Multi-stage impeller that can be used in a compressor and compressor having a multi-stage impeller

Abstract

The compressor includes a rotatable impeller configured to increase the pressure of one or more fluids from the compressor inlet to the compressor outlet. The compressor includes primary and secondary impeller sections having a first and second set of impeller blades, respectively, and configured to pressurize a first and second fluid source. In another aspect, a refrigeration system includes a condenser, an evaporator, an expansion device, an economizer or intercooler, and a compressor. The compressor includes a rotatable impeller including a primary impeller section having a first set of impeller blades and configured to pressurize refrigerant received from the evaporator, and a secondary impeller section having a second set of impeller blades configured to pressurize refrigerant received from the economizer or intercooler.

Description

Related Applications

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63 / 426,545, filed November 18, 2023, and entitled MULTI-STAGE IMPELLER USABLE WITH A COMPRESSOR AND COMPRESSOR WITH MULTI-STAGE IMPELLER, which is incorporated herein by reference in its entirety. [Technical Field]

[0002] Introduction The present disclosure relates generally to compressors, and more particularly to compressors with multi-stage impellers for improving the efficiency of vapor compression cycles. [Background technology]

[0003] Multi-stage compressor systems are known to improve the efficiency of vapor compression cycles. However, multi-stage compressor systems that use multiple compressors in series have the disadvantage of increased complexity and maintenance. Furthermore, the increased size and complexity of multi-stage compressor systems creates packaging challenges for the entire system.

[0004] Single stage compressor systems, particularly single stage centrifugal compressor systems, are generally more compact and reliable due to their reduced complexity.

[0005] One attempt to improve efficiency while reducing complexity involves compressors that utilize flash gas injected into a space defined by the compressor casing, typically at either the front or rear shroud of the impeller. This system uses, at least in part, compressor disk friction to impart kinetic energy to the flash gas and reduce its velocity relative to the velocity of the gas leaving the impeller, thereby minimizing gas mixing losses. While this system allows for energy recovery from the flash gas, drawbacks of this system include generally reduced compressor efficiency due to the effect of the economizer flow on the primary flow, and cycle efficiency cannot be optimized for the ideal flash pressure.

[0006] In recognizing the aforementioned deficiencies, the disclosure herein describes improving compressor and cycle efficiency while maintaining the simplicity and size advantages of a single-stage compressor. Summary of the Invention

[0007] The following presents a simplified summary of one or more aspects of the invention in order to provide a basic understanding of such aspects. This summary is not an exhaustive overview of all possible aspects, nor is it intended to identify key or key elements of all aspects, nor to delineate the scope of any or all aspects. Its purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

[0008] In one aspect, the compressor system includes a rotatable impeller configured to increase the pressure of one or more fluids from a compressor inlet to a compressor outlet. The compressor further includes a primary impeller section having a first set of impeller blades configured to pressurize a first fluid source and a secondary impeller section having a second set of impeller blades configured to pressurize a second fluid source. In some aspects of the disclosure described herein, the first fluid source can be refrigerant received from an evaporator, and the second fluid source can be refrigerant received from an economizer and / or an intercooler.

[0009] In another aspect of this disclosure described herein, a refrigeration system includes a condenser, an evaporator, an expansion device, an economizer or intercooler, and a compressor, wherein the compressor includes a rotatable impeller having a primary impeller section with a first set of impeller blades and configured to pressurize refrigerant received from the evaporator, and a secondary impeller section having a second set of impeller blades configured to pressurize refrigerant received from the economizer or intercooler.

[0010] In another aspect of this disclosure described herein, an impeller usable in a centrifugal compressor includes an impeller hub having a shrouded primary impeller section having a first set of impeller blades and configured to pressurize a first fluid source, and a secondary impeller section connected to the shrouded primary impeller section and having a second set of impeller blades configured to pressurize a second fluid source.

[0011] These and other aspects of the present invention will be more fully understood from the following detailed description. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of an example of a refrigeration cycle that can be used with a compressor according to aspects of the present disclosure. [Figure 2] FIG. 1 is a partial cross-sectional view of an example compressor according to aspects of the present disclosure. [Figure 3] FIG. 2 is a close-up cross-sectional view of a primary impeller and a secondary impeller of a compressor according to one aspect of the present disclosure. [Figure 4] FIG. 10 is a close-up cross-sectional view of a primary impeller and a secondary impeller according to another aspect of the present disclosure. [Figure 5] FIG. 1 is a partial isometric view of a secondary impeller according to one aspect of the present disclosure. [Figure 6] 1 is a graph of pressure-enthalpy characteristics, specifically pressure versus logarithm of enthalpy, for a single compressor refrigeration cycle. [Figure 7] 1 is a graph of pressure-enthalpy characteristics, specifically pressure versus logarithm of enthalpy, for a refrigeration cycle with a single compressor having a primary impeller and a secondary impeller according to aspects of the present disclosure. [Figure 8] FIG. 10 is a close-up cross-sectional view of a primary impeller and a secondary impeller according to another aspect of the present disclosure. [Figure 9] FIG. 10 is a close-up cross-sectional view of a primary impeller and a secondary impeller according to another aspect of the present disclosure. [Figure 10A] FIG. 1 is a partial view of an example impeller having a forty-five degree (45°) exit angle. [Figure 10B] FIG. 1 is a partial view of an example impeller having a thirty degree (30°) exit angle. [Figure 10C] FIG. 1C is a partial view of an example impeller inlet blade profile that can be used with the impeller of FIG. 10A or 10B. [Figure 10D] FIG. 1C is a partial view of an example impeller inlet blade profile that can be used with the impeller of FIG. 10A or 10B. DETAILED DESCRIPTION OF THE INVENTION

[0013] The detailed description, set forth below in conjunction with the accompanying drawings, is intended to illustrate various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known components are shown in block diagram form to avoid obscuring such concepts.

[0014] I. Terminology Throughout the disclosure, the terms "substantially" or "approximately" may be used as modifiers of geometric relationships between elements or the shape of an element or component. While the terms "substantially" or "approximately" are not limited to specific variations and may cover variations understood by those skilled in the art as acceptable variations, some examples are provided below: In one example, the term may include a variation of less than 10% in the dimensions of an object or component. In another example, the term may include a variation of less than 5% in the dimensions of an object or component. When the terms "substantially" or "approximately" are used to define an angular relationship between one element and another, one non-limiting example of the terms "substantially" or "approximately" may include a variation of 5 degrees or less. These examples are not intended to be limiting and may be increased or decreased based on the understanding of acceptable limits to those skilled in the art.

[0015] For purposes of this disclosure, directional terms are generally expressed relative to a standard frame of reference when the systems and devices described herein are placed in their in-use orientation.

[0016] Terms such as a, an, and the do not refer to only a single entity but include general classes for which specific examples can be used for description. The terms a, an, and the may be used interchangeably with the term at least one. The phrases at least one and including at least one, when followed by a list, refer to any one of the items in the list and any combination of two or more items in the list. All numerical ranges include non-integer values ​​between the endpoints unless otherwise stated.

[0017] In this disclosure, the terms first, second, third, and fourth, among other numerical values, may be used. Unless otherwise specified, it is understood that these terms are used in a relative sense only. In particular, in some aspects, certain components may be interchangeable and / or exist in identical multiples (e.g., pairs). In the case of these components, the designations first, second, third, and / or fourth may be applied to the components merely for convenience in describing one or more of the aspects of the present disclosure.

[0018] The terms fluid or fluid flow are used throughout this disclosure and are not limited to a particular type of liquid but may cover any liquid known in the art, some examples include, but are not limited to, thermal liquids such as liquids, gases, and steam.

[0019] In this context, a summary of aspects of the present disclosure and advantages offered by the present disclosure is provided. This summary and the following detailed description are presented for purposes of illustration and description. It is not intended to limit the disclosure to the form described. Numerous modifications, including combinations of the described aspects, are possible in light of the teachings herein. Some potential modifications have been discussed; others will be apparent to those skilled in the art. Various aspects have been selected and described in order to best explain the principles of the disclosure and various aspects suited to the particular use contemplated. The scope of the present disclosure is, of course, not limited to the examples or aspects described herein, but may be employed by those skilled in the art in any number of applications and equivalent arrangements. Rather, it is hereby intended that the scope be defined by the claims appended hereto.

[0020] II. Overview As described in more detail below, aspects of the disclosure described herein relate to improved compressor systems for improving the efficiency of refrigeration cycles while maintaining the simplicity and size advantages of single-stage compressors. For example, a compressor system is disclosed that includes a single impeller configured to compress a fluid, such as a refrigerant, when a rotational force is provided to the impeller. The impeller includes a first set of impeller blades as a primary impeller section and a second set of impeller blades as a secondary impeller section. The primary impeller section is configured to draw and compress a first fluid source, such as a refrigerant from an evaporator. The secondary impeller section is configured to draw and compress a liquid from a secondary fluid source, such as a refrigerant from an economizer and / or intercooler. By integrating two or more impeller sections into a single impeller, the advantages of multi-stage compression in a thermodynamic cycle (e.g., a refrigeration cycle) can be utilized without the size, weight, and / or packaging disadvantages of using multiple compressors or multiple rotating impellers. Additionally, the single rotating impeller allows the efficiency of the cycle to be increased as previously discussed, while reducing the maintenance of the single rotating impeller.

