GB2347992A

GB2347992A - Cooking oven with gas heated vapour generator

Info

Publication number: GB2347992A
Application number: GB0004295A
Authority: GB
Inventors: Mangina Franco Tassan; Luca Paroni
Original assignee: Electrolux Zanussi Grandi Impianti SpA
Current assignee: Electrolux Zanussi Grandi Impianti SpA
Priority date: 1999-03-17
Filing date: 2000-02-23
Publication date: 2000-09-20
Anticipated expiration: 2020-02-23
Also published as: GB2347992B; ES1045737U; ES1045737Y; GB0004295D0; FR2791125A1; ITPN990009V0; FR2791125B3; DE20003485U1; ITPN990009U1; IT248016Y1

Abstract

A cooking oven comprises a cooking compartment 1, a vapour generator 10 and means 8,9 and 12 for introducing generated vapour into the compartment 1. Vapours enter the compartment 1 behind a perforated partition 5 through a duct 8, connected by tube 9 to the vapour generator output 12. A centrifugal fan forces circulation of air and vapour around the compartment. A drain 2 is provided in the compartment for the removal of condensed water. The vapour generator 10 comprises a gas fired heating assembly disposed below a preset level of water H in a tank 11. The heating assembly 10 comprises a gas burner 15 mounted in an open ended rectilinear combustion chamber 13 with a coaxial surrounding casing 18 forming an annular passage 22 along its length. In use, combustion products from the burner 15 flow X to the end of the combustion chamber 21, are inverted U, and returned Y through the annular passage 22 to the manifold 23 of a a flue 24 increasing heat exchange with the water. The heating assembly may have a corrugated surface 18. The heating assembly may be mounted in a cantilevered relationship with the water tank 11.

Description

COOKING OVEN WITH GAS-HEATED VAPOUR GENERATOR The present invention relates to a cooking oven, in particular for professional use, which is provided with a gas-heated vapour generator.

US-A-4 552 123 discloses an oven of that type which comprises, inter alia, a water chamber in which a preset level of water is created and maintained. Passing through the water chamber is one or more tubes provided with internal radial fins over which flows the combustion products from an adjacent gas burner, the water chamber communicating with the adjoining cooking compartment by way of an opening disposed above the above-mentioned water level. When the burner is in operation, due to the effect of the heat transferred from the combustion products in the upper part of the water chamber, vapour is generated at atmospheric pressure, which is introduced into the cooking compartment by way of the above-mentioned opening.

That appliance, in order to guarantee efficient vapour generation (which is quantified in the text of the patent as being greater than 75%), requires good contact between the fins and the internal surface of the tubes. Production is therefore found to be fairly complex insofar as it involves a kind of hot shrinkage of the tubes which are made from stainless steel on to the fins which are made from mild steel.

The object of this invention is to provide a cooking oven with vapour generation which is highly efficient in regard to a gas-heated generator, which is of a simple construction and which involves a relatively low cost level.

According to the present invention there is provided an oven having a cooking compartment, a vapour generator and means for introduction into the former of the vapour generated by the vapour generator which comprises a chamber in which a preset level of water is created and maintained and a combustion chamber which is heated with a gas burner and is in the form of a rectilinear tube open at the ends and which extends along the water chamber, wherein the combustion chamber is surrounded by a coaxial metal casing disposed below said water level, in such a way as to form a conduit of annular section for the combustion products, which begins in a zone between the end portion of the casing and the terminal section of the combustion chamber and which finishes in a collector manifold communicating with the discharge flue.

In order more clearly to show those features and to indicate the advantages thereof in relation to the state of the art, described hereinafter is a preferred but non-exclusive embodiment of the present invention, with reference to the accompanying drawing in which: Figure 1 diagrammatically shows a view in longitudinal vertical section of a cooking oven for professional use in accordance with the present invention, and Figure 2 diagrammatically shows a view in section taken along line A-A of the vapour generator which equips the oven shown in Figure 1.

As shown in Figure 1 an oven comprises a cooking compartment 1 having a lower drain 2 and a front closure door 3, being capable of accommodating a plurality of superposed pans 4 with the foods to be cooked. Disposed on the other side of the vertical perforated partition or bulkhead 5 which at the rear delimits the cooking compartment 1 there is a centrifugal fan 6 driven by an electric motor 7 and capable of maintaining within the interior of the cooking compartment 1 a forced circulation of hot air and water vapour.

The water vapour is generated at atmospheric pressure in a generator 10 accommodated above the motor 7 and is introduced into the cooking compartment 1 by way of a connecting tube 8, the outlet opening 9 of which is behind the partition or bulkhead 5, at a position corresponding to the fan 6.

