Seyed Amir Hassan Bathaei - Department of Energy, Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Iran.
Masoud Iranmanesh - Department of Energy, Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Iran.
Hossein Amiri - Department of Energy, Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Iran.
Hajir Kourki - Chemical Engineering Department, Polymer Engineering Group Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Iran.

Thermal Energy Storage (TES) for solar thermal systems has attracted great attention because of the intermittent availability of solar energy. In the current paper, new combinations of several Phase Change Materials (PCMs) including a type of paraffin and some mineral compounds like ammonium nitrate and magnesium nitrate hexahydrate were exanimated and their thermo-physical properties were compared. This study targets solar heating systems at different temperature intervals for the TES. Another new approach of this study is to determine the effect of Multi-Wall Carbon Nanotubes (MWCNTs) with two diameters (D) of ۸ and ۱۰-۲۰ nm on paraffin's thermophysical property to improve these properties. An innovative method was used to measure Electrical Conductivity (EC) as it is easier to measure than thermal conductivity (K) to study the effect of nanoparticles on PCM behavior. The results showed that the highest values of improvement over paraffin properties were related to ۵% nanoparticle additive for both nanoparticle diameters among the percentages studied. The addition of ۵ % nanoparticles with ۱۰-۲۰ nm and ۸ nm to paraffin at ۲۵ ° C increased heat conductivity by ۱۴۲% and ۱۵۶%, respectively. The addition of nanoparticles to paraffin improved EC several times such that a diameter of ۸ nm made a ۳۰۰% increase in EC compared to ۱۰-۲۰ nm.

Solar thermal energy storage, phase change materials, Paraffin, MWCNTs, Thermo-Physical Properties