JP4583287B2 - Centrifugal fan - Google Patents

Description

  The present invention relates to a centrifugal fan used in a blower device.

  A blower called a centrifugal fan or a centrifugal blower surrounds a rotating impeller with a cylinder whose radius sequentially increases, that is, a scroll casing, and a suction port is provided on one side wall surface corresponding to the impeller rotating shaft of the scroll casing. Further, a discharge port is disposed on the side surface of the scroll casing facing the blowout side of the impeller.

  The blower principle of a centrifugal fan is that high-speed, high-pressure air is introduced from the suction port into the blades from the center of the impeller, and is moved to the outer periphery of the impeller by the centrifugal force generated by the rotation of the impeller. As it erupts. The air ejected from the impeller passes through the scroll casing, whereby the speed energy is converted into pressure, becomes high-pressure air, and is ejected from the discharge port.

It is the shape of the impeller and the shape of the scroll that determines the efficiency of the centrifugal fan. However, as described above, the scroll that increases the pressure of the air ejected from the impeller is greatly involved in the efficiency. This is the most important part of centrifugal fan design. Therefore, various improvement measures have been proposed.
For example, Patent Document 1 attempts to cope with a difference in speed in the height direction of air ejected from an impeller by changing the scroll diameter not only in the rotation direction but also in the height direction (patent). Reference 1).

However, it is clear that the basic shape of the scroll has the greatest effect on the efficiency rather than the shape in the height direction, and the measures represented by Patent Document 1 should be taken after optimizing the basic shape of the scroll. .
The conversion from the velocity energy to the pressure in the scroll casing described above is performed by gradually changing the radius from the rotation center of the impeller toward the rotation direction of the impeller. There are two major methods.

One is called the Archimedes spiral, in which the radius from the impeller rotation center changes with a linear function of the angle in the rotation direction of the impeller. The other is that the radius from the rotation center of the impeller changes by a logarithmic function of the angle in the rotation direction of the impeller, and is called a logarithmic spiral.
The Archimedes spiral and the logarithmic spiral have some differences in characteristics, but the Archimedes spiral is the mainstream because it is easy to draw and has good blowing efficiency (Non-patent Document 1).

  FIG. 11 shows a centrifugal fan in which an Archimedes spiral impeller 100 is incorporated in a scroll casing 101. In the Archimedes spiral, as shown in FIG. The narrow part, that is, the gap between the tongue and the rate at which the scroll expands, that is, the scroll angle, and the goal of the scroll design is to set the tongue gap and the scroll angle so as to increase efficiency and reduce noise. .

  However, few examples have been proposed for the basic shape of the scroll casing 101, and in particular, there are few examples that touch the specific values of the specifications that define the shape of the scroll casing 101, except for the following Patent Document 2. .

Patent Document 2 proposes 7 to 13 degrees as the optimum value of the scroll angle. However, there is no description about another specification that defines the scroll, that is, the tongue gap, and it is in an incomplete state. In addition, as will be described later, in the experiments conducted by the inventor, it has been found that the scroll angle optimized in Patent Document 2 also changes in relation to the tongue gap.
Japanese Patent No. 3120411 JP 2001-90975 A Fluid Machinery Author Yukio Harada Asakura Shoten

The above-mentioned Patent Document 2 is incomplete, such as the absence of a description of the tongue gap among the specifications necessary to determine the scroll shape, and the description of the basis for the optimum scroll angle being presented. There are many points.

Therefore, before describing specific embodiments of the present invention, the inventor will explain the technical background that led to the present invention.
The inventor made a prototype of a scroll casing in which the scroll angle and the tongue gap were changed to various values using a commercially available centrifugal fan, and measured the air blowing characteristics and noise.
In general, in the analysis of a blower, the ratio between the blower output of the blower and the shaft power of the motor is obtained as the efficiency. Further, the pressure-flow rate characteristics are compared in a dimensionless manner so as not to depend on the rotational speed and the blade diameter. That is, the evaluation is generally performed using the flow coefficient φ, the pressure coefficient ψ, and the efficiency η defined by the following equations, and the embodiment of the present invention will be described accordingly (non-patent) Reference 1).

