Endüstri Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/279
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Article Citation - Scopus: 12On Periodic Solutions of Linear Impulsive Delay Differential Systems(2008) Alzabut, Jehad; Akhmet, M.U.; Alzabut, J.O.; Zafer, A.; MatematikA necessary and sufficient condition is established for the existence of periodic solutions of linear impulsive delay differential systems. Copyright © 2008 Watam Press.Article Citation - WoS: 18Citation - Scopus: 34Comparison of Globoid and Cylindrical Shearer Drums' Loading Performance(South African inst Mining Metallurgy, 2006) Eyyuboğlu, E.Mustafa; Ayhan, M; Eyyuboglu, EM; Endüstri MühendisliğiDrums of a modern longwall shearer are manufactured to include various constructional features conveying extracted material onto the face conveyor as efficiently as possible. Designing a drum with a conical shell or with reduced vane length, consequently with a stepper vane angle, is the most widely employed method in an attempt to increase loading efficiency. This study compares loading performances of two such drums, one having a conical shell with modified loading vanes, the other with a cylindrical shell with reduced vane length, Firstly, the loading performances of drums are predicted and the maximum haulage rate attainable with the drums are calculated. Then the performances of drum are compared by long-term comprehensive underground trials with coal shearers under similar conditions during the production operation of Park Termik Cayirhan coalmine in Turkey. Although higher loading performance is predicted for cylindrical drums, the in situ trials point out that Globoid drums have a slightly higher loading performance than cylindrical drums. Furthermore, the relationship between operational variables, i.e. extraction height, sumping depth, haulage rate and in situ loading performance, were investigated statistically on the basis of data gathered during the underground trials.Article Citation - Scopus: 1Enhanced Nutrients Removal in Conventional Anaerobic Digestion Processes(2009) Othman, M.Z.; Uludag-Demirer, S.; Demirer, G.N.One of the main challenges for one phase anaerobic digestion processes is the high concentration of NH 4 + and PO 4 3- ions in the digested sludge supernatant. This project focuses on enhancing the removal of nutrients during the anaerobic digestion process through fixing both NH 4 + and PO 4 3- ions in the form of struvite (magnesium ammonium phosphate, MAP, MgNH 4PO 4.6H 2O) within the anaerobic sludge. Batch anaerobic digestion tests showed that Mg 2+ concentration in the range 279 - 812 mg/L had insignificant effect on CGP but incurred a slight increase in COD removal. The reactor that had soluble Mg 2+:NH 4 +:PO 4 3- at a molar ratio of 1.28:1:00:1:00 achieved the best performance enhancement of 8% increase in COD removal and 32% reduction in NH 4 + in the reactor supernatant. Overall, the results show that there is a potential to optimise conventional anaerobic digestion such that supernatant lean in P and N, and sludge rich in nutrients are obtained.Article Citation - Scopus: 1Identification of Eco-Efficiency Opportunities in a Small Enterprise Producing Vegetable Oil in Eskisehir, Turkey(Inderscience Publishers, 2007) Tepe, N.; Uludaǧ-Demirer, S.In this study, the current processes and technologies in a small enterprise, Demircanlar Oil Industry1 (Eskisehir, Turkey), were audited and improved from the eco-efficiency point of view. The eco-efficient management of the vegetable oil production processes has been performed on the units of physical processes, extraction and purification. The results obtained indicated that the loss in raw material can be reduced simply by increasing me height of the sieves used to separate foreign materials (leaves, sand, stones, etc.) from sunflower seeds. Results also indicated that production costs and negative environmental impacts can be decreased by minimising the loss of hexane during the extraction process, and the product quality can be improved and product loss can be prevented by adjusting the amounts of bleaching clay and TriSyl® in me bleaching process. Although the reduction in environmental impacts of