Use of an inductor for the homogeneous heating of a product

Abstract

The invention relates to a use of an inductor (3, 117', 117'', 117''', 117'''') for the homogeneous heating of a product by means of a directly heated electrically conductive rectangular heat-imparting means (2), which is in contact with the product, wherein the inductor (3, 117', 117'', 117''', 117'''') is designed as at least one rectangular planar coil (105) or as an arrangement of a plurality of rectangular planar coils (104) which is arranged at least partially in a parallel plane (4) with respect to the heat-imparting means and which extends in this parallel plane (4) over a lower height and width (b2) in relation to the height and width (b1) of the heat-imparting means (2), wherein the winding of the planar coil (105) consists of conductor portions (107, 108) in the form of tubular segments.

Description

[0001] USE OF AN INDUCTOR FOR HOMOGENEOUS HEATING OF A PRODUCT

[0002] The present invention relates to a use of an inductor for heating a product, particularly preferably for heating baked goods.

[0003] Typically, baking trays are used as heat transfer devices for heating baked goods. Induction ovens are already known, but they exhibit a certain degree of inhomogeneity in heat distribution. This is not a problem for the average household, as other oven designs also exhibit a certain degree of inhomogeneity.

[0004] However, when producing baked goods on a large scale, all baked goods should ideally have the same degree of browning.

[0005] JP 2011-18 511 A1 discloses a device for heating a heat medium for heating food, including baked goods. The planar coil consists of a copper wire punched out of an overlying copper plate. Furthermore, JP 2011-18 511 A1 provides an upright magnetic core.

[0006] However, if the device is also required to perform pyrolysis cleaning of the heat transfer medium after heating, this heating method reaches its limits. The annealing temperature of copper alloys can range between 300 and 600°C. Annealing copper results in structural changes, particularly in the area of ​​soiling on the heat transfer medium. The heat is transferred to the coil, causing structural changes in the coil, particularly in the area of ​​the forming of the bending points of the rectangular coil, where additional material stress also occurs due to temperature expansion. As a result, these structural changes in turn create inhomogeneities during inductive heating due to differences in electrical conductivity between the structures of the coil material.

[0007] DE 10 2012 021 027 A discloses a variant for cooling an induction heating device with a cooling medium. The flow of the cooling medium in an arrangement of multiple planar coils is not disclosed in detail. The application is therefore rather conceptual, lacking a more precise coolant flow, and is not applicable to the design concept of JP 2011-18511 A1 and the different materials of a magnetic rod and punched copper wire.

[0008] Based on this preliminary consideration, the object of the present invention is to provide a novel use of an inductor by means of which heating of products by means of a rectangular heat medium is achieved, so that uniform heating takes place and hot spots are avoided.

[0009] In addition, a wide temperature range can be covered without causing material changes to the inductor material, which in turn would cause inhomogeneous induction heating.

[0010] The present invention solves this problem by using the features of claim 1.

[0011] The inventive use of an inductor for the homogeneous heating of a product is achieved by means of an electrically conductive rectangular heat transfer element. This element is heated directly and immediately by induction by the inductor.

[0012] The product, in turn, is heated by the heat radiation from the heat transfer device. It can be in direct contact with the heat transfer device, preferably over a large area. The inductor is designed as at least one rectangular planar coil or as a plurality of rectangular planar coils. This coil(s) is / are arranged at least in a contiguous area in a plane parallel to the heat transfer device. In this parallel plane, the inductor extends over a smaller height and width than the heat transfer device.

[0013] This is unusual. Typically, one strives to achieve homogeneity by heating an object beyond its own width. Therefore, it would be advisable to dimension the inductor larger than the heat transmitter.

[0014] Another unusual feature is the rectangular shape of the inductor, which ensures even greater homogeneity of heat distribution.

[0015] However, it has surprisingly been shown that the widespread use of rectangular inductors leads to a high degree of homogeneity in the heat distribution in the central region, but at the same time also leads to the formation of hotspots at the edges. To reduce these hotspots, particularly at the edges of the rectangular and plate-shaped heat exchanger, preferably flat on at least one side, with a homogeneous plate thickness, contrary to common practice, a reduced dimension of the inductor along the parallel plane compared to the dimension of the heat exchanger is recommended, thereby compensating for the disadvantages of using rectangular inductors.

[0016] For ease of manufacture and heat dissipation, it is advantageous if the winding of the planar coil consists of tube segments.

