Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Design of Acoustic Meta-Material Sound Absorbers by Finite Element Method(Izmir Institute of Technology, 2016) Manoğlu, Kaya; Önen, OnursalAcoustic meta-materials are widely known with their extra-ordinary sound properties like transmission, absorption and orientation which are not available in natural materials. These features are provided by their repeating constructions and various configurations. Sound absorbers are used in a wide variety of applications such as sound treatment in buildings, vehicles, concert halls and any place noise control and/or desirable acoustic properties are required. Traditional sound absorbers are long-known to be inefficient in the low frequency ranges. In this study, to overcome the absorption problem in low frequencies, absorption characteristics of foam based porous structures are analyzed with the addition of locally resonant blocks. Elements embedded in the absorber material with various shapes and properties are investigated by finite elements method to improve sound absorption, especially in the low frequency range. The results showed that embedding air cavities enclosed by thin solid shells to the absorber improves sound absorption in the low frequencies without significant deterioration in the high frequencies.Master Thesis Zeolite Based Composites in Energy Storage(Izmir Institute of Technology, 1999) Negiş, Fikri; Ülkü, SemraIn this thesis, second phases were used for the zeolite-based composites with high thermal conductivity for energy storage applications. Natural zeolite, clinoptilolite received from large deposits in Turkey was used as matrix while aluminum, aluminum hydroxide and graphite were used as second phases for composite preparation.Composites of different compositions (from 10 to 40 wt% additive loading) were prepared by mixing different amount of second phases to the clinoptilolite.Powder mixtures were pelletized using poly vinyl alcohol as a binder. The use of the binder was necessary to obtain mechanically strong pellets. The thermal treatment temperature and press pressure were determined as 150°C and 60 bar for the pellet preparation. Powders were further characterized by thermo gravimetric analysis, differential thermal analysis and differential scanrung calorimetry. These characterizations have shown that three types of water is present in clinoptilolite: external water, loosely bound water and tightly bound water.Thermal conductivities of these composite pellets prepared were determined using hot plate method.Thermal conductivity of pure matrix cIinoptilolite pellets were measured as 0.26 W/mK. Thermal conductivity increased significantly by using aluminum as the second phase while it did not change much for graphite and aluminum hydroxide composites.For composites containing 40% aluminum or aluminum hydroxide or graphite, thermal conductivities of 1.18, 0.50, 0.43 W/mK were measured, respectively. Aluminum containing composites could be used as adsorbent bed materials and by this way, it may increase the performance of adsorption heat pumps.