HEATING ELEMENT AND METHOD FOR MANUFACTURING IT

Abstract: The invention relates to a heating element comprising a carrier of electrically insulating material and a layer with an open structure which is fixed to the electrically insulating carrier in a determined pattern and by means of adhesive, wherein the layer is manufactured from an electrically conducting material with a predetermined specific resistance, this such that heat is generated in the layer when a voltage difference is applied thereover; and a method for manufacturing such a heating element.

Description: HEATING ELEMENT AND METHOD FOR MANUFACTURING IT The present invention relates to a heating element and a method for manufacture thereof . Heating elements known from the prior art are resistance elements consisting of a resistance wire provided with an insulating sheath, over which a voltage difference is applied in order to generate heat. Resistance elements have the drawback that they cannot be deformed such that a curved surface can be followed with good thermal contact . The control for bringing about an even temperature or temperature distribution is further limited. Other heating elements known from the prior art are surface heating elements consisting of a carrier foil onto which a metal foil is glued, wherein tracks are arranged in the metal foil using etching techniques. Although these laminate structures are relatively thin and can follow a surface for heating better than usual resistance elements, the application thereof is still limited. Since the metal foil cannot stretch, such a surface resistance element cannot follow a sharply double-curved surface. Another drawback of surface heating elements is that the chemical process which is used for the etching has an environmental impact . A further drawback is that as a result of the manufacturing process the surface heating elements are uneconomic. Problems further occur at high temperatures with the adhesion of the foils, and the foils themselves. Finally, the power density of such surface resistance elements, and therefore the temperature which can be achieved locally, is limited. The present invention has for its object to provide a heating element, wherein the above stated drawbacks are obviated. According to the invention the heating element comprises a carrier of electrically insulating material and a layer with an open structure which is fixed to the electrically insulating carrier in a determined pattern and by means of adhesive, wherein the layer is manufactured from an electrically conducting material with a predetermined specific resistance, this such that heat is generated in the layer when a voltage difference is applied thereover. The electrical layer is incorporated in a circuit, wherein heat is produced by the resistance of the layer. This heat is transferred to the object or medium for heating via the adhesive and the electrically insulating carrier. The electrically conducting layer preferably consists of one or more strips of electrically conducting material, wherein the strip or strips is or are arranged in a zigzag, spiral or meander-shaped pattern, and is preferably a fabric. The desired resistance can be obtained by a suitable choice of material, wire thickness, density and strip width of the fabric. The fabric can be manufactured from wires of a metal (alloy) , such as stainless steel, iron, tungsten or constantan, or from a hybrid material, such as ceramic or plastic, having similar electric properties. A fabric of thin glass fibres is preferably used for the electrically insulating carrier. The glass fibres have a thickness such that the desired flexibility and heat conduction are obtained while retaining electrical insulation. The whole heating element is hereby a flexible element which can follow the contours of the object for heating, so that good heat transfer can take place through intimate contact with the surface of the object. According to the advantageous further development the measure of claim 9 is applied. Because the heating element itself will have a low heat content and, due to the good contact with the object for heating, will moreover have a good heat transfer therewith, the heating element itself will very rapidly acquire the temperature of the object for heating after the power source has been switched off . The relation between the resistance and the temperature of the heating element can be established in a per se obvious manner. The processing device is embodied herein such that it can determine the resistance of the heating element in the switched-off mode and, by applying the previously found relation, can calculate the prevailing temperature therefrom. In addition, the invention relates to a method for manufacturing a heating element according to claim 10. The layer can first be impregnated with adhesive before a determined pattern is formed therefrom. This is particularly advantageous in the forming of determined patterns, such as a spiral-shaped or meander- shaped pattern. In impregnated state the layer allows of easier cutting to a pattern or of processing in other manner. A pattern can be cut out of a fabric using laser, wherein complicated