GB2054740A

GB2054740A - Cross-flow fans

Info

Publication number: GB2054740A
Application number: GB8023728A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-07-19
Filing date: 1980-07-21
Publication date: 1981-02-18
Also published as: FR2461837A1; IT8005189A0; DE2929140A1; IT1136009B; NL8004169A

Abstract

A housing for a cross-flow fan which is primarily for use with roof ventilators, comprises a guide body 25 to separate the incoming flow from the emerging flow. An impeller 26 is located between the guide body 25 and a baffle plate and the latter being arranged to guide the emerging flow, having a partially spiral shape. The guide body 25 and the baffle plate are so designed and arranged both in themselves and relative to each other that the fan, by maintaining an essentially low and constant level of dynamic energy at its outlet, operates to a flat and horizontal or approximately horizontal pressure/volume characteristic. The centre of turbulence during normal operation, is moved somewhat towards the interior of the impeller 26 and away from the impeller vanes and is held in this position. During restricted flow operation, the centre of turbulence is maintained in approximately the same radial position, moving along the inside of the row of impeller vanes against the direction of impeller rotation, a maximum of dynamic energy being, in addition, converted into static energy on the way to the housing outlet 15. <IMAGE>

Description

SPECIFICATION Housing for a cross-flow fan, especially for use with roof ventilators The invention relates to a housing for a crossflow fan, especially for use with roof ventilators.

A previously proposed type of housing comprises a guide body to separate the incoming and emerging flows and a baffle plate, between which and the guide body the impeller is located, to guide the emerging flow, this baffle plate having a partially spiral shape. It is an object of the present invention to design a fan, substantially this type, the performance and pressure/volume characteristics of which are such as to maintain a constant pressure within the duct system even with multiple ducting and independent of the number of systems connected and of the state of flow control prevailing in each duct; at the same time, noise should be reduced to a minimum.

In order to solve these problems, the invention provides for a new fan, the guide body and baffle plate of which are so designed and arranged both in themselves and relative to each other that the fan, by maintaining an essentially low and constant level of dynamic energy at its outlet, operates to a flat and horizontal or approximately horizontal pressure/volume characteristic similar to the so-called boiler characteristic, whereby the centre of turbulence is, during normal operation, moved somewhat towards the interior of the impeller and away from the vane ring and maintained in this position, while, during restricted flow operation, the centre of turbulence is maintained approximately in the same radial position, moving along the inside of the vane ring against the direction of impeller rotation, and whereby a maximum of dynamic energy is converted into static energy on the way to the fan outlet. To achieve this object, the guide body is suitably so arranged in relation to the impeller that it or its imaginary extension extends, at least for the major part, along the outside of a dischargeside area of the impeller, thus in a way sliding underneath or over the impeller. The arrangement may for instance be such that the radius from the impeller centre to the starting point of the spiral forms an angle of less than 1800, preferably between 1300 and 1 600, with the radius extending to that point of the guide body which is nearest to the impeller circumference, the most advantageous angle being 1300 to 1400.This is preferably so arranged that the normal to the outlet end section of the guide body extending through that point of the guide body which, viewed in the direction of flow, is the most distant from the fan outlet, or the normal to the centre line of the fan housing's outlet diffusor or to the central flow line in said outlet diffusor extending through that point of the guide body which, viewed in the direction of flow, is the most distant from the fan outlet, is arranged at a distance corresponding to approximately 10 to 30%, preferably 12.5 to 18%, of the impeller diameter from its parallel tangent of the impeller circumference.In an especially advantageous arrangement, the two radii extending from the impeller centre to the two end points of the guide body's effective zone, within which the flow in the immediate vicinity of the impeller circumference is influenced and the immediately adjoining incoming and emerging flow sections are separated from each other, enclose an angle of 20 to 300, preferably 23 to 250, or the projection of the guide body's effective zone, within which the flow in the immediate vicinity of the impeller circumference is influenced and the immediately adjoining incoming and emerging flow sections are separated from each other, corresponds to approximately 4 to 7% of the length of the impeller circumference.The guide body may for instance be drop shaped, its pointed end directed away from the impeller, or it may have the shape of a drop of uniform thickness or of a wedge, the base of which is facing the impeller circumference.

