WO2012012479A1

WO2012012479A1 - Food processing device with a heat exchanger

Info

Publication number: WO2012012479A1
Application number: PCT/US2011/044600
Authority: WO
Inventors: Alessandro Villani; Alessandro Rigo
Original assignee: Premark Feg L.L.C.
Priority date: 2010-07-21
Filing date: 2011-07-20
Publication date: 2012-01-26
Also published as: ITTO20100632A1; IT1402171B1

Abstract

A heat exchanger (1) including a fan (4) arranged in use within a working chamber of an oven, and at least first and second tube metallic segments (5, 6) which turn, at least partially, about the fan and are associated, respectively, to a combustion chamber (7) associated to a burner, and a hollow space (9) delimited by a liner (10) which covers and shields the combustion chamber and hydraulically connects the first and second segment to each other; wherein the first tube segment (5) includes, starting from the combustion chamber, a first turn (17), which then leads to a succession of straight lengths and turns; and wherein the second segment (6) includes at least two branches (14, 15) parallel to each other which turn about the fan and are connected to a U-turn (16) arranged adjacent to the first turn (17) of the first segment; the latter and the U-turn are mechanically and integrally secured to each other by means of a bracket (18) formed by perforated metallic plates (19,20) defining respective radiant elements.

Description

FOOD PROCESSING DEVICE WITH A HEAT EXCHANGER

The present invention relates to a heat exchanger of an improved type for a food processing/cooking device, such as an oven, and to a forced convention oven provided with such a heat exchanger.

It is known from EP-A-1106933 and from US-A-5915372 a forced convection oven for cooking food using a burner or other device adapted to generate a flow of hot gases as heating source, and a heat exchanger of tubular type which conveys the hot gases through the working chamber of the oven, occupied in use by the food to be cooked, about a fan arranged in the working chamber and then towards an exhaust.

The fan circulates the air in the working chamber in forced manner and about tube lengths or segments of the tubular heat exchanger, arranged adjacent to the fan itself, so as to heat the air, and consequently cook the food, while maintaining a temperature as uniform as possible inside the working chamber.

Although satisfactory, the described heat exchangers and respective ovens display the need for one or more U-turn to connect the straight segments of the tube to each other so as to substantially form a ring of approximately rectangular shape about the fan. In EP-A-1106933 a U-turn connects cantilevered a first tube length coming directly from the burner which turns about the fan with a second tube length, which forms a return ring about the fan which, in turn reaches the U-turn. In this configuration, the combustion chamber may create a hotter point in the working chamber, to the detriment of sought temperature uniformity. Furthermore, the overhangingly suspended U-turn is free to move as a consequence of thermal expansion phenomena: this may cause the induction of undesired stress on the welding in the tube lengths, as well as possible vibrations with consequent generation of undesired noise in use.

DE 20 2004 015 288U1 attempts to solve the problem related to the hot point constituted by the combustion chamber by mixing about the combustion chamber itself the hot burnt gases with part of the gases, which have already circulated in the heat exchanger, and have partially cooled down.

PCTEP2010051952 by the same applicant eliminates the problem constituted by the presence of a hotter point in the working chamber at the combustion chamber of the burner by shielding the same by means of a tubular liner fitted about, and removed from, a continuous side wall of the combustion chamber, so as to create a hollow space about the latter, which is also used as hydraulic union between a first ring-shaped tube length turning about the fan, and a second tube length exiting from the side of the liner and turning about part of the fan.

In all cases, it is found that, despite a certain reduction of the temperature in the first tube length caused by the heat removed from the burnt, but already partially cooled, gases which circulate in the hollow space, the initial part of the first tube length, which is the closest to the burner, may still heat up excessively, forming a hotter point in the working chamber.

It is the object of the present invention to overcome the drawbacks of the prior art, by providing a heat exchanger for a forced convention oven and oven equipped therewith having small dimensions, high reliability, high constructive simplicity and which at the same time guarantees high temperature uniformity in the working chamber, high robustness of the structure defined by the heat exchanger tubes, reduced stresses on the welding seams in the tube lengths of the heat exchanger and substantial absence of vibrations and noises.

The present invention thus relates to a heat exchanger of the perfected type for a food processing/cooking device, such as an oven, as disclosed in claim 1, and to forced convention oven provided with such a heat exchanger, as disclosed in claim 9.

