AXIAL FLOW FUN

Abstract

The invention is directed to dual purposes of increasing air volume and reducing noises of an inline axial flow fan. In the inline axial flow fan including a first axial flow fan unit 100-1, a first honeycomb 200-2, a second axial flow fan unit 100-2 and a second honeycomb 200-2 which are arranged in the order starting from an upstream side in an air flow direction, the first honeycomb includes a stator vane configured to be warped in a “U” shape against a rotation direction of the first axial flow fan unit, while the second honeycomb includes a stator vane configured to direct a trailing edge thereof in parallel to the air flow direction.

Description

CLAIM OF PRIORITY

The present application claims priority from Japanese patent application serial no. 2010-163007 filed on Jul. 20, 2010, the content of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an axial flow fan including axial flow fan units serially arranged in a direction of rotary shafts thereof.

2. Description of Related Art

Home electric appliances and OA/IT apparatuses are equipped with a cooling fan for cooling heat-generating electronic components. More recently, the market has been meeting demands for the downsizing and sophistication of these home electric appliances and OA/IT apparatuses. Along with the downsizing and sophistication efforts, the appliances and apparatuses tend to have an internal structure more densely mounted with the electronic components. This results in the increase in the amount of heat generation.

A compact, high volume axial flow fan is generally employed as a cooling fan to deal with the increased amount of heat generated by the electronic components.

However, in a case where the compact axial flow fan is employed for cooling the electronic components, the fan must be rotated at high speeds to provide a required volume of cooling air. Unfortunately, this entails a problem of noise increase although the air volume is increased by rotating the fan at high speeds.

On the other hand, a structure having the axial flow fan units serially arranged in the direction of rotary shafts thereof is adopted to deal with the increase in pressure loss as a consequence of the high-density mounting of electronic components.

As particularly exemplified by server apparatuses at data centers, machines and equipment designed on the assumption of long hours of continuous operation adopt a structure having a plurality of axial flow fan units operatively arranged in series from the standpoint of ensuring redundancy for preventing the total breakdown of a cooling function associated with the failure of the cooling fan.

In the structure wherein the axial flow fan units are serially arranged and operated, therefore, emphasis is placed on a technique for reducing noises during the operation of outputting the increased volume of cooling air.

U.S. Pat. No. 4,167,861 discloses a structure wherein two axial flow fan units are serially arranged in the direction of rotary shafts thereof. Interposed between the upstream axial flow fan unit and the downstream axial flow fan unit is a device (hereinafter, referred to as “honeycomb”) including a frame and vanes. The frame is called a stator and includes an inside surface and an outside surface. The vanes extend radially from the center of the frame. This honeycomb removes a swirling flow produced in an airflow by the axial flow fan unit, thus suppressing the noise generation.

However, the honeycomb of the U.S. Pat. No. 4,167,861 does not work on the air flow discharged from the downstream axial flow fan unit, although working on the air flow discharged from the axial flow fan unit disposed upstream thereof.

Therefore, the swirling flow in the air flow discharged from the downstream axial flow fan unit cannot be removed although the above-described honeycomb acts to remove the swirling flow from the air flow discharged from the upstream axial flow fan unit. In view of the whole body of the inline axial flow fan, therefore, the U.S. Pat. No. 4,167,861 is not necessarily considered to provide an effective solution to the above-described problem of noise generation.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an axial flow fan adapted to increase the air volume and to reduce the noise of inline axial flow fan units thereof.

The above object is accomplished in an axial flow fan comprising: a first axial flow fan unit disposed on an upstream side with respect to an air flow; a first honeycomb disposed downstream of the first axial flow fan unit; a second axial flow fan unit disposed downstream of the second honeycomb; and a second honeycomb disposed downstream of the second axial flow fan unit, wherein a stator vane constituting the first honeycomb is configured to be warped against a rotation direction of the first axial flow fan unit while a stator vane constituting the second honeycomb is configured to direct a trailing edge thereof in parallel to a direction of the air flow.

