CENTRIFUGAL BLOWER

Info

Publication number: 20130330182
Type: Application
Filed: Aug 22, 2012
Publication Date: Dec 12, 2013
Applicant: Industry-University Cooperation Foundation, Sunmoon University (Asan-si)
Inventor: Jae-Won Kim (Cheonan-si)
Application Number: 13/591,558

Abstract

A centrifugal blower is designed such that D/R, which is a ratio of a radius D of an air inlet to a radius R of an impeller, ranges from 85% to 87%, and such that r/R, which is a ratio of a radius r of a cross-section of a bell mouth of the centrifugal blower to the radius R of the impeller, ranges from 8% to 10%. With such a structure, a geometric size of the bell mouth is optimized, thus enhancing the blowing efficiency of the centrifugal blower. As a result, superior performance of the centrifugal blower can be ensured.

Description

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2012-0062682, filed on Jun. 12, 2012, which is hereby incorporated by reference in its entirety into this application.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to centrifugal blowers and, more particularly, to a centrifugal blower that has improved blowing efficiency.

2. Description of the Related Art

Generally, blowers are mainly used in air conditioners, ventilation systems, etc., which need to handle air. Blowers are classified into axial flow blowers in which the directions of air flow at an inlet and an outlet correspond to the orientation of a rotating shaft, and centrifugal blowers in which when an impeller installed in a scroll casing rotates at high speed, centrifugal force is generated, sucking air and discharging it at increased pressure to the outside.

The purpose of use of the centrifugal blowers is to increase output pressure using centrifugal force. Hence, the centrifugal blowers are widely used in places where the pressure rather than the flow rate must be increased.

A prior technique that pertains to such a centrifugal blower was proposed in Korean Patent Publication No. 10-2001-0105614 (date: Nov. 29, 2001), entitled “Centrifugal blower”.

However, in the conventional centrifugal blower, due to the characteristics of the structure, the instantaneous pressure increase in the air collected in a low pressure part may cause a phenomenon in which the air flows backwards in the scroll casing. This backflow phenomenon causes a reduction in the flow rate, thus reducing the blowing efficiency of the centrifugal blower.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a centrifugal blower in which a bell mouth is installed on a scroll casing so that air is prevented from flowing backwards in the scroll casing, thus minimizing a loss of flow rate, and which is configured such that the geometric size of the bell mouth is optimized, thus enhancing the blowing efficiency of the centrifugal blower.

In order to accomplish the above object, an embodiment of the present invention provides a centrifugal blower, including: a scroll casing having an inlet port formed in an upper surface of the scroll casing, and an outlet port formed in a side surface of the scroll casing; an impeller installed in the scroll casing, the impeller having a cylindrical shape, with a hub disposed in the impeller such that the impeller is rotated by rotating the hub; and a bell mouth having a ring shape and disposed on an edge of the inlet port of the scroll casing, the bell mouth forming an air inlet of the scroll casing and having a semi-circular cross-section, wherein D/R is a ratio of a radius (D) of the air inlet to a radius (R) of the impeller, and D/R ranges from 85% to 87%.

Furthermore, r/R is a ratio of a radius (r) of the cross-section of the bell mouth to the radius (R) of the impeller, and r/R may range from 8% to 10%.

Preferably, D/R, that is the ratio of the radius (D) of the air inlet to the radius (R) of the impeller, may be 86%, and r/R, that is the ratio of a radius (r) of the cross-section of the bell mouth to the radius (R) of the impeller, may be 9%.

When blowing air, vortexes form below the bell mouth, wherein magnitudes of the vortexes are reduced as a distance between the bell mouth and each of the vortexes increases with respect to a flow direction.

