Preparation And Thermal Properties Of Shape-Stabilized Phase Change Materials For Enhancement Of Thermal Conductivity

Capric acid (CA), lauric acid (LA) and palmitic acide (PA), as organic phase changematerials (PCMs), possess high phase change enthalpy. They could form eutectic mixture,which own the phase change enthalpy of140.5J/g and could be used as new kind of organicPCM. However, these organic PCMs have some inherent limitations, such as low thermalconductivity and need of containers.In order to improve the thermal conductivity of these organic PCMs, a series ofcomposite materials made up of carbon materials and organic PCMs were prepared. Moreover,the effects of the carbon materials on the thermal properties of the PCMs were investigated.Firstly, fatty acids/expanded graphite composites as shape-stabilized phase changematerials were prepared through infiltration method by using the eutectic mixture as PCMs,expanded graphite as skeleton, and the coating compound as membrane. Expanded graphitewas also used to improve the thermal conductivity of the shape stabilized PCMs, N2adsorption curve and SEM images of expanded graphite and the composites indicate thatexpanded graphite has a loose porous structure and the eutectic mixture was effectivelyabsorbed into its porous structure. DSC thermograms and thermal performance test show thatthe composites possess good phase change behavior (the latent heat is95.6J/g, the phasechange temperature is18.4oC) and thermal cycling stability. Under the PCMs endothermicprocess, it can maintain effective temperature in8-17oC for140s, reducing22.2%heatstorage capacity compared with fatty acids temperature effectively. The thermal conductivityof the composite material is also significantly improved (up to0.738W/(m k)) due to thehighly thermal conductive expanded graphite.Secondly, a series of fatty acids/CNTs composite shape-stabilized PCMs were preparedthrough infiltration method by using multi-walled carbon nanotubes as a supporting materialto improve the thermal conductivity of the shape-stabilized PCMs. N2adsorption–desorptioncurves and SEM images of composite shape-stabilized PCMs indicate that the eutecticmixture was effectively absorbed into the porous structure of the CNTs. DSC thermogramsshow that the composite fatty acids/CNTs possess good phase change behavior. And the latentheat of the sample absorbed with80wt%fatty acids can achieve101.6J/g in the meltingprocess and its phase change temperatures and latent heat almost remain unchanged in30times of thermal cycling. Moreover, the thermal conductivities of the composite materials are significantly improved (up to0.666W/(m k)) due to the addition of the highly thermalconductive CNTs.