[0021] For context, a simplified diagram of a refrigeration system and cycle that can be used with the compressor systems described herein is shown in Figure 1. It is noted that the refrigeration cycle described with respect to Figure 1 is not intended to be limiting, and thus, aspects of the present disclosure can be used with and relate to any thermodynamic cycle that requires the use of a compressor.

[0022] Referring to FIG. 1 , an exemplary refrigeration system 100 includes a condenser 102 for removing heat from a refrigerant vapor until the refrigerant vapor condenses to a saturated liquid state; an evaporator 104 for absorbing heat from the environment by converting the liquid refrigerant to a vapor; and a compressor 110 for drawing or absorbing refrigerant and compressing the refrigerant. The condenser 102 can be any type of condenser configured to release heat from the refrigerant via the atmosphere and / or condense water 103 flowing therethrough. The condenser 102 may receive refrigerant from a discharge line 108 of the compressor 110. The flow of refrigerant through the condenser 102 may cause a phase change to a liquid as heat is released from the refrigerant through the condenser 102. The cycle or system 100 may further include an economizer 106 configured to receive liquid or substantially liquid refrigerant from the condenser 102 using a portion of the total refrigerant flow from the condenser 102 to cool the remainder of the refrigerant flow and / or for flash gas management. Although the economizer 106 is provided as an example, the economizer 106 may be used with or replaced by a known intercooler, which may be of a surface or flash type. For example, the economizer 106 and / or intercooler may separate the liquid refrigerant from any refrigerant that has been boiled and / or converted to vapor, which may be referred to in this disclosure as flash gas or flash vapor. The economizer 106 and / or intercooler may receive refrigerant from the condenser 102 via an intermediate expansion valve 111 in a fluid path between the condenser 102 and the economizer 106.

[0023] The liquid refrigerant from the economizer 106 may then be supplied to an expansion valve 109, where it expands to reduce its pressure and temperature. The liquid and gas refrigerant may then be supplied to the evaporator 104 via a liquid line 114, where the expanded liquid evaporates by absorbing heat from the liquid provided via a heat exchanger. In one example, the heat may be absorbed from cycle water or other fluid source 105 that is cycled through the evaporator 104. The gas refrigerant from the evaporator 104 is then supplied to the compressor 110 via a suction line 107, where the pressure and temperature of the gas refrigerant increase as power is supplied to the compressor. As described in more detail below, the compressor 110 may include, for example, multiple impellers. For example, the compressor 110 may include a primary impeller 113 and a secondary impeller 115. The combination of the primary impeller 113 and the secondary impeller 115 may generally be referred to interchangeably as an impeller throughout this disclosure. Furthermore, the primary impeller 113 and the secondary impeller 115 may be referred to interchangeably as the first impeller section and the second impeller section, respectively, throughout this disclosure. The primary impeller 113 may have an inlet in fluid communication with, for example, a suction line 107 from the evaporator 104. The secondary impeller 115 may have an inlet in fluid communication with, for example, the economizer 106 via the flash gas line 112. The outlet or discharge line 108 of the compressor 110 may receive compressed gas refrigerant from both the primary impeller 113 and the secondary impeller 115. While a primary impeller 113 and a secondary impeller 115 are shown, it is noted that additional impellers may be added to further improve efficiency. Furthermore, the disclosed compressor 110 described below may be used, for example, in a multi-stage compressor system. For example, refrigeration system 100 may include a first compressor with a primary impeller 113 and a secondary impeller 115 (or additional impellers), and the system may include a single impeller or a second compressor with a primary impeller 113 and a secondary impeller 115 (or additional impellers).In one example, the refrigerant vapor pressure provided to the secondary impeller 115 is greater than the pressure provided to the primary impeller 113 from the suction line 107 and less than or equal to the output pressure from the compressor 110 provided to the discharge line 108.

[0024] III. Detailed Examples Referring to FIG. 2 , an exemplary compressor 210 may be similar to the compressor 110 of FIG. 1 . The compressor 210 may include an input shaft 216 configured to receive rotational power. The input shaft 216 may be operatively connected to a gear train or drive train 217. The drive train 217 may be operatively connected to an impeller 205 comprising a primary impeller 213 and a secondary impeller 215. The primary impeller 213 may compress a liquid provided at a primary impeller inlet 212. The primary impeller inlet 212 may have one or more electronically or hydraulically controlled vanes 214, for example, to control the flow of fluid to the primary impeller 213. The rotating primary impeller 213 compresses the fluid received at the primary impeller inlet 212 and discharges the compressed fluid to an outlet path 220.

[0025] The secondary impeller 215 is operably connected to the primary impeller 213. In some examples, the primary impeller 213 and the secondary impeller 215 may be joined or formed / machined as a unitary structure. In other embodiments, the secondary impeller 215 may be connectable to or otherwise connected to the primary impeller 213 via one or more known mechanical fasteners or joining methods. In some examples, the primary impeller 213 and / or the secondary impeller(s) may be additively manufactured as two or more separate components joined together or as a single, integrated component. The secondary impeller 215 may be configured in liquid communication with a flash gas or vapor source, for example, from an intercooler and / or an economizer (e.g., economizer 106 of FIG. 1 ). The flash gas or vapor source (e.g., the economizer and / or the intercooler) may be in fluid communication with the interior cavity 218 of the compressor 210. The secondary impeller 215 may compress fluid provided to the internal cavity 218 and discharge the compressed fluid at a secondary impeller outlet (see non-limiting detailed examples in FIGS. 3A and 3B below). The secondary impeller outlet and outlet 220 may be configured in fluid communication to mix the compressed fluid from both the primary impeller 213 and the secondary impeller 215 at the outlet 220.

[0026] Additional details of primary and secondary impellers usable in embodiments of the present disclosure are described in more detail below with respect to FIGS. 3, 4, 8 and 9.

[0027] Referring to FIG. 3 , an example compressor 310 including additional details of the disclosed example embodiments may be similar to compressor 210 shown in FIG. 2 and / or compressor 100 of FIG. 1 . Compressor 300 includes a primary impeller 313 and a secondary impeller operably connected to a drive train (e.g., drive train 217 of FIG. 2 , not shown in FIG. 3 ). Primary impeller 313 may have a plurality of vanes or blades 334 configured to compress fluid provided at primary impeller inlet 312. It is noted that in FIG. 3 , only a subset of blades and / or vanes 334 are labeled with reference numerals so as not to obscure other features of the figure. Furthermore, it is noted that the configuration of the blades and / or vanes is not limited to the configuration shown in FIG. 3 and may include any number of blades and / or vanes in any configuration without departing from the scope of the present disclosure. The primary impeller inlet 312 may have, for example, one or more electronically or hydraulically controlled vanes (not shown in FIG. 3, see, for example, reference numeral 214 in FIG. 2) to control the flow of fluid to the primary impeller 313.

[0028] The vanes and / or blades 334 of the rotating primary impeller 313 are configured to compress fluid drawn into the primary impeller inlet 312 and discharge the compressed fluid at the primary impeller tip 332 into the outlet path 320. In one example, the primary impeller 313 may have a dynamic shroud 333 secured to the primary impeller 313 and configured to rotate with the primary impeller 313. In one example, the dynamic shroud 333 may be of one-piece construction and formed and / or machined as a single component. In another example, the dynamic shroud 333 may be secured to or otherwise connected to the blades and / or vanes 334 of the dynamic shroud 333. The primary impeller 313 may be sealed to prevent leakage of fluid via one or more seals 336 configured to sealingly engage sealing surfaces, features, or sealing features 337 of the primary impeller 313. In one aspect, the one or more seals may include one or more radial or circular labyrinth seal(s) or similar seals that provide a tortuous path to prevent leakage of fluid at the rotating interface of the primary impeller 313. In some examples, the one or more seal(s) 336 and / or features 337 may prevent or impede the passage of fluid by controlling the fluid to pass through various chambers within the seal by centrifugal motion and / or the formation of controlled fluid vortices, while providing no contact with opposing surfaces or seal ring features.

[0029] The secondary impeller 315 may be operably connected to the primary impeller 313. In some examples, the primary impeller 313 and the secondary impeller 315 may be joined or formed / machined as a unitary structure. In other embodiments, the secondary impeller 315 may be connectable to or otherwise connected to the primary impeller 313 via one or more mechanical fasteners or coupling methods. For example, the secondary impeller 315 may be attached to or otherwise coupled to the dynamic shroud 333 of the primary impeller 313.

