EP1774225A1

EP1774225A1 - Device for heating an air circulating oven

Info

Publication number: EP1774225A1
Application number: EP05775240A
Authority: EP
Inventors: Michel Klinger; Jean-Marie Balandier; Jean-François Perrin
Original assignee: SEB SA
Current assignee: SEB SA
Priority date: 2004-06-14
Filing date: 2005-06-08
Publication date: 2007-04-18
Also published as: FR2871556B1; WO2006000702A1; FR2871556A1

Abstract

The invention relates to a device for heating a convector oven, comprising a motorized rotor which can axially suction air contained in the enclosure of an oven and radially force it back, in addition to a hood which can channel the circulating air outside the enclosure of the oven, characterized in that it comprises a heating unit having an area (16) with which a heating element is in contact, wherein said unit (5) comprises an opening (8) which acts as an opening for the suction of air; a plurality of means which can transmit heat by convection to the suctioned air inside the device; means (11, 12, 13, 14) which are disposed at the periphery of the opening (8) and which force back the air heated inside the enclosure of the oven.

Description

DEVICE FOR HEATING AN AIR CIRCULATING OVEN

TECHNICAL FIELD The invention relates to the field of household appliances and more specifically to cooking ovens. It is more particularly air circulation ovens or forced convection.

It is more particularly an effective means for improving the heat transfer between the heating element and the air sucked into the oven.

PRIOR ART In general, the heating devices included in the air circulation furnaces are in the form of radiant heating resistors. This type of heating resistor is generally of circular or helical shape, arranged peripherally with respect to a suction rotor. Thus, the air is drawn axially by the rotor and is discharged radially at the periphery thereof, towards the resistor. It then warms up on contact, and is then injected into the cooking cavity with louvers.

Such a device is described in EP-530 477, in which the heating device does not have a sufficient surface to generate a high efficiency heat exchange. Therefore, to obtain a maximum cooking temperature of about 250 ^° C., it is necessary to bring the heating element to a very high temperature close to 700 ^° C. However, such a solution has a small exchange surface which leads to convective exchange thermal coefficients of the order of 10 to 15 Wm ^"2 .K ^'1. Furthermore, the use of a high temperature heating element requires specific regulation and high temperatures can generate hot spots on different parts of the oven. Thus, the object of the invention is to overcome the problems stated by reducing in particular the temperature of the heating element and consequently the associated power consumption, while optimizing the cooking time of the food.

DESCRIPTION OF THE INVENTION The invention therefore relates to a device for heating an air circulating oven comprising a motorized rotor adapted to suck axially the air contained in the furnace chamber and to discharge it radially. It also includes a hood adapted to channel the air flowing outside the enclosure of the furnace, before its ré¬ injection into the oven.

It is characterized in that it comprises a heating block having an area with which a heating element is in contact, this block comprising: an opening acting as an air suction orifice; A plurality of means capable of transmitting heat by convection to the air sucked into the device; • means arranged at the periphery of the opening and able to discharge the heated air inside the enclosure of the furnace.

By block is meant not only a solid mass consisting of a single piece, but also its extended meaning, namely elements grouped into a compact mass. Thus, the block may consist of different elements connected to each other by any known means, but may also be developed in the form of a monoblock, resulting from machining or molding.

Thus, the heat is transmitted to the air via a solid piece or an assembly of parts, with which (which) the heating element is in contact. In this way, the heating element can be attached to the heating block, but it can also be embedded within the volume defined by the heating block, and in particular within a groove provided for this purpose.

The contact zone between the heating element and the block may have a substantially flat geometry and a sufficiently large thickness to allow in particular to integrate the heating element within its volume.

According to the invention, the block therefore comprises a suction orifice through which the air contained inside the enclosure of the oven is sucked by means of the rotor. This suction opening may be central or not, a nozzle that can direct the air according to the architecture of the furnace.

In order to generate a large heat exchange surface between the block and the air, the block comprises a plurality of identical or different arrangements for transmitting heat by convection. The heated air is then propufsé inside the furnace enclosure through at least one opening. However, a plurality of openings will be preferred in order to better distribute the heat in the oven.

Advantageously, the means capable of transmitting the heat by convection to the air may be either in the form of fins located in the path of the air sucked and emerging perpendicular to the zone of the heating block, or in the form spikes arranged at the central opening and register in the block area in contact with the heating element.

In other words, in the first case one of the flat faces of the heating block may be facing, or even in contact with one of the walls of the furnace. The other flat face may then have fins that will heat the air propelled radially by the rotor. By the term "fin" is meant not only a protruding blade for increasing the heat-transmitting surface, but also any protruding shape other than a blade.

