Compressor with optimized interstage inlet

Abstract

To provide a multistage centrifugal compressor having an optimized inter-stage inlet.SOLUTION: A compressor is provided. The compressor includes a first stage portion having a first impeller assembly and a first diffuser assembly, a second stage portion having a second impeller assembly and a second diffuser assembly, and an interstage portion located between the first stage portion and the second stage portion. The interstage portion includes a directional vane assembly, a collector passage surrounding the directional vane assembly, and a circumferentially-inserted slot fluidly coupling the collector passage to the directional vane assembly.SELECTED DRAWING: Figure 5

Description

Related Applications

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of and priority to U.S. Provisional Patent Application No. 62 / 885,563, filed August 12, 2019, the entire disclosure of which is incorporated herein by reference. [Background technology]

[0002] Buildings may include heating, ventilation, and air conditioning (HVAC) systems. Summary of the Invention

[0003] At least one embodiment is directed to a compressor that can include a first stage portion having a first impeller assembly and a first diffuser assembly, a second stage portion having a second impeller assembly and a second diffuser assembly, and an interstage portion located between the first and second stage portions. The interstage portion can include a director vane assembly, a collector passage surrounding the director vane assembly, and a circumferential insertion slot fluidly coupling the collector passage with the director vane assembly. [Brief explanation of the drawings]

[0004] [Figure 1] FIG. 1 illustrates a perspective view of a chiller assembly, according to some embodiments. [Figure 2] FIG. 2 is a side view of the chiller assembly of FIG. 1 according to some embodiments. [Figure 3] FIG. 2 is a perspective view of a multi-stage compressor that can be utilized with the chiller assembly of FIG. 1 according to some embodiments. [Figure 4] FIG. 4 is a top view of the multi-stage compressor of FIG. 3 according to some embodiments. [Figure 5] FIG. 4 is a cross-sectional side view of the multi-stage compressor of FIG. 3 according to some embodiments. [Figure 6A] 4 is an additional cross-sectional side view of the multi-stage compressor of FIG. 3 according to some embodiments. [Figure 6B]4 is an additional cross-sectional side view of the multi-stage compressor of FIG. 3 according to some embodiments. [Figure 6C] 4 is an additional cross-sectional side view of the multi-stage compressor of FIG. 3 according to some embodiments. [Figure 6D] 4 is an additional cross-sectional side view of the multi-stage compressor of FIG. 3 according to some embodiments. [Figure 7] FIG. 4 is a perspective view of a direction vane assembly that may be utilized by the multi-stage compressor of FIG. 3 according to some embodiments. [Figure 8] FIG. 8 is a cross-sectional front view of the directional valve assembly of FIG. 7 according to some embodiments. [Figure 9] FIG. 4 is a perspective cross-sectional view of another embodiment of an interstage return channel assembly that may be utilized in the multi-stage compressor of FIG. 3, according to some embodiments. [Figure 10] 4 is a plot depicting circumferential pressure distribution test data for the multi-stage compressor of FIG. 3 in accordance with some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0005] Referring generally to the drawings, there is shown a chiller assembly comprising a multi-stage centrifugal compressor with optimized interstage inlets. Centrifugal compressors are useful in a variety of applications requiring compression of a fluid, such as chillers. To achieve this compression, centrifugal compressors utilize rotating components to convert angular momentum into a static pressure increase of the fluid.

[0006] A single-stage centrifugal compressor has four main components: inlet, impeller, diffuser, and core. The inlet may include a collector or volute. The inlet may be a simple tube that draws a fluid (e.g., refrigerant) into the compressor and delivers the fluid to the impeller. The impeller is a set of rotating vanes that incrementally increase the energy of the fluid as it progresses from the center of the impeller (known as the eye of the impeller) to the outer periphery of the impeller (known as the tip of the impeller). Downstream of the impeller in the fluid path is a diffuser mechanism that acts to slow the fluid, thus converting the fluid's kinetic energy into static pressure energy. As the fluid exits the diffuser, it enters a collector or volute where, due to the shape of the collector or volute, further conversion of kinetic energy to static pressure occurs.

