CENTRIFUGAL COMPRESSOR

Abstract

A centrifugal compressor includes one or more impellers, a casing which covers the one or more impellers, and a silencer. The casing includes a radial passage which guides a gas flowing out from a final stage impeller to a radially outer side, and an outlet scroll passage which communicates the radial passage with an outlet. The silencer includes a perforated plate in which a plurality of acoustic holes are formed, and a space forming body which forms an acoustic space connected to the plurality of acoustic holes. A first surface of the silencer opposite to a surface of the perforated plate defining the acoustic space forms at least part of an inner surface of the casing which defines the outlet scroll passage.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a centrifugal compressor.

Priority is claimed on Japanese Patent Application No. 2018-246653, filed on Dec. 28, 2018, the content of which is incorporated herein by reference.

Description of Related Art

A centrifugal compressor includes one or more impellers which send gas outward in a radial direction by rotation about an axis, and a casing which covers the one or more impellers.

In United States Patent Application, Publication No. 2002/0079158, a centrifugal compressor including a silencer to reduce noise emitted from a centrifugal compressor is disclosed. The centrifugal compressor of Patent Document 1 includes a plurality of impellers which send gas outward in the radial direction by rotation about an axis, a casing which covers the plurality of impellers, and the above-described silencer. The plurality of impellers are arranged in an axial direction of the impellers. An inlet which introduces gas into the inside, an outlet which discharges the gas, and a passage which guides the gas flowing in from the inlet to the outlet through the plurality of impellers are formed in the casing. The passage has a radial passage and an outlet scroll passage. The radial passage is a passage which guides the gas flowing out from the final stage impeller among the plurality of impellers outward in the radial direction. The outlet scroll passage is a passage which extends in a circumferential direction around the axis and allows communication between a radially outer portion of the radial passage and the outlet.

The silencer includes a perforated plate and a space forming body. The perforated plate has a first surface and a second surface, and a plurality of acoustic holes which penetrate from the first surface to the second surface opposite to the first surface. The space forming body forms an acoustic space on the second surface side of the perforated plate. The silencer is disposed so that the first surface of the perforated plate forms part of an inner surface of the casing which defines the radial passage.

SUMMARY OF THE INVENTION

In this centrifugal compressor, it is required to further reduce noise, that is, to further enhance sound absorption effects.

An object of the present invention is to provide a centrifugal compressor which is able to enhance a sound absorption effect.

According to a first aspect of the present invention, there is provided a centrifugal compressor including one or more impellers configured to rotate about an axis and to send a gas to a radially outer side of the axis and to guide the gas from an inlet to an inside to discharge the gas from an outlet, a casing configured to cover the one or more impellers, and a silencer. The casing has an outlet scroll passage which extends in a circumferential direction of the axis and communicates with the outlet. The silencer includes a perforated plate in which a first surface and a second surface opposite to the first surface and a plurality of acoustic holes penetrating from the first surface to the second surface are formed, and a space forming body configured to form an acoustic space connected to the plurality of acoustic holes on a second surface side of the perforated plate. The first surface of the silencer forms part of an inner surface of the casing which defines the outlet scroll passage.

The centrifugal compressor of the aspect includes a silencer which uses the principle of a Helmholtz resonator. Tests were performed on a relationship between the sound absorption coefficient of the silencer using the principle of a Helmholtz resonator and the velocity of the gas flowing through the passage. As a result, it was found that the sound absorption coefficient of the silencer which faces a passage portion increases as the velocity of the gas flowing through the passage portion decreases.

The velocity of the gas flowing through the outlet scroll passage is lower than that of the gas flowing through the radial passage. The silencer in this aspect is disposed such that the first surface of the perforated plate forms at least part of the inner surface of the casing which defines the outlet scroll passage. Therefore, in this aspect, the sound absorption coefficient can also be increased by a silencer which faces a portion of the radial passage in which a flow rate of the gas is faster than that in the outlet scroll passage, and thereby the sound absorption effect can be enhanced.

Here, in the centrifugal compressor of the first aspect, the first surface of the silencer may form only part of the inner surface of the outlet scroll passage.

Further, in the centrifugal compressor of the first aspect, a first silencer and a second silencer may be provided as the silencers. In this case, the casing may have a radial passage which guides the gas flowing out from a final stage impeller of the one or more impellers to the radially outer side and communicates with the outlet scroll passage. The first surface of the first silencer may form part of the inner surface of the outlet scroll passage, and the first surface of the second silencer may form part of an inner surface of the casing which defines the radial passage.

Since the centrifugal compressor of the aspect includes the first silencer and the second silencer, it is possible to increase a sound absorption amount compared with a case in which only the first silencer is provided.

In the centrifugal compressor according to the aspect having the second silencer, the first surface of the second silencer may not form an inner surface in an inner region including an end radially inward with respect to the axis but may form at least part of the inner surface in an outer region on the radially outer side from the inner region in the radial passage.

In the radial passage, the velocity of the gas is lower in the outer region than in the inner region. Thus, in this aspect, the sound absorption coefficient of the second silencer can be increased.

Further, in the centrifugal compressor according to any one of the aspects having the second silencer, a short distance silencer and a long distance silencer may be provided as the second silencers. In this case, the short distance silencer may be disposed at a position closer to the final stage impeller than the long distance silencer is in a radial direction of the axis, and inner diameters of the plurality of acoustic holes of the short distance silencer may be smaller than those of the plurality of acoustic holes of the long distance silencer.

Tests were performed regarding the relationship between the sound absorption coefficient of the silencer using the principle of a Helmholtz resonator, the velocity of the gas flowing through the passage, and the inner diameter of the acoustic holes formed in the perforated plate. As a result of the test, it has been found that the sound absorption coefficient increases when the inner diameter of the acoustic holes is reduced. In other words, it has been found that even when the velocity of the gas flowing through the passage is high, a decrease in the sound absorption coefficient can be curbed by reducing the inner diameter of the acoustic holes. In the radial passage, the velocity of the gas is higher at a position close to the final stage impeller in the radial direction than at a position far from the final stage impeller.

In this aspect, since the inner diameters of the plurality of acoustic holes of the short distance silencer is smaller than those of the plurality of acoustic holes of the long distance silencer, even when the short distance silencer is disposed in a region in which the velocity of the gas is high, a decrease in the sound absorption coefficient of the short distance silencer can be curbed.

To solve the above problem, according to a second aspect of the present invention, there is provided a centrifugal compressor including one or more impellers configured to rotate about an axis and to send a gas to a radially outer side of the axis, a casing configured to cover the one or more impellers and to guide the gas from an inlet to an inside to discharge the gas from an outlet, and a short distance silencer and a long distance silencer as silencers. The casing has an outlet passage which guides the gas flowing out from a final stage impeller of the one or more impellers to the outlet. Each of the short distance silencer and the long distance silencer includes a perforated plate in which a first surface and a second surface opposite to the first surface and a plurality of acoustic holes penetrating from the first surface to the second surface are formed, and a space forming body configured to form an acoustic space connected to the plurality of acoustic holes on a second surface side of the perforated plate. Both the first surface of the short distance silencer and the first surface of the long distance silencer form part of an inner surface of the casing which defines the outlet passage. A distance along the outlet passage from the final stage impeller to the short distance silencer is shorter than that along the outlet passage from the final stage impeller to the long distance silencer. Inner diameters of the plurality of acoustic holes of the short distance silencer are smaller than those of the plurality of acoustic holes of the long distance silencer.

Also in this aspect, since the inner diameters of the plurality of acoustic holes of the short distance silencer are smaller than those of the plurality of acoustic holes of the long distance silencer, even when the short distance silencer is disposed in a region in which the velocity of the gas is high, a decrease in the sound absorption coefficient of the short distance silencer can be curbed.

In the centrifugal compressor according to any one of the aspects, at least part of the space forming body of the silencer may be formed of the same material as that of the casing and may be integrally formed with the casing.

In this aspect, as a portion of the silencer, a portion except part of the space forming body formed integrally with the casing can be easily installed in and separated from the casing.

Here, in the centrifugal compressor of the aspect, the perforated plate may be formed of a material having a linear expansion coefficient larger than that of the casing.

In this aspect, due to a difference in the linear expansion coefficient between at least part of the space forming body and the casing and the perforated plate, a gap is formed between the perforated plate and at least part of the space forming body, and a gap is formed between the perforated plate and the casing according to the situation of the centrifugal compressor.

When the gas compressed by the centrifugal compressor contains a component which becomes a liquid at room temperature, and the centrifugal compressor is cooled and the centrifugal compressor and the gas therein reach room temperature, some of the gas changes to a liquid. The liquid may remain in the acoustic space of the silencer. For example, in a starting process of the centrifugal compressor, all the liquid in the acoustic space may not be vaporized, and some of the liquid may remain as a liquid. In this case, a problem that the silencer cannot absorb sound in a target frequency range may occur.

