Some standard content:
ICS 17.140. 01
National Standard of the People's Republic of China
GB/T20431—2006/IS014163:1998 Acoustics
Guidelines for noise control by silencers
Acoustics--Guidelines for noise control by silencers (ISO14163:1998IDT)
Published on July 25, 2006
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China Administration of Standardization of the People's Republic of China
Digital Defense
Implementation on December 1, 2006
Normative References
3 Terms and Definitions
Performance, Selection and Design Considerations·4
4.1 Performance Requirements
Selection and Design of Mufflers||t t||4.3 Design of special silencers
5 Types of silencers, general principles and operating considerations 5.1
Acoustic and aerodynamic characteristics of silencers 5.3
Sound propagation paths
Acoustic influence of installation
Abrasion resistance and protection of sound-absorbing material surfaces
Fire hazards and protection against explosions
Opening and closing of equipment
Corrosion
Hygiene requirements and risks of contamination
Inspection, cleaning and decontamination
6 6.3 Exhaust venting muffler
7 Measurement technology...
7.1 Laboratory measurement
7.2 Field measurement
7.3 Measurement of automobile muffler
8 Muffler information
8.1 Information provided by the user
8.2 Information provided by the manufacturer
Appendix A (informative appendix)
Appendix B (informative appendix)
|Appendix C (Informative Appendix)
GB/T20431—2006/ISO14163:19988
The influence of the spectral distribution of sound on the nominal value of the sound attenuation effect of 1/3 octave band or octave bandThe working temperature of the sound source and the temperature limit of the sound absorbing materialAppendix D (Informative Appendix)
References
GB/T20431-—2006/IS014163:1998This standard is equivalent to ISO14163:1998 "Guidelines for Noise Control of Acoustic Mufflers". In the preparation of the standard, according to the requirements of my country's national standards, some ISO standards in the normative references and references are replaced by the corresponding national standards being implemented in my country. Some terms, formats and text descriptions are more in line with the relevant standards and practices in my country. All appendices to this standard are informative appendices. This standard is proposed by the Chinese Academy of Sciences.
This standard is under the jurisdiction of the National Technical Committee for Acoustic Standardization (SAC/TC17). This standard was drafted by: Beijing Labor Protection Science Research Institute, Acoustics Institute of Chinese Academy of Sciences, Beijing Green Creation Acoustics Engineering Co., Ltd.
The main drafters of this standard are: Li Xiaokuan, Ren Wentang, Li Xiaoping, Dai Genhua, Geng Xiaoyin, Xiangfangming, Zhao Zunyu. GB/T20431-2006/IS014163:1998 cited
Whenever the air sound cannot be controlled at the sound source, the use of silencers is a very effective way to reduce noise on the propagation path. Silencers have many applications. Its design is based on different combinations of various noise reduction mechanisms such as sound absorption, sound reflection and reaction to the sound source. This standard systematically introduces the principles, performance data and applications of silencers. VWww.bzxZ.net
1 Scope
GB/T20431—-2006/IS0141631998 Acoustics
Guide to noise control with silencers
This standard deals with the practical selection of silencers for noise control in gaseous media, and specifies the acoustic requirements and operating requirements that can be agreed upon by the supplier or manufacturer and the user of the silencer. This standard describes the basic principles of silencer operation, but is not a design guide for silencers.
The silencers described in this standard are suitable for: reducing system noise and preventing crosstalk in heating, ventilation and air conditioning (HVAC) equipment; preventing or reducing sound transmission through vents in rooms with high sound levels; reducing exhaust venting noise generated by high-pressure ducts; reducing intake and exhaust noise generated by internal combustion engines; and reducing inlet and outlet noise from fans, compressors and turbines. Silencer is classified according to type, performance characteristics and application. This standard does not discuss active and adaptive passive noise control systems in detail.
