Tunnel oven and heating module for tunnel oven

Abstract

A heating module for a tunnel oven, the tunnel oven for providing heat to items to be baked within the oven and comprising a conveyor for conveying in a direction of conveyance the items to be baked through the oven, the heating module comprising elongate radiative elements.

Description

[0001] TUNNEL OVEN AND HEATING MODULE FOR TUNNEL OVEN

[0002] Field of the invention

[0003] The present invention relates to the heating of items in a tunnel oven. More specifically, the present disclosure relates to a heating unit for a tunnel oven typically used to bake items of food, such as biscuits.

[0004] Background to the invention

[0005] It is known to bake items as they travel through a conveyor in a tunnel oven. Setting the tunnel oven to be suitably adjusted to bake a particular item can be a timeconsuming and expensive process, involving a trial-and-error approach to the adjustment of oven parameters whilst observing the effect of such adjustments on baked food characteristics and quality attributes.

[0006] It is in this context that the present inventions have been devised.

[0007] Summary of the invention

[0008] In accordance with an aspect of the present invention, there is provided a heating module for a tunnel oven, the tunnel oven for providing heat to items to be baked within the oven and comprising a conveyor for conveying in a direction of conveyance the items to be baked through the oven, the heating module comprising: a first elongate radiative element arranged to emit radiative heat radially outwards over a first limited angular range centred around a first direction of radial emission; a second elongate radiative element arranged to emit radiative heat radially outwards over a second limited angular range centred around a second direction of radial emission; whereby the first elongate radiative element is rotatable in such a way that the first direction of radial emission is variable; whereby the second elongate radiative element is rotatable in such a way that the second direction of radial emission is variable; whereby the first direction of radial emission has a component which is anti-parallel to the direction of conveyance when the module is in place; whereby the second direction of radial emission has a component which is parallel to the direction of conveyance when the module is in place.

[0009] Each elongate radiative element is orientated normal to the direction of conveyor motion, spanning the width of the conveyor. The elements may be positioned above and below the conveyor.

[0010] The conveyor conveys items in a direction which is parallel to the length of the tunnel oven.

[0011] In accordance with a second aspect of the present invention, there is provided a method of configuring a tunnel oven to bake items within the oven, the tunnel oven comprising a conveyor for conveying in a direction of conveyance the items to be baked through the oven, and further comprising at least one heating module, whereby the heating module comprises: a first elongate radiative element arranged to emit radiative heat radially outwards over a first limited angular range centred around a first direction of radial emission; a second elongate radiative element arranged to emit radiative heat radially outwards over a second limited angular range centred around a second direction of radial emission; whereby the first elongate radiative element is rotatable in such a way that the first direction of radial emission is variable; whereby the second elongate radiative element is rotatable in such a way that the second direction of radial emission is variable; whereby the first direction of radial emission has a component which is anti-parallel to the direction of conveyance when the module is in place; whereby the second direction of radial emission has a component which is parallel to the direction of conveyance when the module is in place; in which method the following steps are carried out: each of the first and the second elongate radiative elements is powered to emit radiation; an item to be baked is placed on the conveyor, whereupon the item is conveyed through the tunnel oven and irradiated with radiation from the first elongate radiative element and the second elongate radiative element; the item is inspected following its irradiation; setting one or both of the first direction of radial emission and the second direction of radial emission dependent on the inspection of the item.

[0012] Samples of baked items are taken across the width of the conveyor for inspection. The objective of the adjustments is to achieve uniform baked food attributes, irrespective of the position of an item across the width of the conveyor.

[0013] The inspection of an item may be an evaluation of the item. An evaluation of an item may associate a value to the item. A value may be a value representing the moisture content of an item. A value may be a value representing the colour or tone of an item. Further parameters of a baked item which may be utilised in evaluation include volume, height, surface texture, for example whether the surface is cracked or not, mechanical strength or taste (for example, burnt or undercooked).

[0014] The inspection of the item may be performed by an operator, which operator then proceeds to set each of the first direction of radial emission and the second direction of radial emission is dependent on the inspection of the item.

[0015] Items may be inspected following irradiation across with width of the conveyor. For example, an item may be evaluated by assessing or measuring its colour. An item may be evaluated by determining the final moisture content in the item.

