WO2015155758A1

WO2015155758A1 - An induction heating module and a convection oven thereof

Info

Publication number: WO2015155758A1
Application number: PCT/IL2015/050304
Authority: WO
Inventors: Tomer KUJMAN
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-04-10
Filing date: 2015-03-24
Publication date: 2015-10-15
Anticipated expiration: 2016-10-10
Also published as: IL232081A0

Abstract

The present invention relates to an inductively heated convection oven, comprising: a) an outer housing having a plurality of different sides joined together to form an enclosed space with at least one of the sides forming a door to provide access to the enclosed space; b) an inner housing having a plurality of different sides joined together to form an enclosed oven space - spaced from and supported within the sides of the outer housing and having at least one side thereof facing the door of the outer housing providing access to the interior of the enclosed oven space; c) at least one ventilation fan adapted for circulating air around the enclosed oven space, wherein the flow path of the circulated air is defined by the space between the inner and outer housing; d) at least one induction heating unit supported within the space intermediate respective confronting sides of the inner and outer housings and arranged in a plane that is essentially parallel to a respective side of a magnetically susceptible element to maximize the inductive coupling to said element; and e) control means for electrically exciting the induction heating unit at a relatively high frequency of the order of kilohertz to thereby magnetically induce the generation of induction heating at the flow path of the circulated air.

Description

AN INDUCTION HEATING MODULE AND A CONVECTION OVEN

THEREOF

Field of the Invention

The present: invention relates to the field of convection ovens (or any other cooking appliance that uses the convection principle, such as Combi Steamer and etc.) heated by IH (Induction Heating) means. More particularly, the present invention relates to a baking oven, in particular a baking cabinet that has a baking chamber in which the goods to be baked can be placed, one or more heating units based on IH method, an air ventilation fan which draws air from the baking chamber and one or more outlets for dispensing the heated air into the baking chamber.

Background of the invention

Convection ovens are the norm in most commercial bakeries and commercial kitchens. Convection ovens may be heated with electricity, gas or oil. The difference between convection ovens and traditional (radial or thermal) ovens is that the convection oven heating mechanism is based on a heating unit and an air circulation mechanism.

Convection based baking oven, in particular a baking cabinet, usually comprising a baking chamber into which the goods to be baked can be introduced, a unit for heating a heating medium, having an inlet for receiving the heating medium from the baking chamber and an outlet for dispensing the heated heating medium into the baking chamber, and comprising a first flow channel for conveying the heating medium between the baking chamber and the inlet and a second flow channel for conveying the heating medium between the outlet and the baking chamber. Therefore, as a result, this forms a closed heating circuit in which the heating medium, such as air, circtilates. Convection oven circulates hot air through heating unit. Most electrical heating devices are made of several resistive heating devices with a smooth surface-heating structure. A more advanced approach uses finned heating elements to enlarge the heat radiation. Both methods characterized by high power consumption.

Induction Heating (IH) concept is familiar for more than a decade and has established itself as a dominate heat treatment technique especially in the metal production, forging, tube welding, melting and other metal processing industries.

The basic electromagnetic phenomenon that induction-heating process relays on is quite simple. By generating an alternating current in an induction coil a time-variable magnetic field will be produced. The magnetic field will have the same frequenc3' as the coil current. The strength of the magnetic field in a specific point is depending on the current flowing in the induction coil, the number of turns, the coil geometry, and the distance from the coil. The time-variable magnetic field will induce eddy currents in the workpiece located near the coil.

Alternating eddy currents produces heat in the workpiece according to Joule effect (Ι^Λ2 R) since eddy currents are a direct result of the magnetic flex flowing throw the workpiece the currents in the coil windings needs to be high (or the number of turns) for a fast heating process.

Another important phenomenon usually called "skin effect" describes the non-uniform current through a conductor when an alternating power source is applied. The current density will decrease from the surface of the conductor towards its center. The layer that the current flows through is called Reference depth or Penetration depth. Reference depth depends on the frequency and material properties as described in Equation (1):

where

p - electric resistivity [Ω-cm]

μ - permeability of the air

/ - frequency [Hz]

Several more electromagnetic phenomena, such as proximity effect, ring effect, and end and edge effects plays an important role in understanding the induction heating phenomena but for sake of clarity would not be discussed in this description.

