FAN, MORE PARTICULARLY RADIAL OR DIAGONAL FAN

Abstract

A fan (1), more particularly a radial or diagonal fan, comprising a motor (4), an impeller (3) driven in rotation by the motor (4), an inlet nozzle (5) and a nozzle plate (2) extending around the inlet nozzle (5), wherein the impeller (3) essentially consists of a base disk (10), a cover disk (8) and several wings (9) extending between them, the nozzle plate (2) has an edge folded towards the pressure side and the cover disk (8) is rounded on its outer edge towards the suction side, and wherein the fold (6) of the nozzle plate (2) and the rounding of the cover disk (8) are shaped and dimensioned in such a way that the outflow from the impeller (3) close to the cover disk interacts with the bend of the nozzle plate (2).

Description

FIELD

The present disclosure relates to a fan, more particularly a radial or diagonal fan. The fan includes a motor, an impeller driven in rotation by the motor, an inlet nozzle and a nozzle plate extending around the inlet nozzle. The impeller essentially consists of a base disk, a cover disk and several wings extending between them.

BACKGROUND

Radial or diagonal fans of the type in question are well known from practice. By way of example only, reference is made to DE 10 2017 110 642 A1, which, viewed in itself, shows a radial fan arrangement.

Regardless of the specific design and application, fans of the type in question should have high—identical—efficiencies both when installed and on the test bench. This requirement seems trivial. However, it had to be determined that impellers and thus corresponding fans optimized for a specific installation situation can have rather disadvantageous behavior on the test bench.

Accordingly, impellers of radial and diagonal designs have been developed that have very high efficiencies under test bench conditions, but do not have these efficiencies in specific installation situations. There are also radial and diagonal impellers that have very high efficiencies under pressure-side installation conditions, but have lower efficiencies under test bench conditions. This situation is problematic, especially since the test bench and thus the test bench conditions are intended to provide information about the performance of the fan in the specific application.

SUMMARY

The present disclosure is therefore based on the object of designing and developing the generic fan in such a way that it has the highest possible efficiency both in the pressure-side installation situation and under test bench conditions. At least any differences between the two situations should be as small as possible.

The preceding object is solved, in an embodiment, by a fan with the features of claim 1. The nozzle plate then has an edge that is folded towards the pressure side, while the cover disk is rounded on its outer edge towards the suction side. The fold of the nozzle plate and the rounding of the cover disk are shaped and dimensioned in such a way that the outflow from the impeller close to the cover disk interacts with the bend of the nozzle plate.

According to the present disclosure, it is about the combination of a special nozzle plate with a special cover disk, wherein the nozzle plate has an edge that is folded or bent towards the pressure side and the cover disk is rounded towards the suction side, namely has a curvature. These two features can be seen in combination and have a synergistic effect in that the outflow from the impeller close to the cover disk interacts with the fold of the nozzle plate. This achieves local stabilization similar to an installation situation, so that the fan according to the present disclosure shows the same or almost the same efficiency on the test bench as in a specific installation situation.

It is advantageous if, in a section on a plane through the fan axis that can be assigned to a circumferential position of the impeller or the cover disk or the nozzle plate, the tangential extension of the inner cover disk contour facing the wings intersects the nozzle plate at its radially outer edge, including its fold, over at least 90%, and, in an embodiment, over 100%, of the circumferential positions. This further enhances the advantages according to the present disclosure, particularly with regard to the stabilization of the air flow.

The rounding of the cover disk is advantageously a strong curvature on the outer edge of the cover disk, which can be seen in combination with the folded edge of the nozzle plate.

Specifically, the inner (wing-side) contour of the rounding and thus of the outer edge of the cover disk at the outer end of the cover disk in the area of the impeller exit of the air flow conveys an exit direction that can be defined by a straight, tangential extension of the cover disk. The curvature gives the air a particular exit direction, wherein the structural design of the curvature can be designed such that the air exit direction is constant or variable over the circumference of the cover disk. Any or different influences across the circumference of the cover disk can be implemented.

Furthermore, the air exit direction can, in an embodiment, be directed backwards with respect to the main flow direction, towards the nozzle plate. However, such a design is not mandatory.

It is of further advantage, in an embodiment, if the air exit direction at the outer end of the cover disk, i.e., at its curvature area, has an angle to the radial direction of more than 35°, and, in an embodiment, more than 45°. As a result, the outflow from the impeller close to the pressure disk is diverted towards the nozzle plate or its fold. This results in an interaction.