The design of the new fan according to the invention results in a flat, horizontal or approximately horizontal characteristic similar to the so-called boiler characteristic, which, in applications such as roof ventilators, has the important advantage of a constant pressure within the duct system independent of the number of systems connected or the state of flow control prevailing in each system. When the flow of the fan is restricted, the pressure remains approximately constant. In addition to this, the noise level of the new fan is very acceptable, an important consideration in certain applications.

The fan outlet is suitably designed as a diffusortype, steadily widening channel. This may be achieved by providing, between the impeller circumference at the discharge side and the fan outlet, a relatively small, preferably slightly helical or curved duct widening towards the outlet in the manner of a diffusor.

The measures according to the invention provide the advantage of converting a maximum of dynamic energy into static energy on the way from the impeller exit to the fan outlet, while on the other hand, by means of the design of the guide body and its arrangement in relation to the impeller, moving the vortex core (centre of turbulence) as far as possible from the vane ring towards the interior of the impeller, so that only a minimum of flow lines exchanges momentum with the vane ring at high speeds and the vortex core maintains an approximately even distance from the vane ring even during restricted flow operations while moving along the inside of the vane ring against the direction of impeller rotation; this prevents excessive pressure rises at any point of the characteristic, while maintaining an approximately level pressure characteristic.

The drawing shows embodiments of the subject of the invention.

Figs. 1 and 2 are diagrammatic representations of the flow conditions prevailing in a first embodiment of the invention during normal and restricted flow operation, Fig. 3 illustrates the flow conditions prevailing in a variant of the arrangement according to Fig. 2, Fig. 4 shows the pressure/volume characteristic of the arrangement according to Figs. 1 to 3, Figs. 5 to 10 are diagrammatic side views of various modified embodiments of the subject of the invention, Fig. 11 is a diagrammatic side view of yet another variant of the subject of the invention, Fig. 12 is a diagrammatic side view of another modified embodiment of the subject of the invention, and Fig. 13 shows the pressure/volume characteristics of various fans according to the invention.

The arrangement shown in Figs. 1 and 2 is a cross-flow fan, especially for use with roof ventilators, comprising an impeller 1 and a housing having a guide body 4 separating the incoming flow according to arrow 2 from the emerging flow according to arrow 3 and a baffle plate 5, between which and the guide body 4 the impeller 1 is located, to guide the emerging flow, this baffle plate 5 having a partially spiral shape.

In the arrangement according to Figs. 1 and 2, the baffle plate 5 and the guide body 4 are so designed and arranged both in themselves and relative to each other and to the impeller 1 that the fan, by maintaining an essentially constant and low level of dynamic energy at its outlet, operates to a fiat and horizontal or approximately horizontal pressure/volume characteristic as illustrated at point 9 in Fig. 4, whereby the centre of turbulence 10 is, during normal operation, moved somewhat towards the interior of the impeller and away from the vane ring, thus no longer being so close to the inner vane circle, with the result that flow lines 11, having extremely high speeds, no longer or only marginally permeate the impeller, which therefore exchanges momentum with flow lines 12 of lower speed only.During normal operation, the vortex core is, in the arrangement according to the invention, held in the position shown in Fig. 1, while, during restricted flow operation, being maintained in approximately the same radial position, moving along the inside of the vane ring against the direction 13 of impeller rotation. Fig. 2 shows that the centre of turbulence, while still maintaining the same radial distance from the vane ring as during normal operation as in Fig. 1, has migrated from its point of origin against the direction of rotation.In addition to this, the invention provides for the conversion of a maximum of dynamic energy into static energy on the way to the housing outlet 14, which, as is illustrated in Fig. 5, can be achieved by designing the fan outlet 1 5 as a diffusor-type steadily widening duct, the arrangement according to Fig. 5 providing for a relatively long, preferably slightly helical or curved duct 1 7 between the outlet side of the impeller circumference at point 1 6 and the fan outlet 15, this duct slightly widening towards the outlet in the manner of a diffusor, dimension h2for instance being greater than dimension h, and dimension h3 perhaps greater than dimension h2.Downstream of the fan outlet, this embodiment of the invention provides for a set of guide vanes or baffle plates 1 8 to deflect the flow upwards and diametrically away from the housing inlet 1 9. This flow behaviour of the fan according to the invention is illustrated in Fig. 4, 9 representing the pressure/volume characteristic, a the operating pressure during normal operation and b the operating pressure during restricted flow operation, both having approximately equal pressure levels with differing volumes. In either case, the static pressure prevailing in the system is held constant, in spite of considerable changes in volume.Since, in restricted flow conditions, the centre of turbulence migrates against the direction of rotation, virtually the same flow lines still permeate the impeller at constant speeds, and there is little change of momentum, for flow lines now return into the impeller towards the centre of turbulence to a greater degree, which in turn means that, while the same amount of energy is still being transmitted by pressure, there is no longer so much energy transported. The arrangement according to Fig. 3 illustrates restricted flow conditions similar to the arrangement according to Fig. 2, having however a small return duct 8, by which the flow from the discharge side is conveyed in the direction of the impeller.For this reason, the characteristic shown in Fig. 4 has shifted into the position 20 as illustrated by a broken line, there being more pressure avaiiable since the centre of turbulence has moved closer to the vane ring as a result of the return flow. Fig. 1 3 provides a diagrammatic representation of three characteristics 21, 22, 23 illustrating the effects of the intensity of the return flow, the lower characteristic 21 representing the gradient without return flow, characteristic 22 with slight return flow and characteristic 23 with somewhat stronger return flow. The arrangement according to the invention moreover results in considerably lower noise levels being generated by the fan, since flow lines of very high speeds no longer permeate the impeller. The flat characteristic is symptomatic for fans with low noise levels.

