FR2683026A1 - ELECTRIC HEATING APPARATUS WITH ENAMELLED CANVAS HEATING ELEMENT AND TEMPERATURE COMPENSATED RESISTIVE TRACK. - Google Patents

Abstract

Electric heating device comprising a heating element (1) consisting of at least one enameled sheet bearing on one of its faces a resistive track (2) produced by screen printing and mounted in an enclosure comprising, near the heating element, an input d 'fresh air (30) at its lower part and a hot air outlet (31) at its upper part, the heating element being mounted in the enclosure by means of supports (28, 29), at least one of these supports (29) being placed in the path of the hot outlet air and creating temperature peaks of the air outlet which bypasses it, characterized in that the heating element comprises directly above each disturbing support, a zone (7) with reduced heating to compensate for the temperature peaks caused by the presence of the support (29).

Description

The present invention relates to electric heaters and is

  relates more particularly to electric heaters comprising an enclosure in which is mounted at least one heating element constituted by an enamelled sheet on which is

  formed by screen printing a resistive track.

  In accordance with the new standards for electric heaters, an enameled sheet heating element of the aforementioned type must, when it is placed vertically, have a uniform temperature in

  any point on the surface of the sheet.

  This temperature uniformity is generally obtained by varying the pitch between the horizontal parallel sections of the resistive track, making it possible to obtain temperature uniformity on the plate.

arranged vertically.

  Furthermore, it is necessary that an electric convector provided with a heating element in enamelled sheet metal with a resistive track obtained by screen printing has a uniform temperature rise over the whole extent.

from the air outlet of the device.

  In known devices with heating elements

  enamelled sheet metal with resistive tracks obtained by serial

  written, the enamelled sheets are mounted in the bodies-

  series of devices by means of supports, some of which are in the path of the air leaving the device and thereby create disturbances in the flow of the

air outlet.

  These disturbances resulting in temperature peaks which compromise the regularity of the

  temperature of the air outlet of the device.

  The invention aims to remedy the drawbacks of known devices by creating a heating device

  electric which while being of a relative construction-

  simple, satisfies the conditions of temperature uniformity on the surface of the heating element and

  regularity of the temperature of the air outlet of the appliance

  reil imposed by the aforementioned standards.

  It therefore relates to an electric heating device comprising a heating element consisting of at least one enamelled sheet carrying on one of its faces a resistive track produced by screen printing and mounted in

  an enclosure comprising near the heating element

  fant, a fresh air inlet at its bottom and a hot air outlet at its top, the element

  heater being mounted in the enclosure by means of

  ports, at least one of these supports being placed in the path of the hot outlet air and creating ridges of

  temperature of the air outlet which bypasses it, characteristic

  risé in that the heating element comprises at the base of each disturbing support, a zone with heating

  reduced compensation for temperature peaks provo-

quées by the presence of the support.

  The invention will be better understood using the

  description which follows, given only as

  example and made with reference to the accompanying drawings, in which: FIG. 1 is an elevation view of a heating element with conventional enameled sheet for an electric heating appliance; Fig 2 is a plan view of a first embodiment of enamelled sheet heating elements according to the invention; Fig 3 is a plan view of a second embodiment of enamelled sheet heating elements according to the invention; Fig 4 is a plan view of a variant of the enameled sheet heating element of Fig 3; Fig 5 is a schematic sectional view of an electric heater comprising a heating element with enamelled sheet according to the invention; Figs 6 and 7 schematically show enamelled sheet heating elements designed respectively to be supported by two and three intermediate supports; FIG. 8 is a curve representing the air outlet temperature of an electric heater with a conventional enameled sheet heating element; and Fig 9 is a curve corresponding to that of Fig 8 for an electric heater whose heating element is provided with compensation means

according to the invention.

  The conventional heating element shown in FIG. 1 essentially comprises a sheet 1 of enamelled sheet on one of the faces of which a resistive track 2 is formed by screen printing, formed for example of an alloy of silver and lead or of aluminum, whose successive sections 3 extend horizontally along the large dimension of the sheet 1 and are interconnected by short vertical sections 4 disposed at both ends

sheet metal 1.