[0016] Baked items may be evaluated in this way during an initial set up of a baking run for a tunnel oven. This enables a real time evaluation to be performed. This in turn facilitates a straightforward adjustment and set up of the tunnel oven, which is advantageous over the alternative time-consuming and expensive iterative process in which the emitter assemblies would all need to be removed, modified in some way, then reinstalled before further production trials were conducted. Using the approach herein disclosed avoids having to make several attempts to arrive at a satisfactory configuration for the emitters in an iterative process. The tunnel oven into which the presently disclosed heating module is intended to be fitted is generally known in the art of industrial baking and, more generally, food production. Other technical fields in which a tunnel oven is or may be known or used include paper technology, glass technology, plastic technology, ceramics.

[0017] The radiative heat which is emitted by an elongate radiative element is typically infrared radiation. If the tunnel oven is utilised to bake food, it may be particularly advantageous for the elongate radiative elements of the heating module to emit short wavelength infrared radiation. For example, a short wavelength tungsten emitter operating at around 1900°C replicates the wavelength distribution typically delivered by a natural gas burner flame positioned directly above the conveyor, in which the adiabatic flame temperature is around this value and which is conventional in food preparation. This has important implications for the processing of food, since the ability of food to absorb incident infrared radiation is highly dependent on wavelength. For a conventional resistive heater, such as is found in the grill of a domestic oven, the emitter temperature would be much lower - around 700°C. The infrared radiation associated with this emitter temperature cannot be absorbed by many water-based food types anywhere near as well, and so the food surface is susceptible to charring because the incident heat cannot be conducted away into the bulk of the food.

[0018] A tunnel oven may be around 100 m in length. A tunnel oven is typically split up into different zones. A single zone usually accommodates a plurality of heating modules, typically 10 to 40. The heating modules may be spaced at intervals of 0.75 -1.5 m along the length of the zone. Heating modules may be located above and the conveyor. Additionally or alternatively, heating modules may be located below the container.

[0019] A heating module of the type presently disclosed has an elongate length typically in the range 0.8 m - 3.0 m, and is always similar in value to the width of the conveyor. The length of the heating module is perpendicular to the length of the oven when the module is mounted in place in the oven.

[0020] An item to be baked in the tunnel oven is generally placed on the conveyor at the oven entrance. The conveyor may be an open mesh or a solid metal sheet. With an open mesh conveyor, the underside surfaces of the food will also receive radiative heat from any radiative elements positioned below the conveyor. The conveyor then transports the item along the inside of the oven. As it moves through the oven, the item is irradiated by radiative heat originating from the radiative elements of the heating modules mounted in the oven. The radiative heat is typically infrared radiation. In this way an item is baked during its passage through the oven on the conveyor from the oven entrance to an oven exit at the distal end of the oven. The conveyor typically defines a plane.

[0021] As an item moves down the oven on the conveyor and approaches a heating module mounted in the oven, it first approaches the first elongate radiative element of the module, which first elongate radiative element irradiates the item with radiation, typically infrared radiation. The first elongate radiative element is rotatable to vary the direction of radiation radially emitted. The first elongate radiative element is typically arranged to radiate along 50% of its length, divided up as 25% of its length at a proximal end and along 25 % of its length at a distal end. Rotating such a first elongate radiative element which delivers heat principally to the edges of the conveyor will deliver an amount of direct radiant heat to the food on the edges of the conveyor which varies dependent on the angle of rotation.

[0022] Where an elongate radiative element irradiates across the width of the conveyor of a tunnel oven, the radiant heat flux which is incident on an item on the conveyor belt typically peaks at the centre of the conveyor, and typically falls off towards the sides of the conveyor. Such a distribution of radiant heat flux results in items positioned towards the sides of the conveyor (for example) being subjected to less radiative heat than items which are positioned centrally between the two sides of the conveyor. As this leads to uneven cooking of these items, this is undesirable.

[0023] If each of the first and the second elongate radiative elements is arranged to emit radiative heat radially outwards over a proportion of its total length, additional radiant heat flux may be provided at the sides of the conveyor. In this way, a more even distribution of radiant heat flux at the conveyor level may be realised and the uniformity of how items may be cooked in the tunnel oven is increased.

[0024] The heating module may comprise a third elongate radiative element arranged to emit radiative heat radially outwards. Between the positions of approach to the heating module and departure from the heating module, the item passes below the heating module, where its upper surface may be irradiated by radiation from the third elongate radiating element of the module.

