VANEAXIAL BLOWER SYSTEM INCLUDING ROTOR FAN HAVING CURVED BLADES

TECHNICAL FIELD

[0001]The field of the disclosure relates generally to a vaneaxial blower system including a rotor fan having curved blades.

BACKGROUND OF INVENTION

[0002]Blowers are commonly used in the heating, ventilation, and air conditioning (HVAC) industries for moving indoor air. In a known blower, air is drawn into the indoor air moving system and then forced out an outlet into the indoor space. Known blowers include an impeller or fan to move the air through the outlet into the indoor space. The efficiency of a blower when moving high-pressure air can be increased by using a vaneaxial fan, the vaneaxial fan improving the movement of air in the axial direction out the outlet via guide vanes.

[0003]Axial fans can experience stall conditions when the static pressure rise across fan blades reaches the fan operating static pressure developing limit, resulting in a reduction of flow velocity though the fan beyond a level at which the flow velocity initially falls to zero and subsequently reverses. As flow velocity reverses, it causes separation of air from the fan blades resulting in air turbulence with the separated air flow buffeting the fan blades. This aerodynamic instability induces stress within the blades that can result in mechanical failure of the fan motor, which otherwise requires balance across the fan blades to operate efficiently. To mitigate stall conditions, axial fans are conventionally oversized relative to the required specifications of a given application, which is not economical.

[0004]Therefore, there is a need in the art to provide vaneaxial blower systems that can improve laminar flow, improve the static pressure profile of the blower, and reduce turbulence of the fan blades.

BRIEF DESCRIPTION

[0005]In one aspect, a vaneaxial blower system has an axis of rotation and includes a rotor fan and a stator. The rotor fan includes a hub, a rotor inlet, a rotor outlet, and rotor blades. Each rotor blade of the rotor blades has a hub end coupled to the hub, a tip end opposite the hub end, a leading edge extending between the hub end and the tip end, and a trailing edge extending between the hub end and the tip end. The stator includes a stator inlet, a stator outlet, and stator blades. The stator blades are positioned downstream from the rotor blades. Each rotor blade has a hub width between the trailing edge and the leading edge at the hub end, and a tip width between the trailing edge and the leading edge at the tip end. The tip width is larger than the hub width. The trailing edge of each rotor blade includes a concave portion and a convex portion forming an S-shape. The concave portion extends from the tip end to the convex portion. The convex portion extends from the concave portion to the hub end.

[0006]In another aspect, a rotor fan for a vaneaxial blower system has an axis of rotation, and includes a hub, a rotor inlet, a rotor outlet, and rotor blades. Each rotor blade of the rotor blades has a hub end coupled to the hub, a tip end opposite the hub end, a leading edge extending between the hub end and the tip end, and a trailing edge extending between the hub end and the tip end. Each rotor blade has a hub width between the trailing edge and the leading edge at the hub end, and a tip width between the trailing edge and the leading edge at the tip end. The tip width is larger than the hub width. The trailing edge of each rotor blade includes a concave portion and a convex portion forming an S-shape. The concave portion extends from the tip end to the convex portion. The convex portion extends from the concave portion to the hub end.

[0007]In yet another aspect, a method of assembling a vaneaxial blower system having an axis of rotation includes coupling a rotor fan to a stator such that the stator is positioned downstream from the rotor fan. The rotor fan includes a hub, a rotor inlet, a rotor outlet, and rotor blades. The method also includes positioning the rotor blades around the hub such that the rotor fan rotates around the axis of rotation and directs airflow toward stator blades of the stator. Each rotor blade of the rotor blades has a hub end coupled to the hub, a tip end opposite the hub end, a leading edge extending between the hub end and the tip end, and a trailing edge extending between the hub end and the tip end. Each rotor blade has a hub width between the trailing edge and the leading edge at the hub end, and a tip width between the trailing edge and the leading edge at the tip end. The tip width is larger than the hub width. The trailing edge of each rotor blade includes a concave portion and a convex portion forming an S-shape. The concave portion extends from the tip end to the convex portion. The convex portion extends from the concave portion to the hub end.