  In the lower left corner of the sheet 1, looking at FIG. 1, at least two connection terminals for the heating element thus formed are provided.

  supply terminals for the electric heater

  fant. Along the long sides of the sheet 1 are indicated by marks 6, locations of supports

  intended to ensure the mounting of the sheet in the coach-

  of an electric heater.

  So that the temperature delivered by the heating element of Fig 1 is regular over its entire height when it is mounted vertically, the distance or not between the track sections 3 is made variable On

  seen in Fig 1, starting from the bottom of the heating element

  fant that the density of the sections of runway 3 is decreasing

  health from the bottom to the top of the heating element. Thus, the zones of the sheet metal located higher and which benefit from the heating which they receive from the zones of the sheet metal located below, receive less heat from their own sections of track due

  greater distances between them.

  The heating element according to the invention represents

  shown in Fig 2 also includes an enamelled sheet 1

  on which a resistive track is deposited by screen printing

  tive 2 whose successive sections 3 extend horizontally-

  and have a decreasing density from the bottom

to the top of the item.

  On this element, reference numerals 6 also indicate the mounting mounting locations of the element inside the body of a

electric heater.

  We see in Fig 2 that these locations are six in number, two locations of support elements at each end of the sheet 1 and two intermediate locations 6, one at the bottom of the element

  and the other at the top of it

  cement 6 upper intermediate, must be placed a fixing support which will be on the path of the outlet air from the electric heater and which

  will create temperature peaks at this location.

  In order to compensate for these temperature peaks, the heating element 1 according to the invention comprises, directly above the intermediate location 6, a zone 7 devoid of a resistive track, obtained by bypassing

  of its perimeter by the resistive track 2.

  For this purpose, the resistive track 2 of the heating element comprises a first lower part 8 in which the horizontal sections 3 of the resistive track extend almost over the entire large dimension of the heating element 1 This lower part 8 is extended upwards by a first upper part 9 whose sections of resistive tracks 10 also extend horizontally but only between an edge of the zone 7 devoid of resistive track and a first edge

end 11 of the sheet 1.

  A third upper part 12 disposed on the other side of the area devoid of resistive tracks 7 comprises horizontal track sections 13, extending between the other edge of the area 7 devoid of track and the

  end edge 14 of the sheet 1 opposite the edge 11.

  It can therefore be seen that such an arrangement makes it possible to obtain

  nir a zone 7 devoid of a resistive track, surrounded by

  the resistive track 2 of the heating element.

  In order to prevent the upper horizontal section 3 of the heating element from causing excessively high temperature rise in the area devoid of track 7 due to its local resistance, this upper section 3 is at the base of the area 7, a portion 15 of increased surface and therefore of reduced resistance allowing the connection between the first and second upper track portions 9 and 12, while ensuring the maintenance of the zone 7 at a temperature below

rest of the heating element.

  In the example which has just been described, the cross section of the resistive track is constant

  except for region 15 of reduced resistance.

  The heating element shown in Fig 3 is

  an architecture similar to that of the heating element

fant of Fig 1.

  Its resistive track 16 also has horizontal sections 17 of decreasing density from the bottom

to the top of the item.

  However, this resistive track differs from that of the heating element in FIG. 1 in that each horizontal track section 17 comprises two lateral parts 17 a, 17 b of increasing section starting from each end edge of the element. heating towards the middle of it and joined by an area 18 of increased section which defines with the areas of increased section 18 of the

  other sections of runway 17, a region of lesser heat

  Fement 19 located directly above the locations 6 intended to receive high and low intermediate supports (not shown). Thanks to such an arrangement, there is on the one hand a progressive decrease in the resistance and therefore in the heating capacity from the end edges of the heating element towards the center of it and on the other share a sudden decrease in heating to

  the location of the zones 18 of increased section.

  The heating element shown in FIG. 4 is of a construction very similar to that of the heating element in FIG. 3 It indeed has a resistive track 20 formed by screen printing on one of its faces and which presents, like the track 16 of the heating element of FIG. 3, horizontal sections of track 21 formed from lateral portions 21 a, 21 b of increasing section from the end edges of the heating element towards

the middle of it.