As described above, since a gap is formed between a plurality of parts constituting the silencer, the silencer in this aspect can discharge a liquid from the gap even when a liquid remains in the acoustic space. Thus, in this aspect, a problem in that the silencer cannot absorb the sound in the target frequency range can be avoided, and reduction in the sound absorption effect can be curbed.

In the centrifugal compressor according to any one of the aspects, the silencer may have a drain hole which discharges a liquid in the acoustic space outside of the acoustic space.

Since the silencer in this aspect has the drain hole, even when a liquid remains in the acoustic space, the liquid can be discharged outside the acoustic space from the drain hole. Accordingly, in this aspect, the problem that the silencer cannot absorb the sound in the target frequency range can be avoided, and the reduction of the sound absorption effect can be curbed.

To solve the above problem, according to a third aspect of the present invention, there is provided a centrifugal compressor including one or more impellers configured to rotate about an axis and to send a gas to a radially outer side of the axis, a casing configured to cover the one or more impellers and to guide the gas from an inlet to an inside to discharge the gas from an outlet, and a silencer. The casing has a passage which guides the gas flowing in from the inlet to the outlet through the one or more impellers. The silencer includes a perforated plate in which a first surface and a second surface opposite to the first surface and a plurality of acoustic holes penetrating from the first surface to the second surface are formed, a space forming body configured to form an acoustic space connected to the plurality of acoustic holes on a second surface side of the perforated plate, and a drain hole configured to discharge a liquid in the acoustic space outside of the acoustic space. The first surface of the silencer forms part of an inner surface of the passage.

Since the silencer in this aspect has the drain hole, even when a liquid remains in the acoustic space, the liquid can be discharged from the drain hole to the outside of the acoustic space. Therefore, in this aspect, the problem that the silencer cannot absorb the sound in the target frequency range can be avoided, and the reduction of the sound absorption effect can be curbed.

In the centrifugal compressor according to any one of the aspects having the drain hole, the drain hole may have a first opening which opens in an inner surface of the space forming body which faces the acoustic space, and a second opening which opens in an outer surface of the casing.

In the centrifugal compressor according to the aspect having the second opening which opens in the outer surface of the casing, an opening area of the first opening may be 20% or less of a total opening area of all the acoustic holes in a portion of the perforated plate which defines one acoustic space.

In the centrifugal compressor according to any one of the aspects having the second opening which opens in the outer surface of the casing, the silencer may have a valve capable of partitioning a space in the drain hole from an outer space of the casing.

Further, in the centrifugal compressor according to any one of the aspects having the second opening which opens in the outer surface of the casing, a moisture absorbent may be disposed in the drain hole.

In the centrifugal compressor according to any one of the aspects having the drain hole, the drain hole may have a first opening which opens in the first surface of the perforated plate, and a second opening which opens in the second surface of the perforated plate, and a moisture absorbent may be disposed in the drain hole.

To solve the above problem, according to a fourth aspect of the present invention, there is provided a centrifugal compressor including one or more impellers configured to rotate about an axis and to send a gas to a radially outer side of the axis, a casing configured to cover the one or more impellers and to guide the gas from an inlet to an inside to discharge the gas from an outlet, and a silencer. The casing has a passage configured to guide the gas flowing in from the inlet to the outlet through the one or more impellers. The silencer includes a perforated plate in which a first surface and a second surface opposite to the first surface and a plurality of acoustic holes penetrating from the first surface to the second surface are formed, and a space forming body configured to form an acoustic space connected to the plurality of acoustic holes on a second surface side of the perforated plate. The first surface of the silencer forms part of an inner surface of the casing which defines the passage. At least part of the space forming body is formed of the same material as that of the casing and integrally formed with the casing. The perforated plate is formed of a material having a linear expansion coefficient larger than that of the casing.

Also in the silencer in this aspect, since a gap is formed between a plurality of parts constituting the silencer, the liquid can be discharged from the gap even when a liquid remains in the acoustic space. Therefore, also in this aspect, the problem that the silencer cannot absorb the sound in the target frequency range can be avoided, and the reduction of the sound absorption effect can be curbed.

In the centrifugal compressor according to any one of the aspects, inner diameters of the plurality of acoustic holes may be 0.1 mm or more to 3.0 mm or less.

Further, in the centrifugal compressor according to any one of the aspects, inner diameters of the plurality of acoustic holes may be 0.2 mm or more to 1.0 mm or less.

In one aspect of the present invention, it is possible to increase a sound absorption effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a centrifugal compressor according to a first embodiment.

FIG. 2 is a cross-sectional view of a main part of the centrifugal compressor according to the first embodiment.

FIG. 3 is a graph showing a relationship between a sound absorption coefficient of a silencer and a velocity of a gas flowing through a passage.

FIG. 4 is a cross-sectional view of a main part of a centrifugal compressor according to a first modified example of the first embodiment.

FIG. 5 is a cross-sectional view of a main part of a centrifugal compressor according to a second modified example of the first embodiment.

FIG. 6 is a cross-sectional view of a main part of a centrifugal compressor according to a second embodiment.

FIG. 7 is a cross-sectional view of a main part of a centrifugal compressor according to a third embodiment.

FIG. 8 is a cross-sectional view of a main part of a centrifugal compressor according to a fourth embodiment.

FIG. 9 is a cross-sectional view of a main part of a centrifugal compressor according to a fifth embodiment.

FIG. 10 is a cross-sectional view of a main part of the centrifugal compressor in a state in which the centrifugal compressor according to the fifth embodiment is cooled.

FIG. 11 is a cross-sectional view of a main part of a centrifugal compressor according to a sixth embodiment.

FIG. 12 is a cross-sectional view of a main part of a centrifugal compressor according to a seventh embodiment.

FIG. 13 is a cross-sectional view around a silencer of the centrifugal compressor according to the seventh embodiment.

FIG. 14 is a cross-sectional view around a silencer of a centrifugal compressor according to an eighth embodiment.

FIG. 15 is a cross-sectional view around a silencer of a centrifugal compressor according to a ninth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, various embodiments of a centrifugal compressor according to the present invention will be described with reference to the drawings.

First Embodiment

A centrifugal compressor according to a first embodiment will be described with reference to FIGS. 1 to 3.

The centrifugal compressor according to this embodiment is a multistage centrifugal compressor. As shown in FIG. 1, the centrifugal compressor according to this embodiment includes a rotary shaft 10, bearings 15a and 15b, a plurality of impellers 11, a casing 20, and a silencer 30A. The rotary shaft 10 has a cylindrical shape and rotates around an axis Ar. The bearings 15a and 15b rotatably support the rotary shaft 10. The plurality of impellers 11 are installed on the rotary shaft 10 and rotate around the axis Ar together with the rotary shaft 10. The casing 20 surrounds the impellers 11. The silencer 30A is provided in the casing 20.

Here, a direction in which the axis Ar extends is referred to as an axial direction Da. The bearing 15a side in the axial direction Da is referred to as the first side Da1. The bearing 15b side is referred to as the second side Da2. Further, a radial direction with respect to the axis Ar is referred to as a radial direction Dr. The side closer to the axis Ar in the radial direction Dr is referred to as the radially inner side Dri. The side away from the axis Ar in the radial direction Dr is referred to as the radially outer side Dro. A circumferential direction around the axis Ar is referred to as a circumferential direction Dc.

The rotary shaft 10 is provided to pass through the casing 20 in the axial direction Da. The centrifugal compressor according to this embodiment includes a thrust bearing 15a and a journal bearing 15b as the bearings 15a and 15b. The thrust bearing 15a is provided at an end of the casing 20 on the first side Da1 and supports an end of the rotary shaft 10 on the first side Da1. The journal bearing 15b is provided at an end of the casing 20 on the second side Da2 and supports an end of the rotary shaft 10 on the second side Da2.

The plurality of impellers 11 are arranged in the axial direction Da to be spaced apart from each other in the axial direction Da. An in-impeller flow path 12 through which a gas flows is formed in each of the impellers 11. The in-impeller flow path 12 has an impeller inlet 13 and an impeller outlet 14. The impeller inlet 13 is open from the inside of the in-impeller flow path 12 toward the first side Da1 in the axial direction Da. The impeller outlet 14 is open from the inside of the in-impeller flow path 12 toward the radially outer side Dro. The in-impeller flow path 12 is formed to be gradually directed to the radially outer side Dro as it goes from the first side Da1 to the second side Da2 in the axial direction Da. A cross-sectional area of the in-impeller flow path 12 gradually reduces from the impeller inlet 13 toward the impeller outlet 14. Hereinafter, among the plurality of impellers 11, the impeller 11 located furthest toward the first side Da1 in the axial direction Da is referred to as an initial stage impeller 11a, and the impeller 11 located on the most second side Da2 in the axial direction Da is referred to as a final stage impeller 11b.

