GB2166494A - Fan - Google Patents

Abstract

The fan comprises a radial flow impeller wheel (19) and a rotationally symmetrical housing (11) which includes an axial induction duct (13), an axial discharge duct (16) and a discharge cone (15) narrowing from the region enclosing the impeller wheel towards the discharge duct. Arranged in the discharge cone (15) are guide vanes (25) for straightening the flow and for the conversion of the spin energy contained in the fluid into usable pressure energy. The guide vanes (25) may be formed from a strip of sheet metal and are curved. <IMAGE>

Description

SPECIFICATION Fan The present invention relates to a fan.

Fans of, for example, the kind installable in ducts of air exhaust systems typically induct air or other medium axially towards a radial impeller wheel and discharge the air or other medium axially from the fan housing after flow through the impeller wheel. The housing for these fans is as a rule rotationally symmetrical so that the same conveying conditions exist for all portions of the impeller wheel circumference. The housing can narrow from a housing portion enclosing the impeller wheel radially at a spacing towards a discharge duct which provides the connection to an exhaust duct for the conveyed medium and is frequently of the duct diameter, the part between the discharge duct and the housing portion surrounding the impeller wheel mostly being conical.

In these fans, which for reasons of cost have no duct equipment for the outflowing medium downstream of the impeller wheel at the discharge side, it is unsatisfactory that the spin energy imparted to the conveyed medium during passage through the impeller wheel by this is not regained in usable pressure, but remains as rotational energy in the outflowing current. This leads to an undesired energy loss with the consequence that conveyed quantity and pressure increase are inadequate and, due to the spin remaining in the outflowing medium and to its high component of lowfrequency noises (infrasound), gives rise to duct oscillations and secondary sound emissions at the discharge side, particularly at downstream duct fittings, such as elbows, branch pieces and exhaust gratings.

There is thus a need to remedy these defects and provide an improved fan of this kind.

According to the present invention therefore there is provided a fan comprising a substantially rotationally symmetrical housing having a housing portion for a fan wheel, a frustroconical discharge portion extending from an outlet end of the housing portion and reducing in diameter in direction away from the housing portion, an axial inlet duct at an inlet end of the housing portion and an axial outlet duct at an outlet end of the discharge portion, a radial impeller wheel arranged in the housing portion and guide vanes arranged in the discharge portion to smooth the current discharged by the impeller wheel and to convert spin energy of such current into pressure.

Guide vanes of that kind in the discharge portion, narrowing towards the discharge duct, of the housing lead to a quietening of the current flowing away from the impeller wheel and provide a conversion of the spin energy in the outflowing current into useful pressure. Accordingly, the guide vanes effect an increased conveyed quantity and an increased pressure rise. In view of the quietening of the current as a consequence of the spin removal effected by the guide vanes, an appreciable noise reduction is to be observed in the duct systems adjoining a fan of that kind at the discharge side.

Although it is generally known in radial compressors to quieten the current flowing away from a radial impeller wheel by a downstream guide grating, in which case a ring of guide vanes or guide channels may be concerned, and again partially as pressure energy to regain the spin energy imparted to the conveyed medium during passage through the impeller wheel, these compressors are expensive centrifugal machines usually with several successive compressor stages, in which a respective ring of guide vanes is connected downstream of each impeller wheel. In compressors of that kind, it is also known to convert, after the last compressor stage, a part of the flow energy contained in the conveyed medium in consequence of enlargement of the discharge cross-sections and thus to translate it into pressure increase due to slowing down of the flow speed.In the case of fans of that kind to which the present invention relates, it is thereagainst typical for the housing to narrow from the portion surrounding the impeller wheel to the discharge duct providing the fitting into a duct system, which necessarily leads to a rise in the flow speed of the conveyed current flowing away from the impeller wheel in the region of that part of the housing which narrows towards the discharge duct.

