GB2386927A

GB2386927A - Radial fan with inclined blades

Info

Publication number: GB2386927A
Application number: GB0303590A
Authority: GB
Inventors: Mangina Franco Tassan; Riccardo Furlanetto
Original assignee: Electrolux Professional SpA
Current assignee: Electrolux Professional SpA
Priority date: 2002-02-20
Filing date: 2003-02-17
Publication date: 2003-10-01
Also published as: FR2840034B3; ES1053982U; ITPN20020011U1; FR2840034A1; GB0303590D0; ES1053982Y; DE20302705U1

Abstract

A radial fan with inclined blades comprises a rear surface on to which are attached fan blades 3. These blades are mounted perpendicular to the rear surface, and are inclined so that the radially inner portion of the blades 3 is more advanced than the radially outward part, with respect to the direction of rotation. Additionally, each of the blades has a concave surface 4 with faces radially outwardly. A second surface may be attached to the fan, at the opposite ends of the blades 3 to the rear surface. This front surface may be perpendicular to the axis of rotation, shaped like a funnel (14 figure 3), or be both perpendicular and funnel shaped. The fan may be used in an oven for forced circulation of the gases within the oven, or for extraction of said gases.

Description

IMPROVED FAN FOR COOKING OVEN

The present invention relates to a fan for the forced circulation of the gas 5 mixture present in the cooking chamber, normally air, steam and smoke, and for extracting dry air from the external environment, in an oven for cooking food, especially for catering use. The prior art includes ovens for cooking food by steam which have, in

addition to the traditional properties and cooking systems, the ability to circulate the gases 10 in order to promote uniform temperature and humidity throughout the cooking chamber.

The characteristics and operation of the fan used for the purpose are extensively described in utility model application IT PN00 U 000039 by the present applicant, to which the reader is referred for brevity.

The fans described and cited in the document have "inverted blades", that is 15 curved blades in which the concavity is towards the interior of the fan; it has been observed that this type of fan produces a circulation of the air with both a component in the radial direction, as desired, and a component in an essentially tangential direction. In practice the air is pushed by the fan with an inclination towards the same direction of rotation as the fan, and this produces a markedly nonuniform circulation of the air, which produces a 20 corresponding nonuniformity, and therefore poor quality, of the cooking process.

Another problem that has been observed is the detachment of the filament of flow from the blade towards the trailing edge. This fact becomes more evident after the machine has been used a lot, simply by observing the areas of dirt; air coming in at the centre of the fan receives energy from the blades as it moves towards the periphery and 25 before reaching the trailing edge it detaches from the blade, which reduces the amount of work theoretically exchangeable between the blade and the fluid.

To reduce this characteristic nonuniformity of the flow of air and gas, flow deflectors have hitherto been used to deflect and correct the distribution of air inside the oven and in particular inside the cooking chamber; however, this solution does not 30 completely solve the problem and in any case creates an undesirable increase in the complexity and cost of the oven, together with an obvious reduction in the efficiency of ventilation and greater noise.

-2 Moreover, the radial-blade configuration, although commonly adopted when using the "auto reverse" function, cannot be considered to be satisfactory because it also produces an exiting flow characterized by a forward inclination of the air. Furthermore, in this case again, the efficiency tends to be poorer than with other fan geometries.

5 The need therefore arises to provide a fan for a steam-cooking oven that will allow a forced circulation of the gases that is essentially uniform and radial, does not tend to accumulate dirt, maintains good efficiency, and of course can be manufactured simply and economically.

According to the present invention there is provided a radial fan which is 10 provided on the periphery with a plurality of blades and with a rear surface, the blades being shaped with respective curvatures and being arranged substantially perpendicularly to the rear surface, wherein the blades are inclined with respect to the plane passing through the axis of rotation of the fan and through a point on the respective blade, the inner portion of each of the blades is more advanced than the corresponding outer portion when 15 measured in relation to the direction of rotation, and the curvature of each of the blades has a respective outward-facing concavity.

