EP3193022B1

EP3193022B1 - Centrifugal ventilating fan

Info

Publication number: EP3193022B1
Application number: EP16151037.5A
Authority: EP
Inventors: Halil Kartal; Oktay Hancerli
Original assignee: Silverline Endustri ve Ticaret AS
Current assignee: Silverline Endustri ve Ticaret AS
Priority date: 2016-01-13
Filing date: 2016-01-13
Publication date: 2022-05-25
Anticipated expiration: 2036-01-13
Also published as: DK3193022T3; PL3193022T3; EP3193022A1

Description

Technical Field of the Invention

The present invention relates generally to a centrifugal fan which is intended to be used in extractor hoods. The present invention is particularly related to an improved structure of a centrifugal fan in order to increase energy efficiency in extractor hoods.

Background of the Invention

A centrifugal fan is a mechanical device for moving air or other gases. These fans increase the speed of air stream with the rotating impellers. They use the kinetic energy of the impellers or the rotating blade to increase the pressure of the air/gas stream which in turn move them against the resistance caused by ducts, dampers and other components. Centrifugal fans accelerate air radially, changing the direction of the airflow.
Centrifugal fan structures are designed by taking into account four important factors which are volumetric flow rate, pressure, power and noise. Said centrifugal fans provide very different structures in order to improve these factors. Generally, centrifugal fans are consisted of a fan housing, an impeller, inlet and outlet ducts, a drive shaft and a drive mechanism. The impeller is linked directly to the shaft of an electric motor. Thus, the motor's rotational speed determines the impeller speed. There are three types of impellers whose blades are arranged in there different ways such as forward-curved, backward-curved or radial.
Its operation principle is that the centrifugal fan uses the centrifugal power supplied from the rotation of impellers to increase the kinetic energy of air/gases. When the impellers rotate, the gas particles near the impellers are thrown off from the impellers, and then moves into the fan casing. Therefore, the kinetic energy of gas is measured as pressure because of the system resistance offered by the casing and duct. The gas is then guided to the exit via outlet ducts. After the gas is thrown off, the gas pressure in the middle region of the impellers decreases. The gas from the impeller eye rushes in to normalize this. This cycle repeats and therefore the gas can be continuously transferred.
In these devices, volute tongue has an important effect in order to increase the speed of air/gas stream which causes the increase in energy efficiency. Therefore, in order to reach the best energy efficiency in these centrifugal ventilation fans, manufacturers test different volute tongue angles in the centrifugal ventilation fans. One of the studies done in this field is expressed in the utility model document CN202581616 . Said document discloses a dehumidifier comprising a shell, a snail shaped fan, an air inlet, an air outlet and a snail tongue angle. In this document, the snail tongue angle is determined between 20-40° in order to improve the performance of the dehumidifier. Another patent document which discloses a centrifugal fan is DE2556614 . Said centrifugal fan expresses the volute tongue angle between 25-65°. Other prior art centrifugal fans are known from EP1375925 A2 and EP1701041 A2 .
The present invention aims to provide a centrifugal fan in order to overcome the deficiencies in the prior studies done in this field as well as to provide a centrifugal fan with more energy efficiency. In addition, it is aimed that the centrifugal fan of the invention generates lower noise while operating.

Brief Description of the Figures

Figure 1 is a representative view of the centrifugal fan from one perspective angle in which one of the housing parts is shown with a motor body, and impellers.
Figure 2 is a representative view of the centrifugal fan from another angle in which one of the housing parts is shown with the impellers.
Figure 3 is a unidimensional drawing of the centrifugal fan which shows the curvatures clearly.
Figure 4 is a unidimensional drawing of the centrifugal fan which shows the circles belonging to the curvatures.
Figure 5 shows a simulation demonstrating suction of air/gas in the centrifugal fan.
Figure 6 is a graph which shows the simulation results of the centrifugal fan.