Here, Q, Pt, and ρ are the flow rate, total pressure, and air density, D and L are the impeller diameter and thickness, and u is the speed of the outer periphery of the impeller. T is the motor torque, and ω is the rotational angular velocity of the impeller.
The centrifugal fan used in the experiment is a general multi-blade fan having an impeller diameter of 100 mm, and measurement was performed by combining prototype scroll casings according to the specifications shown in Table 1.

The formula representing the basic shape of the scroll casing is as follows: the impeller diameter is D, the tongue gap is δ, the angle to the tongue is β, and the scroll angle is α, the scroll radius R at an arbitrary angle θ is Equation (Equation 2) is obtained.

FIG. 5 and FIG. 6 are graphs showing changes in the maximum efficiency and noise from the measurement results of the above scroll casing.
FIG. 5 shows changes in maximum efficiency and noise due to tongue gap / impeller diameter. The tongue gap is the point along the scroll casing where the velocity energy of the air starts to gradually convert to pressure in the direction of rotation of the impeller and where the pressure is converted to the pressure, and the portion toward the discharge port is closed. It is known that if the pressure is small, the pressure fluctuation at this point increases and the noise value increases. The tendency that the noise value decreases as the tongue gap in FIG. 5 increases is consistent with the above description.

On the other hand, the fact that the gap between the tongues is large reduces the above-mentioned function of closing, and the efficiency is considered to decrease due to the increase in the gap between the tongues. However, the result shown in FIG. Efficiency increases due to an increase in the gap between the portions.

FIG. 6 shows the change in maximum efficiency depending on the scroll angle. According to Patent Document 2, the efficiency should be greatest when the scroll angle is 7 to 13 degrees, but in FIG. 6, the efficiency is maximum at around 15 degrees.
That is, the results shown in FIG. 5 and FIG. 6 are different from the results under the general idea or different conditions. In order to investigate this cause, the inventor examined how the efficiency and the noise value change under the condition that the tongue gap is constant and the scroll angle is constant.

FIG. 7 shows the maximum efficiency on the horizontal axis, the noise value on the vertical axis, the tongue gap being constant, and the value when the scroll angle is changed with broken lines and circles. The values when the gaps are changed are indicated by solid lines and squares. It can be seen from FIG. 7 that the noise does not change with respect to the change in the scroll angle, and the efficiency changes greatly. That is, the scroll angle is a design parameter that affects efficiency.

On the other hand, with respect to the change in the tongue gap, it can be seen that the efficiency changes simultaneously with the noise. This is because the scroll angle indicates the ratio of the spread of the scroll, and the actual spread of the scroll is obtained by adding a gap to the tongue. This effect is so large that a small centrifugal fan cannot be ignored. As the tongue gap increases, the spread of the scroll is apparently increased even if the scroll angle is constant, and as a result, the efficiency is considered to be increased.

The above is the reason why the efficiency increases due to the increase in the gap between the tongues described above, or the optimum value of the scroll angle changes when the conditions are different, and this makes the optimum specifications of the basic scroll shape clear. It is thought that the scroll design was difficult and incomplete.

  As described above, the scroll specifications that affect the efficiency of the centrifugal fan, that is, the gap between the tongue and the scroll angle, must be relied on by trial and error through trial manufacture and experiment, and a great deal of effort is spent on the design. The actual situation is that the product is manufactured in an imperfect state in terms of design.

  In order to improve such a situation, an object of the present invention is to clarify the specifications of a scroll that optimizes the efficiency and noise of the centrifugal fan, and to provide a centrifugal fan with high efficiency and low noise.

