A Study of the Cross Flow Fan

Abstract

The cross flow fan has developed from the ideas of Mortier in the late 19th century and recently has been used with conspicuous success in small domestic appliances. No satisfactory theory is known, improvements having come from experimental development. The present work is also experimental. A closed-circuit fan test rig was constructed to obtain pressure, volume flow rate and efficiency for fans of various designs. Detailed measurements within the rotors were also obtained by hot-wire traverses. These tests were supplemented by visualization studies in a water test rig. It is found that improved pressure–flow characteristics are obtained by constructing the casing so that the vortex which forms in the fan is allowed to move circumferentially round the rotor as the output is throttled. This preserves a strong vortex and keeps the total pressure approximately constant as the flow is throttled. In many previous designs, which do not allow this kind of displacement, the vortex tends to move towards the centre of the rotor and to diminish in strength, leading sometimes to unstable operation.