A Mie optimization model to determine optical properties of PCM based nanofluids for solar thermal applications of glazing window

Phase change material (PCM) filled in glazing windows keeps its temperature around the melting temperature during phase change, and stores energy in the day and releases energy in the night, which can reduce air-conditioning and heating energy consumption. The optical and thermal properties of phase change material can be improved by filling with nanoparticles to produce PCM based nanofluid, which is also fundamentally important in solar thermal applications of buildings. In the present work, two models to determine optical properties of PCM based nanofluids including Rayleigh and Mie optical scattering models were firstly investigated, in which PCM is paraffin wax and nanoparticle is TiO₂. Then, the Mie optimization model was built and validated by transmittance spectrum measurement data of the paraffin nanofluid. And the influences of nanoparticle concentration and particle diameter on the optical properties of the paraffin nanofluid determined by the Mie optimization model were analyzed, including extinction and scattering characteristics. The results show that the calculation values of the Mie optimization model have a good match with the experimental transmission of the paraffin nanofluid. The larger the concentration of the nanoparticle concentration, the bigger the extinction coefficient and scattering coefficient of the paraffin nanofluid. When the nanoparticle concentration is constant, the larger the particle diameter is, the larger the scattering coefficient is doubled. When the diameter of the nanoparticles increases from 10 nm to 30 nm, the scattering coefficient of the paraffin nanofluid increases by 28.7 times.