[0025] It will be apparent to the person skilled in the art how to rotate the first radiative element and the second radiative element to achieve even baking of a particular item.

[0026] Each of the first, second and third elongate radiative elements is intended to supply radiative heat to items to be baked within the oven which items are positioned on the conveyor as they pass through the oven. Each of the first, second and third elongate radiative elements is intended to extend in length substantially across the width of the tunnel oven when the module is in place. That is to say that each of the first, second and third elongate radiative elements is intended to extend in a direction substantially perpendicular to the direction of conveyance. In this way, the person skilled in the art will recognise that the first, second and (if present) third elongate radiative elements each run parallel to one another. When the heating module is in place in the tunnel oven, the elongate radiative elements are positioned to emit radiative heat towards the conveyor, to thereby provide radiative heat to items to be baked as the items move through the oven on the conveyor.

[0027] An elongate radiative element may comprise a sleeve, the outer surface of which defines the outer form of the element. Radiative heat is generated within the sleeve and the sleeve is typically made from a material which transmits this radiative heat so that it can radiate out from the element. A sleeve may be made from quartz glass for example.

[0028] It is useful to speak of the axis running along the length of an elongate radiative element as the axis of that element. The axis of an elongate radiative element may coincide with the centre of that element, for example the geometric centre, in which case it can be specified by referring to it as the central axis of the element. Equally, the axis of an elongate radiative element need not run down the centre of that element. The axis of an elongate radiative element may run parallel of the central axis of the element.

[0029] An elongate radiative element may be substantially cylindrical in form. Typically, an elongate radiative element is formed from two tubes, such as two quartz tubes, fused together. This construction results in an elongate radiative element with a figure-of- eight cross-sectional form. An elongate radiative element may have a figure-of-eight cross-sectional form. An advantage of such a twin-tubbed construction is that the electrical connections to power the element can be positioned at a single end. This is highly beneficial for easy removal of the heater module, when it requires replacement, for example.

[0030] Each elongate radiative element of the heating module is arranged to emit radiative heat radially outwards. By this, what is meant is that the radiative heat is emitted in a direction perpendicular to the axis, for example the central axis, of the elongate radiative element.

[0031] Each elongate radiative element is arranged to emit radiative heat radially outwards over a limited angular range. By this, what is meant is that radiation is not emitted in all directions, i.e. radiation is not emitted 360° around the axis, but rather radiation is emitted in a limited number of directions, generally within an arc of the elongate radiative element. The limited angular range corresponds to the angular range of the arc within which radiation is emitted. The centre of the arc is called here the direction of radial emission.

[0032] The first limited angular range is typically substantially equal to the second limited angular range.

[0033] Each of the first elongate radiative element and the second elongate radiative element is rotatable in such a way that the direction of radial emission from that element is variable. The first elongate radiative element is rotatable around an axis of the first elongate radiative element, for example around the central axis of the first elongate radiative element. In this way the direction of radial emission from the first elongate radiative element is variable. Similarly, the second elongate radiative element is rotatable around an axis of the second elongate radiative element, for example around the central axis of the second elongate radiative element. In this way the direction of radial emission from the second elongate radiative element is variable.

[0034] Each of the first elongate radiative element and the second elongate radiative element is rotatable in such a way that the direction of radial emission from that element is variable. When the heating module is in place in a tunnel oven, the direction of radial emission has a component which is parallel (or anti-parallel) to the direction of conveyance. Variation in the direction of radial emission of radiation from an elongate radiative element results in variation, i.e. an increase or a decrease, in the magnitude of the component which is parallel (or anti-parallel) to the direction of conveyance.

[0035] Variation in the direction of radial emission of radiation from a radiative element has the consequence at the level of the items on the conveyor that the intensity of radiation incident on the surface (or surfaces) of an item being baked within the tunnel oven is varied.

[0036] The combination of the first, second and third elongate radiative elements enables all exposed sides of an item on the conveyor, i.e. all sides not flat against the conveyor, to be irradiated.

[0037] When present, the third elongate radiative element which is arranged to emit radiative heat radially outwards typically emits radiation over a limited angular range.

[0038] The third elongate radiative element commonly comprises a plurality of emitter tubes, typically two, which are physically arranged parallel to one another. Each emitter tube functions as an elongate radiative element. That is to say, each emitter tube emits infrared radiation radially and along its length. Each emitter tube which forms part of the third elongate radiative element typically emits radiation over a limited angular range, centred its own direction of radial emission.