In the second case, the central opening may have a geometry of complex shape so as to increase the heat exchange surface between the block and the air entering the device. Therefore, it is also possible to make a central opening by means of several slots or holes so as to break the central opening into several small holes. Both types of means capable of transmitting heat by convection can of course be combined to generate a larger heat exchange surface.

The increase in the exchange surface is associated with an increase in air velocities. Advantageously, the air speeds generated by the rotor are greater than 10 m / s. We can then talk about ultra forced convection. The flow rates are also important since they are greater than or equal to 30 l / s, which corresponds, for certain ranges of furnaces, to a replacement of the volume of the oven every second.

These high air velocities and speeds result in completely different cooking modes than those traditionally used in rotary furnaces, since it is then possible to considerably reduce the cooking temperature, compared to such furnaces, for a result. identical.

By such speeds, it is also possible to remove the function "grill" without significant changes in the cooking result. This aspect is important for the cleaning of the oven, since it is freed from the apparent resistances of vault.

In addition, the air speeds being high, it is possible, to a greater extent, to vary this speed, in order to obtain a precise mode of operation. For example, delicate cooking, such as soufflé, requires relatively low speeds so as not to compromise the uniform lifting of the preparation.

Advantageously, the heating device can be arranged at a vertical wall of the furnace. In this way, aspiration and propulsion of the air are carried out in a horizontal direction. It can be attached at the rear wall of the oven, but also at one of the side walls. In practice, the device can be integrated inside an oven using steam to cook the food and thus prevent drying out. Such ovens include a steam injection system inside the furnace chamber. Thus, this type of oven can be described as "steam oven rotating heat" or forced convection.

In a first variant, the heating block is used to generate steam. To do this, a supply of liquid water can be made near the flat surface of the heating block. Runoff on one of its walls then makes it possible to transform this water into steam which is then channeled and then injected into the furnace.

In a second variant, the heating block may comprise at one of its faces a groove, capable of forming a pipe for conveying and superheating the steam. In other words, the water vapor can be achieved by means of a device attached to the heating device. It is then channeled to the vicinity of the heating block, then through a pipe to overheat before injection into the oven.

Advantageously, the heating block can be made of an aluminum alloy. Indeed, aluminum has great qualities in terms of thermal conduction favoring the speed of heat transmission and the homogeneity of the temperature of the heating block.

According to one embodiment, the heating block can be obtained by welding fins on a plate. In other words, the fins can be cut in a profile and then welded to the plate formed by the heating block.

According to another embodiment, the heating block can be obtained by a molding process. In this case, it is not necessary to join the fins with a plate by welding. This embodiment is economically advantageous, and can be easily automated, the multi-functional block can then consist of only one piece "monobloc". However the "monobloc" appearance of the heating block can also be obtained by machining, and does not result solely from a molding process.

SUMMARY DESCRIPTION OF THE FIGURES The manner of carrying out the invention as well as the advantages which result therefrom will emerge from the description of the embodiment which follows, given by way of indication and not by way of limitation, in support of the appended figures in which: Figure 1 is a perspective view of an oven equipped with such a heater; Figure 2 is a perspective view of the heating block according to the invention; Figures 3 and 4 are views of the inner face of two possible variants for producing the heating block, according to the invention; Figure 5 is a view of the outer face of the heating block according to the invention; Figure 6 shows an economically advantageous variant of the invention.

DESCRIPTION OF THE INVENTION As already mentioned, the invention relates to a heating device for a circulating air oven, more commonly known as a rotary heat oven.

As shown in Figure 1, the heater is arranged at a vertical wall of the oven (2). In this representation, the device is attached to the rear wall (15) of the oven (2). By means of a rotor (not shown), the air contained in the enclosure (4) of the oven (2) is sucked by the openings (3) of a grid (6) formed in the vertical wall (15) , the heating device being located immediately behind said grid (6). The heating device being located at the outer face of the vertical wall (15), it is not directly subjected to dirt or fat projections during cooking food.

As shown in FIGS. 2 and 3, the heating device (1) presents an outer substantially planar face (16) which can be in direct contact with the wall (15) of the oven (2). This face (16) is formed by a solid heating block (5) in which is embedded a heating element of the shielded type (not visible).

To this end, the heating block (5) has a thickness e, at the face (16), of the order of 10 mm, in particular to integrate this heating element.

The air is sucked at a central opening (8) by means of a rotor of a motor-fan unit (20), and then exits the device (1) through four openings (11, 12, 13, 14 ) forming a square, then it is injected inside the enclosure (4) of the furnace (2) by the perforations (21, 22, 23, 24) located in the wall (15), facing respectively openings (11, 12, 13, 14). The air emerging at these openings is therefore at a higher temperature than the air entering the opening (8).

