FR2895205A1 - Heating device for e.g. domestic water heater, has resistive layer made of conductive carbon composition and applied on surface of dielectric substrate with controlled thickness, and electrical wires connected to electrodes placed on layer - Google Patents

Abstract

The device (1) has an electrically resistive conducting layer (3) disposed on a surface of a dielectric substrate (2) e.g. film, and extended in a rectangle shape. A resistive layer is made of conductive carbon composition and applied on the surface of the substrate with controlled thickness. Electrical wires (9) are connected to electrodes (7) placed on the layer for connecting the layer to an electrical energy source.

Description

TWO-DIMENSIONAL PASSIVE RESISTANCE The present invention relates to a

  Joule effect heating device whose resistive element is two-dimensional.

  A joule heating device is known comprising a resistive electrically conductive element in the form of a wire which is spirally disposed on a surface of a dielectric substrate. Because of its structure, the contact surface of the wire on the substrate is particularly limited, with the result that the regions of the substrate adjacent to the heating wire reach temperatures much higher than the other areas of the substrate. This presence of these particularly hot areas may present disadvantages in certain areas, for example in any water heater or these areas promote the deposition of limestone. In addition, a breakage of the wire irremediably causes the deterioration of the electrical circuit.

  It has been envisaged to provide a Joule heating device comprising a two-dimensional conductive element, that is, an element extending in both directions of the substrate surface to which it is fixed and whose thickness (usually a few microns) is out of proportion with the other two directions (usually at least several centimeters). The conductive element being an electronically conductive polymer. However, these polymers must be dissolved in expensive and / or aggressive and / or toxic solvents and / or synthesized in situ by oxidation-reduction reactions. In addition, the polymers are difficult to apply accurately to the substrate (problems in terms of constancy of the thickness of the two-dimensional conductive element). Finally, many polymers lose their conductance because of their aging in the presence of water and / or oxygen.

  The aim of the present invention is to provide a heating device by Joule effect making it possible to have a large surface of contact with the substrate on which it is fixed, in order to maximize the surface area of exchange of the heat produced while having a possibility of have a controlled thickness.

  According to the invention, the Joule heating device comprises at least one resistive electrically conductive layer which is deposited on a surface of a dielectric substrate so as to extend in the two generating dimensions of this surface in accordance with comparable orders of magnitude, is characterized in that the electrically conductive layer is made of a conductive carbon ink.

  The conductive carbon ink can be applied to the surface with an easily controlled thickness, especially by coating, screen printing or inkjet.

  Thus, it is possible to obtain a heating device which makes it possible to have a large surface of contact with the substrate on which it is fixed, while having an ease of implementation of the device, in particular by the possibility of regulating accurately 1 thickness of the conductive carbon ink.

  Other advantages and particularities will appear in the description of the embodiment given by way of non-limiting example and illustrated by the drawings in the appendix in which: Figure 1 is a schematic top view of a device according to the present FIG. 2 is a sectional view of the third device along the line II - II of FIG.

  As can be seen in FIGS. 1 and 2, a Joule heating device 1 comprises a substrate 2 which is electrically insulating (for example a film or a textile) and a resistive electrically conductive layer 3, the nature of the substrate 2 depending on the use of the heater 1.

  The resistive layer 3 is deposited on a surface of the substrate 2 in such a way that it extends in the two generating dimensions 4,5 of this surface according to orders of comparable magnitudes. This resistive layer 3 is made of a conductive carbon ink 3. The conductive carbon ink 3 has a resistivity of between 10 and 1010 ohm.m, and preferably between 103 and 104 ohm.m.

  Due to its nature (preferably liquid or pasting) the conductive carbon ink 3 can be easily applied to the substrate 2, for example by screen printing (continuous or discontinuous), by coating or by ink jet (the substrate 2 being able to be, for example glass or ceramic). On the other hand, when the nature of the substrate 2 allows it (for example a film), because of its fineness, the conductive carbon ink 3 can be integrated therein.

  The methods of application make it possible to control the thickness 6 of the resistive layer 3 and thus to obtain a resistive layer 3 of constant thickness over the entire surface to which it is applied. The thickness of the resistive layer 3 is much less important than its dimensions in the two generative directions 4,5. In the present embodiment, the resistive layer 3 extends according to a parallelogram, and more precisely, according to a rectangle.

  In addition, the device 1 comprises a pair of electrodes 7. Each electrode 7 is placed along an edge delimiting the resistive layer 3 which is opposed to the edge along which is placed the other electrode 7. Each electrode 7 s extends over the entire length of the corresponding edge. Each electrode 7 can be made, optionally, of a blade, a flat wire or a braid, in a very conductive material, for example copper, aluminum or iron.

  In addition, in the present embodiment, each electrode 7 rests on a pre-electrode 8 whose spreading dimensions (that is to say according to the generative dimensions 4.5 of the contact surface of the resistive layer 3) correspond to those of the electrode 7. These pre-electrodes 8, for example silver or copper, are deposited by screen printing, coating or electrolysis directly on the resistive layer 3. Due to the methods of deposit that may be used, each pre-electrode 8 is particularly thin, and, for example, has a thickness of about 12 μm.

  Finally, in order to allow its electrical connection with an external power source, the device 1 comprises an electrical connection system 9. In the present case, this system is formed by two electrical wires 9, each wire 9 being connected to an electrode 7 corresponding.

  In particular, in the case where the device 1 is intended for power supply with a voltage greater than 24 V, a dielectric element 10 covers the assembly formed by the resistive layer 3, the electrodes 7 and the pre-electrodes 8, while being through by the electrical wires 9 to allow the electrical connection.

