Elastocaloric Cooling Based on Tailored Rubber Films

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The project aims at the research and development of novel cooling devices using the elastocaloric effect in films of natural and synthetic rubber/rubber-like materials. Natural rubber (NR) has the potential to outperform shape memory alloy–based elastocaloric cooling as it exhibits a unique combination of large latent heat of 17 Jg-1, low stress levels, large reversible strain of several hundred percent and good scalability on miniaturization. Furthermore, NR is environmentally friendly and inexpensive. Two different approaches are pursued to develop rubber-based materials for elastocaloriccooling: (1) NR will be prepared and investigated aiming at understanding the molecular effects on the extent of strain-induced crystallization. (2) Synthetic rubber with varying molecular weight and chemical composition will be developed to investigate the effect oncrystallization, elastocaloric temperature change, hysteresis and fatigue resistance (J. Rühe). Engineering methods and tools will be developed based on the rubber films to realize elastocaloric cooling devices with optimized efficiency and cooling capacity (M. Kohl). In order to overcome the problem of low thermal conductivity, strategies will be developed to adjust film thickness and lateral geometry as well as to introduce and optimize the content of conductive fillers. The evolution of temperature profiles on the device level will be investigated by finite element simulation and thermography tounderstand the load-dependent kinetics of heat/cold generation and of heat transfer. Separation of heat and cold will be investigated for the case of alternating mechanical contact between rubber film and heat source/sink. Thereby, the shape and force of contacting surfaces will be adapted and the influence of thermally conductive layers will be tested. Finally, a demonstrator system will be fabricated and evaluated with respect to cooling capacity and long-term operation.