FABRICATION AND EVALUATION OF ENCAPSULATED PHASE CHANGE MATERIALS FOR LATENT HEAT STORAGE

Abstract

The growing global energy demand and overreliance on fossil fuels like coal and petroleum have resulted in serious environmental issues such as climate change, greenhouse gas emissions, and ecological imbalance. The pursuit of sustainable energy management technologies that can boost energy efficiency while lessening the demand on non-renewable resources has accelerated due to these concerns. Among numerous approaches, thermal energy storage (TES) systems have emerged as a viable alternative for storing excess thermal energy and releasing it whenever it is required. Phase change materials (PCMs) have drawn a lot of attention in this regard because of their capacity to store and release a significant quantity of latent heat during phase transition at constant temperatures. Among the several PCMs, Eicosane (ESE) is well known for its high latent heat storage capacity, non-corrosive nature, chemical stability, and appropriate melting temperature for applications involving low-temperature TES. The core PCM in this work is ESE, which has a melting point of about 38.9 °C and a melting enthalpy of 239.9 J.g-1. Despite its benefits, paraffin-based PCMs have numerous intrinsic drawbacks that limit their practical application, including limited thermal conductivity, poor structural stability, and leakage during the phase change process. As a result, the current thesis is focused on producing advanced material techniques to overcome these obstacles and broaden the application of paraffin-based PCMs. To achieve the desired objectives, ESE was first microencapsulated into polymeric shell of polystyrene (PS) by a mini-emulsion polymerization process aided by probe sonication, where polybutylacrylate (PBA) copolymer shell was also used to increase structural integrity. The resultant microencapsulated phase change materials (MPCMs) showed an encapsulation ratio of 91.9%, encapsulation efficiency of 91.6%, with a melting enthalpy of 220.5 J.g-1. The thermal stability and behaviour of the microcapsules were systematically analyzed using Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) while diffusion tests were carried out to assess leakage resistance. The findings demonstrated that, in comparison to pure ESE, the microencapsulated systems had noticeably improved thermal stability. Additionally, paraffin was encapsulated at the nanoscale to produce nanoencapsulated phase change materials (NPCMs), which further enhanced heat transfer properties and interfacial xxv interactions. The PCM's thermal responsiveness is improved by the increased surface area that the smaller particle size offered, which promotes interaction between the PCM and its surroundings. The synthesized NPCMs possessed an encapsulation ratio of 93.6%, encapsulation efficiency of 87.2%, and melting enthalpy of 224.6 J.g-1. The efficient encapsulation of ESE within the polymeric shell of polystearylmethacrylate was verified using Fourier Transform Infrared Spectroscopy (FTIR), while the particle size distribution of the produced nanocapsules was ascertained. Further research includes the development of microcapsules with varying crosslinking agent ratios within the polymer shell in order to optimize the thermal stability of the MPCM and investigate their effects on structural strength. The thermal performance and stability of these MPCMs were assessed using DSC and TGA techniques, and significant thermal parameters were calculated from the thermograms in order to assess their performance as TES systems. Among the investigated formulations, EPD5 exhibited a melting enthalpy of 170.5 J.g-1, an encapsulation ratio of 62.4%, and an encapsulation efficiency of 68.3%. The encapsulated PCM system was supplemented with synthesized thermal conductive nanoparticles (NPs) to improve the overall thermal performance of the tailored microcapsules. Powder X-ray Diffraction (PXRD) analysis revealed the amorphous nature of the surrounding polymer shell and validated the structural properties of these NPs. The inclusion of NPs improved the thermal response of the encapsulated PCM system. The ZnATH-(O) NP-doped MPCM (Z7) showed a melting enthalpy of 186.8 J.g-1, while the FeATH-(O) NP-doped MPCM (F5) exhibited a melting enthalpy of 226.2 J.g-1, with encapsulation ratios of 77.9% and 94.3%, respectively. In addition to encapsulation techniques, shape-stabilized phase change materials (SSPCMs) were produced using porous supporting material to mitigate seepage during the phase transition of the PCMs. The optimized ESE/MWCNT SSPCM (SS-EM@9) achieved a melting enthalpy of 215.3 J.g-1 and crystallization enthalpy of 212.7 J.g-1, with a thermal storage capacity of 99.8%. The morphological features of the composites were evaluated using Field-Emission Scanning Electron Microscopy (FE-SEM), which revealed the efficient inclusion of PCM inside the porous structure. The obtained SSPCMs showed enhanced thermal stability and remarkable structural integrity. xxvi Overall, this study provides a thorough investigation into the design, synthesis, and characterization of MPCMs, NPCMs and SSPCMs for efficient TES. The synthesized novel materials exhibit improved stability and performance, indicating their potential for real-world applications in TES technologies. This research makes a substantial contribution to the fields of materials engineering, polymer science, and energy storage. It also offers a viable solution to lessen reliance on non-renewable energy sources while promoting sustainable energy management.