In a centrifugal blower according to an embodiment of the present invention, a bell mouth is installed on a scroll casing. The centrifugal blower is designed such that D/R, which is a ratio of a radius D of an air inlet to a radius R of an impeller, ranges from 85% to 87%, and r/R, which is a ratio of a radius r of a cross-section of the bell mouth to the radius R of the impeller, ranges from 8% to 10%. Due to this geometric design of the centrifugal blower, when blowing air, a strong vortex, a medium-size vortex and a weak vortex form in succession below the bell mouth, thus enhancing the blowing efficiency. Thereby, the performance of the centrifugal blower can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an exploded perspective view illustrating a centrifugal blower, according to a preferred embodiment of the present invention;

FIG. 2 is a perspective view illustrating the assembled centrifugal blower according to the embodiment of FIG. 1;

FIG. 3 is a sectional view of the centrifugal blower according to the embodiment of FIG. 1;

FIGS. 4A and 4B are performance plots respectively showing the pressure coefficient and the blowing efficiency as a function of the flow rate coefficient to test the effect of D/R when r/R is fixed to 6%;

FIGS. 5A and 5B are performance plots respectively showing the pressure coefficient and the blowing efficiency as a function of the flow rate coefficient to test the effect of D/R when r/R is fixed to 9%;

FIGS. 6A and 6B are performance plots respectively showing the pressure coefficient and the blowing efficiency as a function of the flow rate coefficient to test the effect of D/R when r/R is fixed to 11%;

FIGS. 7A and 7B are performance plots respectively showing the pressure coefficient and the blowing efficiency as a function of the flow rate coefficient to test the effect of r/R when D/R is fixed to 91%;

FIGS. 8A and 8B are performance plots respectively showing the pressure coefficient and the blowing efficiency as a function of the flow rate coefficient to test the effect of r/R when D/R is fixed to 86%;

FIGS. 9A and 9B are performance plots respectively showing the pressure coefficient and the blowing efficiency as a function of the flow rate coefficient to test the effect of r/R when D/R is fixed to 82%; and

FIGS. 10A and 10B are simulation views showing the result of an analysis of the flow of air in the centrifugal blower, in which r/R is 9% and D/R is 86%, using a CFD program.

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application with color drawing(s) will be provided by the U.S. Patent and Trademark Office upon request and payment of the necessary fee.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described in detail with reference to the attached drawings.

Reference now should be made to the drawings, throughout which the same reference numerals are used to designate the same or similar components.

As shown in FIGS. 1 through 3, a centrifugal blower according to an embodiment of the present invention includes a scroll casing 11, an impeller 17 and a bell mouth 27. The scroll casing 11 includes an inlet port 13 and an outlet port 15. The impeller 17 is installed in the scroll casing 11, and the shape thereof is cylindrical. A hub 19 is disposed in the impeller 17 such that the impeller 17 is rotated by rotating the hub 19. The bell mouth 27 is disposed on the edge of the inlet port 13 of the scroll casing 11. The bell mouth 27 has an annular shape and the cross-section thereof has a semi-circular shape. The bell mouth 27 defines an air inlet 29 of the scroll casing 11.

The inlet port 13 into which air is drawn into the scroll casing 11 is formed in a central portion of an upper surface of the scroll casing 11. The outlet port 15 is formed in a side surface of the scroll casing 11 so that air drawn into the scroll casing 11 is discharged to the outside by the outlet port 15.

The impeller 17 includes the hub 19, and a plurality of blades 21 which is arranged around an outer portion of the hub 19 in a circumferential direction. In the plan view, the impeller 17 has a circular shape. The blades 21 have a predetermined height. Thus, the impeller 17 has an approximately cylindrical shape. An upper end of the impeller 17 is open so that air can be drawn into the open upper end of the impeller 17.

The hub 19 has an arch-shaped cross-section. A rotating shaft 25 of a drive motor 23 is connected to a central portion of the hub 19 so that the hub 19 can be rotated by the operation of the drive motor 23. When the hub 19 rotates, that is, when the impeller 17 rotates, air is drawn into the impeller 17 through the open upper end thereof. The centrifugal force caused by the rotation of the impeller 17 increases the air that is drawn in. The air which has been increased in pressure is discharged through the spaces formed between the blades 21. The air which has been discharged out of the spaces between the blades 21 is discharged to the outside by the outlet port 15 of the scroll casing 11.

The bell mouth 27 is installed on the edge of the inlet port 13 of the scroll casing 11, thus forming the air inlet 29 of the scroll casing 11. The bell mouth 27 has a semi-circular cross-section and is disposed at a position spaced apart from an upper end of the impeller 17 by a predetermined distance. The bell mouth 27 functions to guide the inflow of air and prevent air that flows around the impeller 17 in the scroll casing 11 from flowing backwards.

