Axial fan with fluid recirculation

Abstract

An axial fan comprises a nozzle (2) and a rotatable impeller (6) with free-ending blades (60). The nozzle (2) forms a main flow channel (9) that connects an inlet side (E) of the fan with an outlet side (A) of the fan, thereby defining a main flow direction (S). The nozzle (2) surrounds the impeller (6) without rotating with it. A bypass channel (8) forms a flow connection from an outlet-side area of ​​the nozzle (2) to an inlet-side area of ​​the main flow channel (9) for the purpose of recirculating outlet air into the main flow channel (9) of the nozzle (2). The axial fan reduces noise emissions and enables an extension of the stall-free operating range.

Description

TECHNICAL AREA

[0001] The present invention relates to an axial fan, in particular a fan of a heat pump, for example an air-to-water heat pump. STATE OF THE ART

[0002] Axial fans, also called axial blowers, are commonly used turbomachines for conveying a gaseous medium, especially air. They feature a rotating impeller with blades. The main flow direction of the conveyed air runs parallel to the axis of rotation of the impeller of the axial fan. Fans are designed to convey air as energy-efficiently as possible.

[0003] DE 44 38 184 C1 describes a radiator for an internal combustion engine comprising a radiator shroud and a downstream axial fan. A bypass channel between the radiator shroud and the axial fan is intended to prevent backflow vortices, with the inner wall of the radiator shroud being shaped such that a recirculated bypass flow is deflected in the direction of the main flow.

[0004] WO 2020 / 099027 A1 discloses a diagonal fan with an impeller comprising impeller blades and a centrifugal ring that closes the ends of the impeller blades. The fan motor is located downstream of the impeller in the main flow direction. An inlet nozzle is arranged upstream of the impeller in the flow direction. An annular bypass channel is provided between the inlet nozzle and the centrifugal ring, which directs a swirl-free secondary flow to the inlet side of the nozzle gap. This is intended to increase efficiency.

[0005] Fans should also operate as quietly as possible. However, axial fans with blade tips, i.e., with free-ending blades, generate blade tip vortices that reduce energy efficiency and are largely responsible for noise emissions. PRESENTATION OF THE INVENTION

[0006] It is therefore an object of the invention to create an axial fan with free-ending blades that is improved with regard to its sound emission.

[0007] This problem is solved by an axial fan with the features of claim 1.

[0008] The axial fan according to the invention comprises a rotatable impeller with free-ending blades and a nozzle. The nozzle forms a main flow channel that connects an inlet side of the fan with an outlet side, thereby defining a main flow direction. The nozzle surrounds the impeller but does not rotate with it. A bypass channel forms a flow connection from an outlet-side area of ​​the nozzle to an inlet-side area of ​​the main flow channel for the purpose of recirculating outlet air into the main flow channel of the nozzle.

[0009] The "shovel" is also referred to as a "blade". "Free-ending shovels" are usually called "blade tips", regardless of the shape of the ends.

[0010] The bypass allows a portion of the air to be recirculated from the outlet pressure side (positive pressure area) of the fan to the inlet suction side (negative pressure area) of the fan. Due to the pressure difference, this bypass flow is drawn towards the inlet side.

[0011] The bypass channel reduces blade tip vortices at the tips of the blades and / or deflects them axially thanks to this bypass flow. This deflection and / or reduction of the blade tip vortices minimizes their interaction with neighboring blades, thus minimizing noise emissions and improving aeroacoustic performance.

[0012] Despite recirculating some of the air, the fan's energy efficiency is hardly reduced or even improved. This is because reducing and deflecting the blade tip vortices delays flow separation. The separation point shifts to higher back pressures, thus expanding the separation-free operating range.

[0013] Premature flow separation not only reduces energy efficiency but also leads to instabilities that cause the blades to vibrate and can result in fatigue fractures. This improves the operating range and expands the stable operating range.

