GB694370A - A device for silencing sound in a gaseous medium - Google Patents

Abstract

694,370. Silencing gaseous currents. AKTIEBOLAGET LJUNGSTROMS ANGTURBIN. Aug. 28th, 1950 [Sept. 2, 1949], No. 21210/50 Class 7 (ii). In a device for silencing sound in a gaseous medium comprising a plurality of chambers having mainly parallel sides and closed at one end, such as tubes 2, and in direct communication with an annular channel of flow for the gaseous medium surrounding the tubes 2, and the longitudinal axes of the tubes being parallel to the longitudinal axis of the channel, the lengths of the tubes are so adapted that the natural frequencies of oscillation of the tubes coincide wholly or partially with the frequencies of the oscillating gaseous medium. A circular plate 1 has a flange 3 by which it is secured to a conical casing 7, whilst the.nested tubes 2 extend from the plate 1 into the casing 7, the tube of smallest diameter having the greatest axial length; the channels formed between the tubes 2 are of equal cross-section. The apparatus can be used as an intake or exhaust silencer, the air or other gaseous medium entering or leaving the silencer through an annular opening 9 between the flange 3 and the casing 7 and flow through the annular space between the casing and the tubes 2, which latter space is about twice the cross-section of the channels between the tubes and is of approximately constant area throughout its length. In a modification, the conical casing is perforated and surrounded by porous sound-absorbing material, such as asbestos or glass wool. In a further modification, the silencers of the kind illustrated in Fig. 1, are arranged back-to-back upon a common circular plate, the two conical casing parts being separated by a cylindrical portion. In another modification, a bi-conical casing covered with sound absorbing material houses a conical plate to which the tubes are secured. The radial depth of the annular space from any open end of a tube is small compared to the length of the tube; the free ends of the latter may be streamlined. The tubes may form a series having lengths of 1, ¢, 1/3, “, and so on where 1 corresponds to “ of the wave length of the fundamental tone in the medium to be damped. Parallel pipes or. cells may replace the nested tubes and the plate upon which the tubes are mounted may be carried by the surrounding housing through the intermediary of sound-insulating members.