Detailed Description of the Invention

The present invention is related to a centrifugal fan (1), in particular a snail type centrifugal fan (1), particularly for extractor hoods. Said centrifugal fan (1) structure is intended to be used particularly, but not exclusively, in the ventilation systems for extractor hoods for evacuation of fumes, vapors, or other air-like gases mostly from domestic environments.
The centrifugal fan (1) of the present invention comprises two separate housing parts (2) which can be coupled to each other in a connection plane K in order to protect the inner parts of the centrifugal fan (1). Preferably, said housing parts (2) can be produced by plastic materials. One of the housing parts (2) is not shown in the figures, while the other which comprises a motor body (3) of the centrifugal fan (1) is presented in Figs. 1 and 2. Said motor body (3) is mounted to the housing part (2) so as to be able to rotate axially and is located substantially in the middle of said housing part (2). In addition, said housing parts (2) are preferably arranged in a substantially symmetrical manner with respect to the connection plane K.
As seen in Fig. 1, said centrifugal fan (1) preferably comprises two radial fan impellers (4) which are connected to each other concentrically in a connection plane L. Said radial fan impellers (4) are mounted substantially into the middle of the housing part (2) around the motor body (3), coaxial with the rotation of the motor body (3). Preferably, the centrifugal fan (1) of the invention is constructed such that the connection planes K and L are substantially in alignment in order to provide symmetry in the centrifugal fan (1) when the housing parts (2) are coupled to each other.
There is also defined an outlet (5) for evacuation of the air-like gases in the centrifugal fan (1). Said outlet (5) evacuates the air-like gases substantially in the direction of (y) which is indicated in the figures, and perpendicular to the rotation of the motor body (3).
Each housing part (2) comprises a structure in semi-cylindrical form in order to define the outlet (5) and throat section (6) of the housing part (2). When the housing parts (2) are coupled to each other in the connection plane K, corresponding parts of said throat section (6) are also coupled to each other in a fluid-tight manner and form a cylindrical outlet (5).
Said centrifugal fan (1) sucks the air-like gases towards the inside by rotation of said radial fan impellers (4) by using kinetic energy. There is provided an air inlet section comprising some holes to ensure air flow inside the centrifugal fan (1). Said air inlet section is defined on another housing part which is not shown in the figures. The centrifugal fan structure (1) is configured such that when the two housing parts (2) are coupled to each other in the connection plane K, said air inlet section faces with the open side (7) of the radial fan impellers (4). Consequently, the air-like gas is drawn inside via the rotation of the radial fan impellers (4) driven by the motor body (3).
As seen in Fig. 2, the open side (7) of the radial fan impeller (4) comprises a main opening (8) preferably in a cylindrical form being also coaxial with the rotation axis of the motor body (3).
Preferably, said housing part (2) of the centrifugal fan structure (1) also comprises some protrusions (9) along the connection plane K in order to provide the tight connection between the two housing parts (2), when they are coupled in the connection plane K and twisted around said connection plane K. Also, there may be provided some teeth (10) along the connection plane K which are able to couple with the corresponding teeth on the other housing part which is not shown in the figures. Consequently, the housing parts (2) can be fixed to each other from these teeth (10). Preferably, the housing part (2) also comprises a connection seat (11) which is able to couple with the corresponding seat of the other housing part in the state of engagement.
In addition, the centrifugal fan (1) comprises a tongue section (12) in the region of the outlet (5), which defines the throat section (6) as conventionally known in the snail type fans. Said tongue section (12) causes the cross-section of the air flow channel to be narrowed locally, upon which the said cross section expands again above tongue section (12), and in this expanded region in close proximity to the outlet (5), the pressure of the air flow considerably drops. Said tongue section (12) facilitates also a connection between the two housing parts (2) with the connection spots (13) in the state of engagement. According to new regulations all over the world, it is required and highly preferred that extractor hoods have the A+ energy efficiency which is hardly achieved by way of the conventional snail fans. The inventors have surprisingly noted that the curvatures in said tongue section (12) are of vital importance for increasing the energy efficiency, and it is found that by optimizing the curvatures in the tongue section (12) of the throat, the required level of energy efficiency can be obtained without the undue burden of changing overall design of the conventional snail type fans.
