Fan silencer

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I. Overview of fan silencers: Fan silencers, as well as silencers for blowers and exhaust fans, utilize a resistive sound-absorbing principle that is effective for reducing noise in the mid- to high-frequency range. They also make use of an reactive sound-damping principle that is effective for low- to mid-frequency sounds as well as pulsating noises. In addition, micro-perforated silencers and impedance-combined silencers are employed as well. Then, fan silencers are also divided into several major categories, including centrifugal fan silencers, Roots blower silencers, blower silencers, axial flow fan silencers, and so on. A resistive silencer is a type of absorptive silencer; depending on the structure of its airflow channels, it is generally classified into straight-tube type, plate type, folded-plate type, honeycomb type, acoustic-flow type, labyrinth type, and elbow type, among others. A resistive silencer works by utilizing the frictional and viscous resistances encountered as sound waves propagate through porous sound-absorbing materials, thereby converting acoustic energy into heat energy and dissipating it, thus achieving noise reduction. It is a type of silencer that is widely used among all silencers. 　　A reactive silencer operates on a different principle from a resistive silencer for noise reduction; it cannot absorb sound energy directly. Instead, it makes use of abrupt interfaces in the pipeline or attached resonance chambers to cause certain frequency sound waves traveling along the pipeline to reflect and interfere at those abrupt interfaces, thereby achieving noise reduction. Such silencers are divided into expansion chamber types and resonance-type silencers. 　　In actual noise control projects, noise is often present in a wide frequency band; therefore, resistive sound-absorbing systems and reactive sound-damping structures are typically combined to control high-intensity noise across a wide frequency range. 　　II. Classification and applications of fan silencers: 1: Centrifugal fan silencers: Centrifugal fan silencers are primarily used in various types of high-pressure centrifugal ventilators, aiming to reduce aerodynamic noise at the inlet and outlet areas. They are designed based on the principle of sound absorption through sound-dampening elements; these silencers exhibit excellent acoustic performance as well as good aerodynamic characteristics ； It features a rational structure that facilitates installation; it is a high-volume resistive honeycomb silencer. The resistive section utilizes multi-chamber resistive rubber straight-channel designs along with cross-shaped sound-absorbing elements, thereby ensuring sufficient sound attenuation over a wide frequency range. 　　2: Roots blower silencer: The Roots blower silencer is used to reduce the noise generated by the intake and exhaust air of the Roots blower. It can also be used to reduce noise in exhaust ducts and other high-pressure fans. The rotor blower silencer features a simple structure, light weight, low material consumption, an attractive design, easy installation, and fire resistance. Under the same fan flow conditions, this series of silencers is also suitable for noise suppression in the intake and exhaust of general high-pressure fans. 　　3: Application scope of fan silencers: Fans are a type of general-purpose mechanical equipment with a wide range of applications; they are essential in the production processes of various industries such as electricity, mining, machinery, metallurgy, and chemicals. The noise generated by fans during operation often becomes a source of harm to workers’ health and environmental disturbance. In particular, for fans located near residential areas, the aerodynamic noise emitted from their inlet and outlet is a major factor in environmental pollution; it constitutes a public nuisance and has been one of the main targets for noise pollution control efforts by China’s industrial sector in recent years. 　　Industrial fans are equipment designed for continuous operation. The International Organization for Standardization (ISO) sets a noise standard of ≤90 decibels for such equipment, and China’s new standards are the same; this is also the basis for ensuring that the continuous noise level in industrial enterprises meets the required standards. However, without the use of noise reduction measures, the noise emitted by the air inlets and outlets of fans can reach 110–120 decibels, **which exceeds the specified limits. 　　III. Principles of ventilation and fan silencer design: The spectral characteristics obtained from actual tests of noise sources at various industrial fans’ operating sites are used to determine the required level of noise reduction in specific frequency ranges; this serves as the main basis for designing the sound-absorbing elements and fluid channels. Narrow rectangular channels covered with high-absorbing materials are also employed to enhance the absorption effect. Furthermore, when the noise level of a fan is high, it often has more than one spectral component, and different spectral bands require varying levels of noise reduction. 　　To this end, both the silencers for the ventilation ducts and those for the blower fans are of the impedance acoustic flow type. They utilize a resistive structure that absorbs and reduces high- and medium-frequency noise, as well as a reactive structure that reduces low- and medium-frequency noise. Additionally, resistive channels are equipped with absorption zones for both high and low frequencies, thereby widening the noise reduction frequency range as much as possible to achieve an excellent noise reduction effect.