Such radial fan wheels or radial impellers are employed, for instance, in climate control and ventilation technology.
Radial impellers inclined towards the front having 30-40 vanes that run from the inside to the outside in the direction of rotation, with diameters of 160-400 mm, are employed in ventilation technology in conjunction with flow-shaping spiral housings. Their static efficiency is roughly 30-35%. Such a radial impeller is known from JP 06299993. U.S. Pat. No. 1,447,915 shows a design as a radial ventilator with a converging annular discharge, in which the centrifugally accelerated air is further accelerated by the outlet nozzle that converges radially on the outside.
For larger volume flows, radial impellers inclined towards the rear, in which the vanes are inclined against the direction of rotation, are predominantly used. The usual diameters run between 200 and 1500 mm; diameters above 2500 mm are known for special applications. They are employed, for instance, with spiral housings and without them-free-running-in so-called blower casings. There the air drawn in axially from the outside through the inlet opening exits radially to the outside between the vanes. To reduce undesired noise emission that arises in the operation of radial impellers, either sound-damping (sound-absorbing) measures or constructive measures on the radial impeller itself that exert a noise-reducing effect on the exiting air flow are necessary.
EP 0 848 788 shows a radial impeller in which the outer edges of the vanes comprise a sloped edge inclined towards the axis of rotation and the peripheral sections of the end plates are curved in order to lower the sound pressure in a frequency range of 50-300 Hz.
In the exiting of the air flow from the radial impeller, effects that degrade the efficiency of the conversion of the kinetic energy contained in the flow medium into the desired increase of static pressure arise due to the abrupt widening of the flow cross section. In order to improve this efficiency, static diffuser rings with an impeller cage, as known for instance from EP 1 039 142, are arranged in connection with the radial impeller. Such diffuser rings, however, are difficult to design, decrease available space and are expensive.