Patent Publication Number: US-11649833-B2

Title: Fans

Description:
RELATED APPLICATIONS 
     This application is a 35 U.S.C.371 national stage application of PCT Applicaton Serial No. PCT/AU2018/050146 filed on Feb. 22, 2018, which claims priority to Australian provisional patent application no. 2017900608 filed Feb. 23, 2017, the entire content of which are incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     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. 
     BACKGROUND 
     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&amp;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 invention disclosed herein seeks to overcome one or more of the above identified problems or at least provide a useful alternative. 
     SUMMARY 
     In accordance with a first broad aspect 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. 
     In an aspect, the plurality of blades has a tip solidity ratio in the range of about 0.8 to 1.2. A tip solidity ratio is measured at or toward tips of the plurality of blades. Each of the plurality of blades may also have a twist angle between respective a hub root and a tip thereof in the range of about 15 to 30 degrees and a substantially 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. 
     In yet another aspect, the outer housing includes an inlet cone arranged prior to the flow conditioner to direct air flow into the passageway and an outlet evasee after the flow straightener, the inlet cone and outlet evasee coupling to the duct. 
     In yet another aspect, the inner and outer housings are each generally cylindrical in shape and concentrically arranged about an axis of rotation of the hub. 
     In yet another aspect, the inner housing contains a motor arranged to drive the hub. 
     In yet another aspect, each of the plurality of blades includes a chord toward the tip that is relatively longer than the chord toward the root. 
     In yet another aspect, an angle of attack at the root of each of the plurality of blades is less than an angle of attack at the tip of each of the plurality of blades. 
     In yet another aspect, when viewed in front plan form, leading edges and trailing edges of adjacent ones of the plurality of blades appear to be substantially parallel. 
     In yet another aspect, at least one of leading and trailing edges of each of the plurality of blades are rounded. 
     In accordance with a second broad aspect there is provided, a blade for a fan arrangement as described above and herein in any one of the previous claims. 
     In accordance with a third broad aspect there is provided, an impeller for a fan arrangement as described above and herein. 
     In accordance with a fourth broad aspect there is provided, a ventilation system including one or more fan arrangements as described above and herein fitted to a duct to drive air between an inlet and outlet of the duct. 
     In accordance with a fifth broad aspect there is provided, a method of conveying air using a fan arrangement as described above and herein including fitting the fan arrangement with a duct and operating the fan arrangement to drive air between an inlet and outlet of the duct. 
     In accordance with a sixth broad aspect 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, wherein the plurality of blades have a tip solidity ratio in the range of about 0.8 to 1.2, and wherein each of the plurality of blades has a twist angle between a root and a tip thereof in the range of about 15 to 30 degrees, a substantially constant thickness and a chord length toward the tip is relatively longer than a chord length toward the root. 
     In accordance with a seventh broad aspect 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, wherein the plurality of blades have a tip solidity ratio in the range of about 0.8 to 1.2, and wherein each of the plurality of blades has a twist angle between a root and a tip thereof in the range of about 15 to 30 degrees, a substantially constant thickness profile and a chord toward the tip that is relatively longer than the chord toward the root. 
     In accordance with a eighth broad aspect there is provided, An impeller for a ducted fan arrangement having an inlet and an 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 0.8 to 1.2, and wherein each of the plurality of blades has a twist angle between a root and a tip thereof in the range of about 15 to 30 degrees and a substantially constant thickness. 
     In an aspect, the hub is shaped so as to compress flow as it passes through the plurality of blades. 
     In another aspect, the hub is tapered. 
     In yet another aspect, the each of the plurality of the blades are formed from a metal plate twisted to provide the twist angle. 
     In yet another aspect, each of the plurality of blades includes a chord toward the tip that is relatively longer than the chord toward the root. 
     In yet another aspect, an angle of attack at the root of each of the plurality of blades is less than an angle of attack at the tip of each of the plurality of blades. 
     In yet another aspect, when viewed in front plan form leading edges and trailing edges of adjacent ones of the plurality of blades are substantially parallel. 
     In yet another aspect, at least one of leading and trailing edges of each of the plurality of blades are rounded. 
