FR2811854A1 - Heater for electrical radiator has casing supporting element in casing with electrical insulation layer having high thermal conductivity - Google Patents

Abstract

The heater for an electrical radiator (11) has a tubular resistance element (13) forming a heat conductor with an electrical insulation and a self supporting casing. The casing extends over the full length of the heating conductor. The casing can be enclosed in a layer of electrical insulation. The electrical insulation can have a high thermal conductivity.

Description

Heating element The present invention relates to a heating element such

it

  is also used in electric heaters.

  These heating elements contain a tubular armored resistor, having a heating conductor and a shield, the shield is composed of an electrical insulation and a self-supporting envelope and whose envelope extends

  over the entire length of the heating body.

  Such heating elements can be placed inside

  laughing for example of an electric radiator. The heating element is heated by an electric current which flows to

  through the heating conductor. The heating conductor

  ge heats up due to its electrical resistance. It is brought up to temperatures in which it emits energy in the form of radiation, especially in the infrared band and in the visible near the infrared band. The heat emitted is transferred from the heating conductor through the electrical insulation to an envelope. From the envelope it is transmitted for example to ambient air or to any other medium which must be heated while being isolated

  electrically from the heating conductor.

  - 2 - Such heating elements are used for example in electric radiators in which the body of the radiator frames with its carcass the heating element. The carcass

  has an air inlet and an air outlet. Inside

  laughing carcass is placed the heating element. A convective air current is created inside the carcass of the heat transmitted from the heating element to

  the ambient air contained in the carcass. The hot air has

  dence to mount inside the carcass and therefore to exit by the air outlet. Cold air is sucked through the air inlet, this air inlet sucks the cold air from the room to be heated. In general, the carcass of such an electric radiator is made of metal, in order to improve the transfer of thermal energy from the radiator to the ambient air.

  A problem with such heating elements in use

  tion especially with electric radiators is linked to the fact that especially in rooms with a high humidity of air or in rooms where there can be projection of water to the heating element, no defect or no

  Damage to the electrical insulation of the heating element

  Lant is not eligible. There is a certain risk of electric current passing between the heating conductor and the enclosure through the electrical insulation. The envelope is generally metallic and is in contact with the

  radiator casing, itself made of metal material-

  lique, therefore conductive of electricity. Consequently, it is possible that the envelope and / or the carcass is at a non-zero electrical potential and therefore the electrical discharge through a body or a person even briefly in contact with the radiator or with the envelope of the shielded conductor. -3- is possible. This kind of exposure to humidity is found, for example, when using electric heaters in bathrooms. This risk is partially great if the air humidity is high or if there is a possibility of water contact with the screened resistor. This is why in many standards for electrical equipment it is

  prescribes that an electrical appliance used under these conditions

  there, has two independent electrical insulations

  your ie either class II.

  The object of the invention is therefore to create a heating element

  phant using electrical current suitable for use in

wet rooms.

  The object of the invention is completed by a heating element

according to the invention.

  Such a heating element being especially intended for use in electric heaters comprises a tubular armored resistor. The tubular armored resistor has a heating conductor and a shield. The shielding is composed of electrical insulation and a preferably self-supporting envelope. The envelope is generally made up of metallic material. It extends over the entire length of the tubular conductor. To complete the goal of

  invention, the envelope is surrounded by a layer of insulation

electric tion.

  This layer of electrical insulation prevents contact with the envelope itself being possible. There is a second element of electrical insulation which is independent and external with respect to the shielding of the heating conductor. - 4 -

  According to an advantageous variant, the electrical insulation layer

  outer body is made of a material having

  the highest possible thermal conductivity.

  In addition, it may be advantageous to additionally wrap the electrical insulation layer with a heat radiation element. Advantageously, this heat radiation element is composed of a metallic material, particularly aluminum. According to an advantageous embodiment of the invention, the insulation layer is a solid body, particularly

composed of vermiculite.

  An advantageous embodiment of the invention provides that the electrical insulation layer is of such a thickness that the dielectric strength is greater than 4 kW for a

15 mA current.

  Another advantageous embodiment of the invention provides that the armored tubular conductor comprises rectilinear sectors, parallel to one another, of a length significantly greater than the diameter

  of the armored tubular conductor. Between two straight sectors

  neighboring lines, the electrical insulation layer includes

connecting bridges.

  The insulation layer can consist of two half

  shells manufactured and connected together, the connection of the two half-shells being carried out in an electrically insulating manner and the half-shells having a housing for

receive the armored resistance.

  -5- According to an alternative embodiment, the insulation layer consists of a body in one piece coating

  the armored resistance envelope.

  According to one embodiment of a radiation element enro-

  bant the insulation layer, this radiation element of

  heat is poured over the insulation layer.