The above object is further accomplished in the axial flow fan wherein the stator vane constituting the first honeycomb is warped in a “U” shape.

The above object is further accomplished in the axial flow fan wherein the stator vane constituting the first honeycomb is divided into two parts.

The above object is further accomplished in an axial flow fan comprising: a first axial flow fan unit disposed on an upstream side with respect to an air flow; a first honeycomb disposed downstream of the first axial flow fan unit; a second axial flow fan unit disposed downstream of the first honeycomb; and a second honeycomb disposed downstream of the second axial flow fan unit, the second axial flow fan unit rotating in a different way from the first axial flow fan unit, wherein a stator vane constituting the first honeycomb is configured to direct a ventral side thereof against a rotation direction of the first axial flow fan unit, while a stator vane constituting the second honeycomb is configured to direct a trailing edge thereof in parallel to a direction of the air flow.

The above object is accomplished in the axial flow fan comprising an inline axial flow fan wherein the first and second axial flow fan units and the first and second honeycombs are used as a device for cooling server apparatuses.

The invention can provide the axial flow fan adapted to increase the air volume and to reduce the noise of the inline axial flow fan units thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a structure wherein axial flow fan units and honeycombs are alternately arranged in series;

FIG. 2 is a side view showing the axial flow fan unit;

FIG. 3 is a perspective view showing the axial flow fan unit;

FIG. 4 is a side view showing the honeycomb unit;

FIG. 5 is a perspective view showing the honeycomb unit;

FIG. 6 represents a cylindrical plane containing an inline axial flow fan according to a first embodiment of the invention;

FIG. 7 is chart showing a relation between air inflow velocity and air exit velocity for a rotor blade of the axial flow fan;

FIG. 8 is a graph showing performance curve and resistance curve of the axial flow fan;

FIG. 9 is a diagram showing air flow separation caused by negative preswirl;

FIG. 10 represents a cylindrical plane containing an axial flow fan according to a second embodiment of the invention;

FIG. 11 is a diagram showing a structure of an axial flow fan including axial flow fan units and honeycombs according to a third embodiment of the invention;

FIG. 12 represents a cylindrical plane containing the inline axial flow fan according to the third embodiment of the invention;

FIG. 13 is a diagram showing a structure of an axial flow fan including axial flow fan units and honeycombs according to a fourth embodiment of the invention;

FIG. 14 represents a cylindrical plane containing the inline axial flow fan according to the fourth embodiment of the invention; and

FIG. 15 is a schematic diagram showing a structure of a blade server according to a fifth embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the invention will be described as below with reference to the accompanying drawings. Referring to FIG. 2 to FIG. 5, a brief description is made on an axial flow fan unit and a honeycomb arranged in series.

FIG. 1 is a schematic diagram showing a structure wherein the axial flow fan units and the honeycombs are alternately arranged in series.

FIG. 2 is a side view showing the axial flow fan unit.

FIG. 3 is a perspective view showing the axial flow fan unit.

FIG. 4 is a side view showing the honeycomb unit.

FIG. 5 is a perspective view showing the honeycomb unit.

Referring to FIG. 1, a first axial flow fan unit 1, a first honeycomb 2, a second axial flow fan unit 3 and a second honeycomb 4 are arranged in series in the order starting from an upstream side in an air flow direction indicated by the arrows. Namely, the first axial flow fan unit is disposed on the upstream side while the first honeycomb 2 is disposed downstream of the first axial flow fan unit 1. The second axial flow fan unit 3 is disposed downstream of this first honeycomb 2. The second honeycomb 4 is disposed downstream of this second axial flow fan unit 3.

Referring to FIG. 2 and FIG. 3, the first and second axial flow fan units 1, 3 are centrally formed with a boss 101, respectively. A plurality of rotor blades 102 are provided on an outer periphery of the boss 101. A motor 103 is coupled to the boss 101, which is brought into rotation by the motor 101 so as to rotate the rotor blades 102. Support struts 105 support the motor 103 on a casing 104.

