WO2017081225A1

WO2017081225A1 - Heating unit and laundry dryer

Info

Publication number: WO2017081225A1
Application number: PCT/EP2016/077388
Authority: WO
Inventors: Ian David Hopkin
Original assignee: Dbk David + Baader Gmbh
Priority date: 2015-11-13
Filing date: 2016-11-11
Publication date: 2017-05-18
Also published as: DE102016110023A1

Abstract

A heating unit for a laundry dryer and a laundry dryer equipped with such a heating unit are shown, for which heating elements are designed with PTC resistor elements and corrugated ribs.

Description

Heating unit and Laundry dryer

Description

The invention concerns a heating unit according to the preamble of the patent claim 1 and a laundry dryer with such a heating unit installed.

Such a laundry dryer is shown in the EP 1 538 255 B1 . For this solution, a heating unit is located at the rear panel of a laundry dryer, which in turn is covered. This heating unit heats up an airflow aspirated by a fan to the desired operating temperature, which is then introduced into the drum of the laundry dryer filled with laundry. The heating unit has several heating elements arranged throughout the airflow that are designed as wire resistor elements. These are contacted thermally with heat exchange surfaces, via which the heat generated by the wire resistor elements is transferred to the airflow. The wire resistor elements can also form the heat exchange surfaces themselves. For example, to prevent the heating unit from overheating in case of a fan failure, thermostats are provided, which interrupt power supply of the heating elements in case a maximum temperature is exceeded, so that the laundry dryer does not get damaged. The desired operating temperature (drying temperature) is also maintained by means of such thermostats.

Such heating units with wire resistor elements are inexpensive, have a comparably simple design, whereas the pressure loss during passing through is low. However, a disadvantage is that the control costs to ensure sufficient operational safety are significant.

In order to heat up airflows in automotive engineering, heating units with PTC resistor elements are used, which give off their heat to the airflow via corrugated ribs. For example, such an automotive heating unit is shown in the EP 0 350 528 A1 of the applicant.

EP 2 395 295 A1 also shows an automotive heating unit with heating elements, in which PTC resistor elements are incorporated, and to which heat conducting corrugated ribs are attached. For dust particles or liquids not to cause any damage, the PTC resistor elements are electrically isolated against the corrugated ribs. Documents EP 2 731 399 A1 and EP 2 731 400 A1 each disclose a heater with corrugated rib elements which have pointed crowns with which they lie flat against the heating elements.

A disadvantage is the limited heat transfer from the heating elements to the corrugated rib elements, which results from the line shaped contact and which would have a negative effect particularly with the high heating capacity of laundry dryers.

The invention in turn has the task to create a heating unit and laundry dryer with such a heating unit integrated, which enables improved heat transfer from the heating element to the corrugated rib element with a simple design, low pressure loss and high operational safety.

In case of the heating unit, this task is resolved with the features of patent claim 1 and in case of the laundry dryer with the features of the coordinate patent claim 13.

Beneficial further designs of the invention are subject of the sub-claims.

The claimed heating unit has at least one heating element whose heat can be transferred to an airflow via at least one corrugated rib element, which can bring the airflow to operating temperature. The heating element has PTC resistor elements that are electrically isolated against the corrugated rib element or the corrugated rib elements by means of an insulating sheath between the PTC resistor elements and the corrugated rib element. When using PTC resistor elements, safety elements like for example thermostats for preventing overheating, are no longer needed, as the resistance grows with increasing temperature in case of PTC resistor elements, and the heating capacity reduces consequently. Such a PTC resistor element thus has self-regulating properties, which reliably prevent overheating. In accordance with the invention, the heating element is designed for usage in a laundry dryer, so that damp laundry can be dried via the heating element in the laundry dryer. For this purpose, the corrugated rib element is designed thus permeably that the pressure loss of the airstream is lower than for heating units of the automotive applications. The operational safety of the heating unit is increased due to the PTC resistor elements being surrounded by the electrical insulating sheath at least in sections. This way, direct contact between the PTC resistor elements and particles conveyed in the airflow of the laundry dryer, i.e. fluff, is successfully prevented, so that these do not burn through direct contact with the PTC resistor elements and clog these. Furthermore, an electrical short-circuit is safely prevented. Also in accordance with the invention, flattened contact sections are formed on the corrugated rib element, with which the corrugated rib element lies directly or indirectly against the heating element conducting heat, thus increasing the energy efficiency of the laundry dryer.