In particular, the heat exchanger and the oven thereof according to the invention comprise a fan arranged in use within a working chamber of a food processing device, such as an oven, and at least first and second tube segments, made of metal, turning, at least partially, about the fan, and which are associated to a combustion chamber, associated in use to a burner, and with a hollow space defined by a liner which covers and shields the combustion chamber and hydraulically connects together the first and second segments, respectively; the first tube segment forms a substantially quadrangular ring around the fan, which is laterally inserted into the hollow space and comprises, starting from the combustion chamber, a first turn which then leads to a succession of straight lengths and turns belonging to the first tube segment. The second tube has instead at least two branches parallel to each other which turn about the fan and are connected to each other by a U-turn arranged adjacent to the first turn of the first tube segment.

According to the main feature of the invention, the first turn of the first tube segment is mechanically secured to the U-turn so as to be integral therewith by means of a bracket including, or in one implementation consisting of, perforated metal plates defining respective radiant elements adapted, in use, to receive and transmit heat by conduction from/between the tube segments and to disperse such a heat in the working chamber by radiation and convection.

The bracket is T-shaped and formed by at least two flat plates, integral to each other and arranged reciprocally angled, for example, but not necessarily, secured perpendicular to each other. These two flat plates are welded a first within the U-turn, generally formed by a smaller tube segment constituting the second tube segment, and a second to the first turn and to a central tube of the first tube segment, which departs directly from the combustion chamber to connect with the first turn, forming a continuity system between them.

On one side, the U-turn is no longer cantilevered in the working chamber but is supported by the first tube segment, in turn supported by a side wall of the working chamber. On the other hand, the heat generated in the part of the tube of larger section external to the impeller of the fan (high given the shadow position of the air flow on the impeller) is in this manner dissipated by conduction on the two plates.

This heat is, in turn, dissipated in part by convection with the air and in part by conduction with the smaller section tube. Part of this contribution by convection may further surrender heat to the inner fumes which flow through the second segment of the tube, much further downstream than the combustion chamber, with regards to the direction of movement of the hot gases or fumes in the tube segments, contributing to raising the overall thermal efficiency of the oven.

The advantage of this solution is thus heat dissipation at the first turn, which constitutes a critical overheating point, while the dissipation on the second tube segment allows a better distribution of the temperatures along the two tube segments, and thus a better cooking uniformity.

Furthermore, the second tube segment is no longer totally secured to the first, as in the known constructions with similar layout, and therefore the drawbacks of the prior art, such as overloads on the welding seams due to the relative movements caused by the thermal expansions and risks of vibrations/noise, are avoided.

Further features and advantages of the present invention will be apparent from the following description of a preferred embodiment thereof, exclusively provided by way of non-limitative example, with reference to the accompanying drawings, in which:

figure 1 diagrammatically shows an axonometric, three quarters front view of a forced convection oven provided with a heat exchanger made according to the invention; and

figures 2 and 3 illustrate details of the heat exchanger in figure 1 on enlarged, axonometric scale.

With reference to figures from 1 to 3, numeral 1 indicates as a whole a heat exchanger equipping a forced convention oven 2 of which only the working chamber 3 is diagrammatically shown with dashed line, occupied in use towards the rear bottom thereof, i.e. on the side opposite to an access door (known and not shown), of the heat exchanger 1 and, for the remaining available space, by food to be processed, typically to be cooked (not shown for the sake of simplicity).

The heat exchanger 1 comprises a fan 4 arranged in use within the working chamber 3 and at least a first and a second tube segment, made of metal and indicated, respectively, by reference numbers 5 and 6, which turn at least in part about the fan 4 and which are, respectively, associated the first to a combustion chamber 7, in use associated to a burner 8, and the second to a hollow space 9 delimited by a liner 10, which covers and shields the combustion chamber 7 towards the working chamber 3 and hydraulically connects the first tube segment 5 and the second tube segment 6 to one another.

In particular, the combustion chamber 7 is constituted by a tube delimited by a continuous cylindrical side wall 11 free from perforations, has a symmetry axis A, and is axially cantilevered within the working chamber 3 from a side wall 12 of the same and is mounted coaxially to the burner 8, which may be arranged outside the working chamber 3, or directly all within the combustion chamber 7, in all cases so as not to have exposed surfaces in the working chamber 3.