2 Normative references
The clauses in the following documents become clauses of this standard through reference in this standard. For any dated referenced document, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, parties reaching an agreement based on this standard are encouraged to study whether the latest versions of these documents can be used. For any undated referenced document, the latest version shall apply to this standard. GB/T3767 Acoustics Sound pressure method for determining the sound power level of noise sources Engineering method for approximate free field above reflecting surface (GB/T3767-1996, eqvISO3744:1994)
GB/T6881.1 Acoustics Sound pressure method for determining the sound power level of noise sources Precision method in reverberation chamber (GB/T6881.1—2002, eqvISO3741:1999)
GB/T16405 Acoustics Duct silencer in the absence of airflow Insertion loss measurement laboratory simplified method (GB/T16405-1996, eqvISO11691:1995)
GB/T19512 Field measurement method for acoustic silencers (GB/T19512-2004, ISO11820:1996, IDT) ISO7235 Measurement procedure for acoustic duct silencers Insertion loss, airflow noise and total pressure loss 3 Terms and definitions
The following terms and definitions apply to this standard. 3.1
Silencer
A device that reduces the transmission of sound through a pipe, duct or opening and does not prevent the transmission of the medium. 3.2
(Dissipative silencer) dissipative silencer, absorptive silencer A broadband sound attenuation silencer with relatively small pressure loss, which partially converts sound energy into heat energy through the friction of the pipe lining of porous or fibrous materials.
Reactive silencer
General term for reflective and resonant silencers, whose main attenuation is not sound energy loss. 1
GB/T20431—2006/ISO14163:19983.4
Reflective silencer
Reflective silencer
A silencer that provides single and multiple sound reflections by changing the pipe cross section, adding a resonator to the pipe lining, or adding different lengths of side branches to the side wall of the pipe.
Resonant silencer
Resonator silencer
A silencer that provides sound attenuation by a resonant element with low damping. Note: This element may or may not contain sound absorbing material. 3.6
Blow-off silencer A silencer used for steam discharge and pressure release, which provides sound attenuation by regulating the airflow through large pressure losses in porous materials, reducing the airflow velocity at the outlet, and reacting to the sound source (e.g. reading). 3.7
Active silencer
activesilencer
A silencer that reduces noise by producing interference through the sound of a controllable secondary sound source. Note: Most low-order mode sounds in the duct are effective. 3.8
adaptive passive silencer
Adaptive passive silencer
A silencer equipped with passive sound attenuation elements and capable of dynamically adapting to the sound field. 3.9
Insertion lossinsertionloss
The difference in sound power level radiated through a duct or opening with and without a silencer. Note 1: Insertion loss is expressed in decibels (dB). Note 2: The definition of ISO7235 is adopted.
Insertion sound pressure level difference
insertion sound pressure lever differenceD
The difference in sound pressure level at a certain irradiation point with and without a silencer and without significant external noise. Note 1: Insertion sound pressure level difference is expressed in decibels (dB). Note 2: The definition of GB/T19512 is adopted.
transmissionloss
Transmission loss
The difference in sound power level incident on and transmitted through a silencer. Note 1: Transmission loss is expressed in decibels (dB). Note 2: For standard laboratories, D, is equal to D,; in field measurements, due to measurement limitations, the results of D, and D, often differ. Note 3: The definition of GB/T19512 is adopted.
Discontinuity attenuation discontinuityattenuationD.
Insertion loss caused by discontinuous cross section of muffler. Note: Discontinuous attenuation is expressed in decibel (dB). 2
Propagation loss propagation loss
GB/T20431--2006/ISO14163:1998 The reduction of sound pressure level per unit length in the middle section of a muffler with a fixed cross section and uniform longitudinal structure, reflecting the longitudinal attenuation characteristics of the fundamental frequency mode.
Note: Propagation loss is expressed in decibel per meter (dB/m). 3.14
Outlet reflection loss
outletreflectionloss
The difference in sound power level between the sound incident to the end of the pipe opening and the sound power level transmitted through the end of the pipe opening. Note: Outlet reflection loss is expressed in decibel (dB). 3.15
Spatial distribution of the acoustic field in a pipe (or transverse standing wave modes), which occur independently of each other and have different attenuation. Note: The attenuation of the modes is the least. In narrow and lined pipes, the higher-order modes have a high attenuation. 3.16
cut-off frequency
Cut-off frequency
The lower frequency limit of the propagation of higher-order modes in a hard-walled pipe. Note 1: The cut-off frequency is expressed in Hertz (H2). Note 2: In a pipe with a circular cross-section, the cut-off frequency of the first higher-order mode is .c = 0.57c/C, where:
Sound velocity, in meters per second (m/s);
C is the pipe diameter, in meters (m).
