Patent Description:
The invention relates to a fan arrangement, more particularly, the invention relates to an impulse bladed axial fan and an impeller for such a fan.

Ducted axial fans are used in a variety of applications including the ventilation of tunnels such as mineshafts and roadways. The need for more air and higher pressures have made the need for existing axial fans to become larger, heavier and noisier, thus occupation health and safety (OH&S) issues are then increased in prominence.

Such ducted fans include a fan having blades that are rotatable within a housing that fits with the duct. The blades are shaped and have an aerodynamic profile to cause a pressure differential across the blades to draw are through the housing and hence provide pressure to drive air through the duct. The overall length of the duct may in some instances be relatively long and multiple ducted fans may be utilised to maintain the desired pressure and resulting flow rate. In some examples, the ducted axial fans are staged (one-after-the-other) to achieve the required pressure.

A problem with these ducted fans relates to the efficiency of the fans, noise generated, especially for multi-stage fans, and the degradation of performance of the fans due to blade wear in abrasive environments.

The document <CIT> [US]) discloses an axial cooling fan comprising a fan housing which includes a converging inlet, a motor which is supported in the fan housing, an impeller which is driven by the motor, and an outlet guide vane assembly high extends radially between the motor and the fan housing. The cooling fan may also include a diffuser section which is located downstream of the outlet guide vane assembly and which includes a diffuser tube that is connected to or formed integrally with the fan housing and a tail cone that is connected to or formed integrally with the downstream end of the motor. Each of the impeller blades and the outlet guide vanes may be considered to comprise a radial stack of a number of individual airfoil segments.

Document <CIT> shows another example of a fan arrangement for an in-line duct.

The invention disclosed herein seeks to overcome one or more of the above identified problems or at least provide a useful alternative.

In accordance with the invention there is provided, a fan arrangement for a duct, the fan arrangement including a housing having an inlet and an outlet adapted to communicate air with the duct and an axially rotatably driven impeller supported within the housing between the inlet and the outlet, the impeller including a hub carrying a plurality of blades that span in a radial direction outwardly of the hub, the plurality of blades being shaped to urge air between the inlet and the outlet.

According to the invention, the plurality of blades has a tip solidity ratio in the range of about <NUM> to <NUM>. A tip solidity ratio is measured at or toward tips of the plurality of blades. Each of the plurality of blades also has a twist angle between respective a hub root and a tip thereof in the range of about <NUM> to <NUM> degrees and a constant thickness. The substantially constant thickness may be the profile between a leading edge and a trailing edge and/or substantially constant thickness for the entire blade.

In another aspect, each of the plurality of the blades are formed from a metal plate twisted to provide the twist angle.

In yet another aspect, the hub tapers outwardly in a direction between the inlet and outlet.

In yet another aspect, the housing includes an inner housing supporting the impeller and an outer housing, the inner and outer housing defining a passageway therebetween through which air flows.

In yet another aspect, a post-fan section of the passageway has a cross sectional area that is relatively smaller in comparison to a cross sectional area of a pre-fan section of the passageway.

In yet another aspect, the hub is shaped to provide a tapered transition between the pre-fan and post-fan sections of the passageway.

In yet another aspect, the inner housing includes a nose section, a trailing section with the hub located between the nose section and trailing section, wherein a diameter of the trailing section is greater than a diameter of the nose section.

In yet another aspect, the inner housing includes a tail cone extending from and tapering inwardly from the trailing section.

In yet another aspect, a leading tip of the nose section is shaped to be streamlined.

In yet another aspect, the trailing section includes a flow straightener.

In yet another aspect, the flow straightener is provided in the form a plurality of turning vanes arranged to provide a substantially axial flow.

In yet another aspect, the nose section includes a flow conditioner shaped to guide air to the blades.

In yet another aspect, the flow conditioner is provided in the form of at least one of static and adjustable pre-rotator blades.

The invention is described, by way of non-limiting example only, by reference to the accompanying figures, in which;.

Referring to <FIG>, there is shown a fan arrangement <NUM> for a duct or system of ventilation ducts (not shown) to move or convey air. The fan arrangement <NUM> includes a housing arrangement <NUM> having an outer housing <NUM> and inner housing <NUM> located within the outer housing <NUM> so as to define a passageway <NUM> therebetween. The inner and outer housings <NUM>, <NUM> may be formed of one or more segments joined with one another.

