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    Numerical simulation of electro-deposition process influenced by force convection and migration of ions

    , Article Journal of Electroanalytical Chemistry ; Volume 782 , 2016 , Pages 117-124 ; 15726657 (ISSN) Zahraei, M ; Saidi, M. S ; Sani, M ; Sharif University of Technology
    Elsevier B.V  2016
    Abstract
    Electro-deposition process is one of the main steps in the LIGA procedure to fabricate microstructures. In this paper, one-dimensional modeling of Nickel electro-deposition process is implemented on Rayan and developed for simulation of time-dependence diffusion and migration of charge species with reduction reactions on the cathode surface. This model is proposed by considering governing equations on electro-kinetic phenomena consist of Nernst-Plank equation and Poisson's equation of electric potential. Transport of ions toward the cathode is considered based on the effect of convection, reaction rate, diffusion and migration. The numerical results cover two series of data consisting of... 

    A new empirical correlation for predicting effective molecular diffusivity of gas-heavy oil-porous media systems

    , Article Special Topics and Reviews in Porous Media ; Volume 3, Issue 1 , 2012 , Pages 23-33 ; 21514798 (ISSN) Zamanian, E ; Mirjordavi, N ; Kazemeini, M ; Ghazanfari, M. H ; Sharif University of Technology
    2012
    Abstract
    Molecular diffusivity is an essential parameter for modeling of mass transfer in enhanced oil recovery processes. However, experimentally determined diffusivities for light gas-heavy oil systems in the presence of porous media are relatively rare. A few correlations are available in the literature that predict diffusivity of gases into heavy oil in presence of porous media. In this work the pressure-decay method was applied to obtain effective molecular diffusion of CO 2, CH 4 and N 2-heavy oil systems in both bulk and porous media systems at different temperatures. The diffusivity of gases in heavy oil was determined by matching the numerically calculated pressures to the measured data. A... 

    Infrared thin layer drying of saffron (Crocus sativus L.) stigmas: Mass transfer parameters and quality assessment

    , Article Chinese Journal of Chemical Engineering ; Volume 25, Issue 4 , 2017 , Pages 426-432 ; 10049541 (ISSN) Torki Harchegani, M ; Ghanbarian, D ; Maghsoodi, V ; Moheb, A ; Sharif University of Technology
    Chemical Industry Press  2017
    Abstract
    Saffron is the most precious and expensive agricultural product. A dehydration treatment is necessary to convert Crocus sativus L. stigmas into saffron spice. To the best of our knowledge, no information on mass transfer parameters of saffron stigmas is available in the literature. This study aimed at investigating the moisture transfer parameters and quality attributes of saffron stigmas under infrared treatment at different temperatures (60, 70, …, 110 °C). It was observed that the dehydration process of the samples occurred in a short accelerating rate period at the start followed by a falling rate period. The effective moisture diffusivity and convective mass transfer coefficient were... 

    Accurate analytical model for determination of effective diffusion coefficient of polymer electrolyte fuel cells by designing compact Loschmidt cells

    , Article Fuel ; Volume 199 , 2017 , Pages 551-561 ; 00162361 (ISSN) Izadmehr, M ; Abbasi, M ; Mansouri, M ; Kazemi, A ; Nakhaee, A ; Daryasafar, A ; Sharif University of Technology
    Elsevier Ltd  2017
    Abstract
    Effective diffusion coefficient is an important parameter which needs to be determined in different fields of study, such as cathode catalyst layers of PEM fuel. For this purpose, a Loschmidt diffusion cell can be used. When a porous medium is placed in Loschmidt apparatus, the effective gas diffusion coefficient (EGDC) of this section must be correlated by diffusion coefficient in absence of a porous medium. In the previous researches studying the Loschmidt diffusion cell, a simplifying infinite-length assumption was used in the analytical solution. Therefore, the solution is only applicable for a short time range, and this can result in high error. In order to overcome this challenge, the... 

    Simulation of Mild Steel Corrosion in H2S Aqueous Solution

    , M.Sc. Thesis Sharif University of Technology Fallah Mohammadi, Ehsan (Author) ; Dolati, Abolghasem (Supervisor)
    Abstract
    Corrosion is a main problem for oil and gas industries at refineries and petrochemical process. Presence of sulfur compounds in crude oil and creation a corrosive environment for steel structure, caused failure and unfortunate damages. H2S which present at cracking and sweetening process in sour feed obtain hydrogen atoms that can diffuse into steel structure which involve with its instruments and consequent to hydrogen damage .distribution and storage of these sour environments can be done by high strength low alloy steel (HSLA).Electrochemical hydrogen permeation test were performed to measure the hydrogen permeation current through A106/GR B pipeline steel in the electrolytes simulating... 