[0007] A multi-stage centrifugal compressor may include multiple inlets, impellers, and diffusers. Compared to a single-stage compressor, a multi-stage compressor can achieve a higher overall pressure ratio and better refrigeration cycle performance due to the presence of an economizer, as described in more detail below. A two-stage centrifugal compressor may operate as follows: a main fluid flow may flow through a first inlet, impeller, and diffuser assembly. Upon exiting the first diffuser assembly, the main fluid flow may be combined with a second fluid flow that enters the compressor through a second inlet. The combined main and secondary flows then travel through a second impeller and diffuser assembly before exiting the compressor through a collector or volute. Rather than attenuating the secondary flow at the top of the return channel or injecting the secondary flow into the main fluid flow at another point (both of which aerodynamically disrupt the main fluid flow), embodiments of the present disclosure include a collector cavity fluidically coupled to the secondary flow inlet. The collector cavity allows the secondary flow to be evenly distributed before being inserted into the main flow path, resulting in improved compressor performance.

[0008] 1-2, an exemplary implementation of a chiller assembly 100 is depicted. Chiller assembly 100 is shown to include a compressor 102 driven by a motor 104, a condenser 106, and an evaporator 108. Refrigerant circulates through chiller assembly 100 in a vapor compression cycle. Chiller assembly 100 may also include a control panel 114 for controlling operation of the vapor compression cycle within chiller assembly 100.

[0009] The motor 104 may be powered by a variable speed drive (VSD) 110. The VSD 110 receives alternating current (AC) power having a specific fixed line voltage and fixed line frequency from an AC power source (not shown) and provides power having a variable voltage and frequency to the motor 104. The motor 104 may be any type of electric motor that can be powered by the VSD 110. For example, the motor 104 may be a high-speed induction motor. The compressor 102 is driven by the motor 104 to compress refrigerant vapor from the evaporator 108 through a suction line 112 and deliver the refrigerant vapor to the condenser 106 through a discharge line 124. The compressor 102 may be a centrifugal compressor, a screw compressor, a scroll compressor, a turbine compressor, or any other type of suitable compressor. In each of the embodiments contemplated herein, the compressor 102 is a multi-stage centrifugal compressor.

[0010] The evaporator 108 includes an internal tube bundle (not shown), a supply line 120 for supplying a process fluid to the internal tube bundle, and a return line 122 for removing the process fluid therefrom. The supply line 120 and the return line 122 may be in fluid communication with components within the HVAC system (e.g., an air handler) via conduits for circulating the process fluid. The process fluid is a refrigerant for cooling the building and may be, but is not limited to, water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable liquid. The evaporator 108 is configured to reduce the temperature of the process fluid as it passes through the tube bundle of the evaporator 108 and exchanges heat with the refrigerant. The refrigerant vapor is formed in the evaporator 108 by a refrigerant liquid delivered to the evaporator 108 exchanging heat with the process fluid and undergoing a phase change to a refrigerant vapor.

[0011] The refrigerant vapor delivered by the compressor 102 to the condenser 106 transfers heat to the fluid. The refrigerant vapor condenses into a refrigerant liquid in the condenser 106 as a result of the heat transfer with the fluid. The refrigerant liquid from the condenser 106 flows through an expansion device and back to the evaporator 108, completing the refrigerant cycle of the chiller assembly 100. The condenser 106 includes a supply line 116 and a return line 118 for circulating a fluid between the condenser 106 and an external component of the HVAC system (e.g., a cooling tower). The fluid supplied to the condenser 106 via the return line 118 exchanges heat with the refrigerant in the condenser 106 and is removed from the condenser 106 via the supply line 116, completing the cycle. The fluid circulating through the condenser 106 may be water or any other suitable liquid.

[0012] The refrigerant can have an operating pressure of, for example, less than 400 kPa or about 58 psi. In some embodiments, the refrigerant is R1233zd. R1233zd is a non-flammable fluorinated gas that has a low global warming potential (GWP) compared to other refrigerants utilized in commercial chiller assemblies. GWP is a metric developed to allow for comparison of the global warming impact of different gases by quantifying how much energy emitting one ton of gas absorbs over a given period of time compared to emitting one ton of carbon dioxide.

[0013] 3 and 4, perspective and top views, respectively, of a multi-stage compressor 102 are depicted, according to some embodiments. The multi-stage compressor 102 is shown to include multiple structural components, including, but not limited to, a main inlet passage housing 305, a secondary inlet collector housing 310, a transition region housing 315, and a volute outlet housing 320. The coupling of the main inlet passage housing 305, the secondary inlet collector housing 310, the transition region housing 315, and the volute outlet housing 320 can be achieved using any suitable method (e.g., mechanical fasteners, welding). In various embodiments, one or more of the housing components 305-320 can be fabricated from one or more subcomponents that are inseparably or detachably coupled to one another.

