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A composite PCM was prepared from n-octadecane and mesoporous silica (MPSiO2) nanoparticles. The nanoparticles were added in quantities ranging from 1 wt. % to 5 wt. %, and the thermal conductivity of each composite sample was determined as a function of temperature. The most significant enhancement in thermal conductivity was observed in the sample containing 3 wt. % MPSiO2 nanoparticles. The viscosity of the composite samples was also investigated and it was found that at mass fractions greater than 3%, the viscosity illustrated non-Newtonian behavior.
Nanocomposite phase change materials (PCMs) were prepared by adding silver nanoparticles to isotactic polypropylene (iPP) and an iPP/paraffin wax phase change materials. The Ag nanoparticles were found to be well dispersed in both iPP and the iPP/wax composite, and filler agglomeration was found to increase with increasing filler content. The nanoparticles did not significantly affect the modulus of the iPP on its own, but when Ag and paraffin wax were both added to the iPP PCM, the modulus was improved. The thermal and electrical conductivities of these materials were also investigated. It was found that the most significant enhancement in these two properties occurred in the iPP/wax/Ag nanocomposites. The thermal conductivities of these nanocomposites increased with filler content to a point and then levelled off, while the electrical conductivity was found to increase continuously with filler content. The effect of the cooling rate of the PCMs on the thermal conductivity was also investigated and it was determined that the samples that had been cooled slowly were more thermally conductive than those which had been quenched.
Al2O3, TiO2 nanoparticles, and carbon nanotubes were added to Iraqi paraffin wax in varying quantities to determine the optimum filler content for the enhancement of thermal conductivity. The thermal conductivity was enhanced by 65 and 40% for samples containing 5 wt. % of Al2O3 and TiO2 nanoparticles, respectively. It was concluded that the addition of these nanoparticles to paraffin wax enhanced the thermal conductivity of the phase change material without sacrificing its energy storage capacity.
Nanoparticle suspensions were prepared in two PCMs to determine the effect of the addition of nanoparticles on thermal conductivity and expediting freezing. The base PCMs used were cyclohexane and eicosane, and copper oxide nanoparticles were suspended in these hydrocarbons to produce nano-enhanced PCMs (nePCMs). The enhancement of thermal conductivity and expedited freezing were investigated by analytic, experimental, and numerical methods. The thermal conductivity in the liquid phase was significantly enhanced for the nePCMs, and it was found to increase with increasing filler content, but it decreased with increasing temperature. In the solid phase, the thermal conductivity was found to increase with temperature, as well as with filler content. It was also determined that the incorporation of nanoparticles into the PCMs expedited the freezing process.
The thermal and rheological properties of n-octadecane, a phase change material, with dispersed TiO2 nanoparticles were investigated at varying temperatures. The properties were investigated in both the solid and liquid phases, with varying mass fractions of TiO2 nanoparticles. The thermal conductivity was found to be enhanced in all of the composite samples when compared to the thermal conductivity of pure n-octadecane, and the maximum enhancement occurred at 3 wt. % TiO2 in the solid phase, and 4 wt. % in the liquid phase. The maximum enhancement was approximately 5% in both phases. The results of the rheological testing that was performed on the composite samples indicated that increasing the mass fraction of TiO2 above 2% resulted in a shift from Newtonian to non-Newtonian behavior. A predictive model for estimating the thermal conductivity of this type of composite phase change material was produced by least-squares fitting. The Bingham plastic model was evaluated as a model for predicting the rheological properties of these materials. Both of the models were in good agreement with the experimental data.
