 described above. A pressure detection section 33 is fixed to this opening 32, and the pressure detected by this pressure detection section 33 is transmitted to the differential pressure gauge 30 through a capillary tube 34. In this case, a diaphragm type is used as the differential pressure gauge 30, and the pressure detection parts 28, 33 are connected to the opening 2.
7, 32, a main body 36 which fixes this diaphragm 35 to the openings 27, 32 and forms a liquid chamber 36a filled with pressure transmission liquid between it and this diaphragm 35, and this liquid chamber 3.
It is composed of capillary tubes 29 and 34 that guide the liquid pressure inside 6a to the differential pressure gauge 30. By using the diaphragm type differential pressure gauge 30 in this manner, pressure changes caused by minute turbulence can be averaged within the area of the diaphragm, and internal resistance in the pipe can be reduced. Therefore, the range of fluid types that can be measured is expanded, and it is not only possible to measure single-phase flows such as solutions.
It can also be applied to solid-liquid two-phase flows such as muddy water.

In the density meter 20 configured in this manner, the pressures at the upstream pressure measuring section 26 and the downstream pressure measuring section 31 are detected by the respective detection sections 28 and 33, and the fluid density is determined by the differential pressure gauge 30 based on the differential pressure. Although it is to be measured,
In the density meter 20 according to the present invention, the pressure loss in each of the pressure measuring sections 26 and 31 is made equal in consideration of pressure fluctuations caused by the orifice 25 and the bent pipe section 22 of the upstream pressure measuring section 26, and Density can be easily measured without compensating for pressure loss.

Next, the measurement principle of the present invention will be explained using FIG. FIG. 5 is an explanatory diagram for explaining the pressure distribution of the density meter according to the present invention, and shows a case in which the curved pipe section 22 is temporarily extended to make the pressure distribution easier to see, and the fluid flowing through the pipe body 24 is It flows from the bottom to the top as shown by arrow B in the figure. In the figure, an upstream pressure measuring section 26' provided in a horizontal pipe portion 23' of the tube body 24 has a restriction 25', and this restriction 25' applies a pressure drop ΔP to the fluid. (Refer to the pressure distribution curve m) The pressure drop ΔP at this throttle 25' causes the downstream measurement part 31 of the vertical pipe part 21 to
In this case, a permanent pressure loss L _OSS1 occurs. Furthermore, when fluid flows into the curved pipe section 22 located downstream of the upstream pressure measuring section 26, the fluid becomes a swirling flow, and pressure due to centrifugal force acts on the inner surface of the pipe, so that the pressure of the fluid partially increases. do. This pressure increase gradually decreases along the vertical pipe section 21 as shown by the curve m in the figure, but due to the pressure increase due to the bent pipe section 22, a permanent pressure loss L _OSS2 is caused in the downstream pressure measuring section 31. arise. Further, while the fluid flows through the straight pipe distance L from the terminal end of the curved pipe section 22 to the downstream side pressure measuring section 31, a permanent pressure loss L _OSS3 occurs due to internal friction of the pipe.

Therefore, the total pressure loss in the downstream pressure measuring section 31 is (L _OSS1 +L _OSS2 +L _OSS3 ),
Between this and the pressure loss ΔP at the upstream pressure measuring section 26, there is a partial pressure increase due to the bent pipe section 22, so as is clear from the curve m, at each of these pressure measuring sections 26', 31. This makes it possible to balance pressure loss. That is, the pressure distribution shown by the curve m is due to the pressure drop △P and pressure loss L _OSS1 due to the throttle 25', the pressure increase in the bent pipe section 22 and the resulting pressure loss L _OSS2 , and the internal friction at the straight pipe distance L. Pressure loss L This is a pressure jet generated from the structure of the entire density meter 20 including all _OSS3 , and based on this curve m, the pressure change and pressure loss in the upstream and downstream pressure measuring sections 26 and 31 are equal. The inner diameter of the throttle 25 and the distance L from the curved pipe section 22 to the downstream pressure measuring section 31 may be determined as follows.

Next, in the upstream and downstream pressure measuring sections 26 and 31 provided in this way, the flow velocity V of the fluid in the pipe is
It will be explained that even if there is a variation in the specific weight γ, it does not affect the measurement and there is no need to compensate for it.
As described above, since the pressure change and pressure loss in the upstream pressure measuring section 26 and the downstream pressure measuring section 31 are set to be equal, the following equation holds true.

