FR2826711A1 - HEAT EXCHANGER, ESPECIALLY FOR AUTOMOTIVE VEHICLE AIR CONDITIONING DEVICES - Google Patents

Abstract

A heat exchanger for heating air comprising a plurality of tubes (10<u>a</u>, 10<u>b</u>) for circulating a heat-carrying fluid, a plurality of electric heating bars (30) having resistive elements disposed between the electrodes of the electricity supply, and a set of radiating elements (20) associated with the tubes and heating bars. The radiating elements are made up of crossed blades (20) with contact via the tubes (10<u>a</u>, 10<u>b</u>) and heating bars (30). The bars are engaged with constraint in the openings (28) of the blades in such a way that they can be kept in contact with the blades and in order to apply the electrodes with pressure against the resistive elements.

Description

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Background of the invention
The invention relates to a heat exchanger for heating air, in particular, but not exclusively, for an air conditioning device of a motor vehicle.

Traditionally, in a motor vehicle with a heat engine, the air heating for heating the passenger compartment, demisting or defrosting is provided by a heat exchanger through which the engine coolant flows.

More particularly with certain type of engine, a relatively long time may elapse between the starting of the engine and the moment when the coolant supplies the calories necessary for efficient heating of the air. This is all the more troublesome since, in very cold weather, the air conditioning system is required not only to quickly heat the passenger compartment, but also to ensure effective defrosting or demisting immediately after starting.

To remedy this drawback, it is known to add an electric heating device capable of supplying the required calories as soon as it is switched on. The operation of the electric heating device is interrupted when the calorie needs can be satisfied by the coolant, in this case the engine coolant. Such an electric heating device is commonly formed of electric heating bars associated with radiant elements and is arranged in the air circulation duct to be heated, downstream of the heat exchanger through which the engine coolant passes through. Heating rods generally have resistive elements formed from positive temperature coefficient (PTC) resistors which have the advantage of providing self-protection against excessive heating.

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The addition of such an electric heating device results in an increase in the size and cost of the air conditioning device, even when, for ease of assembly, it is pre-assembled with the liquid heat exchanger, as described in EP 0 919 409.

It has been proposed in document EP 0 857 922 A2 to integrate the additional electric heating into the liquid heat exchanger by replacing some of the pipes through which the heat transfer liquid passes by heating bars. Spacers interposed between the pipes or heating bars function as radiant elements located, with the pipes and heating bars, on the path of the air passing through the exchanger.

The efficiency of the exchanger is reduced when the electric heating is not in operation due to the inactive presence of the bars instead of pipes through which the heat transfer fluid passes. In addition, good heat transfer between the heating bars and the spacers is difficult to achieve.

Purpose and summary of the invention
The object of the invention is to reduce the cost and the bulk of an air heating assembly formed by a heat exchanger with heat transfer fluid and an electric heating device without however affecting its efficiency, whatever operating mode.

This goal is achieved by means of a heat exchanger for air heating comprising a plurality of pipes for the circulation of a heat transfer fluid, a plurality of electric heating bars having resistive elements arranged between electrical supply electrodes, and a set of radiant elements associated with the pipes and heating bars, exchanger in which the radiant elements are formed by fins crossed with contact by the pipes and the heating bars, the bars being engaged with constraint in openings of the heating fins. so as to be kept in close contact with the fins and to apply the electrodes with pressure against the resistive elements.

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The invention is remarkable in that the heating bars are integrated into the heat transfer fluid heat exchanger, sharing the same fins and without replacing the pipes through which the heat transfer fluid passes, while the electrical and thermal contact of the bars heating is provided by mounting under stress in openings of the fins. This results in a simple and compact structure, therefore low costs and bulk, with good heating efficiency.

Advantageously, the heat exchanger comprises at least one row of tubes and at least one row of heating bars, and the heating bars and the tubes located in two parallel rows are offset with respect to each other.

It is thus possible, in the available space, to move the heating bars away from the pipes as far as possible.

According to another feature of the exchanger, the heating bars are arranged downstream of the pipes in the direction of air flow to be heated through the exchanger. The possibility of a significant transfer of calories between the heating bars and the fluid passing through the pipes, when this fluid has a fairly low temperature, is therefore reduced.