Specifically, it is conceivable that the imaginary extension of the cover disk, starting from its curvature area, in an embodiment, over the entire circumference or at least over a large area of the circumference of more than 95%, intersects with the nozzle plate or its fold. This ensures that the air flowing out of the impeller interacts with the nozzle plate or the outer fold.

It has been found that for fans corresponding to the previously discussed features, pressure-side, radially limiting installation conditions can stabilize the core line of a fan optimized for such installation environments compared to an installation condition that is undisturbed on the pressure side. In this way, pressure-side stabilization can be achieved in installation with undisturbed pressure-side installation as well as in installation limited only in the axial direction, so that a fan impeller designed for radially limited pressure-side installation conditions also has excellent efficiency and acoustic values in other installation conditions and on the test bench.

In an embodiment, very special characteristic dimensions of the fan promote the desired properties. It is therefore further advantageous if the ratio of the air exit diameter D_D of the inlet nozzle to the air exit diameter D_L of the impeller at the outer edge of the cover disk is greater than or equal to 70%, and, in a further embodiment, greater than or equal to 75%.

The ratio of the axial height c of the inlet nozzle to the air exit diameter D_L of the impeller is less than or equal to 12% at the outer edge of the cover disk, in an embodiment.

The ratio of the axial distance a between the air flow exit on the cover disk and the open end of the fold of the nozzle plate to the air exit diameter D_L of the impeller on the outer edge of the cover disk is less than or equal to 20%, in an embodiment. It is also advantageous if a+b<w−D_L or a+b<(w−D_L)*tan (α), wherein w=width of the nozzle plate, which represents the smallest side length of a more rectangular contour of the nozzle plate, and b=axial height of the outer fold of the nozzle plate.

The nozzle plate of the fan according to the present disclosure can have any shape, for example it can have a rectangular, preferably square outer contour. The cover disk can advantageously have a larger outer diameter than the base disk in order to also favor the flow conditions. Such an embodiment is also particularly suitable for an installation condition in which the flow tends to continue axially downstream of the fan, i.e., in an installation situation that limits the pressure side radially. The ratio of the outside diameter of the base disk to the outside diameter of the cover disk may advantageously be between 85% and 95%, in an embodiment.

There are then various possibilities for advantageously designing and refining the teaching of the present disclosure. For this purpose, reference is made on the one hand to the claims subordinate to claim 1 and on the other hand to the following explanation of exemplary embodiments of the present disclosure with reference to the drawings. In connection with the explanation of the exemplary embodiments of the present disclosure with reference to drawings, embodiments and refinements of the teachings are also explained in general.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows in a perspective view from the outflow side a fan with an impeller with a strongly curved cover disk, a motor, a suspension and a nozzle plate with a nozzle,

FIG. 2 shows the fan according to FIG. 1 in a section on a plane through the fan axis, seen from the side, wherein the motor is not shown in section,

FIG. 3 shows an enlarged representation of a partial area from FIG. 2, with additional dimensions drawn schematically,

FIG. 4 shows the fan according to FIGS. 1, 2 and 4 in a view from the inflow side,

FIG. 5 shows the fan according to FIGS. 1, 2, 4 and 5 in a view from the outflow side,

FIG. 6 shows in a perspective view a schematic representation of an outflow side portion of a flow pattern of a fan according to the present disclosure calculated by simulation at a first operating point, and

FIG. 7 shows in a perspective view a schematic representation of an outflow side portion of a flow pattern, in a similar representation to that in FIG. 6, of a fan according to the present disclosure in a second operating point.

DETAILED DESCRIPTION OF THE DISCLOSURE

FIG. 1 shows a perspective view from the outflow side of an embodiment of a fan 1 with a radially outer curvature area 7 of the cover disk 8. The fan 1 is a backwards curved radial fan with an impeller 3, consisting of a cover disk 8, one base disk 10 and wings 9 extending between them. The impeller 3 is driven by a motor 4, here an external rotor motor with an electronic pot 21 integrated in the stator 12, to whose rotor 11 (not visible here) the impeller 3 is connected in a rotationally fixed manner.