[0017] Coolant can be piped through the tube segments. This prevents structural changes in the coil material, despite the radiated heat from the heat exchanger, as, for example, annealing of the coil material can be reliably avoided.

[0018] Overall, this also ensures the homogeneity of the heating, since structural changes can cause increased inhomogeneities in the resistance values ​​of the coil material.

[0019] Advantageous embodiments of the invention are the subject of the subclaims.

[0020] It is particularly advantageous if the planar coil is made of a different material than the heat transmitter.

[0021] Particularly preferably, the material of the heat transfer medium can have a lower electrical conductivity, preferably at least 70% lower, than the material of the planar coil. With lower conductivity, the resistance is increased, resulting in stronger framework vibrations when electrical energy is passed through, and consequently, higher heating than in the inductor material.

[0022] For better coupling to the partition wall, the pipe segments can have a rectangular cross-section, thereby achieving a wide radiation surface. The rectangular cross-section of the pipe segments has a width 20% greater than its height, where the height refers to a vertical extension with respect to the heat exchanger. Particularly preferably, the width is twice the height of the rectangular cross-section. Particularly preferably, the pipe segments can form a pipe which has at least terminal coolant connections. At high temperatures and with lossy conduction, e.g. in the material of the inductor, material stress and thermal expansion can occur, which are minimized by this particularly efficient heat dissipation.

[0023] For more efficient dissipation of waste heat in the inductor, the tube can have a central section with at least one additional coolant connection. This prevents boiling of the coolant, which could potentially occur if it were to flow over the entire length.

[0024] It is also advantageous for a better feed-in if the cross section of a line section or a pipe segment, preferably all pipe segments, of the planar coil is larger in a first extension direction than in a second extension direction

[0025] The inductor, preferably the planar coil of an inductor, can advantageously have a smaller distance from the plate-shaped and at least one-sidedly flat heat exchanger in a central region of the heat exchanger than in the end regions of the heat exchanger. This further reduces the tendency toward edge hotspots. The heat exchanger has a substantially uniform plate thickness. The exception to this are the support strips, along which no product is in contact with the heat exchanger.

[0026] The inductor can have a field of several planar coils arranged side by side in both directions. This is advantageous because it reduces temperature differences between the coils and allows for optimized space utilization.

[0027] Furthermore, the distance between two parallel conductor sections in the form of tube segments of a planar coil and / or two adjacent planar coils can be less than the extension of the conductor cross-section of the conductor section of a planar coil.

[0028] In a preferred application, the inductor can be used to heat the heat transfer medium to temperatures above 550°C, preferably above 700°C. This allows for a defined high-temperature application, which can be used, for example, for pyrolysis cleaning of baking trays.

[0029] The aforementioned parallel plane may extend over more than 80%, preferably over more than 90%, of the height and / or width of the heat transmitter.

[0030] This also ensures that the distances are as small as possible in order to achieve a homogenous heat distribution.

[0031] The invention is described in more detail below using exemplary embodiments with reference to the drawings, in which further advantageous variants and embodiments are also discussed. It should be emphasized that the exemplary embodiments discussed below are not intended to be exhaustive descriptions of the invention, but that variants and equivalents not shown are also feasible and fall within the scope of the claims. It shows:

[0032] Fig. 1 schematic side view of an embodiment of a device for indirect inductive heating, e.g. for baked goods and other products to be heated; and

[0033] Fig. 2a-2d embodiments of inductors used according to the invention for use in the device of Fig. 1;

[0034] Fig. 1 shows a schematic representation of a device 1 for the indirect inductive heating of products, in particular products that cannot be heated by direct inductive heating. A particularly preferred embodiment is the application in large-scale production, in particular the continuous production, of baked goods and other products. The following specific application example is explained using a corresponding embodiment based on baked goods production. Alternatively, the device can also be used for the indirect heating of coated products, e.g., for stoving enamels or for CVD deposition or for other comparable manufacturing processes.

[0035] The products for the embodiment shown and described in Fig. 1 are preferably waffles 6. The device 1 can have an outer housing in which an electrically conductive rectangular tray-shaped heat medium 2, for example a baking tray, is arranged.

[0036] The baking tray has a width b2. The baking tray is heated by the device 1, which has an inductor 3. The inductor 3 has an extension parallel to the orientation of the baking tray with a width b1. The waffles 6 are positioned on a support bar 7 of the heat transmitter 2. The extension area of ​​the inductor 3 parallel to the baking tray defines a parallel plane 4.

