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Öğe Calcium deficient hydroxyapatite by precipitation: Continuous process by vortex reactor and semi-batch synthesis(Elsevier Sci Ltd, 2021) Geçim, Gözde; Donmez, Sinan; Erkoç, ErtuğrulPrecipitation of calcium deficient hydroxyapatite nanoparticles in an environmentally benign manner by using only dilute solutions of calcium hydroxide and phosphoric acid without pH adjustment and addition of other chemicals, and water, being the only by-product was investigated by using continuous flow Vortex Reactor (VR) and Semi-Batch Reactor (SBR). The effect of hydrodynamics by changing the Reynolds number of the jets providing residence times of 8.4 ms to 4.37 s for VR, and by changing the stirrer speed between 100 rpm (Re = 2656) and 1000 rpm (Re = 26560) for SBR, on the particle size, particle size distribution, and morphology of the particles was investigated for both systems. It has been shown that it is possible to produce pure phase hydroxyapatite nanoparticles in the desired morphology by changing production system, without resorting to additives. While VR produced rod-like particles with the crystallite size around 4 nm, SBR produced spherical particles with the crystallite size of around 5 nm.Öğe COMPARISON OF 3D OPPOSED JETS GEOMETRIES: 3D COMPUTATIONAL FLUID DYNAMICS (CFD) STUDY(2016) Erkoç, ErtuğrulInfluence of geometry on the mixing mechanism and efficiency is studied by comparing Opposed Jets of Cylindrical and Prismatic shapes, having the same hydraulic chamber diameter by 3D Computational Fluid Dynamics (CFD) models. For the test case, same Reynolds numbers of the jets were provided. The comparison is assessed by hydrodynamics, turbulence parameters and mass transfer inside the mixing chambers. While the hydraulic diameters of the chambers set as equals, the thickness of the jets of the T-Jets mixers set as the diameters of the jets of the Confined Impinging Jets, which resulted in non-equal hydraulic diameters of the Jets. The power spectra of the x and y velocities for T-Jets showed a similar peaks as in 2D chambers, however without the spread of the energy. The results suggests that for T-Jets, Reynolds numbers of the jets alone is not enough to describe the mixing inside the chamber, but the thickness of the jets is also an important parameter since different values of jets thicknesses and depths can provide the same hydraulic diameter. Finally, this study shows that on one hand CIJ promotes a more intense striation of the initial flow scales when compared to the T-jets, on the other hand the latter promotes a broader impingement region and allows larger inlet areas, i.e. higher throughputs, for the same initial scale. The choice of the mixer should then be the trade-off between these two factors. For a better comparison, the same hydraulic diameters of the jets giving the same Reynolds numbers should be investigatedÖğe Gas Flow Hydrodynamics in Vortex Mixers: Flow Visualization and PIV Flow Field Characterization(American Chemical Society, 2021) Geçim, Gözde; Erkoç, ErtuğrulThe gas flow hydrodynamics in a vortex mixer was investigated using flow visualization and particle image velocimetry (PIV) techniques for several Reynolds numbers ranging from Re = 20 to 280 and equal momentum of the jets. The flow regime transition of two methane gas streams coming from two tangential jets was analyzed by the detection of the critical Reynolds number of the flow. This critical point was determined from time-averaged and instantaneous flow images, velocity fluctuations, and hence turbulence intensity values of the vortex mixer. Results show that the flow gained the swirl motion at Re = 70 and the instabilities in the flow started at around Re = 230, where the gas flow hydrodynamics was diffusion controlled. Beyond Re = 230, the flow was unsteady and chaotic flow overruled the molecular diffusion and the ensemble mixing of the gases dependent on the convection was achieved starting from this point. This study sheds light on the gas flow hydrodynamics of a vortex mixer and points out the flow regime transitions.Öğe Gas phase polymerization of ethylene towards UHMWPE(2020) Geçim, Gözde; Erkoç, ErtuğrulFor the first time, ultra-high molecular weight polyethylene (UHMWPE) was produced in gas phase process with a new fluidized bed concept where the solids are dispersed phase and the gas is bulk phase as opposed to conventional fluidized bed reactors (FBRs). With this concept, UHMWPE with average molecular weights about 1-6,9 × $10^6$ g moles ?1 were produced with a commercial supported Ziegler-Natta catalyst by using a gas phase mini semibatch reactor system. Additionally, optimum conditions of gas phase polymerization for the best results of productivity, catalyst activity, molecular weight and crystallinity were determined by Taguchi experimental design and catalyst stability at the optimum condition was tested by video microscopy polymerization. The characterization of products was carried out experimentally by TGA, DSC, FTIR, and NMR.Öğe Numerical study of active mixing over a dynamic flow field in a T-jets mixer-Induction of resonance(Inst Chemical Engineers, 2016) Erkoç, Ertuğrul; Fonte, Claudio P.; Dias, Madalena M.; Lopes, Jose Carlos B.; Santos, Ricardo J.The flow field in a 2D T-jets mixer was simulated to study the effect of the pulsation/modulation of the jets flow rate on the dynamics of mixing. Different strategies, frequencies and amplitudes of the opposed jets flow rate modulation were tested. The modulation frequencies were set as multiples of the natural oscillation frequencies of the dynamics flow field. The natural flow frequencies are determined from the unforced flow, i.e., when the jets are not modulated. It is found that out phase modulation of the opposed jets, with frequencies close to the natural frequencies, cause resonance of the flow enhancing the order of the system, which results in a flow field with a well-defined repetitive generation of vortices. Conversely, when the pulsation frequencies were different from the natural frequencies the flow disorder was enhanced, i.e., the vortices evolution throughout the T jets mixers is less repetitive. The impact of the jets flow rate modulation on the flow field dynamics increases with the modulation amplitude up to the extreme case where it completely drives the dynamics of the system. A design equation for the most energy efficient pulsation of the jets feed streams in opposed jets mixers is proposed. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.Öğe Review on extraction of polyhydroxyalkanoates and astaxanthin from food and beverage processing wastewater(Elsevier Ltd, 2021) Geçim, Gözde; Aydin, G.; Tavsanoglu, T.; Erkoç, Ertuğrul; Kalemtaş, AyşeThe recovery of value-added products from food and beverage processing wastewater, polyhydroxyalkanoates, and astaxanthin, via various chemical and microbiological extraction techniques has been summarized in this contribution. While wastewaters from several food industries like olive oil, brewery, starchy, and agro-cultural have been utilized to produce polyhydroxyalkanoates as an alternative to the petrochemical sources, seafood wastewaters such as mussel processing, shrimp cooking, and chitin production have been used to recover astaxanthin. In these studies, the wastewater's carbon content has been found as an essential parameter for the recovery of polyhydroxyalkanoates and astaxanthin. The type of additional nitrogen source, microorganism properties, ambient conditions, and polymer extraction methods were mostly examined parameters for the polyhydroxyalkanoate recovery. Olive oil mill wastewater has been presented as one of the most promising industries for the recovery of polyhydroxyalkanoate with the highest polymer yield of 4.93 g L?1. Shrimp cooking wastewaters provide one of the highest astaxanthin yields as 10–13 ?g mL?1. In addition to summarizing polyhydroxyalkanoates and astaxanthin yields from various wastewaters, technological obstacles and solutions regarding efficient extraction and large scale production have been discussed in this review. © 2020 Elsevier Ltd