     In accordance with a ninth broad aspect there is provided, a method of forming a fan arrangement for a duct, the method including the steps of: forming a housing having an outer housing and an inner housing so as to form a passageway therebetween, the inner housing supporting a rotatable axially arranged impeller and the housing being shaped such that a pre-impeller section of the passageway is relatively larger in cross section to a post impeller section of the passageway; forming the impeller so as to have a tapered hub between the pre and post impeller sections with the tapered hub carrying a plurality of blades that substantially span in a radial direction between the hub and an internal surface of the outer housing, the plurality of blades being shaped to urge air between an inlet and an outlet of the housing and, forming the plurality of blades so as to have a tip solidity ratio in the range of about 0.8 to 1.2, and so that each of the plurality of blades has a twist angle between a root and a tip thereof in the range of about 15 to 30 degrees and a substantially constant thickness. 
     In accordance with a tenth broad aspect there is provided, a method of forming an impeller for a ducted fan arrangement having an inlet and an outlet, the method including: forming a hub arranged to taper outwardly in a direction between the inlet and outlet; forming a plurality of blades to fit with the hub from a material having a substantially constant thickness so as to have a twist angle between a root and a tip thereof in the range of about 15 to 30 degrees; forming the impellor by coupling the plurality of blades to the hub such that the plurality of blades span in a radial direction outwardly of the hub to urge air between the inlet and the outlet and have a tip solidity ratio in the range of about 0.8 to 1.2. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The invention is described, by way of non-limiting example only, by reference to the accompanying figures, in which; 
         FIG.  1    is a side sectional view illustrating a fan arrangement; 
         FIG.  2    is a perspective side sectional view illustrating the fan arrangement; 
         FIG.  3    is a side exploded parts perspective view illustrating the fan arrangement; 
         FIG.  4   a    is a front side perspective view illustrating an impeller of the fan arrangement; 
         FIG.  4   b    is a topside perspective view illustrating an impeller of the fan arrangement; 
         FIG.  4   c    is a front view illustrating the impeller; 
         FIG.  4   d    is an end view illustrating a blade of the impeller; 
         FIG.  5    is a front view illustrating the blade of the impeller showing section A-A toward a tip and section D-D toward a root of the blade; 
         FIG.  6    is an end view illustrating section A-A as indicated in  FIG.  5   ; 
         FIG.  7    is an end view illustrating section D-D as indicated in  FIG.  5   ; 
         FIG.  8    is an example of a power/volume curve comparison the fan arrangement with a comparable duty two-stage axial fan; and 
         FIG.  9    is an example of a noise/volume curve comparison of the fan arrangement with a comparable duty two-stage axial fan. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS.  1  to  5   , there is shown a fan arrangement  10  for a duct or system of ventilation ducts (not shown) to move or convey air. The fan arrangement  10  includes a housing arrangement  12  having an outer housing  14  and inner housing  16  located within the outer housing  14  so as to define a passageway  17  therebetween. The inner and outer housings  14 ,  16  may be formed of one or more segments joined with one another. 
     The inner housing  16  includes a nose section  18 , a trailing section  20  and an impeller or fan  22  between the nose section  18  and the trailing section  20 . A tail cone  19  is coupled to the trailing section  20  that tapers inwardly toward an axial axis of the housing arrangement  12 . 
     The impeller  22  includes a rotating hub  21  that carries a plurality of likewise rotating blades  23  that extend in a radial direction substantially between the hub  21  and the outer housing  14 . The rotating blades  23  each have a substantially flat profile such that the an arrangement  10  may be considered an impulse bladed axial fan in which the impeller  22  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  14  includes an inlet  24  having an inlet cone  26  adapted to communicate or fluidly couple with the duct and an outlet  27  to re-communicate or fluidly couple with the duct. The inlet cone  26  may be fitted with a grate  25 . The outer housing  14  and the inner housing  16  are, at least in part, generally cylindrical in shape and elongate. The outer housing  14  and inner housing  16  are positioned concentrically about the axis of rotation of the impeller  22 . The nose section  18  includes a streamlined tip  30  being in this example pointed or domed shaped. The impeller  22  is driven by a motor arrangement  44  having a motor  46  such as, but not limited to an electric motor, adapted to rotate the impeller  22 . The motor  46  may be a four pole motor for operation at 50 to 60 Hz, and, as such, in some examples the impeller  22  may be rotated at a fixed speed of about 1500 rpm. In other examples, the motor  46  may have other number of poles and rotate at other suitable speeds. The housing arrangement  12  may be generally formed of a metal such as mild steel. 
