Abstract: A fluid discharge silencer for steam or other vapors or gases (with or without entrained solids or liquids) has an expansion chamber into which the fluid is passed through an inlet duct which discharges the fluid over an extended region of the chamber, flow deflector means in the chamber gradually redirecting the flow of gas from the inlet duct to change the direction of flow and to permit the gas phase components of the fluid to expand; the expansion chamber has an outlet which in use is connected to a silencer such as a parallel splitter silencer for further attenuating noise in the discharge flow. The inlet duct can be an elongated pipe having a longitudinal discharge aperture arrangement discharging the fluid into a trough-like redirecting structure which removes entrained components and redirects the flow.

Abstract: Apparatus for attentuating noise emitted from an inlet port to a centrifugal fan comprises a panel member which is mounted in spaced confronting relationship to the inlet port and includes a rigid backing member, a facing mounted in spaced disposition from the rigid backing member, partitions dividing the space between the rigid backing member and the facing into a plurality of cavities, and acoustic infill in the cavities. The facing has a plurality of perforation zones, and is formed in each perforation zone with small perforations whereby the facing is rendered acoustically permeable over a limited area only. One wall of each cavity includes a perforation zone of the facing, whereby the cavities constitute Helmholtz absorption cavities. The facing is adapted to face the inlet port and transmit noise for attenuation in the cavities.

Abstract: A centrifugal fan is treated acoustically by the provision of tuned noise absorption cavities preferably including absorbent infill between an acoustically permeable scroll and casing of the fan. Alternatively, or in addition an acoustically absorbent panel structure is provided in spaced confronting relationship with the inlet port of the fan. The panel structure has an acoustically permeable facing spaced from a rigid backing and the space may be divided into noise absorption cavities and specifically Helmholtz type absorption cavities, the absorption bands of which are broadened by including acoustic infill. It is most advantageous to provide a multiplicity of Helmholtz absorption cavities tuned to respective different center frequencies of their acoustic absorption bands.