JPH0247640B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pressure pulsation reducing device for a liquid piping system, and in particular to a device for reducing pressure pulsations at a certain frequency such as in a pump piping system. The present invention relates to a pressure pulsation reducing device suitable for.

[Conventional technology]

When pressure pulsations caused by driving a fluid machine such as a pump propagate to a piping system, the piping system vibrates and radiates noise. For example, in a pump, when the impeller blades pass through the discharge volute inlet, a pressure change occurs, which is a pulsation with a frequency equal to the number of blades x the rotational speed, and this pulsation propagates through the water column in the pipe and is transmitted through the pipe system. This caused the problem of the whole unit vibrating and generating noise. In order to cope with the occurrence of such pulsation, various pulsation reduction devices have been conventionally provided. An example of this will be explained with reference to FIG.

In the figure, an air chamber 2 is disposed in the middle of a pipe 1, and the pipe 1 and the air chamber 2 are connected by a thin tube 3 having a cross-sectional area a and a length L. The eigenvalue f _o of the pressure pulsation in the air chamber 2 is becomes. Here, C is the compliance in the air chamber, V is the volume of the air chamber, and L' is the equivalent length of the capillary, which is the length L plus the terminal correction.

When the above-mentioned eigenvalue _fo matches the frequency of the pressure pulsations propagating through the piping system, the inside of the air chamber 2 resonates, and the pressure pulsations propagating through one of the piping systems decreases.

[Problem to be solved by the invention]

By the way, the value of the compliance C is a value related to the compressibility of the air in the air chamber 2, and changes depending on the amount of air in the air chamber 2. Therefore, in order to always cause the air chamber to resonate with the pressure pulsations of a specific frequency propagating through the piping system and to obtain a significant pressure pulsation reduction effect, it is necessary to keep the above-mentioned compliance value constant.

However, the air in the air chamber mixes with the liquid in the piping, or dissolves into the liquid and flows out into the piping, or conversely, the air contained in the liquid in the piping flows into the air chamber, changing the amount of air. . For this reason, there is a problem in that the resonant frequency of the air chamber deviates from the frequency of pressure pulsations propagating through the piping system, and the pressure pulsation reducing effect of the air chamber is reduced. In order to constantly replenish the amount of air lost in the air chamber, equipment such as an air compressor, air piping, and valves are required.
Further, operation work is required for replenishment. In order to solve this fluctuation in the amount of air, there is a proposal to store dry gas such as nitrogen gas instead of air in a bag made of elastic material, place it inside the air chamber, and fill the area around the bag with liquid. However, the structure is complicated and expensive, and depending on the quality of the liquid, the durability of the bag may be a problem.

Further, as another conventional example of a pressure pulsation reducing device for a liquid pipe system, there is one described in JP-A-56-86296. In this conventional example, a resonant cavity is provided outside the fluid piping to reduce pulsation. This conventional example reduces pulsation by interfering with the pulsation flowing into the resonance cavity and the pulsation inside the pipe, so the length of the resonance cavity must be 1/4 wavelength, and the resonance cavity is large. There are drawbacks to becoming Furthermore, since the pulsation is reduced by interference, the entrance of the resonant cavity is wide open, and therefore there is almost no pulsation reduction effect by resonance.

An object of the present invention is to obtain a pressure pulsation reducing device for a liquid pipe system that is compact and has an excellent pressure pulsation reducing effect, with little variation in the pressure pulsation reducing effect.

[Means to solve the problem]

In order to achieve the above object, the present invention arranges a resonant chamber sealed with a rigid material outside a liquid conduit, connects the resonant chamber and the inside of the conduit with a thin tube, and provides a tube inside the resonant chamber. The frequency of the pressure pulsation to be filled with the same liquid as the inside of the pipe, and the volume of the resonance chamber V _r (m ³ ) and the inner diameter of the pipe to be reduced by D (m) is f (Hz).
The volume of the resonance chamber is determined so as to satisfy 25/f≦V _r /D ² ≦250/f.

[Effect]

By configuring the present invention as described above, the resonance chamber resonates with respect to the pressure pulsations propagating within the piping, and the pressure pulsations within the piping can be reduced. At this time, by determining the volume V _r of the resonance chamber so as to satisfy 25/f≦V _r /D ² ≦250/f, it is possible to obtain a compact and significant pulsation reduction effect.

〔Example〕

In general, pressure pulsation absorbers for gas piping, in which the pipes and air chambers are filled with gas, are
Known as a resonance silencer.

However, this pressure pulsation absorbing device has never been used in a liquid piping system filled with liquid instead of gas.

