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fattaheian-dehkordi--sajjad
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Optical bistability in fiber ring resonator containing an erbium doped fiber amplifier and quantum dot doped fiber saturable absorber
, Article Applied Optics ; Volume 51, Issue 29 , 2012 , Pages 7016-7024 ; 1559128X (ISSN) ; Farshemi, S. S ; Sajjad, B ; Shahshahani, F ; Bahrampour, A. R ; Sharif University of Technology
2012
Abstract
In this paper we study the optical bistability in a double coupler fiber ring resonator which consists of an erbium doped fiber amplifier (EDFA) in half part of the fiber ring and a quantum dot doped fiber (QDF) saturable absorber in the other half. The bistability is provided by the QDF section of the ring resonator. The EDFA is employed to reduce the switching power. The transmitted and reflected bistability characteristics are investigated. It is shown that the switching power for this new bistable device is less than 10 mW
Modeling and analysis of the dynamic response of an off-grid synchronous generator driven micro hydro power system
, Article International Journal of Renewable Energy Development ; Volume 10, Issue 2 , 2021 , Pages 373-384 ; 22524940 (ISSN) ; Farooq, H ; Rasool, A ; Sajjad, I. A ; Zhenhua, C ; Ning, L ; Sharif University of Technology
Diponegoro university Indonesia - Center of Biomass and Renewable Energy (CBIORE)
2021
Abstract
This paper models and analyses the dynamic response of a synchronous generator driven off-grid micro hydro power system using Simulink tool of MATLAB software. The results are assessed from various perspectives including regulation through no load to full load and overload scenarios under normal and abnormal operating conditions. The investigation under the normal conditions of no load, linearly changing load and full load divulges that the system operates in a satisfactory manner as generator voltage and frequency remain approximately constant at 1 pu. However, at full load generator voltage and frequency drop 3% and 0.5% respectively from its nominal values but remain within prescribed...
Modeling and analysis of the dynamic response of an off-grid synchronous generator driven micro hydro power system
, Article International Journal of Renewable Energy Development ; Volume 10, Issue 2 , 2021 , Pages 373-384 ; 22524940 (ISSN) ; Farooq, H ; Rasool, A ; Sajjad, I. A ; Zhenhua, C ; Ning, L ; Sharif University of Technology
Diponegoro university Indonesia - Center of Biomass and Renewable Energy (CBIORE)
2021
Abstract
This paper models and analyses the dynamic response of a synchronous generator driven off-grid micro hydro power system using Simulink tool of MATLAB software. The results are assessed from various perspectives including regulation through no load to full load and overload scenarios under normal and abnormal operating conditions. The investigation under the normal conditions of no load, linearly changing load and full load divulges that the system operates in a satisfactory manner as generator voltage and frequency remain approximately constant at 1 pu. However, at full load generator voltage and frequency drop 3% and 0.5% respectively from its nominal values but remain within prescribed...
Assessing new conditions for secretary problem using Multi-Agent Systems
, Article 13th Iranian Conference on Fuzzy Systems, IFSC 2013 ; August , 2013 , Page(s): 1 - 4 ; ISBN: 978147991227-8 ; Sharif University of Technology
IEEE Computer Society
2013
Abstract
The secretary problems are of types of the optimal stopping theory problems and are also distinguished as well known problems in applied probability, statistics and decision theory fields. The importance of these kinds of problems defines many new conditions which have been discussed till now. The significance of these types of problems in social issues causes to define many conditions which are vastly discussed. In this paper, a new condition of this problem is considered. These conditions which have been performed using a real time method are based on Multi-Agent Systems techniques. In this paper, after evaluating this method, the resulted answers are examined using Multi-Agent system...
Novel type of two-impinging-jets reactor for solid-liquid enzyme reactions
, Article AIChE Journal ; Volume 52, Issue 2 , 2006 , Pages 692-704 ; 00011541 (ISSN) ; Sharif University of Technology
2006
Abstract
The isomerization of D-glucose to D-fructose using the immobilized glucose isomerase, as a typical model system of solid-liquid enzyme reactions has been carried out in a novel type of two-impinging-jets reactor (TIJR), which is characterized by a rotating inner cylinder in a stationary one. Because of the impinging process, turbulence, and complex trajectory of the solid particles within the reactor, the fractional conversion of glucose obtained in the TIJR increased dramatically compared to that obtained by conventional reaction systems. A compartment model was considered to describe the pattern of flow [residence time distribution (RTD) of solid particles] within the TIJR. Considering...