[0037] Beyond the parallel plane 4, the inductor 3 has a projection 5 which projects away from the parallel plane 4 from the back plate.

[0038] Typically, one would assume that extending the extent of the inductor 3 beyond the parallel plane 4 of the baking tray would result in a more homogeneous heat distribution across the entire baking tray.

[0039] Thermal investigations of the baking tray have shown that during the inductive heating of a tray-shaped heat medium, such as the baking tray, heat spots and / or heat areas form at the edge areas, which can lead to burning of the baked goods or other products in these areas.

[0040] The solution lies surprisingly in a reduction of the extension of the inductor 3 along the parallel plane 4 to less than the width and length of the baking tray or, more preferably, smaller than this baking tray or any other heat medium.

[0041] The inductors are particularly designed as tubes. These can be liquid-cooled, preferably water-cooled, or air-cooled. The cooling medium can be passed through the tubes.

[0042] Beyond the parallel plane 4, the baking tray has an overhang 5. This prevents an uncontrolled drop in temperature in the edge area of ​​the baking tray.

[0043] The inductor can advantageously extend over at least 70% of the total extent, preferably at least 80% of the total extent, particularly preferably over at least 90% of the total extent of the baking tray in at least one direction, i.e., length or width. The inductor 3 can consist of several partial inductors, in particular several planar coils, wherein the details regarding the extent refer to the total of all partial inductors.

[0044] The inductor 3 and / or all partial inductors are advantageously rectangular in shape. This means that the tubes have numerous right-angled bends, which is complex to manufacture. However, this is necessary to enable particularly homogeneous heat distribution of the baking tray. In particular, the tube cross-section in the area of ​​the bends varies by less than 20%, preferably less than 10%, so that there are no blockage effects in the bend area. This enables even heat dissipation by the coolant within the tubes.

[0045] Furthermore, the inductor is a planar coil inductor. Therefore, there are no stacked windings perpendicular to the parallel plane. The parallel plane can be essentially vertical or horizontal to a substrate.

[0046] The coils 10 shown in Fig. 2a-2d are part of the inductor 3 of Fig. 1 and are preferably designed as flat coils or planar coils. Figures 2a-2d show, among other things, inductors in spiral form 101, overlock form 102, and meander form 103.

[0047] The variant shown in Fig. 2d is particularly preferred. This shows a planar coil arrangement 104 as an inductor with three coils arranged side by side. Each of the coils preferably has two windings 106.

[0048] The structure of the coils is also known as a pancake structure. Figure 2d shows three planar coils 105 arranged one behind the other.

[0049] The extension of the planar coils 105 of the planar coil arrangement 104 in the direction of the width of the baking tray is less than the height of the baking tray. It is therefore recommended to arrange several planar coil arrangements according to Fig. 2d one behind the other to ensure heating across the entire width of the baking tray. This results in a better distribution of the energy supply across the width of the heat exchanger. The conductor cross-section of the inductors 117', 117", 117"', 117"" shown in Figs. 2a-2d is such that it has a greater width than height. The cross-section of the inductor, the wire cross-section or the tube cross-section, can be rectangular. The extension in the width direction is preferably at least twice the height of the conductor cross-section.Whereby the width of the conductor cross-section extends parallel to the heat transmitter and the height of the conductor cross-section runs perpendicular to it and in particular parallel to the surface normal of the heat transmitter.

[0050] The conductor spacings between two parallel conductor sections of a winding and / or two planar coils are preferably smaller than the width of the conductor cross-section. Particularly preferably, the conductor spacings are at least 20% smaller than the width of the conductor cross-section.

[0051] The windings of the planar coils are such that the length of the conductor sections 107 in an extension direction is at least 4 times, preferably more than 8 times, the length of the conductor sections 108.

[0052] Intensive investigations have shown that the homogeneity of the heat distribution of the inductors 117', 117", 117'", 117"" of Fig. 2a-2c and especially Fig. 2d over the entire height of the heat transmitter is particularly good.

[0053] This is particularly illustrated in Fig. 2d. Higher temperature fluctuations were observed in the outer regions of the planar coil arrangement 104, particularly in the area of ​​the conductor sections 107. However, the homogeneity between the conductor sections 107 was particularly high.

