JP2001059499A - Axial flow fan for cold air circulation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce operation noises of a refrigerator by optimizing design factors of a fan such as the number of rotary blades, a hub ratio, a sweep angle, a pitch angle and a maximum camber rate so as to adapt to lowering of the noises of the fan. SOLUTION: An axial flow fan for cold air circulation is constituted of a hub 51 connected to a rotary shaft of a blowing motor and a plurality of (at least 7 or more) rotary blades 55 provided at fixed intervals on an outer peripheral surface of the hub 51. A hub ratio to be a ratio of diameters of an outside diameter (ID) of the hub 51 and an outside diameter(OD) of the fan is set to 0.45 to 0.5 and the diameter of the hub 51 is set within a range of 55±5 mm. An outside diameter of the rotary blade 55 is set within a range of 110±10 mm and a sweep angle θ of the rotary blade 55 is set within a range of 32 deg. to 34 deg.. Pitch angle ψ of the rotary blade 55 are set to ranges of 32 deg. ±2 deg. and 45 deg. ±2 deg. at a rotary blade tip 55a and a rotary blade hub 55b, respectively. A maximum camber position of the rotary blade 55 is set to 0.65.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial fan for supplying air cooled by an evaporator in a refrigerator to a freezing compartment and a refrigerator compartment, and more particularly, to the number of rotating blades of the fan, hub ratio, sweep angle, and the like. Optimum fan design factors such as pitch angle and maximum camber ratio, etc., realize low noise, reduce eddy generated around the fan, and reduce flow resistance. It is about fans.

[0002]

2. Description of the Related Art FIG. 16 is a perspective view of a conventional axial flow fan for cooling air circulation, and FIG. 17 is a sectional view showing an end portion of a rotating blade of the axial flow fan of cooling air according to the conventional technology. Referring to FIGS. 16 and 17, the structure and operation of a conventional cool air circulation axial-flow fan of a refrigerator will be described as follows.

An axial fan for circulating cool air includes a hub 1 connected to a rotating shaft of a blower motor and receiving a driving force of the blower motor, and a plurality of rotating blades 5 provided on the outer peripheral surface of the hub 1 at regular intervals. Be composed. The rotating blades 5 are usually composed of three to four blades, the hub ratio, which is the diameter ratio of the outer diameter of the hub 1 to the fan, is 0.25 to 0.3, and the pitch angle of the rotating blades 5 is 25 ° to 35 °.

Here, the pitch angle is an angle between a straight line connecting the leading edge and the trailing edge of the rotating blade 5 and a line in the radial direction, and how obliquely the rotating blade 5 is inclined with respect to a plane perpendicular to the rotation axis. Means to be formed. However, depending on fan design factors such as the number of rotating blades 5, hub ratio, pitch angle, etc. of the axial fan for cooling air circulation configured as described above, the pressure loss of the large-sized refrigerator and the complicated flow may be reduced. There is a problem that the refrigerator cannot generate a flow suitable for the channel characteristics and the noise of the refrigerator increases.

[0005] Such an axial fan has a BVI in which noise is generated when the subsequent rotating blade 5 hits a vortex zone generated while the front rotating blade 5 rotates with reference to the rotating direction. (Blade vortex
interaction) phenomenon occurs. In recent designs of axial fans, research has been actively conducted to reduce such a BVI phenomenon.

The blade tip 5a of the axial fan is shown in FIG.
As shown in FIG. 7, the cross section of the blade tip 5a formed by a pressure surface 5b on which the pressure due to the air flow acts and a negative pressure surface 5c on the opposite side of the pressure surface 5b on which the negative pressure acts is a gentle curve. Therefore, the recovery of the positive pressure of the air from the pressure surface 5b of the rotary blade 5 to the suction surface 5c occurs rapidly.

Accordingly, the main frequency of the noise generated by the collision of the flow with the peripheral object due to the rotation of the rotary blade 5 is represented by a positive integer multiple of the product of the number of the rotary blades 5 and the number of rotations. Blade passing frequency is lower. By the way, refrigerator compressors, machine room fans,
Refrigerator doors for preventing noise generated from a cooling air circulation fan or the like and flowing to the outside through various paths are generally formed to block high-frequency noise of 700 Hz or more. The low BPF generated by the axial fan can hardly be blocked by the refrigerator door.