In a rectangular pipe with the long side dimension H, the cut-off frequency of the first higher-order mode is fa = 0.50c/H. 3.17
Pressure losspressureloss
The average total pressure difference between the upstream and downstream sides of a muffler. Note 1: Pressure loss is expressed in Pascals (Pa). Note 2: The definition of ISO 7235 is used.
Regenerated sound, flow noise
Regenerated sound, flow noiseThe noise generated by the flow of the medium in a muffler. Note: The sound power level and pressure loss of the regenerated noise measured in the laboratory are related to the distribution of uniform airflow in the lateral direction at the inlet of the muffler. If this uniform airflow distribution cannot be obtained under field conditions, for example due to the design of the upstream ductwork, higher levels of regenerated noise and higher pressure losses will occur.
4 Performance, selection and design considerations
4.1 Performance requirements
4.1.1 In general, the sound pressure level (A-weighted, 1/3 octave band or octave band) should not exceed the specified value in the specified area (for example, in the vicinity of work areas or entertainment venues). The contribution of a sound source can be determined based on the sound power level of the sound source, the directivity index of the sound source, using the law of sound propagation and the distribution of the energy contribution of several parts of the sound source. The required insertion loss of the silencer is obtained by the difference between the allowed sound power level and the actual sound power level of the sound source. When the sound exposure is a simple case determined by the sound source to be attenuated alone, the insertion sound pressure level difference of the silencer can be directly calculated from the difference between the allowed sound pressure level and the actual sound pressure level at the exposure point 3
GB/T20431-2006/ISO14163:1998. When the difference in directivity index with and without a silencer can be ignored, the insertion sound pressure level difference of the silencer is equal to the insertion loss. 4.1.2 The permissible pressure loss cannot be exceeded. Note: This requirement should be stated as clearly as possible. A reasonable limit must be found to replace the less precise provisions such as "as small as possible". Even when pressure losses are considered "unimportant", a limit should be determined from the maximum air velocity that is not allowed to be exceeded, based on mechanical stability, regenerative noise or energy consumption.
4.1.3 The permissible size of the silencer should be as small as possible (considering cost and weight). NOTE: This is the minimum size that cannot be reduced any further (under given process conditions). This size depends on the required sound level reduction, the permissible pressure loss and other restrictions including the materials used (or avoided), the resistance to different stresses, etc. 4.1.4. Other requirements (including materials, service life, leakage, etc.) depend on the application environment of the silencer, such as heat, dust, humid or corrosive gases, high sound pressure levels and high vibration levels in pressure pipelines, and also on the combination of the silencer with equipment for controlling the exhaust, preventing sparks and handling dust particles.
4.2 Selection and design of silencers
Information on silencers can be obtained from the following sources: laboratory measurements in accordance with ISO 7235;
test data from silencer manufacturers; theoretical models for calculating transmission and insertion losses for silencers with circular and rectangular cross-sections, and methods for predicting pressure losses and regenerative noise. The choice of resistive, reactive or exhaust vent silencers should be based on the application conditions or on existing experience with reference to this standard. The results for the insertion loss of resistive silencers obtained by computer programs depend on assumptions about the size and distribution of the air flow resistance in the silencer and the acoustic effect of the cover [18]. Specific geometrical features, such as the deflection of the panels or complex configurations of the absorbers are not easy to calculate. The calculations for parameter variations in design and operating conditions are extremely accurate. The influence of airflow on the performance of reactive silencers requires the use of specialized advanced and complex calculation software.
4.3 Design of special silencers
The design of special silencers is usually repeated in the following steps: a) To roughly specify the duct size in which the gas flow can flow freely and the connecting space for sound distribution, for example using the manufacturer's specifications for similar silencers, and taking into account the basic requirements and limitations; a) To build a model for budgeting and testing; b) To use the model, compare the results with the required sound level attenuation and pressure loss; c) To change the size and sound absorbing materials to achieve the noise reduction requirements or optimize the design; c) To consider the special requirements of the structure.
5 Types of silencers, general principles and operating considerations 5.1 Overview
Silencers are used to:
Prevent gas pulsation and oscillation in equipment;
Reduce the conversion of pulsation and oscillation into sound energy;
- Convert sound energy into heat energy.