[0054] The temperature difference between the highest and lowest values ​​in this range is preferably less than 10°C at the process temperatures described above - i.e. a fluctuation of 5°C around an average value.

[0055] The contact terminals 118 of the planar coil arrangement or the inductor of Fig. 2d are preferably arranged on only one side. This is particularly preferred to avoid interference inductances.

[0056] All illustrated inductors 117 are coils wound or folded in a plane, also called flat coils. The inductors of Figs. 2a and 2b have contact lines 122 in the central region M, which run above or below the plane and enable electrical contact. The illustrated structures exhibit particularly homogeneous heat distribution in both the central and peripheral regions of the respective inductor. Ideally, the heating device is controlled. Temperature control can advantageously be achieved in 10°C increments. This can be accomplished by a control and / or evaluation unit 11.

[0057] Overall, the shape of the inductors 117 achieves temperature homogeneity with a temperature fluctuation of less than 5°C across the height of the baking tray.

[0058] Reference symbol

[0059] 1 device

[0060] 2 heat mediators

[0061] 3 Inductor

[0062] 4 Parallel plane

[0063] 5 Overhang

[0064] 6 waffles

[0065] 7 support strip

[0066] 10 coil

[0067] 11 Control and / or evaluation unit

[0068] 101 Spiral shape

[0069] 102 Overlock

[0070] 103 Meander shape

[0071] 104 planar coil arrangement

[0072] 105 Planar coil

[0073] 106 winding

[0074] 107 ladder section

[0075] 108 ladder section

[0076] 117', 117”, 117'”, 117”” inductor

[0077] 118 contact connections

[0078] 122 contact lines

[0079] M mid-range

Claims

Claims 1 . Use of an inductor (3, 117', 117", 117'", 117"") for the homogeneous heating of a product by means of a directly heated, electrically conductive rectangular heat imparting element (2) which is in contact with the product, wherein the inductor (3, 117', 117", 117'", 117"") is designed as at least one rectangular planar coil (105) or as an arrangement of several rectangular planar coils (104), which is arranged at least in regions in a plane parallel (4) to the heat imparting element and which extends in this parallel plane (4) over a smaller height and width (b2) relative to the height and width (b1) of the heat imparting element (2), characterized in that the winding of the planar coil (105) consists of conductor sections (107, 108) in the form of tube segments.

2. Use according to claim 1, characterized in that the planar coil (105) consists of a different material than the heat transmitter (2).

3. Use according to claim 1 or 2, characterized in that the material of the heat mediator (2) has a lower electrical conductivity, preferably an electrical conductivity lower by at least 70%, than the material of the planar coil (105).

4. Use according to one of the preceding claims, characterized in that the conductor sections (107, 108), in particular the tube segments, have a rectangular cross-section.

5. Use according to claim 4, characterized in that the rectangular cross-section of the conductor section (107, 108) has a width 20% greater than its height, the height relating to a vertical extension with respect to the heat transmitter.

6. Use according to claim 4 or 5, characterized in that the rectangular cross-section has a width twice as large as its height.

7. Use according to one of the preceding claims, characterized in that the pipe segments form a pipe which has at least terminal coolant connections.

8. Use according to one of the preceding claims, characterized characterized in that the pipe has an additional coolant connection in a central region.

9. Use according to one of the preceding claims, characterized in that the inductor (3, 117', 117", 117"', 117"") has a smaller distance from the heat transmitter (2) in a central region of the heat transmitter (2) than in the two end regions of the heat transmitter and that the central region lies in the parallel plane (4) to the heat transmitter (2).

10. Use according to one of the preceding claims, characterized in that the parallel plane extends over more than 80%, preferably over more than 90%, of the height and / or width extension of the heat transmitter.

11. Use according to one of the preceding claims, characterized in that the inductor (3, 117', 117", 117'", 117"") has an array of several planar coils (105) arranged side by side in the direction of width and height.

12. Use according to one of the preceding claims, characterized in that the distance between two parallel conductor sections (107, 108) in the form of tube segments of a planar coil (105) and / or two adjacent planar coils (105) is less than the extension of the conductor cross-section of the conductor section (108) of a planar coil (105).

13. Use according to one of the preceding claims, characterized in that the inductor is used to heat the heat mediator to over 550°C, preferably to over 700°C, preferably for pyrolysis cleaning of the heat mediator (2).

14. Use according to one of the preceding claims, characterized in that the inductor is designed as part of a device for heating baked goods.

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