Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24C—DOMESTIC STOVES OR RANGES ; DETAILS OF DOMESTIC STOVES OR RANGES, OF GENERAL APPLICATION
  • F24C7/00—Stoves or ranges heated by electric energy
  • F24C7/04—Stoves or ranges heated by electric energy with heat radiated directly from the heating element
  • F24C7/043—Stoves

Definitions

• the present invention relates to electric heating elements with a substantially radiative component.
• Electric heaters currently used for example for electric heating generally use the principle of the Joule effect to create a source of heat through a potential drop in resistance, managed by Ohm's law. The heat thus produced is then transferred by different processes.
• the heat is transferred by convection.
• the system includes in a receptacle or envelope a resistor and air inlet and outlet areas.
• the air located in the vicinity of the heated resistance increases its temperature, so its density decreases. It tends to rise; a rising current is established and the hot air is replaced by cold air, which in turn warms up.
• the device made in this mode of transfer is called a convector.
• the heat transfer of the heat resulting from the resistance is obtained by conduction in a fluid which in turn heats an envelope, which transfers its calories to the ambient air by convection and radiation.
• This process is used in traditional central heating where water, steam or oils are most often heat transfer fluids. These devices are commonly called radiators, improperly.
• the transfer of the energy produced at an electrical resistance is essentially obtained by the radiation emitted by the latter, the radiation itself propagating through the room.
• the corresponding apparatus is called in the radiant panel technique.
• the present invention relates to systems operating according to the principles of this third category.
• radiative or essentially radiative it is understood within the meaning of the present description that most of the heat transfer is by radiation, which of course does not exclude that a small part of said transfers is by conduction and or by convection.
• the radiated infrared energy is in first approximation proportional to the fourth power of the Kelvin temperature, according to the law of Stephan and Boltzmann. It follows therefore that the electrical resistance must be brought to a higher temperature, for example at least equal to 15O 0 C and preferably between 300 and 500 0 C for domestic use.
• the devices currently marketed according to this principle comprise a heating body, generally consisting of a resistive sheet of aluminum sheet on which is printed a resistive track in the form of an enamel or a black paint to high emissivity.
• Said high temperature resistive plate is confined in a most often metallic envelope, whose front portion is generally constituted by a grid having circular openings arranged in the form of a honeycomb for the evacuation of radiation.
• a first drawback of such a system is the high cost of producing the resistive elements previously described.
• a second disadvantage comes from the necessity, because of the high temperature of the resistive plate, to move the front grille away from the device, which can lead to a significant extra thickness of the resulting panel.
• a third disadvantage is due to the thermal variations of the room. These variations are caused by the operation of the heater, following a succession of on / off phases of the heater. The use of the devices of the prior art thus causes discomfort associated with more or less pronounced thermal shock, between two successive interlocking of the heater.
• the present invention relates to heating devices which do not have or reduce the known disadvantages of prior devices.
• the heating devices according to the invention also ensure good transparency, a very good efficiency, a minimum space requirement for homogeneous heating and compliance with the safety requirements and standards in force.
• They comprise a heating body comprising at least one thermally and mechanically resistant glass plate, covered with a thin, low-emissivity transparent layer, for example of the SnC> 2: F type, which acts as a resistor in which the electricity which the cross is transformed into heat by Joule effect.
• heating devices in which the heating body comprises such elements.
• the devices described are not essentially high temperature radiant panels in the sense of the present invention but convectors in which a small portion of the heating can be provided by a radiative component.
• the present invention relates to an electric radiant heating device, comprising a heating body consisting of a high temperature resistive element.
• Said heating body is confined in a most often metallic envelope, the front portion of which is for example constituted by a grid for the evacuation of the emitted radiation, preferably in the form of a honeycomb.
• Said device is characterized in that said heating body comprises a thermally and mechanically resistant glass plate, covered with a low emissivity resistive layer, said layer being configured so that the power flux released by the heating element is between 5,000 W / m 2 and 35,000 W / m 2 , for example between 10,000 and 20,000 W / m 2 .