[0014] In preferred embodiments, the bypass channel, at its confluence with the main flow channel, has the same inflow direction as the main flow channel. Preferably, at its confluence with the main flow channel, the bypass channel forms a stepless extension of an inner wall of the nozzle that follows the main and bypass flow directions. Preferably, the fan is shaped such that the bypass flow is discharged parallel to the inside of the nozzle. The bypass flow is thus preferably introduced parallel to the main flow.

[0015] Preferably, the axial fan has a support structure on which the impeller is rotatably mounted and on which the nozzle is fixed in position. The bypass channel is formed between a wall of the support structure and a wall of the nozzle.

[0016] Preferably, the wall of the support element and the wall of the nozzle at the inlet of the bypass channel have the same orientation and inclination. They form the walls of the bypass channel and enable a design that allows for the least turbulence possible merging of the main flow and the bypass flow.

[0017] Preferably, a motor that drives the impeller is positioned upstream of the nozzle in the main flow direction.

[0018] In preferred embodiments, the support element is a motor mount for a motor to drive the impeller. The support element preferably comprises an outer support element and an inner support element, with the nozzle attached to the outer support element and the motor attached to the inner support element. Preferably, struts are provided that fasten the inner support element to the outer support element and give the motor mount the necessary stability.

[0019] The bypass channel is preferably circumferential. Preferably, it is ring-shaped. Preferably, it has few or no interruptions.

[0020] The outlet of the bypass channel is preferably designed as a gap. It is preferably several times smaller in both its flow length and cross-section than the main flow channel. It is preferably located only in the inlet-side region of the fan.

[0021] In some embodiments, the bypass channel has an inlet opening with a larger cross-section than its outlet opening, i.e., its orifice. In other embodiments, the size of its cross-section is approximately constant along its length or increases towards its orifice.

[0022] In some embodiments, the bypass channel forms an arc, preferably at an angle of more than 90°, before it opens into the main flow channel.

[0023] In preferred embodiments, the nozzle tapers at least in its inlet-side region towards the outlet side. In some embodiments, it tapers along its entire length.

[0024] Depending on the design, the nozzle has a length that is greater, approximately equal to, or less than the length of the impeller.

[0025] In preferred embodiments, the bypass channel opens into the main flow channel in the direction of the main flow in the region of the free ends of the impeller blades. Viewed in the axial direction, i.e., in the direction of the main flow, the bypass channel preferably opens into the main flow channel in the region of the blade tips or adjacent thereto, downstream, but preferably, viewed in the axial direction, in the region of the blades.

[0026] Further embodiments are specified in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] A preferred embodiment of the invention is described below with reference to the drawings, which serve only for illustration and are not to be interpreted restrictively. The drawings show: Figure 1 is a perspective view of an axial fan according to the invention from above; Figure 2 is a perspective view of the axial fan according to the invention. Figure 1 from below; Figure 3 a view of the axial fan according to Figure 1 below; Figure 4 shows a cross-section through the axial fan according to Figure 1 Figure 5 shows a perspective view through part of the axial fan according to Figure 1 Figure 6 shows an enlarged section of area D according to Figure 5 and Figure 7, another perspective view through part of the axial fan according to Figure 1 . DESCRIPTION OF PREFERRED EXECUTION FORMS

[0028] In the Figures 1 to 4 Figure 1 shows a preferred embodiment of an axial fan according to the invention. It comprises a motor carrier 1, 3, 4, a nozzle 2, a motor 5 and an impeller 6.

[0029] The motor mount has an outer first support part 1, an inner second support part 3 and struts 4 and forms an air flow opening 7.

[0030] The outermost first support section 1 typically serves as a wall ring for mounting the fan in or on a housing or in or on a building wall. The outermost first support section 1 has a recess that defines an airflow opening 7. The recess is preferably arranged centrally.

[0031] The airflow opening 7 preferably has a circular shape. In this example, the outer support part 1 has a square base. Other base shapes are possible, for example round, oval, or rectangular.