[0008]These and other aspects and features of the present disclosure will be more readily understood when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a side view of an example vaneaxial blower system, the vaneaxial blower system including a rotor fan and a stator;

[0010]FIG. 2 is an end view of the vaneaxial blower system shown in FIG. 1;

[0011]FIG. 3 is a perspective view of the rotor fan of the vaneaxial blower system shown in FIG. 1;

[0012]FIG. 4 is another perspective view of the rotor fan shown in FIG. 3;

[0013]FIG. 5 is a perspective view of the stator of the vaneaxial blower system shown in FIG. 1;

[0014]FIG. 6 is an end view of the stator shown in FIG. 5;

[0015]FIG. 7 is a perspective view of an example rotor blade of the rotor fan shown in FIGS. 3 and 4;

[0016]FIG. 8 is an end view of the rotor blade shown in FIG. 7, illustrating a tip end of the rotor blade;

[0017]FIG. 9 is an end view of the rotor blade shown in FIG. 7, illustrating a trailing edge of the rotor blade;

[0018]FIG. 10 is an end view of the rotor blade shown in FIG. 7, illustrating a leading edge of the rotor blade;

[0019]FIG. 11 is an end view of the rotor blade shown in FIG. 7, illustrating a hub end of the rotor blade;

[0020]FIG. 12 is a perspective view of an example stator blade of the stator shown in FIGS. 5 and 6;

[0021]FIG. 13 is an end view of the stator blade shown in FIG. 12, illustrating a tip end of the stator blade;

[0022]FIG. 14 is an end view of the stator blade shown in FIG. 12, illustrating a hub end of the stator blade;

[0023]FIG. 15 is a perspective view of alternative embodiment of a rotor blade for use with the vaneaxial blower system shown in FIG. 1;

[0024]FIGS. 16A and 16B are schematic diagrams of rotor blade and stator blade angles of an example vaneaxial blower blade;

[0025]FIG. 17 is a table of example rotor blade angles at various points along the rotor blade span;

[0026]FIG. 18 is a table of example rotor blade chord lengths at various points along the rotor blade span; and

[0027]FIG. 19 is a schematic diagram of a representative blade illustrating definitions of sweep angles for blades.

[0028]The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.

DETAILED DESCRIPTION

[0029]In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings.

[0030]As used herein, the spatial terms “upper,” “lower,” “top” and “bottom” as used in the present disclosure shall denote a component, or an element of a component, which is upstream or downstream relative to other components and elements of components unless the context clearly dictates otherwise. The term “upper” or “top” shall denote a downstream component or element of a component, and the term “lower” or “bottom” shall denote an upstream component or element of a component. Where a component has a top surface and a bottom surface, the top surface is parallel to the bottom surface. Such relative spatial terms are used only to facilitate description and are not meant to be limiting.

[0031]The embodiments described herein relate to a vaneaxial blower system. More specifically, embodiments relate to a vaneaxial blower system including a rotor fan and a stator with blades that can improve laminar flow, improve the static pressure profile of the blower, and reduce turbulence of the fan blades. For example, the fan blade shape is optimized. In particular, the shape and geometry of each blade, as well as the distance between blades can affect the static pressure profile of the axial fan and thus mitigate stalling conditions. Additional embodiments can include a retrofit system package and reduced sound output.

[0032]FIGS. 1 and 2 illustrate an example embodiment of a vaneaxial blower system 100. Vaneaxial blower system 100 includes a rotor 102 and a stator 104 positioned downstream from rotor 102, as defined by the direction of airflow 106 channeled through vaneaxial blower system 100. Due at least in part to configurations of rotor 102 and stator 104, vaneaxial blower system 100 provides improved performance in comparison to conventional systems. For example, in a wind tunnel performance evaluation, vaneaxial blower system 100 provides a static head of 2.3 inches of water column, at a flow of 1500 cubic feet per minute, rotations per minute of 2,400, a power consumption of 967 watts, and a noise of less than 55 decibels.

[0033]In some embodiments, vaneaxial blower system 100 further includes a motor (not shown) coupled to rotor 102. For example, the motor may include a motor casing and a motor shaft extending therefrom. In some embodiments, the motor is coupled within vaneaxial blower system 100 by mounting the motor casing to stator 104. The motor shaft extends from the motor casing for coupling to rotor 102. Thus, rotation of rotor 102 is enabled by the actuation of the motor and the resulting rotation of the motor shaft. For example, rotor 102 rotates in a rotation direction R1, as shown in FIG. 2. In further embodiments, the rotor 102 is caused to rotate in any suitable manner.

