JP2024517441A - Fans, more specifically radial or cross-flow fans - Google Patents

Abstract

A fan (1), more particularly a radial or cross-flow fan, comprising a motor (4), an impeller (3) driven in rotation by the motor (4), a suction nozzle (5) and a nozzle plate (2) extending around the suction nozzle (5), the impeller (3) being substantially composed of a base disk (10), a cover disk (8) and several vanes (9) extending between the base disk (10) and the cover disk (8), the nozzle plate (2) having a crease-shaped edge towards the pressure side and the cover disk (8) having a rounded outer edge towards the suction side, the crease (6) of the nozzle plate (2) and the roundness of the cover disk (8) being shaped and dimensioned such that the outflow from the impeller (3) close to the cover disk interacts with the edge of the nozzle plate (2). [Selected Figure] Figure 3

Description

The present invention relates to a fan, and more particularly to a radial or mixed flow fan.
The fan has a motor, an impeller that is rotated by the motor, a suction nozzle, and a nozzle plate that extends around the suction nozzle.
The impeller is comprised of a base disc, a cover disc, and a number of blades extending between the base disc and the cover disc.

Radial or mixed flow fans of the subject type are well known in practice.
By way of example only, see US Pat. No. 5,399,633, which itself shows a radial fan configuration.

Regardless of the particular design or application, the subject type of fan must have the same high efficiency both when installed and on a test bench, a requirement that may seem trivial.
However, with an impeller and corresponding fan optimized for a specific installation, it was necessary to determine whether adverse behavior could occur on a test bench.

Additionally, radial and mixed flow impellers have been developed that exhibit very high efficiencies under test bench conditions, but in certain installations such efficiencies are not achievable.
Also, some radial and mixed flow impellers have very high efficiency under installation constraints on the pressure side, but are less efficient under test bench conditions.
These challenges exist because test benches and test bench conditions are intended to provide information about fan performance in a specific application.

DE 10 2017 110 642 A1

The present invention is therefore based on the objective of designing and developing a general purpose fan in such a way that it provides the highest possible efficiency both in pressure side installation situations and in test bench conditions.
The difference between the two situations should at least be as small as possible.

The aforementioned object is solved by a fan having the features of claim 1.
The nozzle plate has a creased edge towards the pressure side, while the cover disk has a rounded outer edge towards the suction side.
The creases in the nozzle plate and the radius of the cover disk are shaped and dimensioned such that the outflow from the impeller proximate the cover disk interacts with the creases in the nozzle plate.

The present invention relates to a combination of a special nozzle plate and a special cover disk, where the nozzle plate has a creased edge towards the pressure side and the cover disk is rounded (i.e. curved) towards the suction side.
These two features can be combined, resulting in a joint effect in that the outflow from the impeller close to the cover disc interacts with the folds in the nozzle plate.
This makes it possible to achieve a local stabilization similar to the installation situation, so that the fan according to the invention shows the same or almost the same efficiency on the test bench as in the particular installation situation.

It is advantageous if, in a cross section of the impeller, cover disk or nozzle plate in a plane passing through the fan axis which can be assigned to a circumferential position, a tangential extension of the inner shape of the cover disk facing the blade intersects radially outside this extension with the nozzle plate including the fold in at least more than 90% of the circumferential positions, preferably more than 100%.
This further enhances the advantages of the present invention with regard to stabilizing the air flow.

It is advantageous if the rounding of the cover disk has a strong curvature on its outer edge, which can be seen in combination with the crease-shaped edge of the nozzle plate.

In particular, the rounded inner (blade side) shape and therefore the inner shape of the outer edge of the cover disk directs the exit direction of the air flow in the impeller outlet region at the outer end of the cover disk in the direction of a straight extension of the tangential direction of the cover disk.
The curvature gives the air a particular exit direction, and the curvature can be designed so that the exit direction of the air is constant or variable around the circumference of the cover disc.
Any or different influences can be exerted over the circumference of the cover disc.

Additionally, the exit direction of the airflow may be directed rearward relative to the main flow direction, toward the nozzle plate.
However, such a design is not essential.

It is further advantageous if at the outer end of the cover disc, i.e. in the curved region of the cover disc, the outlet direction of the air flow has an angle of more than 35° to the radial direction, preferably this angle being more than 45°.
As a result, the outflow from the impeller near the cover disk is deflected towards the nozzle plate or fold.
This results in an interaction.

