GB2378732A

GB2378732A - Impeller for a fan

Info

Publication number: GB2378732A
Application number: GB0112462A
Authority: GB
Inventors: Richard Hayes Teague
Original assignee: Fans & Blowers Ltd
Current assignee: Fans & Blowers Ltd
Priority date: 2001-05-22
Filing date: 2001-05-22
Publication date: 2003-02-19
Anticipated expiration: 2021-05-22
Also published as: GB0112462D0; GB2378732B

Abstract

An impeller 13 for rotable mounting in a fan, the impeller comprising a plurality of blades 20 extending radially and bladelets 23 in the spaces between the blades. The bladelets 23 are significantly shorter than the blades 20, having a length of 50% or less of the blades 20 length and act to promote the efficiency of the fan by preventing fluid circulation in the spaces between the blades. The impeller 13 may be used in a centrifugal fan or an axial fan. In a preferred embodiment the impeller is rotably mounted in a fan casing having an inlet and an outlet such that in use rotation of the impeller forces fluid from the inlet to the outlet.

Description

FAN The present invention relates to fans, such as centrifugal fans or axial fans. It is particularly concerned with the impeller of such a fan.

Centrifugal fans (also known in some countries as radial fans) are used in many situations where it is desired to increase the pressure of a flow of air or other fluid their use, for example, in chemical plants, in ventilation systems, for the supply of combustion air to burners for gas boosting, for landfill gas extraction, and in heating systems. They may also be used to handle the pumping of mixtures of gas with dust or other particulate materials, which mixtures can be made to flow in the manner of a fluid. Centrifugal fans may also be used to provide suction.

Known centrifugal fans have a casing containing an impeller which rotates to draw air from an inlet to an outlet of the fan, and increase the pressure of the air or provide suction as it does so. The impeller has a plurality of blades, and the rotation of the impeller moves air past the blades. In one known type of centrifugal fans, the blades are normally held between two parallel plates of the impeller, with those plates

rotating within a casing. One plate has an aperture therein through which air can pass from the inlet of the fan to the space between the plates, where it is forced outwardly by the blades to the circumference of the impeller, and hence to an outlet. Such known impellers usually have blades equally-spaced around the impeller, and impellors for different purposes may have differently shaped blades. In a centrifugal fan, the blades may be flat in the direction of the axis of rotation, or may be curved either in the direction of, or against, the flow of the fluid. The blades may be in the form of a sheet or may have an aerofoil cross-section.

In another known type of fan, the blades project from a hub to form a paddle-like arrangement, and the impeller the does not have the parallel plates as described previously. Others have only one plate, and yet others have at least one conical plate, with the aid of the cone at the axis of the impeller.

It is also known to provide multiple stage fans, in which there are a plurality of impellers in series.

Normally, each impeller has its own outer casing, with the casings then being secured together to form the whole fan.

In an axial fan, air is pumped from an inlet to an outlet via an impeller, the blades of which are inclined

to the axis of rotation in a manner similar to an aeroplane propeller.

At its most general, the present invention proposes that bladelets are provided between at least some of the blades of the impeller. The bladelets are significantly shorter than the blades and may extend from the periphery of the impeller (or close to that periphery) generally inwardly. It has been found that the use of such bladelets increases the efficiency of the fan.

It is believed that the reason for this increase in efficiency is that, in conventional centrifugal fans, there is fluid circulation in the space between each blade and the next. The bladelet used by the present invention then interrupt that circulation. Thus, it is preferable that at least one bladelet is provided between each pair of adjacent blades. Moreover, since the aim of the bladelet is to break up air flow, it has been found that there is no gain in efficiency in providing more than one bladelet between each pair of blades, and the bladelet is preferably equally-spaced from the adjacent blades. However, arrangements involving multiple bladelets between adjacent blades, or bladelets closer to one blade than the other, are possible within the present invention.

According to the present invention there may be provided a fan having a casing with an inlet and an outlet and a rotatable impeller within the casing for forcing fluid from the inlet to the outlet, wherein the impeller comprises a plurality of blades extending generally radially for acting on the fluid as the impeller rotates, pairs of blades each having a space therebetween bounded by the corresponding blades and the parts of the circles circumscribing the radially inner and outer edges of the blades, and at least one bladelet between at least one pair of blades, the at least one bladelet extending into the space between the corresponding pair of blades from the boundary of that space, the length of the bladelets being 50% or less of the length of the blades.