[0034]As illustrated in FIGS. 1-4, rotor 102 includes a rotor fan 108 and a rotor shroud 114 extending around rotor fan 108. Rotor fan 108 includes a rotor hub 112 and a plurality of rotor blades 116 arranged circumferentially about rotor hub 112 and extending between rotor hub 112 and rotor shroud 114. In some embodiments, rotor fan 108 includes seven to nine of rotor blades 116. Rotor fan 108 has an inner diameter in a range 8.5 inches (in.) to 9.5 in., and an outer diameter in a range of 15 in. to 16 in. In alternative embodiments, rotor fan 108 includes any number of rotor blades 116 and is any suitable size.

[0035]Rotor 102 includes a rotor inlet 118 and a rotor outlet 120 defined at least in part by rotor shroud 114. Rotor inlet 118 is positioned in downstream communication from the blower system inlet. Rotor shroud 114 may be shaped to facilitate receiving airflow 106 within rotor inlet 118. For example, rotor shroud 114 includes a first rim 122 defining rotor inlet 118. Rotor shroud 114 further includes a flared inlet section 124 extending from first rim 122, and a main body section 126 extending from flared inlet section 124. In the illustrated example, flared inlet section 124 has a frustoconical shape such that first rim 122 has a larger diameter than main body section 126.

[0036]In some embodiments, vaneaxial blower system 100 includes an inlet air flow director (not shown) coupled to rotor 102 and positioned upstream of rotor inlet 118. In at least some embodiments, vaneaxial blower system 100 is positioned within an air moving system that can have a square, circular, or other suitable geometric cross-sectional shape. For example, the inlet air flow director is shaped to direct airflow 106 channeled through a duct into rotor inlet 118 of vaneaxial blower system 100.

[0037]Rotor hub 112 includes an inner cap 128, an outer ring 130, and an annular wall 132 extending radially between inner cap 128 and outer ring 130. A plurality of spokes 134 extend axially from annular wall 132 and radially between inner cap 128 and outer ring 130 to provide support to rotor 102. In the example, a cone 136 is coupled to rotor hub 112 and extends radially from rotor hub 112 on the inlet side. Cone 136 facilitates airflow 106 entering rotor fan 108 through rotor inlet 118 and being directed towards rotor blades 116. In alternative embodiments, rotor fan 108 includes any rotor hub 112 that enables rotor fan 108 to operate as described herein.

[0038]As illustrated in FIGS. 5 and 6, stator 104 includes a stator hub 138, a stator shroud 140, a plurality of stator blades 142 extending therebetween, a stator inlet 144, and a stator outlet 146. In the example embodiment, stator shroud 140 at least partly defines stator inlet 144 and stator outlet 146. Stator inlet 144 is positioned in downstream communication from rotor outlet 120. Stator outlet 146 is arranged for airflow 106 to exit stator 104.

[0039]In the example, stator hub 138 includes an inner ring 148, an outer ring 150, and an annular wall 152 extending radially between inner ring 148 and outer ring 150. A plurality of spokes 154 extend axially from annular wall 152 and radially between inner ring 148 and outer ring 150. Inner ring 148 may be used as a mounting point for a motor (not shown). For example, a motor may be press fit (as a whole motor or using stator hub 138 as a shell) into stator hub 138 such that stator hub 138 acts as a heat sink that is subject to convection of the airflow channeled through stator 104. In the example, a cone 156 is coupled to stator hub 138 and extends axially outward from stator hub 138 on the outlet side. Cone 156 facilitates airflow exiting stator outlet 146. In alternative embodiments, stator 104 includes any stator hub 138 that enables stator 104 to operate as described herein.