Referring to FIG. 4 and FIG. 5, the first and second honeycombs 2, 4 each include an inside frame 201 and an outside frame 202. The inside frame 201 and the outside frame 202 are interconnected by a plurality of stator vanes 203 extending radially from the inside frame 201.

According to the above-described patent literature 1, the honeycomb 2 is interposed between the first axial flow fan unit 1 and the second axial flow fan unit 3 but the second honeycomb 4 on the downstream side is not provided. In the structure of the patent literature 1, therefore, a swirling flow can be removed from an air flow discharged from the first axial flow fan unit 1 by the effect of the honeycomb 2 but the swirling flow cannot be removed from the air flow discharged from the second axial flow fan unit 3.

In this connection, the present inventors have achieved the following embodiments by installing the second honeycomb 4 downstream of the second axial flow fan unit 3 and making various studies on the configuration of the stator vanes of the second honeycomb 4.

First Embodiment

FIG. 6 represents a cylindrical plane containing an inline axial flow fan according to a first embodiment of the invention.

Namely, FIG. 6 represents the cylindrical plane containing fragmentary views of cross sections of the rotor blades 102 of the first and second axial flow fan units 1, 3 and cross sections of the stator vanes 203 of the first and second honeycombs 2, 4 shown in FIG. 1.

In FIG. 6, as seen from an upstream side in an air flow direction indicated by the arrows, a rotary rotor blade 102a of the first rotary axial flow fan unit 1 (hereinafter, referred to as “first rotor blade 102a”) is disposed on the upstream side. A stationary stator vane 203a of the first honeycomb 2 (hereinafter, referred to as “first stator vane 203a”) is disposed downstream of this rotor blade 102a. A rotary rotor blade 102b of the second axial flow fan unit 3 (hereinafter, referred to as “second rotor blade 102b”) is disposed downstream of this stator vane 203a. A stationary stator vane 203b of the second honeycomb 4 (hereinafter, referred to as “second stator vane 203b”) is disposed downstream of the rotating rotor blade 102b.

The first rotor blade 102a and the second rotor blade 102b rotate in the same direction and have rotary shafts in aligned relation. The first stator vane 203a is warped in a “U” shape against a rotation direction of the rotor blade 102a and the rotor blade 102b. The second stator vane 203b is configured to direct a trailing edge thereof in parallel to the air flow direction.

These honeycombs 2, 4 allow the air flow to enter the rotor blade 102a at a relative velocity 302a for a rotational field and at an absolute velocity 303a for a static field. In the rotational field commonly represented by the three-dimensional cylindrical coordinate system, the relative velocity is given as a sum of a circumferential velocity and the absolute velocity.

Passing through the rotor blade 102a, the air flow exits at a relative velocity 302b for the rotational field and at an absolute velocity 303b for the static field.

FIG. 7 is a chart showing a relation between air inflow velocity and air exit velocity for the rotor blade of a common axial flow fan.

Referring to FIG. 7, the air flow enters the rotor blade at a relative inflow velocity 302(a) and a relative inflow angle 305(a) for the rotational field, and at an absolute inflow velocity 303(a) and an absolute inflow angle 304(a) for the static field. After passing through the rotor blade, the air flow exits at a relative exit velocity 302(b) and a relative exit angle 305(b) for the rotational field and at an absolute exit velocity 303(b) and an absolute exit angle 304(b) for the static field. The air flow is varied in velocity as follows due to the effect of the rotor blade. In the rotational field, a velocity variation is given by a difference 306(b) between the relative inflow velocity 305(a) and the relative exit velocity 305(b). In the static field, a velocity variation is given by a difference 306(a) between the absolute exit velocity 303(b) and the absolute inflow velocity 303(a).

