JP2734478B2 - Pressure pulsation absorber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pressure pulsation absorber applied to a pipe such as a pump for transferring water or oil.

[Conventional technology]

FIG. 7 is a structural explanatory view of a conventional pressure pulsation absorbing device. In the figure, the conventional pressure pulsation absorbing device includes a side branch (branch pipe) 10 shown in FIG. 1A, an enlarged pipe 11 shown in FIG. 2B, a reservoir tank 12 shown in FIG. There are accumulators 13 and the like shown in FIG. 2D, each of which has a considerably larger shape than the pipe 1, and absorbs and attenuates the pressure pulsation of the liquid 5 in the pipe 1.

[Problems to be solved by the invention]

In the conventional pressure pulsation absorbing device as described above,
The side branch 10 shown in FIG. 7A has a narrow frequency range to be tuned, and the amount of absorption greatly differs due to a slight change in pulsation. In addition, the expansion pipe 11 shown in FIG. 3B cannot obtain the absorption effect unless a large expansion ratio is taken, and is accompanied by such complications as an increase in size, an increase in pressure loss, and generation of secondary noise due to flow. . Further, the reservoir tank 12 shown in FIG. 3C has a large capacity, and the installation place is limited. Further, the accumulator 13 shown in FIG. 3D is large and expensive, and acts only on a part of the pipe 1, so that the absorption effect is limited.

[Means for solving the problem]

The pressure pulsation absorbing device according to the present invention is intended to solve the above-mentioned problem, and is a material having flexibility in which the acoustic characteristic impedance substantially matches the liquid in the pipe, which is attached to the pipe in contact with the liquid in the pipe. A gas container, a gas sealed inside the gas container with the liquid in the pipe balanced with pressure, and an intervening gas between the gas container and the liquid in the pipe made of a porous material. And a perforated tube for maintaining the shape of the gas container.

[Action]

That is, in the pressure pulsation absorbing device according to the present invention, the gas is filled in the inside of the pipe while balancing the pressure with the liquid in the pipe, and is made of a flexible material whose acoustic characteristic impedance substantially matches that of the liquid in the pipe. The gas container is attached to the pipe in contact with the liquid in the pipe, and the shape is maintained by a porous pipe made of a porous material and interposed between the gas container and the liquid in the pipe. By maintaining the shape of the gas container with a porous tube made of material and interposed between the gas container and the liquid in the pipe, the acoustic characteristic impedance of the liquid in the pipe of the gas container substantially matches the acoustic characteristic impedance. A flexible material can be used. In this gas container, the gas is sealed in a balanced manner with the liquid in the pipe and the pressure, and the liquid in the pipe and the gas in the gas container come into contact with each other via a flexible material whose acoustic characteristic impedance substantially matches. As a result, the space between the liquid in the pipe and the gas in the gas container approaches an extremely ideal free boundary surface. As a result, the force between the liquid in the pipe and the gas in the gas container interacts at an extremely ideal free boundary surface, and the gas in the gas container absorbs and attenuates the pressure pulsation of the liquid in the pipe. Let it.

〔Example〕

FIGS. 1 to 4 are explanatory views of the structure of the pressure pulsation absorbing device according to the first to fourth embodiments of the present invention, and FIGS. 5 and 6 are explanatory views of their operation. In FIG. 1, the pressure pulsation absorbing device according to the first embodiment, as shown in FIG.
A porous tube 4 made of a gas permeable material such as a porous plate or a porous metal having the same diameter as that of the porous tube 4 is provided. An annular portion formed between the porous tube 4 and the casing 2 is flexible and highly ductile such as rubber. A gas container 3 made of a material is provided. The gas container 3 is provided with a gas sealing plug 7 from which the gas 6 is sealed.

In FIG. 2, the pressure pulsation absorber according to the second embodiment reduces the diameter of a perforated tube 4 made of a perforated plate or a porous metal without enlarging the pipe 1, as shown in FIG. As in the first embodiment, the periphery of the liquid column is in contact with the gas container 3 made of a flexible and highly ductile material such as rubber.

In FIG. 3, the pressure pulsation absorber according to the third embodiment, as shown in the figure, forms a perforated tube 4 made of a perforated plate or a porous metal into a tubular shape, and fills a gas 6 therein in advance. The filled gas container 3 is placed in the pipe 1.

In FIG. 4, the pressure pulsation absorbing device according to the fourth embodiment has a pocket 2 provided on one side of a pipe 1 via a porous tube 4 and a gas container 3 provided therein, as shown in the figure. As in the third embodiment, a part of the liquid column is brought into contact with the gas 6 via a flexible and highly ductile material such as rubber.

