Shape-stable phase change composites based on carbonized waste pomelo peel for low-grade thermal energy storage

Abstract

Phase change materials (PCMs), like polyethylene glycol (PEG), have been widely applied to the storage and utilization of low-grade thermal energy, which is a momentous part of energy utilization and conversion. Furthermore, one of the important ways to solve the practical problems of easy leakage and slow speed of heat storage of PCMs is to prepare the phase change composites (PCCs) featured with stable shape, high enthalpy retention and improved thermal conductivity. For this purpose, we focused on the waste bio-based pomelo peel, which was converted into biochar as the supporting material of PEG through a simple carbonization process, then vacuum impregnated with four different molecular weights of PEG to obtain the PCCs characterized by no leakage, high loading and enhanced thermal diffusion ability. The DSC results revealed that the melting enthalpy of several PCCs were about 160 J/g, which were slightly lower than that of pure PEG, but the relative enthalpy efficiency still exceeded 90%. Meanwhile, PCCs had excellent thermal stability and cycling stability, and the mass loss in 200 heat-cooling cycles was only 2.69% at most, which is beneficial to the preservation of enthalpy. The tests of solar-thermal conversion and storage manifested that PCCs could make full use of the solar radiation heat energy, with the efficiency of about 75%∼x223C 80%. With the low-cost and waste-recycling, this work provides a new choice for further efficient and comprehensive utilization of low-grade thermal energy including solar radiation heat energy.