TWI827145B - Centrifugal compressor - Google Patents

Abstract

A centrifugal compressor including an air inlet, a flow channel, a volute passage, an air inlet guide vane, a first-stage impeller, a second-stage impeller, a deswirl vane base and an economizer injection passage is provided. The flow channel has a first diffuser section, a first turning section, a reflux section, a second turning section and a second diffuser section. The volute passage is connected to the second diffuser section. The first-stage impeller is disposed between the air inlet and the first diffuser section. The second-stage impeller is disposed between the second turning section and the second reflux section. The deswirl vane base has a plurality of deswirl wings located in the reflux section and a plurality of injection holes communicated with the deswirl section. Each deswirl wing has a first wing portion, a second wing portion and a trench located between the first wing portion and the second wing portion. The injection holes are respectively seated in the trenches, and the economizer injection passage is communicated with the injection holes.

Description

centrifugal compressor

The present invention relates to a centrifugal compressor, and in particular to a two-stage centrifugal compressor.

A common two-stage centrifugal compressor includes a first-stage impeller and a second-stage impeller. The first-stage impeller is located upstream of the flow channel, and the second-stage impeller is located downstream of the flow channel. First, the first fluid (such as gaseous refrigerant, air or carbon dioxide, etc.) flows from the inlet guide vane along the long axis direction of the drive shaft to the first-stage impeller. Then, the first-stage impeller pressurizes the first fluid and drives the second-stage impeller. A fluid flows into the flow channel along the centrifugal direction. Then, the first fluid turns in the first turning section of the flow channel and flows toward the second-stage impeller along the centripetal direction. Specifically, the second-stage impeller is configured corresponding to the second turning section of the flow channel, and the economizer injection channel is connected to the second turning section of the flow channel to inject the second fluid (such as gaseous refrigerant, air or carbon dioxide, etc.) The second turning section of the flow channel allows the first fluid and the second fluid to form a third fluid in the second turning section of the flow channel. After that, the third fluid flows to the second-stage impeller, and is pressurized by the second-stage impeller and flows to the volute flow channel along the centrifugal direction.

Generally speaking, a return flow can be provided between the first-stage impeller and the second-stage impeller. The guide vane base, and the second flow system from the economizer is guided by the multiple return wings on the return guide vane base to be injected into the second turning section of the flow channel. Furthermore, a return channel is formed between any two adjacent return wings, and the second fluid easily generates turbulence in the return channel, resulting in the inability of the first fluid and the second fluid to mix uniformly, and resulting in fluid pressure loss. Increase and decline in aerodynamic efficiency, etc., thus affecting the performance of centrifugal compressors.

The present invention provides a centrifugal compressor, which helps reduce the turbulence between the bases of return guide vanes and improves compression efficiency.

The invention proposes a centrifugal compressor, which includes an air inlet, a flow channel, a first-stage impeller, a second-stage impeller, a return guide vane base and an economizer injection channel. The flow channel is connected to the air inlet and has a first expansion section, a first turning section connected to the first expansion section, a return section connected to the first turning section, a second turning section connected to the return section, and a second turning section connected to the first turning section. The second expansion section of the section and the volute flow channel connecting the second expansion section. The first-stage impeller is arranged between the air inlet and the first diffusion section. The second stage impeller is arranged between the second turning section and the second expansion section. The return guide vane base is disposed between the first-stage impeller and the second-stage impeller, and has a plurality of return wings located in the return section and a plurality of injection holes connected to the return section. Each return wing has a first wing part, a second wing part and a slit separating the first wing part and the second wing part. The plurality of injection holes respectively fall into the plurality of slits. The economizer injection channel is connected to the plurality of injection holes.

In an embodiment of the present invention, the slits of the above-mentioned return wing have relative There are two exits, and the distance between the two exits is D. The distance between the injection hole and one outlet is between 1/4D and D.

In an embodiment of the present invention, the first wing portion of the above-mentioned return wing has an outer end portion relative to the slit, and the second wing portion of each return wing has an inner end portion relative to the slit. The distance between the outer end of the first wing and the inner end of the second wing is S, and the distance between the slit and the inner end of the second wing is between 3/4S and 1/2S. between.

