How to control fan noise

Update:04-08-2016
Summary:

Fans have many sources of noise and high decibels, whic […]

Fans have many sources of noise and high decibels, which is an important factor in environmental complaints. Based on the prevention and control of boiler fan noise, this paper discusses the harm of wind turbine noise and the comprehensive control technology of noise reduction and energy saving. 1. Harm of environmental noise pollution The impact and harm of noise on the human body can be generally divided into two aspects: labor protection and environmental protection. The former refers to harming people's physical health and causing various diseases. The latter refers to disturbing the environment and affecting people. Normal work and life. The main harms of noise to human health are: damage hearing, causing noise deafness; causing cerebral cortex excitation and balance disorders, cerebrovascular function damage, leading to neurasthenia; damage to cardiovascular system, triggering digestive disorders, affecting endocrine; disturbing people's normal Life, rest, language conversations and daily work and study, distraction and reduce work efficiency. 2, the basic principles of noise control The formation of noise pollution is mainly three factors, namely: sound source, media and receiver. Only when these three exist at the same time can they interfere with the listener. Starting from these three aspects, the purpose of controlling noise is achieved by means of reducing the sound source, limiting the noise propagation, and blocking the reception of noise. In the specific noise control technology, three methods of sound absorption, sound insulation and noise reduction can be adopted. Measures. 2.1 Sound Absorption When sound waves are incident on the surface of an object, part of the sound energy is absorbed by the object and converted into other forms of energy, called sound absorption. The sound absorption performance of the material is expressed by the absorption coefficient, and the larger the sound absorption coefficient, the better the sound absorption performance of the material. The sound absorption properties of the material are related to the nature of the material, the structure and the angle of incidence of the sound waves and the frequency of the sound waves. The sound absorbing mechanism of the porous sound absorbing material is that there are numerous small interpenetrating holes inside the material. When the sound waves are incident on the surface of these materials and then incident into these small pores, the air in the pores is caused to move close to each other. The air on the wall of the hole and the surface of the fiber is not easy to move due to friction and viscous motion resistance, so that the sound energy is converted into heat energy and consumed. Therefore, the sound absorbing material with good performance should be porous, the holes and the holes should penetrate each other, and the through holes should communicate with the outside, so that the sound waves can enter the inside of the material. For a 1000 Hz sound wave, the sound absorption coefficient of a 10 cm thick ultrafine glass wool is 0.87. 2.2 Sound insulation The method used for sound insulation is to close the noise source and control the noise in a small space. This sound insulation structure is called sound insulation cover. When the acoustic wave encounters the shield, a part of the incident acoustic energy is reflected due to the change of the interface characteristic impedance, a part is absorbed, and a part of the acoustic energy penetrates into the shield to continue to propagate. The sound insulation properties of the material can be expressed by the sound transmission coefficient. The smaller the sound transmission coefficient, the less the sound energy that is transmitted through, and the better the sound insulation performance of the material. The sound insulation properties of the material are related to the structure and properties of the sound insulator and the frequency of the incident sound waves. 2.3 Muffling Muffling is to fix the porous sound absorbing material on the inner wall of the airflow passage or fixed in the pipeline in a certain way to achieve the purpose of weakening the aerodynamic noise. The noise reduction can generally reach 10-50 decibels. 