patterns adjusted to the desired distribution of heat over the surface can be formed. Air inclusions are prevented by mutually fixing the layer and the carrier with adhesive under a condition of reduced pressure. The invention is now further elucidated with reference to the drawings . In the drawings : Figure 1 shows a part of a heating element according to the present invention, Figure 2 shows a cross-section along line II-II in figure 1, Figure 3 shows a device for performing a method for manuf cturing a heating element, Figure 4 shows another embodiment of a heating element, Figure 5 is an illustration elucidating a method for manufacturing a heating element as shown in figure 4, Figures 6-11 show applications of a heating element according to the present invention. Figure 1 shows a part of a heating element according to the invention. The heating element comprises a carrier of electrically insulating material 1 and a layer with an open structure 2, which is fixed to electrically insulating carrier 1 in a determined pattern and by means of adhesive 3. The layer is manufactured from an electrically conducting material with a predetermined specific resistance, with the purpose of generating heat in the layer when a voltage difference is applied over the layer. Layer 2 consists of diverse strips which are arranged in a zigzag pattern. Layer 2 is for instance formed from a fabric of metal wire. Carrier 1 is for instance formed from a fabric of glass fibres. Other materials with similar properties for the intended effect can of course be applied. Using figure 3 a possible method for manufacturing a heating element will be explained hereinbelow. Strips 2 are first placed on carrier 1 in zigzag manner. An adhesive 3 is then applied to at least the strips 2. The whole is placed in a tray so as to form a closed housing together with cover 5, so that the adhesive 3 fixes the strips to the carrier under a condition of reduced pressure (vacuum) . Glueing strips 2 and carrier 1 together under vacuum ensures that air inclusions disappear. Air inclusions obstruct heat generation. Cover 5 is provided on the underside with ribs 6 to press strips 2 firmly against carrier 1 during the glueing. Heat is simultaneously added to adhesive 3 to make it soft and ensure that the openings in the fabric of strips 2 and of carrier 1 are completely filled with adhesive 3. Figure 4 shows a heating element, wherein layer 2 is fixed in a spiral-shaped pattern between two electrically insulating carriers 1. Layer 2 contains two terminals 7 over which a voltage difference can be applied. Such a heating element finds application in for instance an electric kettle. The heating element can be arranged on the base of an electric kettle and be connected to the electric control circuit of the kettle via terminals 7. When the heating element shown in figure 4 has a diameter of 10 cm, a power density in the order of magnitude of 30 W/cm 2 can be obtained at a power of 3kW. The heating element shown in figure 4 can be manufactured as follows. The fabric 9 from which the pattern of layer 2 must be formed is first impregnated with an adhesive. A spiral-shaped pattern is then cut out of fabric 9 using laser 8. Finally, the spiral-shaped layer 2 is placed on a fabric of glass fibres as electrically insulating carrier and glued thereto. A distance between the spirals is obtained using laser 8 such that no spark-over occurs between the spirals. The heating element can for instance be applied as car seat heating, as shown in figure 6, wherein the electrically conducting layer of the heating element has a meander pattern shown in dashed lines. The element has the required flexibility perpendicularly of the seat part of the seat, strength in the plane of the seat part of the seat and can be distributed over the whole surface of the seat. In addition to seat heating for cars, heating of the seat part of a motorcycle (see figure 8) or cycle is also possible. Another application is for heating water in a boiler (figure 7) or in a pipe (figure 9) which runs for instance to a washing machine or solar energy system. By winding the heating element spirally around a pipe and glueing it thereto, through which pipe flows water, a very simple and inexpensive system for heating water is obtained. The strip or strips themselves can herein be used as sensor to control the outgoing temperature of the water. Figure 10 shows in perspective view an application of the heating element in a solar energy system 100. This solar energy system 100 has a hollow collector 101 on which the solar radiation is incident and in which a heat transfer medium is arranged. Owing to the incident solar radiation the heat transfer medium in collector 101 will evaporate and rise upward in collector 101 and at the top be urged via pipes 102 through a heat exchanger, where the heat transfer medium once again condenses . The heat exchanger consists of a heat storage tank consisting of elongate elements 103 and elongate flat channel plates 104 which are placed between these elements and through which the heat transfer medium runs . The condensed heat transfer medium flows further from the heat exchanger via pipes 105 to