Thermal textile pixels : Out-of-plane and in-plane heat transfer measurements of knitted textiles

Abstract: The human body possesses a highly developed range of senses that help orienting oneself in everyday life. Especially when it comes to navigating, perceiving and reacting to the world around us, people tend to rely mostly on their vision and hearing. Suffering from an impairment of either one, or both of the predominating senses means having to counterbalance this constraint. People suffering from blindness and deaf-blindness compensate their impairment mainly by relying on their haptic perception. In this case, information is usually communicated by braille or vibrotactile means. To offer another non-visual and non-audial communication concept this thesis work introduces, the thermal textile pixels. A thermal textile pixel consists of an external thermal device, able to generate hot and cold thermal impulses, and a textile interface to transmit the signal. In order to design such thermal textile pixel it was crucial to be aware of the thermal transfer occurring through and within an textile. Numerous research studies have examined the thermal properties of textiles, especially in the context of clothing comfort, thermal comfort. Nevertheless, it should be considered that as a thermal textile pixel, the textile forms part of a system, governed by many parameters. Therefore, for designing such a device it is important to be aware of the temporal and spatial resolution of the thermal transmitted signal. These characteristics are influenced by multiple textile parameters. For this purpose, a thermal study has been performed investigating in- and out-of-plane signal transmission by textiles in combination with an external thermal device. Using an external thermal device such as a Peltier element allowed to expose the specimens to heating as well as to active cooling. Different knitted structures and material combinations have been examined to gain a first impression on the behaviour of thermal pixels. It was found that thickness and density were the most influential factors for out-of-plane heat transfer. In-plane was found influenced mainly by fibre conductivity. An anisotropic behaviour was noted in-plane, as well as between in- and out-of-plane for heat transfer. Investigating active cooling signals, it was found that a significant decline of performance was noted for all specimens. Plain PA was found to be most suitable for the transmission of heat signals. But did not perform equally well during active cooling phases. Plain Shieldex was observed to perform most steady during heating and active cooling.