Investigation On Thermophysical Properties Characterization Of Composite Phase Change Materials For Thermal Energy Storage

With nearly constant temperature, phase change materials (PCMs) absorb and release a large amount of heat by taking advantage of their latent enthalpy upon melting/solidification, These features makes PCMs can serve as an integrated buffer in renewable energy systems. However, a major drawback of traditional PCMs is there relatively low thermal conductivity. Recently, nano-scale or micro-scale nanoparticles (Carbon nanotubes, graphene, Ag nanoparticles, etc.) were used as additives to prepare composite PCMs with high thermal conductivity.Due to the diversity of particles type, measurement instrument and sample preparation method, existing conclusions about the thermal characters of nano-enhanced PCMs are substantially fragmented. As a result, present work focuses on the influences of filler morphology (especially 1-D and 2-D shape), size, loading on the key thermophyscial properties (thermal conductivity, viscosity, latent enthalpy, etc.) of composite PCMs. Results show that the specimens containing 2-D (graphite nanosheets, hexadecanol boron nitride, graphene nanosheets, etc.) possess an remarkable thermal conductivity. The thermal conductivity of eicosane were enhanced 400% by graphene nanosheets at the loading of 10 wt.%, and the latent enthalpy of samples still maintained above 220 kJ/kg. Except for the high intrinsic thermal conductivity, the remarkable performance of 2-D nanofillers on thermal conductivity enhancement were considered to be a result of their unique planer structure that contributes to lower thermal interface resistance.Generally, phase change transition goes through the composition or decomposition of PCM crystals, and the grain size and crystallinity of PCM crystals would determine the heat transfer behavior of composite PCMs, thus some other factors regulating the effective thermal conductivity were investigated, such as hybrid nanofillers, temperature near the melting point and cooling rate of PCMs. The morphological characterization and DSC techniques were also involved to analyze the observed results. It was found that both the temperature close to melting point and lower cooling rate of PCMs would lead to a higher thermal conductivity.Furthermore, a carbon aerogel (CA) containing nitrogen-doped graphene was fabricated using chitosan as raw material. The synthesized CA was infiltrated with 1-hexadecanol to prepare a composite PCM. A thermal conductivity enhancement of 107.9% was achieved by CA compared to the baseline of pure 1-hexadecanol. DSC results showed the promising reversible properties and a satisfied latent heat capacity of around 220 kJ/kg.