[0040]Referring to FIGS. 1-6, during operation, rotor 102 rotates under the power of a motor while stator 104 remains stationary. Airflow 106 enters vaneaxial blower system 100 via a blower system inlet and travels toward rotor 102. Airflow 106 enters rotor 102 from a hemispherical area in front of rotor inlet 118. Airflow 106 enters rotor shroud 114 through rotor inlet 118, flows through rotor shroud 114, interacts with rotor blades 116 and is then discharged from rotor 102 through rotor outlet 120 towards stator 104. Rotor blades 116 split airflow 106 into two streams (suction and pressure) as rotor 102 accelerates to a required velocity and smoothly reunite the streams at trailing edge 164 of rotor blades 116. Rotor blades 116 have an angle-of-attack such that they will produce air movement (airflow) through rotor 102. Airflow 106 accelerates to a desired velocity as it follows across the rotor blade 116 surface. Rotor blades 116 are oriented such that airflow 106 discharged from rotor 102 has a directional component that is generally non-linear relative to a centerline.

[0041]A boundary layer develops across leading edge 162 of the rotor blade 116, radially outward from rotor hub 112 and from leading edge 162 to trailing edge 164. The air remains attached to rotor blade 116 as long as the velocity, viscosity, and friction parameters remain balanced. If the velocity is too high, the boundary layer will separate from the surface and begin to tumble, which indicates the onset of a stall condition and is detrimental to the overall performance. The provided geometries (angles and measurements) along rotor blades 116 contribute to the smooth flow of air along rotor blades 116 from leading edge 162 to trailing edge 164 and from rotor hub 112 to the blade tip. This geometry is selected such that the pressure, flow, sound, and power consumption are optimized.

[0042]Airflow 106 enters stator 104 via stator inlet 144 and travels through stator 104, in the direction of a blower system outlet. Stator blades 142 are oriented to straighten airflow 106 that flows to the stator 104 from rotor 102, and discharge airflow 106 from stator 104 that is generally longitudinally aligned with a centerline. Airflow 106 is discharged from stator 104 through stator outlet 146.

[0043]Stator blades 142 are configured with a geometry such that, as the air leaves trailing edge 208 of rotor blades 116, the air attaches to stator blades 142 with as little turbulence as possible. Stator blades 142 are configured to straighten any swirling airflow from rotor 102 and to convert the velocity of the air to pressure by reducing the velocity. The geometry is therefore selected to reduce the occurrences of air separation and minimize noise created from the conversion of air velocity to pressure.

[0044]The geometry (angle and contour) of blades 116, 142 at respective hubs 112, 138 contribute not only to the mechanical strength of blades 116, 142 but to the angle-of-attack. The selection of the geometry can limit the amount of change to the contour of blades 116, 142. As the chords of blades 116, 142 move away from respective hubs 112, 138, blades 116, 142 are contoured to provide the optimal performance within the limits of the above requirements insomuch as the boundary layer does not separate and blades 116, 142 are manufacturable based on the selected method of manufacture; molded, machined, and the like.

[0045]At the tip of rotor blade 116, the geometry selected is optimized to the same requirements with the added consideration of the air flowing radially off the tip of rotor blade 116. Techniques can be used, by varying the design angles and contours of the tip, to minimize these tip effects. Noise can be a major consideration when selecting these parameters. Stator 104 has the same requirements as rotor 102 with the exception that the tips of stator blades 142 are attached to the stator shroud 140 in some examples, which provides structural support to stator blades 142. The contour along the chord and span of blades 116, 142 between respective hubs 112, 138 and tips can be selected within the limits of manufacturability to optimize the attached flow along blades 116, 142. Additionally, trailing edge 164 of rotor blades 116 are axially spaced from leading edge 162 of stator blades 142 by an optimized distance based on the radial distance from the rotation axis.

[0046]In the example embodiment, the cross-sections of rotor blades 116 and stator blades 142 are substantially constant in thickness. Alternatively, rotor blades 116 and stator blades 142 may define an airfoil shape having a thickness that changes between the trailing and leading edges.

[0047]In the example, the angles of rotor blades 116 and stator blades 142 are optimized for minimal flow separation along the blade span through the majority of operating conditions. Such minimal flow separation increases the efficiency and reduces the sound emission of vaneaxial blower system 100. Additionally, the number of rotor blades 116 and stator blades 142 is optimized based on at least one design criteria, such as desired airflow (CFM), static pressure, and efficiency. In the example embodiment, rotor 102 includes nine rotor blades 116 and stator 104 includes twenty-one stator blades 142. Alternatively, rotor 102 and stator 104 can include any number of blades that facilitates operation of vaneaxial blower system 100 as described herein. The cross-sections of rotor blades 116 and stator blades 142 are substantially constant in thickness. Alternatively, rotor blades 116 and stator blades 142 can define an airfoil shape having a thickness that changes between the trailing and leading edges.

