Evaluation of Thermal Energy Storage of Phase Change Materials Based on Polyethylene Glycol Core and Thermal Conductive Polystyrene Shell for Heat Transfer Fluid Applications

Hypothesis: Solid/liquid phase change materials (PCMs) are among the materials used to store thermal energy. By nanoencapsulating these materials, the problem of leakage during melting can be solved and the thermal efficiency of the system can be increased. In previous studies, researchers have used complex and expensive methods to prepare nanocapsules of PCM. In this work, in order to simplify and reduce the time and costs of the synthesis process, the difference in the solubility parameter of the core and shell materials at different temperatures and the sequence in phase separation have been used for the synthesis of PCM nanocapsules. Methods: In order to make the desired PCM nanocapsule, the difference in solubility parameters of polyethylene glycol, polystyrene and toluene at temperatures of 5, 25 and 80ºC has been used. In fact, this difference in the solubility parameter creates a homogeneous solution of these three substances at a temperature of 80 ºC. By decreasing the temperature to 25°C, primary cores are formed and solid polyethylene glycol nanoparticles are completely separated. Further, by decreasing the temperature to 5ºC, polystyrene is separated from the solution and completely covers the nanoparticles of polyethylene glycol. In this way, using the sedimentation with temperature gradient method, polyethylene glycol nanoparticles were first synthesized, and polyethylene glycol nanoparticles were coated with polystyrene deposition. Also, to increase the thermal conductivity of the shell and the thermal efficiency of the PCM system, carbon nanoparticles have been used in polystyrene shells. Findings: Examining and evaluating the morphology of the synthesis PCM system in this work confirmed the creation of a polyethylene glycol/polystyrene core/shell nanocapsule. The thermal energy absorption efficiency of the heat transfer fluid prepared from these nanoparticles at the applied temperature of 55 ºC is about 17% more than that of water.