Centrifugal compressor with recirculation structure

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;
• a recirculation structure including a recirculation path and a recirculation discharge cavity;
• an impeller disposed downstream of the recirculation discharge cavity, the impeller being attached to a shaft rotatable about a shaft rotation axis, the inlet portion extending axially to the impeller, the recirculation discharge cavity being separate from and radially surrounding the inlet portion;
• a plurality of recirculation discharge guide vanes disposed to surround the recirculation discharge cavity, the plurality of recirculation discharge guide vanes being circumferentially arranged with respect to the shaft rotation axis of the shaft, and the plurality of recirculation discharge guide vanes being disposed upstream of a most upstream portion of the impeller, each of the plurality of recirculation discharge guide vanes being rotatable about a vane rotation axis parallel to the shaft rotation axis of the shaft, the plurality of recirculation discharge guide vanes being disposed externally of the inlet portion in a radial direction of the shaft;
• a motor arranged to rotate the shaft in order to rotate the impeller;
• a diffuser disposed in the outlet portion downstream of the impeller,
• the recirculation structure being configured and arranged to impart a swirl to a flow of refrigerant into the inlet portion, with a velocity of a recirculation flow caused by the swirl being higher than a velocity of the flow of the refrigerant in the inlet portion, and
• the recirculation path supplying the refrigerant from the diffuser to the recirculation discharge cavity, and the recirculation path including a recirculation pipe that introduces refrigerant toward the plurality of recirculation discharge guide vanes;
• an annular groove disposed between the recirculation pipe and the plurality of recirculation discharge guide vanes in a recirculation flow direction of the refrigerant;
• and
• an annular plate disposed between the annular groove and the recirculation discharge cavity, the plurality of recirculation discharge guide vanes being rotatably disposed on the annular plate.