Novel Nano-Enhanced Phase Change Materials for Thermal Energy Storage Applications

Abstract

The increasing demand for efficient and sustainable thermal energy storage (TES) systems has driven extensive research into phase change materials (PCMs). Despite their high energy storage capacity, the low thermal conductivity of PCMs limits their application. This thesis investigates the development and enhancement of nano-enhanced PCMs (nano-PCMs) through the incorporation of various nanoparticles, aiming to improve their thermophysical properties, stability, and cost-effectiveness for use in energy-efficient building applications. This study introduces novel approaches to enhancing PCMs by integrating multi-walled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNP), and titanium dioxide (TiO2) as both single and hybrid nanoparticles. Paraffin, with a phase change temperature of 27-29 °C, was selected for this study due to its alignment with the nominal indoor comfort temperature of buildings and its versatility for various TES applications within this temperature range. Advanced characterisation techniques, including Fourier-Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Thermal Conductivity Analyzer, were employed to evaluate the thermophysical properties and stability of the developed nano-PCMs. The key findings reveal that the GNP+MWCNTs hybrid at 1.0 wt.% achieved a remarkable thermal conductivity enhancement of 170% at 25°C, significantly improving thermal performance. TiO2-based PCMs showed minimal reductions in latent heat, with decreases of -3.7%, -5.2%, and -5.5% for TiO2, TiO2+GNP, and TiO2+MWCNTs, respectively, at 1 wt.%. These results underscore the potential of TiO2 as a cost-effective nanomaterial for enhancing PCM stability and performance. The investigation into surface-functionalised MWCNTs demonstrated superior stability and thermal performance. Functionalised MWCNTs-based PCMs exhibited a 158% increase in thermal conductivity at 25°C and maintained their performance over time, unlike unfunctionalised MWCNTs. The hybrid configurations of functionalised MWCNTs with TiO2 nanoparticles revealed minimal reductions in latent heat, with the F-MWCNTs+TiO2 (25:75) hybrid showing only a -0.36% decrease during melting and -1.19% during crystallisation. A comparative analysis highlights the overall improved performance of hybrid nanoparticles. The GNP+MWCNTs hybrid combination displayed the highest thermal conductivity, while the TiO2+functionalised MWCNTs hybrid at various concentrations (25:75, 50:50, 75:25) exhibited enhanced stability and cost-effectiveness, making them suitable for large-scale applications. Specific heat capacity (Cp) values of functionalised MWCNTs-based nano-PCMs were notably higher, with maximum values of 3.5 J/g°C and 2.5 J/g°C at 25°C and 45°C, respectively. The enhanced stability and thermal properties of nano-PCMs, particularly those with hybrid nanoparticles, position them as effective solutions for thermal energy storage in energy-efficient buildings and renewable energy systems. Overall, this research demonstrates the novel potential of nano-enhanced PCMs to address thermal management challenges in modern building applications, contributing to sustainable and cost-effective energy management solutions.