Preferably there is at least one bladelet between each pair of blades.

It is preferable that the or each bladelet extends inwardly from the circle circumscribing the radially outer edge of the blades. That circle may be the periphery if the impeller, if the blades extend to that periphery. If the blades stop short of that periphery, e. g. where that periphery is defined by a plate or plates on one or both sides of the blades, the blades still extend inwardly from the circle defined by the outer

edges of the blades. It has been found that such an arrangement, in which the bladelets extend inwardly from that outer circle is more efficient at interrupting fluid circulation in the space between adjacent blades and other arrangements. However, the present invention is not limited to arrangements in which the bladelets extend inwardly from that outer circle. For example, the bladelets may extend inwardly from the inner circle.

However, there is then the possibility that the circulatory flow will be established between the blades radially outwardly from the bladelets. Therefore, if the bladelets extend inwardly from the inner circle, rather than the outer circle, they may have to be larger to provide sufficient effect. It should be noted that the present invention also encompasses bladelets at other positions within the space between the blades, but again such positions are thought to be less efficient.

As stated above, the bladelet is 50% or less of the length of the blade. Indeed, bladelets shorter than this are possible, particularly for larger fans, and the length of the bladelet may then be 40% or less, more preferably 33% to 10% less of the length of the blade.

This may also be expressed in terms of actual size, in that a bladelet of 50mm 25mm is normally acceptable for practical fans.

The bladelets will normally conform in shape to that part of the blades adjacent the periphery of the impeller. Thus, if the blades extend inwardly directly away from the periphery, so will the bladelets. If the direction of the blades is off-set relative to the axis of rotation, then again the bladelets will similarly be off-set.

Where the present invention is embodied in a centrifugal fan, the bladelets will preferably be secured to circular plate (s) between which the blades are located. In an axial fan, it may be necessary to provide an annular ring secured to the tips of the blades, with the bladelets then extending axially inwardly from that ring. It may further be necessary to provide a further ring to secure the inner tips of the bladelets. In an axial fan, the bladelets may have an aerofoil crosssection, in the same manner as the blades.

An embodiment of the present invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a view of a centrifugal fan in which the present invention is embodied; Fig. 2 shows a plan view of an impeller for the fan of Fig. 1; Fig. 3 shows a side view of the impeller of Fig. 2; and

Fig. 4 shows various blade configurations that can be used in the present invention.

Referring first to Fig. 1, a centrifugal fan has a generally circular casing 10 with an inlet 11 at its axis. The casing 10 may have a mounting plate 12 to enable the fan to be positioned in a vertical configuration. Within the casing 10 is an impeller 13, which can be seen in Fig. 1 through the inlet 11, with the impeller 13 rotating to draw air into the inlet 11, and out from an outlet 14. The impeller is driven by a motor 15.

In its external appearance, the fan of Fig. 1 is conventional. The present invention is primarily concerned with the configuration of the impeller. This is shown in more detail in Fig. 2.

Fig. 2 shows that the impeller has the plurality of blades 20 spaced around the axis of rotation 21. In this embodiment, the blades 20 extend from the periphery of the impeller 13 but do not extend directly towards the axis 21. Instead, their direction is off-set in a way which is referred to as being backward relative to the direction 22 of rotation of the impellor 13. Between each pair of adjacent blades 20 is a bladelet 23. These bladelets extend from the outer periphery of the impeller inwardly in a direction generally similar to the

direction of the blades 20, but the bladelets 23 are significantly shorter than the blades 20 as can be seen from Fig. 2. In the embodiment of Fig. 2, the bladelets are approximately 22 percent of the length of the blade, but this depends at least partially on the size of the fan. If the bladelets are to have to desired effect, they cannot be too small and thus the size of the bladelets relative to the size of the blades will increase as the size of the fan decreases. However, the bladelets will be 50% or less, more preferably 40% or less of the size of the blades. Indeed, for most fans of this type, the size of the blade is likely to be 50rnm I 25mm.

