Solid-solid phase change materials (SS-PCMs) offer promising capabilities for thermal energy storage due to their high latent heat density, minimal volume change, and inherent form-stability. This study investigates an experimental case study of the solid-solid phase transition of pentaerythritol (PE) and pentaglycerine (PG) composites enhanced with multiwalled carbon nanotubes (MWCNTs) designed for low to high thermal energy storage systems. The materials were also fabricated as cold pressed tablets and evaluated their phase transition behaviour, subcooling characteristics, and effective thermal conductivity. The effect of MWCNTs on subcooling and their influence on thermal conductivity in cold pressed SS-PCM tablets are also investigated. Differential scanning calorimetry analysis of powders revealed that pure PE exhibits a solid-solid transition at approximately 199 °C with latent heat around 280 kJ/kg in a closed experimental setup, significantly reducing mass loss. Pure PG demonstrated a stable phase transition at about 95 °C with latent heat of approximately 183 kJ/kg. Tablets prepared by cold pressing showed increased subcooling effects, notably mitigated by the addition of up to 10 wt.% MWCNTs, which reduced subcooling by about 2.2 °C. However, thermal conductivity decreased unexpectedly from 0.364 W/(m K) for pure PG to 0.269 W/(m K) at 10 wt.% MWCNT loading. This reduction is attributed to increased porosity introduced during tablet fabrication, which enhances phonon scattering and counteracts the intrinsically high thermal conductivity of the MWCNTs. Numerical modelling supported the dominant role of porosity on thermal transfer performance. Despite the reduced thermal conductivity, nanotube-reinforced composites retained high latent heat capacities (>150 kJ/kg), highlighting the potential of PE-based composites for high-temperature applications and PG-based composites for low-temperature thermal energy storage. The results demonstrate the critical influence of fabrication induced microstructure on thermal performance and provide insights for optimizing filler content and densification strategies in solid-solid latent heat storage systems. Future, research should focus on optimizing filler content and porosity reduction to enhance thermal conductivity without sacrificing latent heat performance.
Muhammad et al. (Mon,) studied this question.