Consequently a heating unit is created, which enables improved heat transfer from the heating element to at least one corrugated rib element with a simple design, low pressure loss and high operational safety.

The corrugated rib element can be tensed against the heating element or attached to it.

In case of a preferred further development, the PTC resistor elements are completely enwrapped by the insulating sheath.

The insulating sheath can consist of a polyimide (PI) film, e.g. Kapton, or other heat- resistant and electrically isolating material.

With regard to production, it is simple if the corrugated rib elements are formed of sequences of four mainly flat sections each angled towards each other. In accordance with the invention, these are dimensioned thus large and spaced thus far apart that the pressure loss of the airstream is lower than for heating units of automotive applications.

Thereby advantageously each sequence consists of the flattened contact section, an inclined flank, another flattened contact section and another inclined flank. "Inclined" refers to either the heating element resting against the corrugated rib element or to the two heating elements resting against the corrugated rib element. Contact section means that a heating element is resting against it or at least could rest against it. The latter is the case if the corrugated rib element is located on the outside of the heating unit and there is no heating element located on the outside of the corrugated rib element. The two flanks of the sequence have different attack angles to the adjacent heating element or adjacent heating elements.

Preferably, the flattened contact sections positioned on different sides of the corrugated rib element are roughly the same in size, whereby the flanks are also roughly the same size.

To prevent an excessively high pressure loss with air circulating around the flattened contact sections and flanks, these can be designed according to a corrugated rib element designated as Δ rib, whose crowns do not - as is usual according to the state of the art - adjoin meander-shaped, but are spaced apart, so that the clear span of the corrugated ribs compared to conventional solutions is significantly enlarged and consequently the pressure loss during passing through is decreased and clogging with fluff is prevented. The pressure loss here is particularly low when a distance D between the crowns is designed in such a way that it is at least five times bigger than the width b of the flattened crowns.

At least one rib element can be further developed to form a unit, which has a cover plate for reasons of stability and optimum heat transfer and is positioned between the heating element and the corrugated rib element. In this case, the flattened contact sections of one side of the corrugated rib element are indirectly resting against the heating elements conducting heat. In case of inner corrugated rib elements, that have a heating element each resting against them on either side, a cover plate each is located on either side of the corrugated rib element. The corrugated rib elements are preferably attached to the cover plate or plates by means if crimping, adhering or soldering.

With a corrugated rib element called Z rib, the two flattened contact sections of each sequence and the flank in-between form a Z. The two flanks of each sequence and the flattened contact section in-between form a triangle. The flattened contract sections and flanks (of each sequence) can be roughly the same size here, so that more or less equilateral triangles are formed. To each heating element two contact plates can be assigned, that are also encompassed by the insulating sheath.

The heating element is formed by an intractable sturdy unit, when the contact plates are stuck together on the one hand with the insulating sheath and on the other hand with the PTC resistor elements.

In a first embodiment, the polyimide film has a Teflon coating on both sides. This Teflon coating causes an adhesive effect, which occurs during first heating.

In the first embodiment, the corrugated rib element or the cover plate can be directly connected to the insulating sheath conducting heat. This connection can occur for example by sticking the Teflon coated polyimide film.

In a second embodiment, the heating element has an outer extruded section serving as housing. This is preferably made of aluminium. The extruded section is preferably crimped with the components integrated therein, i.e. the PTC resistor elements, the insulating sheath and the contact plates if required.

In the second embodiment, the corrugated rib elements or the cover plate are attached to the housing of the heating element in a heat conducting manner.

To improve the heating capacity of the heating unit according to the invention, several heating elements can be supported in one frame. It is also possible optionally to keep the heating elements pre-stressed within the frame.

The laundry dryer is designed according to the invention with a heating unit as described above. It can be covered or integrated into this cover, which is positioned at a dryer rear panel.

This cover can be made of plastic, as an excessive exposure of the plastic cover to high temperature is prevented due to the self-regulating properties of the PTC resistor elements. The design can be further simplified if this plastic cover is sealed at the rear panel of the dryer.