P_th=ρu(v_θout−v_θin)=ρu(w_θin−w_θout)  Equation 1

The equation 1 represents the theoretical total pressure rise of the air flow provided by the effect of the rotor blade. In the equation, “P_th” denotes a theoretical total pressure rise; “ρ” denotes an air density; “u” denotes a circumferential velocity; “w_θin” denotes a swirl component of the relative inflow velocity; “w_θout” denotes a swirl component of the relative exit velocity; “v_θin” denotes a swirl component of the absolute inflow velocity; and “v_θout” denotes a swirl component of the absolute exit velocity. The equation 1 means that the theoretical total pressure rise of the air flow is proportional to the velocity variation of the air flow caused by the effect of the rotor blade.

In the above-described first rotor blade 102a, a theoretical total pressure rise corresponding to an inflow velocity and an exit velocity of the air flow through the first rotor blade 102a of FIG. 6 can be calculated from the equation 1.

The air flow exiting from the first rotor blade 102a enters the first stator vane 203a at the absolute velocity 303b for the static field and exits from the stator vane at an absolute velocity 303c as decelerated by the effect of the first stator vane 203a. As a consequence of the configuration of the first stator vane 203a warped in the “U” shape against the rotation direction of the second rotor blade 102b, the absolute velocity 303c contains a swirl component, called a negative preswirl, in the opposite direction to the rotation direction of the second rotor blade 102b.

$\begin{array}{cc}\Delta P_s=\rho \frac{v^2\mathrm{in}-v^2\mathrm{out}}{2}& \mathrm{Equation}2\end{array}$

The equation 2 represents the theoretical static pressure rise in the air flow provided by a common effect of the stator vane. In the equation, “ΔP_s” denotes a theoretical static pressure rise; “ρ” denotes an air density; “v_in” denotes an absolute inflow velocity; and “v_out” denotes an absolute exit velocity. The equation 2 indicates that the absolute velocity of the air flow is decreased by the effect of the stator vane whereby the static pressure in the air flow is increased.

In the first stator vane 203a, a theoretical static pressure rise corresponding to an inflow velocity and an exit velocity of the air flow through the first stator vane 203a of FIG. 6 can be calculated from the equation 2.

The air flow exiting from the first stator vane 203a enters the second rotor blade 102b at a relative velocity 302c for the rotational field and at the absolute velocity 303c for the static field. The air flow passes through the second rotor blade 102b and exits at a relative velocity 302d for the rotational field and at an absolute velocity 303d for the static field. At this time, the swirl component of the absolute inflow velocity in the equation 1 representing the theoretical total pressure rise of the air flow has the negative sign. Therefore, the theoretical total pressure rise is increased in value as compared with a case where the swirl component of the absolute inflow velocity has the positive sign. This effect permits the reduction of the circumferential velocity when as much theoretical total pressure rise as that of a case where the swirl component of the absolute inflow velocity has the positive sign is imparted to the air flow.

L′_A=L_A+60 log₁₀(N′/N)  Equation 3

The equation 3 represents the variation of noise level associated with the variation of motor revolving speed. In the equation, “N” denotes a pre-variation revolving speed; “N′” denotes a post-variation revolving speed; “L_A” denotes a pre-variation noise level; and “L′_A” denotes a post-variation noise level.

If the motor revolving speed is reduced by reducing the circumferential velocity of the second rotor blade 102b, the noise level is lowered as indicated by the equation 3.

The air flow exiting from the second rotor blade 102b enters the second stator vane 203b at the absolute velocity 303d for the static field and exits therefrom at an absolute velocity 303e as decelerated by the effect of the second stator vane 203b. At this time, the air flow obtains as much theoretical total pressure rise as determined by the equation 2.

FIG. 8 is a graph showing performance curve and resistance curve of the axial flow fan.

