Low Noise High Efficiency Centrifugal Blower

Abstract

A centrifugal blower for HVACR applications includes a squirrel cage forward-curved blower fan and a scroll housing. The blower fan comprises a plurality of blades that are configured to emit air radially outward and tangentially from between the blades when the blower fan rotates at a first speed. The air so emitted has a deviation angle defined as the difference between the direction of the emitted air and the blade exit angle. The scroll housing has a spline-shaped wall that has an axial cross-section that is configured such that the deviation angle of the air emitted from the blower fan at an axial plane deviates by no more than fifteen percent circumferentially about the blower fan in-between the spline-shaped wall and the blower fan and such that the average tangential velocity of air between the spline-shaped wall and the blower fan deviates by no more than thirty percent.

Claims

1. A centrifugal blower for HVACR applications, the centrifugal blower comprising a squirrel cage forward-curved blower fan and a scroll housing, the blower fan having a radius and being rotatable about an axis at least a first speed, the blower fan comprising a plurality of blades having a particular blade exit angle and being configured to emit air radially outward and tangentially from between the blades when the blower fan rotates at the first speed, the air so emitted having a deviation angle defined as the difference between the direction of the emitted air and the blade exit angle, the scroll housing having opposite axial sides and a spline-shaped wall extending from one of the axial sides to the other of the axial sides, the spline wall being within two times the radius of the blower fan from the axis, the spline-shaped wall having an axial cross-section that is configured such that the deviation angle of the air emitted from the blower fan at an axial plane located between the axial sides of the scroll housing deviates by no more than fifteen percent circumferentially about the blower fan in-between the spline-shaped wall and the blower fan and such that the average tangential velocity of air between the spline-shaped wall and the blower fan deviates by no more than thirty percent.

2. A centrifugal blower in accordance with claim 1 wherein the spline-shaped wall of the scroll housing has a cross-section perpendicular to the axis that remains constant between and from one of the opposite axial sides of the scroll housing to the other of the axial sides.

3. A centrifugal blower in accordance with claim 1 wherein the spline-shaped wall has an axial cross-section that is configured such that the deviation angle of the air emitted from the blower fan at the axial plane located between the side walls of the scroll housing deviates by no more than fifteen percent circumferentially more than one-hundred and eighty degrees about the blower fan in between the spline-shaped wall and the blower fan and such that the average tangential velocity of air between the spline-shaped wall and the blower fan deviates by no more than thirty percent circumferentially more than one-hundred and eighty degrees about the blower fan.

4. A centrifugal blower in accordance with claim 3 wherein the spline-shaped wall has an axial cross-section that is configured such that the deviation angle of the air emitted from the blower fan at the axial plane located between the side walls of the scroll housing deviates by no more than ten percent circumferentially more than one-hundred and eighty degrees about the blower fan in between the spline-shaped wall and the blower fan and such that the average tangential velocity of air between the spline-shaped wall and the blower fan deviates by no more than ten percent circumferentially more than one-hundred and eighty degrees about the blower fan.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0010] FIG. 1 depicts a blower in accordance with the invention comprising a scroll that has a generally axially uniform cross-section.

[0011] FIG. 2 depicts a computer aided design model of the blower scroll of the blower shown in FIG. 1.

[0012] FIG. 3 shows a schematic of individual forward-curved fan blades of a squirrel-cage blower fan of the type used in the inventive blowers of the present application and shows the terminology associated with such fan blades.

[0013] FIG. 4 schematically shows a forward-curved squirrel-cage fan within a scroll in accordance with the invention and the terminology associated therewith.

[0014] FIG. 5 shows a graph of the radial exit velocity from a squirrel-cage blower fan of the type used in the inventive blowers of the present application.

[0015] FIG. 6 shows a graph of the scroll radius as a function of scroll angle for a scroll in accordance with the invention compared to prior art scrolls.

[0016] FIG. 7 depicts a blower in accordance with the invention comprising a scroll that has a non-axially uniform cross-section.

[0017] FIG. 8 depicts a computer aided design model of a blower scroll in accordance with the invention that also has a non-axially uniform cross-section.

[0018] Reference numerals in the written specification and in the drawing figures indicate corresponding items.

DETAILED DESCRIPTION

[0019] FIG. 1 depicts a blower (20) in accordance with the invention comprising a scroll (22) that has a generally axially uniform cross-section. Like typical blowers, the blower (20) comprises a squirrel-cage fan (24), and a motor (26). Although the motor (26) is housed within the squirrel-cage fan (24) and the scroll (22), it could also be external to the scroll and drive the fan via a shaft.

[0020] The novelty of the invention pertains primarily to the scroll (22) of the blower (20), however, the configuration of the scroll is preferably based on a particular fan (24) being driven by a motor (26) at a particular rotational speed. Of course, the blower (20) will still operate with the fan (24) operating at speeds other than that at which the blower is particularly suited for.

[0021] As shown in FIG. 3, commonly used terminology is used to describe the blades (28) of a squirrel-cage fan (24) and the airflow therethrough. A factor contributing to the overall efficiency of a blower (20) is the deviation angle of the airflow as it exits the fan (24) within the scroll (22). Even while a fan (24) is spinning at a constant rotational velocity, the deviation angle can vary from blade (28) to blade circumferentially around the fan depending on the radial velocity circumferential distribution of airflow through the blades and the tangential velocity of the air circulating around the fan within the scroll (22) at any given circumferential location/point.