A radius D of the air inlet 29 of the bell mouth 27 exerts a crucial influence on the blowing efficiency of the centrifugal blower 10. If the radius D of the air inlet 29 of the bell mouth 27 is excessively small or large, a clear and strong vortex forms below the bell mouth 27, causing a pressure loss in blowing air.

A radius r of the cross-section of the bell mouth 27 influences the operation of the centrifugal blower 10. If the radius r of the cross-section of the bell mouth 27 is excessively small, the volume of the bell mouth is so small that the pressure drag to prevent reverse flows is not enough to control the unwanted flows. If the radius r of the cross-section of the bell mouth 27 is excessively large, not only is the production cost increased but also, because of the limited size of the centrifugal blower 10, a bell mouth 27 with an excessively large cross-sectional radius r cannot be used.

Referring to FIG. 3, to enhance the blowing efficiency of the centrifugal blower 10, D/R, that is a ratio of the radius D of the air inlet 29 to the radius R of the impeller 17, ranges from 85% to 87%. r/R, that is a ratio of the cross-sectional radius r of the bell mouth 27 to the radius R of the impeller, ranges from 8% to 10%.

A range of 85% to 87% for D/R, which is the ratio of the radius D of the air inlet 29 to the radius R of the impeller 17, is the optimal range for enhancing the blowing efficiency of the centrifugal blower 10. Also, not only is the range of 8% to 10% for r/R, which is the ratio of the cross-sectional radius r of the bell mouth 27 to the radius R of the impeller 27, the optimal range for enhancing the blowing efficiency of the centrifugal blower 10 but, additionally, the centrifugal blower 10 can be designed to have a relatively small size.

If D/R, that is a ratio of the radius D of the air inlet 29 to the radius R of the impeller 17, ranges from 85% to 87% while r/R, that is a ratio of the cross-sectional radius r of the bell mouth 27 to the radius R of the impeller 17, ranges from 8% to 10%, when the centrifugal blower 10 blows air, a strong vortex, a medium-size vortex and a weak vortex are created in succession below the bell mouth 27 in the direction in which air flows.

In other words, when the centrifugal blower 10 blows air, vortexes form below the bell mouth 27, wherein the magnitudes of the vortexes are reduced as the distance between the bell mouth 27 and each vortex increases in the direction in which air flows.

In detail, a strong vortex forms just below the bell mouth 27, a medium-size vortex forms below the bell mouth 27 next after the strong vortex, and a weak vortex forms adjacent to the blades 21 on the side where the blades 21 discharge air. These vortexes enhance the blowing efficiency.

If D/R, that is a ratio of the radius D of the air inlet 29 to the radius R of the impeller 17, is less than 85% or greater than 87%, the blowing efficiency is reduced. If r/R, that is a ratio of the cross-sectional radius r of the bell mouth 27 to the radius R of the impeller 17, is less 8%, the blowing efficiency is also reduced. If r/R is greater than 10%, it becomes difficult to reduce the size of the centrifugal blower 10, or the blowing efficiency is reduced.

Preferably, when the ratio (D/R) of the radius D of the air inlet 29 to the radius R of the impeller 17 is 86% and the ratio (r/R) of the cross-sectional radius r of the bell mouth 27 to the radius R of the impeller 17 is 9%, the blowing efficiency of the centrifugal blower 10 is 0.51 which is the highest it can achieve.

Hereinafter, the critical significance of the design of D/R and r/R will be explained experimentally for the sake of conveying an aspect of the present invention.

[Test]

When D/R, that is the ratio of the radius D of the air inlet 29 to the radius R of the impeller 17, was varied from 82% to 91%, and r/R, that is the ratio of the cross-sectional radius r of the bell mouth 27 to the radius R of the impeller 17, was varied from 6% to 11%, the blowing efficiency as a function of the flow rate coefficient was measured.

To facilitate the comparison of the blowing efficiencies, flow conditions and performance variables are dimensionless variables.

The performance variables include a flow rate coefficient, a pressure coefficient, a power coefficient and static efficiency.

(1) The flow rate coefficient is expressed by the following equation.

$φ = \frac{4 Q}{π^{2} {Nd}_{2}^{3}}$

(φ: flow rate coefficient, Q: flow rate, N: the number of revolutions of impeller, d: radius of impeller)

(2) The pressure coefficient is expressed by the following equation.

