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(11) | EP 0 342 484 A3 |
(12) | EUROPEAN PATENT APPLICATION |
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(54) | Very noiseless motor driven centrifugal fan |
(57) The motor driven centrifugal fan (10) according to the present invention has the
inner surface (18) of the volute (12) and possibly also the inner surfaces of the
sidewalls (13) laterally defining the volute which are roughened. The roughness can comprise projections or recesses of irregular shape, for example of orange-peel type, or of regular shape, for example regular polygons or circles which can be arranged along parallel lines which are or not offset from each other. |