In the exemplary embodiment, an inlet nozzle 5 is attached with fastening provisions 14 to a nozzle plate 2, which is connected to the motor 4 on the stator side via a suspension 13, consisting essentially of support struts 19 and a motor support plate 20. The cover disk 8 of the impeller 3 has an inner opening into which the inlet nozzle 5 protrudes. When the fan is in operation, the pumped medium is sucked into the inlet nozzle 5 from the nozzle plate 2, flows into the impeller 3 and is conveyed radially outwards by the wings 9 as a result of their rotational movement. In the exemplary embodiment, the nozzle plate 2 has an approximately rectangular, here square outer contour, and a fold 6 is formed on the radially outer edge, which is directed towards the outflow side, i.e., towards the impeller 3. Furthermore, fastening provisions 30 for fastening the nozzle plate 2 or the entire fan 1 to a higher-level system, for example an air conditioning box unit, a ventilation system or a cooling device, are formed on the nozzle plate 2.

FIG. 2 shows the fan according to FIG. 1 in a section on a plane through the fan axis, seen from the side, wherein the motor 4 with stator 12 and rotor 11 is not shown in section. The curved outer area 7 of the cover disk 8 of the impeller 3 can be clearly seen, as can the fold 6 in the outer area of the nozzle plate 2.

The support struts 19 of the suspension 13 are attached to the nozzle plate 2 by means of fasteners 27, which, in an embodiment, are screwed. The support plate 20 of the suspension 13 is attached to the stator 12 of the motor 4 with fasteners 15, which, in an embodiment, are also screwed. On the rotor 11 of the motor 4, the impeller 3 is connected to fasteners 16 in a rotationally fixed manner, which, in an embodiment, are screwed. The inlet nozzle 5 is attached to the nozzle plate 2 with fasteners 14. In other embodiments, it can also be manufactured integrally as a component with the nozzle plate 2. The inlet nozzle 5 projects into an inner opening which has the cover disk 8 of the impeller 3.

When the fan is in operation, the pumped medium flows from the suction side, in the illustration according to FIG. 2 from the left, into the inlet nozzle 5, from where it enters the impeller 3 and is then conveyed radially outward by the impeller 3 through its rotational movement before it flows away from the fan 1 at the exit 29 of the impeller 3, which extends between the radially outer edges of the cover disk 8 and the base disk 10.

Between the inlet nozzle 5 and cover disk 8 of the impeller 3, in the overlap area, a radial gap 28 is formed, through which a secondary flow enters the impeller 3, which comes from the outflow side of the impeller 3 and thus has the higher pressure level on the outflow side. This secondary flow is essential for high efficiencies and low sound levels of the fan, as it has a stabilizing effect on the flow conditions in the impeller 3.

On the outflow side, the flow flowing out close to the cover disk interacts with the nozzle plate 2, in particular at its fold 6, due to the strongly curved cover disk 8 in the curvature area 7. Advantageous effects can thereby be achieved in a targeted manner. On the one hand, the secondary flow itself is influenced, in particular its swirl is reduced, on the other hand, the behavior of the entire flow flowing out of the impeller 3 at the exit 29 can be significantly influenced. In this way, improvements in terms of efficiency and/or noise emissions can be achieved, at least for a range of operating points of the fan.

FIG. 3 shows an enlarged representation of a partial area from FIG. 2, with additional dimensions drawn schematically. This is the area essential to the present disclosure near the fold 6 of the nozzle plate 2 and near the outer edge of the cover disk 8 of the impeller 3 with its curvature area 7. The inner, flow-guiding contour of the cover disk 8 facing the wings 9 has, as seen in section according to FIG. 3, an exit direction 33 at the radially outer end of the cover disk 8 at the impeller exit, which, as seen in section, is a straight, imaginary tangential extension to the cover disk. Depending on the embodiment, this exit direction 33 can be variable over the circumference of the cover disk, in which case an average exit direction is decisive. In the exemplary embodiment, the exit direction 33 on the cover disk 8 is advantageously inclined backwards significantly beyond the radial direction 32 and, viewed in the outflow direction, points towards the nozzle plate 2, so to speak backwards with respect to the main flow direction of the impeller 3 from left to right in the view shown.

This exit direction 33 advantageously, in an embodiment, has an angle α 26, measured relative to the radial direction 32, of more than 35°, and, in an embodiment, more than 45°, at the outer end of the cover disk 8 or its curvature area 7. As a result, the outflow from the impeller close to the cover disk is diverted towards the nozzle plate 2 or its fold 6.

