Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - Scopus: 7Modification of Grape Pulp With Citric Acid for the Production of Natural Ion Exchanger Resin and Removal of Pb (ii) and Cd (ii) From Aqueous Solutions: Kinetic, Thermodynamics, and Mechanism(Springer Science and Business Media Deutschland GmbH, 2023) Arslanoğlu, E.; Eren, M.Ş.A.; Arslanoğlu, H.; Çiftçi, H.In this study, grape pulp (MGP) modified with NaOH and citric acid was used in the production of natural ion exchangers. The effects of parameters such as initial pH, MGP dosage, temperature, initial metal ion concentration, and contact time on the removal of Pb (II) and Cd (II) ions from aqueous solutions using modified materials were investigated by batch experiments. It was found that the experimental kinetic data fit the second-order model, and the activation energy for Pb (II) and Cd (II) adsorption processes were 20.68 and 38.61 kj mol−1, respectively. Although the initial adsorption rate increases with increasing temperature, the adsorption efficiency slightly decreases. It was calculated that the equilibrium data fit the Langmuir isotherm better, and the maximum adsorption capacities for Pb (II) and Cd (II) adsorption processes were approximately 1.496 and 1.022 mmol g−1 at 25 °C, respectively. Thermodynamic analysis has shown that the adsorption processes of Pb (II) and Cd (II) are exothermic (ΔH°Pb = −35.68 kj mol−1, ΔH°Cd = −21.19 kj mol−1) and have a self-developing character. Graphical abstract: [Figure not available: see fulltext.]. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Article Citation - WoS: 4Citation - Scopus: 5Conductance Fluctuations in Undoped Hydrogenated Amorphous Silicon-Germanium Alloy Thin Films(Elsevier Ltd., 2002) Güneş, Mehmet; Johanson, Robert E.; Kasap, Safa O.; Yang, Jeffrey C.; Guha, SubhenduWe report coplanar conductance fluctuations of device quality, undoped hydrogenated amorphous silicon-germanium alloy thin films (a-SiGe:H) measured from 430 to 490 K. The a-SiGe:H alloys produce noise power spectra similar to coplanar undoped a-Si:H films in the same temperature range. The noise power spectrum S(n) does not fit a single 1/fα power law but rather has two distinct regions, each accurately fitted by a power law, but with different slopes. The low frequency slope α1 is similar to that observed in undoped a-Si:H films varying from 1.30 to 1.46 for different Ge concentrations and shows a slight temperature dependence. At higher frequencies, the slope α2 is less than unity and temperature independent but depends on the Ge content of the film. α2 decreases from 0.60 for no Ge (pure a-Si:H) to 0.15 for 40 at.% Ge. The noise power at lower frequencies increases and at higher frequencies decreases substantially as the temperature increases from 430 to 490 K. We infer that similar noise mechanisms are operating in undoped a-SiGe:H and a-Si:H films but that the Ge content is influencing the noise, particularly the slope at higher frequencies. In addition, the noise has the expected quadratic dependence on bias current and obeys Gaussian statistics.Article Citation - WoS: 61Citation - Scopus: 66The Use of Metal Piece Additives To Enhance Heat Transfer Rate Through an Unconsolidated Adsorbent Bed(Elsevier Ltd., 2010) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraThe effects of metal piece additives on effective thermal conductivity and diffusivity of an unconsolidated adsorbent bed in which adsorbent is silica gel were investigated. The metal piece additives were copper, brass, aluminum and stainless steel with two different sizes as 1.0-2.8 mm and 2.8-4.75 mm. The effective thermal conductivity and diffusivity of the mixed bed were predicted by comparison of the experimental results with the solution of dimensionless heat conduction equation for the bed. The performed experiments showed that the addition 15wt% of aluminum pieces with sizes between 1.0 and 2.8 mm enhances the effective thermal diffusivity and conductivity of a pure silica gel bed by 157% and 242%, respectively. © 2010 Elsevier Ltd and IIR.Article Citation - WoS: 27Citation - Scopus: 28Effects of Wall-Located Heat Barrier on Conjugate Conduction/Natural- Convection Heat Transfer and Fluid Flow in Enclosures(Taylor and Francis Ltd., 2008) Hakyemez, Erinç; Mobedi, Moghtada; Öztop, Hakan FehmiThe effects of a heat barrier, located in the ceiling wall of an enclosure, on conjugate conduction/natural convection are investigated numerically. The vertical walls of the enclosure are differentially heated and the horizontal walls are adiabatic. Heatline technique is used to visualize heat transport. The variations of average Nusselt number, dimensionless heat transfer rate through the ceiling wall, and dimensionless overall heat transfer rate are studied. Calculations are performed for different Rayleigh numbers (10 3≤ Ra ≤ 10 6), thermal conductivity ratios (1 ≤ K ≤ 100), dimensionless locations of the heat barrier (0 < X h < 1),and two dimensionless ceiling wall thicknesses (D = 0.05 and D = 0.20). For high thermal conductivity ratio (K = 100), the heat barrier considerably reduces the dimensionless overall heat transfer rate. The effect of the heat barrier on dimensionless heat transfer rate through the enclosure increases as the Rayleigh number decreases. For low Rayleigh number (i.e., Ra = 10 3), a location exists in the ceiling wall for which the dimensionless overall heat transfer rate is minimum.Article Citation - WoS: 4Citation - Scopus: 3Evaluation of the Effectiveness of the Bulk Thermal Stresses for Kraft Recovery Boiler Fireside Deposit Cleaning(Tappi Press, 2006) Özcan, Selçuk; Tran, HonghiRemoval of fireside deposits from the heat transfer tubes in kraft recovery boilers is carried out by sootblowing and occasionally "chill-and- blow" practices. During chill-and-blow, black liquor flow is reduced to rapidly cool the deposits.Thermal stresses generated in the deposit as a result of thermal shock can effectively weaken the deposit, facilitating its cleaning. For this study, we investigated the mechanical weakening effect of thermal stresses generated by the transient temperature gradients. We quantified the mechanical weakening effect due to thermal shock by measuring the decrease in biaxial flexure strength of a preheated sodium chloride disk at various quenching times and surface heat transfer coefficients. We observed that the mechanical weakening occured by transient thermal stresses as well as crack propagation. Approximately 35% loss in biaxial flexure strength could be achieved at heat transfer coefficients above 3.3·103 W/m 2K, and at quenching durations above 40 s.