The insertion loss results for silencers installed in ducts usually depend on these three mechanisms. According to its main attenuation mechanism, the silencer can be divided into:
-resistive silencer;
-reactive silencer, including resonance type and reflection type silencer; exhaust vent silencer:
active silencer.
The advantages and disadvantages of resistive and reactive silencers are shown in Table 1. GB/T20431-—2006/ISO14163:1998 Table 1 Typical advantages and disadvantages of different types of silencers Type of silencer
Resistive silencer
Resonance type
Reactive silencer
Reflection type
5.1.1Resistive silencer
Broadband attenuation, small pressure loss
Tunable attenuation, not easy to pollute
Sturdy and durable;
Suitable for places with large pressure pulsation, high sound level, polluted airflow, and strong mechanical vibration Disadvantages
Easy to pollute and mechanically damage
Narrow band attenuation, easily affected by airflow
Produces large pressure loss, there is a sound passing band (a band with little or no attenuation), and the acoustic performance is sensitive to airflow
It converts sound energy into heat energy to produce wide-band sound energy attenuation, and the pressure loss is relatively small. When the resistive silencer is used in a pipeline carrying polluted gas with dust or scaling, the surface of the sound absorbing material should be prevented from being covered or blocked. Porous sound absorbing bodies made of fine fiber materials or thin-walled structures may be mechanically damaged due to the large amplitude of pressure changes. 5.1.2 Resonant silencers (resistive)
Reduce the conversion of gas pulsations and oscillations into acoustic energy and absorb the acoustic energy. Individual resonators are installed as bypasses on the pipe wall. A group of resonators is used in the pipe as a lining or separation element (grid) to produce a limited pressure drop. Depending on the required attenuation, the resonators are mostly tuned to medium and low frequencies. Their characteristics are limited to a narrow frequency band, they are sensitive to grazing incident airflows and may (under certain unsuitable conditions) have a negative effect, so that pure tones are produced. 5.1.3 Reflective silencers (resistive)
Reduce the conversion of gas pulsations and oscillations into acoustic energy. Due to their robustness, they can be used in situations where the application of resistive silencers is not suitable and a larger pressure loss is allowed, such as airflows carrying dust, or airflows with high flow velocities and high pressure pulsations, as well as in situations of strong mechanical vibrations. The airflow affects the maximum attenuation and the frequency. In certain frequency bands, very low or even negative attenuation may occur. 5.1.4 Exhaust venting silencers
They are installed in steam and high-pressure gas release pipes. Their effect comes from the reaction to the sound source (such as valves) or from reducing the air flow velocity through the expanding surface. At this time, the effect of converting sound energy into heat energy is very small. Large pressure losses require the silencer to have good mechanical stability. Its performance will be affected by gas inclusions. Ice formation is also very dangerous. 5.1.5 Active silencers
Mainly include a speaker combination driven by an appropriate microphone signal input amplifier. Effective control is carried out through a high-performance computer and controller. These special devices are not involved in this standard. In the low frequency band, active silencers are very effective, while passive resistive silencers usually have less attenuation.