Advantageously, seen in a section through the fan axis, the imaginary extension of the cover disk 8 or its curvature area 7 in the form of the (middle) exit direction 33 intersects with the nozzle plate 2 or its outer fold 6. The middle exit direction 33 advantageously, in an embodiment, intersects with the nozzle plate 2 or its outer fold 6 over the entire, rather angular circumference of the nozzle plate 2, but at least over a large area of the circumference of more than 95%. This ensures the advantageous interaction of the flow flowing out of the impeller 3 with the nozzle plate 2 or its outer fold 6.

It was found that pressure-side, radial-limiting installation conditions (walls), which may not be applied to the axle as a rotational body, can stabilize the characteristic of a radial fan optimized for such installation environments, compared to a pressure-free installation condition. With the measure described, such pressure-side stabilization can be achieved even in an installation that is actually undisturbed on the pressure side or only limited in the axial direction, so that the fan impeller optimized for radially limited pressure-side installation conditions also has excellent efficiency and acoustic values in the other installation conditions.

FIG. 3 shows some characteristic axial extension dimensions for the fan, such as, for example, the axial distance a 25 of the flow exit on the cover disk 8 to the open end of the fold 6 of the nozzle plate 2, the axial height b 24 of the fold 6 of the nozzle plate 2 or the axial extent c 23 of the inlet nozzle 5. In addition, some characteristic dimensions are shown in the radial direction, such as the exit diameter D_D 22 of the inlet nozzle 5, the exit diameter D_L 18 of the impeller 3 on the outer edge of the cover disk 8 and a width w 17 of the nozzle plate 2, which is intended to represent the smallest side length of a more rectangular contour of the nozzle plate 2. The diameters are measured with respect to the fan axis.

It is advantageous to have a large nozzle ratio D_D/D_L>70%, and, in an embodiment, advantageously >75%, in order to achieve high volume flows and to enable the design of an axially compact inlet nozzle 5 with a very low axial extension c 23. The axial height c 23 of the inlet nozzle 5 then has a ratio c/D_L<12% in relation to the outer diameter D_L 18. This is advantageous because then, in combination with a certain axial height b 24 of the fold 6 of the nozzle plate 2, a small axial distance a 24 of the outflow surface from the impeller 3 on the cover disk contour to the outer edge of the fold 6 can be achieved to promote the desired flow interaction. A ratio a/D_L not greater than 20% is advantageous. Further advantageous in this sense is a<w−D_L or a<(w−D_L)*tan(α). In order to achieve an effective interaction of the current leaving the impeller 3 with the outer fold 6 of the nozzle plate, a certain minimum height b 24 of the fold 6 is advantageous, in particular the ratio b/D_L to the diameter D_L 13 of the impeller 3 on its cover disk 8 is greater than or equal to 2%, and further advantageous >=3%, in an embodiment.

In FIG. 4, the fan 1 according to FIGS. 1, 2 and 4 is shown in a view from the inflow side. Within the inlet nozzle 5 of the impeller 3 you can see the base disk 10 and parts of the wings 9 as well as the rotor 11 of the motor 4, to which the impeller is attached with fasteners 16. The wings 9 have a three-dimensional shape and a large part of the concavely curved suction side of the wings 9 can be seen in the view. In this view it can also be seen the rectangular, here even square, outer contour of the nozzle plate 2 or its outer edge, on which also the fold 6 can be seen. Furthermore, both the fasteners 27, with which support struts (19) are fastened to the nozzle plate 2, as well as fastening provisions 30, with which the fan 1 can be fastened to a higher-level system, can be seen.

FIG. 5 shows a view from the outflow side of the fan 1 as shown in FIGS. 1 to 4. The stator 12 of the motor 4 with the electronics pot 21 integrated thereon can be seen. The stator 12 is attached to the suspension 13 or its motor support plate 20 with fasteners 15. The base disk 10 and the cover disk 8 of the impeller 3 can be seen, since the latter has a larger outer diameter than the former. Such an embodiment is particularly suitable for an installation condition in which the flow continues to flow axially after the fan, i.e., an installation situation that limits radially downstream of the fan impeller. Advantageously, in an embodiment, the ratio of the outside diameter of the base disk 10 to the outside diameter of the cover disk 8 is approximately between 85% and 95%. Areas near the rear edge of the 6 wings 9 can be seen in the exemplary embodiment. They extend on the cover disk 8 to at most a few millimeters almost or completely up to its outer diameter, whereby the flow guidance along the curved contour of the cover disk 8 on its curved outer area 7 is favored.

