FAN FOR SMOKE AND VAPOUR EXTRACTION SYSTEM, IN PARTICULAR FOR KITCHENS AND EXTRACTION SYSTEM INCORPORATING SUCH A FAN

Abstract

A fan (1) for a smoke and/or vapour extraction system that includes an impeller (3) located within a diffuser or volute (2), the impeller (3) being driven by an electric motor (24); the impeller (3) having a body (20) having a flat part (21) from which a plurality of radially arranged blades (33) extend; these blades are separated from each other by a variable distance based on a periodic function. In addition to this, the diffuser (2) has an air delivery or discharge conduit (5) having a cross-section increasing from an inlet to its outlet (6).

Claims

1. A fan (1) for a smoke and/or vapour extraction system comprising: an impeller (3) located within a diffuser or volute (2), an electric motor (24) having an output shaft (31) that drives the impeller (3), the output shaft having an axis of rotation (N) that is common with impeller (3), said impeller (3) comprising a body (20) having a flat part (21) from which a plurality of radially arranged blades (33) extend, said blades (33) being spaced apart from each other by a variable distance according to a periodic function, the diffuser (2) has an air delivery or outlet conduit (5) having a transverse cross-section which increases from an inlet towards an outlet (6), said transverse cross-section being identified in a plurality of planes containing said axis of rotation (N) of the output shaft (31) of the electric motor (24), said conduit starting in a first portion (4) of the diffuser containing the impeller (3).

2. The fan according to claim 1, wherein said first portion (4) of the diffuser (2) contains the impeller (3) and supports the electric motor (24), and said first portion (4) of the diffuser comprises an edge (44) located at a short distance from the blades (33) of the impeller (3).

3. The fan according to claim 2, wherein said edge (44) of the first portion is present within a recess (28) provided in the impeller (3) defined by two concentric annular and spaced apart portions (21A, 21B) of a body (20) of the impeller that support the blades (33) of the impeller.

4. The fan according to claim 1, wherein the first portion (4) is associated with a structure of the smoke and/or vapour extraction system.

5. The fan according to claim 4, wherein the smoke and/or vapour extraction system is an extraction hood for a cooking surface of a kitchen.

6. The fan according to claim 3, wherein the first and second annular portions (21A, 21B) of the body (20) of the impeller (3) bound a central cavity (22) of said body which contains the electric motor (24), the blades (33) also being connected to a third portion (23) enclosing the cavity (22) in a plane (P) at a distance from the plane (Z) in which the first and second annular portions (21A, 21B) of the body (20) of the impeller (3) lie, said blades (33) supporting such third portion (23).

7. The fan according to claim 3, wherein the recess (28) present between the first annular portion (21A) and the second annular portion (21B) of the body of the impeller (3) is an open hollow space, the blades (33) of the impeller (3) being located in said hollow space.

8. A system for the extraction of smoke and/or vapours such as smoke and/or vapours produced on a cooking surface during preparation of food, said extraction system comprising a fan according to claim 1.

9. The extraction system according to claim 8, wherein said fan includes the diffuser (2) having the first portion (4) which is hollow, containing an electric motor (24) that drives the impeller (3) having the blades that are arranged at variable mutual distances according to a periodic function.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] For a better understanding of this invention there are appended purely by way of example, but without any limitation, the following drawings in which:

[0031] FIG. 1 shows a lateral perspective exploded view of a fan according to the invention with some parts omitted for greater clarity;

[0032] FIG. 2 shows a cross-section of the assembled fan along the line 2-2 in FIG. 1;

[0033] FIG. 3 shows a magnified perspective view of one side of an impeller of the fan in FIG. 1;

[0034] FIG. 4 shows a magnified perspective view of another side of the impeller in FIG. 3; and

[0035] FIG. 5 shows a perspective view of another side of the fan in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] With reference to the figures mentioned, a fan according to the invention is indicated generically by 1. This comprises a diffuser 2 and an impeller 3; in particular the diffuser has a first portion 4 containing impeller 3 (see in particular FIG. 5) and a second portion 5 (delivery conduit) which is open at a free extremity or outlet 6. First portion 4 has an opening 8 at which impeller 3 is located within diffuser 2, said opening 8 defining an extraction opening for air containing smoke and/or vapours from an area in which these form.

[0037] In one embodiment of the invention fan 1 is inserted within a kitchen extraction hood and the smoke and/or vapours are generated from a cooking surface where food is in the course of preparation. This hood may be of the type which is externally associated with a kitchen cabinet located above such cooking surface, inserted within such cabinet, a part of the cooking surface or independently attached thereto; otherwise the hood may be an independent element placed at a distance from the cooking surface.

[0038] Second portion or delivery conduit 5 of the diffuser may be attached to a conduit or pipe which carries smoke and/or vapours outside the environment in which the smoke is generated (for example the kitchen), or conduit 5 may open within such environment, in which case the smoke and/or vapours are returned after they have been suitably filtered.

[0039] Preferably there is a grease trap filter associated with a structure of the extraction hood, not shown in the figures, to which the fan is attached at opening 8 of the fan.

[0040] Between extraction opening 8 and filter 11 there is a suitable distance (for example of 10-50 mm) to allow the flow of air to pass towards the extraction cross-section.