In an embodiment of the present invention, the airfoil of the above-mentioned return airfoil includes a concave and convex airfoil, a plano-convex airfoil, a symmetrical airfoil, an S-shaped airfoil and a flat airfoil.

In an embodiment of the present invention, the above-mentioned centrifugal compressor further includes a drive shaft, and the first-stage impeller and the second-stage impeller are sleeved on the drive shaft.

In an embodiment of the present invention, the central axis of the above-mentioned injection hole is parallel to the driving shaft.

In an embodiment of the present invention, the central axis of the above-mentioned injection hole is perpendicular to the return section.

In one embodiment of the present invention, the above-mentioned injection hole includes a tapered hole, a straight hole, or a combination of a tapered hole and a straight hole.

In an embodiment of the present invention, the slits of the above-mentioned return wing include arc-shaped slits or linear slits.

In one embodiment of the present invention, the above-mentioned return guide vane base has a first surface located in the return section and a second surface opposite to the first surface, and the plurality of injection holes penetrates the first surface and the second surface. .

In an embodiment of the present invention, the first wing portion and the second wing portion of the above-mentioned return wing protrude from the first surface.

In an embodiment of the present invention, the above-mentioned injection hole has a first opening connected to the slit and a second opening relative to the first opening, and the aperture of the first opening is smaller than the aperture of the second opening.

In an embodiment of the present invention, the above-mentioned injection hole is located in the return section adjacent to the first turning section.

In an embodiment of the present invention, the above-mentioned injection hole is located at the second turning section away from the return section.

In one embodiment of the present invention, the centrifugal compressor further includes an economizer, which is connected to the economizer injection channel and is arranged outside the centrifugal compressor.

In an embodiment of the present invention, the centrifugal compressor further includes an air inlet guide vane, which is arranged at the air inlet.

In an embodiment of the present invention, the above-mentioned return guide vane base has a third surface located in the first expansion section and a fourth surface opposite to the third surface, and the plurality of injection holes penetrates the third surface and Fourth surface.

In an embodiment of the present invention, the first wing portion and the second wing portion of each of the above-mentioned return wings protrude from the third surface.

Based on the above, in the centrifugal compressor of the present invention, the injection position of the second fluid falls within the return section of the flow channel, so that the first fluid and the second fluid have a longer flow path before flowing to the second-stage impeller. to mix evenly. On the other hand, the second fluid injected into the return section of the flow channel splits in the slit and undergoes the first adjustment. flow, continue, the second fluid flows from the return section to the second turning section along the outer peripheral edge of the second wing portion of the return wing, and performs a second rectification to make the second fluid in the return section consistent with the flow direction of the first fluid , and reduce the generation of turbulence, so that the first fluid and the second fluid can be evenly mixed in the flow channel, thereby reducing fluid pressure loss and improving aerodynamic efficiency, thereby improving the compression efficiency of the centrifugal compressor.

In order to make the above-mentioned features and advantages of the present invention more obvious and easy to understand, embodiments are given below and described in detail with reference to the accompanying drawings.

100:Centrifugal compressor

101: Sealed space

102:Seals

110:Air inlet

120:Flow channel

121: First expansion section

122: The first turning point

123:Reflow section

124: The second turning point

125: Second expansion section

130: Volute runner

140:Inlet guide vane

150: Drive shaft

160:First stage impeller

170:Second stage impeller

180:Return guide vane base

180a: First return guide vane base

180b: Second return guide vane base

181, 181a~181e, 181’: return wing

182, 182’: Injection hole

183, 183’: First wing

183a: Outer end

184, 184’: Second wing

184a:Inner end

185, 1851, 185’: slit

185a:Export

186, 1861: First surface

186’:Third surface

187: Second surface

187’:Fourth surface

188:First opening

189:Second opening

190:Energy saver injection channel

A1, A2: aperture

D, D1, S, S1: distance

F1: first fluid

F2: Second fluid

F3: Third fluid

R:Region

FIG. 1A is a schematic cross-sectional view of a centrifugal compressor according to an embodiment of the present invention.

