Preparation And Properties Of Capric-palmitic-stearic Acid Ternary Eutectic Mixture/Expanded Graphite Composite Phase Change Material

With the growing global energy situation,energy conservation and environmental protection have been paid more and more attention by the world.However,due to the discrepancy between thermal energy supply and its demand in time and space,resulting in the irrational use of energy and a lot of waste.Phase change materials(PCMs)refer to materials that can store or release heat energy during their phase transition process at a nearly constant temperature,appling PCM can realize the control of environmental temperature and the match of energy supply and demand in the time and space.Among the PCMs,fatty acids have been explored in many applications such as low temperature refrigeration and,solar energy storage,building energy conservation,heat recovery and indoor temperature controlling,due to their desirable characteristics,proper phase change temperature,low cost and the advantage of easily impregnation,or directly incorporation into conventional building materials.The phase transition temperature of PCMs can be utilized in the field of construction should between 20°C and 32°C.Capric acid(CA),palmitic acid(PA),stearic acid(SA)were chose as PCM,then the CA-PA-SA ternary eutectic mixture with a mass ratio of CA:PA:SA = 79.3:14.7:6.0 was prepared,the theoretical phase transition temperature of CA-PA-SA was 25.7°C.The CA-PA-SA ternary eutectic mixture was prepared through melt-blending according to the ratio,and only one solid-liquid phase change peak can be observed,which indicating a successful preparation of CA-PA-SA ternary eutectic mixture.In order to overcome the low thermal conductivity and leakage during the phase change process of PCM,high thermal conductivity of expanded graphite(EG)acted as a supporting material,the CA-PA-SA/EG composite PCM containing 85 wt.%,90 wt.%,and 95 wt.% CAPA-SA were prepared.The CA-PA-SA content of 90 wt.% was selected to carry on the follow-up characterization,at which the composite PCM had high latant heat and can effectively prevent PCM leakage from EG.As the packing density of composite PCM was increased from 435.7 to 743.3 kg·m-3,their thermal conductivity accordingly increased from 1.125 to 5.225 W·(m·K)-1.The initial decomposition temperature of the prepared composite PCM was 108.8oC,indicated it had good stability at the applied ambient temperature.Thermal performances of CA-PA-SA ternary eutectic mixtures and CA-PA-SA/EG composite PCM were tested.As a result of the increase in the thermal conductivity of CAPA-SA/EG composite PCM than CA-PA-SA,it takes 3400 s by heating CA-PA-SA and for CA-PA-SA/EG composite PCM only 300 s,3400 s by cooling CA-PA-SA and just 1022 s for CA-PA-SA/EG composite PCM.Thermal property characterizations after 500 heating/cooling cycles was tested,it can be found that there are no obvious difference in the phase change temperatures and latent heat indicated that CA-PA-SA/EG composite PCM had excellent thermal reliability,suitable for the field of building energy conservation.