Patent GB-829012-A (GB)
Title: Improvements in or relating to fluid flow mufflers
IPC: B64F1/26
Filed: 1956-05-07
Abstract: 829,012. Silencing gaseous &c. currents. ANDERSSON & CO. A.B., J. R. May 7, 1956 [May 11, 1955], No. 14102/56. Class 7(2) In a silencer, particularly for suppressing noise in flowing gaseous media, comprising a duct 10 having sound-absorbing walls, the duct is provided with at least one impervious, helically - extending, sound-absorbing partition 13 which, with the interior of the duct, forms one or more separate helically-extending flow passages for the entire fluid flow. As shown in Fig. 1, a core tube 11, having a plain or perforated wall, and provided with transverse partitions and a filling of porous, sound-absorbing material, is disposed coaxially within the duct 10, a strip 13 being wound helically about the tube 11 to define a single fluid flow passage. The duct 10 is perforated, covered with close-mesh wire gauze 23 and surrounded by a tubular casing 21, the space between the casing and duct being divided by partitions 22 into compartments partly or entirely filled with a porous sound-absorbing material; alternatively, the duct is lined with sound-absorbing material. The strip 13, the pitch of which may vary, consists of (a) porous soundabsorbing material, (b) a metal wall covered with sprayed asbestos fibre, (c) a perforated wall 17, Fig. 4, covered with close-mesh wire gauze 18 spaced apart from and on one or both sides of a metal plate 15, the space or spaces between the plate and wall or walls being partly or entirely filled with sound-absorbing material. (d) porous sound-absorbing material 19, Fig. 5, disposed between perforated plates 17 covered with gauze 18, and (e) two spaced apart and parallel walls of sintered metallic material. In modifications, (a) the tube 11 is omitted, and (b) the internal surface of the duct is sprayed with asbestos fibre and there is a helically twisted strip which divides the duct into two, parallel, fluid flow passages; alternatively (a) the duct 25, Fig. 10, has an internal, coaxially disposed, perforated tube 28 the external surface of which is covered with wire gauze 29, the space between the tube and duct being partly or entirely filled with soundabsorbing material or (b) a sound-absorbing tube of sintered metallic material, the space between the tube and duct being void or filled with a porous sound-absorbing material. In another modification, a number of silencer units, Fig. 12, are connected in parallel, each unit comprising a pile of sections 32, Fig. 13, disposed in a vertical pocket 33 square in cross-section; a number of such pockets are formed in a casing 34 of reinforced concrete. Each section 32 comprises a perforated tube 35 secured to and extending between spaced, parallel plates 36, 37 interconnected by angle pieces 38 between which is disposed wire gauze 139. Between the latter and the tube 35 is a filling of glass wool. A helically twisted partition 39 within the tube is formed by spaced, parallel and perforated metal plates 40, covered on the inner faces thereof with gauze, and a filling of glass wool. In a further modification, a nozzle 45, Fig. 15, surrounding a tube 46 is associated in an air-tight manner with the tail portion 44 of the jet nozzle of an aircraft, the exhaust stream from the nozzle being mixed with cooling air passing through an annular passage 47 and then flowing through a conically-divergent diffuser 48 to a silencer 49 provided with helical strips 26, 26<SP>1</SP> intersecting each other at right angles to divide the interior of the duct into four gas-flow passages. A flow diverter 50 directs the gases upwardly. The silencing device may be applied to a ventilating system wherein air is propelled by a high-speed blower.