FIG. 1B is an enlarged schematic diagram of the region R in FIG. 1A .

2A to 2C are schematic views of the return guide vane base from different viewing angles according to an embodiment of the present invention.

3 to 7 are schematic top views of the return guide vane base in other embodiments of the present invention.

Figure 8 is a partially enlarged schematic diagram of a centrifugal compressor according to another embodiment of the present invention.

Figure 9 is a partially enlarged schematic diagram of a centrifugal compressor according to yet another embodiment of the present invention.

FIG. 1A is a schematic cross-sectional view of a centrifugal compressor according to an embodiment of the present invention. FIG. 1B is an enlarged schematic diagram of the region R in FIG. 1A . Please refer to FIGS. 1A and 1B . In this embodiment, the centrifugal compressor 100 may be a two-stage centrifugal compressor and includes an air inlet 110 , a flow passage 120 , an air inlet guide vane 140 , a drive shaft 150 , and a third The first-stage impeller 160, the second-stage impeller 170, the return guide vane base 180 and the economizer injection channel 190. The air inlet 110 is connected to the flow channel 120, in which the air inlet guide vane 140 is arranged in the air inlet 110, and the first-stage impeller 160, the second-stage impeller 170, the return guide vane base 180 and the economizer injection channel 190 are along the Runner 120 configuration. In addition, the first-stage impeller 160 and the second-stage impeller 170 are sleeved on the drive shaft 150 to rotate synchronously and in the same direction with the drive shaft 150 .

In detail, the flow channel 120 has a first expansion section 121, a first turning section 122, a return section 123, a second turning section 124, a second expansion section 125 and a volute flow channel 130, and the first expansion section 121. The first turning section 122, the return section 123, the second turning section 124 and the second expansion section 125 are arranged in sequence between the air inlet 110 and the volute channel 130.

The air inlet 110 is connected to the first expansion section 121 , and the first-stage impeller 160 is arranged between the air inlet 110 and the first expansion section 121 . The first turning section 122 is connected to the first expansion section 121 , and the return section 123 is connected to the first turning section 122 . The second turning section 124 is connected to the return section 123 , and the second expansion section 125 is connected to the second turning section 124 . The second-stage impeller 170 is disposed between the second turning section 124 and the second diffusion section 125 , and the volute flow channel 130 is connected to the second diffusion section 125 .

During the operation of the centrifugal compressor 100, the first fluid F1 (such as gas The refrigerant (state refrigerant) is guided to the air inlet 110 by the inlet guide vanes 140 and flows toward the first-stage impeller 160 along the axial direction (for example, parallel to the long axis direction of the drive shaft 150 ). Next, the first-stage impeller 160 pressurizes the first fluid F1 and drives the first fluid F1 to flow into the first diffusion section 121 along the centrifugal direction (for example, the long axis direction away from the driving shaft 150 ). Then, the first fluid F1 flows from the first expansion section 121 into the first turning section 122 and is turned to flow into the return section 123 along the centripetal direction (for example, close to the long axis direction of the driving shaft 150 ). On the other hand, the centrifugal compressor 100 further includes an economizer (not shown). The economizer is connected to the economizer injection channel 190 and is disposed outside the centrifugal compressor 100 . Among them, the economizer injection channel 190 is connected to the return section 123 to inject the second fluid F2 (for example, gaseous refrigerant) into the return section 123, so that the first fluid F1 and the second fluid F2 form a third fluid F3 in the return section 123. . Then, the third fluid F3 flows from the return section 123 into the second turning section 124 . Afterwards, the second-stage impeller 170 pressurizes the third fluid F3 and drives the third fluid F3 to flow into the second diffuser section 125 along the centrifugal direction, and then flows from the second diffuser section 125 into the volute channel 130 .