[0039] When the third elongate radiative element is in place, the arrangement is typically such that the plane perpendicular to the conveyor and containing the central axis of the third elongate heating element forms a plane of symmetry of the emitted radiation. In other words, the radiation which is emitted from the third elongate radiative element is distributed in a pattern which has a plane of reflective symmetry, the plane being perpendicular to that of the conveyor and passing through the axis of the third elongate element.

[0040] The heating module may comprise a rotary mechanism arranged to rotate the first elongate radiative element and to rotate the second elongate radiative element. The rotary mechanism arranged to rotate the first elongate radiative element and to rotate the second elongate radiative element may rotate the two elements independently. The rotary mechanism arranged to rotate the first elongate radiative element and to rotate the second elongate radiative element may rotate the two elements in concert. The rotary mechanism arranged to rotate the first elongate radiative element and to rotate the second elongate radiative element may rotate the two elements in concert so that the two elements rotate symmetrically. It may be that the rotary mechanism is manually operable.

[0041] Typically the first and second elongate radiative elements are rotationally positioned in a symmetrical manner. The symmetrical arrangement is such that the component of the first direction of radial emission which is anti-parallel to the direction of conveyance when the module is in place has substantially the same magnitude as the component of the second direction of radial emission which is parallel to the direction of conveyance when the module is in place. In this way, even baking of items being baked in the oven is possible.

[0042] The first elongate radiative element may be arranged to emit radiative heat along a portion of its length, the portion typically being 50 %. The second elongate radiative element may be arranged to emit radiative heat along a portion of its length, the portion typically being 50 %. The third elongate radiative element may be arranged to emit radiative heat along a portion of its length, the portion typically being 100 %.

[0043] Typically, the first elongate radiative element is arranged to emit radiative heat along 20-50% of its full length. For example, the first elongate radiative element may be arranged to emit radiative heat along 50% of its full length, i.e. along half of its full length. This may also be thought about in terms of half of the full length of the first elongate radiative element being arranged to not emit radiation, i.e. half of the full length of the first elongate radiative element being passive. The length of an elongate radiative element over which that element is arranged to emit radiation is referred to as the active length. In other words, half the length of the first elongate radiative element (or less) is passive, and half the length (or less) is active. The active length need not be a continuous length. The first elongate radiative element may be arranged to emit radiative heat along 50% of its full length or less, for example the first elongate radiative element may be arranged to emit radiative heat along 40% of its full length, or less, for example the first elongate radiative element may be arranged to emit radiative heat along 30% of its full length, or less, for example the first elongate radiative element may be arranged to emit radiative heat along 20% of its full length. Typically, half of the active length of an elongate radiative element is positional at a proximate end of the element and half of the active length of the elongate radiative element is positional at a distal end of the element. Typically, the length of the first elongate radiative element which is passive forms a continuous length which is centrally positioned in the element. The first elongate radiative element may thereby be arranged to emit in two lengths, each being a quarter of the full element length long. One of the two lengths is positioned at a proximal end of the first elongate radiative element, and the other is positioned at a distal end.

[0044] The second elongate radiative element is typically identical to the first elongate radiative element and is subject to the same considerations, such as its rotational placement. The above considerations given for the first elongate radiative element also apply to the second elongate radiative element.

[0045] Typically, the emissive power of an elongate radiative element as utilised in the presently disclosed heating module, expressed as emission energy per unit of length, is uniform over the active length of the element. In this way, over any period of time, an elongate heating element which emits radiative heat along 50 % of its length, emits half the radiation of that emitted by an elongate heating element which emits along its whole length.

[0046] The elongate radiative elements in a heating module are typically arranged to have a balanced power rating.

