Browsing by Author "Demir, Hasan"

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An experimental and theoretical study on the improvement of adsorption heat pump performance
(Izmir Institute of Technology, 2008) Demir, Hasan; Ülkü, Semra
Adsorption heat pumps, which have considerably sparked attentions in recent years, have the advantage of being environmentally friendly and operating with heat sources such as waste heat, solar and geothermal energies as well as storing the energy.The present investigation covers working principle of adsorption heat pumps, a detailed literature survey on the performed studies, information about adsorption phenomena, experimental results of two differently designed and constructed systems, numerical simulation of heat and mass transfer in an annular adsorbent bed, and microcalorimetric study for obtaining isosteric heat of adsorption for water vapor-silica gel pair. The two intermittent adsorption heat pumps can operate without any leakage. The silica gelwater was employed as the adsorbent-adsorbate pair in both of the systems. The temperature and pressure in the evaporator, condenser and adsorbent bed were measured and the coefficients of performance, total entropy generation, the second law efficiency, specific heating and cooling power values were calculated based on these measured values for all of the representative cycles. The heat transfer area of the second designed adsorption heat pump is 550% greater than the first designed adsorption heat pump and this increase resulted in 170% and 200% of improvements in specific heating power (SHP) and specific cooling power (SCP) values respectively. The silica gel granules were mixed with small size metal pieces in order to accelerate heat transfer in the bed. Experiments were performed to measure the thermal diffusivity through the adsorbent bed in which adsorbent is mixed with metal pieces. It was observed that the mixing of silica gel grains with 10wt% of small size aluminum pieces increases the SHP and SCP values of the second heat pump by 250%.
Synergistic effect of natural zeolites on flame retardant additives
(Izmir Institute of Technology, 2004) Demir, Hasan; Ülkü, Semra
Intumescent flame retardant systems were proposed to increase flame retardancy performance of polymers without environmental hazard. An intumescent system consisting of ammonium polyphosphate (APP) as an acid source and blowing agent, pentaerythritol (PER) as a carbonific agent and natural zeolite (clinoptilolite, Gördes II) as a synergistic agent was used in this study for flame retardancy of polypropylene (PP). APP and PER combination were examined at different ratios (0.25, 0.33, 0.5, 1, 2, 3, and 4) for optimization of formulation of flame retardancy. The zeolite was incorporated into flame retardant formulation at four different concentrations (1,2, 5, and 10wt%) to investigate synergism with the flame retardant materials. Filler content was fixed at 30w% of total amounts of flame retardant PP composites. The zeolite and APP were treated with two different coupling agents namely, 3-(trimethoxysilyl)-1-Propanethiol and (3-aminopropyl)-triethoxysilane for consideration influence of surface treatments on mechanical properties and flame retardant performance of composites.To investigate thermal behaviour of flame retardant PP composites with and without zeolite, samples were heated on optic microscope hot stage. Both of the composites behaved similarly during heating from room temperature to 203oC. Molten pentaerythritol was observed as a second phase in molten polypropylene at 203 oC. Bubble formations were not observed. Flame retardants did not cause any foam formation during processing of mixture at 190oC in rheomixer and hot press. SEM pictures of non-burnt and burnt flame retardant (FR) PP composites with and without zeolites did not reveal significant difference considering foam size and shape compared to composites without zeolite. Zeolite crystals did not exhibit any deformation during burning of composite.Flammability of FR-PP composites were determined by UL-94 flame test in air. Burning rate of composite was measured for flammable composite in atmospheric condition. The limiting oxygen index (LOI) test method provided measuring the minimum concentration of oxygen in a flowing mixture of oxygen and nitrogen that supports combustion of pure PP, zeolite reinforced PP and flame retardant PP composites. The best flame retardant performance was achieved with APP:PER(3:1)+PP+2% zeolite and APP:PER(2:1)+PP+5% zeolite formulations, exhibiting 37.4 and 38% LOI values respectively. LOI values reached maximum value 41% with mercapto silane treated APP:PER(2:1) at 5w% Zeolite PP composite Young's modulus of composites decreased with increasing amounts of APP in composite on the contrary to their elongation at break properties.