DE3708056A1 - Heating element for heating flowing media - Google Patents

Abstract

The heating element for heating flowing media contains as heat exchanger a metal body consisting of several individual bodies (1, 2). The individual bodies exhibit many openings (3), which are expanded conically on the intake side. PTC elements (11), which serve for heating, are installed between the individual bodies. These PTC elements (11) are encapsulated with a plastic layer (14), from which the cross pieces (4, 6) are also made, which serve for mechanical fixation of the individual bodies (1, 2). When the heating element is installed in a pipe, the annular cover (7) acts as thermal and electrical insulation, because the individual bodies (1, 2) also serve to supply current to the PTC elements (11). <IMAGE>

Description

The invention relates to a heating element for heating flowing Media in which the heat exchanger is made of a good heat conductor Metal, in particular from aluminum or copper or from alloy with a high proportion of these metals existing, with rules moderately arranged, slightly ko in the direction of flow nically tapered through openings provided with metal body serves in which the volume of all between the passage openings of parts of the metal body are the same or is greater than the volume of all through openings, the Metal body with disc-shaped, ceramic PTC thermistors (PTC- Resistors) is heated on part of the surface of the metal body with thermally and electrically conductive art glue are attached.

It is known to use a ceramic thermistor as a heating element, also called PTC resistor. There is a PTC thermistor made of doped polycrystalline ceramic material with perovskite structure structure based on barium titanate, its essential properties the interaction of semiconductors and ferroelectricity is. As a result of this property results in a certain temperature range a pronounced positive temperature co efficient of resistance. From a certain temperature, the Curie temperature, which depends on the chemical composition of the Ti tanate ceramics, the resistance rises almost by leaps and bounds by some powers of ten.

If a current flows through the PTC thermistor, the heating occurs until it reaches Curie temperature, then due to the skyrocketing resistance, hardly from To be flowed through electricity and therefore energy to sta bilize. As soon as the PTC thermistor is cooled, it can be used again be flowed through by electricity and heat up again (self stabilization). This makes a PTC thermistor particularly suitable as  Self-regulating heating element. Overheating and follow Lich destruction of such a heating element is thus out closed.

As already mentioned, the maximum temperature of the heating element can be specifically adjusted via the material composition. Temperatures of up to 320 ° C can currently be achieved.

As a rule, PTC thermistors are thinner than slices or in the form Plates made on which gros on two opposite Metal electrodes with no barrier layer are applied those who, as is well known, e.g. predominantly silver or Contain nickel.

It is known and to be noted that the PTC thermistor ceramic is especially important in the surface area in connection with the metal electrodes a pronounced sensitivity to certain external influences has, because only by a targeted metal coating, at the the barrier layer between the semiconducting thermistor rial and the metallic electrode material is degraded or does not arise, the PTC effect is effective. This metal coating tion must therefore, just like the ceramic body itself, be damaged influences are preserved.

The use of PTC thermistors to heat up flowing media is known. So in DE-PS 28 04 818 is an electrical Heating device described, especially for beverage preparation machines whose heating effect is based on the use of PTC Heating elements based, these heating elements through deposits Made of electrically insulating and good heat-conducting material are insulated from heating plate segments and free space me between adjacent heating plate segments with an elec Filled insulating and good heat-conductive filling compound could be.

From DE-OS 28 04 749 or DE-PS 28 04 749 is a through known heater, the heating elements of PTC ceramic be stand and its heat exchanger from itself to one essentially  Lichen cylindrical arrangement of complementary cylinder sectors is built up, the cylinder sectors by a cylinder jacket are braced around the circumference and the heating elements between facing surfaces of neighboring zy lindersectors are arranged and by the pressure on the cylin sectors are pressed.

An electrically insulating but good heat-conducting connection between the heating element and the cylinder sector achieve is located between the heating element and the cylinder an alumina ceramic. Possibly existing intermediate spaces that are not filled by the aluminum oxide ceramic are with a thermally conductive and electrically isolate the filling compound, such as silicone rubber, cast around.

An air heating device is known from DE-OS 31 19 302. The heat radiating arrangements made of metal are in here Contact with the surfaces of the electrodes of the respective Heating elements with a positive temperature coefficient. The heating elements can be between two radiation arrangements thanks to heat-resistant and heat-conductive silicone adhesive layers be clamped, and the protruding parts of the electrodes of the Heating elements can be electrically connected through lead wires conductive adhesive layers must be connected. But it is also possible thanks to a heat-resistant and electrically conductive able to glue the electrical connecting wires immediately to connect to the radiation arrangements.

