Investigation of Heat Transfer Enhancement Techniques in Thermal Energy Storage with Phase Change Materials

Abstract

Rising demand for indoor thermal comfort and modern living standards has significantly increased global energy consumption. Within the EU, buildings account for approximately 40% of total energy use, with space heating and hot water representing nearly 80% of that total figure. Currently, these needs are predominantly met through systems operated by gas, oil, or electricity, contributing to environmental issues including climate change and air and water pollution. Decarbonising the residential sector through improved energy efficiency and the integration of renewable energy sources is a key strategy for reducing energy consumption and greenhouse gas emissions.
Among renewable energy options, solar energy holds significant promise due to its abundance and accessibility. However, its intermittent nature poses integration challenges without appropriate storage solutions. Thermal energy storage (TES) system offers the potential to bridge this gap by capturing and storing thermal energy for later use. Among TES technologies, latent heat thermal energy storage (LHTES) using Phase Change Materials (PCMs) offers high energy density, operational flexibility, and cost-effective performance. The integration of PCMs in building components and domestic hot water systems can reduce energy demand and support demand-side management using stored solar or off-peak energy.
This Ph.D research investigates the enhancement of PCMs through the incorporation of carbon-based particles to improve their thermal conductivity and performance in LHTES systems. A range of PCMs with phase change temperatures between 55°C to 65°C were identified and several nano enhanced PCMs (NePCMs) were prepared and characterised. The research presents a systematic experimental investigation of particle morphology, size, and concentration on PCM performance. Both expanded graphite (EG) and graphene nanoplatelets (GNPs) were used to evaluate thermal conductivity improvements and overall material behaviour. The research includes systematic evaluation of the thermophysical properties, including latent heat, thermal conductivity, density (solid and liquid), and viscosity, as well as the microstructural impact assessed via Scanning electron microscope (SEM) and XRD analysis.
Empirical material correlations were developed to assist in future system design. The findings highlight the impact of particle type and size on performance, with some composites, such as OM65 with 6 wt.% graphene nanoplatelets (GNPs – 6-8nm), showing thermal conductivity enhancements of up to 276%.
These material level results were further validated under real operating conditions. Selected materials were tested in a custom-built coil-in-tube heat exchanger. This work contributes to ongoing development of standardised performance metrics and design criteria for PCM-based TES systems, supporting their practical application in residential heating and hot water systems. Notably, the experimental comparison was done between OM55 and OM55 based NePCM. By bridging this gap, this research offers new insights into material selection, preparation, and testing strategies that can inform future research and practical integration of LHTES systems.

Date of Award	30 Sept 2025
Original language	English
Awarding Institution	Northumbria University
Supervisor	Carolina Costa Pereira (Supervisor), Ulugbek Azimov (Supervisor), Khalid Lafdi (Supervisor) & Dominic Groulx (Supervisor)