• the device can be attached to a wall or wall or mobile.
• the low emissivity layer is disposed on the rear face of the glass plate, that is to say on the opposite side with respect to the location of the grid in the device.
• the heating body comprises a double glazing and the resistive layer is disposed on the inner face of the first glass plate, relative to the front of the device.
• the square resistance of the resistive layer is between 2 and 20 ⁇ / D, preferably between 5 and 10 ⁇ / D.
• the thickness of the resistive layer is between 0.2 and 2 micrometers.
• the low emissivity resistive layer is a thermal infrared reflective layer, for example of the tin oxide type, doped with antimony or with fluorine or indium oxide doped with tin.
• the glass plate is typically constituted by a thermally resistant glass and sufficiently insulating at the operating temperature of the heating body, preferably borosilicate glasses or vitro-ceramics.
• borosilicate glasses or vitro-ceramics For surface powers of between 5,000 W / m 2 and 10,000 W / m 2 , or even 15,000 W / m 2 , it is also possible according to the invention to use conventional silica-soda-lime glasses with a high voltage temperature ( of "strain point" high according to the English term), that is to say typically greater than 400 0 C or 500 0 C or even 600 0 C and preferably tempered, such as safe glass ® marketed by the company Saint Gobain Glass France.
• the glass compositions are for example of the silico-soda-lime type.
• the expression silico-soda-lime is used here in the broad sense and concerns any glass composition consisting of a glass matrix which comprises the following constituents (in percentage by weight):
• compositions adapted to the present invention have the following mass proportions:
• compositions have expansion coefficients below 35.10 -7 / ° C, and a lower annealing temperature greater than 65O 0 C.
• the Eagle 2000 glass sold by Corning Inc. is an example of this family of glasses.
• the glasses containing boron have a thermomechanical resistance capable of rendering them usable for the present application: SiO 2 78-86% B 2 O 3 8-15% Al 2 O 3 0.9-5% MgO 0-2%
• compositions are the Pyrex ® glass marketed by Corning Inc.
• the glass plate is further quenched to improve its resistance to thermal shock.
• the quenching can be thermal or chemical.
• the device is configured according to the present invention to be connected to the sector through at least two conductor strips of the current in intimate electrical contact with the resistive layer.
• additional conductive strips are arranged on one or more low-emissivity layers so as to delimit at their level resistive sectors connected in series.
• the invention also relates to the heating body as previously described.
• Figure 1 illustrates a heating body according to the invention.
• FIG. 2 schematizes a radiant panel incorporating a radiating glass substrate according to the invention.
• a heating body according to the invention comprising a borosilicate-based glass plate coated with a 500 nm layer of doped tin oxide F was synthesized according to techniques well known in the art.
• FIG. 1 describes a heating body 5 thus constituted which can be connected via conductive strips 6 and connection means 7 to a 220-volt power supply network, which then has a power flux-density of 5000 W / m 2 .
• the resistive layer 8, deposited on the face 9a of the plate 9, has a height of 400 mm and a length of 1000 mm.
• the conductive strips 6 are placed on either side of the layer 8, in the direction of the height.
• the power of a radiant panel incorporating this heating body is of the order of 2000 Watts and theoretically allows to heat a room of about 20 m 2 .
• the conductive strips 6 are arranged along the vertical edges of the glass plate 9 and constitute buses supplying the current to the resistive layer 8.
• connection wire 7 is connected to the 220-volt power network.
• FIG. 1 is purely illustrative and variants would not be outside the scope of the invention, in particular associating one or more resistive layers distributed on the glass plate in different zones of electrical resistance arranged in series, being in parallel, for example according to the principles described in patent EP 878 980 B1.
• the arrival of the current is effected by means of two conductive copper lines screen-printed or glued, placed in close electrical contact with the layer resistor of SnC> 2: F.