[0047] Commonly a tunnel oven is powered utilising three-phase AC power. Typically, the elongate radiative elements of a heating module according to the present disclosure are connected in such a way that the three phases are balanced when power is supplied. This is important in terms of supply grid loading. For example, a first elongate radiative element of a heating module may be powered by the first phase of a three-phase AC power supply, a second elongate radiative element of a heating module may be powered by the second phase of a three-phase AC power supply and a third elongate radiative element of a heating module may be powered by the third phase of a three-phase AC power supply. Such an arrangement is suitable if each of the first, second and third elongate radiative elements each has a substantially similar power rating. Dependent on the relative power ratings of the elongate radiative elements an alternative arrangement may be suitable. For example, if each of the first and second elongate radiative elements of a heating module is active along 50% of its length and passive along 50%, and if a third elongate radiative element is active along 100% of its length, all else being equal, the first and second elongate radiative elements may be connected in series to balance the power ratings. If a third elongate radiative element comprises two emitter tubes, a first phase may supply the series connection of the first and second elongate radiative elements, a second phase may supply one of the emitter tubes, and a third phase may supply the other of the emitter tubes. In this way, a system of three equal loads is established.

[0048] A controller may control the power supply to the elongate radiative elements.

[0049] Typically, a controller may control the power supply to the elongate radiative elements in a binary fashion, i.e. by switching between an on-state, in which power is supplied to an elongate radiative element, and an off-state, in which no power is supplied to an elongate radiative element. A controller may control the power supply to the elongate radiative elements supplying power in a continuous manner. A controller may control the power supply to the elongate radiative elements supplying power in a variable manner. A controller may control the power supply to the elongate radiative elements supplying power in a continuously variable manner.

[0050] A controller may control the power supply to the elongate radiative elements of a heating module installed in a tunnel oven. A controller may control the power supply to the elongate radiative elements of a plurality of heating modules installed in a tunnel oven. A controller may control the power supply to the elongate radiative elements of a heating module installed in a tunnel oven in a binary fashion. A controller may control the power supply to the elongate radiative elements of a heating module installed in a tunnel oven in a continuously variable manner. A controller may control the power supply to the elongate radiative elements of a first heating module installed in a tunnel oven in a binary manner, and to a second heating module installed in the tunnel oven in a continuously variable manner. A controller may control the power supply to the elongate radiative elements of a first heating module installed in a tunnel oven in a continuously variable manner, and to all other heating modules installed in the tunnel oven in a binary manner. A group of heating modules may define a zone of the tunnel oven. For example, a zone may comprise ten heating modules above the conveyor, each of which according to the first aspect of this disclosure. Furthermore, a zone may comprise ten heating modules below the conveyor. Each module may have two rotatable elongate radiative elements and two emitter tubes forming a third elongate radiative heating element. A controller may typically control nine of the aforementioned heating modules above the conveyor in a binary on / off manner, and the tenth heating module in a manner in which the power supplied to the heating elements may be varied continuously. A similar system may operate independently, to control the heating modules below the conveyor. By controlling the heating units in this way, control of the baking process may be controlled by varying the total delivered radiative intensity in a zone, while the wavelength distribution received by the food during its transition through the zone remains nearly constant. If a larger number of elongate radiating emitters in a zone were to be controlled using a variable voltage supply, this would affect their emitter temperatures and hence the wavelength distribution of the emitted radiation incident on the food as it travels through a zone of the oven.

[0051] A controller may be utilised to control the power supplied to the elongate radiative emitters. The wavelength of the radiative heat supplied by an elongate radiative emitter is an important aspect of the current disclosure. For example, as discussed above, in the production of food it may be advantageous to irradiate the items being baked with short wavelength infrared radiation. Control of the elongate radiative emitters, which may be tungsten element emitters, may thus also be an important consideration. If an elongate radiative emitter were to be modulated by adjusting the supply voltage, that would affect the emitter temperature and hence the wavelength distribution. If a tunnel oven comprises ten heating modules, it may be preferable to control nine of these in an on / off control mode and the tenth in a continuously variable mode. This gives control increments of 10% in each zone (0-90%), together with a fine-tune control of 0-10% added to this from the last module.

[0052] The heating module may comprise shielding along the length of a radiative element, the shielding defining the limited angular range over which heat is emitted.

[0053] The shielding may comprise or take the form of a screen which partially envelops an elongate radiative element, or if an elongate radiative element is formed of a plurality of tubes, which partially envelops each tube. The shielding typically prevents the transmission of radiative heat. The internal surface of the shielding positioned closest to the elongate radiative element (or tube) may be arranged to reflect radiative heat which impinges upon it. The radiation is thereby redirected. In this way, by suitable design of the shielding the angular range of radiative heat emitted by an elongate radiative element may be limited. The shielding may be separate from the elongate radiative element, or it may be an integrated constituent of the elongate radiative element.