It is, of course, not essential that the blades and the bladelets extend right to the periphery of the impellor, but this is normally preferred for maximum efficiency.

Fig. 3 shows a side view of the impeller 13 of Fig.

2. It has two generally parallel circular plates 30,31, the plate 30 not being visible in the sectional view of Fig. 1. The blades 20 and the bladelets 23, are secured to these plates 30,31 e. g. by rivets or by welding, to form a rigid structure. The plate 30 (often referred to as a backplate) has a opening 32 at the axis of rotation, with a hollow hub 33 extending therethrough. The hub 33

receives a drive shaft (not shown) from the motor 15.

Note that it would alternatively be possible to drive the shaft via a belt or other coupling.

Air is drawn in to the inlet 11 of the fan and passes to the space between the plates 30,31 (the plate 31 often being referred to as a shroud). The blades 20 then force the air axially outwardly to the periphery of the impeller 13. That periphery is open, and therefore air is forced in to the space between the impeller 13 and the casing 10, but the movement of that air due to the rotation of the impeller 13 also gives the air at the periphery an tangential component of movement, causing it to flow to the outlet 14.

Other blade configurations can be used. Figs. 4a to 4d show four different blade configurations which can be used in the present invention. The bladelets will then conform generally to the part of the blade adjacent the periphery of the impeller.

As has been mentioned earlier, the present invention is not limited to centrifugal fans, and may be used in axial fans in which an impeller similar to an aeroplane propeller has an outer ring with the bladelets extending inwardly therefrom. There may also be an inner ring to secure the inner tips of the bladelets. Air is then pumped from one side of the impeller to the other. In

all cases, the use ot the bladelets increases the efficiency of the fan. It is possible, but not normally necessary, to provide more than one bladelet between each pair of blades, and the present invention also encompasses arrangements in which bladelets are provided only between some of the pairs of blades, even though such an arrangement will be less efficient.

It has previously been mentioned that fans having multiple impellers in series. The present invention may be used in any or all stages of such a fan.

Moreover, although Fig. 3 illustrates an embodiment with parallel plates 30,31 it is possible for at least plate 30 (the shroud) to be conical, so that the width of the blades 20 is wider in the axial direction at the air inlet than it is at the outer periphery. The bladelets would then increase in width as they extended from the outer periphery.

Claims

Claims 1. An impeller for rotatable mounting in a fan to force fluid from an inlet to an outlet of the fan, the impeller comprising a plurality of blades extending generally radially, pairs of blades each having a space therebetween bounded by the corresponding blades and the parts of the circles circumscribing the radially inner and outer edges of the blades, and at least one bladelet between at least one pair of blades, the or each bladelet extending into the space between a corresponding pair of blades from a peripheral region of that space, the or each bladelet having a length of 50% or less of the length of the blades.
2. An impeller according to claim 1 wherein there is at least one bladelet between each pair of blades.
3. An impeller according to claim 1 or claim 2 wherein the or each bladelet extends into a space between a corresponding pair of blades from the boundary of that space.
4. An impeller according to claim 3 wherein the or each bladelet extends inwardly from the circle circumscribing the radially outer edge of the blades.

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5. An impeller according to any one of the above claims wherein the length of the or each bladelet is 33% to 10% of the length of the corresponding blades.
6. An impeller according to any one of the above claims wherein the blades and the bladelets are secured to a plate on one side of the blades.
7. An impeller according to any one of the above claims wherein the radially inner edges of the blades are spaced from the axis of the impeller.
8. An impeller according to claim 7 wherein the blades extend from their radially outer to radially inner edges along a line offset from the axis of the impeller.
9. A fan having a casing with an inlet and an outlet, and a rotatably mounted impeller according to any one of the above claims, within the casing.
10. A fan according to claim 9 wherein the fan is a centrifugal fan.
11. A fan according to claim 9 or claim 10 wherein the inlet is adjacent a central region of the impeller.

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12. A fan substantially as described in any one embodiment herein with reference to Figures 1,2 and 3 and Figure 4a, 4b, 4c or 4d.
13. An impeller substantially as described as in any one embodiment herein with reference to Figure 2, Figure 3 and Figure 4a, 4b, 4c or 4d.