[0014] The main inlet passage housing 305 may include an inlet 325 coupled to a suction pipe (e.g., suction line 112) that delivers the main supply of refrigerant vapor from an evaporator (e.g., evaporator 108) to the multi-stage compressor 102. In some embodiments, the inlet 325 includes or is coupled to a flow straightening element (not shown) having a plurality of flow directing vanes. The flow straightening element may be positioned upstream of a first stage impeller (described in further detail below with reference to FIGS. 5 and 6 ) positioned within the main inlet passage housing 305 to ensure axial flow at the first stage impeller inlet, thereby increasing the performance of the compressor 102.

[0015] The main inlet passage housing 305 is shown coupled to a secondary inlet collector housing 310. The secondary inlet collector housing 310 may include an inlet 330 coupled to an economizer (not shown) for delivering a secondary supply of refrigerant vapor to the multi-stage compressor 102. An economizer is a type of sub-cooler that can provide increased capacity, efficiency, and coefficient of performance (COP) to the chiller assembly 100. The economizer circuit may include a flash tank, an inlet line to the flash tank connected to a condenser (e.g., condenser 106) or the main refrigerant line downstream of the condenser, an expansion device incorporated in the inlet line, a first outlet line from the flash tank connected to the main refrigerant line upstream of the expansion device, and a second outlet line from the flash tank connected to the inlet 330 of the compressor 102. During operation, the economizer circuit improves system efficiency by providing refrigerant vapor at an intermediate pressure through the inlet 330, thereby increasing the pressure 3 and 4, in some embodiments, the inlet 330 is located at the top of the compressor 102, and the main inlet 325 and the secondary inlet 330 are oriented perpendicular to one another. However, the main inlet 325 and the secondary inlet 330 can be oriented in various directions relative to one another depending on the intended application, such that the main inlet 325 and the secondary inlet 330 may not be perpendicular to one another.

[0016] The secondary inlet collector housing 310 is shown coupled to a transition area housing 315. The secondary refrigerant flow provided by the economizer may flow circumferentially around the compressor before proceeding through an insertion slot formed by coupling the secondary inlet collector housing 310 to the transition area housing 315. Upon joining the main refrigerant flow, the combined main and secondary refrigerant flow proceeds to flow through a second stage impeller (described in further detail below with reference to FIGS. 5 and 6 ) housed within the transition area housing 315. The transition area housing 315 is likewise shown coupled to a volute outlet housing 320. The volute outlet housing 320 may include a flow path extending around the compressor and terminating at an outlet 335. The outlet 335 may be coupled to a discharge passage (e.g., discharge line 124) that delivers refrigerant vapor to a condenser (e.g., condenser 106). Although depicted as separate components in Figures 3 and 4, in other embodiments, two or more of the secondary inlet collector housing 310, the transition region housing 315, and the volute outlet housing 320 may be cast or machined as a single component.

[0017] Multi-stage compressor 102 is further shown to include a first diffuser actuation assembly 340 and a second diffuser actuation assembly 345. First diffuser actuation assembly 340 may be configured to operate a first diffuser assembly downstream of the first impeller, while second diffuser actuation assembly 345 may be configured to operate a second diffuser assembly downstream of the second impeller. In various embodiments, one or both of the diffuser assemblies may be a variable geometry diffuser (VGD) mechanism having a diffuser ring movable by actuation assembly 340 or 345 between a first retracted position, in which flow through the diffuser gap is unimpeded, and a second extended position, in which the diffuser ring extends into the diffuser gap to vary fluid flow through the diffuser gap. In other embodiments, multi-stage compressor 102 includes only a single diffuser actuation assembly. A single diffuser actuation assembly may control only the first stage of the compressor 102, only the second stage of the compressor 102, or both the first and second stages simultaneously.

[0018] Referring now to Figures 5 and 6A-6D, cross-sectional views of a multi-stage compressor 102 are depicted according to some embodiments. As shown, refrigerant vapor from the suction line travels through the inlet 325 of the main inlet passage housing 305 and approaches the first impeller assembly 500. As specifically depicted in Figure 6, the refrigerant vapor emerging from the suction line can be referred to as a main refrigerant stream 615. During rotation, the impeller assembly 500 compresses the main refrigerant stream 615, imparting a tangential velocity to it, which then directs it radially and tangentially outward toward the diffuser assembly. The diffuser assembly reduces the radial and tangential velocities of the main refrigerant stream 615 and increases its static pressure. The diffusion process is controlled through the operation of the first diffuser ring 620 by the first diffuser actuation assembly 340. In various embodiments, the diffuser can include vanes or can be vaneless. The region extending from the inlet 325 through the outlet of the first diffuser ring 620 comprises the first stage portion 600 of the multi-stage compressor 102 .

