US Patent 9745996 Fan

A fan casing includes an impeller housing, a mixed-flow impeller located within the impeller housing, and a motor for driving the impeller. The impeller includes a hub connected to the motor, and a plurality of blades connected to the hub, each blade comprising a leading edge located adjacent the air inlet of the impeller housing, an inner side edge connected to and extending partially about the outer surface of the hub, an outer side edge located opposite to the inner side edge, and a blade tip located at the intersection of the leading edge and the outer side edge. The leading edge comprises an inner portion located adjacent the hub, and an outer portion located adjacent the blade tip, and wherein the inner portion is swept rearwardly from the hub to the outer portion, and the outer portion is swept forwardly from the inner portion to the blade tip.