the factory could not be valuated, the study showed that the factory can be managed more eco-efficiently without undergoing major process changes with an immediate benefit of approximately 12,000 USD. Copyright © 2007 Inderscience Enterprises Ltd.Article Control of Trichloroethylene Emissions From Sparging Systems by Horizontal Bio- and Chemo-Barriers(Selper Ltd, Publications Div, 2005) Tezel, U; Demirer, GN; Uludag-Demirer, SThe scope of this study was to develop a continuous system to clean-up a trichloroethylene (TCE) contaminated gas stream, where biotic and abiotic removal mechanisms are undertaken sequentially simulating the horizontal bio- and chemo-barriers proposed for the in-situ remediation of the contaminated sites. The bio- and chemo-barriers were simulated by using glass columns packed with granular anaerobic mixed culture and Fe(0) filings, respectively. The effect of gas residence time, which is adjusted by the gas flowrate, on the TCE removal efficiency of the reactor system was investigated. TCE removal efficiency of over 90% was achieved at gas residence times above 1hr. Furthermore, the effluent of reactor system contained only ethane and ethylene, which are non-toxic by-products of TCE reduction reactions, along with trace amounts of TCE.Article Citation - WoS: 39Citation - Scopus: 56Effects of Circumferential Pick Spacing on Boom Type Roadheader Cutting Head Performance(Pergamon-elsevier Science Ltd, 2005) Eyyuboglu, EM; Bolukbasi, NEffects of equal and unequal circumferential pick spacing on the performance of boom type roadheaders having cylindrical cutting heads are investigated. For this purpose, two experimental cutting heads with equal and unequal circumferential spacing are designed and manufactured. The cutting head with unequal circumferential spacing is specifically designed to prevent tool-holder overlap at the nose section. Manufacturing difficulties associated with equal circumferential pick spacing due to tool-holder overlap are discussed with solid modeling and practical applications. The heads are tested at Park Cayirhan Coal Mine in Turkey and their cutting performances are analysed. Although better cutting performance for equal circumferential spacing are predicted by force-balance analysis, in situ measurements of instantaneous (net) traversing speed and cutting rate, pick consumption rate and machine vibration show that no significant difference exists between the performances of the two cutting heads. (C) 2005 Elsevier Ltd. All rights reserved.Article Citation - WoS: 205Citation - Scopus: 231Ammonia Removal From Anaerobically Digested Dairy Manure by Struvite Precipitation(Elsevier Sci Ltd, 2005) Uludag-Demirer, S; Demirer, GN; Chen, SAmmonia is one of the most important contaminants impairing the quality of water resources. When this is considered along with the fact that the global demand for nitrogenous fertilizers is in constant rise, the need for recovery as well as removal of nitrogen is well justified. Crystallization of N and P in the form of struvite (MgNH4PO4 center dot 6H(2)O), which is a slow releasing and valuable fertilizer, is one possible technique for this purpose. This study investigated the removal of NR4+ through struvite precipitation from the effluents of one- (R1) and two-phase (R2) anaerobic reactors digesting dairy manure. To force the formation of struvite in the anaerobic reactor effluents, Ma(2+) ion was added by using both Mg(OH)(2) and MgCl2 center dot 6H(2)O. To prevent the effect of different total phosphorus (TP) concentration in the effluents of RI and R2, as well as to not limit the formation of struvite, an excess amount Of PO43- (0.14 M) was added in the form of NaHPO4. Different stoichiometric Mg2+:NH4+:PO43- ratios were tested to determine the required Mg2+ concentrations for maximum NH4+ removal by keeping NH4+:PO43- ratio constant for the effluents of reactors RI and R2. The results revealed that very high NH4+ removal efficiencies (above 95%) were possible by adding Mg 21 ions higher than 0.06 M concentration in the effluents from reactors RI and R2. It was also observed that the initial pH adjustment to 8.50 using NaOH did not result in any significant increase in the removal