U.S. GOVERNMENT RIGHTS

[0001] The invention was made with U.S. Government support under contract

DE-AR00000144 awarded by the Department of Energy. The U.S. Government has certain rights in the invention

CROSS-REFERENCE TO RELATED APPLICATION

[0002] Benefit is claimed of US Patent Application Ser. No. 61/599,901, filed February 16, 2012, and entitled "Hybrid Compressors and Compression Systems", the disclosure of which is incorporated by reference herein in its entirety as if set forth at length.

BACKGROUND

[0003] The disclosure relates to compressors. More particularly, the disclosure relates to hybrid centrifugal/supersonic compressor systems.

[0004] As perceived high global warming potential (GWP) refrigerants are phased out or banned, there is a need to find low GWP alternatives. Water is a potential refrigerant that has several advantages: 1) it is book-kept as zero GWP; 2) it is potentially more efficient than HFC refrigerants if some form of staging and inter-cooling is used; 3) it has high heat of vaporization (and therefore low mass flow rate for a given capacity); and 4) it offers the possibility of direct contact heat exchange. The major disadvantages of water are: 1) low absolute pressure and therefore low vapor density; 2) high pressure ratio; and 3) high compressor discharge

temperature. Even with its high heat of vaporization, the evaporation pressure for water is so low that very high compressor volumetric flow rates are required. To achieve high suction volumetric flow rates as well as high pressure ratio, multistage centrifugal or axial compressors may be needed with many blade rows, at the expense of additional aerodynamic losses and

manufacturing cost.

[0005] One of the options to achieve a high compression ratio is a rotary supersonic compression system. Due to water's high speed of sound, however, a very high rotational speed is necessary to achieve the required inlet Mach number and pressure ratio. For example, a pressure ratio of 7 requires an impeller tip speed of 2,800 ft/sec (850 m/s). There are many technical challenges to such high speed operations. The centripital stress, for example, will be far beyond the yielding stress limit of most available materials.

[0006] US Pregrant Publication 2005/0271500A1 (the '500 publication) of Lawlor et al. discloses a compressor that has, effectively, the parallel combination of two two-stage compression paths. Each of these two paths involves an associated centrifugal impeller followed by a supersonic rotor. Each of these four stages is on a shared (common) shaft to rotate as a unit.

[0007] US Pregrant Publication 2010/0329856A1 of (the ^* 856 publication) of Hofer et al. discloses a compressor that has a centrifugal impeller in series with two radial supersonic rotors. The upstream impeller rotates oppositely to the rotation of the first supersonic rotor and in the same direction as the rotation of the second supersonic rotor.

SUMMARY

[0008] One aspect of the disclosure involves a compressor having an inlet. An outlet is downstream of the inlet along a flowpath when the compressor is in a first operational condition. A centrifugal impeller is mounted for rotation about an impeller axis. A supersonic rotor is mounted for rotation about a rotor axis and configured to rotate opposite the impeller and tangentially compress in the first operational condition.

[0009] In various implementations/embodiments, the impeller axis and rotor axis may be coincident. There may be a single impeller, a single supersonic rotor, a single inlet, and a single outlet. There may be multiple pairs of such impellers and rotors and one or more each of inlets and outlets. There may be additional compression stages between the inlet and the outlet. The supersonic rotor may comprise a plurality of nested spiral segment passageways. The supersonic rotor may have an axial inlet and an axial outlet. The centrifugal impeller may have an axial inlet and an axial outlet. A first electric motor may be coupled to the impeller to drive rotation of the impeller and a second electric motor may be coupled to the rotor to drive the rotation of the rotor.

[0010] There may be a stator intermediate the impeller and rotor and carrying respective first and second bearings supporting the impeller and rotor. At least one ramp may have a leading edge spaced radially outboard of an adjacent inboard surface of the supersonic flowpath thereahead. There may be an exemplary 3-10 said ramps. A shroud may be mounted to rotate as a unit with the supersonic rotor. The shroud may have a sawtooth forward edge/end defining compression passageway leading edges. The leading edges may be along thinned regions formed by relieved regions of an outer diameter (OD) surface of the shroud. A bleed system may have ports in the rotor.