The inner housing <NUM> includes a nose section <NUM>, a trailing section <NUM> and an impeller or fan <NUM> between the nose section <NUM> and the trailing section <NUM>. A tail cone <NUM> is coupled to the trailing section <NUM> that tapers inwardly toward an axial axis of the housing arrangement <NUM>.

The impeller <NUM> includes a rotating hub <NUM> that carries a plurality of likewise rotating blades <NUM> that extend in a radial direction substantially between the hub <NUM> and the outer housing <NUM>. The rotating blades <NUM> each have a substantially flat profile such that the an arrangement <NUM> is considered an impulse bladed axial fan in which the impeller <NUM> drives the airflow by momentum imparted to the air as opposed to a pressure differential as utilised by typical aerofoil ducted axial fans.

The outer housing <NUM> includes an inlet <NUM> having an inlet cone <NUM> adapted to communicate or fluidly couple with the duct and an outlet <NUM> to re-communicate or fluidly couple with the duct. The inlet cone <NUM> may be fitted with a grate <NUM>. The outer housing <NUM> and the inner housing <NUM> are, at least in part, generally cylindrical in shape and elongate. The outer housing <NUM> and inner housing <NUM> are positioned concentrically about the axis of rotation of the impeller <NUM>. The nose section <NUM> includes a streamlined tip <NUM> being in this example pointed or domed shaped. The impeller <NUM> is driven by a motor arrangement <NUM> having a motor <NUM> such as, but not limited to an electric motor, adapted to rotate the impeller <NUM>. The motor <NUM> may be a four pole motor for operation at <NUM> to <NUM>, and, as such, in some examples the impeller <NUM> may be rotated at a fixed speed of about <NUM> rpm. In other examples, the motor <NUM> may have other number of poles and rotate at other suitable speeds. The housing arrangement <NUM> may be generally formed of a metal such as mild steel.

A pre-fan section <NUM> of the passageway <NUM> is defined between the nose section <NUM> and the outer housing <NUM>. The pre-fan section <NUM> thereby having a generally annular shaped cross section through which air passes from the inlet <NUM> to the impeller <NUM>. A post-fan section <NUM> of the passageway <NUM> at the trailing section <NUM> is defined between the inner housing <NUM> and the outer housing <NUM>. The post-fan section <NUM> thereby also having a generally annular shaped cross section through which air passes from impeller <NUM> towards the outlet <NUM>. The pre-fan section <NUM> has a relatively larger cross sectional area in comparison to the post-fan section <NUM>. The trailing section <NUM> may include or terminate with an evasee <NUM> (an outward tapered diffuser section) prior to an expander section <NUM> as defined between the tail cone <NUM> and the outer housing <NUM>.

More specifically, in this example, outer housing <NUM> has a relatively constant diameter along its length. However, the nose section <NUM> has a relatively narrower or smaller diameter in comparison to the post-fan section <NUM> thereby the pre-fan section <NUM> has a relatively larger cross sectional area in comparison to the post-fan section <NUM>. The hub <NUM> is shaped to transition between the nose section <NUM> and the trailing section <NUM>. In this example, the hub <NUM> is generally truncated frusto-conical in shape to provide a generally straight tapered surface <NUM> in side profile between the nose section <NUM> and the trailing section <NUM>. The blades <NUM> extend radially from the tapered surface <NUM> of the hub <NUM>. The tapered surface <NUM> of the hub <NUM> provides compression of the airflow as it passes through the blades <NUM> into the outlet section <NUM>. The nose section <NUM> may include a further likewise tapered section <NUM> immediately prior to the tapered surface <NUM> of the hub <NUM>.

The pre-fan section <NUM> includes a flow conditioner <NUM> is provided in the form of at least one of a static and adjustable pre-rotator blades <NUM> that extend radially from the nose section <NUM> to the outer housing <NUM>. In examples wherein the pre-rotator blades <NUM> are adjustable, the pre-rotator blades <NUM> may be used to control the fan characteristics such as the volumetric flow rate output. When controllable pre-rotator blades <NUM> are used, the impeller <NUM> may be operated at a fixed rotation speed and the pre-rotator blades <NUM> may be used control the volumetric flow rate whilst the impeller <NUM> is maintained as the fixed speed.

The pre-rotator or pre-fan blades <NUM> guide air to the impeller arrangement <NUM>. The post-fan section <NUM> includes one or more flow straighteners <NUM> provided in the form of turning vanes <NUM> extending radially from the trailing section <NUM> to the outer housing <NUM>. One or both of the pre-rotator blades <NUM> and the turning vanes <NUM> support and suspend the inner housing <NUM> within the outer housing <NUM>.