All embodiments illustrated in Figs. 5 to 1 2 show that the guide body is so arranged in relation to the impeller that it or its imaginary extension extends, at least for the major part, along the outside of a discharge-side area of the impeller, thus in a way sliding underneath or over the impeller, depending on viewpoint. In the arrangement according to Fig. 5, the longitudinal centre or bisecting line of the guide body 25 is arranged tangentially or approximately tangentially relative to the impeller; viewed from the fan inlet, the guide body extends over the impeller 26 to a certain extent. In the arrangement according to Fig. 6, the discharge-side external surface 27 or the guide body 28 extends approximately tangentially relative to the impeller 29. The same applies for the arrangement according to Fig. 7, while in the other embodiments of the subject of the invention, the inlet-side external wall of the guide body extends tangentially or approximately tangentially relative to the impeller. All these measures contribute towards shifting the centre of turbulence radially inwards away from the vane ring, as has been explained above.Figs. 6 and 7 further illustrate that, in the arrangement according to the invention, the radius extending from the centre 30 or 31 of the impeller towards the starting point 32 or 33 of the spiral - i.e. the radius designated as 34 or 35 -- encloses an angle cra or 2 of less than 180 , preferably of 1200 to 1 600 or especially of 1300 to 1400, with the radius 36 or 37 extending towards that point 38 or 39 of the guide body 28 or 40 which is closest to the impeller circumference. If the point of the guide body closest to the impeller adopts this position, the centre of turbulence is once again to a certain extent moved away from the vane ring towards the interior of the impeller.

The effect at which the invention aims is also supported by the arrangement according to Figs. 6 and 8 to 11, wherein the normal 50, 51,52, 53, 54 to the outlet end section 55, 56, 57, 58, 59 of the baffle plate extending through that point 45, 46, 47, 48, 49 of the guide body which, viewed in the direction of flow, is the most distant from the fan outlet, is arranged at a distance corresponding to approximately 10 to 30%, preferably 12.5 to 1 8%, of the impeller diameter from its parallel tangent 60, 61, 62, 63, 64, 65 of the impeller circumference.In the variant according to Fig. 7, the normal to the central flow line 62 of the outlet diffusor or to the central line of the outlet diffusor extending through that point 61 of the guide body which, viewed in the direction of flow, is the most distant from the fan outlet, is again arranged at a distance corresponding to approximately 10 to 30%, preferably 5.5 to 18%, of the impeller diameter from the tangent 60. These measures, too, contribute to the positioning and aligning of the guide body in such a way that the vortex core is forced towards the interior of the impeller during normal operation, while, during restricted flow operation, slightly moving along the inside of the vane ring against the direction of rotation, thereby maintaining its radial position.

