Axial fan configurations

Abstract

A two stage axial fan includes a tubular fan housing, first and second motors which are positioned in series in the fan housing, a first impeller which is positioned in the fan housing and is driven by the first motor, and a second impeller which is positioned in the fan housing and is driven by the second motor. The first motor is positioned on a first foot-mounted motor support structure which is connected to the fan housing and the second motor is positioned on a second foot-mounted motor support structure which is connected to the fan housing.

Claims

1. A two stage axial fan which comprises: a tubular fan housing; a first impeller which is positioned in the fan housing and is driven by a first motor; and a second impeller which is positioned in the fan housing and is driven by a second motor; wherein the first and second impellers are positioned coaxially and the first impeller is positioned upstream of the second impeller; wherein the first impeller comprises a tip stagger angle of between 40° and 65° and a radius ratio of between 0.4 and 0.65, and wherein the second impeller comprises a tip stagger angle of between 45° and 70° and a radius ratio of between 0.4 and 0.65; and wherein the first and second impellers are driven by the motors to rotate in opposite directions.

2. The two-stage axial fan of claim 1, wherein each of the first and second impellers comprises a tip stagger angle of 45°, a hub stagger angle of 16° and a radius ratio of 0.50.

3. The two-stage axial fan of claim 1, wherein the first impeller is rotated at a first speed and the second impeller is rotated at a second speed which is 0.8 times the first speed, and wherein the first impeller comprises a tip stagger angle of 58°, a hub stagger angle of 38° and a radius ratio of 0.65, and the second impeller comprises a tip stagger angle of 59°, a hub stagger angle of 53° and a radius ratio of 0.65.

4. The two-stage axial fan of claim 3, wherein the first impeller comprises a tip camber angle of 19° and a hub camber angle of 35°, and wherein the second impeller comprises a tip camber angle of 23° and a hub camber angle of 28°.

5. The two-stage axial fan of claim 4, wherein the first impeller comprises a midspan solidity of 1.0 and an aspect ratio of 0.7, and wherein the second impeller comprises a midspan solidity of 0.9 and an aspect ratio of 0.6.

6. The two-stage axial fan of claim 1, wherein the first impeller comprises a tip stagger angle of between 40° and 60° and a radius ratio of between 0.4 and 0.6, and wherein the second impeller comprises a tip stagger angle of between 50° and 70° and a radius ratio of between 0.4 and 0.6.

7. The two-stage axial fan of claim 6, wherein the first impeller comprises a tip stagger angle of 45°, a hub stagger angle of 16° and a radius ratio of 0.5, and wherein the second impeller comprises a tip stagger angle of 55°, a hub stagger angle of 46° and a radius ratio of 0.5.

8. The two-stage axial fan of claim 7, wherein the first impeller comprises a tip camber angle of 23° and a hub camber angle of 41°, and wherein the second impeller comprises a tip camber angle of 27° and a hub camber angle of 37°.

9. The two-stage axial fan of claim 8, wherein the first impeller comprises a midspan solidity of 1.1 and an aspect ratio of 1.1, and wherein the second impeller comprises a midspan solidity of 0.8 and an aspect ratio of 1.0.

10. The two stage axial fan of any of claims 1-9, wherein the first impeller is positioned upstream of the second impeller and the first and second impellers are positioned between the first and second motors.

11. A two stage axial fan which comprises: a tubular fan housing; a first impeller which is positioned in the fan housing and is driven by a first motor; and a second impeller which is positioned in the fan housing and is driven by a second motor; wherein the fan comprises a flow coefficient at free air which is greater than or equal to 0.15; wherein the first impeller comprises a tip stagger angle of between 40° and 60° and a radius ratio of less than or equal to 0.6, and wherein the second impeller comprises a tip stagger angle of between 50° and 70° and a radius ratio of less than or equal to 0.6; and wherein the first and second impellers have different tip stagger angles and the same radius ratio.

12. The two-stage axial fan of claim 11, wherein the first impeller comprises a tip stagger angle of 45°, a hub stagger angle of 16° and a radius ratio of 0.5, and wherein the second impeller comprises a tip stagger angle of 55°, a hub stagger angle of 46° and a radius ratio of 0.5.