Although IH is not new in the industrial market it has not yet fully spread in the as a heat treatment method due to large initial costs. Nevertheless, due to high power abilities along with extremely low power consumption IH devices are slowly emerging at high power applications were power consumption expense is much larger than the initial costs.

It is an object of the present invention to provide a convection oven with reduced power consumption.

It is another object of the present invention to provide a convection oven heated by IH means.

It is another object of the present invention to provide an option to heat convection oven by inducing eddy currents in the air ventilation fan.

It is another object of the present invention to provide an option to heat convection oven by inducing eddy currents in a Heat sink located in the airflow channel. Other advantages and objects of the invention will become apparent as the description proceeds.

Summary of the Invention

The present invention relates to an inductively heated convection oven, comprising: a) an outer housing having a plurality of different sides joined together to form an enclosed space with at least one of the sides forming a door to provide access to the enclosed space;

b) an inner housing having a plurality of different sides joined together to form an enclosed oven space-spaced from and supported within the sides of the outer housing and having at least one side thereof facing the door of the outer housing providing access to the interior of the enclosed oven space;

c) at least one ventilation fan adapted for circulating air around the enclosed oven space, wherein the flow path of the circulated air is defined by the space between the inner and outer housing;

d) at least one induction heating unit supported within the space intermediate respective confronting sides of the inner and outer housings and arranged in a plane that is essentially parallel to a respective side of a magnetically susceptible element to maximize the inductive coupling to said element; and

e) control means for electrically exciting the induction heating unit at a relatively high frequency of the order of kilohertz to thereby magnetically induce the generation of induction heating at the flow path of the circulated air.

According to an embodiment of the invention, the magnetically susceptible element is a heat sink.

According to an embodiment of the invention, the magnetically susceptible element is the ventilation fan. According to an embodiment of the invention, the induction heating unit includes a planar magnetic core and multilayer Printed Circuit Board (PCB) coil. According to an embodiment of the invention, the magnetic core is an open E-core.

According to an embodiment of the invention, the induction heating unit includes helically-wound shaped inductive heating coils. The inductive heating coil can be a conductor, in particular a conductor made of litz wire or any other type of conductor such as hollow water cooled, etc.

In another aspect, the present invention relates to an induction heating module for a convection oven, comprising: an induction heating unit coupled to a magnetically susceptible element in a way that maximize the inductive coupling to said magnetically susceptible element, and which magnetically induce the generation of induction heating at the flow path of circulated air.

Brief Description of the Drawings

In the drawings:

Figs. 1A and IB schematically illustrate an induction heating unit and a corresponding heat sink that combined together into a heating module adapted for dissipating heat into a surrounding medium, according to some embodiment of the invention;

Fig. 2 schematically illustrates a baking oven which has, one baking cabinet, an outlet for air circulation and the heating module of Fig. IB, wherein the heating module includes Induction Heating units (based on PCB with E -cores) and a heated Heat Sink, according to an embodiment of the present invention;

Fig. 3 schematically illustrates a more focused view of the two IH (based on E-core) along with a heated air ventilation fan and the heated Heat Sink; Fig. 4A schematically illustrates an IH module based on a Litz wire, according to another embodiment of the invention;

Fig. 4B schematically illustrates a focused view of two IH (based on Litz wire of Fig. 4A) along with the heated air ventilation fan and the heated Heat Sink, according to another embodiment of the present invention;

Fig. 5 schematically illustrates a baking oven which has, one baking cabinet, outlets for dual air circulations and the heating module of Fig. IB, according to another embodiment of the present invention

Detailed Description of the Invention

Throughout this description the term "convention oven" is used to indicate an oven, in particular a baking cabinet which has a baking chamber in which the goods to be baked can be placed, an IH based heating unit, an air ventilation fan which draws air from the baking chamber and one or more outlets for dispensing the heated air into the baking chamber. This term does not imply any particular shape, construction material or geometry, and invention is applicable to all suitable ovens.

