FR2785360A1 - Method of silencing fluid flows in pipes involves using diffuser with perforated and non-perforated sections along its length - Google Patents

Abstract

The method of silencing a fluid flow in a pipe involves using a diffuser with a frontal section, which is non-perforated, a perforated middle section (10) and a downstream non-perforated section (11). The diffuser has a cylindrical shroud, which is concentric

Description

The present invention relates to a device for modifying the
flow characteristics of a fluid to reduce the sound production which is due to it
associated.

The setting in motion of a fluid for industrial applications
is in fact accompanied by sound production, notably of aerodynamic origin
linked: in the case of the existence of a pipeline with discontinuities of flow
such as sudden changes in section, obstacles, elbows, pipe junctions,
existence of a control valve; in the case of venting of pressurized gas (discharge purge of
boiler, gas pressure relief vent, tank safety valve
pressure) when the fluid expands.

In this regard, it is clear that this sound production can be due to its
impact causing discomfort for residents or hearing trauma for
workers working on such installations.

The proposed device overcomes this drawback. It allows indeed a
fractionation of the flow of a fluid whose sound production is to be reduced due to
its flow by passage through a network of perforated diffusers
specially designed for a reduction in overall sound power
generated with modification of the spectral distribution of the acoustic power
residual by depletion in low frequencies.

According to the particular embodiments: 'this network is single-stage (1 single envelope on which the
orifices) this network consists of one (if single-stage) or several (if multi-stage)
diffusers of cylindrical shape in a nonlimiting exemplary embodiment the openings of the diffuser (s) can vary in number, position,
geometry.

The accompanying drawings illustrate the invention. Figure 1 shows in section a device
with single-stage diffuser. Figure 2 shows in section a device with multi-stage diffuser.

With reference to these drawings, the device comprises a connecting piece
metallic (1) composed of a perforated plate in its center with an opening of
characteristic dimension (D) adapted in shape and size to the existing network upstream at
equip (tank, pipeline). On this connection piece is linked
perpendicular to the opening, according to a first characteristic, a mono network
stage or multi-stage of diffusers made up of perforated surfaces (2) with openings
varying in number, position and geometry.

In this regard, the diffuser is typically of elongated shape and: an upstream portion (9) non-perforated, of length L1, substantially less than the
dimension D of a perforated middle part (10), of length L2 substantially greater than the
dimension D of a non-perforated downstream portion (11) of length L3 substantially less than the
dimension D of a closed end (12) opposite the inlet, of dimension
roughly equivalent to D.

The fluid entering the network passes through the upstream part (9), the middle part (10),
the downstream part (11) of the diffuser, is reflected on the closed end (12), is returned in
largely towards the middle part (10) and enters the lateral orifices.

In addition, and typically, the casing (in the case of a mono diffuser
stage) or the casings (in the case of a mufti-stage diffuser) is (are) cylindrical
(s), and concentric in the case of a multi-stage diffuser.

The number of stages, as well as the quantity and dimension, geometry, mean center distance and
distribution of the orifices, are specially studied to obtain in each section
characteristic of the silencer (4) (5) (6), but also upstream (7) and downstream (8) a
particular distribution of the thermodynamic characteristics of the fluid (pressure,
density, temperature, speed, acoustic impedance, flow) allowing the adaptation of
flow regimes at each characteristic section of the silencer (4),
(5), (6), but also upstream (7) and downstream (8) favorable to a decrease in
very high proportions of the overall sound power generated and at a
modification of the spectral composition of the residual acoustic power with
significant depletion in the lowest frequencies.

The sizing of the orifices is carried out so: 'for low values of the fluid flow, the presence of the proposed device does not
not disturb the flow, regulated by the part of the network located upstream, one of which
limiting sound production can be easily achieved by means of an ineffective silencer at low frequencies which are difficult to attenuate, integrated into the proposed device (see below) or dissociated. for higher values of the fluid flow: the network regulation is
performed at the proposed device, which has the effect of:
to significantly reduce the sound production of the part of the
network located upstream of the proposed system
to relocate sound production to the level of the proposed device which,
by design, greatly reduces the residual acoustic power by
considerably depleting it at low frequencies, this residual power
can be easily treated using a silencer with no bass efficiency
frequencies difficult to attenuate (integrated into the proposed device: see below) or
dissociated.

 According to a second characteristic, the device also includes an outer casing (3).

According to the particular embodiments: 'this envelope is full and coated or not with absorbent materials (foam
of thickness substantially greater than 10 mm and of substantially lower density
at 200 kg / m3) on its inner face allowing part of the
residual power conveyed by the fluid downstream of the perforation diffusers
multiple.

The device according to the invention is mainly intended: to be inserted in a circuit downstream of zones comprising discontinuities
flow causing significant sound production such as sudden changes in section of a pipe, obstacles, elbow, pipe junction, control valve; '' to be used to equip decompression vents in the context of expansion
(venting for example) of pressurized gases such as purges of
boiler discharge, gas pressure relief vent, safety valve
a pressure tank.

Claims (1)

CLAIMS I-DEVICE FOR REDUCING PRODUCTION  SOUND RELATED TO THE FLOW OF A FLUID BY PASSAGE  - downstream of a connecting piece (1)  allowing connection with a network located upstream  -through a network of perforated diffusers (2) including  the number of stages as well as the quantity, dimension, geometry and distribution of the orifices are specially studied to obtain in each characteristic section of the silencer (4) (5) (6), but also upstream (7) and downstream of that because of its presence, a particular spatial distribution of the thermodynamic characteristics of the fluid (pressure, density, temperature, speed, acoustic impedance, flow) favorable to a reduction in very large proportions, of the overall acoustic power generated and to a modification of the spectral composition of the residual acoustic power with significant depletion at the lowest frequencies, below 16,000 Hz,  this diffuser being typically of elongated shape and: an upstream portion (9) not perforated, of length L1, substantially less than the  dimension of a perforated middle part (10), of length L2 substantially greater than the  dimension of an unperforated downstream part (11) of length L3 substantially less than the  dimension D of a closed end (12) opposite the inlet, of dimension  roughly equivalent to D.  so that  the fluid entering the network passes through the upstream part (9), the middle part (10), the downstream part (11) of the diffuser, is reflected on the closed end (12), is largely returned to the middle part and enters the side holes and that  the fluid is downstream of the perforated diffusers channeled by an envelope (3) which can if necessary be coated with an absorbent in order to obtain superior performance in terms of loss by insertion. DEVICE ACCORDING TO CLAIM 1  Characterized in that the silencer is installed upstream of a sound trap of another type with which it is associated in a separate envelope or not for increased performance.