[0030] The secondary impeller 315 may be significantly reduced in size, diameter, and / or volume as compared to the primary impeller 313. For example, the outer or major diameter of the secondary impeller 315 may be 70% to 85% of the outer or major diameter of the primary impeller 313. In another example, the outer or major diameter of the secondary impeller 315 may be 40% to 95% of the outer or major diameter of the main or primary impeller 313. In another example, the outer or major diameter of the secondary impeller 313 may be 40% to 85% of the outer or major diameter of the main impeller 313.

[0031] Additionally, the blades of the secondary impeller may have a blade profile with increased twist compared to the primary impeller. For example, the blades of the secondary impeller 315 may have a blade exit angle that is five degrees (5°) to 30° lower than the blades of the primary impeller 313. For reference, a blade exit angle of 90° includes blades that are purely radial at the exit. The reference example 90° exit angle provides the highest lift capacity but tends to reduce the flow capacity range of the impeller.

[0032] 10A is a partial view of an impeller 1015a in which the impeller blades 1034a have a 45° exit angle. An impeller with 45° exit blades may be usable with the secondary impeller(s) described herein and may offer a good trade-off. In one embodiment, an impeller with 45° exit blades may be used as the primary impeller(s) described herein. Low blade exit angles (i.e., less than 45°) are not typically used in compressors due to reduced lift capacity. However, for the secondary impeller(s) described herein (i.e., secondary impeller 315), low blade exit angles (e.g., less than 45°) may be preferred in one embodiment and may provide the necessary lift for the economizer cycle described herein.

[0033] FIG. 10B shows an example of an impeller with blades 1034b at a 30° angle at the outlet. A 30° blade angle at the outlet can be used with the secondary impeller(s) described herein. Comparing the 45° outlet blade profile of FIG. 10A with the 30° outlet blade profile of FIG. 10b, it can be seen that as the blade outlet angle decreases, the blades appear more "spiral" or "twisted." Thus, in one example, the blade profile of a secondary impeller described herein (i.e., secondary impeller 315) may be more spiral or twisted than the blade profile of the primary impeller (i.e., primary impeller 313).

[0034] As noted above, the foregoing blade angle profiles are provided as non-limiting examples. As noted above, the blade exit profile of the secondary impeller(s) described herein may be 5° to 30° lower than the blade exit profile of the primary impeller(s) described herein.

[0035] 10C and 10D show partial views of a first exemplary impeller inlet with blades 1014c having a first blade inlet profile and a second exemplary impeller inlet 1015d with blades 1034d having a second blade inlet profile. In some examples, the first blade inlet profile or the secondary blade inlet profile can be used with any one of the blade outlet profiles shown in FIGS. 10A and 10b, or any combination thereof.

[0036] Additionally, the secondary impeller blades and / or vanes may be correspondingly adjusted to reduce the compression ratio of the economizer fluid flow through the compressor compared to the suction line fluid flow through the compressor. In one example, the secondary impeller blades and / or vanes may be adjusted, and the outer or major diameter of the secondary impeller 315 may be reduced as described above to reduce the compression ratio.

[0037] In one example that can be used in the embodiments described in this disclosure, the economizer refrigerant flow rate through the compressor secondary impeller 315 can be half or approximately half the primary suction line flow rate through the primary impeller 313.

[0038] In one example that can be used in the embodiments described in this disclosure, the economizer refrigerant flow through the compressor secondary impeller 315 can be at or about half the omega (i.e., head factor) of the primary suction line flow through the primary impeller 313. For example, the head factor is defined by the following formula:

number

[0039] Let ΔHi = isentropic compression enthalpy, then the head factor of the economizer refrigerant flow may be half or about half the head factor of the suction line refrigerant flow.

[0040] Utilizing the primary impeller 313 and secondary impeller 315 as described throughout this disclosure allows for optimization of the geometry of the primary impeller 313 and / or secondary impeller 315 to increase the overall efficiency of the refrigeration cycle while reducing the efficiency impact or any reduction in efficiency caused by compression of the economizer fluid stream by the secondary impeller 315 on the compression of the suction line fluid stream by the primary impeller 313. For example, since the vapor from the economizer or intercooler (e.g., the economizer fluid stream from the flash gas line 112 in FIG. 1 ) requires less kinetic energy than is required to adequately compress the gas received from the evaporator via the suction line (e.g., the suction line 107 in FIG. 1 ), the secondary impeller 315 may be adjusted (e.g., in any one or any combination of diameter, size, volume, and / or blade / vane configuration) to reduce the efficiency impact of compression of the economizer fluid stream on the compression of the suction line fluid stream. In one example, the tip diameter of the secondary impeller 315 (e.g., the distance from axis RR to tip 352) may be selected to adjust the flow of suction line fluid and / or the compression ratio of the economizer fluid to the economizer pressure. In some examples, the distance from RR or the major diameter from one primary impeller tip 332 to the opposite impeller tip of the primary impeller 313 may be greater than the distance from axis RR or the major diameter from one secondary impeller tip 352 to the opposite impeller tip of the secondary impeller 315.

[0041] As shown in FIG. 3 , the secondary impeller 315 may have one or more blades and / or vanes 354. It is noted that FIG. 3 references a reduced number of the blades and / or vanes 354 to avoid obscuring the view. Furthermore, it is noted that while a particular vane / blade configuration is shown in FIG. 3 , any vane and / or blade configuration may be utilized without departing from the scope of the present disclosure. The vanes and / or blades 354 of the rotating secondary impeller 315 are configured to compress fluid received from an economizer and / or intercooler (e.g., via the flash gas line 112 in FIG. 1 ), which may be referred to interchangeably herein as an economizer fluid flow. In one example, the economizer fluid flow may be provided to an internal cavity 318 of the compressor casing. As shown by the exemplary dashed line with flow arrowheads in Figure 3, economizer fluid may be suctioned into or otherwise fed to secondary impeller inlet 335, and the compressed economizer fluid stream may exit secondary impeller 315 at secondary impeller tip or tips 352. In one example, secondary impeller tip or tips 352 may be in fluid communication with outlet path 320, thereby mixing or partially mixing the compressed economizer stream and the suction line fluid stream before exiting compressor 310. In one example, compressor 310 may include a separation wall 371 at the outlet of secondary impeller 315.

[0042] The separation wall 371 may be utilized to delay mixing of the economizer fluid stream with the suction line fluid stream until the flow velocity of the suction line fluid decreases. Delaying mixing of the economizer fluid stream with the suction line fluid stream until the velocity difference between the suction line fluid stream and the economizer fluid stream decreases reduces mixing losses that might otherwise occur. One or any combination of the separation wall length, geometry, and / or location of the separation wall relative to the primary impeller tip(s) 332 and / or secondary impeller tip(s) 352 may be optimized to reduce the velocity difference between the compressed economizer fluid stream and the suction line fluid stream where they diverge at the outlet path 320.

[0043] In one example, the secondary impeller 315 may also have a dynamic shroud 358 secured to the secondary impeller 315 and configured to rotate with the secondary impeller 315. In one example, the dynamic shroud may be of one piece construction and formed and / or machined as a single component with the primary impeller 313 and the secondary impeller 315. In another example, the dynamic shroud 358 may be secured to or otherwise connected to the blades and / or vanes 354 of the dynamic shroud 358. The secondary impeller 315 may be sealed to prevent fluid leakage via one or more seals 356 configured to sealingly engage sealing surfaces, features, or sealing features 357 of the secondary impeller 315. In one aspect, the one or more seals may include, for example, one or more radial or circular labyrinth seal(s) that may resemble or include one or any combination of the features of the seal or seals 336 described in detail above and / or the sealing surface or features 337 of the primary impeller 313. As noted above, the tip diameter of the secondary impeller (e.g., the major diameter of the compression-side secondary impeller) may be adjusted or otherwise optimized to effectively achieve a desired compression ratio of the economizer fluid flow and / or the suction line fluid flow, as described above.

[0044] Referring to FIG. 4, an example compressor 410 including additional details of an example embodiment is disclosed and may be similar to compressor 210 shown in FIG. 2 and / or compressor 100 of FIG. 1, and may also share features of compressor 310 of FIG. 3. In one example, a primary difference between compressor 310 and compressor 410 may be a floating, stationary or fixed (i.e., non-rotating) shroud 458, whereas compressor 310 of FIG. 3 utilizes a dynamic (i.e., rotating) shroud. Stationary shroud 458 may be biased or otherwise configured to have a static net force (e.g., as indicated by arrows FF) toward the blades and / or vanes 454 of secondary impeller 415. Force FF may be provided by one or more springs and / or any biasing member or members. Because the fixed (floating) shroud 458 does not rotate with the blades and / or vanes of the secondary impeller 415, the clearance between the blade / vane tips and the shroud 458 can be reduced to as low as possible while preventing and / or reducing friction between the blade / vane tips and the shroud 458. In one exemplary embodiment, the clearance between the surfaces of the shroud 458 facing the secondary impeller blades / vanes 454 during compressor operation can be less than 50 micrometers (μm). In another exemplary embodiment, the clearance between the surfaces of the shroud 458 facing the secondary impeller blades / vanes 454 during compressor operation can be between 5 μm and 15 μm. In yet another embodiment, the clearance can be between 7 μm and 13 μm or more, preferably about 10 μm. In general, it is desirable to reduce the clearance as much as possible while reducing or eliminating friction due to contact between the blades / vanes 454 and the shroud 458.

