CN110594197B

CN110594197B - Centrifugal fan and range hood

Info

Publication number: CN110594197B
Application number: CN201910878729.1A
Authority: CN
Inventors: 霍星凯
Original assignee: Foshan Shunde Midea Washing Appliances Manufacturing Co Ltd
Current assignee: Foshan Shunde Midea Washing Appliances Manufacturing Co Ltd
Priority date: 2019-09-17
Filing date: 2019-09-17
Publication date: 2021-08-31
Anticipated expiration: 2039-09-17
Also published as: CN110594197A

Abstract

The invention discloses a centrifugal fan and a range hood, wherein the centrifugal fan comprises: a volute; an impeller disposed within the volute; and the flow limiting piece is arranged on the inner side of the volute and corresponds to the end surface of the impeller, and the flow limiting piece and the end surface of the impeller are arranged at intervals. The technical scheme of the invention can improve the backflow phenomenon between the volute and the end surface of the impeller.

Description

Centrifugal fan and range hood

Technical Field

The invention relates to the field of fans, in particular to a centrifugal fan and a range hood.

Background

Referring to fig. 1 to 3, the multi-blade centrifugal fan includes an impeller 10 ', a volute 30', an air inlet ring, a motor 20 ', and the like, wherein the motor 20' is mounted on a back plate of the volute through a motor bracket, and the air inlet ring is mounted on a front plate of the volute. When the impeller 10 'runs at high speed, a large negative pressure region is generated in the impeller 10', a part of air flow enters the impeller 10 'from the air inlet ring under the action of pressure difference, and a part of air enters from an opening (a rear air inlet 35') of the volute back plate. The airflow passes through the impeller 10' to do work, then enters the volute under the action of the centrifugal force of the impeller, and finally is discharged through the outlet of the volute.

Because the airflow pressure at the outlet of the blade is often large, and the airflow pressure at the air inlet ring (namely the front plate of the volute) and the opening of the back plate of the volute is small, under the action of pressure difference, the airflow at the outlet of the blade often generates backflow in the area close to the back plate of the volute and the front plate of the volute, and the noise of the fan and the air inlet efficiency of the fan are influenced.

Disclosure of Invention

The invention mainly aims to provide a centrifugal fan, aiming at improving the backflow phenomenon between a volute and the end face of an impeller.

In order to achieve the purpose, the centrifugal fan provided by the invention comprises

A volute;

an impeller disposed within the volute; and

and the flow limiting piece is arranged on the inner side of the volute and corresponds to the end surface of the impeller and is arranged at intervals with the end surface of the impeller.

Optionally, the flow restrictor comprises a first annular segment having an inner diameter that tapers in a radial and outward direction along the impeller.

Optionally, an orthographic projection of the first annular segment on the impeller end face is located inside the impeller.

Optionally, the outer periphery of the first annular segment is flush with the outer periphery of the blades of the impeller.

Optionally, a circle passing through the inner periphery of the blade of the impeller is taken as an inner circle, and a circle passing through the outer periphery of the blade of the impeller is taken as an outer circle;

the width of the first annular section in the radial direction of the centrifugal fan is equal to the distance between the inner circle and the outer circle.

Optionally, a distance between an outer periphery of the first annular segment and the impeller end face is greater than or equal to 5 mm.

Optionally, the first annular segment comprises a circular arc segment or a straight segment.

Optionally, the flow restriction comprises a second annular section located at the periphery of the impeller, and the inner diameter of the second annular section is increased in the radial and outward direction of the impeller.

Optionally, the second annular segment comprises a circular arc segment or a straight segment.

Optionally, the flow restrictor further comprises a third annular segment at an outer periphery, the third annular segment engaging and being secured to the inner surface of the volute.

Optionally, the supercharging ring further includes a fourth annular section located on the inner peripheral edge, and the fourth annular section is attached to and fixed to the inner surface of the volute.

Optionally, the flow restrictor is formed recessed toward an end face of the impeller.

Optionally, the flow restrictor is provided separately from the volute.