Preferred design examples of the invention are explained in more detail in the following based on schematic drawings. The following is illustrated:

Figure 1 shows a greatly simplified rear view of a laundry dryer according to the invention;

Figure 2 shows a schematic partial side view of the laundry dryer according to figure

1 ;

Figure 3 shows a side view of another design example of a laundry dryer according to the invention;

Figure 4 shows a heating unit with two heating elements according to a first embodiment for the laundry dryer from the previous figures;

Figure 5 shows a detail A of the heating unit from figure 4;

Figure 6 shows a corrugated rib element with Δ ribs;

Figure 7 shows a section of a corrugated rib element with Z ribs;

Figure 8a shows a heating element according to the first embodiment with corrugated rib elements as per figure 6;

Figure 8b shows the design from figure 8a in a cross-section;

Figure 9a shows the heating element according to the first embodiment with corrugated rib elements as per figure 7;

Figure 9b shows the design from figure 9a in a cross-section;

Figure 10a shows the heating element according to the second embodiment with corrugated rib elements as per figure 6;

Figure 10b shows the design from figure 10a in a cross-section;

Figure 1 1 a shows the heating element according to second embodiment with corrugated rib elements as per figure 7; and

Figure 1 1 b shows the design from figure 1 1 a in a cross-section. Figure 1 shows the basic design of the rear view of a laundry dryer 1 . This has a drum 2, which holds the laundry to be dried. Drying occurs by means of convection, where a dry, heated airflow 12 is fed into the drum 2.

To heat up the airstream 12, a covered heating unit 8, covered by a suggested cover 6, is located at a dryer rear panel 4, which is supplied by fresh air aspirated from the environment by means of a fan 10, or by circulating dehumidified air. This airstream 12 is then heated to operating temperature by the heating unit 8, for example 105°C to 125°C, and then supplied to the drum 2 via a feed opening.

According to the side view in figure 2, the cover 6 is sealed to the dryer rear panel 4 and encompasses the fan 10 as well as the heating unit 8. This can be attached to the dryer rear panel 4 or integrated into the cover 6.

The heated airstream 12 is then fed into the suggested drum 2. In the design example according to figure 2, the heating unit 8 covers a cylinder port 16 for the heated airstream.

After flowing through the drum 2, the airflow then moist with water can be dehumidified in a condenser or discharged into the environment.

Furthermore, in the illustrations according to figures 1 and 2, a drum axis 14 is shown.

In the design example according to figure 3, the heating unit 8 is not inserted flush into the cylinder port 16, but diagonally into a duct 42 limited by the cover 6 and the dryer rear panel 4, so that in principle, the deflection of the airflow 12 up to the cylinder port 16 partially only occurs downstream of heating unit 8.

Figure 4 shows a detail drawing of the heating unit 8 inserted in the area of the cylinder port 16 according to figure 2 or integrated into the cover 6 in a first design example of an initial embodiment, whereby the flattened contact sections 38 according to the invention or flattened crowns 38 can only be seen in figure 5. The heating unit 8 has for example two heating elements 18, that are each equipped with a large number of PTC resistor elements 22. These PTC resistor elements 22 are in thermal contact with corrugated rib elements 24, which are circulated by the airflow 12 to be heated. The direction of flow is vertical to the drawing plane in figure 4. The flow cross- section is basically limited by corrugated ribs of the corrugated rib elements 24.

For the heating unit 8 according to figure 4, two heating elements 18 are supported in a frame 28 with three corrugated rib elements 24 as layer construction, and are pressed together or tensioned for example by means of spring elements 30, so that there is sufficient thermal conduction. Alternatively or additionally, the heating elements 18 can also be glued together with the corrugated rib elements 24.

The basic design of the heating elements 18 of the first design example of the initial embodiment is explained based on figure 5, which shows detail A from figure 4. As explained, each heating element 18 has a number of PTC resistor elements 22 (also called PTC components), which are electrically contacted via two contact plates 32, 34. The PTC resistor elements 22 in particular can be glued together with the contact plates 32, 34 (see figure 5).

The contact plates 32, 34 are connected to a power supply via connections that are located at the sides of the frame 28, whereby either one of the heating elements 18 or both heating elements 18 are controlled.

The layer construction consisting of the contact plates 32, 34 and the PTC resistor elements 22 in-between is inserted into an insulating sheath 36 for the first embodiment, which thus electrically insulates the contact plates 32, 34 and the PTC resistor elements 22 to the outside. With this insulating sheath 36, a direct contact with particles, i.e. fluff, is prevented in the airstream 12, so that their combustion and consequently clogging of the PTC resistor elements 22 is prevented. This means that the corrugated rib elements 24 are electrically isolated, and a short-circuit is thus safely prevented. This insulating sheath 36 is designed in such a way that such a contact is reliably prevented. The corrugated rib elements 24 for the first design example of the initial embodiment according to figure 5 are thus not in direct thermal contact with the PTC resistor elements 22 or their contact plates 32, 34, but are located at the insulating sheath 36 with their flattened crowns 38. This system is thus designed in such a way according to the invention that sufficient thermal contacting occurs without direct electrical contact.