In a fan with a discharge cone which adjoins the impeller wheel at the discharge side and in which the discharge speed of the conveyed medium rises, a reduction in the spin energy contained in the outflowing medium current and the conversion thereof into useful pressure is realised by simple means. It has proved to be expedient for the edges which bound the guide vanes radially inwardly to extend at least nearly parallel to the rotational axis of the impeller wheel and at a spacing from these, which lies between 0.7 and 1.1 times the radius of the discharge duct. The entry edges at the impeller wheel side of the guide vanes, which radially outwardly follow the housing outline in the region of the discharge cone, can in that case extend in a plane at least nearly parallel to a base disc of the impeller wheel.

Preferably, the part of each vane lying at the front in flow direction of the conveyed medium has a curvature directed oppositely to the spin current flowing away from the impeller wheel and at the discharge side has a planar part extending in direction of the axial discharge and effecting an axial alignment of the medium current. It has in that case proved to be advantageous if the planar parts at the dis charge side and lying at the front in flow direction extend in radial planes of the housing.

The guide vanes can to advantage have a shape which is curved circularly against the spin direction in the case of the vane portion outwardly of the radius of the discharge duct whilst the vane portion in the region of that radius is planar and extends radially.

For preference, the curvature of the parts, lying at the front in flow direction, of the guide vanes extends in circumferential direction and the guide vane surfaces are described by paths extending parallel to the axis of the impeller wheel. Such a construction of the guide vanes with a curvature extending in only one direction makes possible a particularly simple manufacture of the vanes. It is possible for the vanes to be constructed integrally with that part of the housing with the discharge cone and, for example in the execution of this housing part as an injection-moulded part, a problem-free and undercut-free removal from the mould in direction of the narrowing discharge cone can be effected along its rotational axis.

The guide vanes can, however, be constructed as moulded parts fastened in the discharge cone by gluing, rivetting, welding or clamping. The vanes can also be punched parts which form a guide ring with a band, which is bent into circular shape and inserted into the discharge duct. The vanes can be produced through punching-out of a planar material strip and subsequent plastic deformation, wherein the band bent into circular shape consists of a strip of the original material strip.

The punching-out of the guide vanes from a planar strip while leaving behind a band connecting the individual guide vanes together leads to an extremely simple and cheap manner of manufacture which, in particular, also makes possible simple assembly of the guide vane ring thus created. In that case, the arrangement can be so designed that the guide vanes are connected together by portions which are shaped out towards one side of the band and folded together at least in the region of the band and which form parts of the guide vane ends at the discharge side. The portions, which are folded together and by means of which the guide vanes are connected together, can extend over the entire axial length of the vanes in the region of the radially inner edges of the vanes.

An embodiment of the present invention will now be more particularly described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a schematic partly sectional and partly elevational view of a fan embodying the invention; Fig. 2 is a cross-section on the line ll-ll of Fig. 1; Fig. 3 is an enlarged detail view according to Ill in Fig. 2; Fig. 4 is a partly sectional view similar to that of Fig. 1, showing a guide vane arrangement; Fig. 5 is a plan view of a guide vane strip showing different stages in production of guide vanes of the arrangement; Fig. 6 is a side elevation of the guide vane strip of Fig. 5; and Fig. 7 is a diagram showing the increase, achieved by a fan embodying the invention, in conveying pressure and in the conveying quantity compared with a conventional fan.

Referring now to the drawings, there is shown in Fig. 1 a fan 10 comprising a housing 11 which is rotationally symmetrical about a longitudinal axis 12 of the fan and consists of a front housing part 14 provided with an axially directed intake duct 13 and a rear housing part 15, which is connected therewith in a plane extending transversely to the fan axis and which is constructed as a discharge cone 17 reducing from the connecting plane of the housing parts 14 and 15 to a discharge duct 16 for providing a connection to a pipe duct.

Arranged in the housing 11, the greatest radial extent of which is determined by the front housing part 14 and which ends in the region of the connecting plane between the housing parts 14 and 15, is a radial impeller wheel 19 which is driven by a drive motor 18 integrated into the housing and which has an axial induction opening 20 adjoining the induction duct 13. The impeller is closed off by a planar base disc 21 on the side lying opposite the induction opening. The impeller wheel has radial vanes 22 which extend around the induction opening and are disposed between the base disc 21 and a cover band 23 at the induction side, which reaches to the induction duct 13.

