Rotating diffuser in centrifugal compressor

A centrifugal compressor includes a shaft defining an axis, an impeller mounted to the shaft for rotation about the axis, and a diffuser section including a first wall, a second wall, and an opening defined between the first wall and the second wall. The opening of the diffuser section is arranged in fluid communication with the impeller. The first wall is rotatable about the axis and rotation of the first wall about the axis is mechanically driven.

BACKGROUND

Exemplary embodiments disclosed herein relate generally to a centrifugal compressor, and more particularly, to a diffuser structure for use in a centrifugal compressor of a refrigeration system.

Existing centrifugal compressors typically include a power driven impeller through which an inflow of refrigerant is induced for radially outward flow into a diffuser. A diffuser of the compressor commonly includes an annular passage defined by a wall surface of a fixed plate axially spaced from a shaped wall surface of a shroud. The diffuser has an inlet end receiving the impeller outflow and an outlet end from which refrigerant is provided to a compressor volute that is circumferentially divergent for example. Kinetic energy is converted by the diffuser of the compressor into a static pressure rise within the diffuser. The stationary walls of the diffuser may cause high shear stress resulting in pressure losses that impair the performance of the compressor.

BRIEF DESCRIPTION

According to an embodiment, a centrifugal compressor includes a shaft defining an axis, an impeller mounted to the shaft for rotation about the axis, and a diffuser section including a first wall, a second wall, and an opening defined between the first wall and the second wall. The opening of the diffuser section is arranged in fluid communication with the impeller. The first wall is rotatable about the axis and rotation of the first wall about the axis is mechanically driven.

In addition to one or more of the features described above, or as an alternative, in further embodiments the first wall includes a plurality of pieces and at least one of the plurality of pieces is mechanically driven about the axis.

In addition to one or more of the features described above, or as an alternative, in further embodiments rotation of the first wall about the axis is mechanically driven by at least one of the impeller and the shaft.

In addition to one or more of the features described above, or as an alternative, in further embodiments rotation of the first wall about the axis is mechanically driven by a motor.

In addition to one or more of the features described above, or as an alternative, in further embodiments the second wall is stationary.

In addition to one or more of the features described above, or as an alternative, in further embodiments the second wall is rotatable about the axis.

In addition to one or more of the features described above, or as an alternative, in further embodiments the first wall is rotatable about the axis at a first speed and the second wall is rotatable about the axis at a second speed, the first speed being distinct from the second speed.

In addition to one or more of the features described above, or as an alternative, in further embodiments the first wall and the second wall are connected by at least one coupler.

In addition to one or more of the features described above, or as an alternative, in further embodiments the at least one coupler has an airfoil shape.

In addition to one or more of the features described above, or as an alternative, in further embodiments the second wall is freely rotatable about the axis.

In addition to one or more of the features described above, or as an alternative, in further embodiments the second wall is mechanically driven about the axis.

According to another embodiment, a centrifugal compressor includes a shaft defining an axis, an impeller mounted to the shaft for rotation about the axis, and a diffuser section including a first wall, a second wall, an opening defined between the first wall and the second wall. The opening of the diffuser section is arranged in fluid communication with the impeller. The first wall is rotatable about the axis, and rotation of the first wall about the axis is driven by engagement of a fluid flow within the opening and a surface of the first wall facing the opening.

In addition to one or more of the features described above, or as an alternative, in further embodiments the first wall includes a plurality of pieces and at least one piece of the plurality of pieces is driven about the axis by engagement of the fluid flow within the opening and a surface of the at least one piece of the first wall facing the opening.

In addition to one or more of the features described above, or as an alternative, in further embodiments the plurality of pieces includes at least a first piece and a second piece, the first piece being rotatable about the axis at a first speed and the second piece being rotatable about the axis at a second speed, the first speed being different than the second speed.

In addition to one or more of the features described above, or as an alternative, in further embodiments at least one of the plurality of pieces of the first wall is mechanically driven about the axis.

In addition to one or more of the features described above, or as an alternative, in further embodiments at least one of the plurality of pieces of the first wall is stationary.

