WO2004070174A1

WO2004070174A1 - Sound absorber for hot gas

Info

Publication number: WO2004070174A1
Application number: PCT/EP2004/001026
Authority: WO
Inventors: Wolfgang Riese
Original assignee: Wolfgang Riese
Priority date: 2003-02-04
Filing date: 2004-02-04
Publication date: 2004-08-19
Also published as: DE20301721U1

Abstract

Disclosed is a sound absorber for hot gas penetrating the sound absorber at a certain operating temperature lying within a predefined temperature range. Said sound absorber comprises a flow duct for the gas, which is delimited by interior walls. According to the invention, at least one wall area of the inner wall is provided with at least one layer made of a thermoplastic material, e.g. PTFE, the plastication temperature of which lies within the predefined temperature range, preferably between 200° and 300° C. Sound absorption is rendered particularly effective by adjusting the softening temperature of the plastic material to the operating temperature of the gas.

Description

Hot gas silencer

The invention relates to a muffler for hot gas which flows through the muffler with an operating temperature in a predetermined temperature range. The silencer has at least one flow channel for the gas and at least one wall delimiting the flow channel.

A typical field of application of the invention, to which the invention is not restricted, is the sound attenuation on compressors, especially screw compressors, for generating compressed air. The compressed air emerging on the pressure side of a screw compressor typically has a temperature in the range from 200 ° C to 300 ° C, usually between 220 ° C and 280 ° C, in continuous operation. From DE 100 11 023 AI a silencer of a particularly flat box construction is known, which is particularly suitable for attachment to the pressure side of screw compressors and has a good damping effect for the noise occurring on the pressure side of a screw compressor, especially for the high-frequency noise components. The present invention is particularly suitable for use with a silencer of this known type, but is not limited to this type.

The invention has for its object to provide a silencer that has a good damping effect, in particular with regard to the high-frequency noise components, for a hot gas with a predetermined operating temperature, such as Compressed air generated by a screw compressor.

The achievement of the object is specified in claim 1. The subclaims relate to further advantageous features of the invention. It has surprisingly been found that a thermoplastic material which is in the softened or plasticized state at the operating temperature of the hot gas is outstandingly suitable for absorbing high-frequency sound waves in the gas and absorbing them in an energy-consuming manner. An embodiment is explained in more detail with reference to the drawings. It shows:

1 is a plan view of the muffler of the type known from DE 100 11 023 AI,

Fig. 2 is a side view of the muffler

Fig. 3 is a plan view of the muffler similar to Fig. 1, but with the top wall removed

4 shows a section through the muffler along the line A-A of FIG. 1st

5 and 6 in the same representation as Fig. 3 and Fig. 4 shows a modified embodiment of the silencer.

Fig. 7 in the same representation as Fig. 4, an embodiment of the silencer designed according to the present invention.

8 shows a section along line B-B of FIG. 7.

First, the type of silencer known from DE 100 11 023 AI is described with reference to FIGS. 1 to 6.

The muffler shown consists of a housing 1 of flat box shape with a bottom wall 3, a top wall 5 and peripheral walls 7. In the bottom wall, an inlet opening 9 is provided for compressed air supplied by the compressor. In the top wall 5 there is the outlet opening 11 for the sound-damped compressed air, namely laterally offset from the inlet opening 9 near a side wall of the housing 1. In the plan view, the housing 1 is essentially rectangular, apart from an indentation 13 provided next to the outlet opening 11, which creates space for the attachment of a pressure relief valve 14.

As shown, the outlet opening 11 preferably has a substantially larger cross section than the inlet opening 9. In particular, the diameter of the outlet opening 11 can be more than twice the diameter of the inlet opening 9. The housing 1 has the shape of a flat box or a disk. This means that the height of the housing is less than half and preferably less than a third of the width and / or length of the housing.

The interior of the housing 1 enclosed by the bottom wall 3, the top wall 5 and the peripheral walls 7 is divided into two flat chambers by a partition wall 15 running parallel to the bottom wall 3 and top wall 5, namely an inlet chamber 17 and an outlet chamber 19. The partition wall 15 has a passage area 21, which is formed by numerous closely arranged small openings or perforations, which connect the inlet chamber 17 with the outlet chamber 19. The passage region 21 is laterally offset from the inlet opening 9 and the outlet opening 11 on the side of the inlet opening 9 opposite to the outlet opening 11. The partition 15 is impermeable outside the passage region 21. As a result, the compressed air entering the inlet opening 9, which impinges on the impermeable part of the partition wall 15, is forced into a flow path which runs from the inlet opening 9 parallel to the bottom wall 3 and partition wall 15 through the inlet chamber 17 to the passage area 21, then finely distributed through the small openings of the passage area 21 into the outlet chamber 19, and then along the outlet chamber 19 parallel to the top wall 5 and bottom wall 3 to the outlet opening 11 and exits from this, as indicated in Fig. 4 by the arrows.