The liner 10 is defined, in the non-limiting example shown, by a cylindrical tube or may be defined by a bushing with section having profile composed by a semicircular part and by a frustum-shaped part, in all cases of traversal width greater than that of the tube defining the combustion chamber 7, so as to delimit the hollow space 9 between them; the first tube segment 5 forms about the fan 4 a substantially quadrangular ring which departs in axis, axially cantilevered, from the liner 10 starting from the combustion camber 7, with a central tube 13, of diameter larger than or equal to that defining the combustion chamber 7 and smaller than that defining the liner 10, to which it is fluid-tightly butt-connected, e.g. by welding.

In this manner, the first tube segment 5 receives therein the hot fumes or gases produced by the burner 8 and then inserts itself laterally into the hollow space 9 through the liner 10, so that the fumes which have crossed it so as having been partially cooled down to heat the chamber 3, touch the wall 1 1 warming up and thus removing the heat in excess, to then be conveyed through the hollow space 9 into the second tube segment 6. The latter has at least two branches 14 and 15 parallel to each other which turn about the fan and which are hydraulic and mechanically connected to each other in series by a U-turn 16.

A first branch 14 of the tube segment 6 exits laterally from the hollow space 9 through the liner 10 and receives the burnt gases, which have been heated by crossing the hollow space 9 and touching the wall 11, while a second branch 15 of the tube segment 6, in the embodiment illustrated directly connected to the branch 14 by the U-turn 16, performs in the illustrated example an L about the fan 4 to then be connected in known manner to an exhaust, not shown, to which, according to the relative arrangement of the fan 4 and the segment 15, could also be connected directly without forming the illustrated L.

The tube segment 5 comprises, starting from the combustion chamber 7 and in addition to the mentioned central tube 13, a first turn 17, which then leads to a succession of straight lengths 18 (indicated in succession, starting from turn 17, with references 18b, 18c, 18d) and turns, all belonging to the first tube segment 5 and which complete the ring layout of the same.

According to one of the main features of the invention, the U-turn 16 which connects to each other the branches 14 and 15 of the second tube segment 6 is arranged adjacent to the turn 17 of the first tube segment 5 and is oriented with a given angle (a right angle in the non- limiting example shown) with respect to a symmetry axis B of the turn 17; the turns 16 and 17 are further mechanically secured to each other by means of a bracket 18 (figures 2 and 3) including (or in one embodiment consisting of) perforated metallic plates 19,20 defining respective radiant elements adapted in use to receive heat by conduction from the tube segments 5 and 6, in particular from the segment 5, hotter with respect to 6, because crossed in use by the hot gases/fumes which have just left the combustion chamber 7, and to disperse such heat in the working chamber 3 by radiation and by convection as well as transporting part of such heat, by conduction, from the tube segment 5 towards the cooler tube segment 6 to heat in part the gases/fumes which cross the tube segment 6 itself, in addition to the heat already removed by the same gases in the hollow space 9.

In the illustrated case in point, the first branch 14 of the second tube segment 6 forms about the fan 4 a portal structure (i.e. shaped as an upside-down U) formed by a first length 21 and by a third length 22 of such a branch 14, which define the posts thereof, and by a second length 23 of the branch 14, which joins the lengths 21 and 22 defining the cross beam.

The first length 21 is directly supported by the U-turn 16 and, indirectly, through the bracket 18, by the turn 17 of the first tube segment 5, while the third length 22 is directly supported, from the mechanical-structural point of view, by the liner 10, which is supported in use by a side wall 12 along with the burner 8 and the working chamber 7 so as to be cantilevered.

According to an aspect of the invention, the bracket 18 is substantially T-shaped and is fitted straddling both the first turn 17 of the first tube segment 5 and the U-turn 16 of the second tube segment 6, so that the U-turn 16 is supported mechanically by the first turn 17 of the tube segment 5 and, consequently, by the entire assembly of the latter.

With particular reference to figures 2 and 3, the T-shaped bracket 18 is formed by (or in one embodiment consists of) a first flat plate 19 integrally fixed, by welding, to the U-turn 16 of the tube segment 6 straddling an intrados side thereof (i.e. inside the turn); and of a second flat plate 20 integrally fixed, by welding, to the first turn 17 of the first tube segment 5 straddling an extrados side thereof (i.e. outside the turn) and integrally connected by welding with the first plate 19 in an angular way with respect to the latter, in the non-limiting example shown perpendicularly (but not necessarily) to the plate 19.