Specifically, an imaginary extension line of the cover disk starts from the curved region of the cover disk and intersects with the nozzle plate or the nozzle plate fold, preferably over the entire circumference or over a wide area of at least 95% or more of the entire circumference.
This ensures that the air exiting the impeller interacts with the nozzle plate or outer folds.

For fans corresponding to the aforementioned features, a radially restricted installation condition on the pressure side can provide a more stable fan core line optimized for such an installation environment compared to an undisturbed installation condition on the pressure side.
In this way, stabilization of the pressure side can be achieved in installations where the pressure side is not disturbed, as in the case of axial-only installations, and fan impellers optimized for installations where the pressure side is radially limited will provide superior efficiency and acoustics in other installations and on test benches.

Specifically, very specific and distinctive dimensions of the fan facilitate desirable characteristics.
It is therefore further advantageous if the ratio of the air outlet diameter DD of the suction nozzle to the air outlet diameter DL of said impeller is at the outer edge of the cover disc greater than or equal to 70%, preferably greater than or equal to 75%.

The ratio of the axial height c of the suction nozzle to the air outlet diameter DL of the impeller is less than 12% at the outer edge of the cover disk.

The ratio of the axial distance a between the airflow outlet on the cover disk and the open end of the fold in the nozzle plate to the airflow outlet diameter DL of the impeller is less than 20% at the outer edge of the cover disk.
Advantageously, a+b<w-DL, or a+b<(w-DL)*tan(α), where w is ^the width of the nozzle plate, representing the length of the smallest side of the somewhat rectangular outline of the nozzle plate, and b is the axial height of the outer crease of the nozzle plate.

The nozzle plate of the fan according to the invention may have any shape, for example a rectangular, preferably square, outline.
To obtain favourable flow conditions, the outer diameter of the cover disc is advantageously larger than the outer diameter of the base disc.
Such an embodiment is also particularly suited to installation conditions where the flow tends to continue axially downstream of the fan, i.e., installations that are radially restrictive on the pressure side.
Advantageously, the ratio of the outer diameter of the base disc to the outer diameter of the cover disc is between 85% and 95%.

Various possibilities exist for advantageously designing and improving the present invention.
To this end, reference is made, on the one hand, to the claims dependent on claim 1 and, on the other hand, to the following description of an embodiment of the invention which makes reference to the drawings, in which:
In connection with the description of the embodiments of the invention with reference to the drawings, embodiments and improvements of the invention are also generally described.

FIG. 2 shows a perspective view from the outflow side of a fan having an impeller with a strongly curved cover disk, a motor, a suspension and a nozzle plate with nozzles. FIG. 2 is a cross-sectional view of the fan according to FIG. 1 taken transversely in a plane passing through the fan axis, the motor not shown; 3 is an enlarged view of a partial area of FIG. 2 with additional dimensions generally indicated; FIG. 4 shows the fan according to FIGS. 1, 2 and 3, viewed from the inlet side; FIG. 5 shows the fan according to FIGS. 1, 2, 3 and 4, viewed from the outflow side; FIG. 2 is a schematic perspective view of the outflow part of the flow pattern of a fan according to the invention calculated by simulation in a first operating situation; FIG. 7 is a schematic perspective view similar to FIG. 6 of the outflow portion of the flow pattern of a fan according to the invention in a second operating condition.

FIG. 1 shows a perspective view from the outflow side of an embodiment of a fan 1 having a radially outer curved region 7 of a cover disc 8 .
The fan 1 is a backward curved radial fan having an impeller 3 consisting of a cover disc 8, a base disc 10 and blades 9 extending between the cover disc 8 and the base disc 10.
The impeller 3 is driven by a motor 4 (here, an external rotor motor having an electronic pot 21 built into a stator 12), and the impeller 3 is connected to its rotor 11 (not shown) in a manner that fixes the direction of rotation.

In the embodiment, the suction nozzle 5 is attached to the nozzle plate 2 by fasteners 14, and the nozzle plate 2 is connected to the motor 4 on the stator 12 side via a suspension 13 consisting essentially of a support post 19 and a motor support plate 20.
The cover disc 8 of the impeller 3 has an internal opening into which the suction nozzle 5 projects.
When the fan 1 is operated, aspirated air is drawn through the nozzle plate 2 into the suction nozzles 5, flows into the impeller 3 and is carried radially outward by the rotational movement of the blades 9.
In the embodiment, the nozzle plate 2 has a substantially rectangular (here, square) outer shape, and a fold 6 is formed on the radially outer edge of the nozzle plate 2 toward the outflow side (i.e., toward the impeller 3).
Furthermore, the nozzle plate 2 is formed with fasteners 30 for fixing the nozzle plate 2 and the entire fan 1 to a higher-level system (for example, an air conditioning box unit, a ventilation system, or a cooling device).