[0054] The shielding may be a reflective surface on the surface of the sleeve which provides the outer form of the radiative element. The reflective surface may be on the outer surface of the tube, for example on the outer surface of the sleeve. The reflective surface may be on the inner surface of the tube, for example on the outer surface of the sleeve.

[0055] The first elongate radiative element may comprise shielding along its length. The shielding may define the limited angular range over which the first elongate radiative element emits heat.

[0056] The second elongate radiative element may comprise shielding along its length. The shielding may define the limited angular range over which the second elongate radiative element emits heat.

[0057] The third elongate radiative element may comprise shielding along its length. If the third elongate radiative element comprises two elongate radiative element units, a stationary elongate radiative element and an auxiliary stationary elongate radiative element, then each of the stationary elongate radiative element and the auxiliary stationary elongate radiative element typically comprises shielding.

[0058] The shielding of each of the stationary elongate radiative element and the auxiliary stationary elongate radiative element typically defines the limited angular range over which each of these elements emits heat.

[0059] The first limited angular range and the second limited angular range may be substantially of a first value.

[0060] The limited angular range over which each elongate radiative element emits radiation may subtend an angle of 180° or less, i.e. 90° or less either side of the direction of radial emission. The limited angular range over which each elongate radiative element emits radiation may subtend an angle of 120° or less, i.e. 60° or less either side of the direction of radial emission. The limited angular range over which each elongate radiative element emits radiation may subtend an angle of 90° or less, i.e. 45° or less either side of the direction of radial emission.

[0061] Typically, the whole length of an elongate radiative element extends beyond the width of the conveyor. The whole length of an element typically extends by a short amount beyond the width of the conveyor. The short amount might be 1 to 5% of the length of the element.

[0062] The items to be baked in the oven are positioned in an area of food array, the width of which is typically less than the width of the conveyor.

[0063] The width of the conveyor is typically in the range of 0.8 m to 3.0 m.

[0064] Typically, the whole length of an elongate radiative element extends beyond the width of the conveyor. The whole length of an elongate radiative element typically extends by a short amount beyond the width of the conveyor. The short amount might be 1 to 10% of the length of the elongate radiative element. The short amount might be 1 to 5% of the length of the elongate radiative element.

[0065] With the first direction of radial emission having a component which is anti-parallel to the direction of conveyance when the module is in place, and the second direction of radial emission having a component which is parallel to the direction of conveyance when the module is in place, an item transported along the length of the oven on the conveyor is irradiated by heat from the first radiative elements as it approaches it, and is irradiated by heat from the second radiative element as the item moves past it.

[0066] The elongate radiative element may be arranged to emit radiation along the whole length of the central section. The elongate radiative element may be arranged to emit radiation along a fraction of the whole length of the central section. The fraction of the whole length of the central section may be a continuous fractional length of the elongate radiative element, or a plurality of continuous lengths of the elongate radiative element. The fraction of the whole length of the central section which emits radiation when the element is in operation may be variable. Typically, electrical power is supplied to an elongate radiative element to power the emission of radiation. Typically, the electrical connection is made at one end of an elongate heating element.

[0067] The elongate radiative elements are typically spaced apart from each other in such a way that when the module is mounted in the oven the radiative elements are spaced apart from each other in the direction of conveyance. The third elongate radiative element may be mounted between the first and second elongate radiative elements. The first elongate radiative element and the second elongate radiative element typically define a first plane within which both radiative elements lie. The third elongate radiative element may lie within this first plane, or it may not lie within this first plane.

[0068] The third elongate radiative element arranged to emit radiative heat radially outwards may do so over a third limited angular range centred around a third direction of radial emission.

[0069] A third elongate radiative element may comprise a plurality of emitting tubes which typically lie in a second plane.

[0070] The first plane may coincide with the second plane. The first plane may not coincide with the second plane.

[0071] When the module is mounted in the oven, each of the first plane and the second plane is typically parallel to the conveyor. When the module is mounted in the oven, the distance between the conveyor and the first plane may be greater than the distance between the conveyor and the second plane.

[0072] The first radiative element is rotatable. The first radiative element may be rotatable around its central axis. The first radiative element may be rotatable around an axis which is parallel to its central axis.

[0073] The heating module may further comprise a plurality of fins distributed along the length of the elongate radiating elements.