Continuing from the above, the injection position of the second fluid F2 falls within the return section 123 of the flow channel 120, so that the first fluid F1 and the second fluid F2 have a longer flow path to evenly mix before flowing to the second-stage impeller 170. Thereby, the compression efficiency of the centrifugal compressor 100 is improved. The first fluid F1 and the second fluid F2 may be gaseous refrigerant, air, carbon monoxide, carbon dioxide, oxygen, hydrogen or related mixed gases.

2A to 2C are schematic views of the return guide vane base from different viewing angles according to an embodiment of the present invention. Please refer to Figure 1B, Figure 2A and Figure 2B. In this embodiment, the return guide vane base 180 is disposed between the first-stage impeller 160 and the second-stage impeller 170. It has a plurality of return wings 181 located in the return section 123 and a plurality of injection holes 182 connected to the return section 123 . The plurality of return wings 181 are arranged in a radial pattern, and each return wing 181 is provided with an injection hole 182 . In detail, each return wing 181 has a first wing part 183, a second wing part 184 and a slit 185 between the first wing part 183 and the second wing part 184, and the first wing part 183 and the second wing part 184. The wings 184 are separated by slits 185 . In addition, the injection hole 182 falls within the slit 185, the economizer injection channel 190 is connected to the injection hole 182, and the injection hole 182 is connected to the return section 123 through the slit 185, so the second fluid F2 can pass through the injection hole 182 and Slit 185 injects recirculation section 123 .

As shown in FIGS. 1A and 1B , the central axis of the injection hole 182 is parallel to the driving shaft 150 and substantially perpendicular to the return section 123 , so the second fluid F2 can be directly injected into the return section 123 along the axial direction. In other embodiments, the central axis of the injection hole 182 is inclined to the return section 123 , so the second fluid F2 can be sprayed obliquely into the return section 123 .

Please refer to FIG. 1B , FIG. 2A , FIG. 2B and FIG. 2C . In this embodiment, the airfoil of the return wing 181 is a concave and convex airfoil, and the slit 185 of each return wing 181 is an arc-shaped slit. On the other hand, the return guide vane base 180 has a first surface 186 located in the return section 123 and a second surface 187 opposite to the first surface 186, and the plurality of injection holes 182 penetrate the first surface 186 and the second surface. 187. Specifically, the first wing portion 183 and the second wing portion 184 of each return wing 181 protrude from the first surface 186. When the second fluid F2 flows into the slit 185 from the injection hole 182, the second fluid F2 can flow into the slit 185. A split flow is generated in the slit 185 and a first rectification is performed to flow along the two opposite wing surfaces of the second wing portion 184 respectively, thereby achieving the third flow through the near-wall effect. The effect of secondary rectification occurs and flows from the return section 123 to the second turning section 124 .

As shown in FIGS. 1B , 2B and 2C , each injection hole 182 has a first opening 188 connected to the slit 185 and a second opening 189 opposite to the first opening 188 , wherein the first opening 188 is connected to the first surface. 186, and the second opening 189 is connected to the second surface 187. In detail, the second fluid F2 from the economizer injection channel 190 flows from the second opening 189 to the first opening 188 , and then flows from the first opening 188 into the slit 185 . Since the hole diameter A1 of the first opening 188 is smaller than the hole diameter A2 of the second opening 189 , it helps to increase the pressure loss of the second fluid F2 when the second fluid F2 is injected into the slit 185 or the return section 123 .

As shown in FIG. 1B , in this embodiment, the injection hole 182 may be a tapered hole, and the hole diameter gradually decreases from the second surface 187 to the first surface 186 . In another embodiment, the injection hole 182 may be a straight hole, and the hole diameter remains consistent from the second surface 187 to the first surface 186 . In yet another embodiment, the injection hole 182 may be a combination of a tapered hole and a straight hole, where the tapered hole is connected to the second surface 187 and the straight hole is connected to the first surface 186 .

As shown in Figure 2C, in this embodiment, the slit 185 of each return wing 181 has two opposite outlets 185a, where the distance between the two outlets 185a is D (that is, the length of the slit 185) , and the distance D1 between the injection hole 182 (for example, the first opening 188 of the injection hole 182) and one outlet 185a is between 1/4D and D. For example, the injection hole 182 may be positioned at the center of gravity of the return wing 181 .