Optionally, the impeller includes a front disk, a rear disk and a plurality of blades, the front disk and the rear disk are arranged at intervals, the plurality of blades are respectively connected with the front disk and the rear disk, and the plurality of blades are arranged at intervals along the circumferential direction of the front disk;

a rear air inlet is formed in the surface, facing the rear disc, of the volute, and the flow limiting piece is arranged on the surface, facing the rear disc, of the volute; and/or the flow restrictor is arranged on the surface of the volute casing facing the front disc.

The invention also provides a range hood which comprises the centrifugal fan.

According to the invention, the distance between the volute and the impeller end face is changed by arranging the flow limiting piece between the volute and the impeller end face, so that the distance between the volute and the impeller end face is gradually reduced in the direction far away from the axis of the impeller (namely the direction from inside to outside), and the gradually-reduced flow channel is formed in the direction from inside to outside, thus the speed of airflow entering from the volute can be accelerated, airflow backflow at the outlet of the impeller can be effectively prevented, the air inlet efficiency is greatly improved, and the noise of the fan is improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.

FIG. 1 is a schematic structural diagram of a conventional centrifugal fan;

FIG. 2 is a cross-sectional view of the centrifugal fan of FIG. 1;

FIG. 3 is an enlarged view taken at A in FIG. 2;

FIG. 4 is an exploded view of one embodiment of a centrifugal fan according to the present invention;

FIG. 5 is a schematic structural view of the centrifugal fan in FIG. 4;

FIG. 6 is a cross-sectional view of the centrifugal fan of FIG. 4;

FIG. 7 is an enlarged view at B in FIG. 6;

FIG. 8 is a schematic view of the structure of the flow restrictor of FIG. 6;

FIG. 9 is a schematic plan view of the flow restrictor of FIG. 8;

FIG. 10 is a cutaway view of the flow restrictor of FIG. 8;

FIG. 11 is an enlarged view at C of FIG. 10;

FIG. 12 is another cutaway schematic view of the centrifugal fan of FIG. 4;

fig. 13 is a schematic sectional view of a flow restrictor in another embodiment of a centrifugal fan of the present invention.

The reference numbers illustrate:

the implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that, if directional indications (such as up, down, left, right, front, and back … …) are involved in the embodiment of the present invention, the directional indications are only used to explain the relative positional relationship between the components, the movement situation, and the like in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indications are changed accordingly.

In addition, if there is a description of "first", "second", etc. in an embodiment of the present invention, the description of "first", "second", etc. is for descriptive purposes only and is not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In addition, the meaning of "and/or" appearing throughout is to include three juxtapositions, exemplified by "A and/or B," including either the A or B arrangement, or both A and B satisfied arrangement. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention.

The invention provides a centrifugal fan.

In the embodiment of the present invention, as shown in fig. 4 to 6, the centrifugal fan includes an impeller 10, a motor 20, and a volute 30, the motor 20 is fixed to the volute 30, the impeller 10 is disposed in the volute 30, and the impeller 10 is mounted on a driving shaft of the motor 20.

Impeller 10 includes preceding dish 11, back dish 13 and a plurality of blade 12, and preceding dish 11 and back dish 13 interval set up, and a plurality of blades 12 are followed the circumference interval of preceding dish 11 sets up, blade 12 connect respectively preceding dish 11 with back dish 13. I.e. the blades 12 are circumferentially distributed evenly in a plane perpendicular to the front disc 11 and the rear disc 13 and the blades 12 are parallel to each other.

The front disk 11 is substantially circular, one end of the front disk 11 is an air inlet end of the centrifugal fan, and an air inlet ring 40 is usually installed at the front disk 11. The impeller 10 may be a single-layer impeller, and for the single-layer impeller 10, the rear disk 13 is provided with a relief hole into which the driving shaft of the motor 20 extends and is adapted. This impeller 10 also can be double-deck impeller, and for double-deck impeller 10, double-deck impeller 10 still includes the well dish, and the well dish is located between front bezel 11 and the back plate 13, is equipped with the abdicating hole that the drive shaft that supplies motor 20 stretched into and the adaptation on the well dish.