FIG. 2 shows a cross-section of the fan 1 according to FIG. 1 in a transverse view in a plane through the fan axis, where the motor 4 with the stator 12 and the rotor 11 is not shown.
The outer curved area 7 of the cover disk 8 of the impeller 3 is clearly visible, as are the folds 6 in the outer area of the nozzle plate 2 .

The support posts 19 of the suspension 13 are attached to the nozzle plate 2 by fasteners 27 (preferably screwed).
A support plate 20 of the suspension 13 is attached to the stator 12 of the motor 4 by fasteners 15 (preferably screwed).
On the rotor 11 of the motor 4, the impeller 3 is connected in a rotationally fixed manner to a fastener 16 (advantageously screwed).
The suction nozzle 5 is attached to the nozzle plate 2 by fasteners 14 .
In other embodiments, the suction nozzle 5 can be manufactured as an integral part of the nozzle plate 2 .
The suction nozzle 5 projects into an internal opening of the impeller 3 which has a cover disk 8 .

When the fan 1 is operating, the air to be sucked in flows into the suction nozzle 5 from the suction side, which is on the left side in FIG. 2, enters the impeller 3, is carried radially outward by the rotational movement of the impeller 3, and leaves the fan 1 at the outlet 29 of the impeller 3, which extends between the radially outer ends of the cover disc 8 and the base disc 10.

In the overlap region between the suction nozzle 5 of the impeller 3 and the cover disk 8, a radial gap 28 is formed through which the secondary flow coming from the outlet side of the impeller 3 flows into the impeller 3, which causes an increase in the pressure level on the outlet side.
This secondary flow has the effect of stabilizing the flow conditions within the impeller 3 and is therefore essential for achieving high efficiency and low noise levels for the fan 1.

On the outflow side, the strongly curved cover disc 8 in the curved region 7 ensures that the flow emerging from the area close to the cover disc 8 interacts with the nozzle plate 2 , in particular at the fold 6 .
In this way, advantageous effects can be achieved in a targeted manner.
On the one hand, the secondary flow itself is influenced, in particular the vortices are reduced.
On the other hand, the behavior of the entire flow leaving the impeller 3 at the outlet 29 can be significantly affected.
In this way, improvements in efficiency and/or noise may be achieved, at least over a range of operating conditions of the fan 1 .

FIG. 3 is an enlarged view of a partial area of FIG. 2 with additional dimensions shown diagrammatically.
This area is the area of interest in the present invention, near the fold 6 of the nozzle plate 2 and near the outer edge of the cover disc 8 of the impeller 3 which has a curved area 7 .
The inner flow guiding shape of the cover disk 8 facing the blades 9, as can be seen in the cross-sectional view of FIG. 3, has an outlet direction 33 at the radially outer end of the cover disk 8 at the outlet of the impeller 3, which, when viewed in cross-section, is the direction of an imaginary straight tangential extension of the cover disk 8.
In some embodiments, this exit direction 33 may vary over the circumference of the cover disc 8, in which case an average exit direction is determined.
In this embodiment, the outlet direction 33 of the cover disk 8 is advantageously inclined significantly rearward from the radial direction 32 and points towards the nozzle plate 2 when viewed from the outflow direction and points rearward, so to speak, with respect to the main flow direction from the left to the right of the impeller 3 in the figure.

Advantageously, this exit direction 33 has an angle α 26 to the radial direction 32 at the outer end of the cover disk 8 or of its curved region 7 which is greater than 35° (preferably greater than 45°).
As a result, the outflow from the impeller 3 in the portion close to the cover disc 8 is deflected towards the nozzle plate 2 or its folds 6 .

Advantageously, when viewed in a cross section through the fan axis, an imaginary extension of the (average) outlet direction 33 of the cover disk 8 or of its curved region 7 intersects with the nozzle plate 2 or with the outer fold 6 thereof.
The average exit direction 33 intersects with the nozzle plate 2 or with its outer folds 6 over the entire circumference of the nozzle plate 2 or over a significant angle of the entire circumference of the nozzle plate 2, at least over a wide area exceeding 95% of the circumference.
In this way it is ensured that the flow exiting the impeller 3 interacts favourably with the nozzle plate 2 or with the folds 6 on its outer surface.

