LOW FLOW CHARACTERISTIC IMPROVIDING SYSTEM FOR CENTRIFUGAL FAN AND COMPRESSOR

摘要

PURPOSE:To prevent noise of a centrifugal fan under low flow, by providing a path for circulating a portion of air and returning to the upper stream of impeller at the portion of air path innercircumferential face facing with the upper stream end of impeller. CONSTITUTION:An inner tube 6 having innercircumferential face flat with that of an air path 2 is provided in an annular recess 5 formed at the portion of innercircumferential face of air path 2 facing with the upper stream end of impeller 3. The inner tube 6 and the recess 5 are forming a path 7 for returning/ circulating a portion of air to be fed through rotation of the impeller 3 from the impeller 3 to the upper stream. Since the apparent flow will not drop at the inlet of impeller, the low flow characteristic is improved to prevent the low frequency noise.