The surface of the volute 30 facing the front disc 11 is provided with a front air inlet 34, and the front air inlet 34 is used as a main air inlet; the surface of the volute 30 facing the rear disc 13 is opened with a rear air inlet 35. Specifically, the volute 30 generally includes a front volute plate 31, a shroud 32 and a back volute plate 33, the front volute plate 31 and the back volute plate 33 are respectively disposed at two opposite ends of the shroud 32, the front disk 11 is disposed near the front volute plate 31, the back disk 13 is disposed near the back volute plate 33, the front volute plate 31 is provided with a front air inlet 34, the back volute plate 30 is provided with a back air inlet 35, and the motor 20 is generally fixed to the back volute plate 33.

Generally, when the motor 20 is operated at a high speed, a large amount of heat is generated, and if the heat is not dissipated in time, the performance of the motor 20 and the life of the motor 20 are affected. For this reason, the common form is to open heat dissipation holes on the back disk 13 (single-layer impeller 10) or the middle disk (double-layer impeller 10) of the impeller 10, and the volute back plate 33 is also opened (back air inlet 35), so as to form forced convection to dissipate heat of the end cover of the motor 20 through the air flow injection effect.

The impeller 10 is a working component of the centrifugal fan, and the motor 20 is a driving source of the impeller 10. When the impeller 10 is driven by the motor 20 to run at a high speed, a large negative pressure area is generated inside the impeller 10, and under the action of pressure difference, a part of air flow enters the impeller 10 from the air inlet ring 40, and a part of air flow enters from the opening of the volute back plate 33. Enters the volute 30 under the action of the centrifugal force of the impeller 10 and is finally discharged through the outlet of the volute 30.

Since the airflow pressure at the outlet of the vane 12 tends to be relatively high, and the airflow pressure at the inlet ring 40 (i.e. at the front plate 31 of the volute) and the opening of the back plate 33 of the volute is relatively low, under the action of the pressure difference, the airflow at the outlet of the vane 12 tends to generate backflow at the area close to the back plate 33 of the volute and the area close to the front plate 31 of the volute, which affects the noise of the fan and the air inlet efficiency of the fan.

Referring to fig. 7 to 9, for this, the centrifugal fan in the embodiment of the present invention further includes a flow restriction element 50, the flow restriction element 50 is installed inside the volute 30, the flow restriction element 50 is disposed corresponding to an end surface of the impeller 10, and the flow restriction element 50 is disposed at an interval from the end surface of the impeller 10.

Specifically, the end surface of the impeller 10 refers to the end surface of both ends of the impeller 10 distributed in the axial direction, that is, the front end surface or the rear end surface, the front end surface being the end surface formed by the front disk 11, and the rear end surface being the end surface formed by the rear disk 13.

In some embodiments, the flow restriction 50 is disposed on a surface of the volute 30 facing the rear disk 13, i.e., the flow restriction 50 is disposed on the volute back plate 33 and between the rear disk 13 and the volute back plate 33. Because the air inlet of the fan is mainly the air inlet ring 40 (i.e. the front air inlet 34 at the front plate 31 of the volute and the air inlet at the back plate 33 of the volute is relatively small, the airflow at the outlet of the blade 12 tends to generate backflow in the area between the back plate 33 of the volute and the back plate 13 of the impeller 10 under the action of the pressure difference, which affects the noise of the fan and the air inlet efficiency of the fan. In this embodiment, by arranging the flow limiting piece 50 between the volute back plate 33 and the impeller 10 back plate 13, the distance between the volute back plate 33 and the impeller 10 back plate 13 is changed, so that the distance between the volute back plate 33 and the impeller 10 back plate 13 is the minimum at the position where the flow limiting piece 50 is arranged, and therefore the size of the flow channel can be changed, when the airflow enters from the volute back plate 33 and passes through the flow limiting piece 50, the pressure of the airflow is increased, so that the speed of the airflow entering from the volute back plate 33 can be increased, the airflow backflow at the outlet of the impeller 10 can be effectively prevented, the air intake efficiency is greatly improved, and the fan noise is improved.

