Investigation of low-temperature phase change material (PCM) with nano-additives improving thermal conductivity for better thermal response of thermal energy storage

The low thermal conductivity of organic phase change materials (PCMs) limits the heat transfer rate and increases the charging/discharging time of the latent heat thermal energy storage (LHTES). Among the efforts to improve the thermal response of LHTES is to directly increase the thermal conductivity of PCMs by adding highly conductive nanoparticles. The paper presents experimental investigation on improving the thermal conductivity of low-temperature PCM sold as RT22 HC, which can be used in passive or active cooling and heating systems in buildings. For this purpose, admixtures of graphene (GNP) and titanium dioxide (TiO 2 ) nanoparticles at different mass fractions (in range of 1-5 %) were tested. The results of the research for the nano-enhanced PCMs (NEPCMs) indicate that the addition of GNP or TiO 2 nanoparticles increases, respectively, the thermal conductivity by 0.35-0.51 W/m center dot K or 0.23-0.31 W/m center dot K in the solid state, and by 0.11-0.18 W/m center dot K or 0.10-0.12 W/ m center dot K in liquid. The highest thermal conductivity value of 0.67 W/m center dot K was measured in the solid state for RT22 HC with admixture of 5 % GNP and with SDBS (surfactant). The addition of GNP with SDBS reduces the heat capacity of the base PCM (RT22 HC) by 6-27 %, and the addition of TiO 2 nanoparticles with SDBS by 15-25 %, depending on the mass fraction of the nanoadditives. The novelty of this study are tests of the NEPCM thermal conductivity using the pipe Poensgen apparatus method for liquid and solid states and determination of the optimal mass fraction of nanoadditives in the NEPCM in terms of thermal conductivity and heat storage capacity characteristics. Application of this research results may contribute to a better thermal response of LHTES and reduce the use of fossil fuels in building heating and cooling systems.