[0041] First portion 4 of diffuser 2 is hollow with respect to an extremity portion of diffuser 2 itself, has a wall 13 closing off the diffuser and contains impeller 3. Such impeller 3 has a body 20 having a first annular flat portion 21A delimiting a central hollow cavity 22, a second annular portion 21B, coplanar with the first and concentric therewith (and located internally within first portion 21A) and a third flat portion 23 enclosing cavity 22 in a plane P distant from plane Z in which first and second portions 21A and 21B lie.

[0042] Between first and second annular portions 21A and 21B there is therefore a through annular hollow 28 whose function will be described below.

[0043] An electric motor 24 is located within cavity 22 of impeller 3 and within first portion 4 of diffuser 2. Motor 24 is attached to enclosing wall 13 and diffuser 2 by means of screws 26.

[0044] Motor 24 has an output shaft 31 which is of one piece in any known way with impeller 3. In particular a seat 27 for attaching such shaft 31 to impeller 3 is provided in third flat portion 23 of impeller 3.

[0045] The latter has a plurality of radially arranged blades 33 of one piece with first and second portions 21A and 21B of impeller body 20. These blades are arranged at variable distances from each other; in particular such distance varies according to a periodic function such as a sinusoidal or similar function.

[0046] The words “varies according to a periodic function” means that the angular distance between each pair of blades along the edge of impeller 3 varies on passing from one blade 33 to the next and the next one again according to a non-linear mathematical function (that is, for example, what happens if the distances are constant or increase according to a linear function of the type Y=ax), but according to a variable mathematical function (law) along the inner circumference of the impeller (for example y=A sin (m.Math.x), where m is the periodicity within the circumference, where m≧1). In other words, starting from an initial blade 33, and moving along the entire impeller, returning to such initial blade and repeating such movement several times, a function which describes the variation in the distances between the blades will be a periodic function (for example the sinusoidal function).

[0047] Thanks to this characteristic, when the impeller rotates there is produced noise whose intensity is defined by the formula

BPF=nt/60

where
BPF=Blade Pass Frequency, or frequency (in Hz) of the noise generated by the movement of the rotating blades
n=rotation speed (revolutions per minute)
t=number of blades.

[0048] The noise generated is very much less than that generated by the rotation of an impeller having equally spaced blades, because for the same number of blades the frequency of the noise generated is displaced into a portion of the audible spectrum where the human ear is less sensitive.

[0049] As mentioned, impeller 3 has a first flat annular portion 21A and a second flat annular portion 21B. Blades 33, of slightly arched shape, are located in an arched manner between first and second portions 21A and 21B and are of one piece therewith.

[0050] Such blades 33 are also of one piece with third portion 23 enclosing cavity 22 of the impeller (which thus has a substantially recessed shape, but project laterally to such portion 23 being attached to first and second portions 21A and 21B.

[0051] In this way portion 23 is “supported” by blades 33 (of one piece with portion 21) at a distance from such first portion 21.

[0052] Impeller 3 is located in first portion 4 of the diffuser and rotates substantially within aforesaid first portion 4 which is recessed with respect to a perimetral part 40 having points 41 at which such first portion 4 is attached to the structure of the extraction hood (not shown).

[0053] Perimetral part 40 has an inner edge 44 shaped in such a way as to fit within annular recess 28 of impeller 3 containing it (see FIG. 2). Air can pass through such recess. This makes it possible to limit the recycling flow of air within the diffuser, creating a kind of seal between the static part (diffuser 4) and the rotating part (impeller 3) of fan 1.

[0054] On one side of first portion 4 of diffuser 2 there is a third portion 43 of such diffuser which also delimits outlet 6 of delivery conduit 5.

[0055] FIG. 1 also shows other known components (generically indicated by 100) which are commonly used for the electrical connections of fan 1. These components will therefore not be further described.

[0056] The fan so obtained is relatively easy to construct owing to the arrangement of the blades which are of one piece with the first and second annular portions 21A and 21B of body 20 of impeller 3, which makes moulding easier. In addition to this, the specific arrangement of the blades not only makes it possible to direct the air towards conduit 5 in an optimum way, but also makes it possible to have rotation with no or at any event little noise generation.

[0057] As the volute or diffuser also has an increasing cross-section from the inlet to conduit 5 to its extremity or outlet 6, there is optimum pressure recovery, minimising head losses, bringing about an appreciable improvement in the performance of the fan in terms of throughput, pressure and fluid dynamic efficiency. This increasing cross-section can be seen in a plurality of planes containing an axis of rotation of motor 24 or its output shaft 31; one example of a cross-section as indicated above is FIG. 2 where one of the aforesaid planes is that of the figure. From what is illustrated in FIG. 2 it will be noted that cross-section K1 of the volute is smaller than cross-section K2 of that volute.

[0058] Finally it is possible to obtain a diffuser of height less than 150 mm, measured parallel to the axis of the shaft of motor 31, making it possible to reduce the height of the hood to 110 mm, with a consequent saving in the metal material of which the latter is made, and to construct an extraction system that is compact but at the same time has high efficiency.

[0059] A preferred embodiment of the invention, which is to be considered only as an example of the latter and whose characteristics are defined by the following claims, has been described.