Fan shroud with integral air supply

摘要

A shroud for an axial blade fan provides a circumferential, axially directed flow of air between the fan blade tips and the shroud to improve fan efficiency. The shroud preferably includes a smaller, centrally disposed fan which is driven by an auxiliary motor, a circumferentially extending generally toroidal plenum, a plurality of hollow spokes providing fluid communication between the fan and the plenum, a circular throat which directs air toward the annulus between the shroud and the fan blade tips and a throat adjacent, circumferential Coanda surface which controls and guides air exiting the throat. Air is provided to the shroud plenum at a pressure of between about 2 and 10 inches water gauge (4 to 20 Torr). The narrowest region of the circular throat has a width of between about 1 mm to 5 mm. Adjustment of the air pressure and throat dimension allows accurate control of the velocity profile of the air flow through the annulus.