  This very simple device 1 makes it possible to have a heating device 1 by the Joule effect whose resistance which is fixed by the supply voltage and the power required, can be controlled by determining the thickness 6 (generally of a few microns). a few tens of microns) or the spreading surface (according to the two 4.5 directional dimensions which can each extend over centimeters, decimetres, or even meters, depending on the applications) of the resistive layer 3, or by determining the nature of the layer (and therefore its resistance). It is thus possible to have a contact surface between the resistive layer 3 and the variable substrate 1 in shape and size in very large proportions, a variable surface heating power according to the contact surface. It is thus possible to be able to vary the surface temperature of the substrate 1 at its contact surface with the resistive element 3 between ambient temperature and 150.degree. C. It is also possible to have a large heating surface in the form of employing only one large resistive element, and not a parallel assembly and / or series of small elements of the thermistor type.

  The interest of the invention can be highlighted by the comparison of two Joule heating devices having the same electrical characteristics of power (1100 W), voltage (220 V), intensity (5 A) and resistance (44). Ohm).

  A one-dimensional resistive element in the form of a wire 850 cm long and 0.35 mm in wire diameter has a resistance area of 0.0093 m2, which corresponds to a surface of the substrate of 0.12 m2 . Its linear resistivity is 5.10-5 Ohm.cm, the surface power of the resistance is 117.7 kW / m2 (and that of the substrate is 9.17 kW / m2). The surface temperature of the substrate is 196 C for a radiating power of 30%, 260 C for a radiating power of 50%, and 307 C for a radiant power of 70%. A two-dimensional resistive layer according to the present invention being in the form of a rectangle 60 cm long, 40 cm wide, and having a thickness of 12 μm has a surface area of 0.24 m 2, to which corresponds a surface of the substrate of 0.24 m2. Its surface resistance being of 29.33 Ohm / square (equivalent to a line resistivity of 3.52.10-2 Ohm.cm), the surface power of the resistance (and the substrate) is 4583 W / m2. The surface temperature of the substrate is 122 C for a radiant power of 30%, 175 C for a radiating power of 50%, and 215 C for a radiant power of 70%.

  Thus, for the same radiant power, the temperature of the surface is decreased from 75 C to 90 C.

  It is therefore easy to have a radiant heating device whose surface temperature is less important than that of devices with one-dimensional resistive elements.

  The other advantages of the present invention relate to the great variability of the electrical power supply of the heating device 1: it can be made by battery or on mains, the electric current can be alternating or continuous, the supply voltage can vary according to a very large amplitude, for example very low (from 1 to 10 V), low (from 24 to 48 V), average (110 to 380 V) or high (several thousands of volts), the vehicle intensity can vary considerably, by example of a few milliamperes to dozens of amperes. The value of the resistance can thus vary over a wide range of values, thus the surface resistance can range from 0.1 to 10,000 Ohm / square, and preferably from 5 to 1,000 Ohm / square.

  The invention may be used either in a heat transfer mode by radiation and convection, or in a conductive heat transfer mode with mild transfer due to the importance of the exchange surface. Therefore, the invention can be implemented in the various heating devices of the building, whether in the tertiary (ceiling heating), in the domestic (floor heating or wall heaters), or in the frost protection devices or off-ice (on roads, airstrips, garage access).

  Elie may also be used in domestic water heaters, in soft radiating heaters for animal husbandry or in horticulture, in rapid and low-gradient heat exchange systems in industry, or in sports or professional clothing with battery power.

  Many modifications may be made to the embodiment. It would thus be possible to have several resistive layers deposited on one another, the latter being connected to the electrical connection system 9 via the electrodes 7 and the possible pre-electrodes 8. It would also be possible for the device to include the electrodes 7. but not the pre-electrodes 8, or vice versa.

Claims (10)

  A Joule heating device (1) comprising at least one resistive electrically conductive layer (3) which is deposited on a surface of a dielectric substrate (2) so as to extend in both generative dimensions (4). 5) of this surface according to comparable orders of magnitude, characterized in that the resistive layer (3) is made of a conductive carbon ink (3).   2. Device (1) according to claim 1, characterized in that the resistive layer (3) extends in a parallelogram, preferably in a rectangle.   3. Device (1) according to claim 1 or 2, characterized in that the resistive layer (3) has a resistivity between 10 and 1010 Ohm.m, and preferably between 103 and 109 Ohm.m.   4. Device (1) according to one of claims 1 to 3, characterized in that the resistive layer (3), of constant thickness, is serigraphy or deposited by coating or ink jet.   5. Device (1) according to one of claims 1 to 4, characterized in that the substrate (2) is a film or a textile. 20 25   6. Device (1) according to one of claims 1 to 5, characterized in that it comprises a pair of electrodes (7) which are placed on two opposite edges of the resistive layer (3), a connection system The electrical connection (9) connects to the electrodes (7) to enable the resistive layer (3) to be connected to an energy source.   7. Device (1) according to claim 6, characterized in that each electrode (7) extends over the entire length of the corresponding edge.   8. Device (1) according to claim 6 or 7, characterized in that each electrode (7) rests on a pre-electrode (8) whose spreading dimensions correspond to those of the electrode (7).   9. Device (1) according to claim 8, characterized in that the pre-electrodes (8) are deposited by screen printing, coating or electrolysis.   10. Device (1) according to one of claims 1 to 9, characterized in that a dielectric element (10) covers the resistive layer (3) and, as the case, the electrodes (7) and the pre-electrodes (8) while leaving free an electrical connection system (9).