In order to solve the above-mentioned problems, the present invention provides an impeller in a scroll casing, forms a suction port on one side wall surface of the scroll casing substantially corresponding to the rotation center of the impeller, and blows out the impeller. In a centrifugal fan having a discharge port on the side of the scroll casing facing the side, starting from an arbitrary straight line perpendicular to the rotation center of the impeller at an angle β in the rotation direction of the impeller, from the straight line The distance from the center of the impeller at an angle θ in the rotational direction of the impeller is (rt + (ro−rt) × (θ−β) / (360−β) where D is the diameter of the impeller. ) The shape of the scroll casing is formed to be × D, the rt is set in the range of 0.6 to 0.7, and the ro is set in the range of 0.7 to 0.9. .
(Where rt is the ratio of the starting point radius of the scroll casing to the impeller diameter, and ro is the ratio of the end point radius of the scroll casing to the impeller diameter.)

According to the centrifugal fan of the present invention, the air blowing efficiency can be improved. Moreover, if it is the same motor, the reduction of electric power can be aimed at compared with the conventional structure.
Further, in the present invention, noise can be reduced as compared with the conventional example, and among them, the high peak wing passing noise that is annoying is greatly reduced. Expected to be improved.

The present invention has been made on the basis of the experimental facts described in the above problems of the present invention, and the embodiments shown in the drawings will be described in detail below with reference to the drawings.
The embodiment of the present invention shown in FIGS. 1A and 1B will be described using Archimedes spiral.
1A and 1B are perspective views of a centrifugal fan constructed based on the present invention. FIG. 2 is a diagram showing a basic scroll shape based on the present invention.

  1A and 1B, a multi-blade impeller (impeller) 1 has a large number of blades 2 arranged on a common circumferential surface at regular intervals in the circumferential direction and along the axial direction. One end of the blade 2 is supported by a main plate 3 connected to a rotating shaft, and the other end of the plurality of blades 2 is supported by an annular sub-plate 4. A centrifugal fan (also referred to as a multi-blade blower) assembled with a multi-blade impeller 1 includes the multi-blade impeller 1 in a scroll casing 6 having a suction port 5a formed on one side wall surface. The rotating shaft of the motor M is connected to the main plate 3 of 1 to rotationally drive the multi-blade impeller 1.

The multi-blade impeller 1 includes a plurality of circumferentially arranged between a main plate 3 centered on a hub 7 joined to a rotating shaft of a motor M and a sub plate 4 positioned on a suction side of a centrifugal fan. The wing | blade 2 is being fixed via the axial part of both ends. The multi-blade impeller 1 rotates with the rotating shaft of the motor M as the motor M rotates, and creates an airflow toward the outer periphery of the multi-blade impeller 1.
The multi-blade impeller 1 is located at the scroll center of the scroll casing 6, and the air flowing from the suction port 5 a of the one side wall surface 6 a of the scroll casing 6 by the rotation of the multi-blade impeller 1 Out of the multi-blade impeller 1 in the direction. Next, the air flow whose pressure has increased along the scroll casing 6 flows out from the discharge port 5 b formed on the side surface 6 b of the scroll casing 6.

In FIG. 2, the scroll radius at an arbitrary angle θ is represented by (rt + (ro−rt) × (θ−β) / (360−β)) × D, where rt is the scroll start point radius and the blade. It is the ratio with the diameter of the car, and ro is the ratio between the scroll end point radius and the diameter of the impeller.
Here, in the examples, rt was set to rt = 0.65 in the optimum range of 0.6 to 0.7 according to the present invention. In addition, ro is set to ro = 0.81 in the optimum range of 0.7 to 0.9 according to the present invention.
In the conventional example, the tongue gap is set to 5% of the impeller diameter, and the scroll angle is set to 10 degrees based on the optimum range 7 to 13 degrees of Patent Document 2.
As for other specifications, the impeller is a multi-blade impeller having a diameter of 100 mm, the scroll starting point position β is 85 degrees, the suction port diameter is 75 mm, and the scroll thickness is 54 mm. The example and the conventional example are the same.
Based on the above specifications, Table 2 shows the results of measuring the characteristics and noise of a centrifugal fan incorporating the prototype scroll casing 6 according to the present invention and the scroll casing according to the conventional design.

