Paraffin wax, known for its high latent heat, chemical stability, less super-cooling, non-corrosive, low vapor pressure and low cost has drawn extensive attention as one of renewable energy storage materials. However, the thermal conductivity of paraffin wax (e.g. paraffin: \~0.26 W/m ^o^C) is unacceptably low which has prevented the paraffin wax from being widely used in high power, transient and large scale systems like renewable energies and waste heat recovery. In order to improve the thermal conductivity of paraffin wax, materials with high thermal conductivity are mixed into the paraffin wax, such as Ni nanoparticles with thermal conductivity around 90 W/m ^o^C.

This research focuses on numerical investigation of the improvement of the thermal conductivity of paraffin/Ni nanoparticles composite in which the Ni nanoparticles are magnetically aligned in the paraffin wax under a uniform magnetic field at different concentrations.  

According to the previous experiment of aligning the Ni nanoparticles in the PDMS (Polydimethylsiloxane) under a uniform magnetic field, the morphology of Ni nanoparticles column structures such as diameter and spacing between columns were obtained for different Ni particle concentrations. Assumptions such as uniformly and continuously distributed columns across the paraffin and negligible interfacial resistance between Ni particle and paraffin were applied in the simulation. To reduce the simulation time and memory, instead of simulate the Ni nanoparticles columns at micro scale level, a unit cell volume of paraffin/Ni particle column structure was simulated and the anisotropic thermal conductivities of the composite were utilized in the phase change model. The mass fraction and melting speed of the paraffin composite shows that the melting of Ni particle embedded paraffin is heavily dependent of the morphologies and concentrations of the Ni nanoparticles in the wax.

Another part of the research is concentrated on the local melting behavior of paraffin/Ni particle composite. A single Ni nanoparticle column structure imbedded in paraffin was simulated under the same thermal condition as the first part. It was found that the paraffin near the Ni particle column will melt before the other location due to the high thermal conductivity of the column. The difference of the melting interface near the column and away the column increases with time. The difference also highly depends on the volume concentration of Ni nanoparticles in the paraffin. In addition, the relationships between thermal conductivity, concentration and the state of nanoparticles in the composite will be presented at the end of the presentation.


Simulation of Phase Change Process of Paraffin Embedded With Microscale Particle Columns

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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