Fig. 1A shows a heating module that can be used in conjunction with the invention. The heating module illustrated in this figure is particularly convenient because it can be applied as an ad-on device to existing convection ovens without the need to carry out major alterations in the structure. The heating module generally indicated by numeral 1 in the figure comprises a heat sink 2 and an Induction Heating (IH) unit (i.e., IH coil) that includes a planar magnetic core 3, multilayer Printed Circuit Board (PCB) coil 4, and an optional dielectric insulator δ. IH coil based on PCB with an open E-core that can be used by the present invention is disclosed in Israeli patent application number 230752 dated January 30, 2014. Fig. IB schematically illustrates a heating module 1 that includes a plurality of planar magnetic cores 3, according to an embodiment of the invention. In these figures, each planar magnetic core 3 is implemented by an open E-shaped magnetic core that is made of ferromagnetic compounds such as ferrites.

Fig. 2 is an overall front view of a novel inductively heated rotating Rack convection baking oven constructed in accordance with the heating module of the invention and also illustrates certain parts of the inductively heated bake oven (while omitting others) in order to better depict the overall construction and relationship of these elements in a completed, inductively heated bake oven assembly according to the invention. The inductively heated bake oven is comprised by an outer housing 10 which can be fabricated from stainless steel or any other kind of alloy, usually made of at least two stainless steel AISI 304 layers along with heat barrier made of compressed panels and flocks of rock wool. An inner housing as shown at 15 is mechanically supported within the outer housing 10 by suitable thermal insulating and mechanically strong structural supports (not shown). The inner and outer housings each have a plurality of different sides joined together to form an enclosed oven space with one of the sides of the outer housing forming a door to provide access to the baking chamber. Rotating rack oven may use a gear mechanism 101 to rotate an inner structure 100 in order to maintain a safe rotation of a baking wagon 16. That side of the inner housing 15 which confronts the door also is open to provide access to the interior of the enclosed oven space provided by inner housing 15. For convenience, it will be assumed that the inner and outer housings 15 and 10 are formed in the shape of cubes having three closed sides and one side that forms the access door. The access door may have a double glass front in order to allow the interior of the oven space to be viewed and includes a handle to facilitate opening and closing of the door.

In order to heat the circulating air a novel approach is suggested. According to an embodiment of the invention a first Induction heating (IH) unit 12 induces eddy currents in a corresponding heat sink 11 located in the outlet of the IH unit 12, which dispends the first stage heated air through the plates of heat sink 11. Heat sink 11 is a passive heat exchanger that dissipates heat into the surrounding medium. The heat sink 11 is located within the oven in such a way that the surrounding medium covers the flow path of the circulated air as received from a ventilation fan 14 (that is rotations are controlled by a motor 20). The baking chamber 16 in which the goods to be baked can be placed is shown together with the air circulation path as indicated by the set of chained arrows. The circulation path of the air is indicated with respect to the direction of the arrows.

In this oven configuration the convention (i.e., the circulation path of the air) works as follows: the ventilation fan 14 draws air from the baking chamber 16 (relatively cooled air) and passes it through the heat sink 11 that heats the air for dispensing the heated air into the baking chamber 16.

According to an embodiment of the invention, the novel oven comprises a second IH 13 unit. In order to increase the heating of the air, the second IH 13 unit induces eddy currents in the ventilation fan 14. The second IH unit 13 is located adjacent to the ventilation fan 14, which turns the blades of fan 14 into an induction heat dissipating device. Of course, in such optional configuration the blades of the ventilation fan 14 should be made of a ferromagnetic metal such as cast iron or stainless steel. It is clear that an oven designer can consider using both heating dissipations methods as suggested by IH 12 and 13 and each one individually.

Fig. 3 schematically illustrates a more focused view of the two IH units 12 and 13 (that are based on E-core and PCB, as generally described with respect to Fig. 1) along with the heated air ventilation fan 14 and the heated heat sink 11.

Fig. 4A schematically illustrates an IH module based on a Litz wire 17 and the heat sink 11, according to another embodiment of the invention. Fig. 4B shows still another alternative construction for the induction heating coils for use in fabricating the novel heated bake oven of the present invention. This figure schematically illustrates a focused view of two IH units 17 and 18 (that are based on Litz wire) along with the heated air ventilation fan 14 and the heated heat sink 11, according to another embodiment of the present invention.