As seen in Fig. 3, said tongue section (12) comprises the curvature B, which plays an important role in behavior of the air flow in the centrifugal fan (1). As seen in the Fig. 4, the curvature B forms the extreme point of the tongue section (12) in the horizontal direction (x). As the impeller (4) rotates in counter-clockwise direction according to Figs. 3-5, for instance, the curvature B convexly facing the rigorous air flow causes a disturbance which deteriorates a laminar flow regime and causes local vortexes to be formed around the periphery of the tongue section (12). The conventional snail type fans comprise a tongue section with a sharp or smoothly curved structure of the above type and therefore are not responsive to the drawbacks such as deterioration of the laminar flow and creating vortexes. It is known that irregular flow regimen in a snail type fan causes energy consumption to increase per volume of the air discharged through the outlet.
It is now found that the aforesaid drawbacks of the conventional fans can be eliminated by the new design of the instant invention whereby the said tongue section (12) defined by the horizontal width H comprises a further curvature D convexly formed through the throat of the outlet (5) which is connected to the first curvature B by way of a longitudinal surface C. It is thereby ensured that the air flow impinging upon said first curvature B neighboring the impeller (4), flows over the surface C and arrives to curvature D whereby said airflow expands smoothly through the area defined by the width G. It is also unexpectedly found that the surface C, if it is formed as a concavely extending curvature, advantageously ensures preserving of the laminar flow through the curvature D and outlet (5).
Referring now to Fig. 4, the curvature B mentioned above is realized with a circle whereby its radius (r_B) is perfectly designed in the range of 2,9 mm to 3,6 mm. The closest vertical distance (A) between the center of the circle belonging to curvature B and the connection plane L of the impellers (4) is preferably arranged inbetween 7-9 mm. As it is shown in Fig. 4, the transverse distance between the center of the circle belonging to curvature B and the center of the impeller (4) is designated as x_b, whereas the longitudinal distance between the center of the circle belonging to curvature B and the center of the impeller (4) is designated as y_b. In the scope of the invention, the x_b/y_b ratio is preferably determined inbetween 0,6 and 0,8.
As noted above, the surface C is preferably formed as a concave curvature which is realized with a circle where its radius (r_c) is advantageously arranged inbetween 55 and 70 mm. The circle of the curvature B is tangent to the circle of the curvature C. The curvature D can be envisaged with a circle whereby its radius (r_d) is advantageously arranged inbetween 10 mm and 25 mm. The circle of the curvature D is again tangent to the circle of curvature C. The inventors are of the opinion that the condition of r_c being substantially bigger than r_d ensures the fact that curvature D does not disturb the air flow and instead a smooth passage of the flow is guaranteed through the outlet (5) defined by the width G. The results of the simulation as demonstrated in Fig. 5 verify that a perfect flow regime is obtained by the arrangement comprising at least two curvatures (B, D) and a surface C extending therebetween substantially in vertical direction.
The tongue section (12) further comprises a surface S which is tangential to the circle of the curvature D. Said surface S is preferably formed as a straight line which is inclined and has an angle with the horizontal axis (x) which is 10 to 15°. The horizontal distance H between the imaginary plane P which is tangential to the curvature B and the imaginary plane T which is tangential to one end of the throat section (6) is preferably determined between 70 mm and 85 mm in the axis of (x). In addition, the horizontal distance G between the vertical plane defined by the center of the circle (D) and the imaginary plane T which is tangential to one end of the outlet section (5) is determined between 55 mm and 62 mm in the axis of (x). Besides these, the vertical distance F between the point where surface S is tangential to the circle of the curvature D and the uppermost horizontal line of the outlet section (5) is advantageously determined between 35 mm and 45 mm in the vertical axis of (y).
With the centrifugal fan (1) of the foregoing explanations, it is noted that A+ energy efficiency in extractor hoods. Therefore, according to a further aspect, the present invention presents extractor hoods comprising the centrifugal fan (1) of the present invention, and also a method for producing the same comprising placing of said centrifugal fan (1) into a hood structure.
In the scope of the invention, in order to manufacture the most efficient centrifugal fan (1) the optimization studies are performed with the ANSYS CFX software. The effect of the values mentioned above to the flow rate and to the pressure of the motor body (3) is calculated with said software whereby the optimum values are verified by experimental analysis. The flow rate and the pressure of the motor body (3) are considered in these changes.

