Jet fan

A jet fan includes a generally cylindrical casing (1), an electric motor (2) accommodated therein, an impeller (3) connected to the electric motor (2), and at least one booster ring (8) disposed concentrically with the casing (1) and located downstream thereof with respect to a direction of an air flow. The booster ring (8) has an aerofoil or arcuated plate sectional profile as viewed in a direction transverse to a longitudinal axis of the casing (1). The booster ring (8) has an upper surface of aerofoil or arcuated plate sectional profile as its inner surface, and also has a leading edge facing an air outlet of the jet fan and a trailing edge of a diameter smaller than that of the leading edge but greater than that of the air outlet.