Phase change materials (PCMs) are substances that absorb or release a significant amount of heat during phase transitions. These are materials that can store thermal energy and have great potential in the field of cooling and heating the buildings with the aim of reducing energy consumption and financial costs. Important properties for selecting PCMs typically include thermal capacity, durability, non-toxicity, with particular importance given to the phase transition temperature and latent heat. Despite having greater latent heat, the liquid-gas transition is impractical for use in infrastructure due to the large change in volume.
In this master's thesis, I studied the thermal characteristics of paraffin-based PCMs and composites using various thermal analysis methods, determining their suitability for use in infrastructure based on these properties. I determined the heat capacity of the materials using the sapphire method, which requires differential scanning calorimetry (DSC) measurements on samples and sapphire, which has a known heat capacity in the selected temperature range. The highest heat capacity was observed in the PCM sample, followed by the composite samples and finally concrete. A high heat capacity is desirable as it allows the material to store more heat. To determine the latent heat and material durability over multiple temperature cycles, I used cyclic DSC, where samples were subjected to a series of cooling and heating cycles. All samples analyzed showed good durability, as the phase transition enthalpies did not decrease, indicating that such materials could be used over a longer period. Additionally, we determined that the highest transition enthalpy was in the PCM sample, followed by the composite with higher content of PCM, and then the composite with a lesser content of PCM. We studied the composition of PCMs and composites using coupled TG-MS and TG-GC-MS techniques. The TG MS analysis signal provides a complex mass spectrum, as all gas species released at a given temperature are analyzed simultaneously, making it challenging to identify all present species. This issue was mitigated using TG-GC-MS, where gases at selected temperatures are collected in separate loops and then separated with GC. Due to this separation, each gas species enters separately in the mass analyzer, and using the mass spectra library, I could determine which species were released. The strongest signals were for hydrocarbons, which was expected since paraffin-based PCMs were used. The most pronounced signal was for octadecane, which matched the specification of PCM28 with a melting point of 28 °C, as this is also the melting point of octadecane. Based on the results obtained, I confirmed that paraffin-based PCMs have a great potential for further research and development for use in buildings.
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