There is a growing need to develop technology to harness previously untapped sources of energy and waste heat is one source of energy that provides significant potential to increase the efficiency of overall energy use in multiple applications. Waste heat as a source of energy supply has relatively low availability and a storage system is required to efficiently utilize the energy. One method for harvesting this waste heat is through the use of phase change material (PCM) as a thermal energy storage (TES) medium.
This work examines the operation of a thermal energy storage device that collects and stores heat in a PCM. The TES relies on the phase change of icosane wax, which possesses a large latent heat of fusion and high thermal storage capacity. However, the icosane wax typically has low thermal conductivity. This work focuses specifically on enhancing the thermal conductivity of the sink by incorporating an additive possessing high thermal conductivity without significantly reducing the storage capacity (volume) of the TES. The performances of both the TES as well as TES with enhanced conductivity are monitored to validate operation.
Three different major experiment sets were performed; one contained only icosane wax as the PCM, a second incorporated a copper foam mesh along with the Icosane to increase the thermal conductivity of the working fluid. Finally, the third comprised of a novel copper matrix with increased surface area and thus, better conductivity for the PCM. The power absorbed by the PCM and the thermal storage potential for each of these tests was also studied in these experiments.
The novel copper matrix showed good promise in greatly increasing the thermal conductivity of the system from 0.49 W/mK in the icosane-only test to 3.90 W/mK. A 200% increase in the power absorbed by the device was also achieved with the copper matrix conductivity enhancer. Results indicate an improvement of average thermal conductivity by a factor of 8 due to this work. A steady state power absorbed of 0.9 kW/m2 was achieved for the preliminary test of unmodified icosane. A similar steady state value of 0.96 kW/m2 was achieved with the copper mesh enhancer. The maximum power absorbed was achieved with the novel copper matrix at 2.76 kW/m2.