[0032] The fan nozzle 2 is attached to the outer support part 1 of the motor mount, preferably at its circumference. They are preferably screwed together. Appropriate screws are provided in the Figures 3, 4 and 6 marked with reference number 24. This is in Figure 3 The nozzle 2 is stationary and, like the motor mount, does not rotate with the impeller 6.

[0033] Preferably, it tapers in the main flow direction, i.e., away from the motor mount and thus from the first mount section 1. It tapers at least in the inflow region. Preferably, it tapers over the entire length of the nozzle 2.

[0034] The inner support part 3 and the air flow opening 7 are preferably arranged coaxially with each other. Preferably, the inner support part 3 and the outer support part 1 are also arranged coaxially with each other.

[0035] The inner support part 3 is designed to receive, preferably to mount, the motor 5, preferably an electric motor. In this example, the inner support part 3 has a motor housing in the form of a dome with a curved surface facing the airflow. This is shown in the Figure 1 and 4 Clearly visible. The main flow direction S is in Figure 3 The inner support part 3 has through-holes for fastening the motor 5 by means of screws in the motor housing and / or for routing power and / or sensor cables.

[0036] The motor support includes the struts 4. They serve to connect the inner support part 3 with the outer support part 1, ensuring sufficient stability for the motor support and thus for the entire fan.

[0037] The design of the engine mount shown here is merely an example. It can also be designed differently. In particular, differently shaped struts can be used, or a grid can be used instead of struts, or other connecting and stabilizing elements can be employed.

[0038] The motor carrier 1, 3, 4 and / or the nozzle 2 is preferably formed in one piece. They are preferably made of plastic.

[0039] The impeller 6, also called a vane wheel or propeller, is preferably attached to the motor 5. It can be rotated by means of the motor 5 around the axis L of the fan and thus of the motor mount.

[0040] In this example, the impeller 6 has three blades 60. The blades 60 are also called leaves or vanes. The blades 60 are arranged on an inner ring 61. Ribs 62 stiffen the inner ring 61 and thus the impeller 6. This is shown in the Figures 2 to 4 clearly visible.

[0041] The blades 60 terminate in free blade tips 600. In this embodiment, the blade tips 600, also called blade tips, are bent upwards opposite to the main flow direction S and are tapered to a point. The tips projecting opposite to the main flow direction S, and thus facing the low-pressure area, preferably extend in an axial direction. Preferably, they are also bent in a circumferential direction, i.e., along the circumference defined by the impeller, opposite to the direction of rotation of the impeller. This is shown in the Figures 4 and 7 They are easily recognizable. However, they can also have other forms.

[0042] The number and shape of the blades 60 and the other components of the impeller 6 are shown here only as examples. The impeller 6 can also be designed differently.

[0043] The fan has an inlet side E and an outlet side A. The rotation of the impeller 6 creates a low-pressure area, or suction side, on the inlet side E and a positive-pressure area, or pressure side, on the outlet side A. These two sides are in Figure 4 marked with the reference symbols E and A.

[0044] To reduce and / or deflect blade tip vortices at the ends or tips 600 of the blades 60, a bypass channel 8 is provided. It is located in the Figures 5 to 7 recognizable.

[0045] The bypass channel 8 is annular, preferably forming a continuous circuit with only the necessary interruptions or without any interruptions at all. It is significantly smaller than the main flow channel, which includes the airflow opening 7.

[0046] The walls of the outer support part 1 and the nozzle 2 form the walls of the bypass channel 8.

[0047] The outer support part 1 has a cover surface 12 on the inflow side and reinforcing ribs 11 on the outflow side. This is shown in the Figures 1 and 2 recognizable.

[0048] The cover surface 12 is closed except for the airflow opening 7. A circumferential outer sleeve 11 projects from this surface towards the outlet side A. A circumferential inner sleeve 14 is located at a distance from the outer sleeve 11. The cover surface 12 projects radially inwards and beyond the inner sleeve 14, forming an inner skirt 13. The skirt 13 is curved and projects with its free end towards the outlet side A. This is in Figure 6 recognizable.