The reason for this is that the compressibility of liquid is much lower than that of gas, so when filling the air chamber with liquid, in order to obtain the same effect as filling the air chamber with gas,
This is because it was considered necessary to make the volume of the air chamber very large.

That is, the compressibility of a liquid, for example water, is approximately 4.75×10 ⁶³
cm ³ /Kg, whereas for gas β=ΔV/V ¹ ΔP=-1/P, for example, if the pressure inside the pipe is 5Kg/cm ² , β=0.2Kg/cm ² and water This is approximately 4,200 times the amount. Here, β is the compressibility, V is the volume of gas (cm ³ ), and P is the pressure (Kg/cm ² ),
ΔV is the amount of change in gas volume when the pressure is changed by ΔP.

Therefore, when the pressure inside the pipe is changed slowly, in order for the same volume of fluid to enter and exit the air chamber (hereinafter referred to as the resonance chamber), the volume of the resonance chamber filled with water is equal to the volume of the resonance chamber filled with air. Approximately 4200 of the volume when
It will require twice as much.

Therefore, the resonance chamber becomes large, the manufacturing cost of the pressure pulsation reduction device increases, and a large installation space is required.

For this reason, pressure pulsation reduction devices that have conventionally used air chambers and whose resonant chambers are filled with liquid have been considered to be completely impractical due to their excessive dimensions.

However, the inventors conducted various tests and found that by sealing the resonant chamber with a rigid material, filling it with liquid, and connecting it to the inside of the conduit with a thin tube, the resonant chamber could not be made large. We have invented a pressure pulsation reduction device that has a large pulsation reduction effect.

Next, specific embodiments of the present invention will be described with reference to FIGS. 2 to 8.

In Figs. 2 and 3, a resonance chamber 2 is connected to the middle of a pipe 1 for transporting liquid, and the pipe and the resonance chamber communicate through a thin tube 3 having a length L and a cross-sectional area a. . A valve 4 is provided at the top of the resonance chamber 2, and gas within the resonance chamber is completely removed by opening this valve. Valve 4 is kept closed during continuous operation. The eigenvalue f _o of the pressure pulsation in this resonant chamber is becomes. Here α is the sound speed in the liquid inside the resonance chamber,
V _r is the volume of the resonant chamber, and L′ is the equivalent length of the capillary between the resonant chamber and the pipe.

In FIG. 4, the difference from FIG. 2 is the shape of the thin tube 3' of the pipe 1 and the resonance chamber 2. That is, in FIG. 2, the shape of the connecting portion is a passage with a circular cross section, but in FIG. 4, it is in the form of a slit.

FIG. 5 shows an example in which this pressure pulsation reducing device is applied to a pump piping system. The pressure pulsation reducing device 2 of the present invention is provided midway through the discharge piping 6 of the pump 5. The ends of the pump suction pipe 7 and the discharge pipe 6 are connected to a tank 8, where the pressure pulsations transmitted by the pump are reflected and a constant number is generated. In Figure 5, the pump has a rotational speed of 2600 rpm and 5 blades, and the frequency of pressure pulsation is 217 Hz. In addition, the pressure pulsation reduction device has a piping diameter of 0.15m, but the volume of the resonance chamber is
It is ^0.0045m3 . As will be described later, this is smaller than a resonance type silencer generally used for gases.

Fig. 6 shows the actual measurement results of the distribution of pressure pulsation in the piping system shown in Fig. 4. The figure shows the case where the pressure pulsation reduction device of the present invention is used (○ mark), and the case where it is not used (x).
It can be seen that the maximum value of pressure pulsation is reduced to about 1/6 compared to that shown in the figure (marked), and the effect of reducing pressure pulsation is remarkable. Note that the value of Z indicates the pressure pulsation width within the resonance chamber.

By the way, the theoretical formula for transmission loss (TL) of a resonant silencer is expressed as follows.

TL=10log{1+(X/f/fn−fn/f) ² } …(3) Here, f is the frequency of pressure pulsation in the pipe, and f _o is the resonance frequency of the silencer. A is the cross-sectional area of the pipe.

FIG. 7 shows the relationship between the frequency f of pressure pulsation and TL. When f matches f _o , TL becomes infinite according to equation (3), but in reality, due to the resistance loss of the fluid flowing in and out of the resonant chamber entrance, even if f = f _r , it is not infinite. It won't happen. For example, a silencer used for air piping is shown by a broken line. Therefore, for practical use as a silencer, the value of X needs to be selected so as not to be too small, and conventional resonance type silencers for air use a range of X≧1.0.

However, the inventors have confirmed through experiments that a pressure pulsation reduction device for liquid piping in which the resonance chamber is filled with liquid can obtain a large pulsation reduction effect even when the above-mentioned X is a small value. That is, the example in FIG.
= 0.17, the pressure pulsations in the piping system are significantly reduced.