[0011] Another aspect of the disclosure involves a compressor having an inlet. An outlet is downstream of the inlet along a flowpath when the compressor is in a first operational condition. A centrifugal impeller is mounted for rotation about an impeller axis. A supersonic rotor is mounted for rotation about a rotor axis and comprises an outer shroud.

[0012] In various implementations/embodiments, the supersonic rotor may have a plurality of compression passageways. In each of the compression passageways, a body may radially divide the passageway into an inboard branch and an outboard branch. The supersonic rotor may be configured to rotate in an opposite direction to the impeller. The impeller may have an axial outlet and the rotor may have an axial inlet and an axial outlet. The supersonic rotor may have a plurality of passageways formed as nested spiral segments. Along leading portions of each passageway, an outer diameter (OD) surface of the shroud may be locally radially recessed.

[0013] Any of the foregoing compressors may be along a refrigerant flowpath in a vapor compression system. A heat rejection heat exchanger may be downstream of the compressor along the refrigerant flowpath. An expansion device may be downstream of the heat rejection heat exchanger along the refrigerant flowpath. The heat absorption heat exchanger may be downstream of the expansion device along the refrigerant flowpath and upstream of the compressor.

[0014] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is an axial sectional view of a compressor.

[0016] FIG. 2 is a schematic view of a vapor compression system including the compressor of FIG. 1.

[0017] FIG. 3 is an enlarged view of a center section of the compressor of FIG. 2.

[0018] FIG. 4 is a partially isolated view of an impeller and rotor.

[0019] FIG. 5 is a partial cutaway view of the rotor of FIG. 4 showing a passageway inlet.

[0020] FIG. 6 is a front view of the rotor partially cutaway to show ramps. [0021] FIG. 7 is an enlarged forward-looking sectional view of a passageway of the rotor cooperating with an inner diameter (ID) surface of the adjacent housing member.

[0022] FIG. 8 is enlarged view of an inlet region of the passageway of FIG. 7.

[0023] FIG. 9 is a velocity diagram.

[0024] FIG. 10 is a partial transverse cutaway view of a rotor wherein ramps are formed along the outer diameter (OD) of the rotor.

[0025] FIG. 11 is a front view of an impeller and rotor system wherein ramps are formed on a sidewall of the rotor.

[0026] FIG. 12 is a partial transverse cutaway view of a rotor wherein ramps are formed by centerbodies radially splitting passageways.

[0027] Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0028] FIG. 1 shows a compressor 20 having a housing 22. At least one inlet is formed along the housing (e.g., a primary inlet 24 along a primary flowpath through the compressor). At least one outlet is formed along the housing (e.g., a primary outlet 26 along the primary flowpath). When the compressor is in a first mode of operation to pump and compress fluid along the flowpath and pass the fluid from the inlet to the outlet, the outlet is downstream of the inlet. To compress the fluid, the compressor includes at least two working elements. A first working element 28 is a centrifugal impeller mounted for rotation about an impeller axis. The exemplary impeller axis is a central longitudinal axis 500 of the compressor. A second working element is a supersonic rotor 30 mounted for rotation about a rotor axis. The exemplary impeller and rotor axes are coincident, being the axis 500. The supersonic rotor is downstream of the centrifugal impeller in the first operational condition and is configured to rotate in an opposite direction to the impeller and tangentially compress the fluid in the first operational condition.

[0029] The rotation of the rotors may be driven by one or more motors (e.g., electric motor(s)). In the exemplary embodiment, there are two motors 40 and 42 respectively coupled to the impeller and rotor. This allows independent control of the absolute (and thus relative) speeds of the impeller and rotor. In alternative embodiments, there may be a single motor driving both the impeller and the rotor (e.g., via an appropriate transmission providing counter-rotation). In the exemplary compressor 20, the motor 40 is in front of the impeller and coupled to the impeller by a shaft 44 passing through the housing; and the motor 42 is behind the rotor and coupled to the rotor by a shaft 46 passing through the housing. The exemplary shafts and motors are coaxial with the axis 500. The exemplary motors are external to the housing, with the shafts passing through shaft seals in the housing.

[0030] FIG. 2 shows a refrigeration system 400 including the compressor 20. Downstream of the compressor along a refrigerant flowpath is a first heat exchanger 402 (which in a normal mode of operation is a heat rejection heat exchanger such as a gas cooler giving up heat to a heat exchange fluid).