The casing 20 has an inlet 20i which guides a gas into the casing 20, an outlet 20o which discharges the gas, and a passage 20p. The inlet 20i is formed on the first side Da1 with respect to the plurality of impellers 11. The outlet 200o is formed on the second side Da2 with respect to the plurality of impellers 11. The passage 20p guides the gas flowing in from the inlet 20i to the outlet 20o via the plurality of impellers 11.

The casing 20 has an inlet casing 21, an intermediate casing 23, and an outlet casing 25. The inlet casing 21 has an inlet 20i and an inlet passage 21p. The inlet passage 21p guides the gas flowing in from the inlet 20i to the impeller inlet 13 of the initial stage impeller 11a. The intermediate casing 23 partitions the two impellers 11 adjacent to each other in the axial direction Da. The intermediate casing 23 is disposed between the inlet casing 21 and the outlet casing 25 in the axial direction Da. The intermediate casing 23 has a plurality of intermediate passages 23p. The intermediate passage 23p guides the gas flowing out from the impeller outlet 14 of the impeller 11 on the first side Da1 to the impeller inlet 13 of the impeller 11 on the second side Da2, among the two impellers 11 adjacent to each other in the axial direction Da.

The intermediate passage 23p has a diffuser passage 23pa, a turning passage 23pb, and a return passage 23pc. The diffuser passage 23pa guides the gas flowing out from the impeller outlet 14 of the impeller 11 on the first side Da1, among the two impellers 11 adjacent to each other in the axial direction Da, to the radially outer side Dro. That is, the diffuser passage 23pa is a passage which extends in the radial direction Dr. The turning passage 23pb is connected to an end of the diffuser passage 23pa on the radially outer side Dro. The turning passage 23pb is a passage which changes a flow of the gas flowing in from the diffuser passage 23pa from the radially outer side Dro to the radially inner side Dri. The return passage 23pc is connected to the turning passage 23pb. The return passage 23pc guides the gas flowing in from the turning passage 23pb to the impeller inlet 13 of the impeller 11 on the second side Da2, among the two impellers 11 adjacent to each other in the axial direction Da.

As described above, the intermediate casing 23 has the intermediate passage 23p. In addition, the intermediate casing 23 forms part of a radial passage 26 as shown in FIG. 2. The radial passage 26 is a passage which guides the gas flowing out from the impeller outlet 14 of the final stage impeller 11b to the radially outer side Dro.

As shown in FIGS. 1 and 2, the outlet casing 25 has an outlet 20o and an outlet scroll passage 27. The outlet casing 25 also forms part of the above-described radial passage 26. The radial passage 26 extends from the impeller outlet 14 of the final stage impeller 11b toward the radially outer side Dro and also expands in the circumferential direction Dc. The intermediate casing 23 forms a first side inner surface 26a among inner surfaces forming the radial passage 26. The outlet casing 25 forms a second side inner surface 26b among the inner surfaces forming the radial passage 26. Both the first side inner surface 26a and the second side inner surface 26b expand in the radial direction Dr and the circumferential direction Dc. The second side inner surface 26b is located closer to the second side Da2 than the first side inner surface 26a. The second side inner surface 26b faces the first side Da1. The first side inner surface 26a faces the second side Da2.

The outlet scroll passage 27 extends in the circumferential direction Dc and allows communication between a portion of the radial passage 26 on the radially outer side Dro and the outlet 20o. An inner surface of the outlet scroll passage 27 which extends in the circumferential direction Dc has an external inner surface 27o, an internal inner surface 27i, a first side inner surface 27a, and a second side inner surface 27b. The external inner surface 270 and the internal inner surface 27i expand in the circumferential direction Dc and the axial direction Da. The external inner surface 27o is located closer to the radially outer side Dro than the internal inner surface 27i. The external inner surface 27o faces the radially inner side Dri. The internal inner surface 27i faces the radially outer side Dro. The first side inner surface 27a and the second side inner surface 27b expand in the circumferential direction Dc and the radial direction Dr. The second side inner surface 27b is located closer to the second side Da2 than the first side inner surface 27a. The second side inner surface 27b faces the first side Da1. The first side inner surface 27a faces the second side Da2.

The radial passage 26 and the outlet scroll passage 27 constitute an outlet passage 25p. The inlet passage 21p, the plurality of intermediate passages 23p, and the outlet passage 25p constitute the passage 20p.

The silencer 30A includes a perforated plate 31 and a space forming body 35. A first surface 32 and a second surface 33 opposite to the first surface 32, and a plurality of acoustic holes 34 are formed in the perforated plate 31. The first surface 32 and the second surface 33 constitute both surfaces of the perforated plate 31. The plurality of acoustic holes 34 penetrate from the first surface 32 to the second surface 33. Inner diameters of the plurality of acoustic holes 34 are preferably 0.1 mm or more to 3.0 mm or less. The inner diameters of the plurality of acoustic holes 34 are, for example, 1.0 mm.

The space forming body 35 is a member which forms a space on the second surface 33 side of the perforated plate 31. The space forming body 35 includes an outer frame 36 which defines an outer edge of a space between the outer frame 36 and the perforated plate 31, and a partition wall 39 which partitions the space into a plurality of acoustic spaces S. Each of the acoustic spaces S communicates with one or more of the plurality of acoustic holes 34. Therefore, the silencer 30A of this embodiment is a silencer which uses the principle of a Helmholtz resonator.

The silencer 30A is disposed so that the first surface 32 of the perforated plate 31 forms part of the external inner surface 27o among the inner surfaces which define the outlet scroll passage 27 in the casing 20.

The inventor performed a test regarding a relationship between a sound absorption coefficient of the silencer using the principle of a Helmholtz resonator and a velocity of the gas flowing through the passage. Test results will be described with reference to a graph shown in FIG. 3. A horizontal axis in the graph shown in FIG. 3 indicates the velocity (Mach number) of the gas flowing through a passage portion which is a portion of the passage through which the gas flows and which faces the perforated plate of the silencer. A vertical axis in the graph shown in FIG. 3 is the sound absorption coefficient of the silencer. Inner diameters of the plurality of acoustic holes in the silencer used in the test are 1.0 mm, similar to the inner diameters of the plurality of acoustic holes 34 in this embodiment.

As shown in the graph of FIG. 3, when the velocity of the gas flowing through the passage portion is Mach number 0.6, the sound absorption coefficient of the silencer facing the passage portion is about 0.2. When the velocity of the gas flowing through the passage portion is Mach number 0.4, the sound absorption coefficient of the silencer facing the passage portion is about 0.4. When the velocity of the gas flowing through the passage portion is Mach number 0.0, the sound absorption coefficient of the silencer facing the passage portion is about 0.6. Therefore, as the velocity of the gas flowing through the passage portion becomes lower, the sound absorption coefficient of the silencer facing the passage portion becomes greater.

As described above, the radial passage 26 extends from the impeller outlet 14 of the final stage impeller 11b toward the radially outer side Dro and also expands in the circumferential direction Dc. Thus, a cross-sectional area of the radial passage 26 gradually increases toward the radially outer side Dro. Therefore, the velocity of the gas flowing through the radial passage 26 gradually decreases as it flows toward the radially outer side Dro. The velocity of the gas flowing through the outlet scroll passage 27 is lower than that of the gas flowing through the radial passage 26.

Since the silencer 30A faces part of the outlet scroll passage 27, the sound absorption coefficient is higher than that of the silencer facing part of the radial passage 26 in which a flow rate of the gas is faster than that in the outlet scroll passage 27. Therefore, the sound absorption coefficient can be enhanced in the silencer 30A.

When the silencer is disposed to face the passage, a pressure loss of the gas occurs due to the presence of the plurality of acoustic holes 34 of the silencer. The pressure loss is proportional to the square of the velocity of the gas. Since the silencer 30A faces part of the outlet scroll passage 27, the pressure loss of the gas can be made smaller than that in a silencer which faces part of the radial passage 26 in which the flow rate of the gas is faster than that in the outlet scroll passage 27.

In the centrifugal compressor according to this embodiment and a centrifugal compressor having the same configuration as that of the centrifugal compressor according to this embodiment except for the silencer 30A, the velocity of the gas at the impeller outlet 14 of the final stage impeller 11b is, for example, Mach number 0.6 to 0.8. In other words, the velocity of the gas at the impeller outlet 14 of the final stage impeller 11b is the velocity of the gas at the end of the radial passage 26 on the radially inner side Dri. The velocity of the gas flowing through the radial passage 26 gradually decreases as it flows to the radially outer side Dro due to the above-described reason. Additionally, the velocity of the gas in the outlet scroll passage 27 is Mach number 0.4 or less. Therefore, the sound absorption coefficient of the silencer 30A which faces part of the outlet scroll passage 27 becomes about 0.4 or more.