ΔP=L _OSS1 +L _OSS2 +L _OSS3 (1) Here, ΔP (pressure drop due to the throttle 25) on the left side is obtained from the following equation.

△P=k・γ・v ² =1/2g (αβ ² ) ²・γ・v ² ...(2) where k: Loss coefficient due to restriction α: Flow rate coefficient β: Orifice diameter ratio g: Gravitational acceleration [m /S ² ] γ: Specific weight [Kg/m ³ ] v: Average flow velocity [m/S] Also, (L _OSS1 +L _OSS2 +L _OS
S3 ) is obtained as follows.

First, the permanent pressure loss L _OS1 of the downstream pressure measuring section 31 due to the pressure drop of the throttle 25 is expressed by the following equation.

L _OSS1 = k ₁・△P = k ₁・1/2g (αβ ² ) ²・γ・v ² ...(3) However, k ₁ = loss coefficient (<1.00) Also, due to the pressure increase in the curved pipe section 22 Permanent pressure loss L _OSS2 is expressed by the following formula.

L _OSS2 =k ₂・S・D/R・1/2g・γ・v ² ……(4
) However, k ₂ : Loss coefficient (<1.00) S: Pressure increase coefficient due to curved pipe section D: Pipe inner diameter [m] R: Bend center radius of curved pipe section [m] Furthermore, permanent pressure loss at straight pipe distance L L
_OSS3 is expressed by the following formula.

L _OSS3 = λ・L/D・1/2g・γ・v ² ...(5) However, λ: Friction loss coefficient due to roughness of pipe inner wall L: Straight pipe distance where L _OSS3 occurs [m] However, Therefore, by substituting equations (2) to (5) into equation (1), we get 1/2g(αβ ² ) ²・γ・v ² =k ₁・1/2g(αβ
² ) ²・γ・v ² +k ²・S・D/R・1/2g・γ・v ² +λ・L
/D・1/2g・γ・v ^2Thus , 1/(αβ ² ) ² =k ₁・1/(αβ ² ) ² +k ₂・S
・D/R+λ・L/D...(6) This equation (6) shows that it holds true regardless of the flow velocity v and the specific weight γ. Furthermore, S, α, and λ are considered to be constant over a wide range, except for a range where the Reynolds number is small, and there is no problem in practice.

In the density meter 20 set in this way, if the detected pressures in the upstream pressure measuring sections 26 and 31 are P ₁ and P ₂ , the fluid density ρ is calculated using the differential pressure (P ₁ - P ₂ ). can be easily determined using the following equation without compensating for the pressure loss inside the pipe.

ρ=γ/g= _P1 - _P2 /H・1/g...(7) However, H: Distance between the upstream and downstream pressure measuring sections, that is, the distance between the upstream and downstream pressure measuring sections 26 and 31 Even in the case where the curved pipe portion 22 is provided, a density meter without errors caused by fluid flow can be obtained.

Furthermore, as shown in FIG.
is directly connected to the horizontal pipe 37 on the inflow side, while the end of the vertical pipe section 21 is connected to the horizontal pipe 38 on the outflow side via a curved pipe 39. Therefore, the upstream side of the upstream pressure measuring section 26 in this density meter 20 is a horizontal pipe 37 having the same inner diameter as the pipe body 24 of the density meter 20.
Since a sufficient straight pipe distance can normally be provided, the pressure measured by the pressure measuring section 26 is a stable pressure that does not fluctuate due to swirling flow or the like. and,
Density meter 2 is also used in downstream pressure measuring section 31 following this.
Since the vertical tube section 21 is located at a distance L from the curved tube section 22, stable pressure can be obtained. Therefore, in this density meter 20, there is no curved pipe that causes a swirling flow just before the two pressure measuring parts, and the fluid pressure is stabilized. A density signal can be obtained.

In addition, in such a density meter 20, the density meter 2
It is possible to sufficiently shorten the vertical distance H _MAX of the installation piping of 0, and the height of the entire device is reduced, making it possible to install it in a narrow installation place in the height direction. The distance H required between the pressure measuring units 26 and 31 is sufficient, and its measurement accuracy is comparable to conventional pressure measuring units.

Note that the upstream pressure measuring section 26 of the density meter 20 described above
As shown in FIG. 6, for example, the aperture 25 is a short tube 40 having the required inner diameter, and an opening 41 is bored in the tube wall to match the pressure measuring opening 27 on the tube body 24 side. It can be obtained by inserting the material into the horizontal tube section 23 of the tube body 24. In this way, there is an advantage that the aperture required to be provided in the upstream pressure measuring section can be easily formed.