Consequently, the insulating sheath 36 must show sufficient heat conduction, but at the same time also ensure an electrical insulation. A particularly suitable material for such an insulating sheath 36 is for example a film made of polyimide (PI), e.g. Kapton. Naturally, other materials can also be used. The insulating sheath 36 can be designed flexibly but also rigidly.

For the first embodiment, the polyimide film has Teflon coating on both sides. This Teflon coating causes an adhesive effect, which occurs during first heating.

In the first design example of the first embodiment, it is intended that the corrugated rib elements 24 with their flattened crowns 38 are stuck together with the insulating sheath 36 via the Teflon coating. Furthermore, the contact plates 32, 34 are stuck together with the insulating sheath 36 via the Teflon coating. If the contact plates 32, 34 in turn are stuck together with the PTC resistor elements 22, this will result in an intractable and sturdy unit. The use of spring elements 30 is then no longer needed.

In a second design example of the first embodiment of the invention, the elements no longer need to be agglutinated or only partially. In this case, the spring elements 30 (see figure 4) are then used for pre-stressing the elements of the heating unit. Naturally, other joining means can also be used.

Figure 6 shows an initial well suited geometry of corrugated rib elements 24, which is also called Δ rib. Such corrugated rib elements 24 are described in the post-published application DE 10 2015 1 1 1 571 .9. The disclosure of this patent application is part of the present application. The corrugated rib element 24 shown in figure 6 has a familiar number of corrugated ribs, whose crowns 38 are flattened on both sides, thus lying flat against the heating element or both heating elements 18. This way, thermal conduction of the corrugated rib element 24 with one heating element 18 or both heating elements 18 is optimal.

The flanks 26 of the corrugated ribs are positioned towards each other at an angle a, so that due to this relatively large attack angle a, a large flow cross-section is provided. In order to improve a heat exchange transverse to the airstream 12 as well as to optimise the mechanical properties (compressive strength), beadings 40 are formed at the flanks 26 of the corrugated ribs, which enable a pressure and temperature compensation between the flow cross-sections limited by the respective corrugated ribs. For the illustrated corrugated rib element 24, three respective beadings 40 are formed at each flank 26 of a corrugated rib.

According to the illustration in figure 6, the attack angle a is selected so that a distance D between two adjacent flattened crowns 38 is at least 5 times as large as the width b of a crown 38. As explained, due to this large clear span between the flanks 26 of the corrugated ribs, the pressure loss can be significantly reduced compared to conventional solutions during passing through.

As explained in the application mentioned above, the corrugated rib element 24 illustrated in figure 6 is produced from a basic element, where the adjacent flattened crowns 38 rest against each other. This very compact basic element is then stretched in longitudinal direction, so that the crowns 38 are then respectively spaced apart, and the flanks 26 are angled against each other.

Naturally, the invention is not limited to the mentioned ratio D/b = > 5.

Figure 7 shows an excerpt of an alternatively well suited corrugated rib element 124, which is called Z rib. It is - as is the corrugated rib element 24 from figure 6 - made from a sheet metal band through trimming or bending with chamfered intersections. The corrugated rib element 124 has several sequences consisting of a flattened contact section 138, a flank 126, another flattened contact section 138 and another flank 126. All first mentioned flattened contact sections 138 of the different sequences are arranged on one level, bringing them all together into an initial heating element 18 in a heat conducting manner. All other flattened contact sections 138 of the different sequences are arranged on another level, bringing them all together into a second heating element 18 in a heat conducting manner.

All flanks 126 and all flattened contact sections 138 of the corrugated rib element 124 are roughly the same size. The two flanks 126 and the flattened contact section 138 of a sequence positioned in-between are inclined against each other at approx. 60 degrees and form an equilateral triangle. These triangles form the through-holes for the airstream 12 and according to the invention are of a size which causes a reduction of the flow resistance of the thus formed heating unit 8.

The chamfered intersections between the flattened contact sections 138 and the flanks 126 rest against each other. In contrast to the corrugated rib element 124 shown in figure 7, the chamfered intersections between the flattened contact sections 138 and the flanks 126 can also be at a short distance to each other.