[0022] In accordance with the present invention, the scroll axial cross-section is configured in a manner to minimize airflow deviation angles circumferentially around the fan (24) from the cutoff location (θcf shown in FIG. 4) to θ.sub.360°, while simultaneously minimizing gradients in the average tangential velocity of the air circulating around the fan. By minimizing these two aspects of the airflow within the blower (20) pressure losses and vortices are minimized within the blower, which adds to the efficiency of the blower and reduces noise emitted from the blower.

[0023] For a blower with a uniform scroll (i.e., one with a generally axially uniform cross-section between its axial sides (30), as shown for example in FIGS. 1 and 2), the scroll shape can be determined via a novel iterative process. The process involves an initial assumption as to the radial velocity (V.sub.r) distribution of air from the fan circumferentially about the fan axis. For example, a linear velocity distribution starting with one half of the average radial velocity at the cutoff location (θcf shown in FIG. 4) and increasing to twice the average radial velocity as θ.sub.s extends circumferentially about the axis to θ.sub.360°. Based on the initial radial velocity distribution, the tangential velocity can be calculated to maintain uniform relative wheel exit flow angles (and therefore uniform airflow deviation angles from the fan blades (28)). An assumption is then made that between the outer wall of the scroll and the squirrel-cage fan airflow follows a free vortex flow and therefore at any given azimuthal angle (θs), the average tangential velocity (V.sub.θ) can be calculated. Following this, an initial multinodal spline curve is defined for the contour of the axial cross-section of the scroll using an iterative mass conservation approach since (V.sub.θ) is a function of the difference between the radius of the scroll and the radius of the fan (in FIG. 4, this difference in radius is labeled b.sub.i). Any number of nodal points can be used to define the spline. Preferably at least four points are used to thereby allow the spline curve to have a non-constant curvature. More preferably, more than ten node points are used. The average tangential velocity V.sub.θ and its gradient along the circumference are then recorded. Following this, a computational fluid dynamics analysis is performed to evaluate the assumptions made in the initial calculations of V.sub.r distribution. The radial and tangential velocities along the circumference obtained from the computational fluid dynamic analysis is then compared to the analytically obtained values. The foregoing steps are then repeated several times (until a desired convergence is reached) but with each time using the radial velocity distribution obtained from the most recent computational fluid dynamics calculation in place of the initially imposed distribution. It should be noted that the V.sub.r values used in the analytical steps represent the average V.sub.r at θs based on the velocity profile of V.sub.r in a span-wise (axial) axial direction of air emitted from the fan (24). An example of such a velocity profile is shown in FIG. 5.

[0024] The axial cross-sectional shape of the scroll (22) resulting from the forgoing is compared to the cross-sectional shape of prior art scroll in FIG. 6. Even though the difference in scroll radius as a function of θs varies slightly between the scrolls shown in FIG. 6, the difference between the configuration of the scroll (22) of the blower (20) of the present invention and those of the prior art has a significant impact on the efficiency of and noise emitted from the blower, thereby making the blower of the present invention more efficient and quieter than the prior art blowers.

[0025] The concepts described above can also be applied to blowers comprising scrolls having non-uniform axial cross-sections. For example, FIG. 7 depicts a blower (50) in accordance with the invention comprising a scroll (52) that has a non-axially uniform cross-section (referred to herein as a variable scroll shape), and FIG. 8 depicts another blower scroll (60) in accordance with the invention having a variable scroll shape. The axial contour of the scrolls (52, 60) having a variable scroll shape can be configured using the methods described above except applying it at several different planes along the blower axis and using the radial velocity profile of the fan along the axis (e.g., FIG. 5) to axially divide the air emitted from the fan into separate theoretical zones. Using the methods describe above the scroll shape circumferential about the axis can be calculated for each axial plane, keeping the average circumferential velocities for each zone equal to each other. The resulting overall scroll shape then achieves a more uniform circumferential velocity in the span-wise/axial direction as compared to a scroll with a uniform scroll shape, and not just uniform circumferential velocity around the axis.

[0026] A scroll configured in accordance with the invention is capable of maintaining the variation in deviation angle of the air emitted from the blower fan at an axial plane located between the axial sides of the scroll housing to within a fifteen percent range, and preferably even a ten percent range, circumferentially about the blower fan in-between the spline-shaped wall and the blower fan. Furthermore, a scroll configured in accordance with the invention is capable of maintaining the variation in the average tangential velocity of air between the spline-shaped wall and the blower fan to within a thirty percent range, and preferably even a ten percent range.

[0027] In view of the foregoing, it should be appreciated that the invention has several advantages over the prior art.

[0028] As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.

[0029] It should also be understood that when introducing elements of the present invention in the claims or in the above description of exemplary embodiments of the invention, the terms “comprising,” “including,” and “having” are intended to be open-ended and mean that there may be additional elements other than the listed elements. Additionally, the term “portion” should be construed as meaning some or all of the item or element that it qualifies. Moreover, use of identifiers such as first, second, and third should not be construed in a manner imposing any relative position or time sequence between limitations. Still further, the order in which the steps of any method claim that follows are presented should not be construed in a manner limiting the order in which such steps must be performed, unless such an order is inherent or explicit.