[0049] The nozzle 2 has at least one skirt projecting outwards and towards the outflow side, which together with the inner jacket 14 and the inner skirt 13 of the first support part 1 form the bypass channel 8.

[0050] In this example, nozzle 2 is shown, see Figure 6A first outer skirt 20 is formed, which is projected from the circumferential wall of the nozzle 2 towards the inlet side E, wherein this circumferential wall of the nozzle 2 transitions into a second outer skirt 21. A groove 22 is formed between the first outer skirt 20 and the second outer skirt 21. The second outer skirt 21 is preferably shorter than the first outer skirt 22. An upper region 23 of the inner wall of the nozzle 2 has the same inclination towards the inside of the inner skirt 13 of the first support part 1. They form the outlet region, which allows the same flow direction for the bypass flow B as for the main flow H.

[0051] At least the inner jacket 12 and the inner skirt 13 of the first support part 1, as well as at least one of the outer skirts 20, 21 of the nozzle 2, are formed circumferentially. Preferably, they are formed identically over their entire circumference. Preferably, this also applies to the outer jacket 11 of the first support part 1 and to the other of the two skirts 20, 21 of the nozzle 2.

[0052] Figure 6 is an enlarged section of the Figure 5 In Figure 5 The first support part 1 and the nozzle 2 are more clearly visible. In the Figures 5 and 7 It can be seen that the bypass channel 8 has an opening 80 into the main flow channel 9. The opening 80 is located in the main flow direction, i.e., in the axial direction of the impeller, after the blade tips 600. Figure 7 It is also evident that the opening 80 or the opening area of ​​the bypass channel 8 is slit-shaped.

[0053] Figure 7shows the flow pattern of the air flowing through the fan.

[0054] Air drawn in by the rotation of the impeller 6 flows from the inlet side E in the form of a main flow H through the main flow channel 9 to the outlet side A. The main flow H is in Figure 7 Represented by several thick, dashed arrows. As in Figure 7 As can be seen, the flow is deflected upon entering nozzle 2, an effect further enhanced by the narrowing of nozzle 2. In other embodiments, there is no narrowing and / or the main flow is not deflected.

[0055] Due to the prevailing pressure conditions, a portion of the airflow exiting nozzle 2 on the outlet side A is recirculated along the outside of nozzle 2 and through bypass channel 8 back into the inlet area of ​​nozzle 2. Other air can also flow from the overpressure area of ​​nozzle 2 into bypass channel 8 and into the main flow channel 9. The bypass flow B is in Figure 7 This is represented by a fine dashed arrow. As can be seen by comparing the arrows of the two flows H and B, the flow directions of the main flow H and the bypass flow B are the same in the region of the opening of the bypass channel 8 into the main flow channel 9. This is achieved in particular by the design of the opening area. Preferably, these flow directions are the same as the direction of the circumferential inner wall of the nozzle 2. This inner wall is, as shown in Figure 7 It is recognizable as being preferably curved and tapering towards the outlet side A.

[0056] Preferably, the bypass channel 8 tapers towards the opening 80. Preferably, the opening 80 has a smaller passage than the inlet of the bypass channel 8. The second outer skirt 21 of the nozzle 2 reduces the cross-section compared to the inlet of the bypass channel 8, which is formed by the first outer skirt 20 and the inner sleeve 14 of the first support part 1. This is shown in the Figure 6 and 7 recognizable. Between the second outer skirt 13 and the opening 80, the bypass channel 8 preferably forms an arc, preferably of more than 90°.

[0057] The bypass channel 8 can also have a different shape. It can be configured differently by a different design of the first support part 1 and / or the nozzle 2 and / or by using at least one further component. In the radial direction of the impeller 6, the bypass channel 8 is preferably arranged at a greater radius than the blade tips. In the axial direction of the impeller 6, the bypass channel 8 is preferably located at the same level as the blade tips. In other embodiments, it is located upstream of the blade leading edge. In other embodiments, it is located between the leading edge and the trailing edge of the impeller 6. The leading and trailing edges are defined by the direction of rotation of the impeller. The impeller can be configured differently. In particular, the blades and / or their blade tips can have different shapes.The bypass channel also improves aeroacoustics and aerodynamics for free-ending blades when there are no pronounced tips or distinctive or specially shaped blade ends.