     A pre-fan section  32  of the passageway  17  is defined between the nose section  18  and the outer housing  14 . The pre-fan section  32  thereby having a generally annular shaped cross section through which air passes from the inlet  24  to the impeller  22 . A post-fan section  34  of the passageway  17  at the trailing section  20  is defined between the inner housing  16  and the outer housing  14 . The post-fan section  34  thereby also having a generally annular shaped cross section through which air passes from impeller  22  towards the outlet  27 . The pre-fan section  32  has a relatively larger cross sectional area in comparison to the post-fan section  34 . The trailing section  20  may include or terminate with an evasee  28  (an outward tapered diffuser section) prior to an expander section  29  as defined between the tail cone  19  and the outer housing  14 . 
     More specifically, in this example, outer housing  14  has a relatively constant diameter along its length. However, the nose section  18  has a relatively narrower or smaller diameter in comparison to the post-fan section  34  thereby the pre-fan section  32  has a relatively larger cross sectional area in comparison to the post-fan section  34 . The hub  21  is shaped to transition between the nose section  18  and the trailing section  20 . In this example, the hub  21  is generally truncated frusto-conical in shape to provide a generally straight tapered surface  36  in side profile between the nose section  18  and the trailing section  20 . The blades  23  extend radially from the tapered surface  36  of the hub  23 . The tapered surface  36  of the hub  21  provides compression of the airflow as it passes through the blades  23  into the outlet section  34 . The nose section  18  may include a further likewise tapered section  37  immediately prior to the tapered surface  36  of the hub  21 . 
     The pre-fan section  32  includes a flow conditioner  35  is provided in the form of at least one of a static and adjustable pre-rotator blades  38  that extend radially from the nose section  18  to the outer housing  14 . In examples wherein the pre-rotator blades  38  are adjustable, the pre-rotator blades  38  may be used to control the fan characteristics such as the volumetric flow rate output. When controllable pre-rotator blades  38  are used, the impellor  22  may be operated at a fixed rotation speed and the pre-rotator blades  38  may be used control the volumetric flow rate whilst the impellor  22  is maintained as the fixed speed. 
     The pre-rotator or pre-fan blades  38  guide air to the impeller arrangement  22 . The post-fan section  34  includes one or more flow straighteners  40  provided in the form of turning vanes  42  extending radially from the trailing section  20  to the outer housing  14 . One or both of the pre-rotator blades  38  and the turning vanes  42  support and suspend the inner housing  16  within the outer housing  14 . 
     Referring to  FIGS.  4   a    to  7 , turning now to the impeller  22 , in particular the blades  23 , each blade includes a twisted blade body  50 , a root  52 , a tip  54 , a leading edge  56  and a trailing edge  58 . In this example, each of the blades  23  includes a twist angle between a hub root of the blade and a tip of the blade in the range of about 15 to 30 degrees. 
     The blade body  50  has a substantially constant thickness across the chord and length. To achieve the constant thickness the blades  23  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  23  function by increasing velocity imparted to the flow through the impeller  22  without substantially increase of pressure. The constant thickness or flat blades  23  therefore functions differently to an aerofoil shape that relies mainly on a pressure differential to drive the flow. The leading edge  56 , trailing edge  58  and tip  54  may be rounded or radiussed to reduce turbulence. The constant thickness or flat blades  23  also inhibit stalling especially when used with pre-rotator blades  38  that move through relatively large angles such as +40 degrees to −40 degrees. 
     The impeller  22  may be generally formed of a metal such as mild steel. It may be appreciated, in from  FIG.  4   c   , that the blades  23  occupy much of the space through which air flows through the impeller  22 . In front plan form view, as shown in  FIG.  4   c   , it may also be appreciated that the leading edges  56  and the trailing edges  58  of adjacent blades  23  are substantially parallel. The blade twist angle is best shown in  FIG.  4   d    and is measured between the blade root  52  and the blade tip  54 . The range is about 15 to 30 degrees. However, preferably, the blade twist angle may be about or close to 19 to 23 degrees, and most preferably about 21 degrees. 
