AXIAL FLOW FAN

Abstract: An axial flow fan comprising a rotor (10) having a hub (3) provided with a plurality of fan blades (4); a casing (1) within which the rotor (10) is mounted; and a flow channel (11) which is formed between the casing (1) and the rotor (10) and which extends from an inlet port (6) of the fan to an outlet port (7) thereof, characterised in that the diameter of the flow channel (11), at a position adjacent the outlet port (7), is at a minimum value.

Description: This invention concerns an axial flow fan. An axial flow fan is known comprising a rotor having a hub provided with a plurality of fan blades, a casing within which the rotor is mounted, and a flow channel which is formed between the casing and the rotor and which extends from an inlet port of the fan to an outlet port thereof. Thus in DE-C-344,374 there is disclosed an axial flow fan comprising a rotor having a hub provided with a plurality of fan blades; a casing within which the rotor is mounted; and a flow channel which is formed between the casing and the rotor and which extends from an inlet port of the fan to an outlet port thereof, the diameter of the flow channel, at a position adjacent the outlet port, being at its minimum value, The flow channel, however, has previously been such that large vortices or eddies have been generated in the air or other fluid flowing through the fan and these large vortices or eddies have reduced the efficiency of the fan. According, therefore, to the present invention there is provided an axial flow fan comprising a rotor having a hub provided with a plurality of fan blades; a casing within which the rotor is mounted; and a flow channel which is formed between the casing and the rotor and which extends from an inlet port of the fan to an outlet port thereof, the diameter of the flow channel, at a position adjacent the outlet port, being at its minimum value, characterised in that there is at least one projection which extends into the flow channel adjacent the outlet port or into the fluid emerging from the latter, so as to reduce the size of vortices generated by the fan. The internal surface of the casing and/or the external surface of the hub may have a part which extends to the outlet port and which is parallel to the axis of the rotor. The hub preferably has a diameter which increases progressively, substantially throughout its axial length, in the direction of the outlet port. The or each projection is preferably carried by the casing or hub adjacent the outlet port. Each projection may extend either perpendicular to or parallel to the rotor axis or may extend at an angle to the latter. There may be a plurality of the said projections whose tips are connected by a ring member. The projections are preferably such as to be adapted to break up efficiency-reducing large vortices which are generally produced in the areas around the outlet port and at the rear end of the hub. The invention is illustrated, merely by way of example, in the accompanying drawings, in which:- Figure 1 is a cross-sectional view illustrating a first embodiment of an axial flow fan according to the present invention, Figure 2 is a cross-sectional view illustrating a prior art axial flow fan, Figure 3 is a cross-sectional view illustrating another prior art axial flow fan, Figure 4 is a cross-sectional view illustrating a second embodiment of an axial flow fan according to the present invention, Figure 5 is a cross-sectional view illustrating a third embodiment of an axial flow fan according to the present invention, Figure 6 is a cross-sectional view illustrating a fourth embodiment of an axial flow fan according to the present invention, and Figure 7 is a cross-sectional view illustrating a fifth embodiment of an axial flow fan according to the present invention. As shown in Figure 2 and as disclosed in US-A-4, 221,546, an axial flow fan is known which is provided with a casing 1 which surrounds a rotor 10 so as to define a flow channel 11 therewith, the rotor 10 having a hub 3 and a plurality of fan blades 4. The diameter of the flow channel 11 decreases in the air flow direction from an inlet port 6 to a constricted "necked-down" portion 13, and then increases again from the necked-down portion 13 towards an outlet port 7. Another prior art axial flow fan, which is shown in Figure 3, is generally similar to that of Figure 2 but, instead of the necked-down portion 13, the casing 1 has a cylindrical central portion 14. Moreover, in the constructions of both Figure 2 and Figure 3 there are no projections provided in the air flow at the area around the outlet port 7. Because of these features, the air flows through a flow channel 11 having a rather complicated internal configuration. Further, large vortices or eddies are generated in the area around the outlet port 7 because the cylindrical shape of the casing 1 which serves to guide the air flow abruptly ends there. Still further, large vortices or eddies are also generated at the rear end of the hub 3 because the cylindrical shape of the latter abruptly ends there. The complicated air flow and the vortices referred to above reduce the efficiency of the axial flow fans shown in Figures 2 and 3. An axial flow fan according to the present invention is therefore shown in Figure 1 which comprises a rotor 10 having a hub 3 provided with a plurality of fan blades 4 which are uniformly distributed over the periphery of the hub 3. A motor (not shown) rotates the rotor 10 with respect to the rotor axis. A support structure 2 supports the motor and the rotor 10 and mounts the latter within a casing 1 so as to provide a flow channel 11 between the casing 1 and the hub 3. Air is drawn in by the fan blades 4 through an inlet port 6 at one end of the flow channel 11 when the rotor is rotated by the motor, and is passed to an outlet port 7 at the opposite end of the flow channel 11. The air that has passed through the flow channel 11 then strikes an annular array of projections 5 which project from the casing 1 and are disposed around the circumferential end portion of the outlet port 7 and also strikes an annular array of projections 8 which project from the rear end of the hub 3. As will be seen, the flow channel 11 has its maximum diameter at the inlet port 6, the diameter of the flow channel 11 decreasing progressively from the inlet port 6 to a position adjacent the outlet port 7 where the said diameter is at a minimum value. The axial cross-sectional shape of both the internal surface of the casing 1 and the external surface of the hub 3 comprises a part of a circle or of an ellipse. The hub 3 has a diameter which increases progressively, throughout its axial length, in the direction of the outlet port 7. Thus the cross-sectional internal surface configuration of the casing 1 and the cross-sectional external surface configuration of the hub 3, since they are parts of a circle or an ellipse, smooth out the air flow passing through the flow channel 11. Moreover, the projections 5, 8, which are in the area around the outlet port 7, reduce the detrimental effects of the large vortices. If there were no such projections provided adjacent the outlet port 7, large vortices causing energy loss would be generated. However, such vortices are divided by the projections 5, 8 into smaller vortices so that the energy loss is kept small. Figure 4 illustrates an embodiment of the present invention which is closely similar to that of Figure 1 and which has projections 5 which extend perpendicular to the rotor axis so that the air passing through the flow channel 11 strikes the projections 5 with the result that the generation of vortices is reduced. The shape and disposition of the corresponding parts of Figures 1 and 4 are, however, slightly different. Figure 5 illustrates a further embodiment in which the projections 5, 8 are arranged parallel to the rotor axis, the generation of vortices also being restricted by means of the projections 5, 8. Figure 6 illustrates another embodiment in which the projections 5 are arranged at an angle with respect to the rotor axis, the generation of vortices also being restricted by means of this type of projection. Figure 7 illustrates a further embodiment in which projections 5 are arranged in an annular array around the outlet port 7, the tips of the projections 5 being connected by a ring member 12.