In other words, the conventional cool air circulation fan mainly has a large low-frequency band and generates a low BPF noise, so that the effect of shielding sound by the refrigerator door, that is, almost no noise reduction effect can be obtained. There is a problem that outside noise is increased.

FIG. 18 is a front view showing a state in which a shroud is provided on an axial fan according to the prior art, and FIG. 19 is a sectional view showing a structure of the shroud according to the prior art.
The conventional shroud 7 is provided around the rotary blade 5, and an annular bulging portion 9 bulging in the direction of airflow is formed at a portion adjacent to the rotary blade 5.

[0010] Such a shroud 7 includes a rotating blade 5.
Is provided in the circumferential direction with a certain gap from the blade tip 5a, and when the axial fan is driven, plays a role of guiding the flow of the cool air when the heat-exchanged cool air flows in the axial direction of the fan. In addition, the annular bulging portion 9 is
Protruding in the form of bulging in the circumferential direction of the part adjacent to
Smooth airflow. That is, the air flow is caused to flow along the curved surface of the annular bulging portion 9 so as to guide the flow of the air flow gently and prevent the flow resistance of the air flow from being generated.

However, in the shroud according to the prior art as described above, as shown in FIG. 20, the annular bulging portion 9 is formed so as to bulge in the inflow direction of the airflow, and the rear surface from which the airflow is discharged is concave. Therefore, there is a problem that air discharged to the rear of the fan hits the concave surface of the annular bulging portion 9 to generate a large vortex, thereby increasing flow loss. That is, the diameter of the annular bulging portion 9 provided around the fan is large, and a part of the air introduced by the fan collides with the concave surface, which is the rear surface of the annular bulging portion 9, to generate a large vortex and generate a large vortex. Since the flow is obstructed, the flow loss increases.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to reduce the number of rotating blades and the number of rotating blades so as to meet the noise reduction of the fan. An object of the present invention is to provide an axial fan for circulating cool air of a refrigerator, which reduces the operation noise of the refrigerator by optimizing fan design factors such as a hub ratio, a sweep angle, a pitch angle, and a maximum camber ratio.

Another object of the present invention is to provide an axial flow fan for cooling air which can improve the structure of a shroud so as to suppress the generation of a vortex in the air discharged behind the fan and minimize the flow loss. Is to do.

[0014]

According to the present invention, there is provided an axial flow fan for circulating cool air of a refrigerator according to the present invention, comprising a hub connected to a motor shaft, and a plurality of rotating blades provided on the hub. The fan design variables such as the number of the rotating blades, the hub ratio, the sweep angle of the rotating blades, the pitch angle, the camber ratio, etc. are selected under optimum conditions, respectively, to achieve a large pressure loss of the refrigerator and complicated flow path characteristics. The present invention is characterized in that a suitable flow of cool air is generated and fluid noise of the fan itself is reduced, thereby reducing the noise of the refrigerator.

Another feature of the present invention is that the hub is connected to the rotating shaft of the blower motor, a plurality of rotating blades are provided at regular intervals on the outer peripheral surface of the hub, and is provided in the circumferential direction of the rotating blade. And a shroud for guiding an airflow, wherein the shroud is provided with an annular bulging portion bulging in the direction of inflow of the airflow, and is discharged to the rear concave surface of the annular bulging portion behind the rotating blade. A swirl reducing means is provided to reduce swirl generated by air.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a perspective view of an axial flow fan for circulating cool air according to the present invention, FIG. 2 is a front view and a plan view of the axial flow fan according to the present invention, and FIG. FIG. 4 is a cross-sectional view taken in a circumferential direction, and FIG. 4 is a cross-sectional view showing an end of a rotating blade of the axial fan according to the present invention.

The structure and operation of an axial fan for circulating cool air of a refrigerator according to the present invention will be described with reference to FIGS.
The axial flow fan for circulating cool air according to the present invention is shown in FIGS.
As shown in FIG. 1, the hub 51 includes a hub 51 connected to a rotating shaft of a blower motor, and a plurality of rotating blades 55 provided at regular intervals on an outer peripheral surface of the hub 51. The rotating blade 5
5 consists of at least seven or more. More specifically, the number of the rotating blades 55 is most preferably nine in consideration of various matters such as efficiency, air volume, and wind pressure.

