CA2565720A1 - Hybrid impeller - Google Patents

Description

HYBRID IMPELLER
FIELD OF THE INVENTION

This invention relates to fans, and more specifically, to a fan impeller having a design combining certain elements of axial and centrifugal fans.

BACKGROUND OF THE INVENTION

A fan is motor-powered air pump that produces a volumetric flow of air at a certain pressure.
The rotating portion of the fan, known as an impeller, comprises a hub with blades (vanes) extending radially from the hub. The impeller converts torque from the motor to increase static pressure of air across the hub.

Axial fans include impellers that rotate to move large amounts of air at low pressure. The air moves in a direction parallel to the fan blade axis. Axial fans can produce a high rate of airflow and are inexpensive to produce, but are useful only in low-pressure environments. Further, axial fans are noisy when the ambient conditions are unfavorable, such as when there is insufficient air or when the airflow is blocked, such as in ductwork.

Centrifugal fans, also known as blowers, use centrifugal force to move the air. Airflow from the blower tends to be perpendicular to the axis of rotation of the impeller, and at a lower flow rate than with axial fans. Centrifugal fans are more expensive to produce than axial fans and can generally operate at about four times the pressure of axial fans.

Axial fans collect air at one face of the blade and exhaust the air at the opposite face of the blade thus moving air parallel to the rotational axis of the blade. Their design usually serves to move air from one face to the other, allowing the inertia of the air to maintain the flow direction at the exhaust. However, when the air mass encounters the blade, it tends to rotate with the blade (drag) due to friction and surface tension forces, and so is accelerated by centrifugal force towards the outer circumference of the blade, off and around the blade tip, causing turbulence to the ambient air that the blade is trying to draw in. Turbulence of air prior to leaving the impeller is detrimental to fan's performance and produces noise.

As shown in US patent 7,101,145 to Tsuchiya et al., stators can be installed in the proximity of the fan blade to control the turbulence and increase the efficiency of the fan. This may improve the performance of the fan, but noise level may still be a problem.

US Patent 6,902,377 to Crocker proposes a fan impeller employing an airfoil shape and a rounded leading edge of the blades, wherein the leading edge overlaps the adjacent blade trailing edge.

Centrifugal fans pull air from an inner circumference and exhaust to an outer circumference, moving air at substantially right angles to the rotational axis of the blade.
Because the cylindrical exhaust plane of the fan is larger than the cylindrical collection plane of the fan, the airfoil design of the individual louvers does not significantly increase efficiency or decrease the decibel level. Patent 7,063,510 to Takeshita et al. attempts to improve effectiveness of the centrifugal fan by opening the face of the blade and allowing some axial air flow before air is recollected and exhausted at the outer circumference.

There is still a need for a fan which combines relatively smooth operation of an axial fan with a relatively higher efficiency of a centrifugal fan.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided an impeller comprising a hub defining an axis of rotation of the impeller, a number of blades integrally coupled to and extending from the hub at a blade angle from an inlet end of the impeller to an exhaust end thereof, and a plate mounted at the exhaust end of the blades and extending radially from the hub so as to significantly obstruct axial flow of air moved by rotation of the blades about the axis of rotation.

The plate may be mounted integrally to the hub and to the exhaust end of the blades and thus be rotatable with the blades. Alternatively, the plate may be stationary but positioned in close proximity to the exhaust ends of the blades to obstruct the axial flow of air.
The plate has an inlet side and an exhaust side. The shape and profile of the exhaust side is of minor importance as long as it does not interfere with the symmetry of the impeller. The inlet side may be shaped to correspond to the shape of the blades at the exhaust end so as to define chambers formed by the walls of the adjacent blades and the surface of the plate, the chambers only open to their outside, away from the hub.

Each blade has a rounded leading edge, preferably having an airfoil profile in cross-section, and a trailing edge extending between the leading edge and the plate.

Due to the above-defined design, the rotation of the impeller blades causes ambient air to be drawn at the leading edges and expelled substantially radially along the trailing edges and the surface of the plate on its inlet side.