In addition to one or more of the features described above, or as an alternative, in further embodiments comprising at least one coupling mechanism positioned between the first wall and an adjacent component of the centrifugal compressor to allow relative rotation between the first wall and the adjacent component.

In addition to one or more of the features described above, or as an alternative, in further embodiments the at least one coupling mechanism includes one of a bearing and a roller assembly.

In addition to one or more of the features described above, or as an alternative, in further embodiments the surface of the first wall facing the opening has a non-planar configuration.

In addition to one or more of the features described above, or as an alternative, in further embodiments the surface of the first wall facing the opening has at least one vane extending into the opening.

DETAILED DESCRIPTION

Referring now toFIG. 1, an example of a centrifugal compressor10is illustrated. As shown, the centrifugal compressor10includes a housing12having an inlet14that directs refrigerant into a rotating impeller16through a series of adjustable inlet guide vanes18. The impeller16is secured to a shaft20by any suitable means to align impeller16along the axis of the compressor10. The impeller16includes a hub22supporting a plurality of blades24. A plurality of passages26defined between adjacent blades24cause the incoming axial flow of a refrigerant fluid to turn in a radial direction and discharge the compressed refrigerant fluid from respective passages26into an adjacent diffuser section30. The diffuser section30is generally circumferentially disposed about the impeller16and functions to direct the compressed refrigerant fluid into a toroidal-shaped volute32, which directs the compressed fluid toward a compressor outlet, or alternatively, toward a second stage of the compressor10, depending on the configuration of the compressor.

As best shown inFIGS. 2 and 6, the diffuser section30typically includes a first wall40, a second wall42, and an opening44formed between the first and second walls40,42. The first wall40and the second wall42may be formed from any suitable material including a metal. The opening44is arranged in fluid communication with the radial flow discharged from the impeller16. As shown, one or both of the first wall40and the second wall42has an outer edge43located near the volute32and an inner edge45positioned adjacent the impeller16. An example of a wall50, such as either the first wall40or the second wall42is illustrated in more detail inFIG. 3. In an embodiment, the wall50is disc-like in shape and has a substantially uniform thickness. Further, the surface52of the wall50configured to face the opening44may have a generally planar configuration. However, embodiments where the wall50has a non-uniform thickness and/or the surface52has a non-planar configuration (seeFIGS. 4A and 4B) are also within the scope of the disclosure. Additionally, although the wall50inFIG. 3is illustrated as being formed from a single piece, in other embodiments, such as shown inFIGS. 4A and 4B, the wall50may be formed from a plurality of pieces positioned adjacent one another. For example, the wall50may include a first piece54aand a second piece54barranged concentrically with the first piece54a. Although only two pieces are shown, embodiments where either wall40,42is formed from any number of pieces54including more than two pieces are also within the scope of the disclosure. In embodiments where the wall50includes a plurality of pieces54, the pieces54may be coupled together, such as via a fastener, adhesive, or another suitable coupling mechanism, or may be separate. Further, the pieces54may, but need not be identical in shape, size, thickness, and contour of the surface52.

Referring again toFIG. 3, in the illustrated, non-limiting embodiment, the wall50includes a plurality of circumferentially spaced, fixed vanes56, extending from the surface52toward the opening44. The plurality of vanes56may be substantially identical, or alternatively, may vary in size, shape, and/or orientation relative to a central axis X of the compressor10. As the refrigerant passes through the passageways58defined between adjacent vanes56, the kinetic energy of the refrigerant may be converted to a potential energy or static pressure. However, it should be understood that embodiments where only one of the first and second wall40,42includes vanes56, or where neither the first wall40nor the second wall42has vanes56extending therefrom into the opening44are also within the scope of the disclosure.

At least a portion of the diffuser section30, is rotatable about the axis X. More specifically, at least one of the first wall40and the second wall42, or at least a portion of either wall40,42, such as one or more of the pieces54thereof for example, are rotatable about the axis X. In an embodiment, rotation of one or more walls40,42of the diffuser section30may be driven by another component. For instance, at least a piece54of the first wall40and/or the second wall42may be coupled to a portion of the impeller16, such as the hub22or a shroud23, such that rotation of the wall40,42is driven by the impeller16. In embodiments where at least one of the walls40,42is directly connected to the impeller16, the at least one wall40,42and the impeller16will rotate in unison, in the same direction and with the same velocity. Alternatively, the wall40,42may be indirectly coupled to the impeller16, such as via a gear train or other coupling mechanism. In such embodiments, the wall40,42, or a portion thereof, may be configured to rotate faster than the impeller, slower than the impeller, or at the same speed as the impeller. Although a wall is described as being coupled to the impeller16, it should be understood that the wall40,42or a piece54thereof may be coupled to any rotating component of the compressor10, such as the shaft20for example.