The invention will be further described by way of non-limitative example with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a fan according to the present invention, 20 shown obliquely from the front (cooking chamber side); Fig. 2 is an end cross section taken on a vertical plane perpendicular to the axis of the fan in Fig. 1; and Fig. 3 is a perspective view of an improved variant of a fan according to the present invention.

25 The present invention is based essentially on the following considerations: given that the object is to give the air or gas mixture a push with a resultant velocity having a greater radial component, and consequently a smaller tangential component, it was felt that this result might be achievable with a type of fan in which the blades were less prone to rotate the air, in contrast to the blades of the prior art whose profile is fairly close to the

30 outer circular perimeter of the fan. It was therefore hypothesized, and successfully verified by experiment, that a fan in which the blades are more steeply inclined with respect to the profile could be effective in achieving the desired object.

With reference to the figures, these show a radial fan 1 used in catering ovens; it is accessible from the front side 2 and its periphery is fitted with a plurality of blades 3 and a rear surface 5 to which the blades are attached.

Compared with the prior art, in which the blades are curved and their

5 concave sides face inwards, the blades of the radial fan according to the present invention have their concave sides 4 facing outwards. Furthermore, the blades are inclined with an inclination "s" between the radius of the fan that passes through each blade and the mean surface of the blade (measured from the line "1" between the forward and rear edges of the blade) - see Fig. 2.

10 Also, the inner portion 6 of the fan is more advanced than the corresponding outer portion 7, if measured with respect to the normal direction of rotation.

If the entry and exit angles of the fluid are appropriately designed, a fan of the type described will produce an almost radial exiting airflow, thus achieving the intended objective.

15 Specifically, it has been observed that a fan as described creates an approximately radial circulation with good efficiency. This result can easily be understood when it is considered that the fluid, after passing into the rotor, passes through the channels between adjacent blades, if the blade is concave it can never detach from the blade. The effect obtained is also known as the "catapult effect" because the blade, with its upward 20 curvature, is always advancing towards the fluid and causes it to detach only at the trailing edge. Additionally, with reference to Fig. 3, to achieve suitable stability of the blades of the fan, an effective fan can be made in accordance with the present invention in which the individual blades are each provided with an outer edge 12 on the opposite side to 25 the rear surface 5, and in which there is an annular surface 13, connected to the rear surface 5, to which the outer edges 12 are attached. For obvious reasons of construction, the annular surface 13 is advantageously made perpendicular to the axis of rotation "O" of the fan, and therefore perpendicular to the fan blades as well.

Lastly, still with reference to Fig. 3, it is particularly advantageous to give 30 the annular surface the shape of a funnel in order to allow the incoming flow to be distributed also to the forward part of the blade, which without this lead-in would be working less efficiently.

Claims

-4 CLAIMS

1. A radial fan which is provided on the periphery with a plurality of blades and with a rear surface, the blades being shaped with respective curvatures and being 5 arranged substantially perpendicularly to the rear surface, wherein the blades are inclined with respect to the plane passing through the axis of rotation of the fan and through a point on the respective blade, the inner portion of each of the blades is more advanced than the corresponding outer portion when measured in relation to the direction of rotation, and the curvature of each of the blades has a respective outward-facing concavity.

2. A fan according to Claim 1, wherein the blades each have an outer edge

remote from the rear surface, an annular surface is connected to the rear surface and perpendicular to the axis of rotation and preferably perpendicular to the blades, and the outer edges are fixed to the annular surface.

3. A fan according to Claim l or 2, wherein the blades each have an outer edge remote from the rear surface, and an annular funnel-shaped surface is mounted on the outer edges. 20

4. A fan constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

5. An oven for cooking food incorporating at least one fan according to any one of the preceding claims for recirculating air, steam or a mixture of the two within a 25 cooking chamber of the oven.