In other words, the impeller is designed for collecting air at the face of the impeller and exhausting it at the circumference.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, Fig. 1 is a perspective view, from the inlet side, of an embodiment of the impeller of the invention, Fig. 2 is a perspective view, from the inlet side, of another embodiment of the impeller of the invention, Fig. 3 is a top view of an embodiment of the impeller, Fig. 4 is a perspective view of the embodiment of Fig. 3 with a peripheral hoop, Fig. 5 is a perspective, cross-sectional view of an embodiment of the invention showing the installation of the peripheral hoop, Fig. 6 is an enlargement of element A of Fig. 5, Fig. 7 is a perspective view of another embodiment of the invention with a peripheral hoop at the leading edges of the impeller blades, Fig. 8 is a perspective view of fan incorporating an impeller of Fig. 3 and a cowling, shown schematically, Fig. 9 is a perspective view, from the exhaust side, of a fan incorporating an embodiment of the impeller of the invention and a cowling, shown schematically, Fig. 10 is a side view of an embodiment of the impeller of the invention with a drive belt groove in the plate, Fig. 11 is a perspective view, from the exhaust side, of a three-blade embodiment of the propeller of the invention, and Fig. 12 is a perspective view from the inlet side of the embodiment of Fig.
12.
DETAILED DESCRIPTION OF THE INVENTION

In the drawings, an impeller of the invention is shown as having an axis of rotation 1 extending through a hub of the impeller. The impeller has three or four blades 2-6 integral with the hub 1 A, 1 B. The propeller defines an inlet end represented by leading edges 2 of the blades, and an exhaust end on the opposite side. As illustrated herein, the hub does not constitute a distinct element, and is instead merged with the blades 2-6 and a back plate 20 mounted on the exhaust side of the impeller. The plate 20 extends radially from the axis 1 to the same extent as the blades 2-6, but it may extend to a larger or smaller degree. The purpose of the plate 20 is to obstruct the radial flow of air moved by rotating blades toward the exhaust side of the fan, i.e.
from the leading surface 2 towards the plate 20. The presence of the plate 20 and absence of space between the edges of the blades at their exhaust end and the plate forms chambers between adjacent blades, the chambers open to the outside and closed at the hub and at the edges between adjacent blades. This design causes air drawn by the leading edges 2 of rotating blades to be expelled mostly in a radial direction, as explained further below.

As can be seen in Figs. 1 and 2, the leading edges have a rounded shape, preferably an airfoil shape, to reduce turbulence of the drawn air.

Ambient air is struck with a rounded surface 2 so as to pull it into the fan without turbulence.
The ambient air is pulled into the fan chambers by a receding surface 3 of the impeller that follows the leading edge. Once air is between two adjacent leading edges, a rear chamber face 4 approaches, compressing the air and accelerating it and exhausting it by centrifugal force along the sharpened trailing (exhaust) edge 5. As the exhausting air rushes past the edge 5, it pulls against the air on the receding surface 3, decreasing the pressure on the receding surface 3 and thereby increasing the velocity of the influx of ambient air.

In a turbine fan application of the impeller, the shape of the initial contact (leading) edge 2 protects the chamber's rear face from the pressure of the high-velocity incoming air, and so encourages a good pressure differential between the receding surface 3 and the chamber's rear face 4. High velocity air exiting the exhaust edge (trailing edge) 5 from the receding surface 3 would pull against the air following the surface of the chamber's rear face, again, lowering the pressure against that face and possibly optimizing the potential for harnessing the energy of the high pressure. The rounded leading edge coupled with the sharpened exhaust edge creates airfoil like dynamics which are expected to result in a relatively silent operation of the fan, even at high rpm.

The depth of the blades, i.e. the distance between the leading edges 2 and the plate 20 is variable according to the application (compare Figs. 1 and 2), and the angle of the receding surface.3 would be such as necessary to enable the receding surface to reach the depth of the blade in the portion of revolution (1 /4) allotted to the chamber. To optimize the air velocity within the chamber in applications requiring high-pressure differentials, the area of the collecting face over the area of the exhaust face should be close to the air pressure at the collecting face over the desired air pressure of the exhausting face. Therefore, the depth of the blades in a turbine application would be greater relative to the radius, while in a pressurizing fan, the depth would be relatively lesser.