Referring to FIG. 8, the air volume of the axial flow fan is generally determined by an operating point defined by intersection of a characteristic curve 401 representing a relation between air volume and pressure loss in an operating environment of the axial flow fan and a characteristic curve 402 representing a relation between air volume and pressure specific to the axial flow fan. Therefore, the fact that the static pressure rise is obtained due to the effect of the second stator vane indicates that the above characteristic curve of air volume versus pressure is converted to a characteristic curve 403 of air volume versus pressure. As a result, the operating point is shifted toward larger air volume. Namely, the air volume is increased.

In this embodiment, if the first axial fan unit 1 shown in FIG. 1 fails, the first axial flow fan unit 1 makes an obstacle. At this time, the second axial flow fan unit 2 is operated at the maximum revolving speed.

As shown in FIG. 6, the negative preswirl is applied to the second rotor blade 102b by the effect of the first stator vane 203a, whereby the air flow can obtain a greater theoretical total pressure rise than in a case where the negative preswirl, expressed by the equation 1, is not applied to the second rotor blade. Further, the effect of the second stator vane 203b provides a larger air volume than in a case where the second honeycomb 4 of FIG. 1 is omitted. That is, in the event of a failure of the first axial flow fan unit 1, the drop of air volume can be reduced.

According to this embodiment as described above, the first stator vane 203a and the second stator vane 203b have different configurations so that the axial flow fan can achieve not only the reduced noise level and the increased air volume but also the effect to suppress the failure induced degradation of performance.

Now, description is made on a case where the first axial flow fan unit 1 and the second axial flow fan unit 2, described with reference to FIG. 1 illustrating the first embodiment of the invention, rotate in different directions.

A set of two axial flow fan units arranged in tandem and rotated in the different directions is generally called a duplicate contra-rotating fan. In this duplicate contra-rotating fan, an air flow through an axial flow fan unit on the upstream side in the air flow direction contains a swirling flow, which acts as the negative preswirl to the downstream fan unit. Hence, the pressure rise increased by the negative preswirl, as described in the first embodiment, can always be prospected.

However, if inflow condition for the air into the upstream axial flow fan unit varies due to the change in the operating environment or the like so that the negative preswirl to the downstream axial flow fan unit is increased too much, an air flow along a dorsal side of the blade becomes unable to withstand such a large pressure rise and sustains flow separation. This results in pressure loss.

Second Embodiment

According to a second embodiment, therefore, there are provided the first rotary rotor blade 102a and a second rotary rotor blade 102c. In the structure wherein the second rotor blade 102c rotates in the different direction, the first stationary stator vane 203a is configured to direct a dorsal side thereof against the rotation direction of the first rotor blade 102a, while the second stationary stator vane 203b is configured to direct the trailing edge thereof in parallel to the air flow direction.

Referring to FIG. 10, the operation of this embodiment is described as below.

FIG. 10 represents a cylindrical plane containing an axial flow fan according to the second embodiment of the invention.

Referring to FIG. 10, the air flow through the first stator vane 203a has the absolute velocity 303c for the static field. The airflow enters the second rotor blade 102c at the relative velocity 302d for the rotational field and at the absolute velocity 303d for the static field. At this time when the air flow enters the second rotor blade 102c, the first stator vane 203a acts to prevent an excessive increase of the negative preswirl. Hence, the pressure loss caused by the air flow separation is prevented while the theoretical total pressure rise expected from the equation 1 may preferably be achieved. As illustrated by the first embodiment, the air flow through the second rotor blade 102c is increased in the static pressure by the effect of the second stationary stator vane 203b.

As described above, this embodiment affords an effect to suppress the loss encountered by the axial flow fan or more particularly the duplicate contra-rotating fan by virtue of the structure wherein the stator vane 203a of the first honeycomb 2 and the stator vane 203b of the second honeycomb 4 have different configurations from those of the stator vane 203a of the first honeycomb 2 and the stator vane 203b of the second honeycomb 4 shown in FIG. 1.

Third Embodiment

A third embodiment of the invention is described with reference to FIG. 11.

FIG. 11 is a diagram showing a structure of an axial flow fan including axial flow fan units and honeycombs according to a third embodiment of the invention.

