Asghar Molaei Dehkordi ---

• Doctor of Engineering
• Faculty Member at Sharif University of Technology

This article introduces a comprehensive model for simulating the hydrodynamics of a draft-plate spouted bed by employing a coupled CFD–DEM (computational fluid dynamics–discrete element method) approach. In contrast to studies focusing on isolated parameters, the present work applies the DEM approach to analyze the combined influence of all pertine...

In this article, the intensification of solids mixing in tapered fluidized beds equipped with an inlet jet and varying apex angles (2.86°, 5.71°, and 8.53°) has been investigated. In this regard, a particle segregation number (PSN) and multi-fluid modeling (MFM) approach were employed to analyze the mixing process. The study utilized solid mixtures...

This article investigates the intensification of solids mixing in tapered fluidized beds with an inlet jet and varying apex angles (2.86, 5.71, and 8.53 degrees). The investigation applied a particle segregation number (PSN) and a multi-fluid modeling (MFM) approach. The solid mixtures considered comprise particles with a density of 2500 kg/m³ and...

The two-dimensional two-fluid model (TFM) incorporating the kinetic theory of granular flow was used to simulate the hydrodynamic behavior of gas bubbles in tapered fluidized beds. Because numerous previous works conducted were mainly focused on the hydrodynamic behavior of the beds such as pressure drop, minimum fluidization velocity, and bed expa...

In this article, the heat transfer of magnetic nanofluids over a sphere has been considered in the presence of an external oscillating uniform magnetic field for a wide range of Reynolds number values (Re). This study incorporates the effect of magnetic permeability and purposes the optimal operating condition for the first time. The significant di...

Choosing the appropriate ion exchange membrane in vanadium redox flow batteries plays an important role in achieving optimal system performance. In this article, the implementation of commercial cation exchange membranes (Nafion 115, Nafion 117, and Nafion 212), anion exchange membranes (FAP 450 and QA-PFE), and the combination of them are investig...

The creation of surfaces with various super nonwetting properties is an ongoing challenge. We report diverse modifications of novel synthesized zirconia-ceria nanocomposites by different low surface energy agents to fabricate nanofluids capable of regulating surface wettability of mineral substrates to achieve selective superhydrophobic, superoleop...

Flow battery innovations should offer significant improvements in performance, without compromising the durability / lifetime, and be cost-effective and scalable. The presentation will review some of the progress that has been made to enhance flow battery performance, and will discuss a number of recent innovations that aim to deliver these charact...

Surfaces with special wettability have aroused lots of attention due to their broad applications in many fields. In this work, we systematically report selective and various fabrications of nanofluids based on readily available materials such as SiO2 nanoparticles and polydimethylsiloxane to create superhydrophobic, superoleophobic, superhydrophili...

Vanadium redox flow batteries (VRFBs) with large energy storage capability are one of the most important electrochemical technologies in the world. The specific design of these batteries has made it possible to increase the storage capacity to very high values. Hence, this technology is referred to as the electricity supplier of cities in the not t...

Ion exchange membranes play an important role to meet optimum performance in redox flow batteries. Herein, a 2D model was developed to investigate the effects of cation exchange membrane (Nafion 212) and anion exchange membrane (FAP 450) on the performance of all-vanadium redox flow batteries. The model predicted results were validated against the...

In this article, a confined-impinging-jets reactor (CIJR) was designed and tested successfully for the synthesis of calcium carbonate nanoparticles using the reactive precipitation method. The proposed CIJR comprised of two opposed nozzles placed in a cylindrical chamber. Effects of various operating and design parameters such as supersaturation, f...

In this article, the novel concept of using magnetic nanofluidic electrolyte for redox flow batteries is demonstrated for the first time. In this regard, the stable magnetic nanofluidic electrolytes are prepared by dispersing magnetic modified multiwalled carbon nanotubes (MMWCNTs) in the positive electrolyte of a polysulfide-iodide redox flow batt...

In this paper, a number of calcium carbonate synthesis experiments have been conducted using an impinging jets reactor to evaluate the effects of temperature, retention time, and elutant on the nanoparticles' mean size and distribution. This type of reactors require much lower residence times for the reactions; hence, they have attracted much atten...

High mixing efficiency that is of great importance in various industrial processes is a significant feature of spinning disk reactors. This work was focused on the characterization of mixing in a new reactor called Double Spinning Disk Reactor (DSDR) by adopting a competitive parallel reaction system known as iodide–iodate test reaction. The propos...

In this paper, we study the role of inlet gas temperature and jet to bed cross-section ratio on hydrodynamics and circulation patterns of particles in a spout-fluid bed. The system is modeled using CFD-TFM approach based on Eulerian-Eulerian method. Simulation results are validated by experimental data measured by (Link 2008. “PEPT and Discrete Par...

In this article, the effects of nonuniform magnetic fields on the hydrodynamics and heat transfer from a heated sphere to its surrounding ferrofluid flow have been investigated. Kelvin body forces originate from the nonuniformity of the applied magnetic field and can generate the vortices behind the sphere leading to a considerable change in the ve...

A new high-speed spinning disk reactor (HSSDR) was proposed and tested successfully. In this regard, barium sulfate (BaSO4) nanoparticles were synthesized using reactive crystallization processes. In this reactor, the rotational disk speed was varied from 5000 to 15 000 rpm. The effects of various design and operating parameters such as the rotatio...

In this article, a three-dimensional numerical simulation based on a Reynolds stress model has been developed to investigate the hydrodynamic behavior of two-impinging-jet spinning disk reactors (TIJSDRs) proposed by Molaei Dehkordi. TIJSDR comprises two coaxial rotating disks separated by a small distance and two-impinging jets introduced at the c...