The mounting of the heating bars in the openings of the fins can be carried out in different ways. Thus, the openings can be substantially L-shaped with two opposite sides forming resiliently deformable wings which extend substantially in the plane of the fins and between which the heating rods are constrained. As a variant, the openings of the fins through which the heating rods pass have flanges which are folded out of the plane of the fins and between which the heating rods are constrained to engage.

The heating bars can be made in different ways.

Thus, in one embodiment, each heating bar comprises a first, a second and a third electrodes in the form of conductive strips arranged parallel to each other, resistive elements arranged between the first electrode and a face of the second electrode, and elements

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resistives disposed between the other face of the second electrode and the third electrode, the first and third electrodes being in pressurized contact with two opposite sides of the openings formed in the fins.

In another embodiment, each heating rod comprises a first and a second electrode in the form of parallel conductive strips, resistive elements disposed between the first electrode and one face of the second electrode, and an insulator disposed on the other face. of the second electrode, the first electrode and the insulator being in pressurized contact with two opposite sides of the openings formed in the fins.

In yet another embodiment, the heating rods are housed in tubes constrained in the openings of the fins. The tube of a heating rod may constitute a first supply electrode, the other, or second, supply electrode being in the form of a conductive strip housed inside the tube while being separated from the wall of the tube, on one side by resistive elements and, on the other side, by resistive elements or an insulator.

Heat and electrically conductive parts can be interposed between the resistive elements and the side of the internal wall of the tube with which they are in electrical contact, said parts conforming to the shape of the internal wall of the tube.

The tubes of the heating rods may have a cross section of generally flattened or oval shape.

The tubes can be open over their entire length along a generatrix, which gives them an elastic deformation capacity, or can be closed. In the latter case, preferably, the tubes of the heating rods are applied with pressure against the edges of the openings in which they are engaged, and wedges are engaged in the tubes to exert a contact pressure between the resistive elements and the electrodes.

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The invention also relates to a motor vehicle air conditioning device provided with a heat exchanger as defined above.

Brief description of the drawings
The invention will be better understood on reading the description given below, by way of indication but not limiting, with reference to the appended drawings in which: FIG. 1 is a partial perspective view of a heat exchanger according to a first embodiment of the invention; - Figure 2 is a partial sectional view, on an enlarged scale, along the plane! -)) of Figure 1; - Figure 3 is a partial sectional view along the plane III-III of Figure 2; - Figure 4 is a partial plan view of a radiant element of the exchanger of Figures 1 to 3; - Figure 5 is a sectional view along the plane VV of Figure 4; FIG. 6 is a sectional view on an enlarged scale of an alternative embodiment of a heating bar for a heat exchanger such as that of FIGS. 1 to 5; - Figures 7A and 7B are partial plan views of alternative embodiments of a heat exchanger according to the invention; - Figure 8 is a partial sectional view of a second embodiment of a heat exchanger according to the invention; - Figure 9 is a partial view of a heating bar of the exchanger of Figure 8 before its integration into the heat exchanger; FIG. 10 is a view on an enlarged scale illustrating the engagement with constraint of a heating bar of the exchanger of FIG. 8; - Figure 11 is a partial view of an alternative embodiment of a heating bar for a heat exchanger similar to that of Figures 8 to 10;

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- Figure 12 is a sectional view of an alternative embodiment of the heat exchanger of Figure 8; - Figure 13 is a partial sectional view, on an enlarged scale, along the plane XIII-XIII of Figure 12; - Figure 14 is a sectional view of another alternative embodiment of the heat exchanger of Figure 8; - Figure 15 is a partial sectional view of another embodiment of a heat exchanger according to the invention; - Figure 16 is an enlarged scale view of a detail of Figure 15; and - Figure 17 is a partial exploded view of a heating bar of the exchanger of Figures 16 and 17.

Detailed description of embodiments of the invention
In the description which follows, we place ourselves within the scope of the application of the invention to the air conditioning devices of motor vehicles with thermal engines. The invention is not however limited to this application and can be used for any heating system combining a heat exchanger with circulation of coolant and an electric heating device.