Note: Active systems currently provide unique solutions for special applications and are not discussed in this standard. 5.2 Acoustic and aerodynamic characteristics of silencers If no specific irradiation point is specified, the attenuation of the silencer is described by the insertion loss D, or by the insertion sound pressure level difference D at a specified position, and is expressed in 1/3 octave bands or octave bands. According to laboratory standard IS07235, the attenuation needs to be measured in 1/3 octave bands, and the octave band value can be calculated by formula (1): Where:
D1/3,1~D1/3.3
Dn=101g()
(10-/m/10
The attenuation values of the three 1/3 octave bands in the octave band are expressed in decibels (dB). (1)
Di/1 is the result of the octave band. For broadband noise and broadband silencers, the octave band attenuation value is sufficient. For pure tone noise and narrowband resonant silencers, the 1/3 octave band should be given. Note 1: The octave band attenuation value may be closely related to the noise spectrum (see Appendix B). 5
GB/T20431—2006/ISO14163:1998 The allowable pressure loss in the airflow is a necessary parameter for selecting a silencer. It cannot exceed the total pressure loss Apt. The total pressure loss Apt depends on the average airflow velocity and gas density. Under airflow conditions, it is described by formula (2): p(+) sign
In the formula:
-the total pressure loss coefficient at both ends of the silencer under uniform airflow conditions defined in ISO7235. (2)
-additional pressure The total pressure loss coefficient is due to the deviation of the air flow conditions on site from the laboratory conditions (the value is estimated empirically). As
Gas density, in kilograms per cubic meter (kg/m). The average air flow velocity at the inlet cross section, in meters per second (m/s). Note 2: The definition of the total pressure loss coefficient is often different from that given in ISO7235. Therefore, it is necessary to check the definition when using any value. For example, a different definition is based on the air flow velocity at the narrowest cross section of the silencer, which leads to a value that is too low. Other parameters that need to be considered that affect the acoustic and aerodynamic characteristics of the silencer are : Regenerative noise;
Maximum suitable size of silencer;
Durability of silencer exposed to airflow, pulsating pressure and mechanical vibration. 5.3 Sound propagation paths
In addition to direct propagation from the outlet of the silencer, it is possible that the noise radiated from the sound source propagates along several paths to the irradiation point (as shown in Figure 1, path 1). Other paths are:
a) radiation from the sound source shell (path 2);
: b) radiation from the pipe wall in front of the silencer (path 3); c) radiation from the silencer shell (path 4);
d) structure-borne sound propagated along the silencer (path 5). Sound propagation along the lateral paths can be prevented by providing the sound source cover and pipe wall with sufficient sound insulation, or by isolating the propagation path of the structure-borne sound by using vibration isolation equipment. Silencing
Figure 1 Sound propagation paths (schematic diagram)
5.4 Acoustic influence of mounting
For a particular application and type of muffler, the sound attenuation that a muffler can provide depends on the characteristics of the sound source connected to its inlet and the characteristics of the end connected to its outlet. The mounting style particularly affects the effectiveness of reactive mufflers and all types of mufflers at low frequencies. The influence of mounting is also important when both the inlet and outlet of the muffler are reactive (i.e., non-absorbing). When these conditions are met, undesirable resonant effects will appear in the system and lead to strong coupling of different parts of the system. Formally, the impact of this installation can be described by equation 6
(3):
where:,
Lwi=Lw2-D,-Dm+E
Lwi is the sound power level radiated from the end of the pipe, in decibels (dB); GB/T20431—2006/ISO14163.1998. (3)
Lw2 is the sound power level radiated from the sound source to the end pipe with silencer, in decibels (dB); D,-transmission loss (see 3.11), in decibels (dB); Dm is the reflection loss at the pipe outlet (see 3.14 and 6.2.2.2), in decibels (dB); E is the acoustic impact of the installation, in decibels (dB); In a resistive silencer system, the amplitude of E usually does not exceed 10dB. E describes the reaction of the reflected sound to the sound source, i.e. the increase or decrease of the emission of the sound source. Note: For highly resistive systems, E may be a large positive value in some narrow frequency bands, indicating that the silencer system actually amplifies the sound power radiated by the sound source. 5.5 Wear and protection of the surface of the sound absorbing material Due to the wear of the resistive silencer material, particles of the filling material may be carried away by the airflow. Note: For mufflers that have been in long-term operation, the concentration of particles in the airflow is still poorly understood. If the surface of the sound absorbing material is damaged, the lower air flow speed can carry away a large number of particles from the wear area. This process will lead to the loss of the entire sound absorbing component (e.g. sheet type). In order to protect the sound absorbing lining of the muffler from contamination by moisture, water or pollutants carried in the airflow (especially in hospitals and food processing industries), metal films are used for sealing. This metal film not only reduces the attenuation characteristics of high frequencies (typical frequencies above 1kHz), but also easily tears during equipment operation. The total pressure difference (static and dynamic pressure) at the inlet and outlet of the sealing device will cause stress on the metal film. High temperatures and the impact of coarse particles will increase the risk of damage. Therefore, when using metal film to protect the sound absorbing lining, great attention should be paid to its thickness, temperature, air flow velocity and gas contamination. 5.6 Fire hazard and protection against explosions Fires that are transmitted through ventilation silencers are particularly dangerous for mechanical equipment that carries oily aerosols. This is particularly likely to occur in chemical laboratories, large kitchens and engine test rooms. Organic substances such as flour or milk powder become explosive when mixed with air. The risk of explosion should also be considered when dusty gases flow through the silencer. When silencers are used in the above situations, flame retardant materials should be used in the silencers in accordance with the relevant building regulations. The deposition of grease, oil or dust in the sound-absorbing material of the silencer can be prevented by using a reasonable silencer shape and its arrangement. Resonant silencers without sound-absorbing materials and that prevent dust deposition meet the requirements for fire and explosion protection. 5.7 Opening and closing of equipment
When the equipment is opened and closed, the silencer installed on the equipment may malfunction. Sufficient space should be left for the installation of the silencer components to allow for large changes in pressure and temperature. In particular, when there are changes in pressure, pressure relief will occur in the metal film armor sound absorbing lining.