13. The two-stage axial fan of claim 12, wherein the first impeller comprises a tip camber angle of 23° and a hub camber angle of 41°, and wherein the second impeller comprises a tip camber angle of 27° and a hub camber angle of 37°.

14. The two-stage axial fan of claim 13, wherein the first impeller comprises a midspan solidity of 1.1 and an aspect ratio of 1.1, and wherein the second impeller comprises a midspan solidity of 0.8 and an aspect ratio of 1.0.

15. The two stage axial fan of claim 11, wherein the first and second impellers are driven by the motors to rotate in the same direction.

16. The two stage axial fan of claim 15, wherein the first motor is positioned upstream of the second motor, the first impeller is positioned between the first and second motors, and the second impeller is positioned downstream of the second motor.

17. The two stage axial fan of any of claim 11 or 12-14, wherein the first and second impellers are driven by the motors to rotate in opposite directions.

18. The two stage axial fan of claim 17, wherein the first motor is positioned upstream of the second motor and the first and second impellers are positioned between the first and second motors.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a side elevation representation of a prior art tube-axial fan;

(2) FIG. 2 is a side elevation representation of a prior art vane-axial fan;

(3) FIG. 3 is a graph comparing the performance of a single vane-axial fan, two vane-axial fans in series and a counter-rotating fan;

(4) FIG. 4 is a side elevation representation of a prior art counter-rotating fan with cantilevered motors;

(5) FIG. 5 is a side elevation representation of a prior art counter-rotating fan having a transmission for driving both impellers with a single motor;

(6) FIG. 6 is a graph comparing the performance of a tube-axial fan and vane-axial fan;

(7) FIG. 7 is a graph, similar to FIG. 3, comparing the performance of a single vane-axial fan, two vane-axial fans in series and a counter-rotating fan;

(8) FIG. 8 is a graph showing an example of a fan performance curve;

(9) FIG. 9 is a graph showing an example of a fan performance curve for an embodiment of the fan of the present invention;

(10) FIG. 10 is a graph showing the flow advantage of an embodiment of the fan of the present invention by comparing conventional two stage fans with a high flow counter-rotating fan;

(11) FIG. 10A is a graph showing the performance of the fan represented in Table 1 in terms of flow coefficient and pressure coefficient;

(12) FIG. 11 is a side elevation representation of one embodiment of the fan of the present invention;

(13) FIG. 12 is a side elevation representation of another embodiment of the fan of the present invention;

(14) FIGS. 13A and 13B are side elevation representations of a reversible vane component which in FIG. 13A is oriented to function as an outlet guide vane and in FIG. 13B is oriented to function an inlet guide vane

(15) FIG. 14 is a representation of an axial fan system which can be configured to create a plurality of individual axial fans; and

(16) FIG. 15 is a graph showing the performance of the axial fans depicted in FIG. 14 in terms of flow coefficient and pressure coefficient.

DETAILED DESCRIPTION OF THE INVENTION

(17) The present invention is applicable to both co-rotating and counter-rotating fans. Nevertheless, a person of ordinary skill in the art will readily appreciate how the teachings of the present invention can be applied to other types of fans. Therefore, the following description should not be construed to limit the scope of the present invention in any manner.

(18) Referring to FIG. 8, fan performance can be described using a graph of static pressure rise vs. airflow, where static pressure rise is defined as the exit static pressure minus the inlet total pressure of the fan. A design point established early in the design phase is the performance target to be achieved for the fan, and this target is used as an operating point for conducting design analysis and optimization. It is common for the stall boundary for a fan to occur at a flow at least 20% lower than the design point flow rate. The fan performance curve of FIG. 8 represents fan performance at various back pressure conditions. The normal operating range of the fan, which is indicated by the solid line, exists between zero static pressure rise, also known as free-air, and the stall boundary. As a result, only the solid line portion of the fan curve represents fan performance. The region beyond free-air having negative pressure rise, which is represented in FIG. 8 by the dashed line, is not a physically realistic operating region for an isolated fan.

(19) In accordance with the present invention, two impellers that are optimized for design points in the negative pressure rise region are combined in series to achieve a two stage fan which is capable of achieving high flow rates and possesses a broad operating range.