Incidentally, as a result of the test, it was found that when the inner diameters of the acoustic holes 34 are reduced, a sound absorption coefficient curve is shifted to the right as shown by a broken line in FIG. 3. That is, it was found that, when the sound absorption coefficient is the same between a case in which the inner diameters of the acoustic holes 34 are large and a case in which the inner diameters of the acoustic holes 34 are small, the velocity of the gas is higher in the case in which the inner diameters of the acoustic holes 34 are small. In other words, it was found that, when the velocity of the gas is the same between the case in which the inner diameters of the acoustic holes 34 are large and the case in which the inner diameters of the acoustic holes 34 are small, the acoustic holes 34 having smaller inner diameters has a higher sound absorption coefficient. Therefore, the sound absorption coefficient can be increased by reducing the inner diameters of the acoustic holes 34. This is considered to be because, when the inner diameters of the acoustic holes 34 are reduced, the pressure loss of the gas passing through the acoustic holes 34 increases, and the influence of the decrease in the sound absorption coefficient due to the velocity of the gas passing through the passage portion is reduced. Therefore, in this embodiment, the inner diameter of the acoustic hole 34 is set to 1.0 mm which is a minimum inner diameter that can be drilled with a drill, or an inner diameter close to the minimum inner diameter.

Hole machining can be performed using a laser as well as drilling. When the acoustic holes 34 are machined with a laser, the acoustic holes 34 having an inner diameter of 1.0 mm or less can be formed. Therefore, considering the case in which the acoustic holes 34 are machined with a laser, the inner diameter of the acoustic hole 34 is preferably 0.2 mm or more to 1.0 mm or less.

[Modified Example of First Embodiment]

Various modified examples of the centrifugal compressor in the first embodiment will be described with reference to FIGS. 4 and 5. In various embodiments and various modified examples of the centrifugal compressor which will be described below, the arrangement or configuration of the silencer is different, but the configuration is otherwise the same as that of the centrifugal compressor according to the first embodiment. Therefore, in the following, the arrangement or configuration of the silencer will be mainly described in various embodiments and various modified examples.

In the silencer 30A according to the first embodiment, the first surface 32 of the perforated plate 31 is disposed to form part of the external inner surface 27o among the inner surfaces defining the outlet scroll passage 27 in the casing 20. As shown in FIG. 4, a silencer 30Aa in a first modified example of the first embodiment has the same configuration as that of the silencer 30A in the first embodiment. However, in the silencer 30Aa, the first surface 32 of the perforated plate 31 is disposed to form part of the second side inner surface 27b among the inner surfaces defining the outlet scroll passage 27 in the outlet casing 25.

As shown in FIG. 5, a silencer 30Ab in a second modified example of the first embodiment has the same configuration as the silencer 30A in the first embodiment. However, the silencer 30Ab is disposed so that the first surface 32 of the perforated plate 31 forms part of the internal inner surface 27i among the inner surfaces which define the outlet scroll passage 27 in the outlet casing 25.

In this way, as in the first embodiment, the silencer 30Aa of the first modified example and the silencer 30Ab of the second modified example are also disposed so that the first surface 32 of the perforated plate 31 forms part of the inner surface which defines the outlet scroll passage 27 in the outlet casing 25. Therefore, as in the first embodiment, the silencer 30Aa of the first modified example and the silencer 30Ab of the second modified example can also increase the sound absorption coefficient and can reduce the pressure loss of the gas.

As described above, the silencer 30A may be disposed so that the first surface 32 of the perforated plate 31 forms part of one of the inner surfaces which define the outlet scroll passage 27 in the outlet casing 25. Therefore, the silencer may be disposed so that the first surface 32 of the perforated plate 31 forms part of the first side inner surface 27a among the inner surfaces which define the outlet scroll passage 27 in the casing 20.

Second Embodiment

A centrifugal compressor according to a second embodiment will be described with reference to FIG. 6.

The centrifugal compressor according to this embodiment includes a first silencer 30B1 and a second silencer 30B2. As in the silencer 30A according to the first embodiment, each of the first silencer 30B1 and the second silencer 30B2 includes the perforated plate 31 in which the plurality of acoustic holes 34 are formed, and the space forming body 35 which forms a plurality of acoustic spaces S.

The first silencer 30B1 is disposed so that the first surface 32 of the first silencer 30B 1 forms part of the external inner surface 27o of the outlet scroll passage 27, as in the silencer 30A in the first embodiment. As described in the modified example of the first embodiment, the first silencer 30B1 may be disposed so that the first surface 32 of the perforated plate 31 forms part of one of the inner surfaces which define the outlet scroll passage 27.

The second silencer 30B2 is disposed so that the first surface 32 of the second silencer 30B2 forms part of the first side inner surface 26a of the radial passage 26. The second silencer 30B2 only needs to be disposed so that the first surface 32 of the perforated plate 31 forms part of the inner surface of the radial passage 26. For example, the second silencer 30B2 may be disposed to form part of the second side inner surface 26b of the radial passage 26.

In the of the radial passage 26, the first surface 32 of the second silencer 30B2 does not form the inner surface in an inner region including an end on the radially inner side Dri and forms at least part of the inner surface in an outer region on the radially outer side Dro from the inner region. As described in the first embodiment, the velocity of the gas flowing through the radial passage 26 is gradually reduced as it flows to the radially outer side Dro. Therefore, in this embodiment, in order to increase the sound absorption coefficient of the second silencer 30B2, the first surface 32 of the second silencer 30B2 is disposed to form at least part of the inner surface in the outer region of the radial passage 26.

The centrifugal compressor according to this embodiment includes the second silencer 30B2 disposed so that the first surface 32 forms part of the inner surface of the radial passage 26 in addition to the first silencer 30B1 disposed so that the first surface 32 forms part of the inner surface of the outlet scroll passage 27, as in the silencer 30A according to the first embodiment. Accordingly, the centrifugal compressor according to this embodiment can further increase a sound absorption amount.

In this embodiment, the inner diameter of the acoustic hole 34 of the second silencer 30B2 is preferably smaller than that of the acoustic hole 34 of the first silencer 30B 1. This is because the second silencer 30B2 is disposed in a region in which the flow rate of the gas is faster than that in the first silencer 30B1.

Third Embodiment

A centrifugal compressor according to a third embodiment will be described with reference to FIG. 7.

The centrifugal compressor according to this embodiment also includes a first silencer 30C1 and a second silencer 30C2, as in the centrifugal compressor according to the second embodiment. Both the first silencer 30C1 and the second silencer 30C2 have the same configuration as those of the silencers in the first embodiment and the second embodiment. That is, each of the first silencer 30C1 and the second silencer 30C2 includes the perforated plate 31 in which the plurality of acoustic holes 34 are formed and the space forming body 35 which forms the plurality of acoustic spaces S.

The first silencer 30C1 is disposed so that the first surface 32 of the first silencer 30C1 forms part of the external inner surface 27o of the outlet scroll passage 27, as in the silencer 30A in the first embodiment. The first silencer 30C1 may be disposed so that the first surface 32 of the perforated plate 31 forms part of one of the inner surfaces which define the outlet scroll passage 27, as described in the modified example of the first embodiment.

The second silencer 30C2 is disposed so that the first surface 32 of the second silencer 30C2 forms part of the first side inner surface 26a of the radial passage 26. The second silencer 30C2 only needs to be disposed so that the first surface 32 of the perforated plate 31 forms part of the inner surface of the radial passage 26. The second silencer 30C2 may be disposed to form part of the second side inner surface 26b of the radial passage 26, for example.

Each of the first silencer 30C1 and the second silencer 30C2 has the plurality of acoustic spaces S. The acoustic spaces S have different volumes, for example, to change a sound absorption frequency range. Therefore, it can be said that both the first silencer 30C1 and the second silencer 30C2 have a silencer for each of the plurality of acoustic spaces S. Here, the second silencer 30C2 has three acoustic spaces S. That is, the second silencer 30C2 includes three silencers 30Ca, 30Cb, and 30Cc. The three silencers 30Ca, 30Cb, and 30Cc in the second silencer 30C2 are arranged in the radial direction Dr. Among the three silencers 30Ca, 30Cb, and 30Cc in the second silencer 30C2, the silencer 30Ca which is closest to the final stage impeller 11b in the radial direction Dr is referred to as a second short distance silencer 30Ca. The silencer 30Cb adjacent to the radially outer side Dro of the second short distance silencer 30Ca is referred to as a second intermediate distance silencer 30Cb. The silencer 30Cc adjacent to the radially outer side Dro of the second intermediate distance silencer 30Cb is referred to as a second long distance silencer 30Cc. Therefore, the velocity of the gas flowing through the passage portion which faces the second short distance silencer 30Ca is faster than that of the gas flowing through the passage portion which faces the second intermediate distance silencer 30Cb.