the underside of collector 101. Solar energy system 100 further has a housing which consists of a transparent upper side 106 formed from a sandwich panel, for instance of polycarbonate, and a tray-like underside 107. Solar energy system 100 is placed with housing 106,107 directly onto roof boarding 108. In order to ensure proper sealing between housing 106,107 and the roof tiles 109 lying on roof boarding 108, the housing further has an apron part 110, which can be adjusted to the form of roof tiles 109 by heating (see also figure 11) . Apron part 110 is coupled slidably to housing 106,107, so that when housing 106,107 expands due to heating as a result of solar radiation the apron part 110 can displace relative to housing 106,107, whereby cracking is prevented. In storage tank 103 is stored water which is heated by heat-exchange with the heat transfer medium. In order to prevent heat loss via roof boarding 108, the housing 106,107 is further filled with a composite insulation structure 111 (see figure 11) . On a part of the elongate elements 103 is arranged the heating element 112 according to the present invention which, in the case of a shortage of radiant heat, contributes toward the heating of the water in elongate elements

Claims: CLAIMS 1. Heating element comprising a carrier of electrically insulating material and a layer with an open structure which is fixed to the electrically insulating carrier in a determined pattern and by means of adhesive, wherein the layer is manufactured from an electrically conducting material with a predetermined specific resistance, this such that heat is generated in the layer when a voltage difference is applied thereover. 2. Heating element as claimed in claim 1, wherein the layer comprises one or more strips of electrically conducting material. 3. Heating element as claimed in claim 2, wherein the pattern is a zigzag, spiral or meander-shaped pattern. 4. Heating element as claimed in any of the claims 1-3, wherein the layer is a fabric. 5. Heating element as claimed in claim 4, wherein the fabric is a fabric of wires of a metal (alloy) , such as stainless steel, iron, tungsten or constantan. 6. Heating element as claimed in claim 4, wherein the fabric is a fabric of wires of a hybrid material, such as plastic or ceramic. 7. Heating element as claimed in any of the claims 1-6, wherein the carrier is a fabric of thin glass fibres . 8. Heating element as claimed in any of the claims 1-7, wherein the adhesive is a glue such as silicon adhesive, epoxy or polyurethane glue. 9. Heating device comprising a heating element as claimed in any of the foregoing claims and a temperature measuring device which comprises a temperature sensor and a processing device connected thereto, wherein the temperature sensor is formed by the heating element . 10. Solar energy system, comprising: - a housing comprising a part permeable by solar radiation arranged on an upper side; - a collector which is arranged in the housing and which comprises an inclining space exposed to solar radiation via the permeable part, through which space can flow a heat transfer medium which flows in a first circulation and is coupled to a second medium circuit, wherein the first circulation takes place in a circulation tank which is filled partially with liquid and partially with vapour thereof and which operates as a circulation system which is driven by natural convection of separate evaporation and condensation; - a heat storage tank which is arranged in the second medium circuit and which is thermally coupled to a wall of the circulation tank, close to a part of the first circulation which is directed downward; and - insulation arranged in the housing, characterized in that a heating element as claimed in any of the foregoing claims is arranged on the heat storage tank. 11. Method for manufacturing a heating element as claimed in any of the claims 1-8, wherein the electrically conducting layer with an open structure is brought into a determined pattern, is then placed on an electrically insulating carrier and finally fixed thereto by means of an adhesive while controlling the prevailing pressure. 12. Method as claimed in claim 10, wherein the layer is first impregnated with an adhesive before the layer is brought into a determined pattern. 13. Method as claimed in claim 10 or 11, wherein the layer is brought into a determined pattern by cutting one or more strips out of a fabric. 14. Method as claimed in claim 12, wherein the fabric is cut using laser. 15. Method as claimed in any of the claims 10- 13, wherein the layer and the carrier are fixed to each other under a condition of reduced pressure. 16. Method as claimed in any of the claims 10- 14, wherein the layer and the carrier are fixed to each other by addition of heat. 17. Method as claimed in any of the claims 10- 15, wherein a glue such as silicon adhesive, epoxy or polyurethane glue is chosen for the adhesive.

Inventors: BERTELS AUGUSTINUS WILHELMUS M, BERTELS, AUGUSTINUS, WILHELMUS, MARIA
Applicants: BERTELS AUGUSTINUS WILHELMUS M, INVENTUM B V, BERTELS, AUGUSTINUS, WILHELMUS, MARIA, INVENTUM B.V.
Application year: 2001
Main classification: H05B3
IPC codes: H05B3