In one of the embodiments of the invention, said values are preferably determined as follows:
A= 8,1 mm, r_B=2,9 mm, r_C=60 mm, r_D=15 mm, E=11,3°, F=37,7 mm, G=58,4 mm, H=72,3 mm, x_b=47,5 mm and y_b=71,9 mm. The best results are obtained with these values whereby the turbulences in the outlet (5) of the centrifugal fan structure (1) are minimized.

Table I. The simulation results of the centrifugal fan (1) done with the ANSYS CFX

	Flow Rate (m³/h)	Static Pressure (Pa)	Voltage (V)	Current (A)	Power (W)
1	723.4	0.6	231.6	1.1	256.3
2	699.4	20	232.0	1.1	253.1
3	708.8	39.2	232.2	1.1	247.6
4	681.3	56.2	232.3	1.1	243.9
5	691.0	78.5	232.8	1.0	238.4
6	661.9	97.2	232.6	1.0	235.2
7	671.3	118.5	232.9	1.0	232.1
8	660.3	137.0	232.7	1.0	226.9
9	652.8	158.5	233.4	1.0	224.4
10	642.2	179.3	233.1	1.0	220.5
11	634.6	198.4	233.9	0.9	217.6
12	623.1	219.6	233.9	0.9	213.6
13	610.1	239.4	233.5	0.9	208.5
14	595.0	262.5	233.7	0.9	205.0
15	582.2	281.5	233.5	0.9	199.9
16	567.5	301.2	233.2	0.8	196.1
17	553.5	318.9	233.5	0.8	192.1
18	536.6	340.2	233.2	0.8	186.8
19	518.3	361.5	234.1	0.8	183.0
20	500.8	379.9	234.1	0.8	178.7
21	482.4	399.5	234.1	0.7	173.2
22	460.5	418.1	232.3	0.7	168.6
23	436.9	441.0	232.9	0.7	162.5
24	418.6	458.7	232.9	0.7	158.6
25	397.3	478.5	232.3	0.7	152.9
26	371.5	500.7	233.2	0.7	149.0
27	338.9	522.1	233.3	0.6	142.1
28	275.7	538.3	233.6	0.5	124.4
29	192.5	561.3	233.6	0.5	113.5
30	145.8	579.3	232.5	0.5	108.5
31	61.3	598.1	232.8	0.5	104.1
32	48.8	608.5	232.7	0.4	96.8

In Table I, the simulation results of the prototypes produced in consideration of the values mentioned above are presented. Said values are obtained according to the EN 61591 and EN 60704 standards. The best efficiency points (bep) and the maximum points of the flow rate, the pressure, and the power values obtained according to these measurements are as follows: $\begin{array}{l} Q \max = 723 m^{3} / h, Ps \max = 608 Pa, W, Q bep = 371 m^{3} / h, Ps bep = 501 Pa, W \\ bep = 148 W . \end{array}$
In Figure 6, a graph which shows the simulation results is presented. The flow rate, the pressure, and the power results obtained by said software shows that FDE (Fluid Dynamic Efficiency) value of the centrifugal fan structure (1) is 35 and its EEI (Energy Efficiency Class) value is 44,5 (A+).

Claims

A snail type centrifugal fan (1) comprising two housing parts (2) which can be coupled to each other in a connection plane K, a motor body (3) mounted in one of the housing parts (2), at least one radial fan impeller (4) mounted around the motor body (3) being coaxial with the rotation axis of the motor body (3), and a tongue section (12) in the region of an outlet (5) of the housing part (2) defining a throat section (6) narrowing the air passageway cross-section in horizontal axis (x) wherein said tongue section (12) comprises;
- a convexly formed first curvature (B) neighboring the impeller (4) forming an extreme point in horizontal direction (x) within the inner volume of the centrifugal fan (1), and

- a further curvature (D) convexly formed through the outlet (5) at an upper position of the first curvature (B) with respect to the vertical axis (y) of the centrifugal fan (1),
whereby, said first curvature (B) extends to the second curvature (D) through a surface (C) which is tangential to the first and second curvatures (B, D), and said surface (C) comprises a concavely formed structure extending between the first and second curvatures (B, D).
A centrifugal fan (1) according to claim 1, wherein radius of the first curvature (B) ranges between 2,9 mm and 3,6 mm.
A centrifugal fan (1) according to claim 1, wherein radius of the second curvature (D) ranges between 10 mm and 25 mm.
A centrifugal fan (1) according to claim 1, wherein radius of the concavely formed surface (C) (r_c) is bigger than radius of the second curvature (D) (r_d).
A centrifugal fan (1) according to claim 4, wherein radius of the concavely formed surface (C) (r_c) ranges from 55 mm to 70 mm.
A centrifugal fan (1) according to claim 1 wherein the tongue section (12) further comprises a surface (S) which is tangential to the circle of the curvature D, said surface (S) being formed as a straight line which is inclined and having an angle of 10° to 15° with respect to the horizontal axis (x) of the centrifugal fan (1).
A centrifugal fan (1) according to claim 1 wherein the horizontal distance (G) in the horizontal axis (x) between the vertical plane defined by the center of the circle belonging to curvature (D) and the imaginary plane T which is vertical plane defined by one end of the outlet section (5) ranges from 55 mm to 62 mm.
A centrifugal fan (1) according to claim 1 wherein the fan comprises a transverse distance (x_b) between the center of the circle belonging to curvature B and the center of the impeller (4), and a longitudinal distance (y_b) between the center of the circle belonging to curvature B and the center of the impeller (4), whereby x_b/y_b ratio ranges from 0,6 to 0,8.
An extractor hood comprising a snail type fan (1) according to claim 1.
A method for producing an extractor hood according to claim 9 comprising placing of a snail type fan (1) according to claim 1 into the hood structure.