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1. (WO2017156056) CENTRIFUGAL COMPRESSOR WITH ADJUSTABLE INLET RECIRCULATION
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WHAT IS CLAIMED IS:

1. A centrifugal compressor adapted to be used in a chiller system, 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 motor arranged and configured to rotate the shaft in order to rotate the impeller; a diffuser disposed in the outlet portion downstream of the impeller; and a casing treatment bypass having an entrance port and an exit port,

the casing treatment bypass being arranged and configured to inject refrigerant from a gap between the impeller and the inlet portion of the casing toward an area between the impeller and the inlet guide vane, and

the exit port of the casing treatment bypass being positioned upstream in a direction of a refrigerant flow with respect to the entrance port of the casing treatment bypass.

2. The centrifugal compressor according to claim 1 , wherein

the impeller includes an impeller hub and an impeller blade surrounding the impeller hub,

the entrance port of the casing treatment bypass faces the impeller blade, and the exit port of the casing treatment bypass opens to the area between the inlet guide vane and the impeller.

3. The centrifugal compressor according to claim 2, wherein

a diameter of the entrance port of the casing treatment bypass is determined based on a diameter of the impeller blade.

4. The centrifugal compressor according to any of claims 1-3, wherein

a cross-sectional area of the exit port of the casing treatment bypass is equal to or greater than a cross-sectional area of the entrance port of the casing treatment bypass.

5. The centrifugal compressor according to any of claims 1-4, wherein the casing treatment bypass includes a hole formed in the inlet portion of the casing.

6. The centrifugal compressor according any of claims 1 -4, wherein the casing treatment bypass includes a plurality of holes formed in the inlet portion of the casing.

7. The centrifugal compressor according to any of claims 1 -6, wherein the casing treatment bypass has a ring shape.

8. The centrifugal compressor according to any of claims 1 -7, wherein a flow path area of the casing treatment bypass is fixed.

9. The centrifugal compressor according to any of claims 1 -7, wherein a flow path area of the casing treatment bypass is adjustable.

10. The centrifugal compressor according to claim 9, wherein

a movable adjusting member is disposed in the inlet portion of the casing so as to at least partly block the flow path area of the casing treatment bypass, and

the flow path area of the casing treatment bypass is adjusted by moving the movable adjusting member in a radial direction perpendicular to an axial direction corresponding to the rotation axis of the impeller.

11. The centrifugal compressor according to claim 9, wherein

the inlet portion of the casing includes a movable sub-portion which is separated from the inlet portion of the casing by the casing treatment bypass, and

the flow path area of the casing treatment bypass is adjusted by moving the sub-portion in an axial direction corresponding to the rotation axis of the impeller.

12. The centrifugal compressor according to any of claims 1-11, wherein the refrigerant is low global warming potential refrigerant.

13. The centrifugal compressor according to claim 12, wherein

the low global warming potential refrigerant is low pressure refrigerant.

14. The centrifugal compressor according to claim 13, wherein

the low pressure refrigerant includes R1233zd.

15. The centrifugal compressor according to any of claims 1-14, wherein the impeller is a mixed flow type impeller.

16. The centrifugal compressor according to any of claims 1-14, wherein the impeller is a radial flow type impeller.