Referring to <FIG>, turning now to the impeller <NUM>, in particular the blades <NUM>, each blade includes a twisted blade body <NUM>, a root <NUM>, a tip <NUM>, a leading edge <NUM> and a trailing edge <NUM>. In this example, each of the blades <NUM> includes a twist angle between a hub root of the blade and a tip of the blade in the range of about <NUM> to <NUM> degrees.

The blade body <NUM> has a constant thickness across the chord and length. To achieve the constant thickness the blades <NUM> may be each formed from a metal plate that is twisted to provide the twist angle. The constant thickness plate, being preferably symmetrical in profile and not aerofoil shaped, are resistive to wear and therefore the performance of the fan arrangement may be maintained over time. The constant thickness or flat blades <NUM> function by increasing velocity imparted to the flow through the impeller <NUM> without substantially increase of pressure. The constant thickness or flat blades <NUM> therefore functions differently to an aerofoil shape that relies mainly on a pressure differential to drive the flow. The leading edge <NUM>, trailing edge <NUM> and tip <NUM> may be rounded or radiussed to reduce turbulence. The constant thickness or flat blades <NUM> also inhibit stalling especially when used with pre-rotator blades <NUM> that move through relatively large angles such as + <NUM> degrees to - <NUM> degrees.

The impeller <NUM> may be generally formed of a metal such as mild steel. It may be appreciated, in from <FIG>, that the blades <NUM> occupy much of the space through which air flows through the impeller <NUM>. In front plan form view, as shown in <FIG>, it may also be appreciated that the leading edges <NUM> and the trailing edges <NUM> of adjacent blades <NUM> are substantially parallel. The blade twist angle is best shown in <FIG> and is measured between the blade root <NUM> and the blade tip <NUM>. The range is about <NUM> to <NUM> degrees. However, preferably, the blade twist angle may be about or close to <NUM> to <NUM> degrees, and most preferably about <NUM> degrees.

In this example, the chord "CAt" at the tip <NUM> of the blades <NUM> is substantially longer relative to the chord "CDr" at the base or root <NUM> of the blades <NUM> (best seen by comparing <FIG>). As such, the solidity ratio at the tip "SRt" at Section "A-A" is in the range of about <NUM> to <NUM>, and the solidity ratio "SRr" at Section "D-D" may be in the order of about <NUM> to <NUM>. In another unit of measure, it is noted that the aspect ratio (being a ratio of its span or blade length to its mean chord) of the blades is quite low due to the relatively long chord. The base or root <NUM> of the blades <NUM> may be shaped or tapered to match the tapering of the hub <NUM>.

The blade tip solidity ratio "SRt" is defined herein as the sum of the tip chord lengths "CAt" of all blades <NUM> at tips <NUM> thereof (i.e. measurement of the chord at section A-A of the blades <NUM> as shown in <FIG>) divided by the perimeter at the diameter "D" of the blades <NUM>. By way of example only, the chord width "CAt" of the blade <NUM> at the tip <NUM> may be, for example, <NUM>. There may be <NUM> blades, so <NUM> x <NUM> gives <NUM>. The diameter "D" may be, for example, <NUM>. Accordingly, the perimeter is π x D which gives <NUM>. The "SRt" Ratio in this example is = <NUM>/<NUM> = <NUM>. Other variations of the "CAt" and "D" may be used. It is noted that "D" is preferably in the range of about <NUM> to <NUM>.

Similarly, the blade root solidity ratio "SRr" is defined herein as the sum of the root chord lengths "CDr" of all blades at hub <NUM> outside diameter (i.e. measured at the root <NUM> at section D-D of the blades <NUM>), divided by hub <NUM> outside perimeter "Hp" (in this example the perimeter is measured at the larger diameter of the tapered hub <NUM> at <NUM>*D where "D" is the diameter the blades <NUM>).

In this example, the hub <NUM> has a relatively large diameter and circumference that results in the solidity ratio being relatively low in comparison, for example, to typical ducted axial fan. The tapered shape of the hub <NUM> may vary from about, but not limited to, <NUM>. 55xD to <NUM>.

