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    Bipolar membrane electrodialysis for mixed salt water treatment: Evaluation of parameters on process performance
    (Elsevier Sci Ltd, 2021) Oner, Muhammed Rasit; Kanca, Arzu; Ata, Osman Nuri; Yapici, Sinan; Yaylali, Neslihan Alemdar
    In the present study, bipolar membrane electrodialysis (BMED) process was employed as an alternative separation method to the distillation unit in the Solvay process for the synthetic soda ash production. The applicability of BMED was investigated by evaluating the effects of system parameters on process performance. Desalination ratio, salt based acid and base conversion ratio, flux, product purity, and energy consumption were defined as the process performance criteria for the BMED systems. Initial salt concentration, applied current and voltage, and initial acid and base concentrations were chosen as system parameters. The results of the study revealed that current/voltage and initial salt concentration are the most effective factors affecting all performance criteria. When all system parameters were considered, BMED provides the desalination ratio in between 90% and 98%, the acid and base conversion ratio of salt in between 60% and 80%, and the energy consumption in the range of 1.54-2.33 kWh/kg acid. Furthermore, the desalinated water can be reused as process water and the distillation unit waste problem can be resolved by the utilization of BMED system.
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    Effect of distance between impeller blade tip and surface on mass transfer to a local electrode in a stirred vessel in a wide range of Sc number
    (Taylor & Francis Ltd, 2022) Yapici, Sinan; Altay, Ilhan
    Stirred vessels are encountered in a wide scale of applications from bench to industrial processes, and the knowledge of the heat/mass transfer rates in these vessels is required for their design, operation and control. This work submits an investigation on the mass transfer to a small circular surface immersed in a stirred vessel in the parameter ranges of 267 < Re <9437, 1473 < Sc <61,422, and 0.022 < x/d(k) < 0.22 for the distance between the impeller blade tip and the transfer surface. The Reynolds number was based on the impeller diameter. The electrochemical limiting diffusion current technique having a potassium ferri-/ferrocyanide system was applied for mass transfer coefficient measurements. Aqueous glycerine solutions were prepared to attain a wide range of Sc numbers. The rate of mass transfer is enhanced with increasing rotation rate, decreasing blade tip-to-electrode surface distance, and decreasing glycerine concentration. The experimental data were well correlated by the relation Sh = 8.517Re(0.473)Sc(0)(.402)(x/d(k))(-0.042). [GRAPHICS] .
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    Heat transfer performance of water and Nanoencapsulated n-nonadecane based Nanofluids in a double pipe heat exchanger
    (Springer, 2017) Doruk, Semahat; Sara, Osman Nuri; Karaipekli, Ali; Yapici, Sinan
    The heat transfer and pressure drop characteristics for the flow of water, which is base fluid, and nanoencapsulated n-nonadecane based nanofluids in a double pipe heat exchanger were investigated. The results showed that no improvement in overall heat transfer coefficient was observed for the nanofluids containing 0.42% and 0.84% solid volume ratios with reference to the base fluid, while an improvement of about 10% was obtained for the nanofluids containing 1.68% solid volume ratio. It was found that the friction factors for the nanofluids exhibited a slight increase reference to the base fluid. A performance analysis based on constant pumping power was also performed.
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    A new application area of electrochemical limiting diffusion current technique: measurement of mixing time and effect of some parameters
    (Springer Int Publ Ag, 2019) Aydin, Ozkan; Arzutug, Mehmet Emin; Yapici, Sinan
    In this study, the electrochemical limiting diffusion current technique, which was employed first time for the mixing time measurement in the stirred tank system by the authors, was applied to determine the effect of some parameters on the global and local mixing times in the range of 3500 <= Re <= 10,000. The technique well sensed that increasing Reynolds number (Re), blade angle and blade number decreased the mixing time. The most effective parameter was observed to be Re, and the blade number and blade angle, in order. In addition, the mixing time was also investigated for solutions added in various volume fractions having different viscosity and density by using local mixing time measurement. It was determined that the mixing time decreased with the Reynolds number, the ratio of the initial solution volume to the total solution volume and the ratio of kinematic viscosity of the solution in the vessel initially to that of the added one viscosity. The ratio of initial solution volume to total solution volume was found to be a more effective parameter than the others in terms of mixing time.
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    A novel method for the measurement of mixing time: A new application of electrochemical limiting diffusion current technique
    (Elsevier Science Inc, 2018) Aydin, Ozkan; Yapici, Sinan
    The purpose of this work is to investigate whether the application of the electrochemical limiting diffusion current technique to the measurement of the mixing time in stirred vessels is possible; and if it is, then to establish a new technique for the measurement of the mixing time in the containers including liquids. For this aim, first the electrochemical limiting current conditions were determined, by observing the voltage-current change with the addition of a small amount of concentrated solution including active ions, that is, tracer, into the stirred system. Then, mixing time was determined by local and global measurements, employing both a local probe and one of the baffles as sensor, respectively. The comparison of the results with those of obtained by conductivity, which showed very good agreement, proved that electrochemical limiting current technique can be used as a means of measuring local and global mixing times as a cheap, simple, fast, straight forward and effective method.
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    Thermal Conductivity and Viscosity of Nanofluids Having Nanoencapsulated Phase Change Material
    (Taylor & Francis Inc, 2016) Barlak, Semahat; Sara, Osman Nuri; Karaipekli, Ali; Yapici, Sinan
    In this study, the thermal conductivity and viscosity of nanofluids, composed of a base fluid and nanoencapsulated phase change material (NEPCM), were investigated experimentally. The NEPCM was prepared by the encapsulation of n-nonadecane as phase change material with diethylenetriamine and toluene-2,4-diisocyanate using interfacial polymerization method. The NEPCM was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) analyses. In the preparation of the nanofluids containing NEPCM, two different base fluids, water and ethylene glycol (EG), were used. The concentration of NEPCM and the working temperature were selected as the main parameters. It was found that the viscosity of the nanofluids decreases with increasing temperature and increases with increasing solid concentration. The viscosity was also expressed as a function of the solid concentration and temperature. The thermal conductivity of the nanofluids was found to increase with increasing temperature. Thermal conductivity exhibited an increasing tendency with increasing solid concentration, but the changes in thermal conductivity according to base fluid are in the range of uncertainty of the measurement for both nanofluids with a solid volumetric fraction lower than 1.68%.
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    Usability of alloys with different composition as electrode for electrochemical reduction of ferricyanide ion
    (Springer Int Publ Ag, 2022) Altay, Ilhan; Yapici, Sinan; Demirkiran, Nizamettin
    An experimental work was performed to investigate the usability of 8 metallic alloys with different composition in electrochemical limiting diffusion current technique employing the cathodic reduction of ferricyanide. All the alloys exhibited a limiting current plateau region in their voltage-current behaviour, but not all gave a wide and smooth plateau, except one with almost pure Ni. With the alloys of including more than 50% Ni, as Ni ratio of the metal increased, smoother and wider plateau was attained, and the electrode containing 99% Ni gave the smoothest plateau. The other alloys tested can only be used as electrode in the limiting diffusion current technique in low flow velocities in which the transfer of the active ion to the electrode surface is as slow as that the mass transfer controls the rate of system.