Study On Phase Change Energy Storage Of PEG System

At present, as for solid-liquid phase change energy storage material, both inorganic and organic, there is a liquid leakage problem during the phase change process, so receptacle is needed to seal them. This will increase cost and the heat resistance between heat transfer medium and phase change material, and cause the decrease of efficiency of heat transfer.The essential of composite phase change material is the compounding of solid-liquid phase change material and other material. The phase change material can keep the shape stable before and after the phase change process, so the solid-liquid phase change material becomes solid-solid phase change material. These materials have little requirement for recipient and can even be used directly, so the cost is cut down. The composite phase change materials not only overcome the disadvantages of single phase change material, but enlarge the application of phase change material.A solid-solid phase change material was synthesized via the two-step condensation reaction of polyethylene glycol (PEG6000) as soft segments with reactant chains of 4,4ËŠ-diphenylmethane diisocyanate (MDI) and glycerol as hard segments. FT-IR,DSC,WAXD,TG,POM, SEM were used to investigate the structural characteristics, phase change behaviors, heat storage characteristics, aggregation structure and phase change mechanism.The results indicate that the phase change material has a blocking cross-linking PU structure. The phase change process is a typical solid-solid phase change with good thermal properties: appropriate phase change temperature, large phase change enthalpy, no liquid leakage in the phase change process and great phase change reversibility. The essential of phase change is the transition from crystal to amorphism of PEG. So this kind polymeric solid-solid phase change materials have a promising market application.The peak temperature Tp and the onset crystallization temperature Tc shifted to the lower temperature and half crystallization time t1/2 decreased with the increasing cooling rate. Kinetics parameters obtained by Ozawa method did not have a good linear relationship, but Mo method described this system very well. The apparent activation energy (Ea) calculated by Ozawa method is larger than that of pristine PEG, which indicates that the PEG chains in PCM need to overcome the astriction of hard segments to transfer from crystal to amorphism.A series of PCM with different phase change temperature and phase change enthalpy can be obtained by changing the content and molecular weight of PEG. Both the phase change temperature and phase change enthalpy of PCM drop rapidly with the decrease of PEG content; enthalpy of PCM, with the same soft segment content but different molecular weight, increase with the increase of molecular weight, when the soft segment molecular weight reaches to a certain value, the enthalpy starts to drop slightly, the change of phase change temperature shows agreement with that of enthalpy. The introduction of hard segments improves the thermal stability of the PCM, but it also greatly influences the perfection of the soft segments crystals, causing the sharp decrease of crystallinity of soft segments.The introduction of graphite does not improve the thermal stability of PCM markedly. The phase change enthalpy decreases with the increase of additive content, but phase change temperature changes slightly. Compared with PCM, the introduction of graphite evidently enhances the heat storage and release rate of composite PCM.