Electrically and thermally conductive adhesives for higher loads operating temperatures are, for example, in US Pat. No. 3,898,422 described. However, the PTC heating element will only be there on the object to be heated with such an adhesive glued over while the second side of the PTC heating element a clamping spring is contacted.

In US-PS 43 46 285 is a heater using a PTC element facility described. The heat radiating body from one good heat-conducting material have holes through which the  Medium to be heated flows. The heat transfer bodies are with the PTC element thermally conductive due to the clamping effect a screw connection or an electrically insulating one Glue connected. In the case of an electrically conductive adhesive the heat transfer body over an additional Zwi position electrically isolated from the PTC element. To the PTC-Ele They can protect elements from the medium to be heated be surrounded by a ring made of plastic. However, in order to The effect of a screw connection is not to be disturbed Thickness of this ring is slightly less than the thickness of the PTC Element. However, this means that there is no longer any complete protection guaranteed because of the thickness tolerances of both the Rin like the PTC elements, a complete seal is not is guaranteed.

From EP-OS 01 94 507 is a heating element for heating current mender media known, in which a metal body as a heat exchanger per serves that be with disk-shaped ceramic PTC thermistors is heated on part of the surface of the metal body are attached with plastic glue. The metal body is there made of heat-conducting metal and has regularly arranged Through openings, the proportion of the through openings of the total volume is less than 50%. The ceramic cold conductors are on opposite parts of the outer surface of the metal body, possibly also inside the me existing cutouts. The second electrode of the PTC thermistor is always in contact via a clamping spring animals. There is therefore only a one-sided decoupling of the exploited heat supplied by the PTC thermistor. This one-sided Decoupling reduces the efficiency of the heating element.

The object of the invention is to provide a heating element for heating flowing media, in particular for use in motor vehicles conditions (heating of the intake air, the air-fuel mixture, Be heating the chassis) and for oil preheating, the a maximum possible decoupling by the heating elements given heat ensures extensive protection of the PTC thermistor compared to the medium to be heated offers  heating medium offers only a low flow resistance, is mechanically, electrically and thermally flexible and can be produced inexpensively.

To solve this problem, the heating element is at the beginning given type according to the invention characterized by the features:

• a) The metal body consists of several, one in the we substantial cylindrical arrangement of complementary single bodies pern, in particular sectors or segments, the same time serve as power supply lines to the PTC thermistors,
• b) between the interfaces of two adjacent individual bodies is at least one ceramic, disk-shaped PTC thermistor included, which with its large bearing the assignments end faces adjacent to each of the two interfaces Conduct single body by means of an electrical and thermal the glue is attached,
• c) in addition, the neighboring individual bodies are among themselves mechanically fixed by placing at least two on each Interfaces located electrically insulating Plastic is present, the pair of these openings wise by at least one bridge from the same art fabric connects,
• d) the cavity that is adjacent between two interfaces cell remains around the PTC thermistor and the adhesive, is completely enveloping with the PTC thermistor, electrical insulating plastic filled,
• e) the plastic for the mechanical fixation of the individual body and for sheathing the PTC thermistor and for filling the Cavities have completely or almost the same thermi expansion coefficients such as that as a heat exchanger metal.

This is an advantageous embodiment of the heating element characterized that the entirety of the metal body forming single body with the same the peripheral surface is provided encircling the ring.

Another embodiment of the heating element is ge  indicates that the plastic for mechanical fixation the single body, for sheathing the PTC thermistor, for filling of the cavities and for encasing the metal body 30 to 50% by weight with glass fibers and / or with microspheres strengthened, injection-moldable, in the hardened state at the Working temperature of sufficiently elastic plastic material, in particular polyphenylene sulfide.

Another embodiment of the heating element is thereby ge indicates that the outer dimensions of the envelope of the Me tall body for later installation in a piping system are dimensioned.

Another heating element is characterized in that the the through used for the formation of the mechanical fixations let openings over to the respective interface of the individual bodies the entire thickness of the metal body are open and this at the openings thereby create a channel with each other, which is just if it is filled with plastic and represents a web.

Another embodiment of the heating element is ge indicates that the plastic to form the web Fillings of the two passage openings on both sides over the Me protrude tall body and these protruding ends through the same plastic material are connected together.

Another embodiment of a heating element is thereby ge indicates that the power leads to a single body at least one plugged into at least one passage opening Connector.