Arranged at a predetermined pitch one relative to the other in the discharge cone of the rear housing 15 are guide vanes 25, the entry edges 26 of which at the impeller wheel side extend in a plane parallel to the base disc 21 of the impeller wheel 19 and at an axial spacing from this at the discharge side. At the housing side, the guide vanes 25 follow the outline of the discharge cone 17 and the discharge duct 16 adjoining this at the discharge side. Radially inwardly, the guide vanes 25 are bounded by edges 27, which extend parallel to the axis 12 of the fan and at a spacing from the fan axis corresponding to about 0.7 times the radius of the discharge duct 16. The inner parts 28 of the guide vanes 25, which parts have a smaller radius than the discharge duct 16, are constructed to be planar and aligned radially to the fan axis, whilst the guide vane parts 29, which are arranged in the region of the discharge cone 17 enlarging conically towards the impeller wheel 19 and the radii of which are greater than the radius of the discharge duct have a curvature which is directed opposite to the spin of the current flowing away radially from the impeller wheel 19 and then deflected in the fan housing in the region of the discharge cone 17 towards the discharge duct 16. However, the guide vane surfaces in the curved region are determined by paths extending parallel to the axis of the impeller wheel 19.

The guide vanes 25 which are curved in only one direction, namely against the spin current, can be shaped sheetmetal parts forming a guide vane ring which is inserted into the rear housing part 15 and the construction of which shall be explained in the following in conjunction with Figs. 3 to 6.

Illustrated in Figs. 3 and 4 by way of detail is the discharge cone 17 of the rear housing part 15 with the discharge duct 16, in which a guide vane ring, produced separately from a sheetmetal strip and carrying the guide vanes 25, is inserted and fastened in suitable manner, for example by gluing, rivetting or spotwelding. Figs. 5 and 6 illustrate the production of this guide vane ring, wherein notches 31 are cut out at one side of a strip 30, the edges 32 of which notches extend obliquely to the strip length direction and form the later vane boundaries at the discharge cone 17, whilst the cut edges 33 extending in the strip length direction after completion of edging and bending operations still to be explained bound a carrier band 34 connecting the individual vanes together.After separation of the strip from the waste material, the strip portions 35 forming the later guide vanes are folded in the manner evident from Fig. 6 along edges 36 extending at right angles to the longitudinai direction of the strip 30 and in a subsequent step are pressed together until mutual abutment of the two portions adjoining the edge 36, while at the same time bends through 90" are effected in opposite directions along the lines 37 and 38.

The portions thus folded together form the planar guide vane parts 28 extending inwardly of the discharge duct 16, whilst the remaining regions of the portions 35 extend substantially perpendicularly to the plane of the strip, as shown at 39 in Fig. 6. These regions, which are adapted along their one edge to the internal outline of the discharge cone by the separation of the strip from the waste material, are then deformed into the circularly arcuately bent parts 29 of the guide vanes, as Fig. 6 shows. This shaping of the vane parts 29 can expediently be carried out together with one of the other bending operations.The radius of curvature or angle of inclination of the entry edge of the guide vanes with respect to the planar part 28 of the vane is to be determined in dependence on the impeller wheel and the opening angle of the discharge cone 16, preferably by aerodynamic measurements. In the finished guide vane band, the guide vanes are arranged at a spacing from each other which corresponds to the pitch measure and is equal to the distance measure between the bend lines 38 and 37 of successive vane blanks.

A length portion corresponding to the internal diameter of the discharge duct 16 is then severed from the guide vane band produced in the manner described above and then bent into circular shape, wherein the external diameter of the band portions connecting the individual guide vanes 25 together must be dimensioned to correspond with the internal diameter of the discharge duct. The thus prefabricated guide vane ring can then be inserted, before uniting the housing parts 14 and 15, from the open side of the discharge cone 17 into this cone to the position evident from Fig. 4, wherein those portions of the band 34 which connect the individual guide vanes together are received within the discharge duct and connected with this.After the assembly, of no further interest here, of the impeller wheel 19 with the drive motor 18, the rear housing part 15 provided with the guide vane ring and the front housing part 14 are then assembled into the complete fan 10.