[0058] The axial fan according to the invention reduces noise emission and enables an extension of the stable operating range. REFERENCE MARK LIST

[0059] 1 Outer support part 10 Rib 11 Outer casing 12 Cover surface 13 Inner skirt 14 Inner casing 2 Nozzle 20 First outer skirt 21 Second outer skirt 22 Groove 23 Upper area of ​​the inner wall 24 Screw 3 Inner support part 4 Strut 5 Motor 6 Impeller 60 Blade 600 Blade tip 61 Ring 62 Rib 7 Air flow opening 8 Bypass channel 80 Outlet 9 Main flow channel A Outlet side B Bypass flow E Inlet side H Main flow L Axis S Main flow direction

Claims

1. Axial fan with a nozzle (2) and with a rotatable impeller (6) having free-ending blades (60), wherein the nozzle (2) forms a main flow channel (9) connecting an inlet side (E) of the fan with an outlet side (A) of the fan and thereby defining a main flow direction (S), wherein the nozzle (2) surrounds the impeller (6) and wherein the nozzle (2) does not rotate with the impeller (6), characterized by that a bypass channel (8) is provided which forms a flow connection from an outflow-side environment of the nozzle (2) into an inflow-side area of ​​the main flow channel (9) for the purpose of returning outflow-side air to the main flow channel (9) of the nozzle (2).

2. Axial fan according to claim 1, wherein the bypass channel (8) has the same inflow direction as the main flow channel (8) when it enters the main flow channel (9).

3. Axial fan according to one of claims 1 or 2, wherein the bypass channel (8) at the point where it enters the main flow channel (9) forms a stepless extension of an inner wall of the nozzle (2) following in the main flow direction (S).

4. Axial fan according to one of claims 1 to 3, wherein the axial fan has a motor (5) for driving the impeller (6), wherein the motor (5) is positioned upstream of the nozzle (2) in the main flow direction (S).

5. Axial fan according to one of claims 1 to 4, wherein it has a support part (1, 3) on which the impeller (6) is rotatably arranged and on which the nozzle (2) is fixedly arranged, and wherein the bypass channel (8) is formed between a wall (14, 13) of the support part (1, 3) and a wall (20, 21, 23) of the nozzle (2).

6. Axial fan according to claim 5, wherein the wall (13) of the support part (1) and the wall (23) of the nozzle (2) have the same orientation and inclination at the inlet of the bypass channel (8).

7. Axial fan according to claims 4 and 6, wherein the support part is a motor support with an outer support part (1) and an inner support part (3), wherein the nozzle (2) is attached to the outer support part (1) and wherein the motor (5) is attached to the inner support part (3).

8. Axial fan according to claim 7, wherein struts (4) are provided which fasten the inner support part (3) to the outer support part (1).

9. Axial fan according to one of claims 1 to 8, wherein the bypass channel (8) is formed circumferentially.

10. Axial fan according to one of claims 1 to 9, wherein the bypass channel (8) is designed to be many times smaller in its flow length and in its cross-section than the main flow channel (9).

11. Axial fan according to any one of claims 1 to 10, wherein the bypass channel (8) has an inlet opening which has a larger cross-section than its outlet opening.

12. Axial fan according to one of claims 1 to 11, wherein the bypass channel (8) forms an arc before it opens into the main flow channel (9).

13. Axial fan according to one of claims 1 to 12, wherein the nozzle (2) tapers towards the outlet side at least in its inlet area, and preferably tapers towards the outlet side over its entire length.

14. Axial fan according to one of claims 1 to 13, wherein the bypass channel (8) opens into the main flow channel (9) in the main flow direction (S) in the region of the free ends of the blades (60) of the impeller (6).

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