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V prvem delu diplomskega dela so predstavljene teoretične osnove akumulacije toplote in opis delovanja fazno spremenljivih snovi (FSS). Prikazana je njihova razdelitev ter našteti osnovni kriteriji, ki jih moramo poznati pri izbiri FSS materiala. Opisani so pogosti problemi, ki so značilni za določeno vrsto FSS, ter kako se lahko le-tem izognemo. V teoretičnem delu so prav tako na kratko opisane metode za določevannje termičnih lastnosti in predstavljene so še vrste latentnih akumulatorjev toplote z izmenjavo toplote na notranjih površinah. V drugem delu smo preučevali vpliv števila ciklov obratovanja fazno spremenljive snovi na termične lastnosti izbranega FSS materiala, in sicer magnezijevega klorida heksahidrata. FSS smo segrevali do 160 ºC in ohlajali do 50ºC za 30 faznih sprememb. Temperaturo tališča in izgubo mase smo določili z TGA/DSC1 analizo. Ugotovili smo, da se temperatura tališča in temperatura kristalizacije minimalno spreminjata. Potrdili smo dejstvo, da pride do nekongurentnega taljenja in do podhlajevanja, kar predstavlja največji problem. Prav tako smo ugotovili, da izguba mase po vsaki fazni spremembi ne vpliva na temperaturo tališča. Izkazalo se je, da je magnezijev klorid heksahidrat ugoden FSS material za akumulacijo toplote, še posebno, če upoštevamo dejstvo, da je problem podhlajevanja možno zmanjšati. Na koncu smo želeli prikazati še, kako bi izgledal FSS akumulator toplote, ki je tipa s prenosnikom toplote. The first part of the thesis presents the theoretical bases of heat accumulation and the description of the operation of phase change materials (PCM). Listed is their distribution and the basic criteria we need to know when choosing PCM materials. Common problems specific to a particular type of PCM are described, and how they can be avoided. The theoretical part also briefly describes methods for determining thermal properties and presents types of latent heat accumulators with heat exchange on internal surfaces. In the second part, the influence of the number of cycles of phase change materials operation on the thermal properties of the selected PCM material, namely magnesium chloride hexahydrate, was studied. The PCM was heated to 160ºC and cooled to 50ºC for 30 phase changes. Melting point and mass loss were determined by TGA / DSC1 analysis. It was found that the melting point and crystallization temperature varied minimally. We confirmed the fact that incongruently melting and subcooling occur, which is the biggest problem. We also found that the mass loss after each phase change did not affect the melting point. Magnesium chloride hexahydrate has proven to be a favorable PCM material for heat accumulation, especially given the fact that the problem of subcooling can be reduced. Finally, we wanted to show you what the PCM heat accumulator looks like with a heat exchanger. |