  The heating element in Fig 4 differs, however.

  dant of that of Fig 3 in that the lateral portions 21 a, 21 b of each of the sections 21 of the resistive track, are joined together without interposition of a zone of

increased section.

  Thus, the temperature compensation is obtained in a central zone 22 of the heating element, simply by a progressive reduction of the resistance and consequently of the heating capacity from the ends of the heating element towards the middle of it. this. In Fig 5, there is shown schematically and in section, an electric heater according to one invention comprising a body 25 of sheet metal constituted by a double walled hollow element facing the flat core 26 of which is mounted an element heater 1 according to the invention, fixed to inclined parts 27 of the body 25 extending on either side of the core 26, by means of lower supports 28 and upper supports

  29 in electrically and thermally insulating material.

  The electric heater presented schematically in Fig 5 is observed at the locations of the supports 28, 29 arranged in the intermediate zone of a heating element such as that of Fig 2. The electric heater further comprises a fresh air inlet 30 at its bottom and hot air outlet 31 at its top The sections 3 of the resistive track are shown for clarity by reliefs of exaggerated thickness Zone 7

  devoid of a resistive track thus appears clearly above

under the support 29.

  A grid 32 is also attached to the supports.

upper ports 29.

  It can therefore be seen that the upper support disposed in the intermediate zone of the heating element 29 is located on the path of the air outlet of the heating appliance represented by arrows F The body of the support 29 constitutes an obstacle to the free movement of

air to the outlet of the device.

  The ascending hot air tends to accumulate at the base of the support 29 and to create a temperature zone

  increased The air which bypasses the support, heats up more

  tage that the air which leaves directly by the air outlet 31 without encountering any obstacle and therefore forms at the outlet temperature peaks which compromise the uniformity of the

  air outlet temperature (Fig 8).

  The zone 7 devoid of a resistive track of the heating element of FIG. 3 disposed directly above the support 29, makes it possible, thanks to a localized reduction in heating, to avoid the formation of an overheated pocket at the base of the support located at the -above this zone 7 and thus provides temperature compensation for the air which

bypasses the support.

  Thus, a roughly uniform temperature is obtained over the entire horizontal extent of the outlet.

hot air 31 (Fig 9).

  In Figs 6 and 7, there is shown schematically-

  two heating elements with resistive tracks 32 and 33

  respectively, of length greater than that of the elements

  heating elements of Fig 2 to 4 and which are intended to be

  attached to the locations designated by the reference numbers

  6, in bodies of electric heating devices

  greater length by means of four lower supports and four upper supports for the element of Fig 6 and five lower supports and five supports

  for the element in Fig 7.

  The heating element of Fig 6 is therefore intended to be fixed to the body of the electric heating appliance which it must equip by two supports arranged at each of

  its lateral ends and by four intermediate supports

  To ensure compensation for overheating

  of the air outlet due to the presence of the intermediate supports

  diaries, the heating element of Fig 6 has at

  vertical to the locations 6 of the two intermediate supports

  upper res, two zones 35, 36 with reduced heating produced by bypassings by the resistive track in a similar manner to that described with reference to the

Fig 2.

  The heating element of FIG. 7 is intended to be supported by three sets of intermediate supports at the upper locations 6 of which are associated zones with reduced overheating 37, 38, 39 produced by bypassing in a manner analogous to that described in

reference to Fig 2 and 6.

  The heating element of FIG. 6, comprises in the zone with reduced heating 35, a region 40 more

  large section intended to connect without causing electricity

  temperature, the right part of the track

  resistive with its intermediate part.

  The heating element of FIG. 7 comprises a first zone of increased section 41 intended to ensure the connection of the right part of the resistive track with one end of the intermediate part thereof situated on one side of the central zone. 38 warm up

  reduced and a second zone of increased cross section 42 of conne-

  xion of the left part of the resistive track with the other end of the intermediate part thereof

  located on the other side of the central area 38.

  Fig 8 shows the temperature curve of the air outlet of an electric heating appliance

  equipped with a heating element with three intermediate supports

  diaries, lacking means for compensating for the overheating

  localized due to the presence of intermediary media

res.