It was found that, when there is a radial installation restriction (wall) on the positive pressure side, rather than a condition relative to the rotating shaft, it is possible to stabilize the characteristics of the radial fan 1 optimized for such an installation environment, compared to an installation condition without any restriction.
Such stabilization of the pressure side in the manner described above can be achieved even when the pressure side is actually undisturbed or only axially constrained, and a fan wheel 3 optimized for a radially constrained pressure side installation will provide superior performance and acoustic values in other installations.

In FIG. 3 some characteristic axial dimensions of the fan 1 are shown, such as for example the axial distance a 25 from the flow outlet of the cover disk 8 to the open end of the fold 6 of the nozzle plate 2, the axial length b 24 of the fold 6 of the nozzle plate 2 or the axial length c 23 of the suction nozzle 5.
Furthermore, some radial characteristic dimensions are shown, such as the air outlet diameter DD22 of the suction nozzle 5, the air outlet diameter DL18 of the impeller 3 on the outer edge of the cover disc 8, and the width w17 of the nozzle plate 2 (representing the length of the smallest side of the rectangular outline of the nozzle plate 2).
These diameters are measured relative to the fan axis.

In order to achieve a high volume flow rate and to be able to design an axially compact suction nozzle 5 with a very short axial length c23, it is advantageous for the nozzle ratio DD/DL to be >70% (preferably >75%).
In this case, the ratio c/DL of the axial length c23 of the suction nozzle 5 to the air outlet diameter DL18 is c/DL<12%.
This is advantageous because, in combination with the particular axial length b24 of the folds 6 of the nozzle plate 2, the axial distance a25 of the outflow surface from the cover disk 8 of the impeller 3 to the outer edge of the folds 6 is short, promoting the desired flow interaction.
It is advantageous if the ratio a/DL is less than or equal to 20%.
Similarly, it is more advantageous if a<w-DL or a<(w-DL) ^* tan(α).
In order to ensure an effective interaction between the flow leaving the impeller 3 and the outer folds 6 of the nozzle plate 2, it is advantageous for the certain minimum length b24 of the folds 6, in particular the ratio b/DL to the diameter DL13 of the impeller 3 on the cover disc 8, to be greater than or equal to 2%, and even more advantageously greater than or equal to 3%.

FIG. 4 shows the fan 1 according to FIGS. 1, 2 and 3 as viewed from the inlet side.
Within the suction nozzle 5 of the impeller 3 one can see the base disc 10 , part of the blades 9 and the rotor 11 of the motor 4 to which the impeller 3 is attached by fasteners 16 .
In this figure the three-dimensional shape of the blades 9 and the concavely curved suction side major part can be seen.
In this figure, the rectangular (here square) outline of the nozzle plate 2 or its outer edge can also be seen, as can the folds 6 thereon.
Additionally, both fasteners 27 can be seen which secure the support posts 19 to the nozzle plate 2, as well as fasteners 30 which can secure the fan 1 to a host system.

FIG. 5 is a view of the fan 1 shown in FIGS. 1 to 4 as viewed from the outflow side.
The stator 12 of the motor 4 in which the electronic pot 21 is integrated can be seen.
The stator 12 is attached to the suspension 13 and to the motor support plate 20 by fasteners 15 .
The base disc 10 and the cover disc 8 of the impeller 3 can be seen, since the outer diameter of the cover disc 8 is larger than the outer diameter of the base disc 10 .
Such an embodiment is particularly suited to installations where the flow continues axially after passing the fan 1, i.e. where there is a radial restriction downstream of the fan impeller 3.
Advantageously, the ratio of the outer diameter of the base disc 10 to the outer diameter of the cover disc 8 is approximately between 85% and 95%.
In the embodiment, the area near the trailing edge of six wings 9 can be seen.
These vanes 9 extend over almost all or all of the outer diameter of the cover disk 8, at most a few millimeters, which helps to direct the flow along the curved shape of the outer curved region 7 of the cover disk 8.

In this embodiment, the suspension 13 comprises a support strut 19 having a substantially circular cross section, and a motor support plate 20 .
For example, other types of engine suspensions made of essentially flat material are also contemplated.