(20) An example performance graph for an 18 inch diameter CR fan which embodies the principles of the present invention is shown in FIG. 9. In this example, both impellers have design points located in the negative static pressure rise region, with their respective stall boundaries located approximately 20% lower than the design point flow, and with much of their individual performance curves residing in the negative pressure rise region. As shown in FIG. 9, the performance of each impeller is defined with respect to its inlet total pressure, so that the inlet total pressure of impeller #2 corresponds to the exit total pressure of impeller #1. As may be seen, while the individual performance curves have a narrow range of operation with positive pressure rise, the combined curve enjoys a large operating range with a high flow rate and positive pressure rise.

(21) The flow advantage obtained by designing a two stage fan with the design points of both impellers in the negative pressure rise region is demonstrated in FIG. 10. In this figure the “High Flow CR” curve represents a design based on the present invention which uses the same motors as the other represented designs. As is evident from FIG. 10, the present invention provides a substantial increase in flow compared to conventional two-stage designs, particularly for low impedance applications.

(22) Impellers designed in accordance with the present invention feature low stagger angles and low to moderate radius ratios. Suitable values for such parameters are set forth in Table 1 below. In Table 1, the flow coefficient is a performance parameter which will be defined below.

(23) TABLE-US-00001 TABLE 1 Impeller Geometry Ranges Tip Radius Flow Coefficient Impeller # Stagger Ratio at Free Air 1 40°-60° ≤0.6 ≥0.15 2 50°-70° ≤0.6 ≥0.15

(24) The impellers of one embodiment of the present invention comprise the stagger angles and radius ratios shown in Table 2. The stagger angle is defined as the angle between the chord line and the axial direction, and the radius ratio is defined as the blade hub radius divided by the blade tip radius. As will be apparent, the specific stagger angles referred to herein are listed as absolute values. A broad array of solidity and aspect ratio may be suitable depending on the performance targets. Example values of impeller solidity and aspect ratio for the impellers of this embodiment are also specified in Table 2. Midspan solidity is defined as the chord divided by the tangential spacing between blades at midspan. Aspect ratio is defined as the blade height divided by the chord.

(25) TABLE-US-00002 TABLE 2 Example Impeller Geometry Tip/Hub Tip/Hub Radius Midspan Aspect Impeller # Stagger Camber Ratio Solidity Ratio 1 45°/16° 23°/41° 0.5 1.1 1.1 2 55°/46° 27°/37° 0.5 0.8 1.0

(26) The resulting performance of the fan represented in Table 2 is shown in FIG. 10A in terms of the dimensionless global duty parameters of flow coefficient and pressure coefficient. These dimensionless parameters, which enable a convenient way to compare overall aerodynamic performance among fans that accounts for differences in fan size and speed, are defined as follows:

(27) $\mathrm{Flow}\mathrm{Coefficient}\Phi =\frac{Q}{{\mathrm{ND}}^3}$$\mathrm{Pressure}\mathrm{Coefficient}\Psi =\frac{\Delta P}{\rho N^2{D}^2}$
where Q is the volumetric flow rate, N is the rotational speed of the first impeller, D is the tip diameter of the impellers, ΔP is the total-to-static pressure rise, and ρ is the inlet density of the air flow. In this regard, it should be noted that although the rotational speed of the second impeller need not be the same as that of the first impeller, the present invention contemplates that the rotational speed of the second impeller is approximately the same as or less than that of the first impeller.

(28) As shown by the combined curve in FIG. 10A, the fan achieves a flow coefficient of approximately 0.23 in free air. To achieve the design target, both impeller design points have a pressure rise which is near zero or negative, and each impeller operates with negative static pressure rise over much of the normal operating range.

(29) FIG. 11 is a representation of one embodiment of a CR fan of the present invention. The two stage fan of this embodiment, generally 10, is shown to comprise a tubular fan housing 12, two electric motors 14A, 14B which are positioned in series in the fan housing, and two impellers 16A, 16B which are each connected to a corresponding motor. Each motor 14A, 14B is supported on a respective motor support 18A, 18B which is connected to the fan housing 12. The motors 14A, 14B are placed in series to thereby provide more available shaft power to the impellers 16A, 16B compared to a single motor of the same diameter. The motor supports 18A, 18B may be, e.g., conventional foot-mounted motor support structures, which not only provide a robust support for the motors 14A, 14B, but also are able to accept many different standard motor frame sizes. The impellers 16A, 16B are located between the motors 14A, 14B and rotate in opposite directions. This arrangement improves motor cooling by fully exposing the motor housings to a predominantly axial mainstream airflow (indicated by arrow A) which is aligned with the motor cooling fins. In addition, the impellers 16A, 16B act as additional heat sinks to cool the motor drive ends, which as shown in FIG. 11 are not directly exposed to the mainstream airflow A. Maintaining a similar torque for the two impellers contributes to improved performance. By maintaining a similar torque, the swirl generated by the first impeller is removed by the second impeller, resulting in low exit swirl. Low exit swirl helps to minimize pressure losses from the downstream motor and motor supports.