Still referring to <FIG>, it may be appreciated that the angle of attack "AD" of the blade <NUM> at the root <NUM> is less than the angle of attack "AA" at the tip <NUM>. In this example, the angle of twist between sections A-A & D-D is between <NUM> to <NUM> degrees, the applicable fan diameter "D" sizing may be between about <NUM> & <NUM> tip diameters, and the blade section radius is between <NUM> to <NUM>. However, as aforesaid, suitable twist angles may be in the range of about <NUM> to <NUM> degrees. It is noted that the sections A-A & D-D are generally "arc" shaped due to the applied twist and the profile of the blades <NUM> is substantially constant. The "arc" at the root section D-D is greater than the "arc" at the tip section A-A.

It is also noted that the chord length of the blades <NUM> is much longer than what is typically used by an impulse bladed impeller and this results in a lower power consumption over the useful range of the impeller <NUM>, as shown in <FIG>. Moreover, the longer chord length provides a similar press-volume (PV) curve in comparison to an example axial fan that may be a two-stage axial fan suitable for a duct having a diameter of up to about <NUM>. Accordingly, the fan arrangement <NUM> herein is particularly suitable to the duct ventilation market. Noise is also reduced as shown in <FIG> in comparison to a two-stage axial fan. It is noted that the fan arrangement <NUM> is capable of pushing about <NUM><NUM>/s at over <NUM> kPa. A traditional two-stage axial fan of similar diameter will stall at least than <NUM> kPa and is only capable of about <NUM><NUM>/s up to about <NUM> kPa.

Advantageously, there has been provided a fan arrangement having an impeller is that has an increased chord length, increased number of blades, a relatively high angle of attack of the blades and the flow compression arising from the tapered hub of the impeller. This provides an advantageous fan arrangement having a similar pressure characteristic over a useful range of the fan. The press-volume (PV) curve is also advantageous and suited the vent duct ventilation market.

Moreover, the fan performance arrangement characteristics mimics the functions of a two-stage axial fan but within a smaller installation envelope thus making the fan lighter and smaller than the comparable axial fans in the market and making installation easier and quicker. The need for less fan installations is also an advantage and results in less installation work whilst using existing cabling. The low end of the pressure volume curve rises higher than the comparable axial fans in the marketplace thus reducing the need for an additional fan, as the duct lengths get longer. The new impeller is smaller in size and features noise reduction characteristics thus noise generation is considerably less that the equivalent single axial fan installation for a given duty.

The impeller blades are made of plate, rather than aerofoil shaped, thus are not affected by wear. The impeller blade design improvements changes its characteristics from a normally high volume PV (pressure-volume) curve to a steeper lower volume steeper PV curve but with a lower power consumption curve over a wide range of volume flow. The pressure range is substantially higher at the lower end than the comparable fans in the market thus delaying the need for the installation of an additional fan. Fundamentally, the fan arrangement provides a smaller, lighter, quieter, more industrious fan for the same ventilation and pressure range with less resistance meaning less relocations, repairs, safety exposure.

The features that may contribute to overcoming the existing problems are as listed below:.

Finally, it is noted that with this new impeller design makes the fan smaller than existing fans for the same duty and may be lighter in weight by up to <NUM>%. The improved performance may delay the need for additional fans for longer ducts lengths. These features may also simplify installation and improve the OH&S as well as being able to use existing wiring. The power characteristic is largely lower for the practical range of duties that the fan is designed for, thus overloading of the fan motor is alleviated.

The reference in this specification to any known matter or any prior publication is not, and should not be taken to be, an acknowledgment or admission or suggestion that the known matter or prior art publication forms part of the common general knowledge in the field to which this specification relates.

While specific examples of the invention have been described, it will be understood that the invention extends to alternative combinations of the features disclosed or evident from the disclosure provided herein.

Claim 1:
A fan arrangement for a duct, the fan arrangement including a housing having an inlet and an outlet adapted to communicate air with the duct and an axially rotatably driven impeller supported within the housing between the inlet and the outlet, the impeller including a hub carrying a plurality of blades that span in a radial direction outwardly of the hub, the plurality of blades being shaped to urge air between the inlet and the outlet,
wherein the plurality of blades have a tip solidity ratio in the range of about <NUM> to <NUM>, and
wherein each of the plurality of blades has a twist angle between a root and a tip thereof in the range of about <NUM> to <NUM> degrees,
characterised in that the impeller (<NUM>) is an impulse bladed impeller in which each of the plurality of blades (<NUM>) have a constant thickness across a chord thereof.