In the following eight figures 8a to 1 1 b, four different minimal heating units are shown, that respectively only have one heating element 18; 1 18 and two corrugated rib elements 24; 124. Naturally, further heating elements 18; 1 18 etc. can be provided on the respective outer sides of the shown corrugated rib elements 24; 124, to form heating units for improved performance. The resulting heating units 8 can also be integrated into a frame 28 (see figure 4).

Figure 8a shows a perspective view of a heating element 18 according to the first embodiment with two corrugated rib elements 24 from figure 6 called Δ rib, while figure 8b shows the arrangement from figure 8a in a cross-section.

A cover plate 44 each is positioned on either side of the corrugated rib element 24, which is attached in a heat conducting manner to the respectively flattened crowns 38 of the corresponding side of the corrugated rib element 24. The cover plates 44 are crimped, glued or soldered with the corrugated rib element 24.

At the end sections, each cover plate 44 is chamfered by approx. 90 degrees, so that chamfered sections 45 of two cover plates 44 that are positioned at the front of the corresponding corrugated rib element 24 point towards each other.

The side of the cover plate 44 facing away from the corrugated rib element is attached to the insulation foil 36 of the heating element 18, more precisely glued to the outer side of the Teflon-coated insulation foil 36.

Figure 8b shows a section of the heating element 18 according to the initial embodiment. Inside the insulation foil 36, the two contact plates 32, 34 and the PTC resistor elements 22 positioned in-between are arranged as described previously, whereby figure 8b only shows a section of a PTC resistor element 22.

Furthermore, figure 8b shows a flank 26 with its three beadings 40 from each of the two corrugated rib elements 24, which has already been described in reference to figure 6. A section of the total of four cover plates 44 of the minimum heating unit is shown.

Figure 9a shows a perspective view of a heating element 18 according to the first embodiment from figures 8a and 8b with two corrugated rib elements 124 from figure 7 called Z rib, while figure 9b shows the arrangement from figure 9a in a cross-section.

The heating element 18 corresponds to that of the previous design example from figures 8a and 8b. The flattened contact sections 138 are attached directly to the outside of the insulating sheath 36, more precisely, the flattened contact sections 138 are glued to the outer side of the Teflon-coated insulation foil 36. Apart from the chamfered intersections, the corrugated rib elements 124 rest against the heating element 18 in a heat conducting manner across the total surface or large-scale. Figure 10a shows a perspective view of a heating element 1 18 according to a second embodiment with two corrugated rib elements 24 from figure 6 called Δ rib, while figure 10b shows the arrangement from figure 10a in a cross-section.

The heating element 1 18 of the second embodiment has - seen from the inside to the outside - the PCT resistor elements 22, the two contact plates 32, 34, the insulation foil 36 formed as polyimide film and a housing 140 on the outside, that is designed as extruded section made of aluminium with approx. rectangular cross-section. The housing 140 is preferably crimped with the components integrated therein, i.e. the PTC resistor elements 22, the insulating sheath 36 and the contact plates 32, 34.

The cover plates 44 are stuck together with the outer sides of the housing 140 or (according to figure 4) supported in the frame 30 by means of the spring elements 28, and tensioned against the outer sides of the housing 140.

Figure 1 1 a shows a perspective view of a heating element 1 18 according to the second embodiment from figures 10a and 10b with two corrugated rib elements 124 from figure 7 called Z rib, while figure 1 1 b shows the arrangement from figure 1 1 a in a cross- section.

The benefit of the solution according to the invention is - as initially explained - that a short-circuit can be reliably prevented due to the electrical isolation of the PTC resistor elements 22, thus improving the electrical safety. For example, there is the so-called "Metal Pin Test", in which test pins with predefined geometry are inserted in the airstream channel, whereby no electrical contacting must occur with conductive elements - this is successfully prevented by the described insulating sheath 36.

Due to the PTC resistor elements 22, the use of thermostats is not needed, as described at the start, for preventing temperatures that are too high. However, in case of particularly high demands on operational safety, of course an NTC temperature sensor, thermostats or control electronics can be additionally used. Due to the electrical insulation of the heating elements 18; 1 18, the heating unit 8 can be directly inserted into a suitable cylinder port 16 of the dryer's rear panel 4, whereby this port can have any contour as there is no problem to design the heating unit 8 according to the contour of the cylinder port 16. In principle it is also possible to insert several heating units 8 into several cylinder ports 16, so that the airstream 12 is distributed to the drum 2.