[0074] Each fin typically is of planar form. Generally, the plane of a fin is positioned perpendicular to an elongate radiative element. Typically, the plane of a fin lies perpendicular to all of the elongate radiative elements in any particular heating module. A fin may typically have a generally rectangular form.

[0075] A plurality of fins is typically distributed in a regular manner along the length of the elongate radiating elements. The distance between neighbouring fins is typically the same distance.

[0076] The fins serve to collimate the radiative heat emitted from the elongate radiative elements.

[0077] The present disclosure extends to a tunnel oven comprising one or more heating modules as herein disclosed. Each of the one or more heating modules is typically replaceable.

[0078] In a further aspect, the present disclosure extends to a method of supplying heat to an item comprising: placing the item on a conveyor of a tunnel oven at an entrance to the oven; utilising a heating module according to any first aspect of this disclosure mounted in the tunnel oven to supply radiative heat to the item is it passes through the tunnel oven on the conveyor.

[0079] Description of the Drawings

[0080] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

[0081] Figure 1 an analysis of lateral heat irradiance from a tungsten emitter.

[0082] Figure 2(a) is a planar view of an arrangement of elongate radiative elements according to an embodiment of the invention; Figure 2(b) is a side view of the elongate radiative elements in a heating module mounted above the conveyor of a tunnel oven.

[0083] Figure 3 illustrates heating modules mounted in a tunnel oven.

[0084] Detailed Description of an Example Embodiment Figure 1 shows the experimental results of measuring the irradiance of a tungsten lamp elongate radiating member. The element is 280 mm in length and was situated 193 mm above the target plane. The measurement targets in the experiments are metal squares, placed side by side along the length direction in which the radiating member extends. The metal squares start off at ambient temperature and warm up during the test. The measurements are based on the metal temperature increase rate and represent incident radiative heat. The measurements in Figure 1 were recorded at 90 s and at 120 s after powering the element and show that equilibrium is reached already at 90 s. What is also clearly shown by these measurements is the drop off in radiant heat flux away from the centre of the radiating member. For a food array on a conveyor which is 200 mm wide, the measurements indicate a drop in radiative flux at the edges of the array of approximately 20 % compared to the maximum. This drop-off in radiative flux towards the sides of the conveyor results in uneven irradiation of items on the conveyor.

[0085] A heating module according to the present disclosure is shown schematically in Figure 2. Figure 2(a) illustrates a plan view of four emitter tubes 11 , 12, 14, 16 forming the elongate radiative elements of a heating module. Outer tube 11 is the first elongate radiative element, and outer tube 12 is the second elongate radiative element. Each of these radiative elements has a passive region extending to 50 % of the length of the element and centred along the length of the element. Each of these elements 11 , 12 is rotatable around its own long axis, as indicated in Figure 2(b). The power rating of each of these elements is 3 kW.

[0086] Two emitter tubes 14, 16 are positioned in-between outer elements 11 and 12. Emitter tubes 14, 16 together form the third elongate heating element. Each of emitter tube 14 and emitter tube 16 has an active length along which radiation is emitted, and which extends along the whole length of the tube. Emitter tubes 14, 16 are rotationally fixed within the heating module. The power rating of each of these elements is 6 kW to ensure 3-phase supply balancing.

[0087] The emitters 11 , 12, 14, 16 are powered using a three phase AC supply. Emitter 14 is powered with one phase. Emitter 16 is powered with a second phase. Emitters 11 and 12 are connected in series and powered with a third phase. In this way three equal loads are created. Figure 2(b) illustrates a side view of the emitter tubes 11 , 12, 14, 16 mounted in heating module 1. Heating module 1 is shown schematically in position within a tunnel oven, and above conveyor 9 of the oven. Items, as exemplified by item 100, are placed on conveyor which conveys them along the tunnel oven where they are baked. A controller 48 is provided.

[0088] Each of emitter tubes 14, 16 is rotationally fixed within the module. The two emitter tubes 14, 16 are mounted symmetrically and each radiates emission radially outwards in a limited angular range centred around a direction. The central direction of emission of emitter tube 14 is in an upstream conveyor direction. The central direction of emission of emitter tube 16 is in a downstream conveyor direction. In the present embodiment, the central direction of emission of emitter tubes 14 and 16 is around 45° to the conveyor normal. This angle has been found advantageous in avoiding overirradiation of items passing below the heating module.