[0031] Downstream of the heat exchanger 402 is an expansion device 404. Downstream of the expansion device along the refrigerant primary flowpath is a second heat exchanger 406. The exemplary heat exchanger 406 is, in the exemplary first mode of operation, a heat absorption heat exchanger (e.g., an evaporator receiving heat from a heat transfer fluid). Downstream of the heat exchanger 406, refrigerant returns to the primary inlet 24. The foregoing is the most basic configuration of vapor compression system. Much more detailed variations with additional branches of the refrigerant flowpath are likely depending upon the implementation.

[0032] FIG. 3 shows further details of the compressor. An intermediate stator 50 is positioned between the impeller and rotor and held to the housing axially and radially. The exemplary housing comprises a center section formed by members 52, 54, 56, and 58. Upstream of the member 52, an inlet end member 60 (FIG. 1) extends from the compressor inlet and is formed as an elbow pierced by the shaft 44 and sealed thereto via a seal (e.g., a seal/bearing assembly 64 (FIG. 1)). An outlet end member 62 may be an outlet conduit.

[0033] The exemplary shafts 44 and 46 may each be assemblies. A section of the shaft 44 near its downstream end 64 forms an impeller shaft and engages a bearing 66 held in a compartment 68 of the intermediate stator. Similarly, a portion of the shaft 46 near its upstream end 70 forms a rotor shaft and engages a bearing 72 held in a compartment 74 of the intermediate stator. In the exemplary embodiment, the downstream end 64 of the shaft 44 is in close facing relation to the upstream end 70 of the shaft 46. The intermediate stator thus supports both the impeller and the rotor by their respective bearings 66 and 72. FIG. 3 further shows a

compartment 80 in the housing member 58 carrying bearings 82 supporting a downstream end portion of the rotor shaft 46 and a seal 84 sealing with that downstream end portion just ahead of a connection to the motor 42. FIG. 3 further shows a seal 90 between the impeller and stator.

[0034] FIG. 4 shows further details of the impeller 28 and rotor 30. Their respective directions of rotation about the axis 500 are shown as 502 and 504. The exemplary impeller includes a plurality of blades 100 (main blades), 102 circumferentially arrayed about a centerbody 104. The exemplary blades are formed in two alternating interspersed sets with the first set of blades 100 (main blades) extending from leading ends/edges 106 at the impeller forward end/inlet 108 to trailing edges 110 at the impeller axial outlet 111. The second blades 102 (splitter blades) have leading ends/edges 112 streamwise recessed relative to the leading ends of the first blades and have trailing ends/edges 114 at the axial outlet at like radial and axial position to the trailing ends of the first blades. The exemplary blades have outer diameter (OD) edges 115 (FIG. 3) in close facing proximity to the inboard/inner/inner diameter (ID)

surface/face 116 of the housing along the housing member 54 (impeller case). When viewed from the front, the exemplary impeller is driven for rotation in a first direction about its axis (counterclockwise in the example). The blades are oriented so as to produce required flow turning. [0035] After exiting the axial outlet 111, the flow proceeds to the supersonic rotor inlet 1 18 (FIG. 3). It passes over the outer diameter (OD) surface 120 of the stator 50 and

circumferentially between a plurality of turning vanes 122 extending radially between the stator OD surface and the adjacent inner/interior surface of the housing (see FIG. 9 velocity diagram). Each vane 122 has a leading edge/end 124 and a trailing edge/end 126. The turning vanes may also serve as a support points of the stator relative to the housing and as inlet ports for cooling air and/ oil for the bearings, and outlet ports for a bleed flow (discussed below).