of NH4+ and the removal of NH4+ in the reactors treated with MgCl2 center dot 6H(2)O was higher than those treated with Mg(OH)(2) for the same Mg2+ concentration. (c) 2005 Published by Elsevier Ltd.Article Citation - WoS: 1Citation - Scopus: 1The Effect of Different Inflation Risks on Interest Rates of the Us(Routledge Journals, Taylor & Francis Ltd, 2009) Yuksel, E.; Akdi, Y.This article examines the effect of different inflation uncertainty measures on interest rates of the US in a Fisher hypothesis framework. Generalized Autoregressive Conditional Heteroskedasticity (GARCH) specification with a time-dependent parameter model is used to obtain three types of inflation uncertainties, namely, impulse uncertainty, structural uncertainty and steady-state uncertainty. It has been observed that the impulse uncertainty has negative but the structural uncertainty has positive impact on both short-term and long-term interest rates. Both of these effects are statistically significant. The influence of steady-state uncertainty on interest rates is positive, but the level of significance depends on the inclusion of output gap. Without the inclusion of output gap, the effect is insignificant, whereas the effect becomes significant when output gap is introduced.Article Citation - WoS: 66Citation - Scopus: 85Removal of Ammonium and Phosphate From the Supernatant of Anaerobically Digested Waste Activated Sludge by Chemical Precipitation(Elsevier Sci Ltd, 2009) Uludag-Demirer, Sibel; Othman, MaazuzaThe removal of ammonium (NH4+) and phosphate (PO43-) from supernatant of anaerobic digestion by magnesium ammonium phosphate (MAP) formation was Studied. To be able to find out the loss of NH4+ by its transformation to NH3, rates of NH4+ removal by aeration and by MAP formation combined with aeration were compared. NH4+ removal by aeration was found to be insignificant. The kinetics of MAP formation was fast. The removal rate of NH4+ and Mg2+ was the smallest and the largest, respectively based on rate constants calculated. The removal of NH4+ showed sensitivity to Mg2+ and PO43- concentrations and controlled the purity of MAP precipitate. The removal of PO43- was found to be Sensitive to mainly Mg2+ ion. These results also indicated that as the supernatant Solution became more saturated in terms of MAP forming ions, the effect of pH increase became insignificant in the removal of ions from the solution. (C) 2009 Elsevier Ltd. All rights reserved.Article Citation - WoS: 18Citation - Scopus: 19A Study on Nutrient Removal From Municipal Wastewater by Struvite Formation Using Taguchi's Design of Experiments(Mary Ann Liebert, inc, 2008) Uludag-Demirer, SibelThe aim of this study is to investigate the removal of NH4+-N and PO43--P from the municipal wastewater by struvite (MgNH4PO4.6H(2)O) formation. The optimization of the NH4+-N and PO43--P removals is made by changing the total concentrations of struvite forming ions (Mg2+, NH4+, PO43-) and pH of the wastewater. The experimental design was made using Taguchi's L-9(3(4)) orthogonal array technique in the first stage of the study. The conditions yielding maximum removals of NH4+-N and PO43--P are found as molar concentration ratio of Mg:N:P of 2:2:2 and 3:3:2, respectively, using the signal-to-noise (S/N) ratio of experimental results. The removal of NH4+-N followed the stoichiometry of struvite formation, while PO43--P removal required the excess amount of Mg2+. The pH of wastewater in which the maximum NH4+-N and PO43--P removals are observed was 9.0. All of the factors tested influenced the removal of NH4+-N opposite to the removal Of PO43--P, in which the concentration of NH4+-N was found insignificant statistically. Therefore, the addition of NH4+ ion is eliminated and Taguchi's L-4(2(3)) orthogonal array was used in the second stage of experimental study. The molar concentration ratios of struvite forming ions (Mg:N:P) were found to be as 1:1:1 and 2:1:1 for maximum NH4+-N and PO43--P removals at the levels of 52.4 and 67.7%, respectively, at pH 9.0 using the S/N ratios of experimental results. The performance of proposed method in removing NH4+-N and PO43--P and foreseen problems related with effluent quality is discussed.