Mechanism Study Of Improving The Performance Of Phase Change Materials Using Nanoparticles

Paraffin is widely used to store thermal energy by taking advantage of the latent heat (heat of fusion) during phase change. An undesirable property of paraffin is the relatively low thermal conductivity that strongly suppresses the energy charging/discharging rates. Introduction of highly conductive materials to form a composite of the paraffin and thermal conductivity promoter is a logical solution. The paraffin was immersed with CuO nanoparticles to improve the thermal performance of paraffin in this paper. Use experimental and numerical simulation methods to investigate the influence of nano-copper oxide powders, volume fraction of the powders on phase change process. The non-isothermal solidification of the paraffin immersed with CuO nanoparticles is investigated to examine how the CuO nanoparticles and the cooling rates affect the relative crystallinity, solidification time and nucleation by DSC. The results show that the nanoparticles improve the nucleation of the paraffin at early stage of the solidification, while it will hinder the growth of nucleation agent as the solidification process proceeds. The cooling rate apparently accelerates the solidification process of the paraffin.The quantity of paraffin and composites for DSC test is about 3-15mg, while it’s not enough for industrial applications. So design a simple test platform to research the solidification and melting process of paraffin and composites in this paper. The solidification time of paraffin decreases with the increasing of the volume fraction of the nano-copper oxide particles. The time decreases by 12.5% and 32.5% for paraffin/0.03 CuO and paraffin/0.05CuO. The experimental result shows that nano CuO will seriously coagulate after 2 weeks.Compare the experimental results and numerical simulation that is not very reliable to verify the data obtain from Fluent, which the melting and solidification model is utilized to simulate the process of phase change. The result indicates that the deviation between experiment result and simulation result for paraffin, paraffin/0.03 CuO and paraffin/0.05 CuO are 10%, 13.4% and 7.8%. Phase interface with the change of time are displayed for paraffin and composites.CuO nanoparticles improve the performance of paraffin during the phase change and decrease the time needed for the solidification process. There are two reasons for this phenomenon, first, the copper oxide increases the thermal conductivity of phase change materials, second, CuO nanoparticles are nucleation agents, promoting the nucleation process.