The first plate (plate 19) of the two plates 19 and 20 is welded to the inside of the U- turn 16 of the tube segment 6, which is formed by a tube of section smaller than (or possibly equal to) that of the tube forming the first tube segment 5, and the second plate (plate 20) is welded to the first turn 17 and, indirectly, to the central tube 13 (which plate 20 can reach - dashed part in figure 2) of the first tube segment 5, which directly departs from the combustion chamber 7 to connect to the first turn 17 through a conical union 24; the bracket 18 consequently forms a continuity system between the tube segments 5 and 6 and, in particular between the turn 16 and the turn 17 with the respective tube 13 directly integral thereto (through the union 24).

In particular, the first flat plate 19 is arranged transversally to respective symmetry axes C and D, which are parallel to each other, of, respectively, a first straight length 25 of the branch 15 and of the first straight length 21 of the branch 14 of the second tube segment 6, which are directly and hydraulically (as well as mechanically) connected to one another by the U-turn 16; furthermore, the plate 19 extends parallelly to such symmetric axes C and D, by a length such as to mechanically connect to one another, transversally to the same, the lengths 25 and 21, but only along the part of the same immediately adjacent to the U-turn 16; from side opposite to the lengths 25,21, the plate 19 is delimited by a curved edge 26 (figure 3) which imitates the profile of the intrados of the U-turn 16.

The flat plate 20 is, instead, arranged transversally to the symmetry axis B of the turn 17 of the first tube segment 5, e.g. perpendicular (but not necessary) to the plate 19, and has in plan substantially the shape of a isosceles trapezoid having the oblique side curved, defining an edge 27 of the same which imitates the profile of the extrados of the turn 17 and possibly extends to the central tube 13.

According to a further aspect of the invention, the plates 19 and 20 which form the bracket 18 have through perforations 28 and 29 shaped as slots and oriented, for the plate 19, parallel to the symmetric axis C,D and, for the plate 20, parallel to symmetry axis A in common to the combustion chamber 7 and the liner 10 which covers it.

Furthermore, the plates 19, 20 have a substantially identical extension by length in direction of the symmetry axes B, C.

This maximizes the radiant effect and make easier both the air circulation with turbulent effect, moved by the fan 4, within the chamber 3, and the heat conduction through the plate 20 from the tube 13 and from the adjacent turn 17, exposed directly to the hot gas flow of the burner 8, towards the plate 19 and, consequently the turn 16 and the lengths 21 and 25 of the "coolest" tube segment 6.

According to the description, a forced convection oven 2 for cooking food made according to the invention comprises a working chamber 3 for accommodating the food to be cooked, the fan 4 arranged in the working chamber 3, a burner 8 associated to a combustion chamber 7 (or an equivalent heating system adapted to product a flow of hot gases) arranged in the working chamber 3, and at least the first and second tube segments 5 and 6 for fluid- tightly conveying the hot gases from the chamber 7 and about the fan 7 then towards the exhaust (known and not shown) through the working chamber 3.

The main feature thereof consists, on one hand in the fact that the combustion chamber 7, despite being accommodated within the working chamber 7, is separated therefrom and thermally shielded by the hollow space 9 which surrounds it; and, on the other hand, in that the U-turn 16 intended to connect the two branches 14, 15 of the tube segment 6 and crossed by the cooler gases is not cantilevered, but is mechanically supported by the upstream tube segment 5 and, at the same time, contributes to cooling the hotter part of this constituted by the turn 17 adjacent to the central tube 13. An oven 2 having a remarkable inner temperature uniformity in the chamber 3 and high thermo-dynamic efficiency is thus obtained.

Claims

1. A heat exchanger(l) comprising a fan (4) arranged in use within a working chamber (3) of a food processing device, such as an oven (2), and at least first (5) and second (6) tube segments, made of metal, turning, at least partially, about the fan (4) and which are associated with a combustion chamber (7), associated in use with a burner (8), and with a hollow space (9) defined by a liner (10) which covers and shields the combustion chamber and hydraulically connects together the first and second segments (5, 6), respectively; wherein the first tube segment (5) forms a substantially quadrangular ring around the fan, which is laterally inserted into the hollow space (9) and comprises, from the combustion chamber, a first turn (17) which then leads to a succession of straight lengths and turns (18,

19) belonging to the first tube segment; characterized in that the second tube segment (6) has at least two branches (14, 15), parallel to each other, which turn around the fan (4) and are connected to each other by a U-turn (16) which is arranged adjacent to the first turn (17) of the first tube segment (5), which first turn is mechanically secured to the U-turn (16) so as to be integral therewith by means of a bracket (18) comprising perforated metal plates (19,

20) defining respective radiant elements adapted, in use, to receive and transmit heat by conduction from/between the tube segments (5,6) and to disperse said heat in the working chamber (3) by radiation and convection.