[0036] The supersonic rotor comprises a rim or body 130 (also called a "hub", although a mechanical "hub" may be radially inboard thereof to mount to a shaft) on which a plurality of compression ramps 132 (FIG. 5) are formed. Each ramp extends from a leading end 134 to a trailing end 136 (FIG. 7) and has a radially outboard surface 138. From the leading end to the trailing end, the ramps each have an external compression part 250 (FIG. 8), a converging part 251, a throat 252, a shock train section 253, and a diffuser 254. The ramps are separated from each other by strakes 140, each extending from a leading end 142 to a trailing end 144 (FIG. 4) and extending radially outward to a shroud 150. In the exemplary embodiment, the shroud, rather than being a stationary portion of the housing, is mounted to or otherwise integrally formed with the supersonic rotor to rotate with it as a unit. The exemplary shroud is, therefore, formed along the outward/OD/circumferential edges of the strakes and has an outboard surface 152 and an inboard surface 154 and a forward end 156 and an aft end 158. The term "shroud" may alternatively designate the entire shroud or the section of shroud along a given passageway. In some implementations, these may be a single piece or individual pieces.

[0037] The shroud, along with the ramps and adjacent strakes forms passageways 160 (FIG. 7) respectively associated with the ramps. Each passageway 160 has an inlet 162 and an outlet 164. The inlets are thus along a forward end/face of the rotor while the outlets are along an aft end/face of the rotor. The exemplary passageways each have a partial circumferential extent around the rotor (e.g., 30-120°, more narrowly, 40-80°. The exemplary shroud inboard surface cooperates with the ramps to define the variation in flowpath cross-section between supersonic rotor inlet and outlet. In the exemplary embodiment, the shroud interior/ID surface has a basic circular cylindrical shape with variation produced by the ramp surface. In the exemplary embodiment, a trailing portion of the passageway downstream of the ramp trailing end 136 is formed along the cylindrical outer diameter (OD) surface of the rotor body and extends to the associated outlet 164. As is discussed further below, to form edges 166 (FIG. 4) along the shroud at passageway inlets, the shroud is effectively relieved in a sawtooth pattern along the forward end of the shroud: one relief for each passageway inlet. A similar sawtooth pattern may exist along the aft end of the shroud defining edges 168 passageway outlets.

[0038] The rotor serves to tangentially compress the fluid, receiving the fluid through an axial inlet and discharging it through an axial outlet 119. The exemplary fluid is discharged with axial and tangential velocity components and may be straightened in the collector 300.

Alternative embodiments may at least partially straighten along the rotor (e.g., via turning vanes or de-spiraling of the passageways). However, an exemplary compression occurs while falling primarily tangentially with small axial component and only a radial component associated with the ramps that otherwise constrained. Thus, in this example, both inlet and outlet flows to the rotor are tangential/axial but essentially non-radial with a primary velocity component being tangential.

[0039] The exemplary ramp leading end/edge 134 is spaced above (radially outboard of) an adjacent portion of the rotor hub (and thus of the supersonic flowpath boundary surface) to define a bleed inlet 200 of a bleed system radially inboard of the passageway inlet 162. FIG. 5 shows a unitarily formed support strut 202 within a bleed chamber 204 immediately downstream of the inlet 200. The exemplary bleed chamber extends beneath/inboard of a leading portion of the ramp to an end 206 (FIG. 7), a bleed outlet port/passageway 208 has an inlet along the rim surface 131 and extends radially inward from the chamber 204 through the rotor rim and leads to a space between the rotor and stator. Therefrom, the bleed 590 (bleed flow) may be fed to a location such as a port in the housing at or near the upstream end of the impeller. An underside 210 of a leading portion of the ramp thus defines the outboard boundary of the bleed chamber 204. The exemplary bleed is used to maintain desired attributes of flow entering the main ramp passageway. As is discussed further, by taking the bleed 590 from a boundary layer along the rim/hub, velocity and quality of inlet flow to the main passageway may be improved/maintained.

[0040] The bleed may pass radially inward between the stator and the rotor. The bleed may then be collected near the shaft and removed.

[0041] In variations, the rotor rim/hub 130 outboard surface may be further contoured. In one example, the outboard surface 131 (FIG. 4) is at constant radius along the forward edge 135 of the rim adjacent the stator (e.g., at the same diameter as the stator outboard surface), the surface may deepen (radially recess from front to rear and upstream to downstream toward the intersection 133 with the next strake (the strake of the next passageway immediately behind the subject passageway (even though that next passageway will be the one to pass a given location on the housing before the subject passageway)). This deepening may allow the bleed inlet 200 to be relatively tall near the intersection 133 than near the front of the rotor. This deepening compensates for the boundary layer being relatively thicker near the intersection 133 than near the front of the rotor.