Another advantageous embodiment of a heating element is characterized in that the power supply to a Individual body takes place via a tab integrally formed thereon.

Another advantageous embodiment of a heating element is characterized in that the power supplies to each other diametrically opposed and designed as pins,  that the heating element rotates after installation in a piping system is cash.

Another embodiment of a heating element is thereby characterized in that to reduce flow resistance conical inlet opening on the inlet side of the individual body overlap so that adjacent passage openings are separated from each other by sharp edges.

The advantages of the invention are that by the beisei sticking the heat transfer body a very good ther mixer contact between the PTC element and the heat exchanger exists, whereby both the generated heat is optimally decoupled pelt, as well as better feedback on self-regulation of the PTC element can be achieved. Furthermore, the structure of the heating element very simple and inexpensive, since it is single Lich from the heat exchangers, the heating elements, the electrical and thermally conductive adhesive as well as for encapsulating the PTC elements and for fixing the heat exchanger art fabric exists. Additional screw connections or clamps len are not required.

In the "Technical Information" 830314 with the title "Kalt conductor as heating elements ", pages 1 to 10, of the company VALVO, the even PTC thermistors and devices heated with PTC thermistors and has a lot of experience in this specialty, it is stated on page 5 under point 5.3, paragraph 2, that preferred with two-sided bonding because of the thermi mechanical stress triggered mechanical stresses There is a possibility that the bond loosened or that cracks occur in the PTC thermistor. The present invention which is not suggested by the prior art these difficulties because in addition to gluing existing special mechanical fixation by means of elastic Plastic prevents these known problems. This was on three heating elements (heating combs) each with 40,000 load cycles (Heating to 230 ° C in approx. 30 seconds, holding time 2 minutes, from cooling to room temperature in 3 minutes, then another cycle)  proven. All three heating combs were full after these tests functioning. There were no cracks or signs of detachment noticeable.

Embodiments of the invention are described in more detail below described and are shown in the drawings. Show it:

Fig. 1 is a plan view of a heating element,

Fig. 2 is a side view of the same heating element,

Fig. 3 a section through the same heating element,

Fig. 4 is a partial sectional view of the same heating element,

Fig. 5 is a plan view of the cut heating element,

Fig. 6 shows a further cross section through the same heating element,

Fig. 7 shows a partial section of the heating element,

Fig. 8 passageways in detail,

Fig. 9 shows an rotatable design of the heating element,

Figure 10 is a plan view of lugs. A heating element with current supply,

Fig. 11 is a section of the heating element with Stromzuführungsla rule.

In Fig. 1 a plan view is shown on a heating element. The heat exchangers used here are two made of aluminum, copper or egg ner alloy with a high proportion of this metal existing individual body 1 , 2 , which have a plurality of passage openings 3 . Towards the inlet opening, these openings 3 are flared, so that due to the small distances between the individual openings 3 , the inlet openings overlap and sharp edges 5 arise which separate two adjacent openings 3 from one another. Therefore, a passage 3 completely surrounded by other passage openings 3 has a hexagonal edge.

The PTC elements lie in the connection plane between the individual body 1 and the individual body 2 . They are completely enclosed in a plastic covering. Passage openings located directly on the connection plane can be designed as openings for webs 4 . The connecting web between these openings can either be produced by milling in the individual body 1 , 2 or by a connection outside the individual body 1 , 2 , for example as a web 6 . In addition, the Einzelkör by 1 , 2 can still be surrounded by an annular sheath 7 , which is used for installation in a metal pipe for thermal insulation and electrical isolation. The mechanical fixation of the two individual bodies 1 and 2 is done only via Verbindungsste ge, such as the web 4 or the web 6 , so that the ring-shaped envelope can also be saved when installed in a non-heat-conducting and possibly electrically insulating plastic tube.

In Fig. 2 is a side view of the heating element is shown. It can be seen again the annular casing 7 , which encloses the two individual bodies 1 and 2 as a thermal insulation. The webs 6 serve to mechanically fix the individual bodies 1 and 2 and hold the individual bodies 1 and 2 together via openings for webs which are not visible here.