(30) Referring to FIG. 12, the present invention may also be applied to a two stage co-rotating fan. The two stage fan of this embodiment, generally 100, includes a tubular fan housing 12, two electric motors 14A, 14B which are positioned in series in the fan housing, two impellers 16A, 16B which are each connected to a corresponding motor, and two guide vane assemblies 20A, 20B which are each positioned downstream of a corresponding impeller. As in the previous embodiment, each motor 14A, 14B is supported on a respective motor support 18A, 18B which is connected to the fan housing 12. In contrast to the previous embodiment, however, only the first impeller 16A is located between the motors 14A, 14B. In addition, the impellers 16A, 16B rotate in the same direction. Thus, the fan 100 is similar to an assembly of two vane-axial fans in series. However, the individual stage and combined performance of the fan 100 are similar to that described in FIG. 9 for the CR fan example. Likewise, the impeller stagger angles and radius ratios are similar to those of impeller #1 defined in Table 2.

(31) To take advantage of the additional shaft power available from the CR fan design shown in FIG. 11, the impellers may be configured to generate high flow rates, as described above, or to operate at high impedance, such as with a stall impedance 15. Table 3 specifies representative ranges of tip stagger and radius ratio which are applicable to both impeller configurations. High flow configurations feature stagger angles and radius ratios at the lower end of the range. High impedance configurations will generally feature radius ratios and/or stagger angles at the higher end of the range.

(32) TABLE-US-00003 TABLE 3 Impeller Geometry Ranges Tip Radius Impeller # Stagger Ratio 1 40°-65° 0.4-0.65 2 45°-70° 0.4-0.65

(33) Especially for high impedance configurations, designing the second stage to operate at a lower speed than the first stage contributes to improved performance. Designing for lower speed reduces the required blade stagger angles and inlet relative velocity, both of which may become excessively high for the second stage and penalize aerodynamic performance. The speed ratio may be defined as follows:

(34) $\mathrm{Speed}\mathrm{Ratio}=\frac{N2}{N1}$
where N2 is the stage 2 rotational speed and N1 is the stage 1 rotational speed. For variable speed fans, this ratio may be controlled and modified during operation. For fixed speed fans, such as a direct drive fan using AC induction motors without variable frequency drives, the speed ratio remains approximately constant during operation and is determined by the respective motor pole counts. A suitable range for the speed ratio is approximately 0.5-1.0.

(35) The impellers of one embodiment of the high impedance configuration comprise the speed ratio, stagger angles, and radius ratios shown in Table 4. A broad array of solidity and aspect ratio may be suitable depending on the performance targets. Example values of impeller midspan solidity and aspect ratio for the impellers of this embodiment are also specified in Table 4.

(36) TABLE-US-00004 TABLE 4 Example Impeller Geometry Rotational Tip/Hub Tip/Hub Radius Midspan Aspect Impeller # Speed Stagger Camber Ratio Solidity Ratio 1 N1 58°/38° 19°/35° 0.65 1.0 0.7 2 0.8 * N1 59°/53° 23°/28° 0.65 0.9 0.6

(37) When configured for high flow rates, each stage has a low pressure rise and would therefore have limited utility as a single stage. However, when configured for high impedance, the two-stage fan impellers are useful as single stage TA fans. The impellers may also be used in combination with an outlet guide vane (OGV)/inlet guide vane (IGV) component, such as shown in FIGS. 13A and 13B, to thereby form VA and IGV fans, respectively. FIGS. 13A and 13B depict a reversible vane component, generally 102, which comprises a hub 104, an outer ring 106, and a plurality of guide vanes 108 that extend radially between the hub and the outer ring. As shown in FIGS. 13A and 13B, the hub 104 may comprise an outer diameter surface 110 which converges from a first side 112 of the vane component 102 to a second side 114 of the vane component.

