Design and Optimization of Composites Tailored for Thermal Energy Storage and Smart Sensing Applications

Abstract

This dissertation seeks to rationally design composites and develop strategies to optimize the performance of composites at system level and to identify metrics to design future composite material systems. Phase change materials are often combined with high thermal conductivity materials to increase power density. However, most of the phase change composites do not have deliberate design strategies and often are based on intuition as the accompanied complex computational techniques are expensive to study detailed parametric studies. Here we present systematic theoretical framework to design and develop composites optimized for thermal energy storage in parallel lamellar structures, to identify critical pitch required to treat the composite as a single effective medium and the optimum volume fraction of the high conductivity materials. The optimization criteria are validated using experiments using 3D printed AlSi12 alloy and octadecane and the system exhibits a critical pitch between a lamella of 1 mm and the optimum volume fraction for high conductivity material is 0.6 – 0.8. We extend the design rules and optimization strategy to cylindrical composite systems with three figures of merit – minimization of temperature rise, maximization of the effective heat capacity and maximization of the effective heat capacity based on mass. When maximizing the effective volumetric heat capacity, the optimum volume fraction for the high conductivity material is 0.3 – 0.5. Finally, when maximizing the effective heat capacity by mass in cylindrical composites, the optimum volume fraction for the high conductivity material is 0.2 – 0.3. Importantly, the optimum values depend on the applied thermal load, which is not captured in existing figures of merit for thermal storage systems, is captured here. We further present design and optimization of composite materials for smart sensing applications using stimuli responsive polymers. We seek to develop and design low-cost polymer composite materials that exhibit luminescence to weak external force using mechanoluminescent materials. We identify optimum thickness, volume fraction of crystals dispersed in polymer composite. Further, we discuss the role of electronegativity to light emission in zinc sulfide particles by dispersing polytetrafluoroethylene particles in the composite matrix.