Classification and principle of air conditioner muffler
The muffler is a device that utilizes the principles of sound extraction, reflection, interference interference, etc., and low airflow and airflow noise in the air conditioning system. According to the difference of the principle of noise elimination, it can be divided into resistive, resistant, resonant and composite.
First, the resistance muffler
The resistive muffler uses the sound absorption of the sound absorbing material to silence the sound. The layout is to make the sound absorbing material firmly on the inner wall of the pipe through which the airflow flows, or to form a resistive muffler in the pipe or the casing according to the affirmative principle, and the sound absorbing material can roughly capture the sound energy department incident thereon. The sonic energy can be extracted because of the porosity and looseness of the sound absorbing material. When sound waves enter the pores, the atmosphere and material in the pores cause tiny vibrations, which are canceled by the friction and viscous resistance, which causes a considerable part of the sound energy to be converted into heat energy.
It has better results for dealing with high frequency and intermediate frequency noise, but it has poor performance for low frequency noise.
1. Tube type muffler: The tube type muffler is the most simple muffler. It only attaches a layer of sound absorbing material to the inner circumference of the pipe wall, so it is also called "pipe liner". It is characterized by easy production and low resistance, but it is only used for smaller air ducts, and the diameter is usually not more than 400mm. The tubular muffler has a positive muffling effect only for medium and high frequency sound absorption. The low frequency performance is very poor.
2. Chip and pattern muffler: The tube muffler has poor performance for low frequency, and it is easy to pass through the medium and high rate noise. When the pipe section area is large, it will affect the noise cancellation result of high frequency noise. Since the high-frequency sound wave (short wavelength) is transmitted in a narrow beam in the tube, when the pipe area is large, the sound wave and the sound-absorbing material of the pipe wall are knocked out, so that the sound-dissipation amount of the high-frequency sound is eliminated, so that the air pipe with a larger cross-section can be The section is divided into several grids, which are the chip and pattern muffler. The chip muffler is widely used and the layout is simple. The pattern muffler should have an effective sectional area not less than the cross section of the air duct, so the volume is large, and the size of each grid should be controlled at about 200 mm × 200 mm. The chip gap of the chip muffler is usually in the range of 100~200mm. When the film spacing increases, the noise reduction amount will drop accordingly.
Second, the resonance type muffler
Sound absorption materials generally have low acquisition power for low frequency noise. It is not economical to increase the sound absorption result by increasing the thickness of the sound absorption material. In order to improve the sound absorption result of low frequency noise, a resonance type muffler is usually accepted. The situation of the resonance type muffler is to connect the cavity with the cavity, and the atmosphere column and the atmosphere in the cavity form an elastic resonance system. When the external noise frequency and the natural frequency of the resonance system are small, the small The atmosphere column in the hole resonates and produces intense friction with the hole wall, and the friction can stun the sound energy, thereby reaching the purpose of sound elimination.
The muffler has a strong frequency selectivity, that is, the effective frequency range is narrow, and the usual low frequency noise reduction can produce a large attenuation. The airflow resistance is small, but the layout is too large due to the resonant cavity.
Third, the resistance muffler
The resistant muffler is formed by connecting a tube and a chamber, and the muffler makes a sound reduction effect by causing the sound wave to be reflected back toward the sound source by a sudden change of the cross section of the duct.
The muffler has good muffling results for medium and low noise, and the layout is simple. Because of the unlucky sound absorption material, it is not affected by high temperature and corrosive gas. Eliminating low frequency noise has a positive result. --Marine air conditioning
In order to ensure a positive noise reduction result, the expansion ratio (ratio of large and small sectional areas) of the muffler should be greater than 4. Therefore, applications in places where the construction space of the equipment room is small are limited.
Fourth, the composite muffler
The composite muffler combines the benefits of a resistive and inflated muffler with good noise reduction for low to high frequency noise. The layout is shown in Figure 14.5. For example, the 1.2m long composite muffler can achieve a low-frequency noise reduction of 10~20dB. Others can deal with air-conditioning systems that cannot use fiber-absorbing materials (such as air-conditioning engineering), and micro-perforated mufflers with metal (aluminum, etc.) can be used. Get good results.
Five, other examples of muffler
In addition to the examples of the muffler discussed above, in actual engineering, some air duct components can be properly treated to eliminate noise. In addition, they also have the benefit of saving construction space.
Commonly used muffler components are:
1. Silencer elbow: When the machine room area is narrow or the noise reduction result needs to be improved for the original structure, the silencer elbow can be accepted. There are two types of anechoic elbows. The ordinary anechoic elbow is silenced by the sound absorbing material attached to the inner side. Usually, the inner edge of the elbow is made into a circular arc, and the outer edge is pasted with a sound absorbing material, and the length of the sound absorbing material is not less than 4 times the width of the elbow. Another type of anechoic elbow is called a resonance type anechoic elbow, the outer edge of which receives the perforated plate, the sound absorbing material and the cavity, and the resonance sound absorbing layout is used to improve the ordinary muffling elbow. The problem.
2. Silencing static pressure box: Set the static pressure box with sound absorption material in front of the fan outlet or the atmosphere diffuser, which can stabilize the airflow and eliminate the sound. The muffling amount of the muffler static pressure box is related to the performance of the sound absorbing material, the area of the sound absorbing material in the box, and the area of the outlet side air duct. The muffler static pressure box can also double as a divided air static pressure box.