As the material of the gas container 3 in the above-described four embodiments, a flexible and highly ductile material having a characteristic whose acoustic characteristic impedance almost matches that of the liquid 5 in the pipe 1 is used. When the liquid 5 in the pipe 1 is water, ρC rubber is optimal.

As described above, the pressure pulsation absorbers according to the first and second embodiments are made of a material such as rubber which is flexible and highly ductile, and whose acoustic characteristic impedance almost matches that of the liquid 5 in the pipe 1. An annular gas container 3 is installed in contact with the inner wall of the pipe 1, and the inside of the gas container 3 is filled with a gas 6 so that the pressure of the liquid 5 passing through the inside of the pipe 1 is balanced with that of the liquid column 3. Instead, the gas 6 rich in compressibility is arranged, and the shape of the gas container 3 is maintained by putting the gas container 3 in a porous plate or a porous tube 4 made of a porous material having air permeability. At the same time, the periphery of the liquid 5 is surrounded by the gas 6. Therefore, the pressure pulsation of the liquid 5 in the pipe 1 is minimized by the cut-off for the reason described later.
Significantly attenuates in the low frequency range below the frequency. The amount of attenuation is proportional to the length of the gas container 3 and can be freely adjusted as needed. The boundary between the liquid 5 and the gas 6 is separated by a material such as rubber which is flexible and highly ductile and has almost the same acoustic characteristic impedance as the liquid 5 in the pipe 1.
The gas 6 does not mix therein, but the forces interact with each other to obtain something close to the free boundary surface. Further, by inserting the gas container 3 into the perforated tube 4 made of a perforated plate or the like, even if the pressure of the liquid 5 decreases, the pressure of the gas 6 is supported by the perforated tube 4 and the gas container 3 is ruptured. There is no.
Therefore, the gas container 3 can be made of a very flexible material whose acoustic characteristic impedance almost matches that of the liquid 5 in the pipe 1, and can be brought close to an extremely ideal free boundary condition. When the pressure of the liquid 5 rises above the set value, the gas container 3 only shrinks, and no particular problem occurs. Pressure pulsations in pumps and the like are generally low in frequency and can be damped very effectively. If the ideal free boundary condition in which the gas 6 wraps around the liquid column can be realized, theoretically, a large pressure pulsation of about 38 db per length corresponding to the diameter of the pipe 1 in a sufficiently low frequency region. A damping is obtained. Actually, sound reduction is not performed so far due to various restrictions, but attenuation can be expected at all frequencies below the minimum cutoff frequency.

It is assumed that an ideal free boundary surface condition in which the gas 6 wraps around the liquid column is realized. In this case, the pressure pulsation in the liquid column as shown in FIG. 5 propagates while forming a specific pressure pulsation mode in the cross section of the pipe. A sound pressure P _mn (x, x) that forms the (m, n) mode at any point (x, y, z) in the pipe
y, z) is expressed by the following equation.

Here, l _y and l _z are the cross-sectional dimensions of the pipe in the y direction and z direction, respectively, A _mn is the amplitude in the x = 0 cross section, and g _ym and g _zn are the m order and the n th order in the y direction and z direction, respectively. Eigenvalue, determined by the boundary conditions of the pipe wall. ω is angular frequency, t is time, and c is sound speed. τ _mn is a transmission coefficient of a pressure pulsation that forms the (m, n) mode and propagates in the x direction, and is given by the following equation.

Here, the double sign-indicates propagation in the downstream direction, and + indicates propagation in the upstream direction. λ is the wavelength. When the root of τ _mn is positive, the pressure pulsation is not attenuated in the x direction, but is attenuated in the x direction when it is a complex number or a pure imaginary number. Attenuation Att _mn per unit length is expressed by the following equation.

Here, I _m (τmn) indicates the imaginary part of the archive. g _ym and g _zn are the solutions of the following equations where the surface impedance of the pipe wall is a condition of the free boundary surface.

Here, π is a pi, i is an imaginary unit, and _{ｙ y} and _{ｚ z} are surface impedances of the pipe wall perpendicular to the y direction and the z direction, respectively. With ordinary copper or concrete rigid wall piping, _{ｙ y} , ζ _z → 、 However, m, n = 0, 1, 2, 3,... That is, there is a solution where m = n = 0, and from equation (2), there is a solution of τ ₀₀ 1 for every wavelength (frequency), and I _m (τ ₀₀ ) = 0, and the equation (3) ) To At
There is a solution where t ₀₀ = 0. That is, for any frequency, the wave propagates in the cross section of the pipe without attenuation as a plane wave (a sound wave mode in which the sound pressure gain and the phase are constant in the cross section of the pipe).