In addition, in some embodiments, the flow restriction 50 is disposed on a surface of the volute 30 facing the front disk 11, i.e., the flow restriction 50 is disposed on the volute front plate 31 and between the front disk 11 and the volute front plate 31. Since the air pressure at the outlet of the impeller 10 is acted by the blades 12 and is much higher than the air pressure at the inlet of the impeller 10 (i.e. the front air inlet 34 of the front plate 31 of the volute), the air flow flowing out of the blades 12 easily flows back to the gap between the front disk 11 and the front plate 31 of the volute under the action of the pressure difference, and vortex is formed in the gap between the front disk 11 and the front plate 31 of the volute to generate noise. Meanwhile, the pressure of the gas entering between the front plate 31 of the volute and the front disk 11 of the impeller 10 from the wind guide ring is small, and the backflow gas is difficult to be brought away from between the front disk 11 and the volute 30, so that the swirl between the front disk 11 and the volute 30 is difficult to improve. In this embodiment, the distance between the front plate 31 of the volute and the front disc 11 of the impeller 10 is changed by arranging the flow limiting piece 50 between the front plate 31 of the volute and the front disc 11 of the impeller 10, so that the distance between the front plate 31 of the volute and the front disc 11 of the impeller 10 is the minimum at the position where the flow limiting piece 50 is arranged, and therefore the size of the flow channel can be changed.

In addition, in other embodiments, a flow restriction 50 is provided on both the surface of the volute 30 facing the rear disk 13 and the surface of the volute 30 facing the front disk 11.

The flow restriction 50 is generally annular and extends circumferentially of the impeller 10. In embodiments where the flow restriction 50 is disposed between the volute back plate 33 and the back plate 13 of the impeller 10, the flow restriction 50 is disposed around the rear air inlet 35. In embodiments where the flow restriction 50 is disposed between the volute front plate 31 and the impeller 10 front disk 11, the flow restriction 50 is disposed around the forward air opening 34. Optionally, the flow restriction 50 is arranged coaxially with the impeller 10 such that the flow path formed between the flow restriction 50 and the impeller 10 is symmetrical.

In one embodiment, the flow restriction 50 includes a first annular section 51, and an inner diameter of the first annular section 51 is gradually decreased from the axis of the impeller 10 to the outer periphery of the impeller 10 (i.e., in a direction along the radial direction of the impeller 10 and outward). Optionally, the inner diameter of the first annular segment 51 is tapered such that the distance between the volute 30 and the end face of the impeller 10 decreases in a radial direction of the impeller 10 and from the inside to the outside. In addition, in other embodiments, the first annular section 51 may also be stepped such that the inner diameter of the first annular section 51 has a tendency to become smaller.

In one embodiment, the orthographic projection of the first annular segment 51 on the end face of the impeller 10 is located within the impeller 10. In this embodiment, the gradually convex surface of the flow restriction 50, i.e. the first annular segment 51, is located entirely within the outer periphery of the impeller 10, i.e. only the distance between the end surface of the impeller 10 and the volute 30 is gradually reduced, so that the flow path tapering phenomenon at a position other than the outer periphery of the impeller 10 is avoided. Alternatively, the outer circumference of the first annular segment 51 is flush with the outer edge of the blade 12 of said impeller 10, i.e. the highest point P of the restriction 50 is flush with the outer edge of the blade 12. Because the airflow flows out after the work of the blade 12 is performed, namely the airflow flowing out from the outer edge of the blade 12 just completes the work, the flow speed at the outer edge of the blade 12 is the maximum. Similarly, the distance L between the outer periphery of the first annular segment 51 and the end face of the impeller 10 is the smallest, i.e., the flow passage therebetween is the smallest at the outer periphery of the first annular segment 51, where the flow velocity of the gas flow is the fastest. Therefore, by aligning the outer periphery of the first annular segment 51 with the outer periphery of the vane 12, the airflow flowing out from between the end surface of the impeller 10 and the volute 30 collides with the airflow flowing out from the vane 12 when the flow rate is the fastest, and the backflow of the airflow flowing out from the vane 12 to between the end surface of the impeller 10 and the volute 30 can be greatly reduced, so that the backflow improving effect can be achieved. Of course, in other embodiments, the outer periphery of the first annular segment 51 may be located outside of the impeller 10, or the outer periphery of the first annular segment 51 may be located inside of the impeller 10.

