04/13/2022
By Sokny Long

The Francis College of Engineering, Department of Mechanical Engineering, invites you to attend a doctoral proposal defense by Che-Fu Su on “Thermal Conductivity Enhancement by Magnetic Alignment of Metallic Micro/Nano particles and Wires in Phase Change Material.”

Ph.D. Candidate: Che-Fu Su
Defense Date: Friday, April 22, 2022
Time: 9 to 11 a.m. EST
Location: This will be a virtual defense via Zoom. Those interested in attending should contact CheFu_Su@student.uml.edu and committee advisor, Hongwei_Sun@uml.edu, at least 24 hours prior to the defense to request access to the meeting.

Thesis/Dissertation Title: Magnetic Assembly of Nanoparticles/nanowires for Thermal Conductivity Enhancement of Phase Change Materials Applications

Committee Chair (Advisor): Hongwei Sun, Department of Mechanical Engineering,
University of Massachusetts Lowell

Committee Members:

  • Zhiyong Gu, Department of Chemical Engineering, University of Massachusetts Lowell
  • Fuqiang Liu, Department of Mechanical Engineering, University of Massachusetts Lowell
  • Sammy Shina, Department of Mechanical Engineering, University of Massachusetts Lowell

Abstract:

Enhancing the thermal conductivity of phase change materials (PCMs) is attracting attention to renewable energy applications such as solar, geothermal, and wind energy. The use of energy storage can significantly improve the efficiency of renewable energy systems due to their intermittent nature. Latent heat thermal energy storage is a particularly attractive technique due to its high capacity can store energy at near constant temperature corresponding to the phase transition temperature of the PCMs. The use of latent heat absorption in PCMs is an important way of storing thermal energy. It has the advantages of high-energy storage density and the isothermal nature of the storage process through melting and solidifying at certain temperatures. A wax material, paraffin has been widely used in variety fabrication according to its characteristics such as high latent heat, chemical stability, no sub-cooling, non-corrosive, and low vapor pressure. However, most PCMs have an unacceptably low thermal conductivity (e.g. paraffin : near 0.25 W/m°C). This poor thermal performance has limited many applications of current PCMs for high power, transient and large scale systems and is one of the major challenges facing energy industries such as renewable energies, waste heat recovery, and energy storage systems. In fact, the drawback of low thermal conductivity can be overcome by dispersing high conductivity fillers for instance nickel (Ni) nanoparticles/nanowires in PCMs.

In the present work, we are exploring a new type of PCMs – nanoparticles/nanowires embedded PCMs (nanoPCM) that are fabricated by the magnetic assembly of nanoparticles/nanowires in PCM followed by nano-soldering technique. The nanoparticles/nanowires were aligned and formed chain-like structures in the magnetic fields. Furthermore, pre-fabricated magnetic pads were employed to direct the motion of the particles/wires in the assembly process. The experimental study has shown the high conductivity chain-like structures are effective in enhancing the thermal conductivity of original PCMs. In addition, the thermal conductivity of the new nanoPCMs strongly depends on the morphology of the Ni nanoparticles/nanowires structures formed by the magnetic assembly. To fundamentally understand the behavior of the nanoparticles/nanowires in the applied magnetic fields, a Monte Carlo (MC) method was integrated with the finite element method (FEM) method to investigate the formation of the nanostructures subjected to an applied magnetic field. It was found that the applied field significantly affect the interactive forces between Ni nanoparticles/nanowires and produces different chain-like nanostructures in the direction of the external magnetic field. The preliminary results have shown the external magnetic field and pre-fabricated interdigital magnetic lines can be utilized to control the orientation and size of the Ni chain-like nanostructures successfully. The future work will focus on the use of other magnetic pads such as triangular magnetic pads for the further investigation of directed magnetic assembly of nanoparticles/nanowires.

All interested students and faculty members are invited to attend virtually.