The diameter of the small openings forming the passage area 21 is preferably chosen to be as small as possible in order to achieve the finest possible division of the air flow in order to achieve effective sound absorption. On the other hand, the openings should not be so small that they are susceptible to clogging by dust particles or the like carried in the compressed air. The diameter of the small openings of the passage area 21 is disadvantageously in the range from 1 to 10 mm, preferably it is approximately 5 mm. The number of small openings forming the passage area 21 is preferably selected in relation to the diameter of the openings such that the sum of the cross sections of all openings, ie the total diameter let cross section of the passage region 21, equal or larger, preferably at least twice as large as the cross section of the inlet opening 9.

Furthermore, as can be seen from FIG. 4, the partition 15 is arranged in such a way that the clear height of the outlet chamber 19 is significantly greater than the clear height of the inlet chamber 17. For example, the clear height of the outlet chamber 19 can be 1.8 to 2.2 -fold, preferably twice the inside height of the inlet chamber 17. As a result of these design measures, the compressed air finds an increasingly larger flow cross-section on its way from the inlet opening 9 through the inlet chamber 17, the passage area 21 and the outlet chamber 19 to the outlet opening 9.

The part of the inlet chamber 17 to the right of the inlet opening 9 in the drawings, designated 17a in FIG. 4, forms a buffer space which does not lie in the flow path of the compressed air from the inlet opening 9 to the outlet opening 11 indicated by the arrows, but buffer pressure peaks and can contribute to internal sound reflections.

Preferably, the housing 1 of the muffler is constructed so that it is composed of three superimposed, generally plate-shaped molded parts, namely a base plate 23 forming the bottom wall 3, an intermediate part 25, which comprises the partition wall 15 and most of the peripheral walls 7, and a cover plate 27, the cover wall 5 with the outlet opening 11 comprises. The three molded parts 23, 25 and 27 are preferably formed from aluminum in a sand casting process. They lie one above the other at horizontal connecting joints and are held together by screws 29 which are provided around the circumference of the housing in the region of the circumferential walls 7. In order to additionally support the bottom wall 3, top wall 5 and partition wall 15, four columns 31 are provided around the inlet opening 9, which, for example, can be molded onto the partition wall 15 and through which connecting screws (not shown) can also extend. The dimensioning of the muffler according to the invention depends on the compressed air volume flow generated by the respective compressor type and required by the downstream consumer, the diameter of the outlet opening 11 being primarily the size which must be adapted to the existing conditions. For a given diameter of the outlet opening 11, the clear height of the inlet chamber 17 is advantageously 0.2 to 0.3 times, preferably 0.25 times this diameter. The respective specific dimensioning should also be chosen from the point of view that the flow resistance of the muffler should be as low as possible if the sound insulation is aimed for.

It has been found that the described construction of the muffler enables an effective reduction in the outlet noise level of a screw compressor, with a reduction in the noise level of, for example, 110 dB to the range of 80 dB being possible. Furthermore, due to its flat, space-saving design, the silencer according to the invention is particularly suitable for use with screw compressors which have to be installed in limited space, for example on silo vehicles. The silencer according to the invention can be placed directly on the compressor in the case of screw compressors of a modern design, the inlet opening 9 of the silencer being able to connect directly to the pressure outlet of the compressor. The muffler according to the invention consists of corrosion-resistant material, preferably cast aluminum, aluminum cast in a sand mold is more advantageous than die-cast because of the low density and the resulting higher insulation value. It is completely free of loosely inserted insulation materials such as glass wool, mineral wool, metal mesh or the like, as are used in conventional silencers. The muffler according to the invention is therefore particularly suitable for use with screw compressors for the pneumatic conveyance of sensitive goods, since there is no risk of contamination of the conveyed goods by corrosion particles or particles of loose insulation materials. The weight of the silencer according to the invention is also lower than the usual silencer. It is assumed, without this assumption being necessary or binding or restrictive for the explanation of the invention, that the ascertained excellent sound-damping effect of the muffler according to the invention is largely based on the reflections on the inner surfaces which extend perpendicularly to the air propagation path and deflect them of the silencer occur and are directed in the opposite direction of flow. These reflections in connection with the changing flow velocities in the individual chamber areas caused by the different flow cross-sections lead to a broadband effective suppression of sound resonances and reduction of sound emissions across the entire frequency range.

5 and 6 show a modified embodiment of the muffler according to the invention, the modification being aimed at promoting the occurrence of the reflections described above. This is done through one or more reflection walls which extend through the outlet chamber 19 transversely to the flow path of the air, each reflection wall leaving one or more passage openings for the air.

In the embodiment shown in FIGS. 5 and 6, the air entering the outlet chamber 19 in the passage area 21 first encounters a first reflection wall 35 as it flows to the outlet opening 11, which wall wall leaves two passage openings 39 exposed at both ends. In the flow direction behind the first reflection wall 35 there is a second reflection wall 37, which is interrupted approximately in the middle by a passage opening 41.