  We have plotted on the abscissa of the graph of the

  Fig 8, the length L of the heating element and in order-

born the temperature t.

  It can be seen that at the locations of the supports such as the support 29 of the device shown diagrammatically in FIG. 5, the temperature curve of the air outlet, the maximum value of which is slightly less than 125, has temperature peaks C1 , C 2 which result from the excessive heating of the air which bypasses each of the supports 29. FIG. 9 represents a temperature curve

  of the air outlet of a device with three intermediate supports

  diaries but compensated in temperature by the presence on the heating element of regions of least heating, such as regions 37,38,39 of the element represented

schematically in Fig 7.

  We see that the air outlet temperature is established almost uniformly, slightly below

  of 1240 C and that the presence of the zones of least heating

  firmly in line with the supports 29 eliminated the temperature peaks and thus ensured almost total compensation for irregularities in the outlet temperature

  air from the electric heater.

  It can be seen that, thanks to the arrangement which has just been described, electrical heating apparatuses are obtained with heating elements made of enamelled sheet metal with resistive tracks which meet almost perfectly the standards.

imposed on manufacturers.

  Such devices not only have a temperature-

  constant over their entire surface when arranged vertically, but also have a practically uniform air outlet temperature over

their entire length.

  In the examples which have just been described, the electric heaters were considered

  as comprising a single heating element made of enamel sheet-

  strip and resistive track obtained by screen printing provided with

  temperature compensation zones.

  One can also envisage the realization of such devices by associating two or more sheets there enamelled each carrying a resistive track, arranged on either side of intermediate supports, so that the temperature compensation of the heating due to the presence of these supports on the path of the air outlet is ensured by the pure and simple absence of the element

  heated above the support considered.

  It is then enough to interconnect elements

  consecutive heaters by simple electric conductors

  only appropriately sized to avoid any

warming up.

Claims (5)

  1 Electric heating appliance comprising a heating element (1) consisting of at least one enamelled sheet carrying on one of its faces a resistive track (2; 16; 20; 32; 33) produced by screen printing and mounted in an enclosure comprising nearby of the element   heating, a fresh air inlet (30) at its lower part   upper and a hot air outlet (31) at its upper part   lower, the heating element being mounted in the enclosure by means of supports (28,29), at least one of these supports (29) being placed on the path of the hot outlet air and creating temperature peaks of the air outlet which bypasses it, characterized in that the heating element comprises at the base of each disturbing support, a zone (7; 19; 22; 35, 36; 37, 38, 39) with reduced heating of compensation for temperature peaks caused by the presence of the support (29).   2 Electric heater according to   claim 1, characterized in that the area (7; 35.36; -   37,38,39) with reduced heating of the heating element is   a zone devoid of a resistive track, obtained by   turning of its perimeter by the resistive track (2; 32; 33). 3 An electric heating device according to claim 2, characterized in that the resistive track (2; 32; 33) has track portions (9,12) located on either side of each zone (7; 35; 36 ; 37,38,39) to   reduced heating, at least some of which are connected   tees between them by a portion of track (15; 40; 41,42) of reduced resistance located directly above the area (7; 35; 37, 39) corresponding.   4 An electric heating appliance according to claim 1, characterized in that the zone (19) with reduced heating is constituted by zones (18) of increased section of the resistive track joining between   them the lateral parts (17 a, 17 b) of horizontal sections   zontals (17) of the resistive track.   Electric heater according to   claim 4, characterized in that the lateral parts   the (17 a, 17 b) sections of hozizontal tracks (17)   are of increasing section from each edge of ex-   end of the heating element towards the middle of it.   6 electric heater according to claim 1, characterized in that the zone (22) with reduced heating is constituted by the direct joining of lateral portions (21a, 21b) of increasing section from the end edges of the heating element in the middle of it, of sections (21) of the track   resistive of said heating element.   7 electric heating device according to claim 1, characterized in that the heating element consists of at least two enamelled sheets each carrying a resistive track, arranged on either side   of a corresponding disruptive support.