As shown in Figure 4, where the rear face of the device has been omitted for reasons of clarity, the inner face (19) of the heating block (5) has means for transmitting heat to the air flowing to the inside the heating device (1). Indeed, the heating block (5) has, at the central opening (8), a plurality of points (10) for heating the air directly to its passage when it enters the inside of the device heating (1). Furthermore, the rotor propels the air sucked radially towards fins (9) also able to transmit heat to the air circulating in the device (1).

In this configuration, the fins (9) emerge perpendicular to a substantially planar zone (7) of the heating block, this face being substantially parallel to the rear wall (15) of the oven when the device (1) is installed in the oven.

The fins (9) participate in the recovery of the air to direct it to the four outlet openings (11, 12, 13, 14). The peripheral walls (18) of the heating block (5), as well as the rear wall of the device (not shown for reasons of clarity) can also guide the air, but also to generate a large heating surface so as to increase the heat transfer.

The air, thus rectified, is directed towards the outlet mouths (31, 32, 33, 34) which each comprise a curved wall (41, 42, 43, 44) for straightening the air in a plane perpendicular to the plane rotor output. The air thus makes a half-turn relative to its entry into the device (1), to exit through the openings (11, 12, 13, 14) respective mouths (31, 32, 33, 34).

Such a heating block (5) is advantageously made of an aluminum alloy by a molding process.

Alternatively, the heating block may be in the form of a machined plate on which the fins (9) are reported by welding or other securing means. Therefore, it is possible to cut the fins (9) in a profile, then come to bring them one by one on the plate.

As shown in Figure 5, the outer face (16) of the heating block (5) may include the heating element (53) attached to the inside of a groove (51). The groove can also be made on the inner face (7) of the block. In a more economical variant, the heating element can be attached to one of these two faces, taking care to achieve a good thermal contact, for example by flattening the surface of the heating element in contact with the face on which it is reported.

In general, any form of contact can be used between the heating element and the heating block: crimping, mechanical locking by rivets, screws, brazing, etc. The essential thing is to obtain a thermal transfer essentially by conduction. However, there may be some radiation, but we will try to obtain the largest possible transfer by conduction. Furthermore, the contact zone between the heating element and the block may have a specific non-planar geometry, such as a cone. In this configuration, the rotor may be in the form of a cone-shaped helix. It can be expected also a convergent.

The heating block may also include a second groove capable of forming a pipe for conveying and superheating steam. According to the proposed example and its arrangement in the oven, such a groove will preferably be provided on the peripheral portion of the heating block, for example using the thickness e to make said groove.

Figure 6 illustrates an economically advantageous variant of the invention, wherein the heating block is simplified. Thus the heating device (101) shown consists of a heating block (55) having an inlet opening (88) enlarged relative to the heating block (5), essentially by the suppression of the spikes (10). The heating element (83) is housed in a groove coming from the bottom wall (86) and whose outer face (70) is located inside the heating block, in which the fins (69) are arranged in particular. the rotor, not shown, but which is shown an opening (85) for positioning and fixing. The output plane of the rotor is therefore substantially parallel to the bottom wall (86). The fins (69) advantageously bear on the outer face (70) of the groove in order to best transmit the heat generated by the heating element (83).

At the periphery of the opening 88 are curved walls (71, -72) from the bottom wall (86) and the end of which is at an angle of 90 ° with the bottom wall. In a similar manner to the heating block (5), four curved walls are thus arranged, angularly distributed.

The heating block (55) is thus positioned, substantially in the same way as the block (5), behind the rear wall (15) of the oven. The shape and size of the openings in this wall depends essentially on the size of the rotor propeller, but a central air inlet opening and perforations (21, 22, 23, 24) facing the ends (61, 62, 63, 64) of the curved walls.

Thus, the air "sucked" by the rotation of the impeller of the rotor, is channeled by the fins (69) to the curved walls whose ends (61, 62, 63, 64), opposite the perforations (21, 22, 23, 24) allow the injection of air into the furnace, the air being heated in its path in the heating block, essentially by the fins and the curved walls.

This alternative embodiment offers, by the lightening of material thus produced, a better reactivity by reducing the thermal inertia related to the rise in temperature of the heating block.