The suspension 13 includes support struts 19, which in the exemplary embodiment have a rather round cross-section, and an engine support plate 20. Other types of engine suspension are also conceivable, for example consisting essentially of flat material.

FIG. 6 is a schematic, perspective representation of a flow pattern calculated by simulation in the exit area of a fan such as the one from FIGS. 1 to 5 at a first operating point, which is characterized by a rather low delivery volume flow, based on speed, impeller diameter and exit area. From the impeller 3 you can see the cover disk 8 with the curved outer area 7 and a flow exit surface 29. You can also see the nozzle plate 2 with inlet nozzle 5 and fold 6. For the sake of completeness, it should be mentioned that the fan is only partially shown. The main delivery volume flow emerging from the impeller is, as can be seen from the projected streamlines 31 shown on a sectional plane through the fan axis, inclined in its entirety towards the nozzle plate 2 or its imaginary radial extension.

What is important is that an air flow emerging near the cover disk 8 at the curved area 7 interacts with the fold 6 of the nozzle plate 2. This can positively influence the course of the main delivery volume flow downstream of the impeller exit 29 and/or the flow conditions in the recirculation area (in particular by reducing swirl) between the nozzle plate 2 and the cover disk 8. The important secondary flow between inlet nozzle 5 and cover disk 8 (see also description of FIG. 3) is significantly influenced by the flow conditions in this recirculation area.

The illustration in FIG. 6 is intended to show only by way of example how an interaction between the air flow emerging from an impeller 3 can take place due to the curved area with the fold 6 of the nozzle plate 2. It is based on a simulation. The streamlines 31 shown are based on local velocity vectors that are projected onto the streamline plane shown.

FIG. 7 is, comparable to FIG. 6, a schematic, perspective representation of a flow pattern calculated by simulation in the exit area of a fan such as the one from FIGS. 1 to 5 at a second operating point, which is characterized by a rather higher delivery volume flow, based on speed, impeller diameter and exit area. From the impeller 3 you can see the cover disk 8 with the curved outer area 7 and a flow exit surface 29. You can also see the nozzle plate 2 with inlet nozzle 5 and fold 6. The main delivery volume flow emerging from the impeller is, as can be seen from the streamlines 31, directed away from the nozzle plate 2 and, seen in section, flows in a direction obliquely away from the nozzle plate 2 or its imaginary radial extension.

What is important here is also that an air flow emerging near the cover disk 8 at the curved area 7 interacts with the nozzle plate 2 or its the fold 6. This can positively influence the course of the main air flow and/or the flow conditions in the recirculation area (in particular by reducing swirl) between the nozzle plate 2 and the cover disk 8. The important secondary flow between inlet nozzle 5 and cover disk 8 (see also description of FIG. 3) is significantly influenced by the flow conditions in this recirculation area.

The illustration in FIG. 7 is intended to show only by way of example how an interaction between the air flow emerging from an impeller 3 can take place due to the curved area with the fold 6 of the nozzle plate 2. It is based on a simulation. The streamlines 31 shown are based on local velocity vectors that are projected onto the streamline plane shown.

To avoid repetition with regard to further advantageous embodiments of the fan according to the present disclosure, reference is made to the general part of the description and to the appended claims.

Finally, it should be expressly noted that the above-described exemplary embodiments of the fan according to the present disclosure merely serve to discuss the claimed teaching, but do not restrict it to the exemplary embodiments.

LIST OF REFERENCE NUMERALS

• • 1 Fan
  • 2 Nozzle plate
  • 3 Fan impeller
  • 4 Motor
  • 5 Inlet nozzle
  • 6 Fold of the nozzle plate
  • 7 Curved outer area of the cover disk
  • 8 Cover disk of an impeller
  • 9 Wings of an impeller
  • 10 Base disk of an impeller
  • 11 Motor rotor
  • 12 Motor stator
  • 13 Suspension
  • 14 Fastener inlet nozzle-nozzle plate
  • 15 Fastener of the stator of the engine to the suspension
  • 16 Fastener of the impeller to the motor rotor
  • 17 Extension w of the nozzle plate transverse to the fan axis
  • 18 Diameter D_L of the impeller on the outside of the cover disk
  • 19 Suspension support strut
  • 20 Motor support plate of the suspension
  • 21 Electronic pot in the motor stator
  • 22 Inlet nozzle diameter D_D at its outflow edge
  • 23 Axial extent c of the inlet nozzle
  • 24 Axial extension b of the fold 6 of the nozzle plate 2
  • 25 Axial distance a of the outer edge of the cover disk 8 to the fold 6 of the nozzle plate 2
  • 26 Angle α between the exit of the inner flow contour of the cover disk at the outer edge to a parallel to the fan axis, seen in a section on a plane through the fan axis
  • 27 Fastener of the support struts to the nozzle plate
  • 28 Radial gap between inlet nozzle 5 and cover disk 8
  • 29 Exit surface from the impeller 3
  • 30 Fastening provisions nozzle plate at superordinate system
  • 31 Projected streamlines in a cutting plane
  • 32 Radial direction
  • 33 Exit direction