従来例との特性比較

Comparison of characteristics with conventional examples

FIG. 3 shows a comparison result of fan characteristics, and FIG. 4 shows a comparison result of noise frequency characteristics.
Regarding noise, the noise value in an open state at a rotational speed of 2000 r / m was measured at a position 1 m from the suction port in an anechoic chamber.

FIG. 3 shows changes in the pressure coefficient ψ and changes in the efficiency η with respect to the flow coefficient φ in the embodiment of the present invention and the conventional example.
The maximum value of the flow coefficient in the embodiment of the present invention exceeds the maximum value of the flow coefficient of the conventional example by about 15%, and the pressure coefficient ψ for the same flow characteristic is larger than that of the conventional example. You can see that it is higher. In other words, it can be seen that the centrifugal fan according to the present invention can obtain larger characteristics than the centrifugal fan according to the conventional design if the rotation speed and size are the same.
As for efficiency, it can be seen from FIG. 3 that the efficiency of the embodiment of the present invention exceeds that of the conventional example, and a large characteristic can be obtained with less energy. Comparing the maximum efficiency, it can be seen that the efficiency is improved by 56% and 7% in the embodiment of the present invention, compared with 49% in the conventional example.

FIG. 4 is a diagram comparing noise frequency characteristics. The solid line shows the noise frequency distribution in the embodiment of the present invention, and the broken line shows the noise frequency distribution in the conventional example. A peak is observed at a frequency of about 1000 Hz. This is a sound generated when the impeller blade passes through the tongue gap, and is called blade passing noise. In the embodiment of the present invention, the blade passing noise is reduced by 10 dB or more, and as a result, the noise value is greatly reduced from 54.6 dB (A) to 51.8 dB (A).
Moreover, the noise value generally displayed as dB (A) represents the average level of noise, and the psychological effects of noise are also specified as in the conventional noise frequency distribution. It is said that if the frequency component of is abnormally large, an irritating sensation is given. From these facts, it can be seen that the embodiment of the present invention further reduces the adverse effects of noise by suppressing the isolated frequency components that are annoying.

Here, a completely new design method and design specifications found by the present inventors will be described in detail.
The present inventor believes that if the actual scroll spread is made constant, the increase in efficiency will not occur due to the tongue gap, and the radius of the scroll end point is made constant and the radius of the scroll start point, that is, the tongue gap is changed. I tried it.
That is, as an equation for the scroll shape, the scroll radius at an arbitrary angle θ is expressed by the following equation (Equation 3).

Here, rt is the ratio between the scroll start point radius and the impeller diameter, and ro is the ratio between the scroll end point radius and the impeller diameter.
Using the above formula, we designed and prototyped a scroll according to Table 3 and measured its performance.

The result is shown in FIG. 8, and as expected, the noise is greatly reduced by the increase of the scroll starting point radius, but the efficiency is gradually lowered.
However, the rate of efficiency reduction is small. When the ratio of the scroll starting point radius to the impeller diameter is 0.6 to 0.7, the efficiency reduction can be suppressed to a level that does not hinder the noise reduction. found.

On the other hand, FIG. 9 shows changes in efficiency and noise when the radius of the scroll end point is changed and the radius of the scroll end point is changed. The efficiency is a ratio of the scroll end point radius to the impeller diameter of about 0.8. It became the maximum, and it was found that the increase in noise was suppressed to an extent that there was no problem.
FIG. 10 shows the maximum efficiency and noise when the ratio of rt, that is, the scroll start point radius and the impeller diameter is constant, and ro, that is, the ratio of the scroll end point radius and the impeller diameter, is indicated by broken lines and circles, and ro That is, the maximum efficiency and noise when the ratio of the scroll end point radius to the impeller diameter is made constant and rt, that is, the ratio of the scroll start point radius to the impeller diameter is changed, are indicated by solid lines and squares. If the scroll end point radius is changed from the locus indicated by the broken line, the noise will remain constant and the efficiency will change. If the scroll start point radius is changed from the locus indicated by the solid line, the efficiency will remain constant and the noise will change. Can be seen to change.

