Zeolite based composites in energy storage

Abstract

In 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.