Compact 5G millimeter-wave dual-band filter with application in filtenna
, Article Microwave and Optical Technology Letters ; Volume 63, Issue 2 , 2021 , Pages 620-625 ; 08952477 (ISSN) ; Jafarieh, A ; Behroozi, H ; Mallat, N. K ; Jamaluddin, M. H ; Sajjad Abazari, S ; Sharif University of Technology
John Wiley and Sons Inc
2021
Abstract
In this article, a dual-band sixth order double symmetric T-slot filter is proposed for the 5G communication systems. This filter contains two duplicate square resonators and a T-shape feedline on the Rogers RT duroid 5880 substrate. Operating at the 28 and 38.5 GHz frequencies from licensed 5G frequency bands and small size make this filter appropriate for different 5G applications. Furthermore, an LC equivalent circuit for the filter has been considered that helps us to have a better sight of this filter. Measurement results show good agreement with simulations. The attenuation on the passband is less than 1 dB. In order to evaluate the filter performance besides other millimeter waves...
Compartment model for steam reforming of methane in a membrane-assisted bubbling fluidized-bed reactor
, Article International Journal of Hydrogen Energy ; Volume 34, Issue 3 , 2009 , Pages 1275-1291 ; 03603199 (ISSN) ; Memari, M ; Sharif University of Technology
2009
Abstract
A compartment model was developed to describe the flow pattern of gas within the dense zone of a membrane-assisted fluidized-bed reactor (MAFBR), in the bubbling mode of operation for steam reforming of methane both with (adiabatic) and without (isothermal) entering oxygen. Considering such a flow pattern and using the experimental data reported elsewhere [Roy S, Pruden BB, Adris AM, Grace JR, Lim CJ. Fluidized-bed steam methane reforming with oxygen input. Chem Eng Sci 1999; 54:2095-2102.], the parameters of the developed model (i.e., number of compartments for the bubble and emulsion phases) were determined and fair agreements were obtained between model predictions and experimental data....
Reactive Crystallization in an Impinging Jets Reactor
, M.Sc. Thesis Sharif University of Technology ; Molaei Dehkordi, Asghar (Supervisor)
Abstract
Reactive crystallization or precipitation is an important industrial process. Many chemicals and biochemicals such as catalysts and pigments are produced by precipitation. Because of the advantages of impinging jets in chemical engineering processes, the main aim of this research was to investigate the application of this method in precipitation and to study the effects of different operating and design parameters on the product’s quality and properties. Two chemical models of barium sulfate and copper oxalate were used as main products. Each of these chemicals was produced by a liquid-liquid reaction of two aqueous solutions, which were fed to an impinging-jets reactor. Effects of...
Solid-Liquid Heterogeneous Catalytic Reactions in a New Two-Impinging-Jets Reactor
, M.Sc. Thesis Sharif University of Technology ; Molaei Dehkordi, Asghar (Supervisor)
Abstract
In this work the transesterification reaction of waste cooking oil in the present of solid catalyst as a type of solid-liquid catalytic reaction, has been studied. For this purpose, two types of alkali solid catalysts were synthesized. CaO-ZrO2 and KOH/γ-Al2O3 catalysts were prepared by co-precipitation and impregnation method, respectively. These catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), BET surface area, and temperature programmed desorption of CO2 (TPD-CO2). The obtained results for the CaO-ZrO2 catalysts indicate that with increasing Ca/Zr atomic ratio, the activity of catalysts increases, but the stability...
Transesterification of waste cooking oil to biodiesel using KOH/γ-Al2O3 catalyst in a new two-impinging-jets reactor
, Article Industrial and Engineering Chemistry Research ; Vol. 53, Issue. 31 , 2014 , Pages 12238-12248 ; ISSN: 08885885 ; Molaei Dehkordi, A ; Sharif University of Technology
2014
Abstract
In this article, the transesterification of waste cooking oil (WCO) to biodiesel fuel (BDF) has been studied using KOH loaded on millimetric γ-Al2O3 particles in a novel type of two-impinging-jets reactor (TIJR). The effects of various parameters such as KOH loading (wt %), catalyst loading, and methanol-to-oil molar ratio on the BDF yield were studied. The catalyst particles with a KOH loading of 25 wt % at appropriate reaction conditions (i.e., catalyst loading = 4 wt % and methanol-to-oil molar ratio = 15:1) and at 65 °C were used in the TIJR. The influences of various operating and design parameters such as jet Reynolds number value, feed flow rate, jet diameter, and the internozzle...
