Improved centrifugal fan, in particular for extractor hoods

Abstract

 A centrifugal fan with a helical external profile, formed by a pair of half-shells which may be coupled to one another, an impeller mounted in the body which can be driven in rotation about a first axis (X), the body being provided with a pair of opposing lateral extraction openings coaxial with the first axis and a tangential delivery opening coaxial with a second axis positioned tangentially with respect to the impeller, a pressure chamber being formed in the body whose volume is formed between the impeller and the helical profile of the body, this helical profile developing from a point at a minimum radial distance from the first axis in a median plane (P) of symmetry of the body (2).

Description

[0001] The present invention relates to a centrifugal fan having the features set out in the preamble of the main claim.

[0002] The invention relates in particular, but not exclusively, to the technical field of centrifugal fans designed for applications in extractor hoods or smoke extractor devices.

[0003] In this particular sector, fans of the above-mentioned type are widely used as extractor devices for vapours, combustion fumes, exhaust gases, i.e. in all applications in which gaseous mixtures are generally to be extracted and conveyed. Typical applications include the use of centrifugal fans with a helical body and a cylindrical drum impeller and axially extending blades. The bodies of these fans are further provided with a lateral extraction opening and a tangential delivery opening between which there extends a helical pressure chamber whose volume is defined between the body and the impeller.

[0004] The main object of the invention is to provide a fan of the above-mentioned type which is particularly compact in terms of its overall dimensions and at the same time ensures the fluid dynamic efficiency and performance needed for the applications for which it is intended.

[0005] A further object is to design a fan which, as a result of the above-mentioned features, can be readily mounted in particular plant engineering conditions, for example to replace other fans of known type of different dimensions and/or configuration or for use with extractor hoods of particular configurations or having design features which limit, possibly substantially, the space available for the mounting and housing of the fan.

[0006] These objects are achieved by the invention by means of a centrifugal fan embodied in accordance with the appended claims.

[0007] Other advantages and features of the present invention will become clear from the following detailed description of a preferred embodiment thereof, given with reference to the appended drawings which are provided purely by way of nonlimiting example and in which:

• Fig. 1 is a perspective view of a fan embodied in accordance with the invention;
• Fig. 2 is a front elevation of the fan of Fig. 1;
• Fig. 3 is a diagrammatic view of a median section of the body of the fan of the preceding drawings.

[0008] With reference to the drawings, a centrifugal fan, designed in particular for use in extractor hoods or smoke extractor devices and embodied in accordance with the present invention, is shown by 1.

[0009] The fan 1 comprises a body 2 with a helical internal profile which is formed by two half-shells 2a, 2b which may be coupled to one another in a detachable manner at a median plane of connection shown diagrammatically by P in the drawings. The two half-shells of the body have substantial mirror symmetry with respect to the connection plane P, as can be seen from the assembled condition of Fig. 1, with the exception of the lateral extraction opening provided on only one of the two half-shells of the body.

[0010] The body 2 houses a cylindrical drum impeller 3 provided with axially extending blades 4, the impeller being able to be driven in rotation about an axis X. The body is also provided with a tangential delivery opening 5, coaxial with an axis shown by Y, positioned tangentially with respect to the impeller, and a pair of second lateral extraction openings 6 coaxial with the axis X, each of which is provided on the respective half-shell.

[0011] A pressure chamber is shown by 7 and is formed within the body along its helical development, the volume of this chamber being formed between the drum of the impeller 3 and the inner surface profile of the body. In Fig. 3, which is a diagram of a median section of the fan belonging to the median plane P (perpendicular to the axis X), the line of the helical profile contained in this median plane is shown by 8. The point along this profile located at the smallest radial distance from the axis X is shown by S. The helical profile 8 therefore develops from the point S, relative to the axis 8, up to a rectilinear end section 9 coupled with the delivery section. The opening 5 of the delivery section is selected in the embodiment described here to be of circular configuration and

[0012] Fig. 3 therefore shows the diametrical dimension of this opening.

[0013] In the diagram of the median section (plane P) of Fig. 3, the overall dimension of the projection of the helical profile 8, extending from the point S, in a direction parallel to the axis Y, is also shown by A.

[0014] The overall dimension of the projection of the profile 8 in a direction perpendicular to the axis Y is also shown by B.

[0015] In the median plane P, the distance between the axis X and the axis Y is shown by C, as can be seen from Fig. 3.

[0016] Taking the ratio between the dimensions C and A (R'= C/A) as the first ratio R' and the ratio between the dimension B and A (R"= B/A) as the second ratio, the ratios R' and R" are selected, in accordance with the invention, within the following intervals of values:

0.075 ≤ R' ≤ 0.165

1.18 ≤ R" ≤ 1.4

[0017] The selection of the ratios R' and R" in the intervals of values shown above, entails, according to tests and trials conducted by the Applicant, the identification of trios of values for the dimensions A, B and C, with which it is possible to obtain a dimension of the body with a helical profile which is particularly compact but at the same time able to ensure appropriate efficiency and performance by the fan and appropriate fluid dynamic behaviour. These choices are therefore an improvement with respect to known solutions, as they are an optimisation of design with respect to the overall dimensions of the body of the fan, in relation to the impellers which may be housed in these spaces.

[0018] The following values represent a particular preferred choice of the ratios R' and R":

R'= 0.156667

R" = 1.23333

[0019] These ratios are reflected by the following trio of values A, B, C:

A = 120 mm

B = 148 mm

C = 18.8 mm

[0020] Tests by the Applicant have shown that when the fan is dimensioned with the above-mentioned ratios, the above-mentioned features which combine a particular compactness of the fan with appropriate efficiency as regards the fluid dynamic performance of the fan are obtained.

[0021] The invention thus achieves the stated objects as it achieves the advantages listed with respect to known solutions.

Claims

1. A centrifugal fan comprising:

- a body (2) with a helical external profile, formed by a pair of half-shells (2a, 2b) which may be coupled to one another,

- an impeller (3) mounted in the body (2) which can be driven in rotation about a first axis (X), the body (2) being provided with a pair of opposing lateral extraction openings (6) coaxial with the first axis (X), and a tangential delivery opening (5) coaxial with a second axis (Y) and positioned tangentially with respect to the impeller,

- a pressure chamber (7), formed in the body (2), whose volume is formed between the impeller (3) and the helical profile of the body (2),

- in a median plane (P) of symmetry of the body (2), perpendicular to this first axis, the helical profile developing from a point (S) at a minimum radial distance from the first axis, characterized in that

- defining the overall dimension of the projection of the helical profile, extending from the point (S), in a direction parallel to the second axis (Y), as the first dimension (A),

- defining the dimension of the projection of the bulk of the profile in a direction perpendicular to the second axis (Y) as the second dimension (B),

- and defining the distance, measured in the plane, between the first (X) and second axis (Y) as the third dimension (C),

- and taking the ratio between the third and first dimension as the first ratio (R') and the ratio between the second and first dimension as the second ratio (R"), the first and second ratios are selected in the following intervals of values respectively:

with C/A = R' 0.075 ≤ R' ≤ 0.165

with B/A = R" 1.18 ≤ R" ≤ 1.4

2. A fan according to claim 1, wherein the ratios R' and R" are chosen as follows:

R'= 0.156667

R" = 1.233333

Drawing