    The determination of effective diffusivity coefficients in a solvent gas heavy oil system for methane

    , Article Petroleum Science and Technology ; Volume 30, Issue 24 , 2012 , Pages 2582-2593 ; 10916466 (ISSN) Zamanian, E ; Dadvar, M ; Kharrat, R ; Ghazanfari, M. H ; Sharif University of Technology
    2012
    Abstract
    In this investigation, an accurate high pressure and temperature diffusion setup was applied to measure the diffusion coefficients of methane in Iranian heavy oils in presence and absence of porous media by using the pressure-decay method. The solvent diffusivity in heavy oil was determined by both graphical and numerical methods. In addition, the effects of the porous medium and the temperature on the molecular diffusion coefficient of the solvent gas in the liquid phase were discussed and finally, using experimental data, a functionality dependence of molecular diffusivity on temperature and porous medium characteristics was proposed  

    Rarefaction effects on gas mixing in micro- and nanoscales

    , Article ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer, MNHMT 2016, 4 January 2016 through 6 January 2016 ; Volume 1 , 2016 ; 9780791849651 (ISBN) Darbandi, M ; Sabouri, M ; Heat Transfer Division ; Sharif University of Technology
    American Society of Mechanical Engineers  2016
    Abstract
    We present the rarefaction effects on diffusive mass transport in micro- and nanoscales using the results of direct simulation Monte Carlo DSMC method. Unlike the previous investigations, the momentum and heat contributions are eliminated from the computations via uniform velocity, pressure, and temperature field considerations. The effects of global Knudsen number on the diffusion phenomenon are studied for the same Peclet number and a unique mixer shape. The results indicate that there is considerable weakening in diffusion mechanism for high Knudsen number cases. As a result, the non-dimensional diffusive mass fluxes would decrease and the non-dimensional mixing length would increase as... 

    Unified model of brain tissue microstructure dynamically binds diffusion and osmosis with extracellular space geometry

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 94, Issue 3 , 2016 ; 15393755 (ISSN) Yousefnezhad, M ; Fotouhi, M ; Vejdani, K ; Kamali Zare, P ; Sharif University of Technology
    American Physical Society  2016
    Abstract
    We present a universal model of brain tissue microstructure that dynamically links osmosis and diffusion with geometrical parameters of brain extracellular space (ECS). Our model robustly describes and predicts the nonlinear time dependency of tortuosity (λ=D/D∗) changes with very high precision in various media with uniform and nonuniform osmolarity distribution, as demonstrated by previously published experimental data (D = free diffusion coefficient, D∗ = effective diffusion coefficient). To construct this model, we first developed a multiscale technique for computationally effective modeling of osmolarity in the brain tissue. Osmolarity differences across cell membranes lead to changes... 

    Quantifying the direct influence of diffusive mass transfer in rarefied gas mixing simulations

    , Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 140, Issue 3 , March , 2018 ; 00982202 (ISSN) Darbandi, M ; Sabouri, M ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2018
    Abstract
    This work utilizes the direct simulation Monte Carlo (DSMC) calculations and examines the influence of rarefication on the mixing length and effective diffusion coefficient in a two-species mixing problem. There have been efforts in past rarefied mixing flow studies to bridge between the mixing evolution rate and Knudsen number. A careful review of those efforts shows that the past derived relations did not determine the weights of Reynolds (or Peclet) number in the rarefaction influences. Although they indicated that an increase in Knudsen would decrease the mixing length, such reductions were primarily due to the Reynolds (or Peclet) reduction. Therefore, those studies could not explicitly... 

    Dynamic Simulation of Wettability Alteration Induced by Low-Salinity-Effect: Study of Phenomena within Thin Water Film

    , M.Sc. Thesis Sharif University of Technology Pourakaberian, Arash (Author) ; Mahani, Hassan (Supervisor) ; Joekar Niasar, Vahid (Co-Supervisor)
    Abstract
    Recent experimental studies have demonstrated that the lowering of brine could alter the wettability of the oil-brine-rock systems from an oil-wetting state toward a more water-wetting state. This so-called “Low-salinity effect” (LSE) is one of the main effects of the enhanced oil recovery technology based on low-salinity waterflooding. “Double layer expansion” (DLE) in the thin brine film is proposed as the principal mechanism of this phenomenon. Nonetheless, the role of the electrical behavior of the oil/brine and rock/brine interfaces on the kinetics and dynamics of this process is not well understood. Moreover, since most of the previous works have either dealt with a thin film at... 