The hub ratio, which is the ratio of the outer diameter (ID) of the hub 51 to the outer diameter (OD) of the fan, is 0.45 to 0.5.
Thus, the diameter of the hub 51 is distributed within a range of 55 ± 5 mm, and the outer diameter of the fan, that is, the outer diameter of the rotating blade 55 is distributed within a range of 110 ± 10 mm.

Sweep angle (θ) of the rotary blade 55
Are distributed in the range of 32 ° to 34 °. Here, the sweep angle (θ) is an angle formed by a straight line connecting the center of the rotary blade hub 55b and the center of the rotary blade tip 55a and a straight line connecting the center of the rotary blade hub 55b and the center of the hub 51. As shown, the rotating blade 55
Is formed to be biased forward in the rotation direction.

The pitch angle (Ψ) of the rotary blade 55
Are distributed at 32 ° ± 2 ° at the rotating blade tip 55a and at 45 ° ± 2 ° at the rotating blade hub 55b. here,
The pitch angle (Ψ) is an angle formed between a straight line connecting the leading edge 57a and the trailing edge 57b of the rotary blade 55 and the X axis perpendicular to the Z axis, which is the rotation axis. It refers to how obliquely the plane is formed with respect to a plane perpendicular to the axis.

The maximum camber position of the rotary blade 55 is 0.65, and is uniformly distributed from the rotary blade hub 55b to the rotary blade tip 55a. The distribution is 8% at the blade hub 55b.

Here, the maximum camber position is a position where the rotary blade 55 is farthest from a cord (CL) which is a straight line connecting the leading edge 57a and the trailing edge 57b of the rotary blade 55,
The distance between the straight line and the rotary blade 55 at this time is the maximum camber (C). The maximum camber rate indicates the ratio between the maximum camber (C) and the length of the cord (CX) in percentage. The maximum camber position is
It is shown as the ratio of the distance (CP) between the leading edge 57a of the blade and the point on the cord where the maximum camber is located with respect to the length (CX) of the cord.

The rake angle indicating the degree to which the rotary blade 55 is inclined with respect to the positive axial direction is zero. As described above, when the sweep angle (θ), the pitch angle (Ψ), and the maximum camber rate of the rotary blade 55 are increased, the fluid noise generated by the fan itself is reduced. In addition, the rotation of the rotary blade 55 increases the BPF, which is the main frequency of the noise generated by the collision of the surrounding object and the flow, and most of the BPF is blocked by the refrigerator door. Significantly reduced.

As shown in FIG. 4, the rotary blade tip 55a of the rotary blade 55 has a pressure surface 56b on which a pneumatic pressure acts, and a negative pressure surface 56a on the rear surface of the pressure surface 56b on which a negative pressure acts. And is formed to bend at a predetermined curvature from the pressure surface 56b toward the negative pressure surface 56a. At this time, the rotating blade tip 55
a preferably has the same curvature as a radius of 0.1 times or less the fan diameter.

As described above, the rotating blade tip 55a
Is formed, the recovery of the positive pressure of the air passing from the pressure surface 56b to the suction surface 56a gradually progresses.
The generation of the swirl zone occurring after 5 is suppressed, and the BVI is weakened. FIGS. 5, 6, 7, 8, and 9 are graphs showing noise generation ratios of the axial flow fan according to the present invention configured and operated according to various design factors, respectively.

That is, the graph shown in FIG. 5 shows the noise ratio according to the hub ratio. When the hub ratio is 0.45 to 0.55, the noise shows the lowest value of 22.3 ± 0.2 dB.
In particular, when the hub ratio is 0.5, the noise represents the lowest value.
The graph shown in FIG. 6 shows the noise rate according to the sweep angle (θ), and the sweep angle (θ) is 32 ° to 34 °.
, The noise represents the lowest value of 22.4 ± 0.2 dB.

The graph shown in FIG. 7 shows the noise rate depending on the pitch angle (Ψ). The pitch angle (Ψ) is 32 ° ± 2 ° for the rotating blade tip 55a and 45 ° for the blade hub 55b.
When distributed as ° ± 2 °, the noise is 22.3 ± 0.2 dB
And the lowest value. The graph shown in FIG. 8 shows the noise rate according to the maximum camber rate (CP). When the maximum camber position (CP) is 0.65, the noise rate is uniformly distributed from the rotating blade hub 55b to the rotating blade tip 55a. Is 11.5% with the rotating blade tip 55a,
When the distribution is 8% at the rotating blade hub 51, the noise is 2%.
It represents the lowest value of 2.5 dB.