     In this example, the chord “CAt” at the tip  54  of the blades  23  is substantially longer relative to the chord “CDr” at the base or root  52  of the blades  23  (best seen by comparing  FIGS.  6  and  7   ). As such, the solidity ratio at the tip “SRt” at Section “A-A” may be in the range of about 0.8 to 1.2, and the solidity ratio “SRr” at Section “D-D” may be in the order of about 1.1 to 1.4. 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  52  of the blades  23  may be shaped or tapered to match the tapering of the hub  21 . 
     The blade tip solidity ratio “SRt” is defined herein as the sum of the tip chord lengths “CAt” of all blades  23  at tips  54  thereof (i.e. measurement of the chord at section A-A of the blades  23  as shown in  FIG.  5   ) divided by the perimeter at the diameter “D” of the blades  23 . By way of example only, the chord width “CAt” of the blade  23  at the tip  54  may be, for example, 350 mm. There may be 11 blades, so 350 mm×11 gives 3850 mm. The diameter “D” may be, for example, 1320 mm. Accordingly, the perimeter is π×D which gives 4147 mm. The “SRt” Ratio in this example is =3850/4147=0.93. Other variations of the “CAt” and “D” may be used. It is noted that “D” is preferably in the range of about 0.8 m to 2.1 m. 
     Similarly, the blade root solidity ratio “SRr” is defined herein as the sum of the root chord lengths “CDr” of all blades at hub  21  outside diameter (i.e. measured at the root  52  at section D-D of the blades  23 ), divided by hub  21  outside perimeter “Hp” (in this example the perimeter is measured at the larger diameter of the tapered hub  21  at 0.7*D where “D” is the diameter the blades  23 ). 
     In this example, the hub  21  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  21  may vary from about, but not limited to, 0.55×D to 0.7×D. 
     Still referring to  FIGS.  6  and  7   , it may be appreciated that the angle of attack “AD” of the blade  23  at the root  52  is less than the angle of attack “AA” at the tip  54 . In this example, the angle of twist between sections A-A &amp; D-D is between 19 to 23 degrees, the applicable fan diameter “D” sizing may be between about 800 mm &amp; 2000 mm tip diameters, and the blade section radius is between 200 to 500 mm. However, as aforesaid, suitable twist angles may be in the range of about 15 to 30 degrees. It is noted that the sections A-A &amp; D-D are generally “arc” shaped due to the applied twist and the profile of the blades  23  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  23  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  22 , as shown in  FIG.  8   . 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 1400 mm. Accordingly, the fan arrangement  10  herein is particularly suitable to the duct ventilation market. Noise is also reduced as shown in  FIG.  9    in comparison to a two-stage axial fan. It is noted that the fan arrangement  10  is capable of pushing about 40 m 3 /s at over 5.7 kPa. A traditional two-stage axial fan of similar diameter will stall at least than 5 kPa and is only capable of about 40 m 3 /s up to about 3.9 kPa. The 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 may be 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:
         Higher pressures for comparable flows: the combination of blade design features and efficient turning vane design leads to a better pressure rise characteristic than comparable axial fans available in the market;   Weight: as the impeller is smaller in size for a given duty, the weight of the impeller will be less than the comparable axial fan on the market at present   Noise: as the impeller is smaller, the blade tip speeds are smaller and thus the generated noise is less;   Installation costs: as only one fan needs to be installed compared to two standard axial fans for a given duty, the installation time is halved;   Maintenance savings: As the impeller is more robust and less dependent on blade shape for impeller performance, the maintenance requirement intervals are likely to be longer;   OH&amp;S concerns: as wear on the standard axial decreases performance dramatically, the likelihood of impeller failure increases due to stall for a given duct length. The risk of injury due to impeller failure is also increased. The delivered air to the end of the duct will decrease to a point that will be insufficient for the work being performed. As generated noise is less, the exposure to high noise sources will be smaller;   Lower power characteristics: the new impulse bladed fan takes advantage of the available motor power compared to the standard axial fan to deliver more pressure at the lower volume end of the curve and slightly higher volumes at lower pressure requirements. The risk of motor overload is reduced without the need for other control systems.       

     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 25%. The improved performance may delay the need for additional fans for longer ducts lengths. These features may also simplify installation and improve the OH&amp;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. 
     Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. 
     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. 
     Many and various modifications will be apparent to those skilled in the art without departing from the scope of the invention disclosed or evident from the disclosure provided herein.