A first embodiment of a heat exchanger according to the invention is illustrated by Figures 1 to 5.

It comprises an air / coolant heat exchanger with a row of conduits 10, intended to be traversed by a cooling liquid from a heat engine, and radiant elements 20 in the form of fins of generally rectangular shape crossed by the conduits. 10.

Each duct 10 comprises a first section 10a forming a rectilinear tube which passes through all of the fins 20, substantially perpendicularly thereto, and a second section 10b forming a rectilinear tube which similarly passes through all of the fins 20.

At a first end of the exchanger, the pipes 10a are connected in common to a manifold (not shown) for supplying the exchanger supplying the engine coolant from the engine and, at this same end of

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the exchanger, the pipes 10b are connected in common to an evacuation manifold (not shown) returning the cooling liquid to the engine.

At the second end of the exchanger, the pipes 10a and 10b are connected by elbows 10c, or pins.

This arrangement, well known, allows to have! The heat exchanger supply and discharge manifolds at the same end thereof, which makes it easier to fit into an air conditioning assembly. Another arrangement could of course be adopted according to which the supply and discharge manifolds are located at two opposite ends of the exchanger.

Furthermore, several rows of pipes 10 could be provided.

The fins 20 are formed by metal sheets, for example aluminum, arranged parallel to each other and leave between them spaces for the circulation of the air to be heated.

Cutouts are made in areas of the surface of the fins to form lamellae 22 which are deformed out of the plane of the fins to form louvers 24 (shown only in Figures 3 to 5) improving heat exchange with air crossing the interchange.

The tubes 10a, 10b are) ogées force in openings 26 made in the fins for the passage of the tubes (Figure 4). This can be achieved by engaging the pipes 10a, 10b by force in the openings 26 or by deformation by pressure inflation of the pipes 10 after their installation.

An air / liquid exchanger as described above is well known and commonly used in motor vehicle air conditioners.

According to the invention, heating rods 30 with electrical resistances are integrated into the heat exchanger by being engaged with constraint in additional openings 28 of the fins 20.

In the embodiment of Figures 1 to 3, the bars 30 comprise a stack formed of a first external electrode

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32a, resistive elements 34, a second internal electrode 36, resistive elements 38, and a third external electrode 32b.

The electrodes 32a, 36 and 32b are formed by metal strips, for example aluminum. They extend over the entire length of the heating bars and protrude at one end of the heat exchanger to form terminals 33a, 37, 33b for connection to an electrical supply circuit (not shown).

In each heating rod, several resistive elements 34 spaced apart from each other are interposed between the electrode 32a and one face of the electrode 36, and several resistive elements 38 spaced apart from each other are interposed between the other face of the electrode 36 and electrode 32b.

The resistive elements 34, 38 are, for example, resistors with a positive temperature coefficient in the form of parallelepipedal blocks or "stones".

The stack formed by the electrodes 32a, 36, 32b and the resistive elements 34, 38 is kept compressed by force-engaging the heating bar in the openings 28.

32a, 32b sont appliquées avec pression par leur face externe. As shown in Figures 3 and 4, the openings 28 have two opposite edges 28a, 28b against which the electrodes

32a, 32b are applied with pressure from their outer face.

bords 28a, 28b. The openings 28 are advantageously L-shaped so that the edges 28a, 28b form wings which can be elastically deformed during the engagement of a bar 30, while remaining substantially in the plane of the fin. The total thickness of the bar is chosen to be slightly greater than the width of the opening 28 between the

edges 28a, 28b.

, 28b.

In this way, pressure is exerted by the edges of the openings 28 on the bars 30. This engagement of the bars 30 with stress in the openings 28 guarantees good thermal contact between the bars 30 and the fins 20 and good electrical contact between the bars. resistive elements and electrodes.

The electrodes 32a, 32b in contact with the fins 20 are brought to the same potential, preferably the reference potential (ground), while the electrode 36 is brought to a positive potential during the operation of the electric heating.