That is, instead of the conventional design parameters of the tongue gap and the scroll angle, the design parameters of the ratio of the scroll start point radius and the scroll end point radius to the impeller diameter are used. The ratio of the scroll starting point radius to the impeller diameter can be controlled independently for noise, and as a result, the optimal scroll basic shape can be used regardless of the size and shape. The specifications can be clarified.

As described above, the air blowing efficiency in the embodiment of the present invention is 56%, which is an improvement of 7% compared to the air blowing efficiency of 49% in the conventional example. In order to obtain an output equivalent to that of the conventional example, 49/56 = 87.5% of energy is sufficient, and it can be seen that the same motor can reduce power of 12.5%.
Further, in the embodiment of the present invention, the noise can be reduced by about 3 dB as compared with the conventional example, and among them, the high peak blade passing noise which is annoying is greatly reduced. The impact is expected to improve further.

Depending on the blade shape of the impeller, the centrifugal fan is divided into a turbo fan whose blade is rotating in the reverse direction, a paddle fan whose blade is in the radial direction, and a multi-blade fan whose blade is in the rotating direction. Therefore, the embodiments and effects of the present invention do not change depending on the type of impeller.

In the embodiments of the present invention, the Archimedes spiral is adopted. However, the gist of the present invention is essentially the same even in a logarithmic spiral and other spirals, and the embodiments and the effects thereof do not change.
Furthermore, by considering the scroll shape also in the height direction, further efficiency improvement and noise reduction can be expected, but as described above, after determining the scroll basic shape according to the present invention, It goes without saying that the embodiments and effects of the present invention are not replaced.
Furthermore, by optimizing the diameter of the suction port and the thickness of the scroll casing, further efficiency improvement and noise reduction can be expected. However, this does not change the embodiments and effects of the present invention.

It is a perspective view which shows embodiment of the centrifugal fan of this invention. FIG. 1B is a perspective view showing an embodiment of the centrifugal fan of the present invention with a part of FIG. 1A cut away. It is a conceptual diagram which shows the scroll curve of embodiment of FIG. 1A. It is the figure which compared the fan characteristic of the Example of the centrifugal fan of this invention, and the centrifugal fan of a prior art example. It is the figure which compared the noise frequency characteristic of the Example of the centrifugal fan of this invention, and the centrifugal fan of a prior art example. It is the figure which showed the change of the maximum efficiency and noise by a tongue part clearance gap. It is the figure which showed the maximum efficiency and the change of a noise by a scroll angle. It is the figure which showed the change locus | trajectory of the maximum efficiency and noise by the change of a tongue part clearance gap and a scroll angle. It is the figure which showed the change of the maximum efficiency and the noise by the scroll starting point radius. It is the figure which showed the change of the maximum efficiency and noise by scroll end point radius. It is the figure which showed the change locus | trajectory of the maximum efficiency and noise by the change of a scroll start point radius and a scroll end point radius. It is a figure which shows the scroll curve by a conventional design.

Explanation of symbols

1 Multi-blade impeller (impeller)
2 Wings 6 Scroll casing 5a Suction port 5b Discharge port 6a Single side wall surface 6b Side surface

Claims (1)

An impeller is disposed in the scroll casing, a suction port is formed on one side wall surface of the scroll casing substantially corresponding to the rotation center of the impeller, and discharge is performed on the side surface of the scroll casing facing the blowout side of the impeller. In the centrifugal fan having an opening, the position starts at an angle β in the rotation direction of the impeller from an arbitrary straight line orthogonal to the rotation center of the impeller, and is positioned at an angle θ from the straight line in the rotation direction of the impeller Of the scroll casing so that the distance from the center of the impeller is (rt + (ro−rt) × (θ−β) / (360−β)) × D, where D is the diameter of the impeller. A centrifugal fan having a shape , wherein the rt is set in a range of 0.6 to 0.7, and the ro is set in a range of 0.7 to 0.9 .
(Where rt is the ratio of the starting point radius of the scroll casing to the impeller diameter, and ro is the ratio of the end point radius of the scroll casing to the impeller diameter.)

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