The blade angle, a characteristic well understood by those familiar with the art, is variable depending on many factors such as the depth of the blades. The present specification will not go into the specifics in this respect.

If the medium being moved by the blade's operation is to be liquid (as in a pump's impeller or a boat's propeller), the ratio of the face area to the exhaust area should be relative to the desired ratio in velocity, and if the pump is only to impart liquid pressure, the area of the inlet face should be fairly equal to the area of the cylinder of the outlet face.

Although the application as above described would vastly improve the effectiveness of the blade over historical designs, as pictured in Figs 1, 2, and 3, there is still a problem of turbulence occurring at the outer tip 6 of the leading edge 2. As shown in Fig. 4, a hoop 7 may be attached to the ends of all leading edges that is slightly raised from the edge, rounded at the collecting edge and sharpened 8 at the exhaust edge. This hoop cleanly separates the accelerated air from the ambient air near the collection face of the fan, preventing turbulence in a preferential manner compared to a stator.

The impeller shown in Figs 1-6 is designed to rotate counterclockwise as viewed from the inlet side. Fig. 7 shows a design for a reversed rotation, but the functionality remains the same.
Most centrifugal fans and pumps, as many axial fans and propellers are designed to exhaust the medium (air or fluid) into a special ductwork cavity. The impeller of the invention can be scaled to fit into these cavities to improve performance and / or reduce noise. Many axial fans and propellers are standalone. To enable this invention to replace these applications, as in Fig. 8 and Fig. 9, a cow19 replaces the hoop 7 to direct the exhausted air or water into an axial flow at exhaust ports 10 (Fig. 9).

The inlet side of the hub in Figs. 1 and 2 is cut out as shown at 1 A to accept a bearing or to facilitate attachment of a drive shaft. In most applications, the center can be drilled through as shown at 1 B to acconvnodate a drive shaft. This shaft would normally be a part of a motor at one end and could be mounted to a bearing at the other end. Of course, in a turbine application, the shaft would facilitate power transmission to whatever the turbine was powering. This shaft might also be used in transmitting power through the fan, from an engine/motor at one face to an alternator or hydraulic pump at the other. Such devices might be attached to the fan by means of a belt and pulley.

Fig. 10 shows a notch (groove) 11 in the outer circumference of the plate 20 to accept a drive belt. The plate 20, disposed at the exhaust end distal to the inlet end and a hoop 7, may be flat, as in Fig. 5 and 9 or have a recess 12 as in Fig. 11 to allow a driving motor to be recessed into the plate 20.

Most applications will employ a four-chamber (vane) design, but the invention is not limited to such embodiments. While a large number of blades may cause some manufacturing difficulties, it is easily conceivable to design a three-blade impeller as shown in Figs. 11 and 12. However, the performance of the three-chamber design would be somewhat lower than the performance of the four-chamber design (given equal circumference and depth). This is in contrast to conventional designs where additional vanes equals additional turbulence, and a four-vane fan has performance only slightly increased over a three-vane fan.

Claims (3)

1. An impeller having an inlet end and an exhaust end, comprising a hub defining an axis of rotation of the impeller, a number of blades integrally coupled to and extending from the hub at a blade angle from the inlet end of the impeller to the exhaust end thereof, and a plate mounted at the exhaust end of the blades and extending radially from the hub so as to significantly obstruct axial flow of air moved by rotation of the blades about the axis of rotation.

2. The impeller of claim 1 wherein each blade has a rounded leading edge.

3. The impeller according to claim 1 wherein the plate is integral with the hub and with the blades at the exhaust end to define intra-blade chambers open to the inlet end and an outer circumference of the impeller.

around the blade tip, causing turbulence to the ambient air that the blade is trying to draw in. Turbulence of air prior to leaving the impeller is detrimental to fan's performance and produces noise.

As shown in US patent 7,101,145 to Tsuchiya et al., stators can be installed in the