In the research project funded by the German Federal Environmental Foundation (DBU), the Chair of Lightweight Automotive Construction (LiA) in cooperation with the project partners of Hotset GmbH has successfully implemented the development of a heatable, hybrid lightweight structure over the past 18 months. In future, heatable hybrid structures based on recycled carbon fibre fleeces (rCF) can be manufactured for a wide range of further applications in addition to the use focused on in the project as a heated floor panel in camping vehicles. Conceivable applications include the de-icing of wind turbine rotor blades or the heating of batteries in electric vehicles, which could open up a new market segment for secondary raw materials.
The heating element uses the mechanism of Joule's heat by employing the excellent electrically conductive carbon fibres. When an electrical voltage is applied, the rCF fleece acts as an electrical resistor, resulting in an efficient conversion of electrical energy into heat. For the design of the hybrid lightweight structure, materials were derived according to the desired mechanical, electrical and thermal requirements for the underfloor heating in the camping vehicle using Ashby's methodical material selection.
The heating elements were then designed by modifying various parameters. Among other things, the weight per unit area of the rCF fleece, the contacting by means of adhesive copper tape and copper wire, the alignment of the fleece layers between the contact points as well as the size of the heating elements were varied and their influence on the achievable heating power was examined. In addition, the homogeneous temperature distribution of the heating elements was the focus of the investigations. In the project, it was possible to show on the basis of thermographic images that the use of rCF fleece with an areal weight of 30 g/m² produces a significantly more homogeneous heat development compared to rCF fleeces with a lower areal weight.
In terms of functional integration, the heating element is combined with the preferred materials to create a functional prototype of the floor heating system, whose property profile could be validated in further investigations. Both in static tests and in the investigation of the achievable temperature development, it could be shown that the desired mechanical, electrical and thermal requirements for use as underfloor heating are achieved. In addition, it could be demonstrated that the use of rCF nonwovens is also suitable for use in more complex geometries with beads and radii due to their good drapability. Also in these cases, the flow results in a homogeneous heat distribution.
The final report of this project will be available at the DBU.