  The foregoing and other features

  ticks are contained in the description and drawings. The

  characteristics-can be taken alone or in combination

  sound of several of them and contained in an embodiment of the invention and present advantageous embodiments of an invention for which protection is claimed.

  A description of the invention is given during the

  description below as a purely indicative example and

  not limiting. Reference is made to the accompanying drawings, of which: FIG. 1 shows a partial section of an electric radiator having a heating element according to the invention, FIG. 2

  shows a partial section through a heating element

  fant according to the invention having an armored resistance and external thermal insulation, and Figures 3a, 3b show the view and a partial section through a layer

insulation according to the invention.

- 6 -

  Figure 1 shows a rear view of an electric radiator

  stick having a heating element according to the invention. The

  electric radiator it has a carcass 12 inside

  eur of which the heating element 13 is disposed. In order to allow good distribution of the heat from the heating element to the room to be heated, the electric radiator It has air outlets 14. These air outlets 14 are arranged at the top of the electric radiator, in order to allow a good output of the convection current generated by the electrical element. At the bottom of the carcass 12 are arranged the air inlets 15. One of the air inlets 15 is located opposite the position of the heating element 13 and extends over most of the rear side of the carcass. 12. The rear side of the carcass 12 is turned in the case of an electric radiator fixed on a wall towards this wall. The opening which extends over a large part of the housing allows an easily achievable fixing of the radiator on a wall or on another fixing element. Typically these are fixed brackets or hooks on a wall or other item

plane arranged vertically.

  Generally the frame 12 of an electric heater 11

  is made of metallic material. This metal material-

  as a general rule, it is brought into contact with the heating element 13 in order to allow good transmission of heat from the heating element 13 to the carcass 12, which enlarges the heat exchange surface between the radiator

it and the surrounding air.

  Figure 2 shows in partial section the front view of a

  heating element according to the invention.

-7

  The heating element is composed of a shielded resistor 16.

  Ia shielded resistance ends in fittings 17. From fittings 17 to the voltage source mixes an appropriately insulated electrical cable. The electric cable often leads to an electrical connection socket, a voltage source which generally has a level of

  alternating voltage of 220 - 240 V at a frequency of 50 Hz.

  The screened resistor is made up of the heating conductor 18 and a screen 19. The screen 19 is made up of electrical insulation 20 and the casing 21. The casing is generally made up of metallic material, for example stainless steel. The electrical insulation is often composed of a vacuum or a ceramic or magnesia material. It must be a material with high resistance

  electric and with resistance to nearby temperatures

  at 1000 degrees Celsius. The enclosure 21 is made of rigid and self-supporting material. The armored resistor is surrounded by a layer of electrical insulation 22. The layer

  of electrical insulation is for example composed of vermicu-

  lite. In any case it is a material that can serve as electrical insulation and at the same time having as high thermal conductivity as possible. In order to

  have sufficient electrical insulation to satisfy

  to comply with the protection standards for "Class II" electrical devices, that is to say those that can be used in humid rooms or rooms where there may be water splashes, it will be necessary that the resistance of isolation

  ] electric is greater than 4 kV, at a current of 15 mA.

  The vermiculite layer can be obtained by molding as well as by pressing or dipping. It then constitutes a monolithic body enveloping the armored resistance. It is also possible that the electrical insulation layer is prefabricated in the form of two semi-shells 28, a pair

  of semi-shells 28 forming the layer of electrical insulation

  cudgel. The two shells are then linked together by

  electrically insulating material.

  As an alternative, the electrical insulation layer 22 can be obtained by a liquid or pasty mixture other than

  metallic and whose solidification is obtained by reticu-

  lation, polymerization or vulcanization according to its own physical or chemical nature. The important thing is that a layer of electrical insulation covering the armored resistance is created.

  The shielded resistor 16 according to FIG. 2 has several

  siil rectilinear sectors 23 which are parallel to each other. They are connected to each other by a curved sector, particularly in a semi-arc. Looked down its entire length,

  the armored resistor is inside the heating element

  fant arranged in the form of meanders.

  It is possible, but not necessary, that for the purpose of an agri-

  When the contact surface is smoothed and the material of the electrical insulation layer minimized, oblong holes 24 are provided in the insulation layer. These oblong holes 24 are arranged so that the layer

  cd 'insulation 22 at any point of the armored resistance pre-

  feels a thickness that is greater than the minimum thickness required. The required thickness of the insulation layer is

  mainly determined by its dielectric strength.

  In order to have greater mechanical rigidity of the heating element it is possible to provide bridges of -9

  connection 25 between two rectilinear sectors 23 neighboring pa-

  rally to each other. These connecting bridges 25 are

  consisting of the material of the insulation layer 22 and aug-

  especially lie the stability against torsion and the? between the straight sectors. The connecting bridges 25 separate

the oblong holes.

  In addition it is possible to provide an element 26 of radiation

  of heat that surrounds and coats the electrical insulation layer

  stick 20. This radiation layer 26 is for example made

  in metallic material, particularly aluminum.