(38) The reversible vane component 102 is a single fan component which functions as an OGV in one orientation and as an IGV in the reverse orientation. In FIG. 13A the vane component 102 is oriented as an OGV which is normally positioned downstream of the impeller. In this orientation, the first side 112 defines the upstream end of the vane component 102 and the second side 114 defines the downstream end of the vane component. In this regard, the terms “upstream” and “downstream” are defined relative to the direction of airflow through the vane component 102, which is depicted by the arrow A. In FIG. 13B the vane component 102 is oriented as an IGV which is normally positioned upstream of the impeller. In this orientation, the second side 114 defines the upstream end of the vane component 102 and the first side 112 defines the downstream end of the vane component.

(39) In accordance with the present invention, a system of fan components is provided which may be configured to create a plurality of individual axial fans. Such a system offers versatility to address a wide range of fan applications using a few components. For example, FIG. 14 demonstrates how one system of fan components may be configured to form a plurality of fans. In this example, the system of fan components, generally 116, comprises a first TA fan 118, a second TA fan 120, and a reversible vane component 102. Each TA fan 118, 120 comprises a tubular fan housing 12A, 12B, an electric motor 14A, 14B which is positioned in the fan housing, an impeller 16A, 16B which is connected to the motor, and a motor support 18A, 18B on which the motor is supported.

(40) In one configuration of the system 116, the first and second TA fans 118, 120 are connected together to form a two-stage CR fan 122. If as shown in FIG. 14 the housings 12A, 12B comprise end flanges 124A, 124B, the TA fans 118, 120 may be connected together by bolting the adjacent end flanges together.

(41) In another configuration of the system 116, the first TA fan 118 may be used by itself a single-stage tube-axial fan TA-1. The first TA fan 118 may also be combined with the vane component 102 (oriented as an OGV) to form a single-stage vane-axial fan VA-1. Similarly, the second TA fan 120 may be used by itself as a single-stage tube axial fan TA-2 or combined with the vane component 102 (oriented as an IGV) to create a single-stage inlet guide vane fan IGV-2.

(42) Thus, the system 116, which comprises three fan components, may be configured to form up to five different fans. The two-stage CR fan 122 has the greatest axial length and input power requirement. TA-1 and TA-2 have the smallest axial length and are the lowest cost. VA-1 and IGV-2 have intermediate axial lengths and offer improved performance relative to TA-1 and TA-2.

(43) FIG. 15 is a relative performance comparison of the various fan created from the system of fan components 116. The CR fan 122 has the highest performance and is suitable for high impedance applications. TA-1 is suitable for low impedance applications and VA-1, TA-2, and IGV-2 are appropriate for moderate impedance applications. Of the single stage fans, VA-1 provides the highest performance, while IGV-2 provides slightly less performance but with additional throttling range. TA-2 provides the lowest performance of the group but is also capable of throttling to moderate impedance. Each fan has different performance characteristics, length, weight, and cost attributes to enable a variety of fan options suitable for applications with differing requirements and constraints.

(44) The reversible vane component 102 may be a simple, low cost design with a circular arc profile that is uniform from hub-to-tip. In the OGV configuration, the trailing edge meanline angle will preferably be near 0 degrees, which leads to good performance in the IGV configuration by minimizing incidence losses. The vane camber level should be consistent with the VA throttling range required, and the vane solidity level should be sufficient for the camber level to achieve good performance. Table 5 lists the characteristics of a reversible vane component which is suitable for use with the impellers represented in Table 4.

(45) TABLE-US-00005 TABLE 5 Reversible Vane Geometry Tip/Hub Tip/Hub Radius Mid-span Aspect Stagger Camber Ratio Solidity Ratio 20°/20° 40°/40° 0.65 1.4 0.4

(46) It should be recognized that, while the present invention has been described in relation to the preferred embodiments thereof, those skilled in the art may develop a wide variation of structural and operational details without departing from the principles of the invention. For example, various features of the different embodiments may be combined in a manner not described herein. Therefore, the appended claims should be construed to cover all equivalents falling within the true scope and spirit of the invention.