Centrifugal compressor with motor cooling
A centrifugal compressor includes a casing, an inlet guide vane, an impeller, a motor, a diffuser and a cooling medium delivery structure. The motor includes a rotor mounted on the shaft and a stator disposed radially outwardly of the rotor to form a gap between the rotor and the stator. The cooling medium delivery structure includes inlet and outlet conduits located to supply and discharge a cooling medium to and from the motor. The shaft has an external shape different than an internal shape of the rotor to form at least one axial passageway between the shaft and the rotor. The cooling medium is supplied through the gap and the at least one axial passageway to cool the rotor.
1. A centrifugal compressor adapted to be used in a chiller, the centrifugal compressor comprising:
a casing having an inlet portion and an outlet portion;
an inlet guide vane disposed in the inlet portion;
an impeller disposed downstream of the inlet guide vane, the impeller being attached to a shaft rotatable about a rotation axis;
a diffuser disposed in the outlet portion downstream from the impeller; and
a motor arranged to rotate the shaft in order to rotate the impeller, the motor including a rotor mounted on the shaft and a stator disposed radially outwardly of the rotor to form a gap between the rotor and the stator;
a cooling medium delivery structure including an inlet conduit located to supply a cooling medium to the motor and an outlet conduit located to discharge the cooling medium from the motor,
the shaft having an external shape different than an internal shape of the rotor to form at least one axial passageway between the shaft and the rotor along an axial length of the shaft at least as long as an axial length of the rotor, and
the inlet conduit being located to supply the cooling medium through the gap and the at least one axial passageway to cool the rotor, and the outlet conduit being located to discharge the cooling medium from the gap and the at least one axial passageway.
2. The centrifugal compressor according to claim 1 , wherein
the external shape of the shaft is different than the internal shape of the rotor to form a plurality of axial passageways between the shaft and the rotor along the axial length of the shaft at least as long as the axial length of the rotor.
3. The centrifugal compressor according to claim 2 , wherein
the external shape of the shaft includes an annular section and a plurality of grooves extending radially inwardly from the annular section.
4. The centrifugal compressor according to claim 3 , wherein
the grooves are substantially equally spaced from each other along a circumferential direction about the annular section.
5. The centrifugal compressor according to claim 3 , wherein
each of the grooves includes a first sidewall, a second sidewall circumferentially spaced from the first sidewall and a trough wall connecting radially inner ends of the first and second sidewalls.
6. The centrifugal compressor according to claim 5 , wherein
the first sidewall of each groove is substantially parallel to the second sidewall of the groove as viewed in axial cross section.
7. The centrifugal compressor according to claim 5 , wherein
each groove has a centerline equally spaced from the first and second sidewalls as viewed in axial cross section, and the centerline of each groove is inclined relative to a radial direction of the shaft.
8. The centrifugal compressor according to claim 7 , wherein
the shaft rotates in a rotation direction during operation of the centrifugal compressor, and
each centerline is inclined so that a radially outer end is disposed circumferentially further in the positive rotational direction than a radially inner end of the centerline.
9. The centrifugal compressor according to claim 7 , wherein
the shaft rotates in a rotation direction during operation of the centrifugal compressor, and
each centerline is inclined so that a radially inner end is disposed circumferentially further in the positive rotational direction than a radially outer end of the centerline.
10. The centrifugal compressor according to claim 5 , wherein
the shaft rotates in a rotation direction during operation of the centrifugal compressor, and
at least one of the first sidewall and the second sidewall of each groove is angled so that a radially outer end is disposed circumferentially further in the positive rotational direction than a radially inner end.
11. The centrifugal compressor according to claim 5 , wherein
the shaft rotates in a rotation direction during operation of the centrifugal compressor, and
at least one of the first sidewall and the second sidewall of each groove is angled so that a radially inner end is disposed circumferentially further in the positive rotational direction than a radially outer end.
12. The centrifugal compressor according to claim 3 , wherein
a total cross sectional area of the plurality of grooves is larger than a total cross sectional area of the gap as viewed in axial cross section.
13. The centrifugal compressor according to claim 12 , wherein
the total cross sectional area of the plurality of grooves is approximately double the total cross sectional area of the gap as viewed in axial cross section.
14. The centrifugal compressor according to claim 1 , wherein
a total cross sectional area of the at least one axial passageway is larger than a total cross sectional area of the gap as viewed in axial cross section.
15. The centrifugal compressor according to claim 14 , wherein
the total cross sectional area of the at least one axial passageway is approximately double the total cross sectional area of the gap as viewed in axial cross section.
16. The centrifugal compressor according to claim 1 , wherein
the cooling medium is refrigerant used in the chiller.
17. The centrifugal compressor according to claim 16 , wherein
the refrigerant is a low pressure refrigerant (LPR).
18. The centrifugal compressor according to claim 17 , wherein
the low pressure refrigerant (LPR) is R1233zd.
19. The centrifugal compressor according to claim 16 , wherein
the refrigerant is a low global warming potential (GWP) refrigerant.
20. The centrifugal compressor according to claim 19 , wherein
the low global warming potential (GWP) refrigerant is R1234ze or R1234yf.
21. The centrifugal compressor according to claim 16 , wherein
the cooling medium delivery structure does not include a pump.
22. The centrifugal compressor according to claim 16 , further comprising a magnetic bearing rotatably supporting the shaft.
23. The centrifugal compressor according to claim 22 , wherein the magnetic bearing includes
a first radial magnetic bearing element disposed on a first axial end of the motor,
a second radial magnetic bearing element disposed on a second axial end of the motor, and
a third axial thrust bearing element disposed on one of the first and second axial ends of the motor.
24. The centrifugal compressor according to claim 23 , wherein
at least a portion of the inlet conduit is axially disposed closer to one of the first or third magnetic bearing elements than the first axial end of the motor.
25. The centrifugal compressor according to claim 23 , wherein
at least a portion of the outlet conduit is axially disposed closer to one of the second or third magnetic bearing elements than the second axial end of the motor.