3, fan noise control technology Boiler room blower and induced draft fan noise is generally around 90 decibels, because the boiler flue gas temperature is as high as 180 ° C, the use of closed sound insulation will lead to poor heat dissipation, motor temperature is too high, and even burned the motor. Therefore, the process combines noise reduction and energy saving of the fan. Through practice, the comprehensive treatment plan for energy-saving and noise-reduction of boiler fans is as follows: the process layout of the boiler room remains unchanged, the blowers and the induced draft fans are respectively placed in the sound insulation room, and they are connected with the host by the ventilation pipes, at the top of the sound insulation room. Open the air inlet on the upper or wall surface, and install a muffler for the air in the machine room. When the plane is arranged, the blower is close to the side of the boiler room, the air inlet is on the windward side, and the motor is placed in the middle of the airflow passage. When the boiler is running, because the blower generates negative pressure in the sound insulation chamber, a large amount of outdoor fresh air will automatically enter the sound insulation chamber. First, heat exchange with the air blower motor will cause it to cool down, and the indoor temperature will remain at about 50 °C. In this scheme, the noise reduction capability of the sound insulation chamber and the air inlet muffler is relatively large, and the noise reduction effect is easily realized. The blower sends the preheated air to the boiler for combustion, recycling energy, and has certain economic benefits. In order to ensure the treatment effect and the normal operation of the boiler equipment, in the design and construction, according to the specific requirements, considering the sound intensity, sound frequency and other factors of noise, detailed design of sound insulation, sound absorption and ventilation heat dissipation, and detailed processing. The size and thickness of the sound insulation chamber, the type and thickness of the sound absorbing material are calculated. The noise reduction of the intake muffler is generally about 25dB (A). Minimize the noise radiation area and remove unnecessary metal surfaces. The vibration of the control panel is connected by a soft material between the sound source and the sound enclosure and the foundation. The connecting pipe of the blower and the thin-wall steel chimney are the weak links of noise control. The 5cm thick glass fiber cotton is wrapped around the pipe wall, and then tightly welded with steel wire, and then brushed with 2cm thick steel mesh. The glass fiber cotton is fixed on the steel plate to absorb the reverberation noise in the sound insulation chamber. 4, noise reduction and energy saving effect 4.1 Noise reduction effect If the fan noise is 90 decibels, the sound insulation cover of 3mm steel plate, the theoretical sound insulation is 32 decibels. The sound insulation cover is lined with 10cm thick glass wool, and its sound absorption coefficient is 0.87. When the muffler is installed in the intake pipe, the actual sound insulation is TL=32+10 log20.87=30 decibels, so the fan noise is treated: T=90 -30=60 decibel sound pressure level and sound intensity are the objective physical quantities reflecting the sound. The subjective perception of the human body on noise is expressed by loudness: N=2(N-40)/10(Song) The fan loudness before treatment is: N1= 2(90-40)/10=32(Song) The loudness of the fan before treatment is: N2=2(60-40)/10=4(Song) Therefore, the loudness of the equipment before and after the treatment is reduced by 87.5%. There are three aspects: 1 convection heat dissipation of the induced draft fan and the wall of the pipeline, 2 radiating heat of the induced draft fan and the wall of the pipeline, and heat dissipation of the 3 fan motor. In this scheme, the noise reduction capability of the sound insulation chamber and the air inlet muffler is relatively large, and the noise reduction effect is easily realized. The blower sends the preheated air to the boiler for combustion, recycling energy, and has certain economic benefits. In order to ensure the treatment effect and the normal operation of the boiler equipment, in the design and construction, according to the specific requirements, considering the sound intensity, sound frequency and other factors of noise, detailed design of sound insulation, sound absorption and ventilation heat dissipation, and detailed processing. The size and thickness of the sound insulation chamber, the type and thickness of the sound absorbing material are calculated. The noise reduction of the intake muffler is generally about 25dB (A). Minimize the noise radiation area and remove unnecessary metal surfaces. The vibration of the control panel is connected by a soft material between the sound source and the sound enclosure and the foundation. The connecting pipe of the blower and the thin-wall steel chimney are the weak links of noise control. The 5cm thick glass fiber cotton is wrapped around the pipe wall, and then tightly welded with steel wire, and then brushed with 2cm thick steel mesh. The glass fiber cotton is fixed on the steel plate to absorb the reverberation noise in the sound insulation chamber. According to the ventilation engineering principle, the energy-saving noise reduction system can also recover part of the heat. After practice, using boiler fan noise energy-saving and noise-reduction technology, it not only reduces noise pollution, but also protects the living environment of the people, and recycles energy, achieving the unification of economic and environmental benefits.

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