In this embodiment, the inner diameters of the acoustic holes 34 of the second long distance silencer 30Cc and the second intermediate distance silencer 30Cb are the same. In this embodiment, the inner diameter of the acoustic hole 34 of the second short distance silencer 30Ca is smaller than those of the acoustic holes 34 of the second long distance silencer 30Cc and the second intermediate distance silencer 30Cb. Thus, even when the velocity of the gas flowing through the passage portion which faces the second short distance silencer 30Ca is high, a decrease in the sound absorption coefficient of the second short distance silencer 30Ca can be curbed.

The inner diameters of the acoustic holes 34 of the second short distance silencer 30Ca, the second intermediate distance silencer 30Cb, and the second long distance silencer 30Cc are preferably smaller than that of the acoustic hole 34 of the first silencer 30C1. This is because passage distances of the second short distance silencer 30Ca, the second intermediate distance silencer 30Cb, and the second long distance silencer 30Cc are shorter than that of the first silencer 30C1 and the velocity of the gas flowing in the passage portion which faces each of the second short distance silencer 30Ca, the second intermediate distance silencer 30Cb, and the second long distance silencer 30Cc is faster than that of the gas flowing through the passage portion which faces the first silencer 30C1. The passage distance is a distance along the outlet passage 25p from the impeller outlet 14 of the final stage impeller 11b. In this case, for example, when the inner diameter of the acoustic hole 34 of the first silencer 30C1 is 1.0 mm, the inner diameter of the acoustic hole 34 of each of the second long distance silencer 30Cc and the second intermediate distance silencer 30Cb is set to 0.8 mm, and the inner diameter of the acoustic hole 34 of the second short distance silencer 30Ca is set to 0.6 mm.

The inner diameter of the acoustic hole 34 of the second intermediate distance silencer 30Cb may be smaller than that of the acoustic hole 34 of the second long distance silencer 30Cc, and the inner diameter of the acoustic hole 34 of the second short distance silencer 30Ca may be smaller than that of the acoustic hole 34 of the second intermediate distance silencer 30Cb. In this case, for example, when the inner diameter of the acoustic hole 34 of the first silencer 30C1 is 1.0 mm, the inner diameter of the acoustic hole 34 of the second long distance silencer 30Cc is set to 0.8 mm, the inner diameter of the acoustic hole 34 of the second intermediate distance silencer 30Cb is set to 0.6 mm, and the inner diameter of the acoustic hole 34 of the second short distance silencer 30Ca is set to 0.5 mm.

Fourth Embodiment

A centrifugal compressor according to a fourth embodiment will be described with reference to FIG. 8.

The centrifugal compressor according to each of the above-described embodiments includes a short distance silencer 30Da and a long distance silencer 30Db as the silencer. Each of the short distance silencer 30Da and the long distance silencer 30Db includes the perforated plate 31 in which the plurality of acoustic holes 34 are formed, and the space forming body 35 which forms the plurality of acoustic spaces S, as in the silencer according to each of the above-described embodiments.

The centrifugal compressor according to each of the above-described embodiments includes the silencer disposed so that the first surface 32 of the perforated plate 31 forms part of the inner surface of the outlet scroll passage 27. However, the centrifugal compressor according to this embodiment does not include a silencer disposed so that the first surface 32 of the perforated plate 31 forms part of the inner surface of the outlet scroll passage 27. Instead, the centrifugal compressor according to this embodiment includes a short distance silencer 30Da and a long distance silencer 30Db disposed so that the first surface 32 of the perforated plate 31 forms part of the first side inner surface 26a of the radial passage 26. The short distance silencer 30Da and the long distance silencer 30Db may be disposed so that the first surface 32 of the perforated plate 31 forms part of the inner surface of the radial passage 26. The short distance silencer 30Da and the long distance silencer 30Db may be disposed to form part of the second side inner surface 26b of the radial passage 26, for example.

The short distance silencer 30Da is disposed on the radially inner side Dri from the long distance silencer 30Db. Thus, the passage distance of the short distance silencer 30Da is shorter than that of the long distance silencer 30Db. In this embodiment, the inner diameter of the acoustic hole 34 of the short distance silencer 30Da is smaller than that of the acoustic hole 34 of the long distance silencer 30Db. Specifically, for example, the inner diameter of the acoustic hole 34 of the long distance silencer 30Db is 0.8 mm, and the inner diameter of the acoustic hole 34 of the short distance silencer 30Da is 0.5 mm.

Accordingly, in this embodiment, even when the velocity of the gas flowing through the passage portion which faces the short distance silencer 30Da is higher than that of the gas flowing through the passage portion which faces the long distance silencer 30Db, a decrease in the sound absorption coefficient of the short distance silencer 30Da can be curbed. Since the inner diameter of the acoustic holes 34 of each of the silencers 30Da and 30Db is selected in consideration of the velocity of the gas flowing through the passage portion which faces each of the silencers 30Da and 30Db, the decrease in the sound absorption coefficient can be curbed only with the silencers 30Da and 30Db in which the first surface 32 of the perforated plate 31 forms part of the inner surface of the radial passage 26.

Fifth Embodiment

A centrifugal compressor according to a fifth embodiment will be described with reference to FIGS. 9 and 10.

The centrifugal compressor according to this embodiment is a modified example of the centrifugal compressor according to the first embodiment. The centrifugal compressor according to this embodiment is different from the centrifugal compressor according to the first embodiment only in the configuration of the silencer, and the other configurations are the same as those of the centrifugal compressor according to the first embodiment.

A silencer 30E according to this embodiment includes a perforated plate 31e in which a plurality of acoustic holes 34 are formed, and a space forming body 35e which forms a plurality of acoustic spaces S, as in the silencer 30A according to the first embodiment. The silencer 30E in this embodiment is disposed so that the first surface 32 of the perforated plate 31e forms part of the inner surface of the outlet scroll passage 27, as in the silencer 30A in the first embodiment.

The space forming body 35e of the silencer 30E in this embodiment includes an outer frame 36e which forms a space between the outer frame 36e and the perforated plate 31e on the second surface 33 side of the perforated plate 31e, and a partition wall 39e which partitions the space into a plurality of acoustic spaces S, as in the space forming body 35 of the silencer 30A in the first embodiment. The outer frame 36e has a bottom wall 37 and a side peripheral wall 38. The bottom wall 37 faces the perforated plate 31e with an interval therebetween. The side peripheral wall 38 is located between the perforated plate 31e and the bottom wall 37 and defines a side periphery of the above-described space. The partition wall 39e is integrally formed with the side peripheral wall 38 of the outer frame 36e. Among the above-described portions of the space forming body 35e, the bottom wall 37 is formed of the same material as that of the outlet casing 25 and is integrally formed with the outlet casing 25. In other words, the bottom wall 37 is formed by part of the outlet casing 25. Among each of the portions of the space forming body 35e, a portion excluding the bottom wall 37, and the perforated plate 31e are formed of a material having a larger linear expansion coefficient than that of the outlet casing 25.

A recessed portion 28 is formed in the outlet casing 25. As shown in FIG. 10, the recessed portion 28 is formed to be recessed from the inner surface of the outlet scroll passage 27 toward the outer side of the outlet casing 25. A portion of the recessed portion 28 which forms a bottom surface forms the bottom wall 37 of the space forming body 35e. In this embodiment, a portion of the silencer 30E excluding the bottom wall 37 is fitted into the recessed portion 28. However, the portion of the silencer 30E excluding the bottom wall 37 is not fixed into the recessed portion 28.

As shown in FIG. 10, when the centrifugal compressor is stopped and the perforated plate 31e and the outlet casing 25 have the same temperature, that is, when the centrifugal compressor is sufficiently cooled, there is a gap between the outer frame 36 of the space forming body 35e and an inner surface of the recessed portion 28. At this time, there are also gaps between the perforated plate 31e and the inner surface of the recessed portion 28 and between the perforated plate 31e and the outer frame 36 of the space forming body 35e. However, when the centrifugal compressor is driven, and the temperature of the perforated plate 31e and the temperature of the outlet casing 25 are increased, and the perforated plate 31e and the outlet casing 25 have substantially the same temperature, that is, when the centrifugal compressor is warmed, there is no gap between the outer frame 36 of the space forming body 35e and the inner surface of the recessed portion 28, as shown in FIG. 9. Further, there is also no gap between the perforated plate 31e and the inner surface of the recessed portion 28 or between the perforated plate 31e and the outer frame 36 of the space forming body 35e. Accordingly, there is no gap between a plurality of parts constituting the silencer 30E during the operation of the centrifugal compressor, and the silencer 30E can exhibit a sound absorption function.