Referring to FIG. 11, the embodiment has the structure including the first axial flow fan unit 1, the first honeycomb 2, a second honeycomb 2a, the second axial flow fan unit 3 and a third honeycomb 4 which are arranged in the order starting from the upstream side in the air flow direction indicated by the arrows.

FIG. 12 represents a cylindrical plane containing the inline axial flow fan according to the third embodiment of the invention.

Referring to FIG. 12, this embodiment has the structure wherein the first stationary stator vane 203a is warped at a leading edge thereof against the rotation direction of the first rotary rotor blade 102a, wherein the second stationary stator vane 203b is warped at a trailing edge thereof against the rotation direction of the first rotor blade, and wherein the third stationary stator vane 203c is configured to direct a trailing edge thereof in parallel to the air flow direction.

In other words, the first stator vane 203a and the second stator vane 203b are two parts that form the first stator vane 203a described in the first embodiment shown in FIG. 6. If the “U” shaped stator vane 203a is to be formed in an integral mold, the molded product may have such a configuration as not to be demolded. In this embodiment, therefore, the stator vane is formed of two separate parts, such as to facilitate the molding process.

Next, the operation of this embodiment is described with reference to FIG. 12.

The air flow through the first rotor blade 102a enters the first stator vane 203a at an absolute velocity 301b for the static field. The air flow passing through the first stator vane 203a via the static field enters the second stator vane 203b at the absolute velocity 303c, the swirl component of which is reduced in the static field. The air flow through the second stator vane 203b has the absolute velocity 303d, which contains the negative preswirl against the second rotary rotor blade 102b. When the negative preswirl is applied to the air flow entering the second rotor blade 102b, the swirling flow of the air flow is reduced by the effect of the first stator vane 203a. Thus is obtained an effect to suppress the production of flow separation from the air flow passing through the second stator vane 203b. As a result, the loss caused by the air flow separation can be reduced or preferably eliminated.

As described above, this embodiment has the structure wherein the stator vane 203a of the first honeycomb 2 and the stator vane 203b of the second honeycomb 2a, shown in FIG. 11, have the different configurations. Therefore, the embodiment can afford the effect to suppress the loss caused by the flow separation from the air flow, the flow separation occurring when the negative preswirl is applied to the air flow into the second axial flow fan unit 3 by means of the honeycomb.

Another advantageous effect of this embodiment is that the first stator vane 203a and the second stator vane 203b can be relatively easily formed by molding, as described above.

Fourth Embodiment

A fourth embodiment of the invention is described with reference to FIG. 13.

FIG. 13 is a diagram showing a structure of an axial flow fan including axial flow fan units and honeycombs according to a fourth embodiment of the invention.

Referring to FIG. 13, the embodiment has the structure including the first honeycomb 2, the first axial flow fan unit 1, the second honeycomb 4, the second axial flow fan unit 3 and a third honeycomb 5 which are arranged in the order starting from an upstream side in the air flow direction indicated by the arrows.

As shown in FIG. 14 representing a cylindrical plane containing the structure shown in FIG. 13, the first stationary stator vane 203a is configured to be warped at a trailing edge thereof in the rotation direction of the first rotary rotor blade 102a. The second stationary stator vane 203b is configured to be warped in a “U” shape against the rotation direction of the second rotary rotor blade 102b. The third stationary stator vane 203c is configured to direct a trailing edge thereof in parallel to the air flow direction.

Next, the operation of this embodiment is described with reference to FIG. 14.

The air flow passes through the first stator vane 203a to obtain the absolute velocity 303b for the static field before entering the first rotor blade 102a. Since an operating environment assumed in a design phase differs from an actual operating environment, the loss may be caused by the air flow separation which may occur depending upon the air inflow condition varied due to the change in the operating environment. A function of the first stator vane 203a is to reduce or preferably to eliminate this loss.