[0019] After flowing past the first impeller assembly 500 and the first diffuser ring 620 The primary refrigerant stream 615 then makes an axial turn and mixes with the secondary refrigerant stream 625. The secondary refrigerant stream 625 may be provided by an economizer and may enter the multi-stage compressor 102 through the inlet 330. The secondary refrigerant stream 625 may flow through a circumferential collector passage 515 formed within the secondary inlet collector housing 310 before joining the primary refrigerant stream 615. By traveling through the circumferential collector passage 515, the secondary refrigerant stream 625 is more evenly distributed around the circumference of the compressor 102, resulting in minimal turbulence when the secondary refrigerant stream 625 joins the primary refrigerant stream 615. As shown, in some embodiments, the collector passage 515 has a substantially uniform (constant) cross-sectional area around the entire circumference of the compressor 102. In other embodiments, the cross-sectional area of ​​the collector passage 515 may not be uniform around the circumference of the compressor 102. For example, the cross-sectional area of ​​the passages may increase or decrease linearly or non-linearly as the refrigerant progresses around the circumference of the compressor 102. Additionally, the cross-sectional area of ​​the passages may be implemented using a variety of different geometries.

[0020] Secondary flow insertion slots 530 fluidly couple collector passages 515 to director vane assembly 505. After secondary refrigerant flow 625 is distributed around collector passages 515, it flows through secondary flow insertion slots 530, which extend around the entire circumference of compressor 102, to join main refrigerant flow 615. Because secondary flow insertion slots 530 are located in the region where secondary inlet collector housing 310 is coupled to transition area housing 315, the geometry of secondary flow insertion slots 530 (i.e., length, width, insertion angle relative to the other flow paths) is determined by the geometries of secondary inlet collector housing 310 and transition area housing 315, as well as the characteristics of the interface between housing components 310 and 315. As shown in FIG. 6A , secondary flow insertion slots 530 are substantially parallel (i.e., ±10°) to the flow path of secondary inlet 330 and perpendicular to the flow path of main inlet 325.

[0021] Upon combining, main flow 615 and secondary flow 625 pass through directing vane assembly 505. As described in further detail below with reference to Figures 7 and 8, directing vane assembly 505 may be configured to straighten combined refrigerant flows 615 and 625 and reduce the tangential velocities of their components. As specifically depicted in Figure 6A, the region beginning at the outlet of first diffuser ring 620, including circumferential collector passage 515, and extending through the outlet of directing vane assembly 505 comprises interstage return channel portion 605 of multi-stage compressor 102.

[0022] After exiting the directing vane assembly 505, the combined main flow 615 and secondary flow 625 approach the second impeller assembly 510. Similar to the first impeller assembly 500, the second impeller assembly 510 includes a set of rotating vanes that compress the combined main flow 615 and secondary flow 625 and impart a tangential velocity to them. The rotation of the first impeller assembly 500 and the second impeller assembly 510 is driven by a drive connection 525 to a motor (e.g., motor 104). As shown in FIG. 5, the drive connection 525 is a direct drive connection. In other embodiments, the drive connection 525 may include a gearbox or other transmission system.

[0023] The second impeller assembly directs the combined main flow 615 and secondary flow 625 into the diffuser assembly. The diffuser assembly reduces the radial and tangential velocities of the combined flow and increases its static pressure. In various embodiments, the diffuser assembly can be vaned or vaneless, depending on the application. The diffusion process is controlled through the operation of the second diffuser ring 630 by the second diffuser actuation assembly 345. After passing through the diffuser gap area regulated by the second diffuser ring 630, the combined flows 615 and 625 enter the volute passage 520. In various embodiments, the cross-sectional area of ​​the volute passage 520 is adjusted to allow the refrigerant vapor to pass through the diffuser. The cross-sectional area of ​​the volute passage 520 may increase or decrease linearly or non-linearly as the refrigerant vapor progresses from the outlet of the ring 630 to the volute outlet 335 (described above with reference to Figures 3 and 4). For example, in one exemplary embodiment, the cross-sectional area of ​​the volute passage 520 increases non-linearly as the refrigerant vapor progresses toward the volute outlet 335. The area extending from the second impeller assembly 510 through the volute passage 520 comprises the second stage portion 610 of the multi-stage compressor 102, as specifically depicted in Figure 6A.