$ψ = \frac{2 Δ P}{π^{2} N^{2} d_{2}^{2}}$

(ψ: pressure coefficient, ΔP: density of air in working fluid, N: the number of revolutions of impeller, d: radius of impeller)

(3) The power coefficient is expressed by the following equation.

$λ = \frac{4 M}{15 ρ π^{3} N^{2} d_{2}^{5}}$

(λ: power coefficient, M: power consumption of motor, N: the number of revolutions of impeller, d: radius of impeller, ρ: dimensionless negative pressure)

(4) The static efficiency is expressed by the following equation.

$η = \frac{φψ}{λ}$

(η: static efficiency, φ: flow rate coefficient, ψ: pressure coefficient, λ: power coefficient)

Dimensionless variables made by nondimensionalizing the above performance variables may begin from infinity. However, in the test of this embodiment, the ratio (r/R) of the cross-sectional radius r of the bell mouth 27 to the radius R of the impeller 17 is about 10%.

Setting r/R to about 10% in the test is based on Generation Mechanisms of Low-Frequency Centrifugal Fan Noise that was published by Fehse, K.-R and Neise, W in Aeroacoustics Conference (1998).

The following Table 1 shows the measurements of the blowing efficiency according to the flow rate coefficient while varying D/R and r/R.

TABLE 1 r/R 6% 7% 8% 9% 10% 11% D/R (10/155) (11/155) (12.5/155) (14/155) (15.5/155) (17.5/155) 91% 0.46 0.46 0.47 0.48 0.47 Impossible embodiment 90% 0.46 0.46 0.47 0.48 0.47 Impossible embodiment 89% 0.47 0.46 0.47 0.48 0.47 Impossible embodiment 88% 0.47 0.47 0.47 0.48 0.48 Impossible embodiment 87% 0.48 0.48 0.50 0.50 0.50 0.47 86% 0.49 0.49 0.50 0.51 0.50 0.48 85% 0.48 0.48 0.50 0.50 0.50 0.48 84% 0.47 0.47 0.47 0.47 0.48 0.47 83% 0.47 0.47 0.47 0.47 0.47 0.46 82% 0.47 0.47 0.47 0.47 0.47 0.46

According to Table 1, it can be confirmed that when D/R, that is the ratio of the radius D of the air inlet 29 to the radius R of the impeller 17, is 86%, and when r/R, that is the ratio of the cross-sectional radius r of the bell mouth 27 to the radius R of the impeller 17 is 9%, the blowing efficiency of the centrifugal blower 10 is the highest.

FIGS. 4A and 4B are performance curves respectively showing the pressure coefficient and the blowing efficiency as a function of the flow rate coefficient to test the effect of D/R when r/R is fixed to 6%.

Referring to FIGS. 4A and 4B, as the flow rate coefficient increases, the blowing efficiency increases, and then after the blowing efficiency reaches the maximum, that is, the highest efficiency, it is reduced. When D/R is 86%, the blowing efficiency is the highest.

When r/R is 6% and D/R is 91%, only a strong vortex forms below the bell mouth 27. The strong vortex forms a dead zone at a portion through which air flows, thus deteriorating the blowing efficiency.

If r/R is 6% and D/R is 86%, a very weak vortex forms below the bell mouth 27. This prevents a strong vortex from forming below the bell mount 27, so that the blowing efficiency is improved compared to the case where r/R is 6% and D/R is 91%.

When r/R is 6% and D/R is 82%, a strong vortex, a wide vortex and a strong vortex form in succession below the bell mouth 27, thus reducing the blowing efficiency.

FIGS. 5A and 5B are performance curves respectively showing the pressure coefficient and the blowing efficiency as a function of the flow rate coefficient to test the effect of D/R when r/R is fixed to 9%.

As shown in FIGS. 5A and 5B, the blowing efficiency is highest when D/R is 86%.

FIGS. 6A and 6B are performance curves respectively showing the pressure coefficient and the blowing efficiency as a function of the flow rate coefficient to test the effect of D/R when r/R is fixed to 11%.

