Device For Attenuating The Noise Generated By The Expansion Of Gases Into The Atmosphere

Abstract

A device for attenuating the noise generated by the expansion into the atmosphere of the gases an industrial installation. The device utilizes an exterior type Coanda ejector, the body of which has an annular cavity followed by a slot and further by an outer curving profile and a converging cone; the ejector lies in an attenuator ending in an exhaust cone.

Description

FIELD OF THE INVENTION

This invention relates to a device for attenuating the noise generated by the expansion of gases into the atmosphere, especially in industrial plants.

BACKGROUND OF THE INVENTION

There are known dampers with depression ribs, which attenuate noise by diffraction of the sound waves traversing depressive networks. The absorbtion of waves which have undergone diffraction is attained by the sound-absorbing coating provided on the ribs and by intensifying the turbulent mixing of the jets leaving the depression networks, with the surrounding air within a Coanda effect space.

These dampers manifest a strong attenuation of noise within a broad frequency range but have the disadvantage of large overall dimensions and of considerable complexity.

Other devices for noise attenuation have a converging inlet nozzle for the ejected air connected to an inlet attenuator, an inner-type Coanda ejector followed by a diffuser, an outlet attenuator and an exhaust nozzle. Opposite the converging inlet nozzle formed by a slot network and a converging channel, a damping screen is disposed at an adequate distance. The inner type Coanda ejector is provided with an annular cavity into which the exhaust gases flow; these gases also traverse an annular slot and adhere in form of an annular jet to the Coanda ejector wall, and bend along a neck towards the lower part of the diffuser, outlet attenuator and exhaust nozzle. The elements of the damper are provided with sound-absorbing walls or surfaces.

This latter device is of difficult construction because of the annular laminating chamber, and is of undesirable the a large size and weight.

SUMMARY OF THE INVENTION

The device according to this invention eliminates the disadvantages mentioned above in that it is composed of an outer type Coanda ejector consisting into of a support, a body formed with an annular cavity and a slot, an outer profile and a cone, the ejector being placed inside an active attenuator, composed of two sections fastened to one another and having the inner walls lined with sound-absorbing material, the attenuator being continued by a widening exhaust nozzle. The gases which are to be vented into the atmosphere are supplied by a pipe with sound-absorbing material-lined walls upon the same distance as the lower section of the active structure attenuator. The gases entering the nozzle annular cavity traverse the slot as a thin annular jet adhering to and bending to conform to the outer profile wall and the cone of the nozzle, causing a violent induction of the ambient air from an upstream location proximal to a damping screen provided by the gradual increase of the cross section of the discharge nozzle.

DESCRIPTION OF THE DRAWING

The sole FIGURE of the drawing is a longitudinal section through the drawing showing a longitudinal section of the device.

SPECIFIC DESCRIPTION

The device according to this invention is composed of an outer profile upwardly tapered Coanda ejector 1, an active tubular attenuator formed by two axially aligned continuous sections 2 and 3, an upwardly frustoconically divergent exhaust nozzle 4, a damping screen 5 at the lower intake end, which functions to limit the propagation of noise and forms part of a support 6 of the device.

The Coanda ejector 1 is formed by a central support 7, a body 8 provided at the outside with an outwardly upwardly bulging Coanda profile 9 and a cone 10.

The ejector is provided with an annular cavity a, formed out of two halves, in this case the first half being realized inside the body 8 and the second half by an outer groove of the support 7.

The annular cavity a is continued into the slot f opening outwardly adjacent the Coanda outer profile 9.

The cone 10 and the upper section 3 of the active structure attenuator form a nozzle j of increasing flow section, which is extended by the exhaust nozzle 4, the shape of which is determined depending upon the geometrical characteristics of the ejector and the parameters of the expanding gas.

The attenuator formed by the sections 2 and 3 have a sound-absorbing coating.

For supplying the fluid to be exhausted, the device is provided with a pipe 11 adequately acoustically treated (i.e., surrounded by acoustic insulation) over the length thereof within the section 2 of the active attenuator, the pipe 11 forming with the ejector 1 the central part of the device.

The gas expansion noise attenuating device according to this invention works in the following way:

The gases which are to be vented into the atmosphere are led by way of the pipe 11, into the annular cavity a of the outer profile Coanda ejector 1 and from there they pass through the circular slot f as a thin annular jet.

Due to the Coanda effect, the thin annular gas jet adheres to the wall 9 of the exterior type Coanda nozzle, bending therealong and generating a violent induction of the upstream air (arrow above screen 5).

In the case of hot gases, by mixing up with the incoming air they are cooled. The gas mixture, in continuing to flow between the walls of the attenuator section 3 and the cone 10 are continually slowed due to the gradual increase of the transverse flow across section. This slowing down continues also inside the nozzle 4 for to the same reason.

The flowing of the gas through the circular slot f causes the structural modification of the noise created by the jet, by moving the acoustic spectrum into the domain of the high and of the very high frequencies, in simultaneously modifying the directivity of the noise created by the jet by way of directing its predominant components towards the sound-absorbing layers of the sections 2 and 3 forming the active attenuator. The attenuation of the jet with the frequencies thus modified is easily done by the active structure of the sections 3 and 4.

Likewise, because of the strong depression existing upstream from the ejector slot f, the propagation of the jet generated acoustic waves in that direction is rendered more difficult

Because downstream from the slot f the jet velocity is continually throttled to the outlet, the discharge of the mixture into the atmosphere is done practically noiselesly.

Claims

We claim:

1. A device for attenuating the noise generated upon expansion of a gas into the atmosphere, comprising:

a duct lined with sound-absorbing material and having an inlet end open to the atmosphere and an outlet end opposite said inlet end;

a body in said duct between said ends and defining a constriction therein, said body having an outwardly bulging portion turned toward said inlet end and curving complexly toward the inner wall of said duct in the direction of said outlet end, and a tapering portion converging toward said outlet end and merging with the surface of said bulging portion, said tapering portion defining with said wall of said duct a progressively increasing flow cross-section in the direction of said outlet end, and means forming an annular outwardly open slot immediately adjacent said bulging portion for distributing the expandable gas onto the surfaces of said portions for Coanda flow therealong; and

means communicating with said slot for delivering said gas thereto.

2. The device defined in claim 2 further comprising an outwardly diverging discharge nozzle lined with sound-absorbing material and connected to said duct at said outlet end, and a sound-absorbing screen affixed to said duct and spaced from said inlet end thereof while extending transversely to said duct.

3. The device defined in claim 2 wherein said means communicating with said slot includes a pipe extending axially through said duct between said inlet end and said slot, said device further comprising a sheath of sound-absorbing material around said pipe in said duct.

4. The device defined in claim 3 wherein said duct is provided in at least two axially aligned and interconnected tubular sections.