[0024] While the cross-sectional shape of the collector passage 515 is illustrated and described with respect to FIG. 6A as being circular, it will be understood that the cross-sectional shape of the collector passage 515 may be implemented using any shape that meets mechanical and packaging requirements. Some examples of alternative cross-sectional shapes that may be used are illustrated, for example, in FIGS. 6B-6D. With specific reference to FIG. 6B, a rectangular shape of the collector passage 515 is illustrated within the inlet 330. With specific reference to FIG. 6C, a triangular shape of the collector passage 515 is illustrated within the inlet 330. With specific reference to FIG. 6D, an elliptical shape of the collector passage 515 is illustrated within the inlet 330. The collector passage 515 may also be positioned offset or symmetrical with respect to the secondary insertion slot 530.

[0025] 7 and 8, which depict a perspective view and a cross-sectional front view, respectively, of a direction vane assembly 505, according to some embodiments. Assembly 505 may alternatively be referred to as a "deswirl" vane assembly. Assembly 505 is shown to include a plurality of direction vanes 700 positioned between an upstream plate 705 and a downstream plate 710. The outer periphery of upstream plate 705 is shown to include a radiused outer lip 715, while the inner periphery of upstream plate 705 is shown to include a conical portion 720. During operation, a mixture of the main refrigerant flow (e.g., main flow 615) and the secondary refrigerant flow (e.g., secondary flow 625) combines and flows from the area surrounding the rounded outer lip 715, past the directing vanes 700, along the conical portion 720, through the central opening 730 in the downstream plate 710, before approaching the second impeller (e.g., second impeller assembly 510). The secondary flow 625 is distributed around the collector passages 515 (depicted in FIG. 5) before combining with the main flow 615, thereby minimizing unsteady disturbance to the main flow 615.

[0026] 8, the directional vanes 700 are shown to have a substantially airfoil-like shape. Although the directional vane assembly 505 is shown to include seventeen directional vanes 700, the vane assembly 505 can include any number of directional vanes having any desired vane shape or geometry based on the operating characteristics of the multi-stage compressor 102 (e.g., the compressor operating pressure). In some embodiments, the orientation of the directional vanes 700 can be fixed relative to the upstream plate 705 and the downstream plate 710. In other embodiments, the directional vane assembly 505 can include an actuation assembly used to modify the orientation of the directional vanes 700.

[0027] Referring now to FIG. 9 , another embodiment of an interstage return channel assembly 900 that may be utilized in the multi-stage compressor 102 is depicted. The assembly 900 is shown to include a secondary inlet collector housing 905 coupled to a transition region housing 915. In contrast to the embodiment depicted in FIGS. 5-6 , the assembly 900 is shown to include a modified flow path for a secondary stream 920 of fluid provided from an economizer. Instead of traveling through a flow path formed by the junction of the secondary inlet collector housing 905 and the transition region housing 915, the transition region housing 915 is shown to include a secondary outlet 925 and a secondary insertion slot 935. Both the secondary outlet 925 and the secondary insertion slot 935 may extend around the entire circumference of the compressor 102.

[0028] Upon entering the inlet collector housing 905 through the inlet 910, a secondary flow 920 of fluid 5-6 , the secondary refrigerant vapor flow path provided by the interstage return channel assembly 900 is less disruptive to the main refrigerant vapor flow and therefore provides better aerodynamic performance; however, the assembly 900 requires a larger axial length and therefore may not be preferred if the overall axial length of the compressor 102 is limited.

[0029] Referring now to FIG. 10 , a plot 1000 depicting circumferential pressure distribution test data for a multi-stage compressor 102, according to some embodiments, is shown. The x-axis 1002 represents the position, in degrees, of a pressure measurement device positioned within the secondary flow insertion slot 530. For example, a 0-degree position may correspond to the position of the inlet 330, while a 180-degree position may be located opposite the inlet 330. The y-axis 1004 represents pressure measurements in pounds-force per square inch absolute (psia). Each line on the plot 1000 depicts the results of an independent test run (i.e., the plot 1000 depicts the results of several independent test runs). As shown, the test data demonstrates that the circumferential pressure discrepancy between the maximum and minimum pressure measurements per test run is less than 0.2% of the average pressure value. In contrast, multi-stage compressors not utilizing the optimized interstage inlets of the present disclosure have pressure distribution non-uniformities in the range of 1% or greater. Greater circumferential uniformity in the secondary flow results in improved chiller performance.