[0042] In the exemplary embodiment, the surface 131 is at constant radius from the passageway outlets to the rear edge/end 137 of the rotor rim.

[0043] Along the leading portion, the outboard surface 138 extends radially outward to define a compression zone 220 extending to a throat 222. Thereafter, the passageway expands in an expansion zone 224 to the end 136 of the ramp and finally in a straight zone 226 to the outlet 164. The expansion zone functions as a diffuser so as to additionally compress the subsonic part of the flow and slow it down. FIG. 5 further shows an outwardly circumferentially concave leading portion 240 of the shroud outer surface along the passageways. FIG. 8 shows this portion radially inwardly spaced from the interior/inner/inner diameter (ID) surface 242 of the adjacent housing section 56. The gap between this leading portion and the ID surface 242 tapers to relatively small at a junction with an intact circular cylindrical portion of the shroud.

[0044] The leading portion 240 functions so as to mitigate shock effects. When the flow hits the ramp external compression section 250 (at and extending downstream from end/edge 134), a series of oblique compression waves 530 are formed. Those waves are focused at the leading edge 166 of the shroud and reflect. The pressure is gradually increasing after each wave. Then those waves are reflected. The reflected wave 540 returns to the ramp throat 252. In the throat there is a terminal shock 544 after which the flow becomes subsonic and the rest of the compression is in the diffuser section.

[0045] A contoured leading edge portion 170 of the shroud is formed by making the edge 166 of the shroud thin and then gradually increasing the thickness of the shroud wall. This thin leading edge produces weaker bow shock that can interact with the focused oblique waves. The radial clearance between the shroud OD surface 152 and housing ID should be very small to prevent leakage.

[0046] The exemplary thinning of the edge portion 170 is achieved on the OD surface 152 via the concave region/portion 240. The exemplary thinning toward the leading edge/end 166 generally limits bow shock generation. By thinning along the OD surface 152 rather than the ID surface 154, shock intensity is concentrated radially outward (shock 550 shown extending to the housing ID surface 242) with relatively limited shock intensity radially inward. This inclination and the associated radially inward offset of the leading edge 166 from the surface 242 also helps align the surface 154 with the flow outside the boundary layer along the surface 242. This improves inlet flow quality.

[0047] Similarly, FIG. 5 shows a concavely contoured leading region/portion 260 of the strake downstream of the edge 142. As with the thinning provided by the region/portion 240, this mitigates the effect of the leading bow shock by both reducing overall bow shock significance due to edge thinning and concentrating the bow shock outward due to thinning principally being along the outer/forward surface of the strake.

[0048] Thus, the impeller centrifugally compresses an impeller inlet flow 580 (FIG. 3) and discharges it to the stator as a compressed flow 582 (FIG. 4) having tangential and axial components. This flow 582 becomes a supersonic inlet flow 584 approaching the compression passageways 160. Thus, between the impeller outlet/discharge flow 582 and the rotor inlet flow 584, the tangential velocity may be maintained. In this example, the axial velocity is

substantially also maintained as is the lack of radial velocity component. It can thus be seen that by having the impeller and rotor counter-rotate (and avoiding a need for tangential direction reversal) tangential velocity may efficiently be maintained, thus, increasing the relative Mach number of the inlet flow to the rotor. The flow 584 is discharged as a subsonic flow 586.

Supersonic flow 584 enters the convergent section along the ramp and is near isentropically compressed along/within the convergent section. Shock-down to a subsonic state occurs at the throat and subsonic diffusion occurs downstream. This may provide an efficient and compact diffusion process to convert dynamic pressure to static pressure.

[0049] After exiting the outlets 164, the flow passes into a collector chamber or plenum 300 and, therefrom, out the compressor outlet.