2. A heat exchanger according to claim 1, characterized in that the said bracket (18) is T-shaped and is mounted straddling the first turn (17) of the first tube segment (5) and the U-turn (16) of the second tube segment (6), so that the U-turn (16) is mechanically supported by the first turn (17).

3. A heat exchanger according to claim 2, characterized in that said T-shaped bracket (18) consists of a first flat plate (19) integrally fixed to the U-turn (16) of the second tube segment (6) straddling an intrados side thereof; and of a second flat plate (20) integrally fixed to the first turn (17) of the first tube segment (5) straddling an extrados side thereof and integrally connected with the first plate (19) in an angular way, preferably in a substantially perpendicular way, to the same.

4. A heat exchanger according to claim 3, characterized in that said first flat plate (19) is arranged transversally to respective symmetry axes (C,D) parallel to each other, of two corresponding first straight lengths (25,21) of the first (14) and second (15) branches, respectively, of the second tube segment (6), directly hydraulically connected together by the U-turn (16); and in that, in combination, it extends parallel to said symmetry axes (C,D) over a length such that the flat plate mechanically connects said first lengths (25,21) of the first and second branches (14, 15) together, crosswise with respect to the same, only along a part thereof immediately adjacent to the U-turn (16); while, on the opposite side, the first plate (19) is delimited by a curved edge (26) imitating the intrados profile of the U-turn (16).

5. A heat exchanger according to claim 3 or 4, characterized in that said second flat plate (20) is arranged transversally to a symmetry axis (B) of the first turn (17) of the first tube segment (5) and angularly with respect to the first plate (19), e.g. perpendicularly, but not necessarily, with respect to the same and in plan view, is substantially in the shape of an isosceles trapezoid having a curved oblique side, which imitates the extrados profile of the first turn (17).

6. A heat exchanger according to one of the preceding claims, characterized in that said plates (19,20) forming said bracket (18) have thorough perforations (28, 29), slit shaped and oriented, for a first plate (19), parallel to the symmetry axes (C,D) of two corresponding first straight lengths of the first and second branches (14, 15), respectively, of the second tube segment (6); and for a second plate (20), parallel to a common symmetry axis (A) of the combustion chamber and of the liner coating the same.

7. A heat exchanger according to claim 6, characterized in that said plates (19,20) have a substantially equal length extension, in the direction of the symmetry axes (C,D) of said two first straight lengths of the first and second branches (14,15) of the second tube segment (6).

8. A heat exchanger according to one of the preceding claims, characterized in that a first branch (14) of the second tube segment (6) forms a portal structure around said fan, which is formed by first (21) and third (22) lengths of the first branch defining the posts thereof and by a second length (23) of the first branch, joining the first and third lengths defining the cross beam thereof, the first length (21) of the first branch (14) being directly supported by the U-turn (16) and, through said bracket (18), by the first turn (17) of the first tube segment (5), while the third length (22) of the first branch is directly supported by said liner (10), which is supported in use by a side wall (12) of the working chamber (3) so as to be cantilevered.

9. An oven (2) for forced convection cooking of foods comprising a working chamber (3) to housing the foods to be cooked, a fan (4) arranged within the working chamber, and at least first and second tube segments (5,6) to fluid-tightly convey hot gases through the working chamber, which first and second tube segments are associated with a combustion chamber (7) associated in use with a burner, and a hollow space (9), respectively, which hollow space is defined by a liner (10) which covers and shields the combustion chamber (7) towards the working chamber (3) and hydraulically connects together the first and second segments (5,6); wherein the first tube segment (5) forms a substantially quadrangular ring around the fan, which is laterally inserted into the hollow space (9) and, from the combustion chamber, comprises a first turn (17) which leads then to a succession of straight lengths and turns (18, 19) belonging to the first tube segment; characterized in that the second tube segment (6) has at least two branches (14, 15), parallel to each other, which turn around the fan (4) and are connected to each other by a U-turn (16) which is arranged adjacent to the first turn (17) of the first tube segment (5), which first turn is mechanically secured to the U-turn so as to be integral therewith by means of a bracket (18) comprising perforated metal plates (19, 20) defining respective radiant elements adapted, in use, to receive/transmit heat by conduction from/between the tube segments (5,6) and to disperse said heat in the working chamber (3) by radiation or convection.