    A depthwise averaging solution for cross-stream diffusion in a Y-micromixer by considering thick electrical double layers and nonlinear rheology

    , Article Microfluidics and Nanofluidics ; Volume 19, Issue 6 , 2015 , Pages 1297-1308 ; 16134982 (ISSN) Ahmadian Yazdi, A ; Sadeghi, A ; Saidi, M. H ; Sharif University of Technology
    Springer Verlag  2015
    Abstract
    Both nonlinear rheology and finite EDL thickness effects on the mixing process in an electroosmotically actuated Y-sensor are being investigated in this paper, utilizing a depthwise averaging method based on the Taylor dispersion theory. The fluid rheological behavior is assumed to obey the power-law viscosity model. Analytical solutions are obtained assuming a large channel width to depth ratio for which a 1-D profile can efficiently describe the velocity distribution. Full numerical simulations are also performed to determine the applicability range of the analytical model, revealing that it is able to provide accurate results for channel aspect ratios of ten and higher and quite... 

    Effects of zirconia content on characteristics and corrosion behavior of hydroxyapatite/ZrO2 biocomposite coatings codeposited by electrodeposition

    , Article Surface and Coatings Technology ; Volume 262 , January , 2015 , Pages 166-172 ; 02578972 (ISSN) Shojaee, P ; Afshar, A ; Sharif University of Technology
    Elsevier  2015
    Abstract
    HAp and HAp/ZrO2 composite coatings were successfully electrodepesited on 316L stainless steel substrates in the solutions containing ZrO2 particles at different concentrations. The effects of ZrO2 content on characteristics of the coatings were investigated using X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), scanning electron microscopy (SEM) and bonding strength test. Polarization and electrochemical impedance spectroscopy measurements were carried out in order to evaluate corrosion behavior of the coatings. In-vitro test in SBF and further SEM observations were performed to examine bioactivity of the coatings. HAp/ZrO2 composite coatings showed better... 

    Study of self-diffusion in two binary solutions, glycerol-water and methanol-water using diffusion-ordered spectroscopy

    , Article Scientia Iranica ; Volume 23, Issue 3 , 2016 , Pages 1175-1183 ; 10263098 (ISSN) Fadaei, E ; Tafazzoli, M ; Sharif University of Technology
    Sharif University of Technology 
    Abstract
    The concentration and temperature behaviors of the self-diffusion coefficient were analyzed in glycerol-water and methanol-water solutions using Diffusion-Ordered Spectroscopy (DOSY) experiment. Our results indicate that the self-diffusion coefficient dips with increasing concentration and decreasing temperature. The concentration behavior shows that there is hydrogen bond interaction between water and alcohol, which declines the self-diffusion coefficients of both in the aqueous binary mixtures. The self-diffusion activation energies were estimated 13.6, 29.4, and 32.8 (kJ/mol) for methanol and 24.8, 25.5, and 27.6 (kJ/mol) for water in the methanol-water solutions with 0.03, 0.10, and 0.20... 

    Infrared thin layer drying of saffron (Crocus sativus L.) stigmas: Mass transfer parameters and quality assessment

    , Article Chinese Journal of Chemical Engineering ; 2016 ; 10049541 (ISSN) Torki Harchegani, M ; Ghanbarian, D ; Maghsoodi, V ; Moheb, A ; Sharif University of Technology
    Chemical Industry Press 
    Abstract
    Saffron is the most precious and expensive agricultural product. A dehydration treatment is necessary to convert Crocus sativus L. stigmas into saffron spice. To the best of our knowledge, no information on mass transfer parameters of saffron stigmas is available in the literature. This study aimed at investigating the moisture transfer parameters and quality attributes of saffron stigmas under infrared treatment at different temperatures (60, 70, ..., 110°C). It was observed that the dehydration process of the samples occurred in a short accelerating rate period at the start followed by a falling rate period. The effective moisture diffusivity and convective mass transfer coefficient were... 