It is important that the passage openings 39 of the first reflection wall 35 and the at least one passage opening 41 of the second reflection wall 37 are offset from one another, so that a tortuous flow path is forced on the air. The flow cross section of the flow openings 39 of the first reflection wall 35 and / or the flow opening 41 of the second reflection wall 37 is preferably approximately the same size or larger than the cross section of the inlet opening 9. The contraction of the muffler described above is known per se. In the following, it serves as a non-restrictive embodiment to explain the design of the silencer according to the present invention, reference being made to FIGS. 7 and 8. In Figs. 7 and 8, parts corresponding to the parts shown in Figs. 1 to 6 are given the same reference numerals.

The muffler shown in FIGS. 7 and 8 differs from that shown in FIGS. 1 to 4 in the following: Both the inflow opening 9 and the passage area 21 of the partition wall 15 are opposite each one on the underside of the intermediate plate 15 and the top wall 5 Layer 43 or 44 made of a thermoplastic, preferably PTFE. Each PTFE layer 43 or 44 preferably consists of a stack of thin PTFE plates, e.g. 10 plates each with a wall thickness of 1 mm. In the area where the PTFE layer 43 or 44 is attached, the thickness of the intermediate plate 15 or the cover plate 5 is preferably reduced, so that a recess for accommodating the PTFE plates 43 or 44 is formed.

A perforated plate 42 or 45 is preferably arranged in front of each of the PTFE layers 43 or 44. Each perforated plate 42 or 45 is preferably made of metal, that is to say is a perforated plate. Each perforated plate preferably has a multiplicity of holes with a diameter of approximately 5 mm. For example, each perforated plate can consist of V4A steel with a thickness of 1.5 mm or from an Al-Si-Mg alloy with a thickness of 3 mm.

The perforated plates 42 and 45 and PTFE plates 43 and 44 form a solid and indestructible unit with the material of the partition wall 15 or top wall 5 in the manner of a sandwich construction. The perforated plates 42 and 45 and PTFE plates 43 and 44 can also be mechanically fastened to the partition 15 or top wall 5 by screws (not shown).

If the silencer is arranged on the compressed air outlet side of a screw compressor, compressed air flows through it, the operating temperature of which is between 220 ° C and 280 ° C and is reached after a few minutes of operation. In this The temperature range becomes PTFE thermoplastic, but essentially does not lose its consistency. Experiments have shown that the transition of the PTFE to the thermoplastic state is excellently suited to absorbing and reducing high-frequency sound waves.

Wall layers made of plastic, which becomes thermoplastic at operating temperature, can also be applied in other areas of the walls delimiting the flow path of the gas. The attachment of the PTFE layers 43 and 44 shown in FIGS. 7 and 8 in the regions of the intermediate wall 15 or cover wall 5 opposite the inflow opening 9 or the throughflow openings 21, which represent impact and deflection surfaces for the compressed air, has, however, been found proven to be particularly effective because here the impact and the deflection of the hot compressed air result in a particularly intensive interaction with the thermoplastic plastic.

In a modification of the described embodiment, PTFE layers can also be applied to all inner surfaces of the muffler delimiting the flow path. It is particularly effective to attach PTFE layers to reflection walls which extend transversely to the direction of flow of the gas, for example to the reflection walls 35 and 37 shown in FIG. 5, against which the gas flows.

The coating of inner surfaces of the muffler with a plastic, such as PTFE, which softens at the operating temperature of the hot gas, can be carried out according to the invention in any muffler construction and is not restricted to the contraction described in FIGS. 1 to 6. In particular, the muffler does not need to have an intermediate wall 15 and no numerous flow openings 21. The construction can be modified so that the flow path of the gas has a cross section that extends over the entire clear height between the bottom wall 3 and the top wall 5.

Claims

claims

1. Muffler for hot gas which flows through the muffler during operation with an operating temperature in a predetermined temperature range, the muffler having an at least one flow channel for the gas-limiting inner wall, characterized in that the inner wall (5, 15) has at least one Has wall area which is provided with at least one layer (43, 44) made of a thermoplastic, the plasticization temperature of which is in the predetermined temperature range.

2. Silencer according to claim 1, characterized in that the plasticizing temperature of the plastic is in the temperature range between 200 ° C and 300 ° C.

3. Silencer according to spoke 1 or 2, characterized in that the layer (43, 44) made of plastic is a perforated plate (42, 45) upstream.

4. Silencer according to one of claims 1 to 3, characterized in that at least one wall region having the plastic layer is located in a baffle or deflecting wall (5, 15) on which the gas flowing in the flow channel impinges.

5. Silencer according to one of claims 1 to 4, characterized in that the plastic layer (43, 44) consists of PTFE.

6. Silencer according to claim 5, characterized in that the layer (43, 44) consists of a stack of PTFE plates.