AU639729B2 - Centrifugal fan - Google Patents

Description

r 7 j j I i Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-62 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Application Number: Lodged:

S

.Coplete Specification Lodged: Accepted: Published: Rriority: Related Art: Class Int. Class arne of Applicant: o Address of Applicant: 'Ad tal Inventor: Address for Service: Complete Specification TO BE COMPLETED BY APPLICANT GRAHAM LAWRENCE OKE Howden Road, Fulham, South Australia, Australia GRAHAM LAWRENCE OKE Care of R K MADDERN ASSOCIATES, 345 King William Street, Adelaide, South Australia, Australia for the invention entitled: "CENTRIFUGAL FAN" The following statement is a full description of this invention, including the best method of performing it known to me.

This invention relates to improvements in the construction of a centrifugal fan wherein a scroll surrounds a wheel having blades extending therefrom, either radially, inclined forwardly, or inclined rearwardly, but always with a radial component of direction.

Heretofore it has been thought that air will enter the wheel substantially constantly over the area of the intake, change direction from an axial into a radial direction through 90', and be impelled by the centrifugal force imparted thereto by the blades, continuously increasing in volume within the scroll the outer wall of which progressively increases its radial dimension outwardly from the wheel in a downstream direction to accommodate the extra air.

Careful study over a number of years however has indicated that there appears to be a fallacy in the accepted principles of design, and the air tends not to flow outwardly from the whole of the wheel periphery in a radial manner as has been presupposed with earlier designs, but rather that 4 the airflow is inclined to have a very significant component "10. of direction which is tangential to the wheel periphery, and by an angle which will vary with air velocity, and other factors, These findings appear logical when consideration is given to the eddies which occur over the surfaces of the wheel blades, and to the effect of those eddies increasing as velocity increases. Eddies also increase due to change of direction and also impingement of the air stream against the inner surface of the small wall. Having recognised the existence of the tangential component of direction, it is consistent to believe that the angle should increase with velocity, and this assumption has been confirmed correct empirically by the inventor herein.

It is widely recognised and accepted that the minimum amount of interference with airflow direction or velocity provides the minimum loss of efficiency, and therefore this invention has as its object to provide a structure which will take advantage of the discovery which has been made.

Thus this invention is characterised in that the inlet and outlet conduits are both so inclined to a plane in which the wheel blades rotate that air both when entering the wheel and when discharged from the wheel possesses a component of direction which is tangential to the wheel periphery.

An embodiment of the invention is described hereunder in some detail with reference to and is illustrated in the accompanying drawings in which:- Fig 1 illustrates diagrammatically airflow from an impeller fan into a discharge conduit, as it has been found 00 to exist in practice, *6 0 0 .06. Fig 2 is a fj )nt elevation of a fan assembly, including inlet and outlet conduits, Fig 2 being a view of an X-Y plane, Fig 3 is an end elevation of Fig i, that is, a view of a Y-Z plane, *0 0 Fig 4 is a plan of Fig 3, that is, a view of an X-Z plane, and 0 Fig 5 illustrates some empirical results of a test, comparing the results achieved with equipment in a prior art I: configuration (Fig 5a), an identical outlet, but with the inlet inclined as shown in the drawings Figs 2, 3 and 4 (Fig 5b), and the configuration illustrated in Figs 2, 3 and 4 (Fig 5c) (complete with inclined inlet and outlet).

Referring first to Fig 1, the airflow arrows indicate the major airflow through an impeller wheel of a centrifugal fan, as determined empirically by the inventor. Very little air flows through the blades between the neck 15 and the location L, but eddy currents build up high static pressure within the scroll. The results of the tests reported herein tend to indicate that high static pressure is at the expense of airflow, since the invention achieves a much higher efficiency.

In this embodiment illustrated in Figs 2, 3 and 4, a centrifugal fan 10 comprises a wheel 11 having a plurality of blades 12, the wheel being contained within a scroll 13 which defines an air passage 14 which increases in cross-sectional area by increasing its radial distance away from the wheel 11, in a direction of rotation from a neck 15 to an outlet conduit 16. The description in this paragraph could also apply to a prior art fan, and, as with prior art fans, the blades 12 Ara. 1. f- p- *dT- ^i can be forwardly or rearwardly inclined in accordance with prior art. In some embodiments of the invention they $.so can be helical. Air inlet conduit 17 and air outlet conduit 16 both have a component of direction tangential to the periphery of wheel 11, and in this embodiment they are coaxial.

However in prior art, the outlet chute 16a (Fig 4) was o* at right angles to air inlet conduit 17(a), and it has been generally assumed that the airflow through the passage 14 was a constantly increasing flow which was guided by the wall 18 of the scroll 13 to be tangential at the outlet. This is not the case according to empirical tests conducted by the inventor, and the path of maximum velocity is shown as 20 in the drawings, being displaced in plan from the plane in which the wheel rotates by an angle of 30', and it has been found that the magnitude of the angle is a function of air velocity, and other factors including wheel width/diameter ratio. However, the range of angle of displacement is likely to be between 15" and In this embodiment therefore the outlet conduit 16, instead of being tangential as shown at 16a in Fig 2, is also displaced by 30", in the direction of airflow, so as to -n encompass the path of major velocity The reference planes X-Y (Fig Y-Z (Fig 3) and X-Z (Fig 4) are expressed in terms of Cartesian co-ordinates, wherein the wheel 11 rotates in an X-Y plane about a Z axis.

The neck 15 is considered to lie in the X-Z plane. With these references, the axes of the outlet and inlet conduits are inclined with respect to the plane containing axis of rotation and neck 15 by about 40' to the X-Y plane (Fig 2).

The angles of inclination are not critical, and best conditions for different fan assemblies will incur different iiiclination angles. However, the second inclination is likely to be in the range of 20' to Fig 5a indicates airflow rates in ft/second issuing from test equipment arranged in a conventional configuration, and @e the flow rate was 447 cubic ft/minute for a motor current consumption of 2.61 amps. When inlet conduit 17 was inclined as shown, the flow rate increased to 459 cubic ft/minute, and motor current reduced to 2.60 amps. When, however, the configuration was further changed to that illustrated in Figs 2, 3 and 4, the flow rate increased to 519 cubic ft/minute and current to 2.64 amps.

00 0 A great advantage of this invention is thus that the efficiency of a fan is increased considerably, prior art centrifugal fans notoriously having a low efficiency (usually well below s! Low efficiency is associated with eddy currents, formation of which generate noise, but by more nearly approximating straight line flow, eddy currents, and therefore noise, are reduced. Further associated pressure at stall point is greater than in prior art fans.

Claims (1)

1. 3. A centrifugal fan according to claim 1 further characterised in that the inlet and outlet conduits are S inclined to said plane in which the wheel blades rotate by an Sangle of between 151 and 500. 4 A centrifugal fan according to claim 3 further characterised in that said angle of inclination is about 300. A centrifugal fan according to any one of claims i, 3 or 4 further characterised in that the axes of the inlet and outlet conduits are inclined with respect to a plane containing the axis of rotation of the wheel blades and the neck of the scroll by between 20* and 600. S: 6 A centrifugal fan according to claim 5 further characterised in that said angle of inclination with respect to said plane containing the axis of rotation and neck is about S400 7 A centrifugal fan according to any preceding claim wherein said inlet and outlet conduits are co-axial. 8 A centrifugal fan substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. Dated this 22nd day of November 1990 GRAHAM LAWRENCE OKE By his Patent Attorneys i R K MADDERN ASSOCIATES 4 OI