    Moisture diffusivity and shrinkage of broad beans during bulk drying in an inert medium fluidized bed dryer assisted by dielectric heating

    , Article Journal of Food Engineering ; Volume 92, Issue 3 , 2009 , Pages 331-338 ; 02608774 (ISSN) Hashemi, G ; Mowla, D ; Kazemeini, M ; Sharif University of Technology
    2009
    Abstract
    Drying behavior of broad beans (Vicia faba) was studied in a pilot scaled fluidized bed dryer with inert particles assisted by dielectric heating. The effective diffusion coefficient of moisture transfer was determined by Fickian method at four different air drying temperatures of 35, 45, 55 and 65 °C. Correlations for moisture diffusivity as a function of moisture content and temperature of the drying medium were developed. The values of moisture diffusivity were obtained within the range of 1.27 × 10-9-6.48 × 10-9 m2/s and the activation energies for FBD and FBD + DE were found to be 27.71 and 17.10 kJ/mol, respectively. The shrinkage behavior of the broad beans was also investigated by... 

    Impact of oil polarity on the mixing time at the pore scale in low salinity waterflooding

    , Article Energy and Fuels ; Volume 34, Issue 10 , 16 September , 2020 , Pages 12247-12259 Mohammadi, S ; Mahani, H ; Ayatollahi, S ; Niasar, V ; Sharif University of Technology
    American Chemical Society  2020
    Abstract
    The efficiency of low salinity waterflooding, particularly during tertiary mode injection, is highly controlled by in situ mixing between the stagnant regions holding high salinity water (HSW) and the flowing regions containing low salinity water (LSW) because it impacts directly the electrokinetics of wettability alteration and the time scale of the low salinity effect. This study aims to address the effects of oil polarity and charged rock surfaces on the time scale of mixing and transport under two-phase flow conditions. A systematic series of micromodel experiments were performed. The micromodels were first saturated with high salinity formation brine and oil (both model and crude oil);... 

    Charge transport properties in nanocomposite photoanodes of DSSCs: Crucial role of electronic structure

    , Article EPJ Applied Physics ; Volume 57, Issue 2 , February , 2012 ; 12860042 (ISSN) Samadpour, M ; Taghavinia, N ; Iraji Zad, A ; Marandi, M ; Tajabadi, F ; Sharif University of Technology
    Abstract
    TiO 2 nanorods, TiO 2 nanorod/TiO 2 nanoparticle and TiO 2 nanorod/ZnO nanoparticle composite structures were integrated as photoanodes in backside illuminated dye-sensitized solar cells (DSSCs). Incorporation of TiO 2 nanoparticles into the bare nanorods increased the dye loading and improved the short-circuit current density (J sc) from 2.22 mA/cm 2 to 3.57 mA/cm 2. ZnO nanoparticles electrochemically grown into the TiO 2 nanorod layer could increase the surface area. Nevertheless, this considerably reduced the J sc to 0.57 mA/cm 2 and consequently cell efficiency. Electrochemical impedance spectroscopy (EIS) results showed that ZnO incorporated samples have better effective diffusion... 

    Simulation of activity loss of fixed bed catalytic reactor of MTO conversion using percolation theory

    , Article Chemical Engineering Science ; Volume 66, Issue 23 , December , 2011 , Pages 6199-6208 ; 00092509 (ISSN) Izadbakhsh, A ; Khorasheh, F ; Sharif University of Technology
    2011
    Abstract
    In this investigation, a reactor model for prediction of the deactivation behavior of MTO's porous catalyst in a fixed bed reactor is developed. Effect of coking on molecular transport in the porous structure of SAPO-34 has been simulated using the percolation theory. Thermal effects of the reaction were considered in the model and the temperature profile of the gas stream in the reactor was predicted. The predicted loss in catalyst activity with time-on-stream was in very good agreement with the experimental data. The resulting coke deposition and gas temperature profiles along the length of reactor suggested a reaction front moving toward the outlet of the fixed bed reactor at the... 

    Cu surface segregation in Ni/Cu system

    , Article Vacuum ; Volume 84, Issue 4 , 2009 , Pages 469-473 ; 0042207X (ISSN) Rasuli, R ; Iraji zad, A ; Ahadian, M. M ; Sharif University of Technology
    Abstract
    We report experimental evidence of Cu surface segregation in Ni/Cu system, during deposition of Ni film onto Cu substrate at room temperature and during heat treatment in vacuum. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) by Tougaard's analysis results show that surface segregation defeats in competition with increase in Ni thickness and terminates when thickness of Ni increase to more than 4 nm. Surface energy and concentration were calculated using contact angle measurements and the results confirm that segregation reduces the surface energy. Surface segregation during heat treatment at 150-220 °C range as a function of time initially shows linear mass...