Patent ID: 8313290

Claim:
A centrifugal compressor comprising: a rotating shaft, an impeller attached to the rotating shaft; at least one vaneless diffuser provided on a downstream side of the impeller; an inlet flow channel; and a return channel, wherein the at least one vaneless diffuser includes a first vaneless diffuser with a constant flow channel height provided on the downstream side of the impeller, and a second vaneless diffuser in which a flow channel height decreases in a flow direction from an inlet to an outlet, provided on the downstream side of the first vaneless diffuser, wherein an inlet radius ratio r m /r imp as a ratio between an inlet radius r m of the second vaneless diffuser and an outlet radius r imp of the impeller becomes smaller in accordance with a decrease in a flow channel height ratio b m /r imp as a ratio between an inlet flow channel height b m of the second vaneless diffuser and the outlet radius r imp of the impeller, and wherein the inlet radius ratio rm/rimp of the second vaneless diffuser is given as a function r m /r imp ≦1.03+3.0·b m /r imp of the flow channel height ratio b m /r imp of the second vaneless diffuser.