[0045] In one aspect of the present disclosure, the blades and / or vanes 454 of the secondary impeller 415 may be configured to provide a pressure field and / or aerodynamic thrust during rotation of the secondary impeller 415. The pressure field and / or aerodynamic thrust may oppose a biasing force FF that creates a desired clearance between the tips of the blades / vanes 454 and the shroud 458 during operation of the compressor 410. By applying the Navier-Stokes equations to a thin fluid film, the pressure field load capacity of the blades / vanes and working fluid of the secondary impeller 415 can be calculated. The aforementioned Navier-Stokes equations may be solved using computational fluid dynamics (CFD) software. The aforementioned calculations can be simplified to the Reynolds equation for a plane of rotation perpendicular to the axis of rotation (thrust). For example, the following equation can be used to calculate the pressure field load capacity: μ

number

number

[0046] Using the Navier-Stokes equations described above or the exemplary Reynolds equations above, the geometry of the secondary impeller 415 and / or the blades / vanes 454 of the secondary impeller 415 can be optimized to achieve a desired clearance (e.g., the clearance described above) between the blades / vanes 454 and the shroud 458 while reducing or eliminating friction due to contact between the blades / vanes 454 and the shroud 458. Additional details of blade / vane profiles that may be associated with the illustrated secondary impeller 415 are described below with respect to FIG.

[0047] As described above, the compressor 410 of FIG. 4 may include a primary impeller 413 and a secondary impeller 415 operatively connected to a drive train (e.g., drive train 217 of FIG. 2 ). The primary impeller 413 may include a plurality of vanes or blades 434 configured to compress fluid provided at the primary impeller inlet 412. It is noted that in FIG. 4 , only a subset of the blades and / or vanes 434 are labeled with reference numerals so as not to obscure other features of the figure. It is further noted that the blade and / or vane configuration is not limited to the configuration shown in FIG. 4 and may include any number of blades and / or vanes in any configuration without departing from the scope of the present disclosure. The primary impeller inlet 412 may include, for example, one or more electronically or hydraulically controlled vanes (not shown in FIG. 4 , see, e.g., reference numeral 214 of FIG. 2 ) to control the flow of fluid into the primary impeller 413.

[0048] The vanes and / or blades 434 of the rotating primary impeller 413 are configured to compress fluid drawn into the primary impeller inlet 412 and discharge the compressed fluid at the primary impeller tip 432 into the outlet path 420. In one example, the primary impeller 413 may have a dynamic shroud 433 secured to the primary impeller 313 and configured to rotate with the primary impeller 313. In one example, the dynamic shroud may be of monolithic construction and formed and / or machined as a single component. In another example, the dynamic shroud 433 may be secured to or otherwise connected to the blades and / or vanes 434 of the dynamic shroud 433. The primary impeller 413 may be sealed to prevent leakage of fluid via one or more seals 436 configured to sealingly engage sealing surfaces, features, or sealing features 437 of the primary impeller 413. In one aspect, the one or more seals may include, for example, one or more radial or circular labyrinth seal(s), or any type of seal that provides a tortuous path to prevent leakage of fluid at the rotating interface of the primary impeller. In some examples, one or more seal(s) 436 and / or feature 437 may prevent or impede the passage of fluid by controlling the fluid to pass through various chambers within the seal through centrifugal motion and / or the formation of controlled fluid vortices, while providing no contact with the opposing surface or seal ring feature(s).

[0049] The secondary impeller 415 may be operably connected to the primary impeller 413. In some examples, the primary impeller 413 and the secondary impeller 415 may be joined or formed / machined as a unitary structure. In other embodiments, the secondary impeller 415 may be connectable to or otherwise connected to the primary impeller 413 via one or more mechanical fasteners or coupling methods. For example, the secondary impeller 415 may be attached to or otherwise coupled to the dynamic shroud 433 of the primary impeller 413.

[0050] The secondary impeller 415 may be significantly reduced in size, diameter, and / or volume as compared to the primary impeller 413. For example, the outer or major diameter of the secondary impeller 415 may be 70% to 85% of the outer or major diameter of the primary impeller 413. In another example, the outer or major diameter of the secondary impeller 415 may be 40% to 95% of the outer or major diameter of the main or primary impeller 413. In another example, the outer or major diameter of the secondary impeller 413 may be 40% to 85% of the outer or major diameter of the main impeller 413.

[0051] Additionally, the blades of the secondary impeller 415 may have a blade profile with increased twist compared to the primary impeller. For example, the blades of the secondary impeller 415 may have a blade exit angle that is five degrees (5°) to 30° lower than the primary impeller 413. For reference / comparison, a blade exit angle of 90° includes blades that are purely radial at the exit. The reference example 90° exit angle provides the highest lift capacity but tends to reduce the flow capacity range of the impeller.

[0052] 10A is a partial view of an impeller 1015a in which the impeller blades 1034a have a 45° exit angle. An impeller with 45° exit blades may be usable with the secondary impeller(s) described herein and may offer a good trade-off. In one embodiment, an impeller with 45° exit blades may be used as the primary impeller(s) described herein. Low blade exit angles (i.e., less than 45°) are not typically used in compressors due to reduced lift capacity. However, for the secondary impeller(s) described herein, low blade exit angles (e.g., less than 45°) may be preferred in one embodiment and may provide the necessary lift for the economizer cycle described herein.

[0053] FIG. 10B shows an example of an impeller with blades 1034b at a 30° angle at the outlet. A 30° blade angle at the outlet can be used in embodiments of the secondary impeller(s) described herein. Comparing the 45° outlet blade profile of FIG. 10A with the 30° outlet blade profile of FIG. 10b, it can be seen that as the blade outlet angle decreases, the blades appear more "spiral" or "twisted." Thus, in one example, the blade profile of a secondary impeller described herein may be more spiral or twisted than the blade profile of a primary impeller.

[0054] As noted above, the foregoing blade angle profiles are provided as non-limiting examples. As noted above, the blade exit profile of the secondary impeller(s) described herein may be 5° to 30° lower in angle than the blade exit profile of the primary impeller(s) described herein.

[0055] 10C and 10D show partial views of a first exemplary impeller inlet with blades 1014c having a first blade inlet profile and a second exemplary impeller inlet 1015d with blades 1034d having a second blade inlet profile. In some examples, the first blade inlet profile or the secondary blade inlet profile can be used with any one of the blade outlet profiles shown in FIGS. 10A and 10b, or any combination thereof.

[0056] Additionally, the secondary impeller blades and / or vanes may be correspondingly adjusted to reduce the compression ratio of the economizer fluid flow through the compressor compared to the suction line fluid flow through the compressor. Utilizing the primary impeller 413 and secondary impeller 415 as described throughout this disclosure allows for optimization of the geometry of the primary impeller 413 and / or secondary impeller 415 to increase the overall efficiency of the refrigeration cycle while reducing the efficiency impact or any degradation in efficiency that the compression of the economizer fluid flow by the secondary impeller 415 has on the compression of the suction line fluid flow by the primary impeller 413. For example, if the vapor from the economizer or intercooler (e.g., the economizer fluid stream from flash gas line 112 in FIG. 1 ) requires less kinetic energy than is required to adequately compress the gas received from the evaporator via the suction line (e.g., suction line 107 in FIG. 1 ), the secondary impeller may be adjusted (e.g., in any one or any combination of diameter, size, volume, and / or blade / vane configuration) to reduce the efficiency impact of compression of the economizer fluid stream on compression of the suction line fluid stream.

[0057] In one example, the tip diameter of the secondary impeller 415 may be selected to adjust the flow of suction line fluid and / or the compression ratio of the economizer fluid to the economizer pressure. In some examples, the distance from RR or the major diameter from one primary impeller tip 432 to the opposite impeller tip of the primary impeller 413 may be greater than the distance from the axis RR or the major diameter from one secondary impeller tip 452 to the opposite impeller tip of the secondary impeller 415.

[0058] As shown in FIG. 4 , the secondary impeller 415 may have one or more blades and / or vanes 454. It is noted that in FIG. 4 , only a subset of the blades and / or vanes 454 are numbered so as not to obscure other features of the figure. It is further noted that while a particular vane / blade configuration is shown in the figure, any vane and / or blade configuration may be utilized without departing from the scope of the present disclosure. The vanes and / or blades 454 of the rotating secondary impeller 415 are configured to compress fluid received from an economizer and / or intercooler (e.g., via the flash gas line 112 in FIG. 1 ), which may be referred to interchangeably herein as an economizer fluid flow. In one example, the economizer fluid flow may be provided to an interior cavity 418 of the compressor casing. As shown by the exemplary dashed lines with flow arrowheads in FIG. 4 , economizer fluid may be aspirated into or otherwise supplied to the secondary impeller inlet 435, and the compressed economizer fluid flow may exit the secondary impeller 415 at an outlet tip or tips 452 of the secondary impeller.