The use of PTC resistor elements 22 also has the advantage or optimised energy efficiency in case of condensate dryers, as the circulating air is already fed into the heating unit 8 with a comparably high temperature after a certain operating time. Due to the self- regulating properties of the heating unit, the electric power is reduced "automatically", without a complex electronic control being needed. The temperature is thus kept constant due to the PTC resistance, rather than controlling a constant heating capacity.

Due to the comparatively low temperatures, the cover 6 can be produced from plastic, for example ABS. According to the invention, their geometry is chosen so that the airstream 12 is optimised with regard to the pressure loss, making efficient drying possible with minimum energy needs.

In principle, an insulating "harness channel" can also be integrated into a conventional cover, to meet the requirements of the previously described metal pin tests.

When using a cover 6 consisting of plastic, its contact edge can be designed as seal, so that the external seal is realised simply without the need for further sealing elements.

A heating unit for a laundry dryer and a laundry dryer equipped with such a heating unit are shown, for which heating elements are designed with PTC resistor elements and corrugated ribs. Reference sign list:

1 Laundry Dryer

2 Drum

4 Dryer rear panel

6 Cover

8 Heating unit

10 Fan

12 Airflow

14 Drum axis

16 Cylinder port

18; 1 18 Heating element

22 PTC resistor element

24; 124 Corrugated rib element

26; 126 Flank

28 Frame

30 Spring element

32 Contact plate

34 Contact plate

36 Electrical insulating sheath

38 Flattened crown / flattened contact section

40 Beading

42 Duct

44 Cover plate

45 Chamfered section

138 Flattened contact section

140 Housing a Attack angle

Claims

Heating unit for a laundry dryer, via which an airstream (12) can be warmed up to operating temperature, the heating unit comprising at least one heating element (18; 1 18), whose heat can be transferred to the airstream (12) via at least one corrugated rib element (24; 124), whereby the heating element (18; 1 18) has PTC resistor elements (22) that are insulated against the corrugated rib element (24; 124) by means of an electrical insulating sheath (36), characterised by flattened contact sections (38; 138) on the corrugated rib element (24; 124), with which the corrugated rib element (24; 124) rests against the heating element (18; 1 18) in a heat conducting manner.

Heating unit according to patent claim 1 , whereby the corrugated rib element (24; 124) has a sequence consisting of a first flattened contact section (38; 138), a first flank (26; 126) inclined against the heating element (18; 1 18), another flattened contact section (38; 138) and another flank (26; 126) inclined against the heating element (18; 1 18).

Heating unit according to patent claim 2, whereby the flattened contact sections (38; 138) are roughly the same size, and the flanks (26; 126) being roughly the same size.

Heating unit according to one of the previous patent claims, whereby the flattened contact sections (38) are spaced at a distance (D).

Heating unit according to patent claim 4, whereby the distance (D) is at least 5 times as big as a width (b) of the flattened contact sections (38).

Heating unit according to one of the previous patent claims, whereby the heating element (18; 1 18) is connected with at least one unit formed out of the corrugated rib element (24) and of one or two cover plates (44).

7. Heating unit according to patent claim 2 or 3, whereby the two flattened contact sections (138) form a Z together with one of the flanks (126) of a sequence, and/or whereby the two flanks (126) from a triangle together with one of the flattened contact sections (138) of a sequence.

8. Heating unit according to patent claim 7, whereby the two flattened contact sections (138) and the two flanks (126) of a sequence are roughly the same size.

9. Heating unit according to one of the previous patent claims, whereby the heating element (18; 1 18) hast two contact plates (32, 34), that are also encompassed by the insulating sheath (36), whereby the contact plates (32, 34) are glued together with the insulating sheath (36) and the PTC resistor elements (22).

10. Heating unit according to one of the previous patent claims, whereby the insulating sheath (36) is a Teflon-coated polyimide film.

1 1 . Heating unit according to one of the previous patent claims, whereby the heating element (1 18) has a housing (140) into which the insulating sheath (36) and the PTC resistor elements (22) are integrated.

12. Heating unit according to one of the previous patent claims, whereby several heating elements (18; 1 18) are supported in a frame (28).

13. Laundry dryer with a heating unit (8) according to one of the previous patent claims.