[0048]FIGS. 7-15 illustrate the geometry of rotor blades 116 and stator blades 142 of vaneaxial blower system 100. As shown in FIGS. 7-11, in the example embodiment, each rotor blade 116 includes a hub end 158 coupled to rotor hub 112 (shown in FIG. 3), a tip end 160 opposite hub end 158, a leading edge 162 positioned on rotor inlet 118 side of rotor blade 116, and a trailing edge 164 positioned on rotor outlet 120 side of rotor blade 116. Leading edge 162 and trailing edge 164 each extend between hub end 158 and tip end 160.

[0049]In the example, trailing edge 164 of each rotor blade 116 is curved. For example, trailing edge 164 of each rotor blade 116 includes a concave portion 166 and a convex portion 168 forming an S-shape. Concave refers to an edge or surface that curves inward toward an interior of blade 116 to define a bowl shape. Convex refers to an edge or surface that curves outward from an interior of blade 116 to define a bulge. Concave portion 166 of trailing edge 164 extends from tip end 160 of rotor blade 116 to convex portion 168 of trailing edge 164. Convex portion 168 of trailing edge 164 extends from concave portion 166 of trailing edge 164 to hub end 158 of rotor blade 116. Accordingly, trailing edge 164 is curved along its entire extension. In the example, concave portion 166 and convex portion 168 each extend along approximately half the extension of rotor blade 116.

[0050]In addition, concave portion 166 has a first radius and convex portion 168 has a second radius. The first radius is different from the second radius. For example, the first radius is larger than the second radius. Moreover, in the example, the first radius of concave portion 166 varies between tip end 160 of rotor blade 116 and convex portion 168 of trailing edge 164. In addition, the second radius of convex portion 168 varies between concave portion 166 of trailing edge 164 and hub end 158 of rotor blade 116.

[0051]In addition, in the example, leading edge 162 is curved. For example, leading edge 162 is concave. In addition, leading edge 162 has a radius that changes along the extension of leading edge 162. For example, the radius of leading edge 162 decreases from hub end 158 to tip end 160 such that leading edge 162 has a more pronounced curve toward tip end 160.

[0052]The curves of trailing edge 164 and leading edge 162 provide specific characteristics for rotor blade 116 and improve performance of rotor blade 116. For example, trailing edge 164 and leading edge 162 curve away from each other approaching tip end 160 to provide an increased width and an increased loading at tip end 160.

[0053]For example, each rotor blade 116 has a hub width HW between trailing edge 164 and leading edge 162 of rotor blade 116 at hub end 158, and a tip width TW between trailing edge 164 and leading edge 162 of rotor blade 116 at tip end 160. Hub width HW and tip width TW are measured in a direction parallel to the axis of rotation of rotor blade 116. In the example, tip width TW is larger than hub width HW. As a result, rotor blades 116 have an increased loading near tip end 160 and a reduced loading near hub end 158, which can be a high loss region. Therefore, rotor blades 116 improve overall efficiency of rotor fan 108 and reduce lower broadband noise generated by the system.

[0054]Moreover, in the example, tip end 160 of rotor blade 116 includes a tip edge 170 extending from leading edge 162 to trailing edge 164. In the example, tip edge 170 is curved and has a radius. For example, the radius of tip edge 170 changes along the extension of tip edge 170. Tip edge 170 may be concave, convex, or combinations thereof. In the example, tip edge 170 is convex along its entire extension.

[0055]In addition, in the example, a blade height is a distance measured from leading edge 162 to trailing edge 164 in a direction perpendicular to the axis of rotation of rotor blade 116. For example, rotor blade 116 has a blade height 165 (shown in FIG. 11) at hub end 158 in a range of 1.7 in. to 1.9 in. and a blade height 167 (shown in FIG. 8) at tip end 160 in a range of 1.7 in. to 1.8 in.