  If the heat resistance of the material of the insulating layer is sufficiently high, an easy way to produce the radiation element 26 in metallic material is to pour it around the electrical insulation layer 22. In this way there , the radiation layer 26 is

  directly adjacent to the electrical insulation layer 22.

  Good protection against the penetration of foreign bodies and against shocks or other external influence of the insulation layer, which for example in the case of use

  of vermiculite does not show great resistance to

  mechanical marks, is clearly improved. In addition, a radiation element 26 can improve the transfer of thermal energy to the ambient air. This radiation element 26 can be in contact or connected with the frame 12 of the electric radiator. Because of its thermal conductivity, the surface of the heater which is used for

  transferring the heat to the ambient air is clearly increased

die.

  In addition, it is possible to adjust according to the characteristics

  desired behavioral behavior, the thermal inertia of the heating element by increasing the thickness of

- 10 -

  the electrical insulation layer and the radiant element

  tion. The thicker they are, the greater the thermal interior of the assembly and therefore the short temperature variations are balanced. A little thermal inertia is sooner desired for auxiliary heaters, heating

  quickly, but not having great temporal stability.

  Your figures 3a and 3b show a front view and a partial side section through a half-shell which can be

  used as an electrical insulation layer 22.

  Figure 3a shows the front view of the half-shell while

  that figure 3b shows the section through the two half

  shells together forming the electrical insulation layer 22. The half-shell 28 is made of insulating material. It is for example Vermiculite. The half-shell includes a

  housing 29 intended to receive armored resistance 16.

  Corresponding to the shape of the armored resistor 16, the housing 29 comprises rectilinear sectors 23 interconnected by half-arcs 30 so as to form a sort of meander inside which the armored resistor 16 can be housed. In order to take into account the thermal expansion of the armored resistor 16 the half-arcs 30 are not formed so as to juxtapose the corresponding part of the armored resistor, but to allow thermal expansion

by having a certain game.

  In order to minimize the insulating material required to form the

  insulation layer, it is possible to provide holes

  long 24 in the areas between the straight sectors 23. However, it must be ensured that the insulation layer

- he -

  in any location at least as large as the minimum layer required. The oblong holes present at the same time

  the advantage of enlarging the exchange area between the ambient air

  ant and the insulation or the radiation layer 26 surrounding the

insulation layer 22.

  In order to increase the stability and in order to have a greater rigidity of the insulation body, it is useful to provide in the straight sectors 23 connecting bridges 25 which

  connect neighboring rectilinear sectors.

  Half-shells as shown in the figures

  3a and 3b can be prefabricated, for example by molding.

  A one-piece insulation layer can be made by molding, pressing, or dipping. Obviously pressing or dipping can be used in the same way to make a half-shell intended to form half of a

insulation layer.

Claims (5)

claims:   1. Heating element especially intended for use in electric radiators, with a tubular armored resistance, comprising a heating conductor and a shield comprising an electrical insulation and a preferably self-supporting envelope, including the envelope   extends over the entire length of the heating conductor   fage, characterized in that the envelope (21) is   tour of an electrical insulation layer (22).   2. Heating element according to claim 1, characterized in that the electrical insulation layer (22) consists of a material having a conductivity as high as possible.   Heating element according to one of the preceding claims.   teeth, characterized in that the electrically insulating layer is surrounded by a radiation element of heat (26).   4. Heating element according to claim 3, characterized in that the heat radiating element (26) is composed of a metallic material, particularly aluminum. -3 -   J. EIémernt heating according to any one of the claims   above, characterized in that the insulating layer (22) is a solid body, particularly consists of vermiculite.   Heating element according to any one of the claims   previous tions, characterized in that the thickness of the electrical insulation layer (22) is chosen such that the electrical insulation resistance is greater at 4 kV for a current of 15 mA.   7. Heating element according to any one of the claims.   tions above, characterized in that the armored resistor (16) comprises rectilinear sectors (23), parallel to one another and of a length significantly greater than the diameter of the armored resistor (16), o in addition in the surrounding of straight sectors (23) the electrical insulation layer forms connecting bridges (25) between two   neighboring rectilinear sectors (23).   Heating element according to any of the claims   above, characterized in that the insulation layer (22) consists of two half-shells   (28) prefabricated and interconnected, the half   shells (28) having a housing (29) for the armored resistance, the assembly of the two half-shells   (28) being produced in an electrically insulating manner.   9. Heating element according to any one of the claims.   tions] to 7, characterized in that the insulation layer   (22) is a single piece body encasing the envelope eg armored resistance.   ] (. Elëmernt chliauffante according to one] lconque of the claims-   tions 3 to 9, characterized in that the heat radiating element (26) is cast around the insulation layer and preferably composed of a metallic material.