A plurality of planar, helically-wound shaped inductive heating coils shown at IH units 17 and 18 are physically supported (by means not shown in Fig. 4) within the space intermediate the respective confronting sides of the inner and outer housings 10 and 15, and are arranged to maximize the inductive coupling between the coils 17 and 18 to the respective associated heat sink 11 and fan 14, respectively. The heat sink 11 and the air ventilation fan 14 are fabricated from sheet members made of ferromagnetic metals capable of being inductively heated through the action of relatively high frequency magnetic induction fields of the order of kilohertz which magnetically induces the generation of heat. For convenience, the physical and thermally insulating supports for the various conductive heating coils 17-18 have not been illustrated in order not to unduly complicate the Figure, and for the same reason the electrical interconnections to the respective coils from a source of relatively high frequency, electrical excitation signals, have not been shown. The spiral coil construction as shown in the figure is used for purpose of illustration only and alternative coil geometries can also be used.

Fig. 5 schematically illustrates a baking oven which has, a baking cabinet 16 with outlets adapted for air circulations, according to another embodiment of the present invention. In this oven arrangement, the ventilation fan 14 is heated by two IH units 12. The ventilation fan 14 located in such a way that at least two flow paths of air circulation are generated from both sides of the fan's blades, wherein the cooled air is returned in both paths from the bottom of the ventilation fan 14. Turning now to the electronic circuit, it is composed of suitable controls and indications for controlling the operation of the oven. For example, an AC to AC converter can be used in order to generate a high frequency AC signals within the IH coils. The frequency and the amplitude of the AC signals will determine the power that will flow to the workpiece (in this case to the heat sink 11 or to the ventilation fan 14) and generate the wanted heat. Various controls for controlling the electronic circuitry are needed such as air flow measurements, several heat measurements, moisture measurement in case a steam generator is in use and etc. None of the above has been shown in order not to unduly complicate the Figures.

As will be appreciated by the skilled person the arrangement described in the figures results in a novel convection oven that enables optimal heat dissipation along with the benefits of a high efficiency IH coil. Therefore enables a new high efficiency oven with significantly reduced power consumption (recent researches on cooking surfaces shows an improved efficiency from about 50% (resistive heating) to 77% (induction heating), since the proposed arrangement enables a more optimal heat dissipation the total efficiency improvement is expected to be even higher). This arrangement obviates disadvantages of existing baking ovens.

The main advantage provided by the invention is that the suggested oven configuration decreases significantly the power consumption upon a conventional baking oven of the type defined hereinabove.

Using IH devices is proved to be more efficient than traditional resistive heating devices. Furthermore by heating the ventilation fan above surrounding temperature will heat the emitted air. Driving the produced hot air through a heated heat sink located in the outlet will enlarge the heat generated by the ventilation fan even more. Unlike resistive heating which usually vises a number of parallel heating elements and therefore cannot change the amount of power in a continuous manner. IH power flow is determined by the frequency (and amplitude) of the current flowing throw the IH coil, and therefor can be easily changed in a continuous manner. More over this feature will decrease the power loses even more since a steady temperature control can be applied (this energy saving feature is relatively similar to the energy saving feature of inverter based air conditioners). All of the above will significantly reduce the amount of electrical power used to operate the above type of oven.

All the above description and examples have been given for the purpose of illustration and are not intended to limit the invention in any way. Many different mechanisms, methods of heating by inductions, electronic and logical elements can be employed, all without exceeding the scope of the invention.

Claims

1. An inductively heated convection oven, comprising:

a) an outer housing having a plurality of different sides joined together to form an enclosed space with at least one of the sides forming a door to provide access to the enclosed space;

e) control means for electrically exciting the induction heating unit at a relatively high frequency of the order of kilohertz to thereby magnetically induce the generation of induction heating at. the flow path of the circulated air.

2. An oven according to claim 1, in which the magnetically susceptible element is a heat sink.

3. An oven according to claim 1, in which the magnetically susceptible element is the ventilation fan.

4. An oven according to claim 1, in which the induction heating unit includes a planar magnetic core and multilayer Printed Circuit Board (PCB) coil.

5. An oven according to claim 4, in which the magnetic core is an open E-core.

6. An oven according to claim 1, in which the induction heating unit includes helically- wound shaped inductive heating coils.

7. An oven according to claim 6, in which the inductive heating coil is a conductor, in particular a conductor made of litz wire.

8. An heating module for a convection oven, comprising: an induction heating unit coupled to a magnetically susceptible element in away that maximize the inductive coupling to said magnetically susceptible element, and which magnetically induce the generation of induction heating at the flow path of circulated air.