When the gas compressed by the centrifugal compressor includes a component which becomes liquid at room temperature, and the centrifugal compressor is cooled, and the centrifugal compressor and the gas therein reach room temperature, some of the gas changes to liquid. The liquid may remains in the acoustic space S of the silencer 30E. For example, in a staring process of the centrifugal compressor, all the liquid in the acoustic space S may not be vaporized, and some of the liquid may remain as the liquid. In this case, a problem that the silencer 30E cannot absorb the sound in a target frequency range occurs.

As described above, in the silencer 30E of this embodiment, when the centrifugal compressor is cooled, the gap is formed between the plurality of parts constituting the silencer 30E. Therefore, even when the liquid remains in the acoustic space S, the silencer 30E can discharge the liquid from the gap. Thus, in this embodiment, the problem that the silencer 30E cannot absorb the sound in the target frequency range can be avoided, and thus reduction of the sound absorption effect can be curbed.

As described above, in the silencer 30E of this embodiment, when the centrifugal compressor is cooled, the gap is formed between the plurality of parts constituting the silencer 30E. Thus, among the parts constituting the silencer 30E, those other than the parts integrally formed with the outlet casing 25 can be easily installed in and separated from the outlet casing 25.

Sixth Embodiment

A centrifugal compressor according to a sixth embodiment will be described with reference to FIG. 11.

The centrifugal compressor according to this embodiment is a modified example of the centrifugal compressor according to the fifth embodiment. The centrifugal compressor according to this embodiment is different from the centrifugal compressor according to the fifth embodiment only in the configuration of the silencer, and the other configurations are the same as those of the centrifugal compressor according to the fifth embodiment.

A silencer 30F in this embodiment also includes a perforated plate 31f in which a plurality of acoustic holes 34 are formed, and a space forming body 35f which forms a plurality of acoustic spaces S, as in the silencers in the first and fifth embodiments. The silencer 30F in this embodiment is also disposed so that the first surface 32 of the perforated plate 31f forms part of the inner surface of the outlet scroll passage 27, as in the silencers in the first embodiment and the fifth embodiment.

The space forming body 35f of the silencer 30F in this embodiment is formed of the same material as that of the outlet casing 25 and is integrally formed with the outlet casing 25. In other words, the space forming body 35f is formed by part of the outlet casing 25. The perforated plate 31f of the silencer 30F is formed of a material having a larger linear expansion coefficient than that of the outlet casing 25. The perforated plate 31f is not fixed to the space forming body 35f.

In this embodiment, when the centrifugal compressor is stopped and the perforated plate 31f and the outlet casing 25 have the same temperature, that is, when the centrifugal compressor is sufficiently cooled, there is a gap between the perforated plate 31f and the space forming body 35f formed integrally with the outlet casing 25. When (a) the centrifugal compressor is driven. (b) the temperature of the perforated plate 31f and the temperature of the outlet casing 25 are increased, and (c) the perforated plate 31f and the outlet casing 25 have substantially the same temperature (i.e., when the centrifugal compressor is warmed), there is no gap between the perforated plate 31f and the space forming body 35f formed integrally with the outlet casing 25. Thus, there is no gap between the plurality of parts constituting the silencer 30F during the operation of the centrifugal compressor, and the silencer 30F can exhibit the sound absorption function.

In the silencer 30F in this embodiment, the gap is formed between the plurality of parts constituting the silencer 30F when the centrifugal compressor is cooled, as in the silencer 30E in the fifth embodiment. Thus, the silencer 30F can discharge a liquid from the gap even when the liquid remains in the acoustic space S. Therefore, also in this embodiment, the problem that the silencer 30F cannot absorb the sound in the target frequency range can be avoided, and the reduction of the sound absorption effect can be curbed.

Also in the silencer 30F in this embodiment, when the centrifugal compressor is cooled, the gap is formed between the plurality of parts constituting the silencer 30F. Thus, among the parts constituting the silencer 30F, those excluding the parts integrally formed with the outlet casing 25 can be easily installed in and separated from the outlet casing 25.

The silencers in the fifth embodiment and the sixth embodiment are modified examples of the silencer 30A in the first embodiment. However, the silencers in the first modified example and the second modified example of the first embodiment, and the second to fourth embodiments may be modified in the same manner as that in the silencer in the fifth or sixth embodiment.

Seventh Embodiment

A centrifugal compressor according to a seventh embodiment will be described with reference to FIGS. 12 and 13.

The centrifugal compressor according to this embodiment also includes a silencer 30G as in each of the above-described embodiments and modified examples. As shown in FIG. 12, the silencer 30G according to this embodiment also includes the perforated plate 31 in which the plurality of acoustic holes 34 are formed, and the space forming body 35 which forms the plurality of acoustic spaces S, as in each of the above-described embodiments and modified examples. The silencer 30G in this embodiment is disposed so that the first surface 32 of the perforated plate 31 forms part of the inner surface of the radial passage 26.

The silencer 30G in this embodiment further includes a plurality of drain holes 40, a plurality of drain pipes 43, and a plurality of valves 44. The drain hole 40 is provided for each of the plurality of acoustic spaces S. The drain pipe 43 is provided for each of the plurality of drain holes 40. The valve 44 is provided for each of the plurality of drain pipes 43. The drain holes 40 include a hole formed in the space forming body 35 and a hole formed in the casing 23 (20). The hole formed in the space forming body 35 and the hole formed in the casing 23 (20) are connected to each other. The drain hole 40 has a first opening 41 and a second opening 42. The first opening 41 is open in an inner surface of the space forming body 35 which faces the acoustic space S. The second opening 42 is open in an outer surface of a lower portion of the casing 23 (20). The first opening 41 is open at a lower portion of the inner surface of the space forming body 35 which faces the acoustic space S. Specifically, as shown in FIG. 13, for example, a position of the lowermost end 41x of the first opening 41 is a position at a distance d2 within an inner diameter d1 of the first opening 41 from the lowermost end Sx of the inner surface of the space forming body 35 which faces the acoustic space S.

The drain pipe 43 is connected to the second opening 42 of the drain hole 40 as shown in FIG. 12. The valve 44 is provided in the drain pipe 43.

Here, as shown in FIG. 13, a portion of the space forming body 35 which includes the first opening 41 that opens in the inner surface facing the acoustic space S and which maintains the inner diameter of the first opening 41 from the inner surface including the first opening 41 in an extending direction of the drain hole 40 is referred to as a first opening portion 41a. An inner diameter of the first opening portion 41a is smaller than that of the other portion of the drain hole 40. In other words, the inner diameter of the drain hole 40 excluding the first opening portion 41a is larger than that of the first opening portion 41a. An opening area of the first opening 41 is 20% or less of the total opening area of all the acoustic holes 34 in a portion of the perforated plate 31 which defines the acoustic space S in which the first opening 41 is open, in other words, all the acoustic holes 34 facing the acoustic space S in which the first opening 41 is open. The opening area of the first opening 41 is preferably 10% or less of the total opening area of all the acoustic holes 34. This is to minimize a decrease in the sound absorption effect due to the acoustic space S even when the acoustic space S and the drain hole 40 communicate with each other. The reason why the inner diameter of the drain hole 40 excluding the first opening 41 is larger than that of the first opening 41 is to allow the liquid which has passed through the first opening 41 to be easily discharged outside the casing 20.

A length t (m) of the first opening portion 41a in the extending direction of the drain hole 40 is preferably a value represented by the following Equation (1).

t≤c/fmax/2  (1)

In Equation (1), fmax (Hz) indicates an upper limit of the sound absorption frequency range by the acoustic space S. and c (m/s) indicates the velocity of sound.

As described above, since the silencer 30G of this embodiment has the drain hole 40, the liquid remaining in the acoustic space S can be discharged outside the acoustic space S. Thus, in this embodiment, the problem in that the silencer 30G cannot absorb the sound in the target frequency range can be avoided, and the reduction of the sound absorption effect can be curbed. When the liquid remaining in the acoustic space S is discharged, the valve 44 is opened. However, when the liquid remaining in the acoustic space S is not discharged, the valve 44 is closed to curb the pressure leak of the gas in the passage.