Referring to FIGS. 6A and 6B, when D/R is 91%, the blowing efficiency is superior, but there is not much difference between this case and the case where D/R is 86%. In addition, it is impossible to embody the case where D/R is 91% and r/R is 11%.

FIGS. 7A and 7B respectively show the pressure coefficient and the blowing efficiency as a function of the flow rate coefficient to test the effect of r/R when D/R is fixed to 91%. FIGS. 8A and 8B respectively show the pressure coefficient and the blowing efficiency as a function of the flow rate coefficient to test the effect of r/R when D/R is fixed to 86%. FIGS. 9A and 9B respectively show the pressure coefficient and the blowing efficiency as a function of the flow rate coefficient to test the effect of r/R when D/R is fixed to 82%.

Referring to FIGS. 7A through 9B, when D/R is 86% and r/R is 9%, the blowing efficiency is 0.51 which is the highest.

The results of the test confirm that when D/R, which is the ratio of the radius D of the air inlet 29 to the radius R of the impeller 17, ranges from 85% to 87%, and r/R, which is the ratio of the cross-sectional radius r of the bell mouth 27 to the radius R of the impeller 17, ranges from 8% to 10%, the blowing efficiency of the centrifugal blower 10 is comparatively superior.

Particularly, it is confirmed that when D/R, that is the ratio of the radius D of the air inlet 29 to the radius R of the impeller 17, is 86% and when r/R, that is the ratio of the cross-sectional radius r of the bell mouth 27 to the radius R of the impeller 17 is 9%, the blowing efficiency of the centrifugal blower 10 is the highest.

FIGS. 10A and 10B are simulation views showing an analysis of the flow of air in the centrifugal blower, in which r/R is 9% and D/R is 86%, using a CFD program.

Referring to FIGS. 10A and 10B, it is shown that a strong vortex forms just below the bell mouth 27, a medium-size vortex forms below the bell mouth 27 in succession to the strong vortex, and a weak vortex forms adjacent to the blades 21 on the side of air discharge by the blades 21. This form of vortexes enhances the blowing efficiency and maximizes the performance of the centrifugal blower 10.

In an embodiment of the present invention, the radius R of the impeller, the radius D of the air inlet and the cross-sectional radius r of the bell mouth are geometrically designed such that a strong vortex, a medium-size vortex and a weak vortex form in succession below the bell mouth. As supported by the results of the above-mentioned test, the enhancement of the blowing efficiency by this embodiment of the present invention has been verified.

Furthermore, it was confirmed by a noise test that the geometric design of the radius D of the air inlet and the cross-sectional radius r of the bell mouth according to an embodiment of the present invention does not affect the noise quality of the centrifugal blower.

Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A centrifugal blower, comprising:

a scroll casing having an inlet port, formed in an upper surface of the scroll casing, and an outlet port formed in a side surface of the scroll casing;

an impeller installed in the scroll casing, the impeller having a cylindrical shape, with a hub being disposed in the impeller such that the impeller is rotated by rotating the hub; and

a bell mouth having a ring shape and disposed on an edge of the inlet port of the scroll casing, the bell mouth forming an air inlet of the scroll casing and having a semi-circular cross-section,

wherein D/R, which is a ratio of a radius (D) of the air inlet to a radius (R) of the impeller, ranges from 85% to 87%.

2. The centrifugal blower as set forth in claim 1, wherein r/R, which is a ratio of a radius (r) of the cross-section of the bell mouth to the radius (R) of the impeller, ranges from 8% to 10%.

3. The centrifugal blower as set forth in claim 1, wherein

D/R, which is the ratio of the radius (D) of the air inlet to the radius (R) of the impeller, is 86%, and

r/R, which is a ratio of a radius (r) of the cross-section of the bell mouth to the radius (R) of the impeller, is 9%.

4. The centrifugal blower as set forth in claim 2, wherein

D/R, which is the ratio of the radius (D) of the air inlet to the radius (R) of the impeller, is 86%, and

r/R, which is the ratio of the radius (r) of the cross-section of the bell mouth to the radius (R) of the impeller, is 9%.

5. The centrifugal blower as set forth in claim 1, wherein, when blowing air, circulating airflows or vortexes form below the bell mouth, and magnitudes of the vortexes are reduced as a distance between the bell mouth and each of the vortexes increase with respect to an inflow direction.