In another embodiment, rotation of at least one of the first wall40and the second wall42, or at least a piece54of either wall40,42, such as one or more of the pieces54thereof, may be driven by a motor, actuator, or other power driven component. The motor may be the same motor used to drive rotation of the shaft20about axis X, illustrated inFIG. 1at34, or alternatively, may be a separate motor, illustrated schematically at60inFIG. 2, located either within or external to the compressor housing12. In an embodiment, the motor coupled to the rotating portion of the diffuser section30is a variable speed motor such that the rotational speed of the first wall40or second wall42coupled thereto may be adjusted, such as in response to one or more operating conditions of the compressor10.

In yet another embodiment, at least one of the first wall40, the second wall42, or a piece54of either wall40,42, is configured to freely rotate about axis X. In such embodiments, rotation will be driven by the flow of refrigerant through the opening44of the diffuser section30. To allow one or more pieces54of the first wall40or the second wall42to rotate freely, the freely rotatable pieces54are mounted to an adjacent portion of the compressor10, such as the housing12, impeller shroud23, shaft20, or another component coupled to the shaft20, via at least one coupling mechanism62that allows for relative rotation there between. In the non-limiting embodiment illustrated inFIGS. 5A-5C, the coupling mechanism62includes a roller assembly. However, any suitable coupling mechanism62, such as a bearing for example, is also within the scope of the disclosure. As shown, a plurality of roller assemblies62are positioned at the interface between a wall, such as wall42of the diffuser section30, and an adjacent component, such as a portion of the impeller16. In the illustrated, non-limiting embodiment, three roller assemblies62are arranged at the interface; however, it should be understood that embodiments including any number of roller assemblies62, such as one, two, or more than three roller assemblies are also within the scope of the disclosure. As shown, a fastener64is used to couple each roller assembly62to the wall42of the diffuser section30. Accordingly, the roller assembly62is rotatable about the respective axis F defined by the mounting fastener63, to allow the adjacent wall42of the diffuser section30to rotate about axis X.

Embodiments where a single wall, either wall40or wall42, has a piece54athat is stationary and a second piece54bthat is rotatable about the axis X is within the scope of the disclosure. Further the wall may have a plurality of pieces, each of which is rotatable about the axis X at different speeds. Various configurations may be used to achieve these different rotational speeds. For example, a wall may have a piece54that is freely rotatable and another piece54that is rotatably driven by a component or motor. Alternatively, or in addition, one of the walls may have a piece54driven by a first component or motor, and another piece54driven by a second component or motor.

In addition, embodiments where at least a piece54of one wall is rotatable and at least a piece54of the other wall of the diffuser section30is stationary, or embodiments where at least a piece54of each of the first wall40and the second wall40are rotatable are within the scope of the disclosure. In embodiments where one or more pieces54of both the first wall40and the second wall42are rotatable, at least a piece54of one of the walls40,42may be freely rotatable and at least a piece54of the other wall may be driven, at least a piece of both walls40,42may be freely rotatable, or at least a piece of both of the walls40,42may be driven.

With reference now toFIG. 6, in an embodiment, such as where a piece of one of the walls40,42is rotatably driven and a piece of the other wall is freely rotatable, one or more couplers64may extend between the first wall40and the second wall42. By including the couplers64, the rotation of the driven piece54of one wall is transmitted to the freely rotatable piece54of the other wall. In an embodiment, the coupler64has an airfoil shape (seeFIG. 6A) to minimize aerodynamic losses within the opening44of the diffuser section30.

A rotating diffuser as illustrated and described herein improves the efficiency of the compressor stage relative to existing compressors having a stationary diffuser, such as by 3-5%.