Thermal Energy Storage with Encapsulated Phase Change Materials for High Temperature Applications

The objective of this research is to develop a storage technology for thermal energy utilizing phase change material (PCM) for high-temperature concentrating solar plant (CSP) applications. The project involves: • Development of an experimental measurement technique to select and characterize EPCM candidates; • Design and testing of a thermal energy storage (TES) system with selected EPCM capsules to demonstrate the technical feasibility of the technology; • Development of a computational model to analyze the dynamic heat transfer performance of TES systems, and compare it with experimental data to verify and improve the model for further applications.;From initial explorations of candidate media, the two salts NaNO3 and eutectic MgCl2-NaCl are selected as storage media with phase change. A specialized calorimeter with requisite size and temperature capability is designed and built to obtain enthalpy values of the phase change materials (PCMs) at temperatures below and above their melting points. The calorimeter tests prove that the salts and the encapsulation methods chosen here can store thermal energy effectively while taking advantage of the latent heat of phase change. Repeated thermal-cycles show sustained performance of the EPCM, with no discernible diminishment in storage capacity.;Stainless steel capsules containing the PCMs are fabricated then and installed in a pilot-scale TES system for performance tests. The test section is first tested using solid copper capsules in place of the EPCM capsules. The results of the testing verify that the current instrumentation is capable of measuring the energy stored or extracted from the EPCM capsules with an error of +/- 5%. The test section is then loaded with EPCM capsules and subjected to thermal cycles with phase change in each cycle. The test section with EPCM capsules successfully demonstrate its ability to transfer thermal energy to and from a transport fluid, achieving energy storage and retrieval in multiple charging and discharging cycles.;Meanwhile a simulation model is developed for the thermal energy storage system and its predictions are found to agree with experimental measurements within +/- 8% in stored energy. The dynamic performance of charging and discharging rates are also well predicted by the simulation model, giving confidence to engineering design capabilities in future applications using encapsulated phase change materials for energy storage.