FIG. 6 is a schematic perspective view of the flow pattern calculated by simulation in the outlet region of a fan 1 such as FIGS. 1 to 5 in a first operating regime, which is characterized by a fairly low volumetric flow rate based on speed, impeller diameter and outlet area.
The impeller 3 has a cover disk 8 with an outer curved region 7 and a flow outlet surface 29 .
Also visible is the nozzle plate 2 with the suction nozzle 5 and the crease 6 .
For complete understanding, it should be mentioned that the fan 1 is only partially shown.
As can be seen from the projected streamlines 31 shown on a cross-sectional plane passing through the fan axis, most of the flow exiting the impeller 3 is inclined entirely toward the nozzle plate 2 or its imaginary radial extension.

What is important is that the air flow near the curved region 7 of the cover disc 8 interacts with the folds 6 in the nozzle plate 2 .
This can positively influence the path of most of the flow downstream of the impeller outlet 29 and/or can positively influence the flow conditions in the recirculation zone between the nozzle plate 2 and the cover disk 8 (in particular by reducing vortices).
The important secondary flows between the suction nozzle 5 and the cover disk 8 (see also the description of FIG. 3) are strongly influenced by the flow conditions in this recirculation zone.

FIG. 6 is intended to show, by way of example, how the air flows exiting the impeller 3 may interact with each other due to the nozzle plate 2 having curved regions 7 and folds 6 .
This is based on simulations.
The illustrated streamlines 31 are shown based on local velocity vectors projected onto the illustrated streamline surface.

FIG. 7, comparable to FIG. 6, is a schematic perspective view of the flow pattern calculated by simulation in the outlet region of fan 1 as in FIGS. 1 to 5 in a second operating regime, which is characterized by a significantly higher volumetric flow rate based on speed, impeller diameter and outlet area.
The impeller 3 has a cover disk 8 with an outer curved region 7 and a flow outlet surface 29 .
Also visible is the nozzle plate 2 with the suction nozzle 5 and the fold 6 .
As can be seen from the flow lines 31, most of the flow exiting the impeller 3 flows away from the nozzle plate 2, and when viewed in cross section, flows obliquely away from the nozzle plate 2 or its virtual radial extension.

What is important here is that the air flow near the curved area 7 of the cover disc 8 interacts with the nozzle plate 2 or its folds 6 .
In this way, the path and/or flow conditions of most of the air flow in the recirculation area between the nozzle plate 2 and the cover disc 8 can be positively influenced.
The important secondary flows between the suction nozzle 5 and the cover disk 8 (see also the description of FIG. 3) are strongly influenced by the flow conditions in this recirculation zone.

FIG. 7 is intended to show, by way of example, how the air flows exiting the impeller 3 may interact with each other due to the nozzle plate 2 having curved regions 7 and folds 6 .
This is based on simulations.
The illustrated streamlines 31 are shown based on local velocity vectors projected onto the illustrated streamline surface.

In order to avoid repetition regarding further advantageous embodiments of the fan according to the invention, please refer to the general part of the description and the appended claims.

Finally, it should be expressly noted that the above-described embodiments of the fan according to the present invention are merely intended to illustrate the claimed teachings and are not intended to limit the teachings to the embodiments.

LIST OF SYMBOLS 1 Fan 2 Nozzle plate 3 Fan impeller 4 Motor 5 Suction nozzle 6 Nozzle plate fold 7 Outer curved area of cover disc 8 Impeller cover disc 9 Impeller blades 10 Impeller base disc 11 Motor rotor 12 Motor stator 13 Suspension 14 Suction nozzle to nozzle plate fastener 15 Motor stator to suspension fastener 16 Impeller to motor rotor fastener 17 Nozzle plate width w across the fan axis
18 . . . Cover disk outer air outlet diameter DL
19 ... Suspension support column 20 ... Suspension motor support plate 21 ... Electronic pot in motor stator 22 ... Diameter DD of outlet end of suction nozzle
23 ... Axial length c of suction nozzle
24 . . . Axial length b of fold 6 of nozzle plate 2
25 . . . Axial distance a from the outer edge of the cover disk 8 to the fold 6 of the nozzle plate 2
26 ... Angle α between the inner shape of the outlet at the outer edge of the cover disk and the radial direction, as seen in a cross section of a plane passing through the fan axis
27 ... Fastener between the support strut and the nozzle plate 28 ... Radial gap between the suction nozzle 5 and the cover disk 8 29 ... Outlet surface of the impeller 3 30 ... Fastener between the upper system and the nozzle plate 31 ... Streamlines projected on the cut surface 32 ... Radial direction 33 ... Outlet direction