Referring to fig. 10 to 12, in an embodiment, a circle passing through the inner circumference of the blade 12 of the impeller 10 is an inner circle R, and a circle passing through the outer circumference of the blade 12 of the impeller 10 is an outer circle R; the width H of the first annular section 51 in the radial direction of the centrifugal fan is equal to the distance between the inner circle R and the outer circle R, so that the first annular section 51 corresponds to the flow channel of the blade 12, the acceleration distance of the first annular section 51 to the airflow is equal to the acceleration distance of the blade 12 to the airflow, the flow velocities of the airflow after the airflow acts on the first annular section and the blade 12 can be closer, and the backflow phenomenon can be improved. In addition, the width of the first annular segment 51 in the radial direction of the centrifugal fan may be smaller or larger than the distance between the inner circle R and the outer circle R, and the effect of improving the backflow may also be achieved.

Referring again to fig. 7, in an embodiment, the distance L between the outer periphery of the first annular segment 51 and the end surface of the impeller 10 is greater than or equal to 5mm, that is, the minimum distance L between the volute 30 and the end surface of the impeller 10 is greater than or equal to 5mm, for example, the minimum distance L between the volute 30 and the end surface of the impeller 10 may be 5mm, 6mm, 10mm, and so on. If the minimum distance L between the scroll casing 30 and the end surface of the impeller 10 is too small, the acceleration of the airflow is too fast, the airflow flowing out from the space between the first annular segment 51 and the end surface of the impeller 10 is sharp and thin, the speed is very fast, the sharp and fast airflow is easy to generate squealing phenomenon, and the noise is large. In the present embodiment, the distance L between the outer peripheral edge of the first annular segment 51 and the end surface of the impeller 10 is defined to be greater than or equal to 5mm, which prevents air flow from being squealing.

The flow restriction 50 also includes a second annular segment 52, the second annular segment 52 being located at the outer periphery of the impeller 10. In the embodiment where the first annular segment 51 is provided, the second annular segment 52 is connected to the outer periphery of the first annular segment 51, and the inner diameter of the second annular segment 52 is increased in the radial direction of the impeller 10 and in the outward direction. Therefore, the flow velocity of the air flow which flows out after being accelerated by the flow channel of the blade 12 has a trend of slowing down when the air flow flows along the second annular section 52 of the flow limiting piece 50, so that the kinetic energy is gradually converted into the static pressure potential energy of the fan, namely, the gradual diffusion is realized, the regional sudden change of the flow velocity of the air flow is reduced, and the static pressure of the fan is obviously improved.

Alternatively, the inner diameter of the second annular segment 52 is gradually larger in a radial direction and an outward direction of the impeller 10, that is, the second annular segment 52 is gradually inclined in a direction away from the first annular segment 51, so as to make the gas flow smoother. In addition, in other embodiments, the second annular segment 52 may be stepped.

In the above, the first annular section 51 includes a circular arc section or a straight line section; and/or, the second annular segment 52 comprises a circular arc segment or a straight segment. Optionally, the first annular segment 51 and the second annular segment 52 are both circular arc segments, so that the formed flow passage is smoother and softer, and the wind pressure loss is smaller. Of course, the first annular section 51 and the second annular section may be a combination of circular arc sections and straight line sections, and the like.

In addition, the flow restrictor 50 is formed recessed toward the end surface of the impeller 10. Specifically, the first annular section 51 and the second annular section 52 are formed by the flow restriction 50 being recessed toward the impeller 10, so that the first annular section 51 and the second annular section 52 are smoothly connected, and the entire flow passage is smoother. Of course, in other embodiments, as shown in FIG. 13, the first and second

annular segments

51 and 52 may be straight segments.

Referring again to fig. 11, in one embodiment, the flow restriction 50 further includes a third annular segment 53 located at the outer periphery, i.e. the third annular segment 53 is located at the outermost side of the flow restriction 50. Optionally, the third annular segment 53 is connected to the outer periphery of the second annular segment 52, and the third annular segment 53 is engaged with and fixed to the inner surface of the scroll casing 30. Alternatively, the third annular segment 53 is a straight line segment, and the third annular segment 53 serves as a fixed segment, so that the contact area with the volute 30 can be increased, and the fixing effect can be improved. And the third annular segment 53 is flush with the volute 30, which can prevent the air flow from flowing between the flow-limiting member 50 and the volute 30 to generate squeal when the fan is running.

