Main fan opening and closing shock absorber damage end is analyzed
The muffler principle and structure of the muffler is a device that can pass airflow and effectively reduce noise. It is usually installed on the intake and exhaust pipes of various aerodynamic devices to reduce the radiation or along the intake and exhaust ports. The noise transmitted by the pipeline. The principle of muffling is mainly to convert the sound wave into heat energy through the sound absorbing structure of the muffler, or to cause reflection interference of the sound wave to reduce or eliminate the noise intensity discharged into the environment. The muffler has many structural forms, which are divided by acoustic principle and can be basically divided into three categories: resistant muffler, resistive muffler and impedance composite muffler.
(1) The structural feature of the resistant muffler resistant muffler is that no sound absorbing material is added inside the muffler, but the sound wave is reflected by the cross section of the muffler channel to reduce the noise intensity. The acoustic principle is similar to the filter in the circuit, and it plays a role in the resistance of acoustics. Its structural form mainly consists of single or multiple expansion chambers, as shown in (a) and (b); or by using bypass branches to make parts The path of the acoustic wave is exactly equal to half a wavelength, and the phases are 180° out of phase, thereby generating interference and weakening the intensity of the noise, and its structure is as shown in (c).
Resistive muffler structure (2) Resistive muffler Resistive muffler mainly applies porous or fibrous sound absorbing material to the internal air passage of the muffler, and uses the friction and viscous resistance of the material to convert the acoustic energy into heat energy. Thereby the noise is attenuated. The resistive muffler has good sound absorption effect on medium and high frequency noise, and its common structural forms are: straight tube type, folding board type, chip type and sound flow type.
Factors Affecting the Performance of the Muffler In addition to its direct relationship with the structural form, the muffler performance of the muffler has a direct impact on its sound absorbing material, channel cross-sectional area, muffler length, and face structure. (1) The selection of sound absorbing materials for sound absorbing materials depends on the frequency characteristics of the noise source. Different materials have different sound absorption coefficients for different frequencies. Even for the same material, different thicknesses and different bulk density have different sound absorption coefficients. In addition, the temperature, humidity, dust content and other conditions of the medium must be considered. The material has a high bulk density and is unfavorable for high-frequency sound wave absorption; the bulk density is low, which is unfavorable for low-frequency absorption. The sound absorption coefficient generally increases with the thickness of the material, but the increase of the sound absorption coefficient after the thickness increases to a certain value is not obvious. Commonly used sound absorbing materials are ultra-fine glass wool, rock wool, fiberboard, foam and the like.
(2) Muffler channel cross-section size The size of the muffler cross-section size is directly related to the medium flow velocity, pressure drop and noise. The choice of the cross-sectional area of ​​the channel also involves the determination of the muffler channel structure. Generally, the effective channel cross-sectional area should not be less than the cross-sectional area of ​​the original inlet and exhaust ports. Otherwise, if the flow rate is too high, the secondary noise generated will increase. Increasing the effective channel cross-sectional area reduces the flow rate and correspondingly the resistance loss is also reduced.
The measures taken are based on the analysis of the above-mentioned causes of damage. We have strengthened the acceptance of the products of the manufacturers so that the products fully meet the requirements of the design drawings. During the installation process, the technicians of the manufacturer and the user unit are instructed on site until the correct installation is completed. After the overhaul in January 1998, the 3 main fans were turned on normally and the muffler operation was restored to normal. Of course, it should be pointed out that although the muffler has a certain noise reduction effect, it is still not enough to truly meet the noise requirements of the environment. The author suggests that because the impedance compound muffler is widely used, the noise cancellation effect is better than the simple resistance muffler. Therefore, the appropriate impedance composite muffler should be selected after detecting the noise property and noise intensity.
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