Claims

1. A fan (1), comprising: motor (4),an impeller (3) driven in rotation by the motor (4),an inlet nozzle (5) anda nozzle plate (2) extending around the inlet nozzle (5),wherein the impeller (3) essentially consists of a base disk (10), a cover disk (8) and several wings (9) extending between them,and wherein the nozzle plate (2) has an edge folded towards the pressure side and the cover disk (8) is rounded on its outer edge towards the suction side,and wherein the fold (6) of the nozzle plate (2) and the rounding of the cover disk (8) are shaped and dimensioned in such a way that the outflow from the impeller (3) close to the cover disk interacts with the edge of the nozzle plate (2).

2. The fan according to claim 1, wherein the section at a plane through the fan axis which can be assigned to a circumferential position of the impeller (3) or of the shroud (8) or of the nozzle plate (2), the tangential extension of the inner shroud contour facing the wings (9) intersects—at its radially outer edge—the nozzle plate (2), viewed including its bend (6), over at least 90%, preferably over 100% of the circumferential positions.

3. The fan according to claim 1, wherein the rounding of the cover disk (8) is designed in the form of a strong curvature (7).

4. The fan according to the claim 1, wherein an inner contour of the rounding and thus of the outer edge of the cover disk (8), at the outer end of the cover disk (8), in the area of the impeller exit, gives the air flow an air exit direction which is defined through a straight, tangential extension of the cover disk (8).

5. The fan according to claim 4, wherein the air exit direction is constant or variable over the circumference of the cover disk (8).

6. The fan according to claim 4, wherein the air exit direction is directed backwards with respect to the main flow direction, towards the nozzle plate (2).

7. The fan according to claim 6, wherein the air exit direction, at the outer end of the cover disk (8), i.e., at its curvature area (7), has an angle α (26) of more than 35°, preferably more than 45°, to the radial direction.

8. The fan according to claim 1, wherein an imaginary extension of the cover disk (8), starting from its curvature area (7), preferably over the entire circumference or over a large area of the circumference of more than 95%, intersects with the nozzle plate (2) or its fold (6).

9. The fan according to claim 1, wherein a ratio of an air exit diameter DD (22) of the inlet nozzle (5) to an air exit diameter DL (18) of the impeller (3) at the outer edge of the cover disk (8) is greater than or equal to 70%, preferably greater than or equal to 75%.

10. The fan according to claim 1, wherein a ratio of an axial height c (23) of the inlet nozzle (5) to an air exit diameter DL (18) of the impeller (3) at the outer edge of the cover disk (8) is less than or equal to 12%.

11. The fan according to claim 1, wherein a ratio of an axial distance a (25) between an air flow exit on the cover disk (8) and the open end of the fold (6) of the nozzle plate (2) to air exit diameter DL (18) of the impeller (3) at the outer edge of the cover disk (8) is less than or equal to 20%.

12. The fan according to claim 9 in that a+b<w−DL or a+b<(w−DL)*tan (α), wherein w=radial width of the nozzle plate (2), which represents the smallest side length of a rather rectangular contour of the nozzle plate (2), and b=axial height of the outer fold (6) of the nozzle plate (2).

13. The fan according to claim 1, wherein the nozzle plate (2) has a rectangular, preferably square outer contour.

14. The fan according to claim 1, wherein the cover disk (8) has a larger outer diameter than the base disk (10).

15. The fan according to claim 14, wherein a ratio of the outer diameter of the base disk (10) to the outer diameter of the cover disk (8) is in the range from/between 85% and/to 95%.

16. The fan according to claim 1, wherein an axial height b (24) of the outer fold (6) of the nozzle plate (2) is at least 2%, advantageously at least 3%, of an outer diameter DL (18) of the cover disk (8) of the impeller (3) at the curvature area (7).