[0059] In one example, the secondary impeller outlet tip or tips 452 may be in fluid communication with the outlet path 420 so that the compressed economizer stream and the suction line fluid stream mix or partially mix before exiting the compressor 410. In one example, the compressor 410 may include a separation wall 471 at the outlet of the secondary impeller 415. The separation wall 471 may be utilized to delay mixing of the economizer stream and the suction line fluid stream until the flow velocity of the suction line fluid decreases. Delaying mixing of the economizer stream and the suction line fluid stream until the velocity difference between the suction line fluid stream and the economizer fluid stream decreases reduces mixing losses that may otherwise occur. One or any combination of the length, geometry, and / or positional relationship of the separation wall to the primary impeller tip(s) 432 and / or secondary impeller tip(s) 452 may be optimized to reduce the velocity difference between the compressed economizer fluid stream and the suction line fluid stream where they diverge at the outlet path 420.

[0060] Referring to FIG. 5, an exemplary profile of the blades of the impeller 515 includes specific configurations of surfaces that can be used in embodiments of the disclosure. In one example, the impeller 515 may be used in conjunction with the floating shroud 458 of FIG. 4 or FIG. 8 below. For example, the blade 544 of FIG. 5 may resemble the secondary impeller blade / vane 454 of FIG. 4 or the secondary impeller blade / vane 954 of FIG. 9. In one embodiment of the disclosure, the blade 554 of the impeller 515 may include a narrow blade portion 554a having a narrower cross-section than an extended portion 554b near the tip of the blade 554. The tip of the blade 554 may have a tip surface 554e. The tip surface 554e may be flat or substantially flat. In some aspects, the tip surface 554e may be shaped to match or substantially match the geometry of the floating shroud surface closest to the tip surface 554e, thereby minimizing clearance therebetween and thus improving sealing or reducing pressure loss between the tip surface 554e and the floating shroud (e.g., floating shroud 458 in FIG. 4). As shown in FIG. 5, the profile of the blades 554 of the impeller 515 may further include a chamfered or curved portion 554c at the transition between the narrow blade portion 554a and the expanding portion 554b. Additionally, the blades 554 may be curved or chamfered at the edge of the tip surface 554e to reduce friction when contact occurs between the tip surface 554e and the floating shroud. In one aspect, the increased cross-sectional area at the expanding portion 554b and / or the curved or otherwise chamfered portion 554c may improve the ability of the impeller 515 to provide a pressure field and / or aerodynamic thrust during rotation of the secondary impeller. The pressure field and / or air thrust may cause the shroud (e.g., shroud 458 in FIG. 4) to counteract the biasing force (e.g., force F in FIG. 4) applied to the shroud, and therefore float to a desired clearance between tip surface 554e and the shroud (e.g., shroud 458 in FIG. 4) during compressor operation. As described above, the pressure field load capacity and working fluid of blades 554 of impeller 515 can be calculated by solving the Navier-Stokes equations.In an exemplary embodiment, the impeller 515 and floating shroud (e.g., shroud 458 in FIG. 4) may be configured to provide an operating clearance of less than 50 micrometers (μm). In another exemplary embodiment, the impeller 515 and floating shroud may be configured to provide a clearance of 5 μm to 15 μm. In yet another exemplary embodiment, the aforementioned clearance (gap) may be 7 μm to 13 μm or more, preferably about 10 μm. In general, it is desirable to reduce the aforementioned clearance as much as possible while reducing or eliminating friction due to contact between the impeller 515 blades and the shroud.

[0061] While several examples are provided above, it is noted that compressors or impellers according to aspects of the disclosure may vary in packaging or modifications (or ease of modification of a standard single-stage compressor). For example, the primary impeller section may be further from the compressor input shaft (i.e., an inverted configuration from the above examples), while the secondary impeller section described above may instead be closer to the compressor hub or input shaft.

[0062] 6 and 7, there is shown an exemplary pressure-enthalpy diagram 600 (FIG. 6) for a single-stage compressor and an exemplary pressure-enthalpy diagram 700 (FIG. 7) for an example system according to the present disclosure.

[0063] Referring to FIG. 8 , an example compressor 810 including additional details of the disclosed exemplary embodiments may be similar to compressor 210 shown in FIG. 2 and / or compressor 100 shown in FIG. 1 and may further share features of compressor 310 shown in FIG. 3 and / or compressor 410 shown in FIG. 4 . Compressor 800 includes a primary impeller 813 and a secondary impeller operably connected to a drive train (e.g., drive train 217 shown in FIG. 2 , but not shown in FIG. 3 ). Primary impeller 813 may have a plurality of vanes or blades 834 configured to compress fluid provided at primary impeller inlet 812. It is noted that in FIG. 3 , only a subset of blades and / or vanes 834 are labeled with reference numerals to avoid obscuring other features of the figure. It is further noted that the configuration of the blades and / or vanes is not limited to the configuration shown in FIG. 8 and may include any number of blades and / or vanes in any configuration without departing from the scope of the present disclosure. The primary impeller inlet 812 may have, for example, one or more electronically or hydraulically controlled vanes (not shown in FIG. 8, see, for example, reference numeral 214 in FIG. 2) to control the flow of fluid to the primary impeller 813.

[0064] The vanes and / or blades 834 of the rotating primary impeller 813 are configured to compress fluid drawn into the primary impeller inlet 812 and discharge the compressed fluid at the primary impeller tip 832 into the outlet path 820. In one example, the primary impeller 813 may have a dynamic shroud 833 secured to the primary impeller 813 and configured to rotate with the primary impeller 813. In one example, the dynamic shroud 833 may be of one-piece construction and formed and / or machined as a single component. In another example, the dynamic shroud 833 may be secured to or otherwise connected to the blades and / or vanes 834 of the dynamic shroud 833. The primary impeller 813 may be sealed to prevent leakage of fluid via one or more seals 836 configured to sealingly engage sealing surfaces, features, or sealing features 837 of the primary impeller 813. In one aspect, the one or more seals may include one or more radial or circular labyrinth seal(s) or similar seals that provide a tortuous path to prevent leakage of fluid at the rotating interface of the primary impeller 813. In some examples, the one or more seal(s) 836 and / or features 837 may prevent or impede the passage of fluid by controlling the fluid to pass through various chambers within the seal by centrifugal motion and / or the formation of controlled fluid vortices, while providing no contact with opposing surfaces or seal ring features.

[0065] The secondary impeller 815 may be operatively connected to the primary impeller 813. One notable difference between the impellers of FIGS. 3 and 8 is that the outer or major diameter of the secondary impeller 815 is larger than the outer or major diameter of the secondary impeller 313 of FIG. 3. In other words, the difference in diameter between the primary impeller 813 and the secondary impeller 815 is smaller than the difference in diameter between the primary impeller 313 and the secondary impeller 315. In some examples, the primary impeller 813 and the secondary impeller 815 may have the same diameter or major diameter. In one example, the number of veins, the veins profile, and / or the veins height of the secondary impeller 315 may be modified to ensure an appropriate pressure or compression ratio. As noted above, the pressure ratio may be optimized using Equations 1, 2, and 3 above. For example, the height of the impeller blades 854 of the secondary impeller 815 may be smaller than the height of the impeller blades 354 of the secondary impeller 315 of FIG. 3.

[0066] In some examples, the primary impeller 813 and the secondary impeller 815 may be joined or formed / machined as a unitary structure. In other embodiments, the secondary impeller 815 may be connectable to or otherwise connected to the primary impeller 813 via one or more mechanical fasteners or coupling methods. For example, the secondary impeller 815 may be attached to or otherwise coupled to the dynamic shroud 833 of the primary impeller 813.

[0067] The secondary impeller 815 may be significantly reduced in size, diameter, and / or volume as compared to the primary impeller 813. For example, the outer or major diameter of the secondary impeller 815 may be 70% to 85% of the outer or major diameter of the primary impeller 813. In another example, the outer or major diameter of the secondary impeller 815 may be 40% to 95% of the outer or major diameter of the main or primary impeller 813. In another example, the outer or major diameter of the secondary impeller 813 may be 40% to 85% of the outer or major diameter of the main impeller 813.

[0068] Additionally, the blades of the secondary impeller may have a blade profile with increased twist compared to the primary impeller. For example, the blades of secondary impeller 815 may have a blade exit angle that is five degrees (5°) to 30° lower than the blades of primary impeller 813. For reference, a blade exit angle of 90° includes blades that are purely radial at the exit. The reference example 90° exit angle provides the highest lift capacity but tends to reduce the flow capacity range of the impeller.

[0069] 10A is a partial view of an impeller 1015a in which the impeller blades 1034a have a 45° exit angle. An impeller with 45° exit blades may be usable with the secondary impeller(s) described herein and may offer a good trade-off. In one embodiment, an impeller with 45° exit blades may be used as the primary impeller(s) described herein. Low blade exit angles (i.e., less than 45°) are not typically used in compressors due to reduced lift capacity. However, for the secondary impeller(s) described herein, low blade exit angles (e.g., less than 45°) may be preferred in one embodiment and may provide the necessary lift for the economizer cycle described herein.

