Microencapsulated Paraffin In Polyurea For Thermal Energy Storage

For many years, in an attempt to reduce the carbon dioxide emissionsand the consumption of finite fossil fuels, many efforts have been devotedto the use of renewable energy sources, such as solar energy, particularlyin areas where low temperature applications are involved. In fact, solarenergy is considered an economic alternative energy. However, the supplyof solar energy is intermittent, variable and unpredictable. Theseproblems can be solved by storage of thermal energy. Latent heat storagematerials have advantages of performing the storage function at nearlyconstant temperature and have large storage capacities. However, thereare some inherent drawbacks when phase change material (PCM) is used inthermal energy storage system, for example, (1) poor heat transfer whenPCM freezes on the latent heat storage devices; (2) highly corrosive tocertain container materials; (3) large change in volume during phasetransition and limit the use of simple container and heat exchangergeometry; (4) highly toxic and poisonous, and require completely sealedstorage system resulting in expensive system. One of the promising waysto solve these problems mentioned above is to choose the encapsulatedPCM as the storage material.In recent times, microcapsules made out of polymers and paraffin waxes werethought to be good thermal energy storage materials, in which the heat is stored aslatent heat of fusion in the paraffin waxes. In this thesis, several microcapsules weremade out of different polyurea using interfacial polycondensation method betweentoluence-2, 4-diisocyanate and three kinds of diamines. Diethylenetriamine,ethylenediamine and 1,6-hexanediamine were employed as water-soluble monomers.The most important properties of these microcapsules, like the chemical structure,particle size distribution, thermal stability and the latent heat of fusion were studied.On the other hand, the polymeric shell does not influence the melting and freezingbehavior of the paraffin waxes in polyurea. Thermal cyclic tests show thatencapsulated paraffin waxes kept its energy storage capacity even after 50 cycles ofoperation. The results obtained from experiments show that encapsulated paraffinwaxes possess a good potential as a thermal energy storage material. In a word,interfacial polycondesation between isocyanate and amine to form polyurea shell is aquick, feasible way for encapsulation of paraffin waxes. Additionally, fatty acids being of an organic compound have similar meltingranges and heats of fusion to organic paraffin substances. However, its low thermalconductivity and corrosive to container pose an obstacle to its wide application. Inthis research project, fatty acid/ silicon dioxide composite phase change materialswere prepared by sol-gel method. The structure and properties of the compositematerial have been studied with FT-IR, DSC and TG. The result shows that phasechange composite material has favorable heat storage performance. It can be used forstorage of solar energy and some other aspects.