Claims (16)

A fan (1), more specifically a radial fan or a cross-flow fan, having a motor (4), an impeller (3) rotated by the motor (4), a suction nozzle (5), and a nozzle plate (2) extending around the suction nozzle (5),
The impeller (3) is substantially composed of a base disc (10), a cover disc (8) and several blades (9) extending between the base disc (10) and the cover disc (8);
The nozzle plate (2) has a fold (6) edge facing the pressure side,
the cover disc (8) has an outer edge which is rounded towards the suction side,
A fan (1), wherein the folds (6) of the nozzle plate (2) and the radius of the cover disc (8) are shaped and dimensioned such that the outflow from the impeller (3) close to the cover disc (8) interacts with the edge of the nozzle plate (2). The fan according to claim 1, characterized in that in a cross section of the impeller (3), the cover disk (8) or the nozzle plate (2) in a plane passing through the fan axis that can be assigned to a circumferential position, a tangential extension of the inner shape of the cover disk (8) facing the blades (9) intersects the nozzle plate (2) including the fold (6) radially outward of the extension at least over 90% of the circumferential positions, preferably over 100%. A fan according to claim 1 or 2, characterized in that the radius of the cover disk (8) is designed with a strongly curved region (7). A fan according to claims 1 to 3, characterized in that the rounded inner shape and therefore the inner shape of the outer edge of the cover disk (8) directs the outlet direction of the air flow in the outlet area of the impeller (3) at the outer end of the cover disk (8) in the direction of a straight extension of the tangential direction of the cover disk (8). A fan as claimed in any one of claims 1 to 4, characterized in that the outlet direction of the air flow is constant or variable around the circumference of the cover disc (8). A fan as claimed in any one of claims 1 to 5, characterized in that the outlet direction of the airflow is directed rearward with respect to the main flow direction and in a direction toward the nozzle plate (2). The fan according to claim 6, characterized in that at the outer end of the cover disk (8), i.e. in the curved region (7) of the cover disk (8), the outlet direction of the air flow has an angle α (26) of more than 35° with respect to the radial direction, preferably the angle α (26) is more than 45°. A fan according to any one of claims 1 to 7, characterized in that the imaginary extension of the cover disk (8) starts from the curved region (7) of the cover disk (8) and intersects with the nozzle plate (2) and the folds (6) of the nozzle plate (2), preferably over the entire circumference or over a wide area of more than 95% of the circumference. A fan according to any one of claims 1 to 8, characterized in that the ratio of the air outlet diameter DD (22) of the suction nozzle (5) to the air outlet diameter DL (18) of the impeller (3) is greater than or equal to 70%, preferably greater than or equal to 75%, at the outer edge of the cover disk (8). A fan as claimed in any one of claims 1 to 9, characterized in that the ratio of the axial height c (23) of the suction nozzle (5) to the air outlet diameter DL (18) of the impeller (3) is less than or equal to 12% at the outer edge of the cover disk (8). A fan according to any one of claims 1 to 10, characterized in that the ratio of the axial distance a (25) between the air outlet on the cover disc (8) and the open end of the fold (6) of the nozzle plate (2) to the air outlet diameter DL (18) of the impeller (3) is less than 20% at the outer edge of the cover disc (8). where w is the radial width of the nozzle plate (2) and represents the length of the smallest side of the somewhat rectangular outline of the nozzle plate (2), and b is the axial height of the outer fold (6) of the nozzle plate (2),
The fan according to any one of claims 9 to 11, characterized in that a+b<w-DL or a+b<(w-DL) ^* tan(α). A fan as claimed in any one of claims 1 to 12, characterized in that the nozzle plate (2) has a rectangular, preferably square, outline. A fan as claimed in any one of claims 1 to 13, characterized in that the outer diameter of the cover disc (8) is greater than the outer diameter of the base disc (10). The fan described in claim 14, characterized in that the ratio of the outer diameter of the base disk (10) to the outer diameter of the cover disk (8) is in the range of 85% to 95%. A fan according to any one of claims 1 to 15, characterized in that the axial height b (24) of the outer fold (6) of the nozzle plate (2) is at least 2%, preferably at least 3%, of the air outlet diameter DL (18) in the curved region (7) of the cover disk (8) of the impeller (3).