As shown in FIGS. 1B and 2C , the first wing 183 of each return wing 181 is further away from the second turning section 124 than the second wing 184 , wherein the first wing 183 has an outer end 183 a relative to the slit 185 . , and the second wing 184 has an angle relative to the slit 185 The inner end 184a. The slit 185 of each return wing 181 is located between the outer end 183 a of the first wing 183 and the inner end 184 a of the second wing 184 , and the inner end 184 a is closer to the second turning section 124 than the slit 185 . The distance between the outer end 183a of the first wing 183 of each return wing 181 and the inner end 184a of the second wing 184 is S (that is, the length of the return wing 181), and the slit 185 and the second wing are The distance S1 between the inner ends 184a of the portions 184 is between 3/4S and 1/2S, that is, the slit 185 is disposed at the center of gravity of the return wing 181 . In addition, the first fluid F1 is rectified in the return section 123 along the space between two adjacent return wings 181, and the second fluid F2 injected into the return section 123 splits in the slit 185 and performs the first rectification, continuing, The second fluid F2 undergoes a second rectification along the outer peripheral edge of the second wing portion 184 of the return wing 181 and merges with the first fluid F1. Among them, the injection hole 182 located in the return wing 181 is located in the return section 123 adjacent to the first turning section 122 and away from (or far away from) the second turning section 124, so that the first fluid F1 and the second fluid F2 are in There is a longer flow path before flowing to the second-stage impeller 170 for uniform mixing, thereby improving the compression efficiency of the centrifugal compressor 100 .

As shown in FIG. 1B and FIG. 2A , the second fluid F2 is injected into the flow channel 120 along the axial direction (for example, parallel to the long axis direction of the driving shaft 150 ), and the injection position of the second fluid F2 is located in the return section of the flow channel 120 Within 123. After the second fluid F2 is injected into the return section 123, the second fluid F2 splits in the slit 185 and performs first rectification. Then, the second fluid F2 flows along the outer periphery of the second wing portion 184 of the return wing 181. The return section 123 flows to the second turning section 124 for a second rectification and merges with the first fluid F1, so that the flow directions of the second fluid F2 in the return section 123 and the first fluid F1 are consistent, and the generation of turbulence is reduced. occurs, so that the first fluid F1 and the second fluid F2 can be uniformly mixed in the flow channel 120 to form the third fluid F3, thereby reducing fluid pressure loss and improving aerodynamic efficiency, thereby improving the compression efficiency of the centrifugal compressor 100.

Please refer to FIG. 1B , the second surface 187 of the return guide vane base 180 is adjacent to the sealed space 101 , in which the economizer injection channel 190 is connected to the injection hole 182 through the sealed space 101 , and the return guide vane base 180 , the second-stage impeller 170 and the machine A seal 102 is provided between the shells to prevent the second fluid F2 from leaking.

3 to 7 are schematic top views of the return guide vane base in other embodiments of the present invention. As shown in Figure 3, the slit 185 of the return wing 181 shown in Figure 2C is an arc-shaped slit. The difference is that the slit 1851 of the return wing 181a of this embodiment is a linear slit, and the linear slit is The tangential direction of the central circle extends. As shown in FIG. 4 , the airfoil of the return wing 181 shown in FIG. 2C is a concave and convex airfoil. The difference is that the airfoil of the return wing 181 b in this embodiment is a flat and convex airfoil. As shown in FIG. 5 , the airfoil of the return wing 181 shown in FIG. 2C is a concave and convex airfoil. The difference is that the airfoil of the return wing 181 c in this embodiment is an S-shaped airfoil. As shown in FIG. 6 , the airfoil of the return wing 181 shown in FIG. 2C is a concave and convex airfoil. The difference is that the airfoil of the return wing 181d in this embodiment is a symmetrical airfoil. As shown in FIG. 7 , the airfoil of the return wing 181 shown in FIG. 2C is a concave and convex airfoil. The difference is that the airfoil of the return wing 181e in this embodiment is a flat airfoil.

