Mufflers And Silencers

No distinction exists between mufflers and silencers. They are often used interchangeably. They are in effect acoustic filters and are used to reduce fluid flow noise. Figure 6.7.8 shows six basic types of silencers. The devices can be classified into:

Dissipative or absorptive silencers whose noise reduction is determined by fibrous or porous sound absorbing liners. Where hot gases are handled, the absorbent may be metal or even ceramic. These devices are good for high-frequency sounds. Reactive silencers whose noise reduction is determined mainly by geometry. These devices are shaped to reflect or expand the sound waves with resultant self-destruction. Reactive silencers are used for low-frequency applications.

Figure 6.7.9 shows a typical muffler that is designed to attenuate sound waves with minimal back pressure. It includes a cylindrical-type unit. The outer portion of the through-pipe conduit contains a number of cavities where noise suppression occurs. A porous packing is sometimes used to increase efficiency. Airflow to the cavities is regulated by the size and number of holes from the center section. Mufflers are effective for high- and middle-frequency noise control.

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