Contributory to this object of the invention is the fact that the radius extending to the starting point of the spiral encloses an angle of 750 to 1100 with the central line of the guide body.

This forcing of the vortex core or centre of turbulence away from the inside of the vane ring is also aided by a large "shadow" corresponding to approximately 1/15 to 1/20 of the impeller circumference being thrown on the impeller circumference by the guide body, the projection of the effective zone 70 according to Fig. 6, within which the flow in the immediate vicinity of the impeller circumference is influenced and the immediately adjoining incoming (arrow 71) and emerging (arrow 72) flow sections are separated from each other, corresponding to approximately 4 to 7% of the length of the impeller circumference and the radii extending from the impeller centre to the two end points of the guide body's effective zone, within which the flow in the immediate vicinity of the impeller circumference is influenced and the immediately adjoining incoming and emerging flow sections are separated from each other, suitably enclosing an angle of 20 to 300, preferably 23 to 250.

The guide body of the variants according to Figs. 7, 8, 9 and 11 is designed in the shape of a drop, the point of which is directed away from the impeller, while the guide body according to Figs. 6 and 10 assumes the shape of-a drop of uniform diameter. In the variant according to Fig.12, the guide body 70 is wedge-shaped, the base 71 being adjacent to the impeller circumference 72.

In this case, the centre line of the wedge having a base adjacent to the impeller circumference encloses an angle of 25 to 500 with the vertical plane 73 containing the axis of impeller rotation (this plane being approximately vertical to the centre plane of the fan outlet).

In the variants according to Figs. 7, 9, 10, 11 and 12, the guide body is hollow, the dischargeside wall section adjoining the impeller-side wall section in the direction towards the fan outlet having at least one opening 80, 81, 82, 83, 84, through which part of the medium flowing towards the fan outlet can return from the discharge side and flow into the hollow space of the guide body, in order to enter the gap between impeller and guide body at 85, 86, 87, 88, 89 by way of the impeller-side wall section.In the arrangement according to Fig. 10, the impeller side wall section, or at least that part of it which is closest to the impeller, consists of perforated plate, as shown at 1 9. In the arrangements according to Figs. 7, 10 and 11, the discharge side wall section of the guide body consists of perforated plate, as shown at 91, 92, 93. The assembly can alternatively be so arranged that the discharge-side wall section of the guide body is provided with an opening allocated to the outlet zone from the discharge duct of the fan and having a variable cross-section, controlled by a pivotable flap or adjustable slide valve.The discharge-side wall section of the guide body may for instance have several openings, each of them being at least partially capable of being covered, or it may consist of perforated plate provided with an adjustable covering element, such as a pivotable flap, an adjustable slide valve or the like, by means of which the flow of the medium may be completely or partially restricted.

In the arrangement according to Fig. 6, the discharge-side wall section of the guide body is, as in the arrangement according to Fig. 10, approximately parallel to the wall section of the baffle plate lying opposite it. In the arrangement according to Fig. 11, the guide body 95 is approximately triangular, the side 97 of the triangle adjacent to the impeller 96 being straight and, together with the impeller circumference, enclosing a gap 98 tapering at least partially in the direction (99) of impeller rotation and also as shown at for instance 88, extending parallel to the impeller circumference.

The return duct may, as in the case of some of the embodiments shown in the drawings, be of approximately uniform width or else, as in the embodiment according to Fig. 12, taper towards the impeller (cf. return duct 100). The central flow line of the medium flowing through the return duct extends, in most of the illustrated embodiments, approximately tangentially with respect to the impeller circumference, whilst extending radially in some others.

Claims

1. A housing for a cross-flow fan, especially for use with roof ventilators, said housing comprising a guide body arranged to separate the incoming flow from the emerging flow and a baffle plate arranged to guide the emerging flow, an impeller being located between the baffle plate and the guide body, the baffle plate having at least in part a spiral shape, the baffle plate and the guide body being so designed and arranged both in themselves and relative to each other that the fan, by maintaining a substantially low and constant level of dynamic energy at its outlet, operates to a flat and horizontal or substantially horizontal pressure/volume characteristic similar to the so called boiler characteristic, the centre of turbulence being, during normal operation, moved towards the interior of the impeller and away from an annular vane arrangement and held in this position, while, during restricted flow operation, being maintained in substantially the same radial position, moving along the inside of the vane arrangement in a direction opposite to that of impeller rotation, a maximum of dynamic energy being converted into static energy during passage to an outlet of the housing.