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FIG. 6 shows an alternative embodiment of a heating bar 30 '. This comprises a stack formed of an external electrode 32 ′, resistive elements 34 ′, an internal electrode 36 ′ and an electrical insulator 39 ′ in the form of a strip. The electrode 36 'has one face in contact with the resistive elements 34' and the other face in contact with the strip 39 '. The electrodes 32 ′ and 36 ′ are in the form of metal strips, for example made of aluminum. The strip 39 ′ is made of an electrically insulating but thermally conductive material, for example alumina.

The bar 30 ′ is engaged with stress between the opposite edges 28a, 28b of openings 28 of the fins, which guarantees good thermal contact between the bar and the fins and good electrical contact between the resistive elements and the electrodes.

FIG. 3 shows that the pipes 10a, 10b and the bars -1, 1 Ob and the bars 30 form rows parallel to each other. The bars 30 have positions offset from those of the tubes 10 10J2, along the rows. In the example of FIG. 3, the pipes 10a 10b and bars 30 have, in section, a staggered arrangement. The offset between pipes and bars allows them to be separated as far as possible in the available space. This limits the transfer of calories between the bars and a fluid circulating in the pipes. Such a transfer would in fact be detrimental when the bars are in operation to compensate for an insufficient caloric intake by the fluid circulating in the pipes.

le tubulures, les barreaux 30 sont disposés en aval des tubulures 10a, 10b dans la direction (flèche F) d'écoulement de l'air à réchauffer à travers l'échangeur. In an alternative embodiment shown in FIG. 7A, and again with the aim of limiting the transfer of heat from the bars to

the pipes, the bars 30 are arranged downstream of the pipes 10a, 10b in the direction (arrow F) of flow of the air to be heated through the exchanger.

FIG. 78 illustrates an alternative embodiment similar to that of FIG. 7A, with two additional rows of pipes 10'a, 10'b.

Figures 8 to 11 show another embodiment of a heat exchanger according to the invention. This embodiment differs from that of Figures 1 to 5 by the realization of

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heating bars, the other elements being similar and being designated by the same references.

In the embodiment of FIGS. 8 to 10, the heating rods 130 comprise a longitudinally split tube 132 with a flattened section having an opening or slot 131 over the entire length of a generatrix in a part of the tube connecting two substantially plane parallel faces. opposites 132a, 132b.

Tube 132 encloses a feed electrode 136 in the form of a conductive strip extending the entire length of the tube. Resistive elements 134 are interposed between one face of electrode 136 and the internal wall of one of the flat faces (132a) of tube 132 while an insulating strip 137 is interposed between the other face of electrode 136 and the other flat face (132Q) of the tube 132. The tube 132 constitutes the other supply electrode for the resistive elements 134.

des parois 132a, 132b lorsque les lèvres 131a, 131b de l'ouverture 131 sont rapprochées. Before insertion into openings 28 of the fins 20, each tube 132 is slightly open (FIG. 9), the total thickness of the resistive elements 134, of the electrode 136 and of the insulator 137 being slightly greater than the distance measured between them. internal faces

walls 132a, 132b when the lips 131a, 131b of the opening 131 are brought together.

The dimensions of the tube 132 and of the openings 28 (FIG. 10) are chosen so that the engagement with constraint of the tube 132 between the edges 28a, 28b of the openings 28 causes the lips 131a, 131b to come together. In this way, an effective contact pressure is exerted to ensure good thermal transmission between the bar and the fins and good electrical contact between the resistive elements and the electrodes (see detail in FIG. 8).

FIG. 11 illustrates a variant embodiment of the heating bar 130. According to this variant, the tube 132 forming an electrode contains resistive elements 134 interposed between one face of the electrode 136 and the internal wall of one of the flat faces ( 132a) of the tube 132 and other resistive elements 138 interposed between the other face of the electrode 136 and the internal wall of the other flat face (132b) of the tube 132. There is an arrangement of resistive elements similar to that of the bar 30 of Figures 1 to 3.