[0070] FIG. 10B shows an example of an impeller with blades 1034b at a 30° angle at the outlet. A 30° blade angle at the outlet can be used in embodiments of the secondary impeller(s) described herein. Comparing the 45° outlet blade profile of FIG. 10A with the 30° outlet blade profile of FIG. 10b, it can be seen that as the blade outlet angle decreases, the blades appear more "spiral" or "twisted." Thus, in one example, the blade profile of a secondary impeller described herein may be more spiral or twisted than the blade profile of a primary impeller.

[0071] As noted above, the foregoing blade angle profiles are provided as non-limiting examples. As noted above, the blade exit profile of the secondary impeller(s) described herein may be 5° to 30° lower in angle than the blade exit profile of the primary impeller(s) described herein.

[0072] 10C and 10D show partial views of a first exemplary impeller inlet with blades 1014c having a first blade inlet profile and a second exemplary impeller inlet 1015d with blades 1034d having a second blade inlet profile. In some examples, the first blade inlet profile or the secondary blade inlet profile can be used with any one of the blade outlet profiles shown in FIGS. 10A and 10b, or any combination thereof.

[0073] Additionally, the secondary impeller blades and / or vanes may be correspondingly adjusted to reduce the compression ratio of the economizer fluid flow through the compressor compared to the suction line fluid flow through the compressor. In one example, the secondary impeller blades and / or vanes may be adjusted as described above to reduce the compression ratio.

[0074] In one example that can be used in the embodiments described in this disclosure, the economizer refrigerant flow rate through the compressor secondary impeller can be half or about half the primary suction line flow rate through the primary impeller 31.

[0075] In one example that can be used in the embodiments described in this disclosure, the economizer refrigerant flow through the compressor secondary impeller can be half or about half the omega (i.e., head factor) of the primary suction line flow through the primary impeller 31. For example, as outlined above, the head factor is defined by Equation 1:

[0076] Utilizing the primary impeller 813 and secondary impeller 815 as described throughout this disclosure allows for optimization of the geometry of the primary impeller 813 and / or secondary impeller 815 to increase the overall efficiency of the refrigeration cycle while reducing the efficiency impact or any reduction in efficiency caused by compression of the economizer fluid stream by the secondary impeller 815 on the compression of the suction line fluid stream by the primary impeller 813. For example, since the vapor from the economizer or intercooler (e.g., the economizer fluid stream from flash gas line 112 in FIG. 1 ) requires less kinetic energy than is required to adequately compress the gas received from the evaporator via the suction line (e.g., suction line 107 in FIG. 1 ), the secondary impeller 815 may be adjusted (e.g., in any one or any combination of diameter, size, volume, and / or blade / vane configuration) to reduce the efficiency impact of compression of the economizer fluid stream on the compression of the suction line fluid stream. In one example, the tip diameter of the secondary impeller 815 (e.g., the distance from axis RR to tip 852) may be selected to adjust the flow of suction line fluid and / or the compression ratio of the economizer fluid to the economizer pressure. In some examples, the distance from RR or the major diameter from one primary impeller tip 832 to the opposite impeller tip of the primary impeller 313 may be greater than the distance from axis RR or the major diameter from one secondary impeller tip 852 to the opposite impeller tip of the secondary impeller 815.

[0077] As shown in FIG. 8 , the secondary impeller 815 may have one or more blades and / or vanes 854. It is noted that FIG. 8 references a reduced number of the blades and / or vanes 854 to avoid obscuring the view. Furthermore, it is noted that while a particular vane / blade configuration is shown in FIG. 8 , any vane and / or blade configuration may be utilized without departing from the scope of the present disclosure. The vanes and / or blades 854 of the rotating secondary impeller 815 are configured to compress fluid received from an economizer and / or intercooler (e.g., via the flash gas line 112 in FIG. 1 ), which may be referred to interchangeably herein as an economizer fluid flow. In one example, the economizer fluid flow may be provided to an interior cavity 818 of the compressor casing. As shown by the exemplary dashed line with flow arrowheads in FIG. 8 , economizer fluid may be inducted into or otherwise fed to secondary impeller inlet 835, and a compressed stream of economizer fluid may exit secondary impeller 815 at secondary impeller tip or tips 852. In one example, secondary impeller tip or tips 852 may be in fluid communication with outlet path 820, thereby mixing or partially mixing the compressed economizer stream and the suction line fluid stream before exiting compressor 810. In one example, compressor 810 may include a separation wall 871 at the outlet of secondary impeller 815. Separation wall 871 may be utilized to delay mixing of the economizer fluid stream and the suction line fluid stream until the flow velocity of the suction line fluid decreases. Delaying the mixing of the economizer fluid stream with the suction line fluid stream until the velocity difference between the suction line fluid stream and the economizer fluid stream is reduced reduces mixing losses that may otherwise occur.One or any combination of the length, geometry, and / or positional relationship of the separation wall to the primary impeller tip(s) 832 and / or secondary impeller tip(s) 852 may be optimized to reduce the velocity difference between the compressed economizer fluid flow and the suction line fluid flow where the two diverge at the outlet path 820.

[0078] In one example, the secondary impeller 815 may also have a dynamic shroud 858 secured to the secondary impeller 815 and configured to rotate with the secondary impeller 815. In one example, the dynamic shroud may be of one piece construction and formed and / or machined as a single component with the primary impeller 813 and the secondary impeller 815. In another example, the dynamic shroud 858 may be secured to or otherwise connected to the blades and / or vanes 854 of the dynamic shroud 858. The secondary impeller 815 may be sealed to prevent fluid leakage via one or more seals 856 configured to sealingly engage sealing surfaces, surfaces, or sealing features 857 of the secondary impeller 815. In one aspect, the one or more seals may include, for example, one or more radial or circular labyrinth seal(s) that may resemble or include one or any combination of the features of the seal or seals 836 described in detail above and / or the sealing surface or features 837 of the primary impeller 813. As noted above, the tip diameter of the secondary impeller (e.g., the major diameter of the compression-side secondary impeller) may be adjusted or otherwise optimized to effectively achieve a desired compression ratio of the economizer fluid flow and / or the suction line fluid flow.

[0079] Referring to FIG. 9 , an example compressor 910 including additional details of an example embodiment is disclosed and may be similar to compressor 210 shown in FIG. 2 and / or compressor 100 of FIG. 1 , and may further share features of compressor 310 of FIG. 3 , compressor 410 of FIG. 4 , and / or compressor 810 of FIG. 8 . In one example, a primary difference between compressor 810 and compressor 910 may be a floating, stationary or fixed (i.e., non-rotating) shroud 958, whereas compressor 810 of FIG. 8 utilizes a dynamic (i.e., rotating) shroud. Stationary shroud 958 may be biased or otherwise configured to have a static net force (e.g., as indicated by arrow FF) toward the blades and / or vanes 954 of secondary impeller 915. Force FF may be provided by one or more springs and / or any biasing member or members. Because the fixed (floating) shroud 958 does not rotate with the blades and / or vanes of the secondary impeller 915, the clearance between the blade / vane tips and the shroud 958 can be reduced to as low as possible while preventing and / or reducing friction between the blade / vane tips and the shroud 958. In one exemplary embodiment, the clearance between the surfaces of the shroud 958 facing the secondary impeller blades / vanes 954 during compressor operation can be less than 50 micrometers (μm). In another exemplary embodiment, the clearance between the surfaces of the shroud 958 facing the secondary impeller blades / vanes 954 during compressor operation can be between 5 μm and 15 μm. In yet another embodiment, the clearance can be between 7 μm and 13 μm or more, preferably about 10 μm. In general, it is desirable to reduce the clearance as low as possible while reducing or eliminating friction due to contact between the blades / vanes 954 and the shroud 958.

[0080] In one aspect of the disclosure, the blades and / or vanes 954 of the secondary impeller 915 may be configured to provide a pressure field and / or aerodynamic thrust during rotation of the secondary impeller 915. The pressure field and / or aerodynamic thrust may oppose a biasing force F that creates a desired clearance between the tips of the blades / vanes 954 and the shroud 958 during operation of the compressor 910. As described above with respect to FIG. 4, the pressure field load capacity of the blades / vanes and working fluid of the secondary impeller 915 can be calculated by solving the Navier-Stokes equations for a thin fluid film. The foregoing calculations can be simplified to the exemplary Reynolds Equation 1 and Reynolds Equation 2 described above with respect to FIG. 4.

[0081] Using the Navier-Stokes equations or the exemplary Reynolds equations described above, the geometry of the secondary impeller 915 and / or the blades / vanes 954 of the secondary impeller 915 can be optimized to achieve a desired clearance (e.g., the clearance described above) between the blades / vanes 954 and the shroud 958 while reducing or eliminating friction due to contact between the blades / vanes 954 and the shroud 958. Additional details of blade / vane profiles that may be associated with the illustrated secondary impeller 915 are described above with respect to FIG.