In one embodiment, the flow restriction 50 further comprises a fourth annular section 54 at the inner periphery, i.e. the fourth annular section 54 is located innermost of the flow restriction 50. Optionally, the fourth annular section 54 is connected to the inner periphery of the first annular section 51, and the fourth annular section 54 is engaged with and fixed to the inner surface of the scroll casing 30. Similarly, the fourth annular section 54 is a straight line section, and the fourth annular section 54 serves as a fixed section, which can increase the contact area with the scroll casing 30 and improve the fixing effect. And the fourth annular section 54 is flush with the volute 30, so that the air flow flowing between the flow-limiting piece 50 and the volute 30 can be prevented from generating squealing when the fan runs.

The flow restriction member 50 in the embodiment of the present invention may be provided separately from the scroll casing 30, and of course, the flow restriction member 50 may also be formed integrally with the scroll casing 30. In one embodiment, the flow restriction 50 and the volute 30 are separately formed, and they can be connected in various ways, such as by screwing the flow restriction 50 to the volute 30, or by welding the flow restriction 50 to the volute 30, or by snapping the flow restriction 50 to the volute 30. It should be noted that the connection manner of the flow restriction 50 and the scroll 30 is not limited to the above. Specifically, mounting holes are formed in the third annular segment 53 and the fourth annular segment 54, and fasteners such as screws or bolts are inserted through the mounting holes to be fixed to the scroll casing 30.

The invention also provides a range hood, which comprises the centrifugal fan, the specific structure of the range hood refers to the above embodiments, and the range hood adopts all the technical schemes of all the above embodiments, so that the range hood at least has all the beneficial effects brought by the technical schemes of the above embodiments, and further description is omitted.

The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A centrifugal fan, comprising:

a volute;

an impeller disposed within the volute; and

the flow limiting piece is arranged on the inner side of the volute and corresponds to the end face of the impeller and is arranged at intervals with the end face of the impeller;

the flow-limiting piece comprises a first annular section, and the relative distance between the first annular section and the impeller is reduced along the radial direction of the impeller and the outward direction of the impeller;

the orthographic projection of the first annular section on the impeller end face is located in the impeller, and the distance between the outer periphery of the first annular section and the impeller end face is larger than or equal to 5 mm.

2. The centrifugal fan of claim 1, wherein an outer periphery of the first annular segment is flush with an outer edge of a blade of the impeller.

3. The centrifugal fan according to claim 2, wherein a circle passing through an inner peripheral edge of a blade of the impeller is an inner circle, and a circle passing through an outer peripheral edge of the blade of the impeller is an outer circle;

4. The centrifugal fan of claim 1, wherein the first annular segment comprises a circular arc segment or a straight segment.

5. The centrifugal fan as claimed in claim 1, wherein the flow restrictor comprises a second annular segment located at an outer periphery of the impeller, a relative distance between the second annular segment and the impeller in a radial and outward direction of the impeller being in a tendency to increase.

6. The centrifugal fan of claim 5, wherein the second annular segment comprises a circular arc segment or a straight segment.

7. The centrifugal fan of claim 1, wherein the flow restrictor further comprises a third annular segment at an outer periphery, the third annular segment engaging and being secured to an inner surface of the volute.

8. The centrifugal fan of claim 1, wherein the flow restrictor further comprises a fourth annular segment at an inner periphery, the fourth annular segment engaging and being secured to an inner surface of the volute.

9. The centrifugal fan according to any one of claims 1 to 8, wherein the flow restrictor is formed recessed toward an end surface of the impeller.

10. The centrifugal fan of claim 1, wherein the flow restrictor is disposed separate from the volute.

11. The centrifugal fan according to claim 1, wherein the impeller comprises a front disk, a rear disk and a plurality of blades, the front disk and the rear disk are arranged at intervals, the plurality of blades are respectively connected with the front disk and the rear disk, and the plurality of blades are arranged at intervals along the circumferential direction of the front disk;

12. A range hood comprising a centrifugal fan according to any one of claims 1 to 11.