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plan de l'ailette 20 (figure 13). Les rebords 128a, 128b appuient sur les faces planes opposées 132a, 132b du tube 132, ce qui assure un bon contact thermique entre le barreau 130 et l'ailette 20, ainsi qu'un bon contact électrique entre les éléments résistifs 134 et les électrodes 132, 136. Figures 12 and 13 illustrate an alternative embodiment of the heat exchanger of Figure 8 which differs from the latter in that the openings 128 of the fins 20 in which the tubes 132 are engaged have a shape corresponding to that tubes 132 with their slot 131 substantially closed. The openings 128 have flanges 128a, 128b folded back substantially perpendicular to the

plan of fin 20 (figure 13). The flanges 128a, 128b bear on the opposite flat faces 132a, 132b of the tube 132, which ensures good thermal contact between the bar 130 and the fin 20, as well as good electrical contact between the resistive elements 134 and the electrodes. 132, 136.

In the embodiment of FIG. 12 (as in that of FIG. 8), the substantially planar faces of the tubes 132 are parallel to the direction of flow (arrow F) of the air through the exchanger.

According to the variant illustrated in FIG. 14, these substantially planar faces can be inclined with respect to the direction of flow in order to promote heat exchange with the air. The fin apertures 128 are oriented correspondingly.

Figures 15 to 17 illustrate yet another embodiment of a heat exchanger according to the invention, which differs from that of Figure 8 by the embodiment of the heating bars.

As shown in Figures 15 and 16, the heating rods 230 are housed in closed tubes 232 with an oval or elliptical section. The bars are engaged in openings 228 of corresponding shape formed in the fins 20.

The tubes 232 are applied with pressure to the edges of the openings 228. For this purpose, in a manner known per se, the tubes may be deformed by inflation under pressure after engagement in the openings 228, so that intimate contact is established between the tubes 232 and the fins 20.

The tube 232 encloses a frame 240 in the form of a section extending longitudinally in the tube with edges 240a, 240b which substantially follow the shape of the wall of the tube in its opposite zones 232c, 232d of section having a smaller radius of curvature. The frame 240 is made of an electrically insulating material, for example of

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plastic and has housings 242 spaced from each other by dividing walls 244, or by ribs 246.

Resistive elements 234 are arranged in the housings 242 and are applied, on one side, to one side of a strip-shaped electrode 236, and, on the other side, to adaptation pieces 235 made of a material. electrical and thermal conductor, for example aluminum. The adaptation pieces 235 have a face 235b in contact with the resistive elements and an opposite face 235a in contact with a part of the internal wall of the tube 232 in a zone 232a of cross section with a greater radius of curvature, taking the shape of this part of internal wall.

One or more longitudinal shims 237 are interposed between the other face of the electrode 236 and the wall part of the tube 232 in a zone 232b opposite to the zone 232a. The wedge or wedges 237 have a face 237a in contact with the electrode 236 and an opposite face in contact with the internal wall of the tube by means of ribs 237b, the envelope of which conforms to the shape of this internal wall.

The wedges 237 are made of an electrically insulating material, for example alumina. They are inserted, after placing the frame 240 with the resistive elements 234, the adaptation parts 235 and the electrode 236, into the tube 232 previously engaged and blocked in the openings 238.

The wedges 237 have in section a dimension such that they are engaged in the tube 232 with stress, possibly with slight deformation of the ribs 237b, to exert a pressure promoting the electrical contact of the resistive elements 234 with the electrode 236 and the tube 232 forming an electrode (via the adapter pieces 235).

occupent par rapport aux tubulures 109., 10b., les mêmes positions que , 10b , les mêmes positions que sur la figure 3. On pourra bien entendu adopter une autre disposition, par exemple telle que celle de la figure 6. In figures 8,12, 14 and 15, the heating bars

occupy with respect to the pipes 109., 10b., the same positions as, 10b, the same positions as in FIG. 3. It is of course possible to adopt another arrangement, for example such as that of FIG. 6.

In the preceding examples, a single row of heating bars is provided, with a bar located opposite the gap between two pipes 10a or 10b of a row of.

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neighboring tubing. Of course, and in particular according to the needs for electric heating, the number of bars in a row could be different, not necessarily in relation to the number of pipes, and several rows of bars could be provided.