Next, another embodiment will be described based on FIGS. 7 and 8. This is formed by forming an enlarged diameter part 42 in the downstream pressure measuring part 31 provided in the vertical pipe part 21, and the upstream pressure measuring part 26 of the horizontal pipe part 23 is formed in the pipe body 24.
It is formed with the same inner diameter as the inner diameter of. Therefore,
There is no need to consider the pressure loss ΔP and L _OSS1 due to the throttle 25 in the embodiment described above. Also,
The pressure increase due to the bent pipe portion 22 is the curve n in the eighth
This pressure increase causes the downstream pressure measuring section 3 to
1, the permanent pressure loss L _OSS2 shown in equation (4) above is
occurs. Then, permanent pressure loss L _OS occurs in the downstream pressure measuring section 31 due to internal friction occurring in the straight pipe distance L from the terminal end of the curved pipe section 22 to the starting end of the enlarged diameter section 42.
_S3 is expressed by the above-mentioned equation (5). Now, the enlarged diameter part 42
Assuming that there is no, as shown by the straight line n′ in the figure,
The pressure loss in the pressure measuring section 31 on the downstream side of the vertical pipe section 21 is the sum of the pressure loss L _OSS2 due to the curved pipe section 22 mentioned above and the pressure loss L _OSS3 due to internal friction (L _OSS
S2 +L _OSS3 ), but this downstream pressure measuring section 31 is formed with an enlarged diameter section 42, and this enlarged diameter section 42
A pressure increase △P′ is added. Therefore, in this embodiment, in order to equalize the pressure change or pressure loss of both pressure measuring sections 26 and 31, the pressure loss (L _OSS2 +L _OS
S3 ) must be balanced by the pressure increase ΔP' due to the enlarged diameter portion 42, and the following equation must hold.

ΔP'=L _OSS2 +L _OSS3 (8) Here, the temporary pressure increase ΔP' at the downstream pressure measuring section 31 in the enlarged diameter section 42 shown on the left side is obtained from the following equation.

△P′=k・γ・v ₂ =1/2g [α′(β′) ₂ ] ²
・γ・v ₂ … …(9) However, k′: Loss coefficient due to the enlarged diameter portion α′: Flow coefficient of the enlarged diameter portion β′: Diameter ratio of the enlarged diameter portion Also, shown on the right side (L _OSS2 +L _OSS3 ) is obtained according to equations (4) and (5) above, so equation (8) is 1/[α'(β') ² ] ² = k ₂・S・D/R+λ・L
/D...(10) becomes. This equation (10) is similar to the equation (6) above, where the flow velocity v
Not only does this hold true regardless of the change in specific weight γ, but also the above-mentioned
Equation (7) holds true, the density can be easily measured, and the height required for installation can be kept low as in the above-described embodiment.

In addition, in the embodiments shown in FIGS. 4 and 7 described above, the vertical tube section 21 and the horizontal tube section 23 are
A density meter 20 using a tube body 24 integrally formed with a curved tube portion 22 is shown. This is the same as the above
Equations (6) and (10) are established when the diameter ratio β, β' of the throttle or enlarged diameter part and the pipe inner diameter D, the bending center radius R of the curved pipe part, the pressure increase coefficient S due to the curved pipe part, etc. change. Therefore, by integrally forming the tube body 24 in this way, such inconvenience can be avoided and accurate measurement can be performed at all times, but the present invention is not limited to this.

Moreover, the pressure measurement openings 27 and 32 provided in each pressure measurement unit 26 and 31 explained in the above-described embodiments
The formation direction is not limited to this, but may be provided at any position as long as it is perpendicular to the flow of the fluid, and this is clear from the measurement principle described above.

Further, in the above embodiment, a diaphragm type pressure gauge 30 having a wide range of application to fluids was used as the differential pressure gauge 30. Any type of differential pressure gauge can be used.

Further, in the above-mentioned embodiment, the fluid is configured to flow from the bottom to the top as shown by arrow B in the figure, but the present invention is not limited to this, and the fluid flows from the top. It can also be applied when the flow is downward. However, in this case, it is necessary to reverse the top and bottom of the density meter so that the upstream pressure measuring section in the above-described embodiment is replaced with the downstream pressure measuring section. The distribution of pressure loss in the density meter in such a case is not at all different from the case of the above-mentioned embodiment, and the value of pressure loss at each pressure measuring section is exactly the same, and as a result, in this case as well, it is simply This makes it possible to determine the density by simple calculation from the pressure actually detected from both pressure measuring sections.