The section shown in FIG. 3 shows one of the possibilities for the mechanical fixation of the individual bodies 1 , 2 . The openings located directly at the connection level, which are to be connected by the web 4 , have no conical inlet openings. Instead, a groove open to the connecting surface is milled over the entire thickness of the respective individual body 1 or 2, as a result of which a connecting channel 8 is formed between the adjacent openings between two adjacent adjacent individual bodies 1 , 2 . The water connecting channel 8 is filled with the same plastic that also forms the annular sheath 7 or serves as a web 6 and thus represents the web 4. With a web 6 there is no connecting channel 8 between the adjacent passage openings, but the mechanically fixing connection arises through the web 6 itself.

In FIG. 4 is another side view shown with a partial section. One recognizes the annular casing 7 , as well as the web 6 , which is provided on both sides with two passage openings, and which serves for the mutual mechanical fixing of the individual bodies 1 and 2 . The section through a larger number of Durchlaßöffnun conditions 3 , which are located in the individual body 1 , clearly shows the sharp edge 5 , which is created by intersecting the conical inlet openings.

The arrow A in FIGS. 3 and 4 shows the direction of flow of the medium to be heated.

FIG. 5 shows a top view of a heating element in section VV of FIG. 2. The cut was made below the conical extension of the passage openings 3 . The openings which are connected to one another by the web 4 in the connecting channel 8 serve for the mutual mechanical fixing of the individual bodies 1 and 2 . The white direct openings 9 , 10 are not connected by a connecting channel, but by the web 6 shown in FIG. 1. Between the individual bodies 1 , 2 are the PTC thermistors 11 , which, as can be seen in FIG. 6, are surrounded by plastic 14 .

In Fig. 6 the heating element of Fig. 1 is shown along the lines VI-VI. No conical inlet widenings are shown here with these passage openings 3 . The hole 10 of FIG. 5 completeness, dig filling plastic filling 13 merges seamlessly with the processes known from Fig. 1 web 6 over and causes thereby a mechanical fi xation of the two individual bodies 1 and 2.

In Fig. 7, the plastic sheath 14 of the PTC thermistor 11 is shown enlarged. With the individual bodies 1 , 2 , the Bele conditions 12 of the PTC thermistor 11 are connected via the electrically and thermally conductive adhesive 15 . The Kaltlei ter 11 is completely shielded from the environment by the plastic covering 14 . An additional seal is provided by the sealing edge 26 , which is located in the connecting surfaces of the individual bodies 1 and 2 .

In FIG. 8, the sharp edges 5 that separate the through openings 3 of one another, can be seen in enlarged form.

In Fig. 9, an embodiment of a heating element is shown, which is suitable, for example, for use as a defroster in a motor vehicle. The basic structure of the Heizelemen tes is already known from FIG. 1, in addition, however, this heating element also has contacts 21 , 22 , which serve as a power supply. Furthermore, these contacts 21 , 22 serve as a mounting element for the positioning of the heating element in a specially designed mounting socket 25 made of plastic. In this mounting socket 25 there are two self-lubricating sleeves 24 , through the bore of which the heating element is rotatably supported by means of the two contact pins 21 , 22 . On the contact pin 22 , a rotary lever 23 is attached outside of the mounting socket, via which the position of the heating element can be adjusted from the outside and can be rotated to a certain extent like a throttle valve.

In the rest position, ie when the heating of the flow air is not necessary, the heating element is parallel to the flow A brought through the flow channel 19 in order to keep the flow resistance as low as possible (dashed round disk). In operation, the heating element is rotated by 90 ° and is thus transverse to flow A. When the operating voltage is applied, the inflowing air is heated.

Another embodiment of the heating element is shown in FIG . The basic structure is the same as already known from FIG. 1, but this embodiment of the heating element has a special configuration of the annular envelope 16 , which makes it particularly suitable for installation in a piping system. There are also power supply tabs 17 , 18 which are in direct electrical contact with the individual bodies 1 , 2 , which in turn serve as power supply to the PTC thermistors.

In Fig. 11 the heating element from Fig. 10 is shown in cross section. It can be seen that in this case the power supply tabs 17 , 18 are molded directly onto the individual body 2 or 1 . The ring-shaped sheath 16 has additional recesses to accommodate sealing rings 20 . Through these sealing rings 20 , an improved seal between the piping system 19 and the heating element is achieved.

Below are some technical data regarding the structure and the possible uses of a heating honeycomb according to the invention specified.

The operating voltage range extends depending on the design of the PTC thermistor from 6 V to 240 V, with powers up to 800 W. are realizable. The highest achievable temperature is included 250 ° C. This value mainly results from the efficient speed of the adhesive and the plastic covering.