The reason for this is that the acoustic characteristic impedance ρα (Kg・s ² /m ³ ) of liquid is significantly larger than that of gas, so the particle velocity with respect to pulsating pressure is extremely small, and therefore, the particles enter and exit at the entrance of the resonance chamber. Therefore, in the pressure pulsation _reduction device for liquid, the resistance of the fluid to
This is thought to be because the TL does not change as shown by the broken line, but changes at a value close to the theoretical value shown by the solid line, resulting in a larger TL value. That is, the relationship between the pulsating pressure ΔP in the pipe and the particle velocity ΔV accompanying the pulsation is expressed by the following equation.

ΔP=ραΔV …(5) where ΔP: Pulsating pressure (Kg/m ² ) ρα: Acoustic characteristic impedance (Kg・
s ² /m ³ ) ΔV; pulsating particle velocity m/s. Here, the ρμ value is approximately 30Kg・s ² /m ³ in the case of air.
In contrast, in the case of water, it is approximately 10 ⁵ Kg・s ² /m ³ . Therefore, for the same ΔP, the particle velocity ΔV of water is approximately 1/3300 of that of air. From this, the flow rate of water entering and exiting at the inlet of the resonance chamber of the silencer is 1/1 compared to that of air.
3300 will suffice, and the fluid resistance loss in this part can be significantly reduced.

FIG. 8 shows the results of examining the pressure pulsation reduction effect by changing the volume of the resonance chamber of the pressure pulsation reduction device in FIG. 5. In the figure, X on the horizontal axis is the value of equation (4),
The vertical axis indicates the ratio of the pulsation amplitude to that when no pressure pulsation reduction device is used. The figure shows that in order to effectively reduce pressure pulsations, it is necessary that X≧0.1, and even if X is greater than 1.0, the effect of reducing pressure pulsations remains almost the same. That is, it is reasonable to select the value of X within the range of 0.1≦×≦1.0.

If a/L' is eliminated from the above reformulation, X=πf _r V _r /α・
It becomes A. Considering that it is used for f ~ f _r and that it is selected as 0.1≦×≦1.0, 0.1/πf≦V _r /a・A≦1.0/πf where A=π/4D ² , α=1000 m/s (Water piping) Therefore, 25/f≦V _r /D ² ≦250/f. That is, by determining the capacity V _r (m ³ ) of the resonant chamber with respect to the inner diameter D (m) of the conduit as in the above equation, it is possible to obtain a silencer that is compact and has an excellent pressure pulsation reducing effect.

In addition, the S values in FIG. 8 are as follows for the embodiment shown in FIG.
The P value is for the embodiment shown in FIG.

〔Effect of the invention〕

As explained above, according to the present invention, a resonant chamber made of a rigid material is arranged outside the liquid conduit, the resonant chamber and the conduit are connected by a thin tube, and the resonant chamber is filled with the same liquid as the inside of the conduit. By doing so, it is possible to obtain a pressure pulsation reducing device for liquid pipes that has a simple and compact structure, has a simple structure, and has strong durability, with less variation in the pressure pulsation reducing effect.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the main part of a conventional pressure pulsation reducing device, FIG. 2 is a sectional view of the main part of the pressure pulsation reducing device of the present invention, FIG. 3 is a sectional view taken along the line - A sectional view showing another embodiment of the present invention, FIG. 5 is a system diagram of a test device for a pressure pulsation reduction device, FIGS. 6 and 8 are line diagrams of the test results in FIG. 5, and FIG. 7 is a resonant type It is a diagram regarding the transmission loss of a silencer. DESCRIPTION OF SYMBOLS 1...Piping, 2...Resonance chamber, 3...Connection part between piping and resonance chamber, 4...Valve, 5...Pump, 6...Discharge piping, 7
...Suction piping, 8...Tank.

Claims (1)

[Scope of Claims] 1. A resonant chamber sealed with a rigid material is arranged outside the liquid conduit, the resonant chamber and the inside of the conduit are connected by a thin tube, and the inside of the conduit is connected to the inside of the resonant chamber. filled with the same liquid, and the volume of the resonance chamber V _r (m ³ ),
When the inner diameter of the pipe is D (m) and the frequency of pressure pulsation to be reduced is f (Hz), the volume of the resonance chamber is determined to satisfy 25/f≦V _r /D ² ≦250/f. A pressure pulsation reducing device for a liquid piping system, characterized in that: 2. The pressure pulsation reducing device for a liquid pipeline system according to claim 1, characterized in that an air vent valve is disposed at the upper end of the resonance chamber.