• Complementary copper lines of the same type can be deposited within this range, then allowing, by a suitable connection, to connect in series the corresponding resistances to the surfaces thus delimited on the conductive layer .
• the layer behaves like an electrical resistance whose value depends on the ratio of the dimensions of the resistive plate.
• the low emissivity layer heats up when it is energized by the Joule effect, and, by conduction, also heats the glass plate.
• the surface of the glass, opposite to the layer, is electrically insulating.
• the plate thus obtained is characterized by a low emissivity and a high reflectivity in the infrared and the glass side by a high emissivity.
• thermal infrared wavelength of 5 to 20 microns
• the device comprises an envelope comprising a frame 1 incorporating fixing means 2 of a known type to a wall, and a front part, turned towards the inside of the room and consisting of a grid 3 whose circular openings 4 are arranged in honeycomb.
• a heating body 5, as previously described in relation to FIG. 1, is disposed inside and made integral with the envelope according to the standard techniques of the art, so that the low-emissivity layer is arranged. facing the wall, that is to say on the glass plate opposite side to the grid, the face 9a of the glass plate 9, thus facing the wall.
• complementary components such as switches and / or thermostats of models comparable to those used for current devices.
• Such an arrangement has the advantage that most of the infrared radiation is emitted to the room and a small part to the wall, because of the low emissivity of the layer and the high surface emissivity of the glass in the area of the infrared (greater than 0.9).
• the layer being chosen at low emissivity, the behavior of the two faces of the heating body is asymmetrical from the point of view of the radiation emitted by the glass, the energies radiated by each face being proportional to their respective emissivities.
• the small thickness of the glass makes the gradient in the thickness very small and it can be assumed that the glass is isothermal.
• the work carried out by the applicant have shown that the surface temperature of the glass substrate constituting the heating body is about 37O 0 C for a value of 20 000 W / m 2 .
• the embodiment given here by way of illustration may give rise to any desirable modification, in particular as regards the power, size or aesthetics of the present device by acting in particular on the dimensions of the heating body, the arrangement resistive layers on the glass plate, the square resistance of the low-emissivity layers, etc.
• the panels according to the invention incorporate heating elements configured in such a way that the surface temperature of the glass substrate constituting the heating body is between about 170 and about 500 ° C., preferably between about 200 and about 400 ° C. which has the advantage on the one hand of a greater heating efficiency, which can be up to 50 or even 60 or even 80% depending on the geometry of the panel considered, the energy radiated per unit area or emittance being proportional to the fourth power of the superficial temperature of the heating body.
• the effectiveness of the radiant panel means the thermal power directly useful for heating and transmitted solely by the radiation of the emitting face of the heating body to the zone to be heated. Efficiency is also defined as the ratio of the power radiated by the emitting face to the total power supplied to the radiant panel.
• the operation of the present system is provided by conductive heat transfer between the resistive layer and the glass plate.
• the emission of infrared radiation is mainly on the side of the glass face, most of the infrared radiation is diffused towards the part to be heated.
• the present heating body by virtue of the specific emissivity and reflectivity properties of these two main components (low emissivity layer and glass plate) previously described, allows an improved homogeneity of the surface temperature of the glass face. transmitter, and this on the entire surface of the panel resulting in a greater feeling of comfort for the user. For the same reasons, the distance between the heating body and the front part of the radiant panel and therefore the thickness thereof can be minimized.
• the power flux-density released by the heating element being between 5,000 W / m 2 and 35,000 W / m 2 , it is possible according to the invention to envisage radiant devices of very small size, having a power of typically between 300 and 2500, or even 3000 Watts.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Surface Heating Bodies (AREA)
• Resistance Heating (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 2006
  • 2006-02-01 FR FR0650359A patent/FR2896943B1/fr not_active Expired - Fee Related
• 2007
  • 2007-01-31 WO PCT/FR2007/050713 patent/WO2007088308A1/fr active Application Filing
  • 2007-01-31 EP EP07731541A patent/EP1980136A1/de not_active Withdrawn

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