[0056]As seen in FIGS. 12-14, each stator blade 142 includes a hub end 172 coupled to stator hub 138, a shroud end 174 coupled to stator shroud 140, a leading edge 176 positioned on stator inlet 144 side of stator blade 142, and a trailing edge 178 positioned on stator outlet 146 side of the stator blade 142. Leading edge 176 and trailing edge 178 each extend between hub end 172 and shroud end 174.

[0057]In the example, hub end 172 and shroud end 174 of stator blade 142 are curved and not parallel to each other. For example, hub end 172 and shroud end 174 of stator blade 142 each have a radius that changes along their extensions.

[0058]In addition, in the example, leading edge 176 and trailing edge 178 of stator blade 142 are curved and not parallel to each other. For example, leading edge 176 and trailing edge 178 of stator blade 142 each have a radius that changes along their extensions.

[0059]FIG. 15 is a perspective view of an example rotor blade 200 for use with rotor fan 108 (shown in FIG. 1). Rotor blade 200 includes a hub end 202, a tip end 204 opposite hub end 202, a leading edge 206, and a trailing edge 208. Leading edge 206 and trailing edge 208 each extend between hub end 202 and tip end 204.

[0060]In the example, trailing edge 208 of rotor blade 200 includes a concave portion 210 and a convex portion 212 forming an S-shape. In addition, leading edge 206 is curved in a concave shape along its entire extension. Moreover, rotor blade 200 has an increased width from a midpoint to tip end 204 because leading edge 206 and trailing edge 208 are curved away from each other toward tip end 204. As a result, rotor blade 200 has an increased loading near tip end 204 and a reduced loading near hub end 202 which can be a high loss region. Therefore, rotor blade 200 improves overall efficiency of rotor fan 108 (shown in FIG. 1) and reduces lower broadband noise generated by the system.

[0061]Rotor blade 200 has a pronounced loading on tip end 204. For example, the ratio of a tip width to a hub width for rotor blade 200 is at least two. In addition, the curves of leading edge 206, trailing edge 208, hub end 202, and tip end 204 provide a profile of rotor blade 200 that facilitates flow attaching to rotor blade 200. In addition, rotor blade 200 includes surfaces (e.g., a suction surface and a pressure surface) 214 that extend between the edges and provide curves following or adding to curves of the edges and facilitate rotor blade 200 interacting with airflow. In the example, surfaces 214 are smooth and free of any features (e.g., holes, protrusions, indents, ribs, etc.).

[0062]FIGS. 16A and 16B are schematic diagrams of a representative blade 300 illustrating definitions of angles for blades (e.g., blades 116, 142, 200 shown in FIGS. 7, 12, and 15). Blade 300 includes a leading edge 302, a trailing edge 304, a tip 306, and a hub 308, and has a center of rotation 310.

[0063]The geometry of blade 300 is optimized by selecting angles of blade 300 to provide desired flow conditions of blade 300. For example, beta (B) and theta (0) angles characterize the geometry of blade 300 at various points along a span of blade 300. Beta (B) and theta (0) angles can be defined by M-prime coordinates in an M-prime vs. Theta coordinate system. M-prime coordinates are converted from Cartesian coordinates in x, y, z format by taking a slice S1 of the blade 300 at a selected span location in a 3-D cartesian space, as shown in FIG. 16A. For example, the slice S1 may be taken at a 50% span of the blade 300 determined by revolving a mean streamline about the Z-axis and intersecting the blade 300. The slice S1 is translated to a flat surface without distorting angles or lengths, as shown in FIG. 16B, to convert the Cartesian coordinates in x, y, z format to M coordinates (m, s). In M coordinates, “m” is the meridional location and “s” is the meridional length fraction. The M coordinates are divided by a radius R to provide M-prime coordinates (m′, theta) as shown in FIG. 16B. Angle θ is defined as an angle measured between a vertical axis 312 and the radius R extending to a point on the slice S1. Radius R and the vertical axis 312 extend through the center axis of rotation 310 of blade 300. A positive angle θ is measured clockwise, and a negative angle θ is measured counter-clockwise from vertical axis 312 shown in FIG. 16A. The slice can be defined along blade 300, for example in reference to hub 308, tip 306, and/or mid-span.

