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Öğe Dehydration kinetics of tincal and borax by thermal analysis(Amer Chemical Soc, 1997) Ekmekyapar, A; Baysar, A; Kunkul, AThe dehydration reaction kinetics of tincal and-borax decahydrate was investigated by thermogravimetry (TG) and differential thermal analysis (DTA). Various methods were used to analyze the TG and DTA data for determination of reaction kinetics. The activation energy, frequency factor, and order of reaction were calculated for both materials. The results obtained from different methods were generally in good agreement. The results of tincal and borax were also compatible.Öğe Dissolution kinetics of an oxidized copper ore in ammonium chloride solution(Croatian Soc Chemical Engineering Technology, 2003) Ekmekyapar, A; Oya, R; Künkül, AThe dissolution kinetics of malachite ore in ammonium chloride solutions has been investigated with respect to the effects of ammonium chloride concentration, particle size, solid/liquid ratio, stirring speed, and reaction temperature. It was determined that the dissolution rate increased with increasing ammonium chloride concentration, stirring speed, and reaction temperature. However, increasing particle diameter and solid to liquid ratio decreased the dissolution rate. Examination of data by heterogeneous model suggested that the dissolution rate is controlled by mixture kinetics. The following mathematical model was proposed to represent the reaction kinetics. 1 - 2(1 - x)(1/3) + (1 - x)(2/3) = 1 . 10(-5) (c)(2.10) . (d(p))(-1.96) . (rho(S/L))(-0.64) . (n)(1.78) . e((-8500/T) . t) The activation energy for the dissolution reaction was calculated as 71 kJ mol(-1). Where x is the reacted fraction of the solid, c is the ammonium chloride concentration, d(p) is the particle diameter, rho(S/L) is the solid to liquid ratio, n is the stirring speed, E is the activation energy, T is the reaction temperature and t is the reaction time.Öğe Effect of operating parameters on magnetic filtration processes(Amer Chemical Soc, 2004) Künkül, A; Ekmekyapar, A; Akmil, C; Abbasov, TThe effect of operating parameters and the effect of the pH of the liquids to be cleaned on the magnetic filter performance in the filtration processes were investigated. The pH of aqueous suspensions containing ferromagnetic particulates was changed in the range of 3-10. The suspensions were prepared in our laboratory. The effect of the size of filter matrix elements (diameter of the ferromagnetic spheres) and filtration velocity on the filter performance was determined. The filter performance of the filter matrix composed of a mixture of different size spheres was also investigated. A magnetic filter performance above 60% was obtained with a filtration velocity of 0.07 m/s. It was observed that if the size of particles and the fraction of ferromagnetic particles in the suspension are varied in a short range, the effect of the initial concentration of corrosion products on the magnetic filter performance is negligible. The experimental results were compared with theoretical calculations and the data in the literature. Suggestions are given about choosing optimum values of the operating parameters for effective filtration of industrial fluids in magnetic filters.Öğe Enhancement of solar thermal energy storage performance using sodium thiosulfate pentahydrate of a conventional solar water-heating system(Elsevier Science Sa, 2005) Canbazoglu, S; Sahinaslan, A; Ekmekyapar, A; Aksoy, IG; Akarsu, FThe time variations of the water temperatures at the midpoint of the heat storage tank and at the outlet of the collector in a conventional open-loop passive solar water-heating system combined with sodium thiosulfate pentahydrate-phase change material (PCM) were experimentally investigated during November and then enhancement of solar thermal energy storage performance of the system by comparing with those of conventional system including no PCM was observed. It was observed that the water temperature at the midpoint of the storage tank decreased regularly by day until the phase-change temperature of PCM after the intensity of solar radiation decreased and then it was a constant value of 45 degreesC in a time period of approximately 10 h during the night until the sun shines because no hot water is used. Heat storage performances of the same solar water-heating system combined with the other salt hydrates-PCMs such as zinc nitrate hexahydrate, disodium hydrogen phosphate dodecahydrate, calcium chloride hexahydrate and sodium sulfate decahydrate (Glauber's salt) were examined theoretically by using meteorological data and thermophysical properties of PCMs with some assumptions. It was obtained that the storage time of hot water, the produced hot water mass and total heat accumulated in the solar water-heating system having the heat storage tank combined with PCM were approximately 2.59-3.45 times of that in the conventional solar water-heating system. It was also found that the hydrated salts of the highest solar thermal energy storage performance in PCMs used in theoretical investigation were disodium hydrogen phosphate dodecahydrate and sodium sulfate decahydrate. (C) 2004 Elsevier B.V. All rights reserved.Öğe Nonisothermal decomposition kinetics of trona(Amer Chemical Soc, 1996) Ekmekyapar, A; Ersahan, H; Yapici, SIn the present work, experiments on the nonisothermal decomposition of trona in thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) devices were carried out, and kinetic analysis of the process was performed by employing four different approaches. It was determined that the process fits a first-order reaction kinetic model and that the value of the activation energy changes, to some degree, depending upon the method used in the analysis, with a maximum deviation of 8.9% from the average value. The activation energy was found to be approximately 112 kJ mol(-1), which is in good agreement with the data from similar studies in the literature.