During the start-up and shutdown phases of the equipment, the temperature often drops below the dew point, especially in the lining of the sound-absorbing material and in the silencer housing. The accumulation of moisture should be avoided (e.g. by drying the equipment). Corrosion problems may also occur. Condensation should be drained away. 5.8 Corrosion
The sheet metal shell, material facings and separation layers of the silencer as well as the mounting flanges should be protected from water, various acids in the exhaust gas and potential differences between different materials. Corrosion can be prevented by selecting special materials (e.g. aluminum) or applying protective facings (e.g. rubber).
5.9 Hygiene requirements and contamination risks
Special requirements should be met in some locations, for example: - clean rooms;
food processing plants,
—hospitals;
—power plants.
GB/T20431-—2006/IS014163:1998 When dust adheres to the surface of the sound absorbing lining, especially when accompanied by moisture, it will cause hygiene problems. Microorganisms (bacteria) can also cause problems, especially when the air temperature rises. Nuclear power equipment may also cause nuclear contamination. In such demanding plants, the surface of the muffler lining should be flat. Large cavities and protruding edges should be avoided, as these will cause the accumulation of dust and water vapor and increase pressure loss. 5.10 Inspection, cleaning and purification
When necessary, the muffler should be inspected, cleaned or replaced. Mufflers have special requirements when used in most heating, ventilation and air conditioning equipment and should be cleaned or purified regularly. Therefore, it is necessary that the sound absorbing sheet can be removed for cleaning (purification) or replacement. In this case, the shell of the muffler should also be cleaned. The sound absorbing sheet can be cleaned with high-pressure gas, steam injection, brushes and solvents, or purification fluids according to the design. After working for a period of time in a dusty airflow state, the dust deposited on the sound-absorbing sheet of the silencer will cause a significant decrease in insertion loss. Therefore, it is also necessary to clean it at intervals. 6 Performance characteristics of various types of silencers
6.1 Resistive silencer
6.1.1 Simple resistive silencer
A simple resistive silencer is a straight pipe with a sound-absorbing inner sleeve, a circular or rectangular cross-section, and no device added (see Figure 2). 2
1—Shell,
A sound-permeable protective surface:
3—Airflow channel;
A sound-absorbing material.
Figure 2 Resistive silencer (schematic diagram)
The sound-absorbing element includes one or more layers of sound-absorbing material and a layer of sound-permeable protective surface. Fine-diameter ore, metal, plastic fiber and open-pore structure foam material, sintered metal foam material or concrete foam material are all used as sound-absorbing materials. In the structure of large particles, the effect of air viscosity is less than that of full flow. In this case, the pressure difference will increase with the square of the air flow velocity. This nonlinear effect can occur in a muffler with air flow passing through the sound-absorbing material or in a muffler with air flow flowing along the surface of the sound-absorbing material. In order to cover fibrous materials and foams that are subjected to high pressure, open-hole metal sheets, metal meshes with diamond mesh or strip mesh, glass fiber or steel fiber cloth, etc. should be used. For medium pressure conditions, metal films, glass fiber or plastic fabrics, etc. should be used. The transmission loss D, (or insertion loss D., see 3.11) of a simple resistive muffler can be determined by formula (4): D, = D, + D.1
Where:
D, is a discontinuous attenuation in decibels (dB); D. is a propagation loss along the muffler in decibels per meter (dB/m); 1 is the length of the muffler in meters (m). 8
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.