[0082] The compressor 410 of FIG. 9 may have a primary impeller 913 and a secondary impeller 915 operably connected to a drive train (e.g., drive train 217 of FIG. 2 ). The primary impeller 913 may have a plurality of vanes or blades 934 configured to compress fluid provided at the primary impeller inlet 912. It is noted that in FIG. 9 , only a subset of the blades and / or vanes 934 are labeled with reference numerals so as not to obscure other features of the figure. It is further noted that the blade and / or vane configuration is not limited to the configuration shown in FIG. 9 and may include any number of blades and / or vanes in any configuration without departing from the scope of the present disclosure. The primary impeller inlet 912 may have one or more electronically or hydraulically controlled vanes (not shown in FIG. 9 , see, e.g., reference numeral 214 of FIG. 2 ) to control the flow of fluid into the primary impeller 913, for example.

[0083] The vanes and / or blades 934 of the rotating primary impeller 913 are configured to compress fluid drawn into the primary impeller inlet 912 and discharge the compressed fluid at the primary impeller tip 932 into the outlet path 920. In one example, the primary impeller 913 may have a dynamic shroud 933 secured to the primary impeller 913 and configured to rotate with the primary impeller 913. In one example, the dynamic shroud may be of monolithic construction and formed and / or machined as a single component. In another example, the dynamic shroud 933 may be secured to or otherwise connected to the blades and / or vanes 934 of the dynamic shroud 933. The primary impeller 913 may be sealed to prevent leakage of fluid via one or more seals 936 configured to sealingly engage sealing surfaces, features, or sealing features 937 of the primary impeller 913. In one aspect, the one or more seals may include, for example, one or more radial or circular labyrinth seal(s), or any type of seal that provides a tortuous path to prevent leakage of fluid at the rotating interface of the primary impeller. In some examples, one or more seal(s) 936 and / or feature 937 may prevent or impede the passage of fluid by controlling the fluid to pass through various chambers within the seal by centrifugal motion and / or the formation of controlled fluid vortices, while providing no contact with the opposing surface or seal ring feature(s).

[0084] The secondary impeller 915 may be operably connected to the primary impeller 913. In some examples, the primary impeller 913 and the secondary impeller 915 may be joined or formed / machined as a unitary structure. In other aspects, the secondary impeller 915 may be connectable to or otherwise connected to the primary impeller 913 via one or more mechanical fasteners or coupling methods. For example, the secondary impeller 915 may be attached to or otherwise coupled to the dynamic shroud 933 of the primary impeller 913.

[0085] The secondary impeller 915 may be significantly reduced in size, diameter, and / or volume compared to the primary impeller 913. The secondary impeller 915 may be significantly reduced in size, diameter, and / or volume compared to the primary impeller 913. For example, the outer diameter or major diameter of the secondary impeller 915 may be 70% to 85% of the outer diameter or major diameter of the primary impeller 913. In another example, the outer diameter or major diameter of the secondary impeller 915 may be 40% to 95% of the outer diameter or major diameter of the main or primary impeller 913. In another example, the outer diameter or major diameter of the secondary impeller 913 may be 40% to 85% of the outer diameter or major diameter of the main impeller 913.

[0086] Additionally, the blades of the secondary impeller may have a blade profile with increased twist compared to the primary impeller. For example, the blades of the secondary impeller 915 may have a blade exit angle that is five degrees (5°) to 30° lower than the blades of the primary impeller 913. For reference, a blade exit angle of 90° includes blades that are purely radial at the exit. The reference example 90° exit angle provides the highest lift capacity but tends to reduce the flow capacity range of the impeller.

[0087] 10A is a partial view of an impeller 1015a in which the impeller blades 1034a have a 45° exit angle. An impeller with 45° exit blades may be usable with the secondary impeller(s) described herein and may offer a good trade-off. In one embodiment, an impeller with 45° exit blades may be used as the primary impeller(s) described herein. Low blade exit angles (i.e., less than 45°) are not typically used in compressors due to reduced lift capacity. However, for the secondary impeller(s) described herein, low blade exit angles (e.g., less than 45°) may be preferred in one embodiment and may provide the necessary lift for the economizer cycle described herein.

[0088] FIG. 10B shows an example of an impeller with blades 1034b at a 30° angle at the outlet. A 30° blade angle at the outlet can be used in embodiments of the secondary impeller(s) described herein. Comparing the 45° outlet blade profile of FIG. 10A with the 30° outlet blade profile of FIG. 10b, it can be seen that as the blade outlet angle decreases, the blades appear more "spiral" or "twisted." Thus, in one example, the blade profile of a secondary impeller described herein may be more spiral or twisted than the blade profile of a primary impeller.

[0089] As noted above, the foregoing blade angle profiles are provided as non-limiting examples. As noted above, the blade exit profile of the secondary impeller(s) described herein may be 5° to 30° lower than the blade exit profile of the primary impeller(s) described herein.

[0090] 10C and 10D show partial views of a first exemplary impeller inlet with blades 1014c having a first blade inlet profile and a second exemplary impeller inlet 1015d with blades 1034d having a second blade inlet profile. In some examples, the first blade inlet profile or the secondary blade inlet profile can be used with any one of the blade outlet profiles shown in FIGS. 10A and 10b, or any combination thereof.

[0091] Additionally, the secondary impeller blades and / or vanes may be correspondingly adjusted to reduce the compression ratio of the economizer fluid flow through the compressor compared to the suction line fluid flow through the compressor. One notable difference between the impellers of Figures 4 and 9 is that the outer or major diameter of the secondary impeller 915 is larger than the secondary impeller 413 of Figure 4. In other words, the difference in diameter between the primary impeller 913 and the secondary impeller 915 is less than the difference in diameter between the primary impeller 413 and the secondary impeller 415. In some examples, the primary impeller 913 and the secondary impeller 915 may have the same diameter or major diameter.

[0092] In one example, the number of pulses, pulse profile, and / or pulse height of secondary impeller 915 may be varied to ensure an appropriate pressure or compression ratio. As noted above, the pressure ratio may be optimized using Equations 1, 2, and 3 above. For example, the height of impeller blades 954 of secondary impeller 915 may be less than the height of impeller blades 454 of secondary impeller 415 of FIG. 4.

[0093] Utilizing the primary impeller 913 and secondary impeller 915 as described throughout this disclosure allows for optimization of the geometry of the primary impeller 913 and / or secondary impeller 915 to increase the overall efficiency of the refrigeration cycle while reducing the efficiency impact or any reduction in efficiency caused by compression of the economizer fluid stream by the secondary impeller 915 on the compression of the suction line fluid stream by the primary impeller 913. For example, if the vapor from the economizer or intercooler (e.g., the economizer fluid stream from flash gas line 112 in FIG. 1 ) requires less kinetic energy than is required to adequately compress the gas received from the evaporator via the suction line (e.g., suction line 107 in FIG. 1 ), the secondary impeller may be adjusted (e.g., in any one or any combination of diameter, size, volume, and / or blade / vane configuration) to reduce the efficiency impact of compression of the economizer fluid stream on the compression of the suction line fluid stream. In one example, the tip diameter of the secondary impeller 915 may be selected to adjust the flow of suction line fluid and / or the compression ratio of the economizer fluid to the economizer pressure. In some examples, the distance from RR or the major diameter from one primary impeller tip 932 to the opposite impeller tip of the primary impeller 913 may be greater than the distance from the axis RR or the major diameter from one secondary impeller tip 952 to the opposite impeller tip of the secondary impeller 915.

[0094] As shown in FIG. 9 , the secondary impeller 915 may have one or more blades and / or vanes 954. It is noted that in FIG. 9 , only a subset of the blades and / or vanes 954 are numbered so as not to obscure other features of the figure. It is further noted that while a particular vane / blade configuration is shown in the figure, any vane and / or blade configuration may be utilized without departing from the scope of the present disclosure. The vanes and / or blades 954 of the rotating secondary impeller 915 are configured to compress fluid received from an economizer and / or intercooler (e.g., via the flash gas line 112 in FIG. 1 ), which may be referred to interchangeably herein as an economizer fluid flow. In one example, the economizer fluid flow may be provided to an interior cavity 918 of the compressor casing.

[0095] As shown by the exemplary dashed line with flow arrowheads in FIG. 9 , economizer fluid may be inducted into or otherwise fed to secondary impeller inlet 935, and a compressed stream of economizer fluid may exit secondary impeller 915 at secondary impeller outlet tip or tips 952. In one example, secondary impeller outlet tip or tips 952 may be in fluid communication with outlet path 920, thereby mixing or partially mixing the compressed economizer stream and the suction line fluid stream before exiting compressor 910. In one example, compressor 910 may include a separation wall 971 at the outlet of secondary impeller 915. Separation wall 971 may be utilized to delay mixing of the economizer fluid stream and the suction line fluid stream until the flow velocity of the suction line fluid decreases. Delaying the mixing of the economizer fluid stream and the suction line fluid stream until the velocity difference between the two streams is reduced reduces mixing losses that might otherwise occur. One or any combination of the length, geometry, and / or location of the separation wall relative to the primary impeller tip(s) 932 and / or secondary impeller tip(s) 952 may be optimized to reduce the velocity difference between the compressed economizer fluid stream and the suction line fluid stream where they diverge at the outlet path 920.