The graph shown in FIG. 9 shows the noise rate according to the rake angle. When the rake angle is 0, the noise is 23.
It represents dB and the lowest value. When the axial fan as described above is applied to a refrigerator, a forward noise characteristic can be obtained as shown in FIG. Here, a graph showing the forward noise characteristic of the existing axial fan is shown in FIG. When comparing the graphs of FIGS. 10A and 10B with each other, when the axial fan of the present invention is applied to the refrigerator, the blowing noise of the refrigerator is lower than when the existing axial fan is applied to the refrigerator. It can be seen that the level is reduced by about 4.3 dB (A).

FIG. 11 is a front view of an axial fan showing a state in which a shroud according to the present invention is mounted, and FIG. 12 is a sectional view taken along line BB of FIG. 11 showing the shroud according to the present invention. The shroud 60 of the present invention is provided in the circumferential direction of the rotating blade 55, and has an annular bulging portion 62 bulging in the direction of air flow in the circumferential direction adjacent to the rotating blade 55, and On the rear surface of the projecting portion 62, there is provided a vortex reducing means for preventing the air discharged to the rear of the rotary blade from hitting the rear surface of the annular bulging portion 62 and reducing the generation of the vortex.

The eddy current reducing means comprises a blocking plate 64 of a fixed length protruding in the direction of air flow along the center of the rear surface of the annular bulging portion 62. The blocking plate 64 is provided with the annular bulging portion 6.
A plurality of protrusions (L) can be provided in accordance with the size of 2, and the protrusion length (L) is formed to be about 1-2 mm longer than the radius of the annular bulging portion 62. That is, when the diameter of the annular bulging portion 62 is large, the size of the generated vortex increases. Therefore, the number of the blocking plates 64 is increased by the diameter of the annular bulging portion 62, and Dividing the rear inner surface of the portion 62 into small sections reduces the size of the generated vortex.

Further, the length of the blocking plate 64 is adjusted by the annular bulging portion 62.
The length formed by the length (L) is smaller than the radius of the fan to prevent the air discharged to the rear of the fan from hitting the inner surface of the circular shape and reduce the generation of the vortex. The flow of the airflow of the shroud will be described. FIG. 13 is a diagram showing the flow of the airflow passing through the shroud according to the present invention. When the fan is driven, air flows in the axial direction of the fan, and a shroud 60 provided around the fan guides the air flow. In particular, the annular bulge 62 formed near the fan allows air to flow along a curved surface,
Minimize the flow resistance of the airflow.

At this time, among the air discharged to the rear of the fan, the air discharged from the edge portion of the air collides with the rear inner surface of the annular bulging portion 62 to generate a vortex, thereby obstructing the flow of the air flow. However, by blocking the air from flowing into the circular inner surface by the blocking plate 64 protruding in the same direction as the flow direction of the air flow, by guiding the air to flow in the axial direction of the fan and suppressing the generation of the vortex. , So that the air discharged to the rear of the fan flows smoothly.

That is, among the air discharged to the rear of the fan, the air discharged at the edge of the rotating blade 55 flows along the rear concave surface of the annular bulging portion 62 while being expanded to the outside, and generates a vortex. Since the blocking plate 64 is formed on the rear surface of the annular bulging portion 62 in the flow direction of the air, the discharged air is prevented from hitting the rear surface of the annular bulging portion 62 and the generation of the vortex is suppressed. And guide the air flow to flow smoothly.

FIG. 14 is a partial sectional view of a shroud showing another embodiment of the eddy current blocking means according to the present invention. The eddy current blocking means according to this embodiment is configured to prevent air from flowing into the rear concave surface of the annular bulging portion 62 bulging in the circumferential direction of the rotating blade 55 of the shroud 60 in the airflow inflow direction. In order to prevent this, a vortex blocking film 68 is provided to close the rear concave surface of the annular bulging portion 62.

The eddy current blocking film 68 is connected at one end to the straight portion of the shroud 60, and is connected between the angle portion 70 and the inner end of the annular bulging portion 62 so that the airflow is reduced. An inclined portion 72 for closing the rear concave surface of the annular bulge 62 in order to prevent it from flowing into the inside of the annular bulge 62.