Mixed-convection flow of Al2O3-H2O nanofluid in a channel partially filled with porous metal foam: Experimental and numerical study
, Article Experimental Thermal and Fluid Science ; Vol. 53 , February , 2014 , pp. 49-56 ; ISSN: 08941777 ; Molaei Dehkordi, A ; Sharif University of Technology
2014
Abstract
Mixed-convection flow of nanofluids inside a vertical rectangular channel partially filled with open-cell metal foam and subject to a constant wall-heat flux was investigated experimentally and numerically. Al2O3-water nanofluids with different concentrations were prepared and their stability was examined using UV-Vis spectroscopy. Dynamic light scattering method was used to determine particle size distribution of the nanofluid feedstock. The outlet temperature and pressure drop were measured for different nanofluid flow rates (i.e., Reynolds number values). In the numerical section, a two-dimensional volume-averaged form of the governing equations was used. The velocity and temperature...
Transient behavior of fluid flow and heat transfer in vertical channels partially filled with porous medium: Effects of inertial term and viscous dissipation
, Article Energy Conversion and Management ; Volume 61 , September , 2012 , Pages 1-7 ; 01968904 (ISSN) ; Molaei Dehkordi, A ; Sharif University of Technology
Elsevier
2012
Abstract
In this article, transient hydrodynamic and heat-transfer behavior of Newtonian fluid flow in vertical parallel-plate channels partially filled with a porous medium has been investigated numerically. In this regard, the influences of macroscopic local inertial term and the viscous heating due to the viscous dissipation were taken into account in the momentum equations of porous region and the thermal energy equations, respectively. Moreover, Forchheimer-Brinkman extended Darcy model was used to model fluid flow in the porous region. In addition, an analytical solution was obtained in the case of negligible Brinkman and Forchheimer number values at the steady-state conditions. The predicted...
Adsorption of xylene isomers on Na-BETA zeolite: Equilibrium in batch adsorber
, Article Microporous and Mesoporous Materials ; Volume 172 , 2013 , Pages 136-140 ; 13871811 (ISSN) ; Khademi, M ; Sharif University of Technology
2013
Abstract
In this article, adsorption of p-xylene, m-xylene, o-xylene, and ethylbenzene on Na-BETA type zeolite in liquid phase at 15, 25, and 35 °C has been studied and the single adsorption isotherms have been obtained and reported. The Langmuir isotherm model was used to describe the experimental adsorption isotherm data. It was found that p-xylene is more strongly adsorbed component followed by ethylbenzene, m-xylene and o-xylene. This means that this adsorbent is selective for p-xylene. Using Langmuir isotherm model, the saturation adsorption capacities of the adsorbent were obtained as follows 143 mg/g for p-xylene, 105 mg/g for ethylbenzene, 83 mg/g for m-xylene, and 68 mg/g for o-xylene at 25...
Effects of contaminants on the mass-transfer characteristics of a two-impinging-streams gas-liquid reactor
, Article Chemical Engineering and Technology ; Volume 34, Issue 11 , 2011 , Pages 1797-1806 ; 09307516 (ISSN) ; Savari, C ; Sharif University of Technology
2011
Abstract
The mass-transfer characteristics of a new type of two-impinging-streams reactor (TISR) was studied by means of sodium sulfite solution as the liquid phase and air as the gas phase, in the presence and absence of various types of surface-active agents (SAAs). The influences of anionic, cationic, and nonionic SAAs on the specific interfacial area and overall volumetric mass-transfer coefficient obtained in the TISR were investigated. It was found that the presence of a little amount of the above-mentioned contaminants increases the specific interfacial area and decreases the overall volumetric mass-transfer coefficient. On the basis of the experimental results obtained for various types of...
Transesterification of waste cooking oil to biodiesel using Ca and Zr mixed oxides as heterogeneous base catalysts
, Article Fuel Processing Technology ; Volume 97 , 2012 , Pages 45-51 ; 03783820 (ISSN) ; Ghasemi, M ; Sharif University of Technology
2012
Abstract
Heterogeneous solid catalysts comprising CaO and ZrO 2 mixed oxides with various Ca-to-Zr molar ratios were synthesized by means of coprecipitation method. These synthesized mixed oxide catalysts were used for the transesterification of waste cooking oil (WCO) as feedstock with methanol to produce biodiesel fuel (BDF) at 65 °C and 1 atm. The influences of Ca-to-Zr molar ratio, catalyst loading, methanol-to-oil molar ratio, and the reaction time on the BDF yield were carefully investigated. In addition, the stability of prepared solid catalysts was studied. These catalysts were characterized by using techniques of X-ray diffraction, X-ray florescence, X-ray photoelectron spectroscopy, surface...