Claims: An axial flow fan comprising a rotor (10) having a hub (3) provided with a plurality of fan blades (4); a casing (1) within which the rotor (10) is mounted; and a flow channel (11) which is formed between the casing (1) and the rotor (10) and which extends from an inlet port (6) of the fan to an outlet port (7) thereof, the diameter of the flow channel (11), at a position adjacent the outlet port (7), being at its minimum value, characterised in that there is at least one projection (5,8) which extends into the flow channel (11) adjacent the outlet port (7) or into the fluid emerging from the latter, so as to reduce the size of vortices generated by the fan. An axial flow fan as claimed in claim 1 characterised in that the internal surface of the casing (1) and/or the external surface of the hub (3) has a part which extends to the outlet port (7) and which is parallel to the axis of the rotor (10). An axial flow fan as claimed in claim 1 or 2 characterised in that the or each projection (5,8) is carried by the casing (1) or hub (3) adjacent the outlet port (7). An axial flow fan as claimed in any preceding claim characterised in that the or each projection (5,8) extends perpendicular to the rotor axis. An axial flow fan as claimed in any of claims 1-3 characterised in that the or each projection (5,8) extends parallel to the rotor axis. An axial flow fan as claimed in any of claims 1-3 characterised in that the or each projection (5,8) extends at an angle to the rotor axis. An axial flow fan as claimed in any preceding claim characterised in that there are a plurality of the said projections (5,8) whose tips are connected by a ring member (12).

Inventors: HIRAMA, HIDEO SEIKO ELECTRONIC COMPONENTS LTD., ISHIDA, TAKASHI SEIKO ELECTRONIC COMPONENTS LTD., KANNO, TAKUZO SEIKO ELECTRONIC COMPONENTS LTD., KOHAMA, YASUAKI INS. OF HIGH SPEED MECHANICS
Applicants: SEIKO ELECTRONIC COMPONENTS LTD.
Application year: 1987
Main classification: F04D29
IPC codes: F04D29