A Propeller Fan is a comparatively simple form of a fan with a sheet metal, 36 bladed impeller directly driven by a motor mounted in the airstream. It utilizes long slender blades twisted in such a manner as to provide some angle of attack on the gas being moved. The propeller that takes the energy lost from the swirl and converts it to usable velocity energy. Similar to a propeller fan, a tube axial fan includes a venturi that surrounds the fan propeller and is designed to reduce the air leak age or vortices created by the spinning prop.