Analysis of nanofluid heat transfer in parallel-plate vertical channels partially filled with porous medium
, Article International Journal of Thermal Sciences ; Volume 55 , 2012 , Pages 103-113 ; 12900729 (ISSN) ; Molaei Dehkordi, A ; Sharif University of Technology
2012
Abstract
In this article, mixed-convective heat transfer of nanofluids in a vertical channel partially filled with highly porous medium was studied. In the porous region, the Brinkman-Forchheimer extended Darcy model was used to describe the fluid flow pattern. Different viscous dissipation models were also applied to account for viscous heating. At the porous medium-fluid interface, interfacial coupling conditions for the fluid velocity and temperature were used to derive the analytical solution using a two-parameter perturbation method. The model used for the nanofluids incorporates the effects of Brownian motion and thermophoresis. With constant wall temperature, velocity and temperature profiles...
Simulation of 3D freely bubbling gas-solid fluidized beds using various drag models: TFM approach
, Article Chemical Engineering Research and Design ; Volume 100 , 2015 , Pages 377-390 ; 02638762 (ISSN) ; Molaei Dehkordi, A ; Sharif University of Technology
Institution of Chemical Engineers
2015
Abstract
In this article, 3D modeling and simulation of bubbling fluidized beds has been conducted using various drag models, and the model predictions were validated against reported experimental data and 2D simulation results. In this regard, different drag models reported in the literature including Gidaspow, Syamlal-O'Brien, Hill-Koch-Ladd, and Wen-Yu were applied. A standard Two-Fluid Model (TFM) closed by the Kinetic Theory of Granular Flows (KTGF) was used to simulate bubbling gas-solid fluidized beds. Excellent agreements between the simulation results and experimental data, concerning bed expansion ratio, gas volume fraction, and time-averaged particles velocity, were found over a wide range...
Transient and steady-state forced convection to power-law fluids in the thermal entrance region of circular ducts: Effects of viscous dissipation, variable viscosity, and axial conduction
, Article Energy Conversion and Management ; Volume 51, Issue 5 , May , 2010 , Pages 1065-1074 ; 01968904 (ISSN) ; Memari, M ; Sharif University of Technology
2010
Abstract
A numerical study was conducted on the transient behavior of a hydrodynamically fully developed, laminar flow of power-law fluids in the thermally developing entrance region of circular ducts with taking into account the effects of viscous dissipation, axial conduction, and variations of viscosity with temperature. In this regard, the unsteady-state thermal energy and momentum equations were solved numerically using a finite-difference method, whereas the steady-state thermal energy equation with constant wall heat flux as the boundary condition was solved analytically as the initial condition of the former. The numerical procedure used in the present work was validated with an analytical...
Synthesis of barium sulfate nanoparticles using a spinning disk reactor: Effects of supersaturation, disk rotation speed, free ion ratio, and disk diameter
, Article Industrial and Engineering Chemistry Research ; Volume 48, Issue 16 , 2009 , Pages 7574-7580 ; 08885885 (ISSN) ; Vafaeimanesh, A ; Sharif University of Technology
2009
Abstract
The aim of this research was to synthesize barium sulfate nanoparticles using a spinning disk reactor. Barium sulfate was produced by continuously pumping two aqueous solutions of BaCl2 and Na2SO 4, respectively, into the chamber of spinning disk reactor, where a liquid-liquid reaction took place to form BaSO4. The influences of various operating and design parameters such as the initial supersaturation, disk rotation speed, free ion ratio, and the disk diameter on the size of barium sulfate nanoparticles were carefully investigated. By varying the supersaturation and disk rotation speed, a broad range of particle size ranging from micrometer sizes down to nanoparticles smaller than 100 nm...
Effects of initial static bed height on fractional conversion and bed pressure drop in tapered-in and tapered-out fluidized bed reactors
, Article International Journal of Multiphase Flow ; Volume 79 , 2016 , Pages 50-61 ; 03019322 (ISSN) ; Molaei Dehkordi, A ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
In this article, a standard 2D Two-Fluid Model (TFM) closed by the kinetic theory of granular flow (KTGF) has been applied to simulate the behavior of tapered-in and tapered-out fluidized bed reactors. In this regard, two types of chemical reactions with gas volume reduction and increase were considered to investigate the effects of initial static bed height on the fractional conversion and bed pressure drop. To validate the CFD model predictions, the results of hydrodynamic simulations concerning bed pressure drop and bed expansion ratio were compared against experimental data reported in the literature and excellent agreement was observed. The obtained simulation results clearly indicate...