No leaf fan

No leaf bath ventilation fan was originally invented by DYSON (Dyson), that is no leaf, in fact, below the turbo exhaust window fans into the air into the hollow ring, through the ring to set the gap to send air. The circular cross section of the air doubling machine is similar to the shape of the aircraft wing, using the Coanda effect and the same effect as the wing lift to increase the air volume. As a result of patents and other issues, in addition to the current Dyson, the basic are some small factories doing, usually noisy.