[0096] Additional aspects of the present disclosure are described in the following sections.

[0097] Item 1. A compressor system including a rotatable impeller configured to increase the pressure of one or more fluids from a compressor inlet to a compressor outlet, the rotatable impeller further including a primary impeller section having a first set of impeller blades configured to pressurize a first fluid source, and a secondary impeller section having a second set of impeller blades configured to pressurize a second fluid source.

[0098] Item 2. The compressor system of item 1, further comprising a primary impeller inlet configured to receive the first fluid source, a secondary impeller inlet configured to receive the second fluid source, and an outlet path configured to mix the pressurized first and second fluids before exiting the compressor.

[0099] Item 3. The compressor system of any one of the preceding items, wherein the first major diameter of the first set of impeller blades is larger than the second major diameter of the second set of impeller blades.

[0100] Item 4. The compressor system of any one of the preceding items, further including a primary shroud connected to both the first set of impeller blades and the second set of impeller blades.

[0101] Item 5. The compressor system of any one of the preceding items, further including a secondary shroud connected to the second set of impeller blades.

[0102] Item 6. The compressor system of any one of the preceding items, further including a floating shroud, the floating shroud configured to maintain a clearance with the second set of impeller blades as the second set of impeller blades rotates relative to the floating shroud.

[0103] Item 7. The compressor system of any one of the preceding items, wherein the floating shroud has a biasing member configured to provide a biasing force toward the second set of impeller blades.

[0104] Item 8. The compressor system of any one of the preceding items, wherein the second set of impeller blades is configured to provide a pressure field when the rotatable impeller rotates, the pressure field opposing the biasing force of the biasing member.

[0105] Item 9. The compressor system of any one of the preceding items, wherein the pressure field opposes the biasing force until equilibrium between the biasing force and the pressure field is achieved, and at the equilibrium, the clearance between the second set of impeller blades and the floating shroud is 50 micrometers (μm) or less.

[0106] Item 10. The compressor system of any one of the preceding items, further comprising a single impeller hub shared by the primary impeller and the secondary impeller.

[0107] Item 11. A refrigeration system including a condenser, an evaporator, an expansion device, an economizer or intercooler, and a compressor, the compressor including a rotatable impeller including a primary impeller section having a first set of impeller blades configured to pressurize refrigerant received from the evaporator, and a secondary impeller section including a second set of impeller blades configured to pressurize refrigerant received from the economizer or intercooler.

[0108] Item 12. The system of item 11, wherein the primary impeller inlet is configured to receive refrigerant from the evaporator and the secondary impeller inlet is configured to receive refrigerant from the economizer or intercooler, and after compression, the compressor is configured to mix the refrigerant from the evaporator and the refrigerant from the economizer or intercooler before the refrigerant is supplied to the condenser.

[0109] Item 13. The system of any one of the preceding items, wherein the first major diameter of the first set of impeller blades is larger than the second major diameter of the second set of impeller blades.

[0110] Item 14. The system of any one of the preceding items, further including a primary shroud connected to both the first set of impeller blades and the second set of impeller blades.

[0111] Item 15. The system of any one of the preceding items, further including a secondary shroud connected to the second set of impeller blades.

[0112] Item 16. The system of any one of the preceding items, wherein the compressor further includes a floating shroud, the floating shroud configured to maintain a clearance with the second set of impeller blades as the second set of impeller blades rotates relative to the shroud.

[0113] Item 17. The system of any one of the preceding items, wherein the floating shroud has a biasing member configured to provide a biasing force toward the second set of impeller blades.

[0114] Item 18. The system of any one of the preceding items, wherein the second set of impeller blades is configured to provide a pressure field when the rotatable impeller rotates, the pressure field opposing the biasing force of the biasing member.

[0115] Item 19. The system of any one of the preceding items, wherein the pressure field opposes the biasing force until equilibrium between the biasing force and the pressure field is achieved, and at the equilibrium, the clearance between the second set of impeller blades and the floating shroud is 50 micrometers (μm) or less.

[0116] Item 20. An impeller usable in a centrifugal compressor, comprising: an impeller hub having a shrouded primary impeller section having a first set of impeller blades and configured to pressurize a first fluid source; and a secondary impeller section connected to the shrouded primary impeller section and having a second set of impeller blades configured to pressurize a second fluid source.

[0117] Item 21. The impeller of item 20, further comprising a secondary shroud connected to the second set of impeller blades.

[0118] This written specification uses examples to disclose aspects of the invention, including preferred embodiments, and to enable one of ordinary skill in the art to practice the aspects, including making and using any device or system and practicing any incorporated methods. The patentable scope of these aspects is defined by the claims, and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that are substantially different from the literal language of the claims. Those of ordinary skill in the art will be able to mix and match aspects from the various described embodiments, as well as other known equivalents for each such aspect, to construct additional embodiments and techniques in accordance with the principles of this application.

Claims

1. 1. A compressor system comprising: a rotatable impeller configured to increase a pressure of one or more fluids from a compressor inlet to a compressor outlet, the rotatable impeller comprising: a primary impeller section having a first set of impeller blades configured to pressurize a first fluid source; a secondary impeller section having a second set of impeller blades configured to pressurize a second fluid source.

2. a primary impeller inlet configured to receive the first fluid source; a secondary impeller inlet configured to receive the second fluid source; an outlet path configured to mix the pressurized first and second fluids before exiting the compressor.

3. 2. The compressor system of claim 1, wherein the first major diameter of the first set of impeller blades is greater than the second major diameter of the second set of impeller blades.

4. The compressor system of claim 1 , further comprising a primary shroud connected to both the first set of impeller blades and the second set of impeller blades.

5. The compressor system of claim 4 further comprising a secondary shroud connected to the second set of impeller blades.

6. 5. The compressor system of claim 4, further comprising a floating shroud configured to maintain a clearance with the second set of impeller blades as the second set of impeller blades rotate relative to the floating shroud.

7. The compressor system of claim 6 , wherein the floating shroud includes a biasing member configured to provide a biasing force toward the second set of impeller blades.

8. 8. The compressor system of claim 7, wherein the second set of impeller blades are configured to provide a pressure field when the rotatable impeller rotates, the pressure field opposing the biasing force of the biasing member.

9. 9. The compressor system of claim 8, wherein the pressure field opposes the biasing force until equilibrium between the biasing force and the pressure field is achieved, and at the equilibrium, the clearance between the second set of impeller blades and the floating shroud is 50 micrometers (μm) or less.

10. The compressor system of claim 1 , further comprising a single impeller hub shared by the primary impeller and the secondary impeller.

11. 1. A refrigeration system comprising: A condenser; an evaporator; an expansion device; an economizer or intercooler; a compressor, the compressor comprising:

1. A refrigeration system comprising: a rotatable impeller comprising a primary impeller section having a first set of impeller blades configured to pressurize refrigerant received from the evaporator; and a secondary impeller section having a second set of impeller blades configured to pressurize refrigerant received from the economizer or intercooler.

12. 12. The system of claim 11, wherein the primary impeller inlet is configured to receive refrigerant from the evaporator and the secondary impeller inlet is configured to receive refrigerant from the economizer or intercooler, and after compression, the compressor is configured to mix the refrigerant from the evaporator and the refrigerant from the economizer or intercooler before the refrigerant is delivered to the condenser.

13. The system of claim 11 , wherein a first major diameter of the first set of impeller blades is greater than a second major diameter of the second set of impeller blades.

14. The system of claim 11 , further comprising a primary shroud connected to both the first set of impeller blades and the second set of impeller blades.

15. The system of claim 14 , further comprising a secondary shroud connected to the second set of impeller blades.

16. 15. The system of claim 14, wherein the compressor further includes a floating shroud, the floating shroud configured to maintain a clearance with the second set of impeller blades as the second set of impeller blades rotates relative to the shroud.

17. The system of claim 16 , wherein the floating shroud includes a biasing member configured to provide a biasing force toward the second set of impeller blades.

18. 20. The system of claim 17, wherein the second set of impeller blades are configured to provide a pressure field when the rotatable impeller rotates, the pressure field opposing the biasing force of the biasing member.

19. 20. The system of claim 18, wherein the pressure field opposes the biasing force until equilibrium between the biasing force and the pressure field is achieved, and at the equilibrium, the clearance between the second set of impeller blades and the floating shroud is 50 micrometers (μm) or less.

20. An impeller usable in a centrifugal compressor, an impeller hub including a shrouded primary impeller section having a first set of impeller blades and configured to pressurize a first fluid source; a secondary impeller section connected to the shrouded primary impeller section and including a second set of impeller blades configured to pressurize a second fluid source.

21. 21. The impeller of claim 20, further comprising a secondary shroud connected to the second set of impeller blades.

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