Centrifugal compressor having vaneless diffuser and vaneless diffuser thereof
View Patent ↗In a high pressure centrifugal compressor, the occurrence of rotating stall noticeable in a comparatively-low specific speed wheel stage is prevented, thereby high efficient fluid performance is obtained and reliability is improved. The centrifugal compressor has a first vaneless diffuser with a constant flow channel height on the downstream side of an impeller, and a second vaneless diffuser in which the flow channel height decreases in a flow direction from an inlet to an outlet on the downstream side of the first vaneless diffuser. These diffusers are combined with an impeller using thick blades.
1. 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.
2. The centrifugal compressor according to claim 1 , wherein an outlet flow channel height b o of the second vaneless diffuser is set to 0.4 to 0.6 times of the inlet flow channel height b m of the second vaneless diffuser.
3. The centrifugal compressor according to claim 1 , wherein the flow channel height ratio b m /r imp of the second vaneless diffuser is equal to or less than 0.1.
4. The centrifugal compressor according to claim 1 , wherein a longitudinal cross-sectional shape of the first and second vaneless diffusers consists of straight lines.
5. The centrifugal compressor according to claim 1 , wherein a longitudinal cross-sectional shape of the first and second vaneless diffusers includes a curve.
6. The centrifugal compressor according to claim 1 , wherein the impeller has wedge-shaped thick blades.
7. A vaneless diffuser for a centrifugal compressor, the compressor comprising:
a rotating shaft;
an impeller attached to the rotating shaft;
at least one vaneless diffuser provided on the 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, 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 an outlet flow channel height b o of the second vaneless diffuser is set to 0.4 to 0.6 times the inlet flow channel height b m of the second vaneless diffuser.