In the shroud according to the other embodiment configured as described above, when the air is discharged to the rear of the rotary blade 55, the inner surface of the annular bulging portion 62 is closed by the eddy current blocking film 68. Since the flow into the inner surface of the annular bulging portion 62 is basically blocked, it is possible to prevent the generation of the vortex, thereby minimizing the flow resistance. That is, when the airflow that has passed through the fan is expanded outward, the airflow is guided by the inclined portion 72 of the eddy current blocking film 68. Therefore, no vortex is generated inside the annular bulging portion 62, and the flow resistance due to the vortex is also reduced. Does not occur.

FIG. 15 is a graph showing a change in noise due to a change in airflow of the conventional shroud and the shroud of the present invention.
In the same figure, P indicates a noise change due to a change in air volume due to a conventional shroud. When the air volume is 0.81 CMM as a reference, noise of 23.6 dB is generated.
Shows a noise change due to a change in the air flow according to the embodiment of the present invention shown in FIG. 13. When the air flow is 0.81 CMM, a noise of 22.4 dB is generated.
FIG. 14 shows a noise change due to a change in air flow according to the embodiment shown in FIG.
Noise of about 1.3 dB is generated.

Thus, it can be seen that the shroud according to the present invention reduces noise by about 1.2 dB to 2.3 dB as compared with the conventional shroud. As described above, the present invention has been illustrated and described with reference to the specific embodiments. However, it is understood in the art that various modifications and changes can be made without departing from the spirit and scope of the invention defined in the appended claims. Anyone with ordinary knowledge can easily understand.

[0039]

As described above, the axial-flow fan for circulating cool air of the refrigerator according to the present invention has a number of rotating blades, a hub ratio, a sweep angle (θ), a pitch angle (Ψ), a maximum camber rate, and the like. By optimizing the design factor of the fan, it is possible to generate a flow of cool air suitable for a large pressure loss of the refrigerator and a complicated flow path characteristic, and to reduce the fluid noise of the fan itself.

Also, in the axial fan according to the present invention, the BPF, which is the main frequency of the noise generated by the collision of the flow with the peripheral object due to the rotation of the rotary blade 55, is more than twice as large as that of the existing fan. There is an advantage that the BPF is shut off by the refrigerator door, and the outflow noise of the refrigerator is greatly reduced.

Further, in the axial flow fan for circulating cool air according to the present invention, since the rotating blade tip 55a is bent at a predetermined curvature, the swirl zone generated after the rotating blade 55 is suppressed, and the swirl zone follows the swirl zone. Rotating blade 55
There is an advantage that BVI, which is a phenomenon that generates noise while colliding, is weakened.

Further, the vortex preventing means is formed behind the annular bulging portion 62 of the shroud to reduce vortex generation of air discharged to the rear of the fan, thereby reducing flow loss and reducing noise generation. There is.

[Brief description of the drawings]

FIG. 1 is a perspective view of an axial fan for cooling air circulation according to the present invention.

2 (a) is a front view and FIG. 2 (b) is a plan view showing an axial fan for cooling air circulation according to the present invention.

FIG. 3 is a sectional view showing a state in which a rotary blade of the axial fan for cooling air circulation according to the present invention is cut in a circumferential direction.

FIG. 4 is a cross-sectional view illustrating an end of a rotating blade of the axial fan for cooling air circulation according to the present invention;

FIG. 5 is a graph showing a noise ratio according to a hub ratio of an axial fan for cooling air circulation according to the present invention.

FIG. 6 is a graph illustrating a noise rate according to a sweep angle of the axial fan for cooling air circulation according to the present invention.

FIG. 7 is a graph illustrating a noise rate depending on a pitch angle of the axial fan for cooling air circulation according to the present invention.

FIG. 8 is a graph showing a noise rate according to a maximum camber rate of the axial fan for cooling air according to the present invention.

FIG. 9 is a graph showing a noise factor due to a rake of the axial fan for cooling air circulation according to the present invention.

FIG. 10 is a graph showing a front noise characteristic of a refrigerator in which a conventional cool air circulation axial fan and a cool air circulation axial fan according to the present invention are applied and compared.

FIG. 11 is a front view showing a state in which the shroud according to the present invention is mounted on an axial flow fan for cooling air.

FIG. 12B—shows a shroud according to the invention;
It is sectional drawing about the B line.

