Enhancement of the Thermal Performance of Organic PCMs using Different Types of Nanoparticles

Abstract

In recent years, phase change material (PCM) composites have attracted lots of attention in latent heat thermal energy storage applications due to its flexible transition temperatures and excellent chemical compatibility. The thermal properties of the conventional organic PCMs such as paraffin wax or polyethylene glycol (PEG) can be significantly enhanced using various types of highly conductive nanofillers. This research investigates the comprehensive set of thermal trends of PCM composites, fabricated from incorporating different fillers (such as graphene nanoplatelets, milled carbon fibre, graphene oxide, graphite, and hexagonal boron nitride) at an extensive range of loading (an average of 1% to 15% by weight) into the PCM matrices and provides an in-depth analysis of heat transfer mechanism. The experimental results from thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) revealed an acute improvement in the thermal properties of common PCMs. For instance, the volumetric heat capacity of the PCM composites exhibited a reduction of roughly 68% at high loadings, as well as the latent heat of fusion decreased by approximately 30% in both paraffin-based and PEG-based composites. Moreover, the thermal conductivity and thermal diffusivity of paraffin wax and PEG could be enhanced up to 334.6%, 3341.1%, 152.6% and 229.2% respectively, while maintaining insignificant changes in phase transition temperature and latent heat of crystallisation. The thermal cyclability was also very convincing for thermal energy storage applications, as these PCM nanocomposites were stable with trivial fluctuations in thermal properties after 100 heating-cooling-heating cycles. The oxidative stability of these PCM composites was maintained up to a temperature of 300℃. To identify the even distribution of nanofillers and observe the agglomeration effect in nanoparticles, Raman Spectroscopy and Scanning Electron Microscopy (SEM) were extensively used. To further confirm that no chemical reactions took place between the constituent materials, Fourier Transform Infrared (FTIR) was used to distinguish the chemical functional groups in each PCM composite. A more advanced technique of Scanning Thermal Microscopy (SThM) was applied to investigate the local temperature gradient across the PCM composites and therefore compute the interfacial conductance and contact resistance between the PCM matrices and nanofillers. In addition, it was found that the experimental results were most comparable with the Maxwell and EMT models. However, there were discrepancies in the data due to many other parameters, such as interfacial contact resistance, aspect ratio of nanofillers, bonding and interactions between interfacial regions, phonon distribution etc. Therefore, a simple modified Maxwell model was proposed to predict the thermal conductivity in this work. Finally, the two best PCM composites were selected for potential utilisation in thermal energy storage systems.

Date of Award	31 Dec 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Adel Nasser (Supervisor), Cristina Valles (Supervisor) & Chamil Abeykoon (Supervisor)