In this embodiment, the second opening 42 of the drain hole 40 for each of the plurality of acoustic spaces S is open in an outer surface of the casing 20. However, for example, when there are three acoustic spaces S, only the second opening 42 of the drain hole 40 of the first acoustic space S may be open in the outer surface of the casing 20. In this case, the second opening 42 of the drain hole 40 in the second acoustic space S is open in the first acoustic space S, and the second opening 42 of the drain hole 40 in the third acoustic space S is open in the first acoustic space S or the second acoustic space S. Even in this case, the liquid remaining in the second acoustic space S and the third acoustic space S flows into the first acoustic space S and is then discharged from the first acoustic space S to the outside of the casing 20 through the drain hole 40.

Eighth Embodiment

A centrifugal compressor according to an eighth embodiment % ill be described with reference to FIG. 14.

The centrifugal compressor according to this embodiment is a modified example of the centrifugal compressor according to the seventh embodiment. A silencer 30H in this embodiment also includes the perforated plate 31, the space forming body 35, the drain hole 40, the drain pipe, and the valve, as in the silencer 30G in the seventh embodiment. The perforated plate 31 has the plurality of acoustic holes 34 formed therein. The space forming body 35 forms the plurality of acoustic spaces S. The drain hole 40 is provided for each of the plurality of acoustic spaces S. The drain pipe is provided for each of the plurality of drain holes 40. The valve is provided for each of the plurality of drain pipes. FIG. 14 shows only part of the perforated plate 31, the space forming body 35, and the drain hole 40 among the parts of the silencer 30H and does not show other elements to clarify the characteristics of the silencer 30H of this embodiment. However, the other elements are the same as the corresponding elements shown in FIG. 12 showing the centrifugal compressor according to the seventh embodiment.

As in the silencer 30G of the seventh embodiment, the silencer 30H in this embodiment is also disposed so that the first surface 32 of the perforated plate 31 forms part of the inner surface of the radial passage 26. The drain hole 40 in this embodiment has a first opening 41h and a second opening, as in the drain hole 40 in the seventh embodiment. The first opening 41h is open in the inner surface of the space forming body 35 which faces the acoustic space S. The second opening is open in the outer surface of the lower portion of the casing 20. The first opening 41h of the drain hole 40 in this embodiment is basically not limited in the opening area, as in the first opening 41 of the drain hole 40 in the seventh embodiment. Therefore, the opening area of the first opening 41h of the drain hole 40 in this embodiment may be larger than that of the first opening 41 of the drain hole 40 in the seventh embodiment.

The silencer 30H in this embodiment further includes a moisture absorbing member 45 disposed in the drain hole 40. The moisture absorbing member 45 includes particles of a plurality of moisture absorbents 46, and an adhesive which connects the particles of the plurality of moisture absorbents 46. The moisture absorbent 46 is a solid which absorbs moisture, or a material which can be handled as a solid while moisture is absorbed. Specifically, the moisture absorbent 46 is silica gel, calcium chloride, calcium oxide or the like. An amount of the moisture absorbent 46 in the moisture absorbing member 45 is determined on the basis of an amount of liquid assumed to remain in the acoustic space S, a moisture absorption capacity of the moisture absorbent 46, an environmental change such as a temperature change and a pressure change in the acoustic space S, and the like.

The moisture absorbing member 45 is disposed at a position in the drain hole 40 including the first opening 41h or a position close to the first opening 41h. In other words, the moisture absorbing member 45 is disposed at a position in the drain hole 40 substantially including the first opening 41h. In a region in the drain hole 40 in which the moisture absorbing member 45 is disposed in the extending direction of the drain hole 40, the moisture absorbing member 45 is provided so that the drain hole 40 is closed. That is, an area of the drain hole 40 in a direction perpendicular to the extending direction of the drain hole 40 is substantially equal to a cross-sectional area of the moisture absorbing member 45 in the direction perpendicular to the extending direction of the drain hole 40. Therefore, in this embodiment, even when the acoustic space S and the drain hole 40 communicate with each other, the decrease in the sound absorption effect due to the acoustic space S can be minimized.

Since the silencer 30H of this embodiment also has the drain hole 40 as described above, the liquid remaining in the acoustic space S can be discharged outside the acoustic space S. Specifically, the liquid component in the acoustic space S is adsorbed by the moisture absorbing member 45 in the drain hole 40. When the liquid component adsorbed by the moisture absorbing member 45 is discharged, the valve 44 is opened. As a result, the liquid component adsorbed by the moisture absorbing member 45 is discharged outside the casing 20 through the drain hole 40 and the drain pipe 43. When the liquid component adsorbed by the moisture absorbing member 45 is not discharged, the valve 44 is closed to curb the pressure leak of the gas in the passage.

Also in this embodiment, the liquid remaining in the acoustic space S can be discharged outside the acoustic space S. Therefore, the problem that the silencer 30H cannot absorb the sound in the target frequency range can be avoided, and the reduction of the sound absorption effect can be curbed. Furthermore, in this embodiment, since the moisture absorbing member 45 is provided in the drain hole 40 to close the drain hole 40, the reduction of the sound absorption effect due to the communication between the acoustic space S and the drain hole 40 is further curbed.

The second opening of the drain hole 40 for each of the plurality of acoustic spaces S in this embodiment is open in the outer surface of the casing 20, as in the seventh embodiment. However, for example, when there are three acoustic spaces S, only the second opening of the drain hole 40 of the first acoustic space S may be open in the outer surface of the casing 20. In this case, the second opening of the drain hole 40 of the second acoustic space S is open in the first acoustic space S, and the second opening of the drain hole 40 of the third acoustic space S is open in the first acoustic space S or the second acoustic space S. The moisture absorbing member 45 is disposed in each of the drain holes 40, as in this embodiments. Also in this case, the liquid remaining in the second acoustic space S and the third acoustic space S flows into the first acoustic space S and is then discharged from the first acoustic space S through the drain hole 40 to the outside of the casing 20.

Ninth Embodiment

A centrifugal compressor according to a ninth embodiment will be described with reference to FIG. 15.

The centrifugal compressor according to this embodiment is a modified example of the centrifugal compressor according to the eighth embodiment. A silencer 30I in this embodiment also includes the perforated plate 31, the space forming body 35, the drain hole 40, and the moisture absorbing member 45, as in the silencer 30H in the eighth embodiment. A plurality of acoustic holes 34 are formed in the perforated plate 31. The space forming body 35 forms a plurality of acoustic spaces S. The drain hole 40 is formed for each of the plurality of acoustic spaces S. The moisture absorbing member 45 is provided for each of the plurality of drain holes 40. However, the silencer 30I according to this embodiment does not include the drain pipe 43 provided for each of the plurality of drain holes 40 and the valve 44 provided for each of the plurality of drain pipes 43 in the silencers 30G and 30H according to the seventh and eighth embodiments

As in the silencer 30G of the eighth embodiment, the silencer 30I in this embodiment is also disposed so that the first surface 32 of the perforated plate 31 forms part of the inner surface of the radial passage 26. Unlike the drain hole 40 in the seventh embodiment and the eighth embodiment, the drain hole 40i of this embodiment is formed in the perforated plate 31. The drain hole 40i has a first opening 41i and a second opening 42i. The first opening 41i is open in the first surface 32 of the perforated plate 31. The second opening 42i is open in the second surface 33 of the perforated plate 31. The second opening 42 is open at a lower portion of the perforated plate 31. Specifically, for example, a position of the lowermost end of the second opening 42 is a position at a distance within the inner diameter of the second opening 42 from the lowermost end in the acoustic space S.

The moisture absorbing member 45 is the same as the moisture absorbing member 45 of the eighth embodiment. The moisture absorbing member 45 is disposed in the drain hole 40i to close the drain hole 40i. Thus, even when the acoustic space S and the drain hole 40i communicate with each other, the decrease in the sound absorption effect due to the acoustic space S can be minimized.

Since the silencer 30I of this embodiment also has the drain hole 40i as described above, the liquid remaining in the acoustic space S can be discharged outside the acoustic space S. Specifically, the liquid component in the acoustic space S is adsorbed by the moisture absorbing member 45 in the drain hole 40i. The liquid component adsorbed by the moisture absorbing member 45 is discharged into the radial passage 26. Therefore, in this embodiment, the problem that the silencer 30I cannot absorb the sound in the target frequency range can be avoided, and the reduction of the sound absorption effect can be curbed. In this embodiment, since the moisture absorbing member 45 is provided in the drain hole 40i to close the drain hole 40i, the reduction of the sound absorption effect can be further curbed as compared with the seventh embodiment. In the silencer 30I according to this embodiment, the drain pipe 43 and the valve 44 in the silencers 30G and 30H in the seventh and eighth embodiments are unnecessary, and the drain hole 40i only needs to be formed in the perforated plate 31. As a result, the silencer 30I can be simplified in structure, and manufacturing cost can be reduced.

