ASA 125th Meeting Ottawa 1993 May

2pNS7. Micro-perforated sheet metal and its application to silencer design.

Mei Q. Wu

6682 Ganymede Rd., Mississauga, ON L5N 6R1, Canada

Micro-perforated sheet metal is used to make no-media silencers, i.e., silencers without fiberglass, mineral wool, or any kinds of fibrous filling materials. The advantages of no-media silencers are that they will not release small fibers to pollute the air and they will not be contaminated by the moisture and bacteria in the air. No-media silencers are extensively used in the air-handling system ducts of hospitals, pharmaceutical factories, and chemical laboratories. This paper summarizes the research work of developing a theory to predict the performance of no-media silencers. The theory is based on Maa's micro-perforation theory. Two modifications have been made to Maa's original theory so it can be applied to air duct silencer design. One of the modifications is to introduce the effect of grazing incident sound wave, and the other is to introduce the effect of air flow. Based on the modified theory, a computer program was developed to calculate the insertion loss and the pressure drop of a silencer. The calculated results were compared with test results. The comparison indicated a reasonably good agreement between the theoretical prediction and the test results. [Work supported by BVA Systems.]