FIG. 13 is a cross-sectional view illustrating an airflow generated by a shroud according to the present invention.

FIG. 14 is a partial sectional view showing another embodiment of the shroud according to the present invention.

FIG. 15 is a graph showing air volume-noise comparing air volume and noise in a shroud according to the present invention.

FIG. 16 is a perspective view showing a conventional axial fan for cooling air circulation.

FIG. 17 is a cross-sectional view showing an end of a rotating blade of a conventional axial-flow fan for cooling air circulation.

FIG. 18 is a front view showing a state in which a shroud is attached to an axial fan for cooling air circulation according to a conventional technique.

FIG. 19 is a sectional view taken along line AA of FIG. 18;

FIG. 20 is a cross-sectional view illustrating an airflow generated by a shroud according to the related art.

[Explanation of symbols]

 51: Hub 55: Rotating blade 55a: Rotating blade tip 55b: Rotating blade hub 57a: Leading edge 57b: Trailing edge θ: Sweep angle Ψ: Pitch angle CP: Maximum camber position

Claims (14)

[Claims] 1. An axial fan comprising: a hub connected to a rotation shaft of a blower motor; and a plurality of rotation blades provided at regular intervals on an outer peripheral surface of the hub, wherein the rotation blade comprises at least seven blades, An axial fan for cooling air circulation, wherein a hub ratio, which is a ratio of a diameter of the hub to an outer diameter of the blade, is 0.45 to 0.55. 2. The axial fan according to claim 1, wherein the number of the rotating blades is nine. 3. The pitch angle of the rotating blade is 32 ° ± 2 ° for the rotating blade tip and 45 ° for the rotating blade hub.
2. The axial fan for cooling air circulation according to claim 1, wherein the fan is distributed at an angle of ± 2 °. 4. The cool air circulation shaft according to claim 1, wherein the maximum camber position of the rotary blade is 0.65 ± 0.05, and is uniformly distributed from the rotary blade hub to the rotary blade tip. Flow fan. 5. The blade according to claim 1, wherein the maximum camber ratio of the blade is distributed at 11.5 ± 0.5% for the rotating blade tip and 8 ± 0.5% for the rotating blade hub. Axial fan for cold air circulation. 6. The sweep angle of the rotating blade is 32 °.
The axial flow fan for circulating cool air according to claim 1, wherein the angle is −34 °. 7. The axial fan according to claim 1, wherein the rotating blade tip of the rotating blade is bent from a pressure surface to a negative pressure surface with a predetermined radius of curvature. 8. The axial flow fan for circulating cool air according to claim 1, wherein the rake angle of the rotating blade is zero. 9. A hub connected to a rotating shaft of a blower motor, a plurality of rotating blades provided at regular intervals on an outer peripheral surface of the hub, and a shroud provided in a circumferential direction of the rotating blade and guiding an air flow. In the axial fan including: the shroud is provided with an annular bulging portion bulging in the inflow direction of the airflow, and on the rear concave surface of the annular bulging portion, air discharged to the rear of the rotating blade is provided. An axial flow fan for circulating cool air, wherein a vortex reducing means for reducing generated vortex is provided. 10. The axial flow fan for cooling air circulation according to claim 9, wherein said eddy current reducing means comprises a blocking plate projecting from a center of a rear concave surface of said annular bulging portion in a flow direction of air flow. . 11. The blocking plate divides a circular rear concave surface into small sections in proportion to a radius of the annular bulging portion.
11. The cooling air circulation axial flow fan according to claim 10, wherein a plurality of cooling fans are provided at regular intervals. 12. The cooling air circulation axial flow fan according to claim 10, wherein the blocking plate is formed to be longer than a radius of the annular bulge by a predetermined length. 13. The cooling air circulation device according to claim 9, wherein said eddy current reducing means comprises an eddy current blocking film for preventing an air flow from flowing into said annular bulging portion. Axial fan. 14. An eddy current blocking film, comprising: an angle portion attached to a linear portion of a shroud behind the annular bulging portion;
A rear concave surface of the annular bulging portion is connected between the angle portion and the inner end of the annular bulging portion to prevent an air flow from flowing into the inside of the annular bulging portion. 2. An eddy current blocking film comprising an inclined portion.
3. The axial flow fan for cooling air circulation according to 3.