The drain discharge mechanism of any one of the silencers 30G, 30H, and 30I in the above-described seventh to ninth embodiments may be applied to the silencer in each of the first to fourth embodiments and each of the modified examples of the first embodiment. The drain discharge mechanism of any one of the silencers 30G, 30H, and 30I in the above-described seventh to ninth embodiments may be applied to a silencer in which the first surface 32 of the perforated plate 31 is disposed to form part of the inner surface of the intermediate passage 23p (shown in FIG. 1).

Further, although the centrifugal compressors in the above-described embodiments and modified examples are all multistage centrifugal compressors, the centrifugal compressor according to the present invention is not limited to the multistage centrifugal compressors. That is, the centrifugal compressor according to the present invention may be a single-stage centrifugal compressor having one impeller.

Claims

1. A centrifugal compressor comprising:

one or more impellers configured to rotate about an axis and to send a gas to a radially outer side of the axis;

a casing configured to cover the one or more impellers and to guide the gas from an inlet to an inside to discharge the gas from an outlet and having an outlet scroll passage which extends in a circumferential direction of the axis and communicates with the outlet; and

a silencer,

wherein the silencer includes a perforated plate in which a first surface and a second surface opposite to the first surface and a plurality of acoustic holes penetrating from the first surface to the second surface are formed, and a space forming body configured to form an acoustic space connected to the plurality of acoustic holes on a second surface side of the perforated plate, and

the first surface of the silencer forms part of an inner surface of the casing which defines the outlet scroll passage.

2. The centrifugal compressor according to claim 1, wherein the first surface of the silencer forms only part of the inner surface of the outlet scroll passage.

3. The centrifugal compressor according to claim 1, wherein:

a first silencer and a second silencer are provided as the silencers,

the casing has a radial passage which guides the gas flowing out from a final stage impeller of the one or more impellers to the radially outer side and communicates with the outlet scroll passage,

the first surface of the first silencer forms part of the inner surface of the outlet scroll passage, and

the first surface of the second silencer forms part of an inner surface which defines the radial passage.

4. The centrifugal compressor according to claim 3, wherein the first surface of the second silencer does not form an inner surface in an inner region including an end on a radially inner side of the axis but forms at least part of the inner surface in an outer region on the radially outer side from the inner region in the radial passage.

5. The centrifugal compressor according to claim 3, wherein:

a short distance silencer and a long distance silencer are provided as the second silencers,

the short distance silencer is disposed at a position closer to the final stage impeller than the long distance silencer in a radial direction of the axis, and

inner diameters of the plurality of acoustic holes of the short distance silencer are smaller than those of the plurality of acoustic holes of the long distance silencer.

6. The centrifugal compressor according to claim 1, wherein at least part of the space forming body of the silencer is formed of the same material as that of the casing and integrally formed with the casing.

7. The centrifugal compressor according to claim 6, wherein the perforated plate is formed of a material having a linear expansion coefficient larger than that of the casing.

8. The centrifugal compressor according to claim 1, wherein the silencer has a drain hole which discharges a liquid in the acoustic space outside of the acoustic space.

9. The centrifugal compressor according to claim 8, wherein:

the drain hole has a first opening which opens in the first surface of the perforated plate, and a second opening which opens in the second surface of the perforated plate, and

a moisture absorbent is disposed in the drain hole.

10. The centrifugal compressor according to claim 1, wherein inner diameters of the plurality of acoustic holes are 0.1 to 3.0 mm.

11. The centrifugal compressor according to claim 10, wherein inner diameters of the plurality of acoustic holes are 0.2 to 1.0 mm.

12. A centrifugal compressor comprising:

one or more impellers configured to rotate about an axis and to send a gas to a radially outer side of the axis;

a casing configured to cover the one or more impellers and to guide the gas from an inlet to an inside to discharge the gas from an outlet and having an outlet passage which guides the gas flowing out from a final stage impeller of the one or more impellers to the outlet; and

a short distance silencer and a long distance silencer as silencers,

wherein each of the short distance silencer and the long distance silencer includes a perforated plate in which a first surface and a second surface opposite to the first surface and a plurality of acoustic holes penetrating from the first surface to the second surface are formed, and a space forming body configured to form an acoustic space connected to the plurality of acoustic holes on a second surface side of the perforated plate,

both the first surface of the short distance silencer and the first surface of the long distance silencer form part of an inner surface of the casing which defines the outlet passage,

a distance along the outlet passage from the final stage impeller to the short distance silencer is shorter than that along the outlet passage from the final stage impeller to the long distance silencer, and

inner diameters of the plurality of acoustic holes of the short distance silencer are smaller than those of the plurality of acoustic holes of the long distance silencer.

13. The centrifugal compressor according to claim 12, wherein at least part of the space forming body of the silencer is formed of the same material as that of the casing and integrally formed with the casing.

14. The centrifugal compressor according to claim 13, wherein the perforated plate is formed of a material having a linear expansion coefficient larger than that of the casing.

15. The centrifugal compressor according to claim 12, wherein the silencer has a drain hole which discharges a liquid in the acoustic space outside of the acoustic space.

16. The centrifugal compressor according to claim 15, wherein the drain hole has a first opening which opens in an inner surface of the space forming body which faces the acoustic space, and a second opening which opens in an outer surface of the casing.

17. The centrifugal compressor according to claim 15, wherein:

the drain hole has a first opening which opens in the first surface of the perforated plate, and a second opening which opens in the second surface of the perforated plate, and

a moisture absorbent is disposed in the drain hole.

18. The centrifugal compressor according to claim 12, wherein inner diameters of the plurality of acoustic holes are 0.1 to 3.0 mm.

19. The centrifugal compressor according to claim 18, wherein inner diameters of the plurality of acoustic holes are 0.2 to 1.0 mm.

20. A centrifugal compressor comprising:

one or more impellers configured to rotate about an axis and to send a gas to a radially outer side of the axis;

a casing configured to cover the one or more impellers and to guide the gas from an inlet to an inside to discharge the gas from an outlet and having a passage which guides the gas flowing in from the inlet to the outlet through the one or more impellers; and

a silencer,

wherein the silencer includes a perforated plate in which a first surface and a second surface opposite to the first surface and a plurality of acoustic holes penetrating from the first surface to the second surface are formed, a space forming body configured to form an acoustic space connected to the plurality of acoustic holes on a second surface side of the perforated plate, and a drain hole configured to discharge a liquid in the acoustic space to an outside of the acoustic space, and

the first surface of the silencer forms part of an inner surface of the passage.

21. The centrifugal compressor according to claim 20, wherein the drain hole has a first opening which opens in an inner surface of the space forming body which faces the acoustic space, and a second opening which opens in an outer surface of the casing.

22. The centrifugal compressor according to claim 21, wherein an opening area of the first opening is 20% or less of a total opening area of all the acoustic holes in a portion of the perforated plate which defines one acoustic space.

23. The centrifugal compressor according to claim 21, wherein the silencer has a valve capable of partitioning a space in the drain hole from an outer space of the casing.

24. The centrifugal compressor according to claim 21, wherein a moisture absorbent is disposed in the drain hole.

25. The centrifugal compressor according to claim 20, wherein:

the drain hole has a first opening which opens in the first surface of the perforated plate, and a second opening which opens in the second surface of the perforated plate, and

a moisture absorbent is disposed in the drain hole.

26. The centrifugal compressor according to claim 20, wherein inner diameters of the plurality of acoustic holes are 0.1 to 3.0 mm.

27. The centrifugal compressor according to claim 26, wherein inner diameters of the plurality of acoustic holes are 0.2 to 1.0 mm.

28. A centrifugal compressor comprising:

one or more impellers configured to rotate about an axis and to send a gas to a radially outer side of the axis;

a casing configured to cover the one or more impellers and to guide the gas from an inlet to an inside to discharge the gas from an outlet; and

a silencer,

wherein the casing has a passage configured to guide the gas flowing in from the inlet to the outlet through the one or more impellers,

the silencer includes a perforated plate in which a first surface and a second surface opposite to the first surface and a plurality of acoustic holes penetrating from the first surface to the second surface are formed, and a space forming body configured to form an acoustic space connected to the plurality of acoustic holes on a second surface side of the perforated plate,

the first surface of the silencer forms part of an inner surface of the casing which defines the passage,

at least part of the space forming body is formed of the same material as that of the casing and integrally formed with the casing, and

the perforated plate is formed of a material having a linear expansion coefficient larger than that of the casing.

29. The centrifugal compressor according to claim 28, wherein inner diameters of the plurality of acoustic holes are 0.1 mm or more to 3.0 mm or less.

30. The centrifugal compressor according to claim 29, wherein inner diameters of the plurality of acoustic holes are 0.2 mm or more to 1.0 mm or less.