magistrsko delo
Mihael Turkovic (Author), Nataša Čelan Korošin (Mentor), Helena Prosen (Thesis defence commission member), Tina Skalar (Thesis defence commission member)

Abstract

Fazno spremenljivi materiali oziroma PCM-i (ang. Phase change materials) so snovi, ki pri faznem prehodu absorbirajo ali sprostijo znatno količino toplote. To so materiali, ki lahko shranijo toplotno energijo in imajo velik potencial na področju hlajenja ter ogrevanja stavb z namenom zmanjšanja porabe energijskih virov in finančnih stroškov. Pomembne lastnosti pri izbiri PCM-ov so običajno toplotna kapaciteta, obstojnost, nestrupenost, še posebej pa sta pomembni temperatura faznega prehoda in talilna oz. izparilna toplota. Čeprav je slednja običajno višja, pa prehod tekoče-plinasto zaradi velike spremembe v volumnu ni primeren za uporabo v infrastrukturi. V tem magistrskem delu sem z različnimi metodami termične analize preučeval termične karakteristike parafinskih PCM-ov in kompozitov ter na podlagi lastnosti določil njihovo primernost za uporabo v infrastrukturi. Toplotno kapaciteto materialov sem določeval s safirno metodo, ki zahteva izvedbo meritev diferenčne dinamične kalorimetrije (DSC) na vzorcih in safirju, ki ima znano toplotno kapaciteto v izbranem temperaturnem območju. Najvišjo toplotno kapaciteto je imel vzorec PCM-a, sledila sta vzorca kompozitov in na koncu beton. Visoka toplotna kapaciteta je zaželena, saj bo material tako shranil več toplote. Za določevanje entalpij prehoda in obstojnosti materiala skozi več temperaturnih ciklov sem uporabil ciklično DSC, kjer so vzorci bili izpostavljeni nizu ciklov hlajenja in segrevanja. Vsi analizirani vzorci so izkazali dobro obstojnost, saj se entalpije faznih prehodov niso manjšale, kar pomeni, da bi tovrstne materiale lahko uporabili skozi daljše časovno obdobje. Poleg tega smo določili, da je najvišjo entalpijo prehoda imel vzorec PCM-a, sledil je kompozit z več dodanega PCM-a in nato kompozit z manjšim deležem PCM-a. Sestavo PCM-ov in kompozitov smo preučevali s sklopitvenima tehnikama TG MS in TG-GC-MS. Signal analize TG-MS poda kompleksen masni spekter, saj se na analizatorju hkrati analizirajo vse plinske zvrsti, ki so sproščene pri določeni temperaturi, zato je določitev vseh prisotnih zvrsti prezahtevna. To težavo smo odpravili z uporabo TG-GC-MS, kjer se pline pri izbrani temperaturi zbira v ločene zanke in se jih nato loči z GC. Zaradi te ločbe vsaka plinska zvrst pride posebej v masni analizator in sem z uporabo knjižnice masnih spektrov lahko določil, katere zvrsti so se sproščale iz vzorca. Najmočnejši so bili signali za ogljikovodike, kar je bilo pričakovano, saj so bili uporabljeni PCM-i na parafinski osnovi. Najbolj izrazit signal je bil za oktadekan, kar je ustrezalo specifikaciji PCM28, ki ima tališče pri 28 °C, saj je to tudi tališče oktadekana. Na podlagi dobljenih rezultatov sem potrdil, da imajo parafinski PCM-i velik potencial za nadaljnje raziskave in razvoj za uporabo v stavbah.

Keywords

fazno spremenljivi materiali;termogravimetrična analiza;TG-GC-MS;diferenčna dinamična kalorimetrija;magistrska dela;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FKKT - Faculty of Chemistry and Chemical Technology
Publisher: [M. Turkovic]
UDC: 543.57(043.2)
COBISS: 228196611 Link will open in a new window
Views: 91
Downloads: 9
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Other data

Secondary language: English
Secondary title: Thermal analysis of phase change materials for application in buildings
Secondary abstract: 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.
Secondary keywords: phase change materials;thermal analysis;composite materials;TG-GC-MS;Termična analiza;Kompoziti;Univerzitetna in visokošolska dela;
Type (COBISS): Master's thesis/paper
Study programme: 1000375
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za kemijo in kemijsko tehnologijo, smer Kemija
Pages: 1 spletni vir (1 datoteka PDF (78 str.))
ID: 25937687