For example, depending on different design requirements, the slits of the return vanes shown in Figures 2C to 7 can be arc slits, linear slits, or a combination of arc slits and linear slits, and the return guide vane base The airfoil of the return wing on the airfoil may be one of the various airfoils shown in FIGS. 2C to 7 or at least a combination of more than two. In addition, in response to actual working conditions According to the requirements, the injection hole can be designed as a straight hole, a tapered hole or a combination of a straight hole and a tapered hole.

Figure 8 is a partially enlarged schematic diagram of a centrifugal compressor according to another embodiment of the present invention. Please refer to FIG. 1B first. The return guide vane base 180 of this embodiment includes a first return guide vane base 180a and a second return flow guide vane base 180b. The first return flow guide vane base 180a is located between the second stage impeller 170 and the second return flow guide vane base 180b. between the guide vane base 180b, and the second return flow guide vane base 180b is located between the first return flow guide vane base 180a and the first-stage impeller 160. The first surface 186 of the first return vane base 180a faces the first surface 1861 of the second return vane base 180b, and the first surface 186 of the first return vane base 180a and the second surface of the second return vane base 180b A surface 1861 is located in the return section 123 . The return wing 181 protrudes from the first surface 186 of the first return vane base 180a and contacts the first surface 1861 of the second return vane base 180b.

Next, please refer to Figure 8. Different from the above embodiment, the return wing 181 of this embodiment protrudes from the first surface 1861 of the second return guide vane base 180b and contacts the first surface 186 of the first return guide vane base 180a. . On the other hand, the injection hole 182 is located at the first return guide vane base 180a and is aligned with the slit 185 of the return flow vane 181 located at the second return flow guide vane base 180b.

Figure 9 is a partially enlarged schematic diagram of a centrifugal compressor according to yet another embodiment of the present invention. Please refer to Figure 9. Similarly, the return wing 181' and the injection hole 182' can be arranged in the first expansion section 121 according to the requirements of different working conditions, so that the return wing 181' protrudes from the second return guide vane base. The third surface 186' in 180b is away from the first surface 1861 and is provided corresponding to the first diffuser section 121 and the first-stage impeller 160. Specifically, the second return guide vane base 180b has a third surface 186’ located within the first diffuser section 121 and a fourth surface 187' relative to the third surface 186', and the plurality of injection holes 182' penetrate the third surface 186' and the fourth surface 187'. In addition, the first wing portion 183' and the second wing portion 184' of each return wing 181' protrude from the third surface 186'.

The injection position of the second fluid F2 falls within the first diffusion section 121 of the flow channel 120. After the second fluid F2 is injected into the first diffusion section 121, the second fluid F2 splits in the slit 185' and performs the third flow. After the first rectification, the second fluid F2 flows from the first expansion section 121 to the first turning section 122 along the outer peripheral edge of the second wing portion 184' of the return wing 181' to perform the second rectification and interact with the first The fluids F1 merge to make the flow directions of the second fluid F2 and the first fluid F1 in the first expansion section 121 consistent, and reduce the generation of turbulence, so that the first fluid F1 and the second fluid F2 can be evenly distributed in the flow channel 120 The third fluid F3 is mixed to form, thereby reducing fluid pressure loss and improving aerodynamic efficiency, thereby improving the compression efficiency of the centrifugal compressor 100 .

To sum up, in the centrifugal compressor of the present invention, the injection position of the second fluid falls within the front end of the return section (or first expansion section) of the flow channel, so that the first fluid and the second fluid are in the flow path. There is a longer flow path before the second stage impeller for uniform mixing. On the other hand, the second fluid injected into the return section (or first expansion section) of the flow channel splits in the slit and undergoes first rectification. Then, the second fluid flows along the second wing of the return wing. The outer peripheral edge flows from the return section to the second turning section, and performs a second rectification, so that the second fluid in the return section (or first expansion section) is consistent with the flow direction of the first fluid, and reduces the generation of turbulence, so that The first fluid and the second fluid can be evenly mixed in the flow channel, thereby reducing fluid pressure loss and improving aerodynamic efficiency, thereby improving the compression efficiency of the centrifugal compressor.