It follows from the foregoing that a heating device according to the invention has many advantages, in particular: the reduction of the temperature of the heating element to values of around 300 ^° C., the reduction of the cooking temperature to maximum values around 200 ⁰ C, without degradation of performance by high air speeds. These high speeds can be envisaged thanks to the large exchange surface of the heating block, which makes it possible to triple or quadruple this exchange surface with respect to a conventional device as described in the preamble of the present invention. The high speeds of the air increase the convective heat transfer and generate a convective transfer coefficient greater than 30 Wm ^"2 .K ^{" 1} , this coefficient being all the higher as the air velocities are high, • the reduction of the electric consumption of the oven by the relatively low temperatures presented, also allowing to reduce the thermal losses resulting in an increase in the overall efficiency of the oven and the resulting energy savings, • its possible combination with a generation device of steam. The fact of presenting a heating block also makes it possible to propose simple solutions of evaporation, the water being able to arrive directly on the block where it vaporizes during its run-off on the surface of the block, • the absence of heating resistances inside the enclosure of the furnace, thus avoiding the risk of fire when the fats are projected on said resistors. The cleaning of the oven is, moreover, facilitated, helped by the lesser polymerization of the grease projected on the less hot walls; • Better control of the air temperature thanks to a greater homogeneity in the cooking chamber and a high flow which allows a greater reactivity of the thermal control device (NTC judiciously implanted + electronic treatment).

Moreover, the reduction of the cooking temperature, with equal performances, makes it possible: • to reduce the overheating of fats and consequently the lesser production of fumes (one moves away from the point of smoke of fats), • to reduce the risks related to the overheating of fats, • to reduce the pathogenic compounds linked to the Maillard reaction (browning) which is too high in temperature, • the reduction of grease projections resulting from meat to be roasted in particular (poultry, ..), • a improvement of taste quality (organoleptic) by a more uniform coloring of foods without over-coloring (charring) due to a more efficient heat transfer

The present invention also makes it possible to design a multifunctional heating subassembly thus comprising a heating block and its heating means, an air duct for the return of this air in the oven, as well as a motor-fan unit for circulating air. air, which allows to realize and test this subset independently of the oven, which facilitates the development of the product and allows implementation in masked time.

Claims

1. Heating device (1, 101) of a furnace (2) with rotating heat having a motorized rotor adapted to aspirate the air contained in the enclosure (4) of the furnace (2) and to repress it radially, and a hood adapted to channel the air circulating outside the oven chamber (2), characterized in that it comprises a heating block (5, 55) having a zone (16, 7, 86) with which a heating element (53, 83) is in contact, said block (5, 55) comprising: • an opening (8, 88) acting as an air suction orifice; A plurality of means capable of transmitting heat by convection to the air sucked into the device (1); • means (11, 12, 13, 14, 71, 72) arranged at the periphery of the opening (8, 88) and able to discharge the heated air inside the chamber (4) of the oven (2).

2. Device according to claim 1, characterized in that the means for transmitting heat by convection air are in the form of fins (9, 69) located in the path of the air sucked and emerging by relative to the zone (16, 7, 86) of the heating block (5, 55).

3. Device according to the preceding claim, characterized in that the fins (9, 69) are substantially perpendicular to the area (16, 7, 86).

4. Device according to one of the preceding claims, characterized in that the means able to discharge the air inside the enclosure (4) of the oven (2) consist of a wall (41, 42, 43, 44, 71, 72) bent at 90 ° to the rotor exit plane, associated with a discharge aperture (11, 12, 13, 14, 21, 22, 23, 24).

5. Device according to one of the preceding claims, characterized in that the contact zone between the heating element (53, 83) and the block is substantially flat.

6. Device according to one of claims 1 to 4, characterized in that the heating element (53, 83) is disposed in a groove in the heating block (5, 55).

7. Device according to claim 2, characterized in that the fins (69) bear on the outer face (70) of a groove in the heating block (5) and accommodating the heating element (83).

8. Device according to one of the preceding claims, characterized in that the means for transmitting heat by convection are in the form of spikes (10) arranged at the central opening (8) and registered in the area (16, 7) of the heating block (5).

9. Device according to one of the preceding claims, characterized in that the heating block (5, 55) consists of a single piece.

10. Device according to one of the preceding claims, characterized in that the air velocities generated by the motorized rotor operating in the oven are greater than 10 m / s.

11. Device according to one of the preceding claims, characterized in that the air flow generated by the motorized rotor operating in the oven is greater than or equal to 30 l / s.

12. Device according to claim 1, characterized in that it is arranged at a vertical wall (15) of the oven (2).

13. Device according to claim 1, characterized in that it is associated with a steam injection system inside the enclosure (4) of the oven (2).

14. Device according to claim 1, characterized in that the block heater (5) generates steam.

15. Device according to claim 1, characterized in that the heating block (5, 55) comprises at one of its faces (16, 17, 86) a groove capable of forming a pipe for conveying and superheating the steam .

16. Device according to claim 1, characterized in that the heating block (5, 55) is made of an aluminum alloy.

17. Device according to claim 2, characterized in that the heating block (5, 55) is obtained by welding the fins (9, 69) on a plate.

18. Device according to claim 1, characterized in that the heating block (5, 55) is obtained by a molding process.