As shown in Figure 2 the vapour generator 10 comprises a chamber 11 which is provided with well-known means (not shown) for filling it and maintaining a predetermined level of water H, and which has in the upper part an opening 12 for intake of the vapour into the connecting tube 8 and subsequent introduction thereof into the cooking compartment 1 by way of the outlet opening 9, as already referred to hereinbefore.

The vapour generator further comprises a tubular combustion chamber 13 made for example of stainless steel, which extends in cantilever relationship along the water chamber 11. The combustion chamber 13 is traversed in the direction of the arrows X by the products from combustion of the flame F of a burner 15 accommodated in a space 14 for a feed of comburent air and it is open at the opposite end 16.

It should be noted that, even if the burner 15 illustrated herein is of the blower type, that is to say provided with a fan 17 for the forced introduction of comburent air into the space 14, good operation of the oven is ensured with any type of gas burner, as described hereinafter.

The combustion chamber 13 is surrounded by a corrugated metal casing 18 which is for example coaxial and which also extends in cantilevered relationship along the water chamber 11. The casing 18 is closed by an end portion 19 which is disposed at a suitable spacing both from the terminal section 16 of the combustion chamber 13 in such a way as to form a zone 21, and from the corresponding wall 20 of the water chamber 11.

There thus remains defined between the external surface of the combustion chamber 13 and the internal surface of the casing 18 a conduit 22 of annular section (which is not uniform, due to the presence of the corrugations of the casing 18) which is capable of having the combustion products flowing therethrough. The conduit 22 begins in the above-mentioned zone 21 at the end of the combustion chamber 13 and finishes in a collector manifold 23 communicating with the discharge flue 24. As is clearly apparent from Figure 2 the water H is introduced into the chamber 11 and maintained at a level therein such that the entire corrugated casing 18 is immersed over its entire length.

Still with reference to Figure 2 the mode of operation of the invention is as follows. Once the gas burner 15 has been lit the surface of the combustion chamber 13 is heated both directly by the flame F and by its combustion products which pass through it over the remainder of the length (as indicated by the arrows X). In accordance with experiments implemented by the applicants, the surface of the combustion chamber 13 can rapidly attain an operating temperature of the order of 800oC whereby it is capable of emitting a substantial amount of radiant heat.

The combustion products thus maintain a high temperature when they pass through the conduit 22 of annular section (see the arrows Y) after they have reversed their direction of movement in the above-mentioned zone 21 (see arrows U). Due to the suction effect on the part of the flue 24, the combustion products flow through the conduit 22 at an increasing speed, thus giving rise to particularly efficient heat transfer to the water contained in the surrounding chamber 11 which in the operating condition reaches a temperature equal to or a little greater than 100oC. The same experiments indicated a level of efficiency equal to about 85 %, that is to say decisively superior to that which can be obtained in accordance with the state of the art.

The advantages of the illustrated embodiment of the invention can thus be summarised as follows: a) the cooking operations carried out with this oven are of a reduced duration by virtue of the efficient generation of vapour; b) by virtue of their mode of mounting in cantilevered relationship, the combustion chamber 13 and the corrugated casing 18 are free to expand due to the effect of the heat, that is to say this reducing the risks of damage to the oven; c) the oven can be equipped with any type of burner insofar as in all cases the combustion products accelerate in passing through the conduit 22 of annular section; and d) the removal of scale from the external surface of the casing 18, during the periodic descaling operations, is facilitated by the undulations of the casing.

Even if the foregoing description refers to the embodiment which is preferred at the present time, it will still be appreciated that the invention may be developed in other forms and alternative configurations within the scope of the appended claims.

Claims

CLAIMS 1. An oven having a cooking compartment, a vapour generator and means for introduction into the former of the vapour generated by the vapour generator which comprises a chamber in which a preset level of water is created and maintained and a combustion chamber which is heated with a gas burner and is in the form of a rectilinear tube open at the ends and which extends along the water chamber, wherein the combustion chamber is surrounded by a coaxial metal casing disposed below said water level, in such a way as to form a conduit of annular section for the combustion products, which begins in a zone between the end portion of the casing and the terminal section of the combustion chamber and which finishes in a collector manifold communicating with the discharge flue.
2. A cooking oven according to claim 1, wherein said metal casing has a corrugated surface.
3. A cooking oven according to claim 1 or claim 2, wherein the end portion of said metal casing is spaced from the corresponding wall of the water chamber whereby the casing extends in cantilevered relationship along the water chamber.
4. A cooking oven according to any one of the preceding claims, wherein said zone between the end portion of the casing and the terminal section of the combustion chamber is capable of producing in the conduit of annular section a flow of the combustion products in the opposite direction to that within the combustion chamber.
5. A cooking oven substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.