The materials suitable as adhesives are already mentioned in the ten US-PS 38 98 422 described. Of course you can too Another adhesive can be used if it does the following Criteria met:

• - temperature resistance at least 250 ° C,
• - Excellent electrical conductivity, specific resistance stood at a maximum of 0.001 ohm × cm,
• - excellent thermal conductivity, at least 12 W / mK,
• - linear coefficient of thermal expansion in the range from 60 to 80 × 10 ^-6 l / K,
• - required tensile strength 20 to 30 kg / cm ² ,
• - elastic properties
• - particle size of the solid fraction less than 15 µm,
• - amount of solids about 72% by weight, solids e.g. silvered Copper particles.

The plastic used is also of considerable importance tung. On the one hand, the plastic is supposed to mechanically and the ceramic protect chemically against the medium to be heated, on the other hand should he the thermomechanical forces on adhesive bond and Ceramic due to the mechanical fixation of the individual mini bodies lubricate. Furthermore, he should possibly use the individual body against one Insulate electrically conductive pipe wall and if necessary also serve as thermal insulation. With this follow  de Requirements for the plastic:

• - temperature resistance at least 250 ° C,
• - linear coefficient of thermal expansion maximum 22 × 10 ^-6 l / K,
• - Flammability according to UL 94 V / O (UL: according to the regulations of the Under writers Laboratories Inc.), i.e. self-extinguishing,
• Resistance to the medium to be heated,
• - tensile strength at least 100 N / mm ² .

This is a material that meets these requirements polyphenylene sulfide reinforced with glass fibers or glass balls by L.N.P. Plastics, Nederland B.V., with a glass content of 40% by weight.

The individual bodies used for heat transfer are preferred made of aluminum or an aluminum alloy in die casting process manufactured. The outer shape depends on the application circular, oval or polygonal. For the construction of the heating system at least two such heat exchangers are required. At The heat exchangers have the respective connection point a flat surface to hold the PTC elements. Possible reason form the metal body composed of the individual bodies are e.g. a 4 quarter cylinder or an out two halves of existing cylinders. Also a tripartite cylin the one that consists of a central block with parallel connecting surfaces and two cylinder segments, can be realized, the Middle block on the plus pole and the two circle segments on the Minus pole of the voltage source can be connected.

It should be noted that the individual bodies serve as power supply and therefore there must always be the possibility of connecting between two single-body PTC element both a po positive as well as negative voltage. The Power supply to the individual body can be via terminals or in a passage plug or pressure springs or similar electrically conductive objects are made. To be noted is in the application, however, that the flowing medium at most may have a low electrical conductivity to a  Avoid short circuit between the individual bodies.

To reduce the flow resistance, the individual have body a large number of regularly arranged passages, the have a circular cross section. The clear expanse takes thereby from the inlet side with a constant radius of curvature up to a maximum of 1/3 of the passage length and then remains constant up to the outlet side or over the entire thickness of the body at most a conicity of two angular degrees.

The radii of curvature of the individual run in the inlet area Passages to each other except for one edge, so that across no areas remain to the direction of flow. Any of these Edges have a radius of 0.1 to 0.2 mm. The top view of the culverts then shows a honeycomb-like shape with a variety of individual hexagonal structures.

The volume of all between the passages Parts of the metal body are the same or a maximum of 30% larger than the volume of all passages.

To make the production of the To reach individual bodies, it is advisable to heat the entire body transferring metal body from identically constructed single body put together.

Further advantages of the invention are as follows:

Compared to the well-known ceramic honeycomb or other heaters asymmetrical decoupling of temperature from PTC thermistors there is a significant cost in the present invention savings of up to 40%.

Several aspects are responsible for this:

On the one hand, contact springs, complex housing cones structures as well as necessary insulating parts away. On the other hand can the number of cold by the symmetrical coupling conductors are reduced. The structure consists of only four  various components such as PTC thermistor, heat exchanger, adhesive About and plastic frame.

With the individual components heat exchanger, PTC thermistor and adhesive the adhesive is preassembled. The final assembly is that Overmolding with the plastic. The overall assembly is limited on two processes that are inexpensive in series production are realizable.  

