Fraunhofer Institute for Manufacturing Engineering and Automation IPA
Fraunhofer Institute for Manufacturing Engineering and Automation IPA

Dispersions for heating elements

Coiled metal wires, printed metal sheets, and graphite layers are the best-known materials used in electrical resistance heating and are thus state of the art. However, on taking a closer look at the pros and cons of metallic resistance heaters, it soon becomes clear: There are alternatives with clear advantages in terms of functionality and application flexibility. 

Advantages and disadvantages of metallic resistance heaters

The advantages of metallic resistance heaters are their mature technology and high heat output. Graphite layers enable full-surface and homogeneous resistance heating. The disadvantages of existing systems with composite materials coupled with metallic particles lie in the very narrow transition range (percolation threshold) from the insulating to the conductive material. With graphite, a high filling ratio is required, which weakens the mechanical properties. A lower filling ratio allows only low outputs. Furthermore, at higher outputs, the limits of mechanical stress on graphite layers are reached, causing them to become brittle and weakening their adhesive properties. In the case of complex surfaces, this is accompanied by a high effort in designing metal-based resistance heating systems. At the same time, a large amount of space is needed to accommodate them. 

Carbon nanotubes (CNT) as an alternative material for heating elements

Carbon nanotubes (CNTs) are particles with a large specific surface area and a high aspect ratio (length to diameter), and which exhibit metallic and semiconducting properties. As a result, carbon nanotube-based functional materials can be produced, providing an attractive alternative to metallic materials or graphite:

Large surface area

Low filler content to achieve electrical conductivity in the system (low percolation threshold)

High aspect ratio

The electrical network remains intact even when components are subjected to mechanical loads (e.g., bending). The fiber-like particles maintain contact, slide against each other, and the transport of electrons is not interrupted, unlike with spherical particles, for example.

Metallic and semiconducting properties

Coupled with the filling ratio, a broad field for the power supply can be achieved.  

Electric floor heating
Electric CNT surface heating
© Fraunhofer IPA
Project example CNT heating element in the paneling of a vehicle door

Cooperation with Fraunhofer IPA: how we can assist companies

Within the scope of development projects, we help our project partners to select the right matrix materials, additives, stabilizers and processing steps. This has enabled us to produce dispersion materials and composites with the necessary properties. Furthermore, we have accompanied our project partners throughout developments by helping them to design of the overall process and integrate it into their application. Energy efficiency, cost-effectiveness and degree of automation are already taken into account and regulated accordingly in the course of the development.

References and application examples

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WINDHEAT - Ice detection and de-icing system for wind turbines

 

Assignment:

To develop a cost-effective and energy-efficient ice detection and de-icing system for small wind turbines

Benefit:

  • Ice and freezing water rapidly detected
  • Rotor blades quickly de-iced
  • Increased wind turbine efficiency

Project partners: Geolgica (E), Polycam (E), ALCEA (I), Kenersys (D), Lincis (P), Inspiralia (E)

Funding: FP7-SME-2012-1-34893

Images: ©Fraunhofer IPA, de-icing system for small wind turbines.

HyMovDelce - Innovative hybrid de-icing systems on control surfaces

 

Assignment:

To develop a multifunctional coating structure with a carbon-based, heatable coating and electrically & thermally insulating paint layers. This included formulation, application and optimization after various tests. The energy efficiency of the developed coatings was assessed in accompanying ice-wind tunnel tests at IFAM.

Benefit:

  • Efficiency improvements based on a new generation of ice protection systems, making it possible to reduce the space required to accommodate the heating elements and to save weight.
  • Technology transfer to the application areas of rail vehicle construction, automotive and the energy sector

Partners: Airbus Operations GmbH, Airbus Defence and Space GmbH, Airbus Group Innovations, Deutsches Zentrum für Luft-und Raumfahrt e.V., Institut für Faserverbundleichtbau und Adaptronik, Technische Universität Braunschweig - Institut für Adaptronik und Funktionsintegration, Bender GmbH Maschinenbau und Streckmetallfabrik, Mankiewicz, Fraunhofer Gesellschaft zur Förderung der angewandten Forschung e.V.

Funding code: 20Y1512E

Images: ©Fraunhofer IPA

AFKAR - Autonomous driving and body concept for an all-electric car

 

Assignment:

To integrate surface heating systems based on CNT coatings

Benefit:

  • High energy efficiency due to passenger proximity
  • Rapid heat generation due to low heat capacity
  • Weight saving and automated production

Project partners: Individual projects in the Body and Infrastructure Cluster

Funding: FSEM - Fraunhofer System Research for Electromobility

Images: © Fraunhofer IPA, thermal image of the integrated heating system (left) and “A glimpse beneath the surface” (right).

Assignment:

To develop a silicone heating pad (resistance heating element)

Benefit:

  • System without any chemical reaction - electrically operated and controllable heating system
  • The CNTs could be incorporated into silicone - Breathable Composite

Images: ©Fraunhofer IPA, silicone heating pad (left) and thermal images (right).

Assignment:

To develop a fan heater (resistance heating element) with low operating temperature without any change in airflow conditions (no pressure drop)

Benefit:

  • High flexibility
  • Heating element easily adapted to the ventilation geometry and required performance by adjusting piping length, wall thickness, etc.
  • Low operating temperature and improved safety: < 110 °C (from approx. 700 °C)

Images: © Fraunhofer IPA, product development from conventional fan heater (left) through simulation (center) to prototype (right).

Image: ©Fraunhofer IPA, observation of heat development in simulation program compared to thermal image of prototype

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