[0030] The construction and arrangement of the systems and methods shown in the various exemplary embodiments are merely exemplary. While only exemplary embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in the size, dimensions, structure, shape, and proportions of various elements, parameter values, mounting arrangements, material use, color, orientation, etc.). For example, the positions of elements may be reversed or otherwise varied, and the nature or number or location of individual elements may be altered or varied. Accordingly, such modifications are intended to be included within the scope of this disclosure. The order or sequence of any process or method steps may be varied or reordered according to alternative embodiments. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the examples without departing from the scope of this disclosure.

Claims

1. A compressor, a first stage portion including a first impeller assembly and a first diffuser assembly; a second stage portion including a second impeller assembly and a second diffuser assembly; an interstage portion located between the first stage portion and the second stage portion, a pointing vane assembly; a collector passage surrounding the steering vane assembly; an interstage portion comprising a circumferential insertion slot fluidly coupling the collector passage with the direction vane assembly.

2. The compressor of claim 1 , wherein the first stage portion further comprises a main inlet configured to deliver a main flow of fluid to the first impeller assembly.

3. The compressor of claim 2 , wherein the interstage portion further comprises a secondary inlet configured to deliver a secondary flow of fluid to the collector passage.

4. The compressor of claim 3 , wherein the main inlet and the secondary inlet are oriented perpendicular to one another.

5. The compressor of claim 3 , wherein the compressor operates as part of a chiller assembly, the main inlet fluidly coupled to an evaporator, and the secondary inlet fluidly coupled to an economizer.

6. The compressor of claim 3 , wherein the circumferential insertion slot and the secondary inlet are parallel to one another.

7. The compressor of claim 3 , wherein the circumferential insertion slot is oriented at an angle relative to the secondary inlet.

8. 4. The compressor of claim 3, wherein each of the main stream of fluid and the secondary stream of flowing fluid is a refrigerant.

9. 9. The compressor of claim 8, wherein the refrigerant is R1233zd.

10. 2. The compressor of claim 1, wherein the cross-sectional area of ​​the collector passage is constant around the circumference of the compressor.

11. 2. The compressor of claim 1, wherein the first diffuser assembly comprises a first diffuser ring movable by a first actuating assembly, and the second diffuser assembly comprises a second diffuser ring movable by a second actuating assembly.

12. The compressor of claim 1 , further comprising a volute passage located at an outlet of the second diffuser assembly.

13. A compressor, a first stage portion including a first impeller assembly and a first diffuser assembly; a second stage portion including a second impeller assembly and a second diffuser assembly; an interstage portion located between the first stage portion and the second stage portion, a pointing vane assembly; a collector passage surrounding the steering vane assembly; a circumferential insertion slot fluidly coupling the collector passage with the direction vane assembly; an interstage section comprising a main inlet configured to deliver a main flow of fluid to the first impeller assembly.

14. The compressor of claim 13 , wherein the interstage portion further comprises a secondary inlet configured to deliver a secondary flow of fluid to the collector passage.

15. The compressor of claim 14 , wherein the main inlet and the secondary inlet are oriented perpendicular to one another.

16. The compressor of claim 14 , wherein the circumferential insertion slot and the secondary inlet are parallel to one another.

17. The compressor of claim 14 , wherein the circumferential insertion slot is oriented at an angle relative to the secondary inlet.

18. A compressor, a first stage portion including a first impeller assembly and a first diffuser assembly; a second stage portion including a second impeller assembly and a second diffuser assembly; an interstage portion located between the first stage portion and the second stage portion, a pointing vane assembly; a collector passage surrounding the steering vane assembly; a circumferential insertion slot fluidly coupling the collector passage with the direction vane assembly; a main inlet configured to deliver a main flow of fluid to the first impeller assembly; an interstage section comprising a secondary inlet configured to deliver a secondary flow of fluid to the collector passage.

19. 20. The compressor of claim 18, wherein the cross-sectional area of ​​the collector passage is constant around the circumference of the compressor.

20. The compressor of claim 18 , further comprising a volute passage located at an outlet of the second diffuser assembly.

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