[0089] A schematic cross-sectional view of several heating modules 1 mounted in a tunnel oven is illustrated in Figure 3. An item 100 for baking in the oven is placed on conveyor 9. The item enters the oven at oven entrance 42, is conveyed on conveyor 9 along the inside of the oven, where it is irradiated by short wavelength infrared radiation emitted from heating modules 1. The item exits the tunnel oven at oven exit 44, whereupon it is inspected by an operator. In the present example, the item 100 is assessed by evaluating the degree to which the surface has browned during baking. An additional assessment may be carried out by measuring the moisture content of the baked item.

[0090] Based on the assessment of the baked item, an operator sets the rotational angle of the emitter tubes 14, 16.

Claims

Claims1 . A heating module for a tunnel oven, the tunnel oven for providing heat to items to be baked within the oven and comprising a conveyor for conveying in a direction of conveyance the items to be baked through the oven, the heating module comprising: a first elongate radiative element arranged to emit radiative heat radially outwards over a first limited angular range centred around a first direction of radial emission; a second elongate radiative element arranged to emit radiative heat radially outwards over a second limited angular range centred around a second direction of radial emission; whereby the first elongate radiative element is rotatable in such a way that the first direction of radial emission is variable; whereby the second elongate radiative element is rotatable in such a way that the second direction of radial emission is variable; whereby the first direction of radial emission has a component which is anti-parallel to the direction of conveyance when the module is in place; whereby the second direction of radial emission has a component which is parallel to the direction of conveyance when the module is in place.

2. A heating module according to claim 1 , further comprising a third elongate radiative element arranged to emit radiative heat radially outwards.

3. A heating module according to claim either of the preceding claims, additionally comprising a rotary mechanism arranged to rotate the first elongate radiative element and to rotate the second elongate radiative element.

4. A heating module according to any one of the preceding claims wherein the first elongate radiative element is arranged to emit radiative heat along a portion of its length, the portion typically being 50 %; the second elongate radiative element is arranged to emit radiative heat along a portion of its length, the portion typically being 50 %; and the third elongate radiative element is arranged to emit radiative heat along a portion of its length, the portion typically being 100 %.

5. A heating module according to any one of the preceding claims, wherein the elongate radiative elements are arranged to have a balanced power rating.

6. A heating module according to any one of the preceding claims, wherein a controller is present to control the supply of power to the elongate radiative elements.

7. A heating module according to any one of the preceding claims, additionally comprising shielding along the length of a radiative element, the shielding defining the limited angular range over which heat is emitted.

8. A heating module according to any one of the preceding claims, further comprising a plurality of fins distributed along the length of the elongate radiating elements.

9. A tunnel oven comprising one or more heating modules according to any one of claims 1 to 8.

10. A tunnel oven according to claim 9, whereby at least one of the heating modules is replaceable.

11. A method of configuring a tunnel oven to bake items within the oven, the tunnel oven comprising a conveyor for conveying in a direction of conveyance the items to be baked through the oven, and further comprising at least one heating module, whereby the heating module comprises: a first elongate radiative element arranged to emit radiative heat radially outwards over a first limited angular range centred around a first direction of radial emission; a second elongate radiative element arranged to emit radiative heat radially outwards over a second limited angular range centred around a second direction of radial emission; whereby the first elongate radiative element is rotatable in such a way that the first direction of radial emission is variable; whereby the second elongate radiative element is rotatable in such a way that the second direction of radial emission is variable; whereby the first direction of radial emission has a component which is anti-parallel to the direction of conveyance when the module is in place; whereby the second direction of radial emission has a component which is parallel to the direction of conveyance when the module is in place; in which method the following steps are carried out:each of the first and the second elongate radiative elements is powered to emit radiation; an item to be baked is placed on the conveyor, whereupon the item is conveyed through the tunnel oven and irradiated with radiation from the first elongate radiative element and the second elongate radiative element; the item is inspected following its irradiation; setting one or both of the first direction of radial emission and the second direction of radial emission dependent on the inspection of the item.

12. A method of supplying heat to an item comprising: placing the item on a conveyor of a tunnel oven at an entrance to the oven; utilising a heating module according to any one of claims 1 to 8 mounted in the tunnel oven to supply radiative heat to the item is it passes through the tunnel oven on the conveyor.

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