• 1 single body
  2 single bodies
  3 passage opening
  4 bridge
  5 sharp edges
  6 bridge
  7 annular casing
  8 connecting channel
  9 opening for web
  10 opening for web
  11 PTC thermistors
  12 Assignment of the PTC thermistor
  13 plastic filling
  14 Plastic sheathing of the PTC thermistor
  15 glue
  16 annular wrapping
  17 Power supply tab
  18 power supply tab
  19 Piping system
  20 sealing ring
  21 power supply pin
  22 power supply pin
  23 rotary lever
  24 sleeve
  25 Installation version
  26 sealing edge

Claims (10)

1. Heating element for heating flowing media, in which a heat exchanger is made of a good heat-conducting metal, in particular aluminum or copper or alloys with a high proportion of these metals, with regularly arranged, slightly conically tapering passage openings ( 3 ) provided in the direction of flow Serves metal body in which the volume of all parts of the metal body located between the passage openings ( 3 ) is equal to or greater than the volume of all passage openings ( 3 ), the metal body with disc-shaped, ceramic PTC thermistors ( 11 ) (PTC resistors) is heated, which are attached to a part of the surface of the metal body with thermal and electrically conductive plastic adhesive, characterized by the features:

• a) the metal body consists of a plurality of individual bodies ( 1 , 2 ) which complement one another to form a substantially cylindrical arrangement, in particular sectors or segments which simultaneously serve as power supplies to the PTC thermistors ( 11 ),
• b) at least one ceramic, disk-shaped Kaltlei ter ( 11 ) is contained between the interfaces of two adjacent individual bodies ( 1 , 2 ), which with its large end faces bearing the coatings ( 12 ) on each of the two interfaces of adjacent individual bodies ( 1 , 2 ) is fixed by means of an electrically and thermally conductive adhesive ( 15 ),
• c) in addition, the adjacent individual bodies ( 1 , 2 ) are mechanically fixed to one another by at least two openings ( 9 , 10 ) at each of the interfaces ( 9 , 10 ) electrically insulating plastic ( 13 ) is present, which these openings in pairs by at least connects a web ( 4 , 6 ) made of the same plastic,
• d) the cavity that remains between two interfaces of adjacent individual bodies ( 1 , 2 ) around the PTC thermistor ( 11 ) and the adhesive ( 15 ) is filled with the electrically conductive plastic ( 14 ) completely enveloping the PTC thermistor ( 11 ),
• e) the plastic for the mechanical fixation of the individual body by ( 1 , 2 ) and for the sheath ( 14 ) of the PTC thermistor ( 11 ) as well as for filling the cavities has completely or almost the same coefficient of thermal expansion as the metal serving as the heat exchanger.

2. Heating element according to claim 1, characterized in that the entirety of the individual body forming the metal body ( 1 , 2 ) is provided with a circumferential surface of the same annular envelope ( 7 ). 3. Heating element according to claim 1 and 2, characterized in that the plastic for the mechanical African fixation of the individual body ( 1 , 2 ), for the sheath ( 14 ) of the PTC thermistor ( 11 ), for filling the cavities for the ring-shaped sheath ( 7 ) the metal body from 30 to 50 wt .-% with glass fibers and / or reinforced with microspheres, capable of injection molding, in the hardened state at working temperature sufficiently elastic plastic material, in particular polyphenylene sulfide. 4. Heating element according to claim 2, characterized in that the outer dimensions of the ringför shaped envelope ( 7 ) of the metal body are dimensioned for later installation in a piping system ( 19 ). 5. Heating element according to claim 1, characterized in that the two openings used for the formation of me mechanical fixations to the respective boundary surface of the individual body ( 1 , 2 ) over the entire thickness of the metal body are open and these two openings thereby one with the other Connection channel ( 8 ) result, which is also filled with plastic and represents a web ( 4 ). 6. Heating element according to claim 1, characterized in that to form a web ( 6 ) the plastic fillings ( 13 ) of the two openings ( 9 , 10 ) protrude on both sides over the metal body and these outstanding En are connected by the same plastic material. 7. Heating elements according to claim 1, characterized records that the power supply to a single body per via at least one, in at least one passage opening plug inserted. 8. Heating element according to claim 1, characterized in that the power supply to a single body by ( 2 ) via a molded on this tab ( 17 ). 9. Heating element according to claim 1, characterized in that the power supplies are diametrically opposed to each other and are designed as pins ( 21 , 22 ) so that the heating element can be rotated after installation in a piping system ( 19 ). 10. Heating element according to claim 1, characterized in that to reduce the flow resistance stood on the inlet side of the individual body ( 1 , 2 ) conical inlet openings so that adjoin each other de passage openings ( 3 ) separated by sharp edges ( 5 ) are.