[0050] Relative to a co-rotating hybrid compressor system such as that of the '500 publication, the counter-rotating system may be implemented to achieve one or more of several advantages. The positions and sizes of the impeller and rotor may be more easily configured to maintain tangential velocity from the exit of the centrifugal stage to the inlet of the supersonic stage, thus increasing the relative Mach number of the entering flow. The use of a rotating shroud may help position the normal shock at the throat and prevent leakage of flow from the higher pressure section of one passageway to the lower pressure section of an adjacent passageway. [0051] The components may be designed by conventional computational fluid dynamics and solid modeling techniques. Various surface profiles may be accordingly optimized beyond the basic detail illustrated. For example, boundary layer effects may lead to uneven inlet Mach numbers across the width (axial span) of the passageway inlet. The shape and orientation of the inlet edge and the downstream thickness profile (e.g., for both the ramp and the shroud) may be optimized accordingly. In one example, the incoming flow may be sliced into several sections along the flow and, for each section, the Mach number evaluated. Two-dimensional ramp positions/profiles may be designed for each slice and then the slices may be stacked together and smoothed. This may be part of an iterative process with further optimizations.

[0052] The various system components may be made from conventional materials and via conventional techniques in the compressor art. For example, the impeller may be cast and/or machined over metallic alloy appropriate for such impellers. The rotor may be machined in multiple pieces and then assembled (e.g., with welding). The rim and portions inboard thereof may be machined as one piece and then the shroud (either as a single piece shroud or multiple pieces) separately machined and assembled thereto. Exemplary rotor material is titanium.

[0053] A controller (e.g., microcontroller, microcomputer, or the like) may be configured via programming or otherwise to control rotor and impeller speeds so as to achieve targets in mass flow rate and/or pressure ratio. Control may be otherwise similar to that of a conventional co-rotating system and be responsive to various entered and/or sensed conditions (such as via pressure sensors such as at the impeller inlet or upstream thereof, the rotor outlet or downstream thereof, and between the two (the interstage)).

[0054] Other variations involve rotor configuration. FIG. 10 shows an inwardly facing ramp 342 on the outer diameter (OD) of the rotor 340. For example, the ramps may be formed as thickened areas along the inner diameter (ID) surface of a shroud 343. The rim/hub 341 is configured to allow more flow turning using the ramp and has a bleed port 208. The ramp on the shroud ingests cleaner flow, because the boundry layer on the ID of the stationary housing is thinner compared to the hub boundary layer. An edge 344 is defined as the leading edge of the ramp and of the shroud along the forward sawtooth. An exemplary inlet 350 to a bleed chamber 352 feeding the bleed port 208 is along the leading face of an elevation 354 on the OD surface 355 of the rim/hub. The exemplary elevation 354 is formed at an angular position along a compression portion of the ramp.

[0055] FIG. 11 shows a rotor 370 and ramps 372 on a sidewall of the rotor. [0056] FIG. 12 shows a rotor 700 wherein the ramp is formed by a centerbody 702 radially splitting the passageway inlet flow into inboard and outboard branches and extending between and mounted to the two adjacent strakes. The centerbody has an outboard surface 708 defining an outboard ramp and an inboard surface 710 defining an inboard ramp, both extending between a leading edge/end 704 and a trailing edge/end 706. The inboard and outboard ramps each cooperate with the respectively adjacent surface 131 or 154 to define a converging part, a throat, a shock train section, and a diffuser. The upper ramp will be expected to receive a higher velocity flow than the lower ramp because of the thicker boundary layer along the surface 131. Accordingly, the upper ramp geometry may be optimized for slightly faster flow than the lower ramp geometry. In such a situation, a bleed port may still be provided in the rim/hub to withdraw low momentum boundary flow from the inboard passageway branch.

[0057] In other variations, an interstage flow is introduced. For example, an interstage cooling flow of the refrigerant (e.g., liquid droplets which evaporate to cool the main flow) may be introduced to the main flow to reduce the temperature at the ramp inlet. The reduced temperature of the main flow reduces the speed of sound which, in turn, reduces the required rotor speed for a desired/target Mach number. This allows reduction of rotor rotational speed, thus reducing the rotor stresses. This also increases efficiency and reduces needed motor power for the rotor. Other variations may involve other introductions of additional flows and/or withdrawal of partial flows.

[0058] In further variations, the bleeds may be controlled (e.g., by valve structures allowing full or partial closing of the bleed ports 208).

[0059] Although an embodiment is described above in detail, such description is not intended for limiting the scope of the present disclosure. It will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, when implemented in the reengineering of an existing compressor configuration or for a given application, details of the existing configuration or given application may influence details of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.