Acceleration of Heat Transfer and Melting Rate of a Phase Change Material by Nanoparticles Addition at Low Concentrations

The thermal analysis of melting process of phase change material in rectangular latent thermal energy storage unit is presented herein. To resolve the low heat transfer rate due to the low thermal conductivity of pure paraffin (the phase change material of this study), the nano-paraffin approach has been numerically investigated. Four nano-metal oxides (Al2O3, MgO, SiO2 and SnO2) with high thermal conductivity are dispersed into the pure paraffin at different concentrations (1 %, 3 % and 5 %, v/v). The adopted mathematical model that has been used to study the mass, momentum, and energy transport processes inside the nano-paraffin systems has been firstly validated by available literature data. The obtained results showed that both heat transfer and solid melting rate are significantly improved in the presence of nanomaterials, with an independent relation to the particles concentration for a long melting time, i.e. up to 10 000 s. However, above 10 000 s, high particles concentration slightly enhanced the liquid fraction. Besides, it is found that the type of particles did not affect appreciably the heat transfer and the solid melting rate. Nevertheless, the enhancing effect of the nano-paraffin system is strongly melting time dependence. For the four investigated metal oxides, the temperature system attained 351 K at 1000 s of operation, whereas that recorded for the pure paraffin at the same time is 345 K, which yields an improvement of 1.7 %. For the same conditions, the liquid fraction passes form 0.04 for pure paraffin to 0.1 for nano-paraffin system, showing 150 % of enhancement in the melting yield.