[0064]As shown in FIG. 16B, the beta (β) angle is defined as the slope of a camber line 314 of blade 300 at a point of reference along the blade 300. Angle β may be measured between the M-prime axis and a line 316 that is tangent to camber line 314 at the point of reference along the blade 300. For example, FIG. 16B shows angle β for the leading edge 302 of the blade 300. A positive angle β is measured clockwise, and a negative angle β is measured counter-clockwise from the M-Prime axis shown in FIG. 16B. Equation Eq (1) states the relationship between angle β and angle β.

β=tan⁻¹(ds/dm)=tan⁻¹(r*dθ/dm)   Eq (1)

[0065]These beta and theta angles are optimized at various spans across the blade such as Span 0 (hub), Span 0.5 (half the width of the blade), and Span 1 (shroud or tip of blade). The blade is then swept to intersect these geometries at the various spans which defines the geometry of the blade. Since the geometries at the various spans form the overall geometry of the blade, any changes to the beta and/or theta angle at any span length will impact the output conditions of the blade.

[0066]The configurations of beta and theta angles of blades are optimized to provide specific flow rate at a specific pressure. Generally, in optimizing for flow rate and pressure, the parameters considered are flow rate, static pressure, noise, and power consumption. The requirement for noise level is to not exceed noise level requirements of centrifugal fans used in the art for the particular application (such as residential or commercial settings which require low noise levels). The power efficiency is at a maximum for the parameters considered. The blade geometry and angles are selected to achieve the optimum combination of these requirements. An iterative process was employed to vary these angles and arrive at the optimum combination.

[0067]FIG. 17 is a table of example rotor blade 116 angles at various points along the rotor blade 116 span. Specifically, FIG. 17 illustrates a range of beta angles and theta angles for leading edge 162 and trailing edge 164 of rotor blades 116 at each of span 0, span 0.5, and span 1. For example, at the rotor hub, the angle beta for leading edge 162 is in the range of 70 degrees to 80 degrees and the angle beta for trailing edge 164 is in the range of 25 degrees to 35 degrees. At the tip end, the angle beta for leading edge 162 is in the range of 80 degrees to 90 degrees and the angle beta for trailing edge 164 is in the range of 60 degrees to 70 degrees. A a span half a distance from the hub end to the tip end, the angle beta for leading edge 162 is in the range of 70 degrees to 80 degrees and the angle beta for trailing edge 164 is in the range of 55 degrees to 70 degrees.

[0068]FIG. 18 is a table of example rotor blade 116 chord lengths at various points along rotor blade 116 span. Specifically, FIG. 18 illustrates chord lengths for rotor blades 116 at each of span 1 (tip end), span 0.75, span 0.5, span 0.25, and span 0 (hub end). Chord length is measured by a straight line extending between points on leading edge 162 and trailing edge 164. For example, rotor blade 116 has a chord length of 5.34 inches (in.) at tip end 160, a chord length of 4.46 in. at span 0.75, a chord length of 0.50 in. at span 0.5, a chord length of 3.97 in. at span 0.25, and a chord length of 3.04 at hub end 158. Accordingly, rotor blade 116 has a larger chord length at tip end 160 and the chord length decreases towards hub end 158, which results in a larger loading on tip end 160 than on hub end 158.

[0069]FIG. 19 is a schematic diagram of a representative blade 400 illustrating definitions of sweep angles for blades (e.g., blades 116, 142, 200 shown in FIGS. 7, 12, and 15). Blade 400 includes a leading edge 402, a trailing edge 404, a tip end 406, and a hub end 408. Also, blade 400 has an axis of rotation 410 and a slice line S2 extending midway between leading edge 402 and trailing edge 404. A sweep angle is defined as an angle measured between a line perpendicular to axis of rotation 410 and a line tangent to slice line S2 at a designated point on span of blade 400. A forward sweep is measured counterclockwise from the perpendicular line and a backward sweep is measured clockwise from the perpendicular line. For example, blade 400 has a backward sweep angle SA1 at tip end 406 and a forward sweep angle SA2 at hub end 408.

[0070]Referring to FIG. 7, for example, blade 116 has a forward sweep angle at tip end 160 in a range of 5° to 8° and a backward sweep angle at hub end 158 in a range of 18° to 23°.

[0071]Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from the study of the drawings, the disclosure, and the appended claims. In the claims the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the claims.

[0072]While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or example and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments.

[0073]The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.

[0074]This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.