As described above, this embodiment has the structure wherein the stator vane 203a of the first honeycomb 2, the stator vane 203b of the second honeycomb 2a and the stator vane 203c of the third honeycomb 5, shown in FIG. 13, have the different configurations. Therefore, the embodiment can afford the effect to prevent the loss resulting from the air inflow condition varied due to the change in the operating environment.

Fifth Embodiment

A fifth embodiment of the invention is described with reference to FIG. 15.

FIG. 15 is a schematic diagram showing a structure of a blade server according to the fifth embodiment of the invention.

Referring to FIG. 15, a blade server 500 includes a casing 501, server blades 502 arranged in the casing, and cooling fan modules 503 for cooling the server blades.

According to the invention, the structure of the first embodiment, for example, may be adopted to form the cooling fan module 503 so that a blade server can attain high air volume and low noise by virtue of the effects of the first embodiment. It is also possible to provide the cooling fan module excellent in redundancy in the event of a failure.

The applications of the cooling fan module according to the embodiment include, but are not limited to the blade server, all kinds of server apparatuses such as rack mount servers and PC servers.

According to the invention as described above, a notable noise reduction can be achieved because the effect of the first honeycomb permits the second axial flow fan unit to be reduced in the revolving speed. In addition, the cooling fan module is increased in the air volume because the static pressure is increased due to the effects of the first honeycomb and the second honeycomb.

In addition, if the first axial flow fan unit should fail, the drop of cooling capacity can be reduced because the second honeycomb is provided.

On the other hand, the first honeycomb acts to prevent the air flow separation occurring in the second axial flow fan unit, thereby suppressing the generation of loss. Furthermore, the first honeycomb also acts to reduce the loss resulting from the varied inflow condition of the air into the first axial flow fan unit.

In addition, the provision of the axial flow fan featuring the low noise and high air volume makes it possible to fabricate a cooling fan module for server that is excellent in redundancy in the event of a failure.

Claims

1. An axial flow fan comprising: a first axial flow fan unit disposed on an upstream side with respect to an air flow; a first honeycomb disposed downstream of the first axial flow fan unit; a second axial flow fan unit disposed downstream of the second honeycomb; and a second honeycomb disposed downstream of the second axial flow fan unit,

wherein a stator vane constituting the first honeycomb is configured to be warped against a rotation direction of the first axial flow fan unit, while a stator vane constituting the second honeycomb is configured to direct a trailing edge thereof in parallel to a direction of the air flow.

2. The axial flow fan according to claim 1, wherein the stator vane constituting the first honeycomb is warped in a “U” shape.

3. The axial flow fan according to claim 1, wherein the stator vane constituting the first honeycomb is divided into two parts.

4. An axial flow fan comprising: a first axial flow fan unit disposed on an upstream side with respect to an air flow; a first honeycomb disposed downstream of the first axial flow fan unit; a second axial flow fan unit disposed downstream of the first honeycomb; and a second honeycomb disposed downstream of the second axial flow fan unit, the second axial flow fan unit rotating in a different way from the first axial flow fan unit,

wherein a stator vane constituting the first honeycomb is configured to direct a ventral side thereof against a rotation direction of the first axial flow fan unit, while a stator vane constituting the second honeycomb is configured to direct a trailing edge thereof in parallel to a direction of the air flow.

5. The axial flow fan according to claim 1, comprising an inline axial flow fan that uses the first and second axial flow fan units and the first and second honeycombs as a cooling device for server apparatuses.

6. The axial flow fan according to claim 2, comprising an inline axial flow fan that uses the first and second axial flow fan units and the first and second honeycombs as a cooling device for server apparatuses.

7. The axial flow fan according to claim 3, comprising an inline axial flow fan that uses the first and second axial flow fan units and the first and second honeycombs as a cooling device for server apparatuses.

8. The axial flow fan according to claim 4, comprising an inline axial flow fan that uses the first and second axial flow fan units and the first and second honeycombs as a cooling device for server apparatuses.