2. A housing for a cross-flow fan according to claim 1, wherein the guide body is so arranged relative to the impeller that the guide body or an imaginary extension thereof extends, at least over a major part, along the outside of a discharge side area of the impeller, thus in a way sliding underneath or over the impeller.

3. A housing according to claim 2, wherein the longitudinal centre of bisecting line of the guide body extends tangentially or substantially tangentially in relation to the impeller.

4. A housing according to Claim 2, wherein the discharge-side outer wall of the guide body extends tangentially or approximately tangentially in relation to the impeller.

5. A housing according to Claim 2, wherein the inlet-side outer wall of the guide body extends tangentially or approximately tangentially in relation to the impeller.

6. A housing according to any of Claims 2 to 5, wherein the radius from the centre of the impeller to the starting point of the spiral forms an angle of less than 1800, preferably 1200 to 1600 and especially 1 300 to 1400, with the radius to that point of the guide body which is nearest to the impeller circumference.

7. A housing according to any of Claims 1 to 6, wherein the normal to the discharge-side end section of the baffle plate extending through.that point of the guide body which, viewed in the direction of flow, is the most distant from the fan outlet, is arranged at a distance corresponding to approximately 10 to 30%, preferably 12.5 to 18%, of the impeller diameter from its parallel tangent of the impeller circumference.

8. A housing according to any of Claims 1 to 7, wherein the normal to the centre line of the fan housing's outlet diffusor or to the central flow line in the outlet diffusor extending through that point of the guide body which, viewed in the direction of flow, is the most distant from the fan outlet, is arranged at a distance corresponding to approximately 10 to 30%, preferably 12.5 to 18%, of the impeller diameter from its parallel tangent of the impeller circumference.

9. A housing according to any of Claims 1 to 8, wherein the radius extending to the starting point of the spiral encloses an angle of 750 to 1100 with the centre line of the guide body.

10. A housing according to any of Claims 1 to 9, wherein the shadow thrown on the impeller circumference by the guide body is large, corresponding to approximately 1/1 5 to 1/20 of the impeller circumference.

11. A housing according to any of Claims 1 to 10, wherein the projection of the effective zone of the guide body, within which the flow in the immediate vicinity of the impeller circumference is influenced and the immediately adjoining incoming and emerging flow sections are separated, corresponds to approximately 4 to 7% of the length of the impeller circumference.

12. A housing according to any of Claims 1 to 10, wherein the radii from the centre of the impeller to the two end points of the effective zone of the guide body, within which the flow in the immediate vicinity of the impeller circumference is influenced and the immediately adjoining incoming and emerging flow sections are separated, enclose an angle of approximately 200 to 300, preferably 230 to 250.

1 3. A housing according to any of claims 10 to 12, wherein the guide body is designed in the shape of a drop, suitably of uniform diameter, the point of which is directed away from the impeller.

14. A housing according to any of claims 1 to 13, wherein the guide body is designed as a wedge, the base of which is adjacent to the impeller circumference.

1 5. A housing according to claim 14, wherein the centre line of the wedge with the base adjacent to the impeller circumference encloses an angle of 250 to 500 with the vertical plane containing the axis of impeller rotation.

1 6. A housing according to any of claims 1 to 15, wherein the guide body is hollow and the discharge-side wall section adjoining the impellerside wall section in the direction of the fan outlet has at least one opening, through which part of the medium flowing towards the fan outlet can return from the discharge-side and flow into the hollow space of the guide body, in order to enter the gap between impeller and guide body by way of the impeller-side wall section, the central flow line of the medium flowing through the return duct extending, for instance, radially in relation to the impeller circumference.

17. A housing according to claims 1 to 12, wherein the guide body is designed in the shape of a triangle, the side of which adjacent to the impeller is straight and encloses a gap with the impeller circumference, which tapers at least partially in the direction of impeller rotation, while also being capable of extending parallel to the impeller circumference.

1 8. A housing for a cross-flow from substantially as hereinbefore described with reference to the accompanying drawings.

19. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.