Although the present invention has been disclosed above through embodiments, they are not intended to limit the present invention. Anyone with ordinary knowledge in the technical field may make some modifications and modifications without departing from the spirit and scope of the present invention. Therefore, The protection scope of the present invention shall be determined by the appended patent application scope.

100:Centrifugal compressor

110:Air inlet

120:Flow channel

130: Volute runner

140:Inlet guide vane

150:Drive shaft

160:First stage impeller

170:Second stage impeller

180: Return guide vane base

190:Energy saver injection channel

F1: first fluid

F2: Second fluid

R:Region

Claims (17)

A centrifugal compressor includes: an air inlet; a flow channel connected to the air inlet and having a first expansion section, a first turning section connected to the first expansion section, and a first turning section connected to the first turning section. The return flow section, the second turning section connected to the return flow section, the second expansion section connected to the second turning section, and the volute flow channel connected to the second expansion section; the first-stage impeller is arranged at the air inlet between the first-stage impeller and the first-stage diffuser section; the second-stage impeller is arranged between the second turning section and the second-stage diffuser section; the return guide vane base is arranged between the first-stage impeller and the second-stage impeller. wherein the return guide vane base has a plurality of return wings located in the return section and a plurality of injection holes connected to the return section, and each of the return vanes has a first wing, a second wing and a second wing. The first wing part and the second wing part are separated by slits, and the injection holes respectively fall into the slits; and the economizer injection channel is connected to the injection holes, wherein each of the return flow The slit of the wing has two opposite outlets, and the distance between the two outlets is D. The distance between the injection hole and the outlet is between 1/4D and D. The centrifugal compressor of claim 1, wherein the first wing portion of each return wing has an outer end portion relative to the slit, and the second wing portion of each return wing has an outer end portion relative to the slit. The inner end of the slit, the outer end of the first wing and The distance between the inner ends of the second wing is S, and the distance between the slit and the inner end of the second wing is between 3/4S and 1/2S. The centrifugal compressor as claimed in claim 1, wherein the airfoil of each return airfoil includes a concave and convex airfoil, a plano-convex airfoil, a symmetrical airfoil, an S-shaped airfoil and a flat airfoil. The centrifugal compressor according to claim 1 further includes: a driving shaft, on which the first-stage impeller and the second-stage impeller are sleeved. The centrifugal compressor of claim 4, wherein the central axes of the injection holes are parallel to the driving shaft. The centrifugal compressor as claimed in claim 1, wherein the central axes of the injection holes are perpendicular to the return section. The centrifugal compressor of claim 1, wherein the injection holes include tapered holes, straight holes, or a combination of tapered holes and straight holes. The centrifugal compressor of claim 1, wherein the slits of each return wing include arcuate slits or linear slits. The centrifugal compressor according to claim 1, wherein the return guide vane base has a first surface located in the return section and a second surface opposite to the first surface, and the injection holes penetrate the first surface with that second surface. The centrifugal compressor of claim 9, wherein the first wing portion and the second wing portion of each return wing protrude from the first surface. The centrifugal compressor of claim 1, wherein each injection hole has a first opening connected to the corresponding slit and a second opening relative to the first opening, and the aperture of the first opening is smaller than The aperture of the second opening. The centrifugal compressor of claim 1, wherein the injection hole is located in the return section adjacent to the first turning section. The centrifugal compressor of claim 12, wherein the injection hole is located at the return section away from the second turning section. The centrifugal compressor as described in claim 1 further includes: an economizer connected to the injection channel of the economizer and arranged outside the centrifugal compressor. The centrifugal compressor as claimed in claim 1 further includes: an air inlet guide vane arranged at the air inlet. The centrifugal compressor of claim 1, wherein the return guide vane base has a third surface located in the first diffusion section and a fourth surface opposite to the third surface, and the injection holes penetrate the The third surface and the fourth surface. The centrifugal compressor of claim 16, wherein the first wing portion and the second wing portion of each return wing protrude from the third surface.

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