If the outer liquid column is wrapped with a gas, the acoustic characteristic impedance of the gas is very small compared to the acoustic characteristic impedance of the liquid, in this case zeta _y, the zeta _z ≒ 0. Substituting this relationship into equations (4) and (5) gives And there is no solution where m = 0 or n = 0. The transmission coefficient in this case is as follows.

Here, f is a frequency. As described above, the root symbol is ≧
In the case of 0, I _m (τ _mn ) = 0 and the amount of attenuation becomes 0. However, when the value in the root is <0, I _m (τ _mn )> 0 and attenuation occurs. In other words, cut off frequency _Then , the (m, n) mode propagates when f ≧ f _cmn and f <f
_The (m, n) mode attenuates at _cmn . If the liquid column is gaseous, the minimum value of f _cmn is Becomes In other words, frequencies below f < _fc11 cannot form any mode and are attenuated. In contrast, since the outer liquid pillar in the case of a rigid wall is the presence of a solution of m = n = 0, the minimum value of f _cmn is f _c00 = 0, and the all of the frequencies to form a propagation mode .

By the way, assuming that the liquid is water in a pipe of l _y = l _z = 1m, C ≒
Since it is 1500 m / sec, f _c11 = 1061 Hz, and pressure pulsation at a frequency lower than this is attenuated. When f = 500 Hz, when the amount of attenuation is calculated using Expressions (8) and (3), Att ₁₁ = 34 db / m, and a very large attenuation effect is theoretically obtained. For reference, FIG. 6 (a) shows a case where the periphery of the liquid column is a rigid wall, and FIG. 6 (b) shows a case where the periphery of the liquid column is a gas.
Shown in dimensional representation. In the former case, the sound pressure antinode mode is on the wall surface, whereas in the latter case, the sound pressure node mode needs to be established on the outer wall surface. From this, it is easy to see that the solution of m = 0 does not hold. Inferred. Further, the present embodiment has described the case where the cross section of the pipe is rectangular, but the cross section is circular,
Alternatively, the same applies to other arbitrary shapes.

Further, the pressure pulsation absorbing device according to the third and fourth embodiments is such that a columnar gas container 3 made of a flexible and highly ductile material such as rubber is inserted into the pipe 1, and the gas container 3
Is filled with gas 6 so that the pressure is balanced with the liquid 5 passing through the pipe 1, so that the gas 6 with high compressibility is always arranged in a part of the liquid column. By placing the gas container 3 in a porous tube 4 made of a porous material having a property, the shape of the gas container 3 is maintained, and the gas 6 exists inside the liquid 5 so that the gas 5 is directly between the liquid 5 and the gas 6. The forces act on each other. in this case,
Although the effect of attenuating the pressure pulsation is not so remarkable as when the liquid 5 is surrounded by the gas 6, a considerable amount of attenuation is obtained according to the ratio of the gas 6 to the liquid 5. Also,
The present invention can be implemented only by inserting the gas container 3 without changing the existing pipe 1. The attenuation of the pressure pulsation is proportional to the length of the gas container 3 as in the first and second embodiments, and the operation of the perforated tube 4 is also the same.

〔The invention's effect〕

The pressure pulsation absorbing device according to the present invention is configured as described above, and the forces between the liquid in the pipe and the gas in the gas container interact with each other at an extremely ideal free boundary surface, and the pressure in the gas container is reduced. Since the gas absorbs and attenuates the pressure pulsation of the liquid in the pipe, the pressure pulsation is attenuated at all frequencies below the minimum cutoff frequency while being small and inexpensive.

[Brief description of the drawings]

1 to 4 are cross-sectional views of a pressure pulsation absorber according to first to fourth embodiments of the present invention. FIG. 1B is a cross-sectional view taken along line bb in FIG. FIGS. 5 and 6 are explanatory views of these operations, and FIGS. 7 (a) to 7 (d) are sectional views of a conventional pressure pulsation absorber. 1 ... piping, 2 ... casing, 3 ... gas container, 4 ...
... Perforated tube, 5... Liquid, 6... Gas, 7.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Manabu Inoue 1-1-1, Wadazaki-cho, Hyogo-ku, Kobe-shi, Hyogo Prefecture Inside Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (56) References A)

Claims (1)

(57) [Claims] 1. A gas container which is attached to a pipe in contact with a liquid in the pipe and is made of a flexible material whose acoustic characteristic impedance substantially matches that of the liquid in the pipe. A gas filled with the pressure balanced with the liquid in the pipe, and a perforated pipe made of a porous material and interposed between the gas container and the liquid in the pipe to maintain the shape of the gas container. Pressure pulsation absorber.