REPOSITORY > RESULTS

Abstract

Development of modern technologies and products that are integrated in the idea of sustainable development, such as renewable energy, low carbon technologies, environmentally friendly production, etc. requires simultaneous development and research of new materials. In the field of automotive industry, there is an obvious development in the direction of electric cars and the improvement of ambient conditions while driving. The biggest problem with electric vehicles is the limited capacity of batteries that limit the range the vehicle makes with one charge. On the other hand, the provision of appropriate working conditions, such as the temperature in the vehicle cabin, also requires additional energy. Heated seats in vehicles have become standard equipment even for low-end vehicles. For most vehicles, heating is provided with special heating elements made of resistive wires. Such heating elements consume a lot of electricity, usually about 20 kWs to heat a seat. In the case of electric cars in winter, when the efficiency of the batteries is much lower, this energy further reduces the vehicle's range.
The basic idea of the doctoral thesis was the development of fabric composite material, which, when connected to the electric voltage, would be uniformly heated over the whole surface and would replace discrete resistive elements in the existing car seats. Due to more direct contact with the driver, lower temperatures, lower thermal capacity and lower losses, such heating could greatly reduce the consumption of electricity.
The composite material was made of a fabric, usually used in the manufacture of car seats (leather, artificial leather, cotton canvas, etc.) and an electrically conductive layer based on carbon nanotubes with various additives applied on the underside of the fabric. Screen printing was found to be the most suitable way of applying the conductive layer to larger pieces of fabric. With the number of deposited layers, the electrical and therefore thermal properties could be tailored.
Measuring the electrical conductivity as a function on the number of applied conductive layers, it was found that the conductivity in this system can be explained with a percolation mechanism.
The impact of the elongation of fabric materials on electrical conductivity was also investigated. When using fabric in car seats, there are tensile stresses producing the strain of the material. Despite the tensile load, the fabric material can be heated but up to about 20-40% lower temperature at the same electric current.
After repeated deposition of the conductive layer on various materials, the surface was investigated by scanning electron microscopy (SEM). Parameters such as roughness, porosity, distribution of carbon nanotubes and the presence of defects (cracks, voids, etc.) were studied. It was found that the surface is quite rough, which is largely contributed by the base material. There are also pores that allow permeability ("breathing") of this material. The bundles of individual carbon nanotubes are interconnected, uniformly covering the surface and forming loops. Such a fiber distribution explains the preservation of conductivity even in the case of elongation under the tensile load.
Thermal resistance of composite materials was also measured since the composition of individual layers of materials on the seat is an important parameter regarding to heat transfer. The heating of fabric materials as a function of the time, and the temperature distribution over the surface during heating was monitored with the infrared camera.
The result of the doctoral thesis is the development of heating fabric composites based on five different materials used in the automotive industry (leather, artificial leather, cotton canvas, laminated canvas and compound foam). The heating of all investigated materials was suitable for use in car seats, the consumption of electricity is more than 30% lower than using discrete wire elements, that is about 7 kWs to heat a seat.