In the above-mentioned embodiment, there are two types of density meters according to the present invention, that is, two pressure measuring parts provided before and after the curved pipe section with the pipe body, and the upstream pressure measuring part is equipped with a restriction. Although the description has been made of the case where the expanded diameter part is formed in the pressure measuring part on the downstream side located away from the curved pipe part, the invention is not limited to this, and it is possible to form a throttle on the pressure measuring part on the upstream side. However, in combination with this, the downstream pressure measuring section may be of a type equipped with an enlarged diameter section and an enlarged diameter section, and in this case, the inner diameter of each pressure measuring section and the curve of the downstream pressure measuring section The straight pipe distance to the pipe portion may be changed as appropriate based on the measurement principle described above.
In short, the density meter according to the present invention includes a pipe body in which a vertical pipe part and a horizontal pipe part are connected via a bent pipe part, and the inner diameter of the upstream and downstream pressure measuring parts provided on both sides of the bent pipe part is In addition, the straight pipe distance of the downstream pressure measuring section from the curved pipe section is determined accordingly, and in this case, the pressure change or pressure loss in both pressure measuring sections is equalized. It is a requirement that the

As explained above, in the density meter according to the present invention, two pressure measuring sections having different inner diameters are provided on both sides of a pipe body having a curved pipe section, and of these pressure measuring sections, the downstream side The pressure measuring section is separated from the bent pipe section by a predetermined straight pipe distance and positioned in a place where pressure fluctuations due to the bent pipe section are small, so that the pressure change or pressure loss in both pressure measuring sections is set to be equal. It eliminates pressure fluctuations in each pressure measuring section, eliminates the need for compensation of measured values, makes it possible to obtain stable and accurate density measurements that are affected by increases and decreases in flow velocity, and requires installation in vertical piping sections. By lowering the installation height of the density meter, the overall height of the device can be kept down, making it possible to install it in installation locations that are narrow and restricted in the height direction, such as tunnels, and is also effective even when the pump output pressure is low. It has excellent practical effects such as:

[Brief explanation of the drawing]

Fig. 1 is a side view showing a conventional density meter installed in a device, Fig. 2 is a graph showing the effect of an extended straight pipe, and Figs. 3 to 5 are an embodiment of a density meter according to the present invention. Fig. 3 is a diagram of its installation state, Fig. 4
The figure is a side sectional view thereof, FIG. 5 is a diagram illustrating its principle, and FIGS. 6 to 8 are diagrams showing other embodiments of the present invention. 20... Density meter, 21... Vertical pipe section, 22...
Bent pipe section, 23... Horizontal pipe section, 24... Pipe body, 25
...Aperture, 26...Upstream side pressure measuring section, 27, 32...
...Pressure measurement opening, 28, 33...Pressure detection section, 30
... Differential pressure gauge, 31 ... Downstream pressure measuring section, 35 ... Diaphragm, 36a ... Liquid chamber, 40 ... Short pipe, 41
...Opening, 42...Enlarged diameter part.

Claims (1)

[Scope of Claims] 1. An L-shaped pipe body formed by connecting a horizontal pipe part and a vertical pipe part via a bent pipe part, and separately provided on the horizontal pipe part and the vertical pipe part of this pipe body. upstream and downstream pressure measuring sections, and a differential pressure gauge to which the fluid pressure in each of these pressure measuring sections is transmitted, and the pressure change or pressure loss of the flowing fluid in the upstream and downstream pressure measuring sections is equal. The pressure measuring parts are formed to have different inner diameters so that the inner diameter of the upstream pressure measuring part is smaller than the inner diameter of the downstream pressure measuring part, and the downstream pressure measuring part is separated from the curved pipe part. A density meter characterized by being placed a predetermined distance apart. 2. A short tube according to claim 1, characterized in that a short tube having an inner diameter smaller than that of the downstream pressure measuring section is fitted inside the tube corresponding to the upstream pressure measuring section. Density meter. 3. Claims 1 or 3, characterized in that the upstream and downstream pressure measuring sections are constituted by diaphragm pressure gauges in which a diaphragm filled with a pressure transmitting liquid faces the opening of a pipe body. Density meter described in Section 2.