Recirculating diffuser

A centrifugal compressor having an impeller wheel mounted for rotation about a central axis for compressing a fluid, and a diffuser for expanding the compressed fluid into a collector chamber, said compressor further including

• a plenum chamber contained in a shroud surrounding said impeller,
• a series of spaced apart deswirl blades circumferentially positioned about the impeller wheel and extending between the collector chamber and the plenum chamber for establishing a first set of deswirl flow passages for placing the collector chamber in fluid flow communication with the plenum chamber,
• a series of spaced apart channel vanes mounted in said plenum chamber about the impeller tip region for reestablishing a second set of channel flow passages for introducing fluid from the plenum chamber into the impeller exit flow, said first and second flow passages combining to adjust the fluid flow to about the exit speed and direction of fluid leaving the impeller, and
• control means for regulating the flow of fluid moving through the deswirl passages to regulate the amount of fluid introduced into said impeller exit flow and thus maintain the total flow moving through the diffuser relatively constant under varying load conditions.