Claims (1)

CLAIMS 1. Heat exchanger for air heating comprising a plurality of pipes (10a, 10b) for the circulation of a heat transfer fluid, a plurality of electric heating bars (30; 30 '; 130; 230) having resistive elements arranged between electrical supply electrodes, and a set of radiating elements (20) associated with the pipes and heating bars, characterized in that the radiant elements are formed by fins (20) crossed with contact by the pipes (10 10Q) 12) and the heating rods (30; 30 '; 130; 230), the rods being constrainedly engaged in openings (28; 128; 228) of the fins so as to be kept in close contact with the fins and to apply the electrodes with pressure against the resistive elements. 2. Heat exchanger according to claim 1, comprising at least one row of pipes and at least one row of heating rods, characterized in that the heating rods (30; 130) and the pipes (10a, 10Q) located in two parallel rows are offset from each other. 3. Heat exchanger according to any one of claims 1 and 2, characterized in that the heating bars are arranged downstream of the pipes in the direction (F) of air flow to be heated through the exchanger. 4. Heat exchanger according to any one of claims 1 to 3, characterized in that the openings (28) of the fins (20) through which the heating bars (30; 30 '; 130) pass

have substantially an I-shape with two opposite sides (28 28Q), 2812) forming elastically deformable wings which extend substantially in the plane of the fins and between which the heating rods are constrained to engage. 5. Heat exchanger according to any one of claims 1 to 3, characterized in that the openings (128) of the fins (20) through which the heating bars (130) have

flanges (128a flanges (128a, 128b) folded out of the plane of the fins between which the heating rods are constrained. <Desc / Clms Page number 15> 6. Heat exchanger according to any one of claims 1 to 5, characterized in that each heating bar (30) comprises a first, a second and a third electrodes (32a, 36, 32b) in the form of conductive strips arranged parallel to each other, resistive elements (34) disposed between the first electrode and one face of the second electrode, and resistive elements (38) disposed between the other face of the second electrode and the third electrode, the first and the third electrode being in pressurized contact with two opposite sides of the openings (28) formed in the fins (20). 7. Heat exchanger according to any one of claims 1 to 5, characterized in that each heating bar (30 ') comprises a first and a second electrodes (32', 36 ') in the form of parallel conductive strips, resistive elements (34 ') disposed between the first electrode and one face of the second electrode, and an insulator (39') disposed on the other face of the second electrode, the first electrode and the insulator being in pressurized contact with two opposite sides of the openings formed in the fins. 8. Heat exchanger according to any one of claims 1 to 7, characterized in that the heating bars (130; 230) are housed in tubes (132; 232) held with constraint in the openings of the fins (20). . 9. Heat exchanger according to claim 8, characterized in that the tube (132; 232) of a heating rod (130; 230) constitutes a first supply electrode, the other, or second, electrode. the feed being in the form of a conductive strip (136; 236) housed inside the tube. 10. Heat exchanger according to claim 9, characterized in that the resistive elements (134; 234) are arranged between one face of the second electrode (136; 236) and a first side of the inner wall of the tube (132; 232). ), an insulator (137; 237) being interposed between the other face of the second electrode and the side of the internal wall of the tube opposite to the first side. 11. Heat exchanger according to claim 9, characterized in that resistive elements (134,138) are interposed <Desc / Clms Page number 16> between each face of the second electrode (136) and opposite sides of the inner wall of the tube (132). 12. Heat exchanger according to any one of claims 9 and 10, characterized in that parts (235) conductive of heat and electricity are interposed between the resistive elements (234) and the side of the internal wall. of the tube (232) with which they are in electrical contact, said parts conforming to the shape of the internal wall of the tube. 13. Heat exchanger according to any one of claims 8 to 12, characterized in that the tubes (132) of the heating rods (130) have a cross section of flattened shape. 14. Heat exchanger according to any one of claims 8 to 12, characterized in that the tubes (232) of the heating rods (230) have a cross section of oval shape. 15. Heat exchanger according to any one of claims 8 to 14, characterized in that the tubes (132) of the heating rods (130) are open over their entire length along a generator. 16. Heat exchanger according to any one of claims 8 to 14, characterized in that the tubes (232) of the heating bars (230) are closed and are applied with pressure against the edges of the openings (228) in which they. are engaged, and wedges (237) are engaged in the tubes to exert contact pressure between the resistive elements (234) and the electrodes (232,236). 17. Motor vehicle air conditioning device, characterized in that it comprises a heat exchanger according to any one of claims 1 to 16.