In operation of the fan 10, the medium to be conveyed is inducted by the impeller wheel 19 through the axially directed induction duct 13 of the front housing part 14 and after the imparting of energy during passage through the impeller wheel issues radially out of this in the housing region with the greatest radial extent. The conveyed current, which flows radially from the impeller wheel and to which a spin is imparted, is then in the region of the discharge cone 17 narrowing towards the discharge duct 16 deflected in direction of the discharge duct and reaches the region of the guide vanes 25, the curvature of which is directed opposite to the spin current and the parts 28 of which, extending over diameters smaller than the diameter of the discharge duct, are directed radially to the fan axis. In view of this structuring of the guide vanes, the outflowing current undergoes smoothing and the spin inherent in the current is then to an appreciable part converted into usable pressure energy.

The pressure-volume diagram of Fig. 7 illustrates the relationship between delivery pressure head and delivery quantity realised by a fan of that kind described above, as shown by the characteristic line 40. The characteristic 41, indicated in dashed lines, thereagainst shows the relationship of pressure head and quantity in a conventional fan without guide vanes. It is evident that the guide vanes have led to an increased pressure rise and an improvement in the delivery quantity.

Claims (13)

1. A fan comprising a substantially rotationally symmetrical housing having a housing portion for a fan wheel, a frustro-conical dis charge portion extending from an outlet end of the housing portion and reducing in diameter in direction away from the housing portion, an axial inlet duct at an inlet end of the housing portion and an axial outlet duct at an outlet end of the discharge portion, a radial impeller wheel arranged in the housing portion and guide vanes arranged in the discharge portion to smooth the current discharged by the impeller wheel and to convert spin energy of such current into pressure.

2. A fan as claimed in claim 1, wherein the guide vanes have radially inner edges extending substantially parallel to the rotational axis of the impeller wheel and at a spacing from that axis substantially equal to 0.7 to 1.1 times the radius of the outlet duct.

3. A fan as claimed in either claim 1 or claim 2, wherein the impeller wheel includes a base disc in a plane normal to the rotational axis of the wheel and each of the guide vanes has an upstream edge facing the impeller wheel and extending substantially parallel to the base disc and a radially outer edge following the profile of the discharge portion of the housing.

4. A fan as claimed in any one of the preceding claims, wherein each of the vanes comprises a curved first portion which is generally upstream with respect to the flow direction through the discharge portion of the housing and the curvature of which is in a direction opposite to the spin direction of said current and a planar second portion which is generally downstream with respect to said flow direction and which extends in the direction of axial discharge through the discharge duct.

5. A fan as claimed in claim 4, wherein the curvature of the first portion of each vane extends generally in the circumferential direction of the housing and the surfaces of each vane are defined by lines extending parallel to the rotational axis of the impeller wheel.

6. A fan as claimed in either claim 4 or claim 5, wherein said planar second portion of each vane extends in a radial plane of the housing.

7. A fan as claimed in any one of the preceding claims, wherein the guide vanes are moulded components mounted in the discharge portion of the housing by gluing, rivetting or welding.

8. A fan as claimed in any one of claims 1 to 6, wherein the guide vanes are punched-out components.

9. A fan as claimed in claim 8, wherein the vanes are punched and bent out of a strip which is circularly bent to dispose the vanes on a circular path and to define an annular band, the band being located in the discharge duct.

10. A fan as claimed in claim 9, wherein each of the vanes is formed in part by a folded portion of the strip, each said folded portion being disposed at the discharge end of the respective vane and connecting the vane to the band.

11. A fan as claimed in claim 10, wherein said folded portion of each vane extends over the entire length of the vane in the axial direction of the housing and defines a radially inner edge of the vane.

12. A fan as claimed in any one of claims 1 to 6, wherein the guide vanes are integral with the discharge portion of the housing.

13. A fan substantially as hereinbefore described with reference to the accompanying drawings.