This article presents a simulation study of tapered-in and tapered-out fluidized bed reactors to investigate the influences of apex angle on the fractional conversion and the pressure drop of the fluidized beds in the presence of two types of chemical reaction with gas volume increase and reduction. The 2D behavior of tapered-in and -out fluidized...

In this article, effects of magnetic fields induced by a finite length solenoid on the forced-convection heat transfer in a pipe partially filled with porous medium have been investigated. In this regard, two-dimensional steady-state fluid flow in the pipe was considered and the Darcy–Brinkman equation of motion was applied to model the fluid flow...

In this paper, a number of calcium carbonate synthesis experiments have been conducted using an impinging jets reactor to evaluate the effects of temperature, retention time, and elutant on the nanoparticles’ mean size and distribution. This type of reactors require much lower residence times for the reactions; hence, they have attracted much atten...

In this article, ferrohydrodynamic forced-convection heat transfer from a heated sphere embedded in a ferrofluid in the presence of the uniform external magnetic field has been studied numerically for the first time over a wide range of Reynolds number value, nanoparticle diameter, particle volume fraction, and magnetic field intensity. Despite the...

Liquid–liquid equilibrium (LLE) data, density, viscosity, and interfacial tension for the ternary system of toluene–acetic acid–water were measured at 298.15 K and 101.7 kPa. The Othmer–Tobias and the Hand correlations were used to check the reliability of the experimental tie-lines. Moreover, the distribution coefficient and the separation factor...

In this article, the behavior of gas bubbles in tapered fluidized beds is investigated with the use of a two-fluid model incorporating kinetic theory of granular flow. The effects of various parameters such as apex angle, particle size, and particle density on the size distribution and the rise velocity of gas bubbles were examined. In addition, th...

In this article, a comprehensive 2D mathematical model has been developed to simulate process intensification of carbon dioxide absorption in the presence of nanoparticles in hollow fiber membrane contactors (HFMCs). The influences of nanoparticle were taken into account considering Brownian motion and Grazing effect as dominant phenomena of mass-t...

In this article, a new double spinning disks reactor (DSDR) has been proposed and tested successfully for the synthesis of barium sulfate nanoparticles by means of the reactive precipitation. The proposed DSDR consists of two coaxial rotating disks placed horizontally in a cylindrical chamber. Continuous precipitation of barium sulfate nanoparticle...

In this work, forced-convection heat transfer of magnetic-sensitive nanofluids has been investigated in the presence of rotating magnetic field. In this regard, laminar, Newtonian, incompressible, and two-dimensional (2D) fluid flow in a horizontal duct subject to constant wall temperature boundary conditions was modeled. Moreover, the fluid was su...

In this article, three-dimensional (3D) forced-convection heat transfer of magnetic nanofluids in a pipe subject to constant wall heat flux in the presence of single or double permanent magnet(s) or current-carrying has been investigated and compared. In this regard, laminar fluid flow and equilibrium magnetization for the ferrofluid were considere...

The way we perceive language is the foundation of our social construction and individual or group relationship. Studies in sociolinguistics attempt to explain this relationship between the use of language and the importance of perception. A distinct discourse, spoken or written, can stem from different sources such as power, culture, social backgro...

In this article, the influences of ferrofluid and magnetic field on the reactive absorption in packed-bed contactors have been investigated. Because of importance of carbon dioxide emission as a global concern, absorption of carbon dioxide was chosen to investigate these effects. In this regard, multitube approach was applied to model the contactor...

Magnetite nanoparticles with an average particle size of 28.8 nm were synthesized, coated with oleic acid, and characterized using various techniques such as DLS, FT-IR, SEM, XRD, VSM, and UV-Vis analysis. A nanofluid consisting of synthesized nanoparticles and 5 wt % acetic acid in toluene as the dispersed phase was prepared and used in the chemic...

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...

The state of solids mixing can be considered as a key factor in accomplishment of high efficiency and a uniform product in gas–solid fluidized-beds operating with several different particle sizes. In the present work, coupled DEM–CFD approach was used to carefully investigate the mixing process of binary particles in flat-bottom spouted beds. In th...

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 w...

In this article, transient two-dimensional mixed convection of nanofluids in the entrance region of a vertical channel has been studied carefully. The geometry under consideration consisted of a parallel-plate channel partly filled with a porous medium with a constant wall temperature. In the free flow region, the two-dimensional flow field has bee...

In this article, a comprehensive model has been developed for analyzing the transport phenomena in hollow fibre membrane contactors operated under non-wetted or partially-wetted conditions. In this regard, the dynamic behaviour of membrane contactors, considering the entrance regions of momentum, thermal energy, and mass transfers, was investigated...

A comprehensive mathematical model has been developed to analyze transport phenomena in wetted wall absorption reactors. In this regard, a wetted wall reactor was modelled considering the entrance regions of momentum, heat, and mass transfer, compressibility of the gas phase as a function of gas temperature, pressure, and composition, and also non-...

The effects of particle size on the solid flow pattern in gas-solid bubbling fluidized beds were investigated numerically using two-fluid model based on the kinetic theory of granular flow. In this regard, the set of governing equations was solved using finite volume method in two-dimensional Cartesian coordinate system. Glass bead particles with m...

A deterministic model based on the discrete population balance equation (PBE) is used to examine the precipitation of barium sulfate nanoparticles in nonionic inverse microemulsion systems. It is shown that coagulation can have a significant effect at low initial reactants concentration. The simulation results show that a bimodal particle size dist...

In this article, the transesterification of waste cooking oil (WCO) to biodiesel fuel (BDF) has been studied using KOH loaded on millimetric gamma-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...

In this article, the problem of combined forced and free convection in vertical porous and regular channels for both regular fluids and nanofluids has been solved using the CFD technique in the entrance regions of momentum and heat transfer taking into account the influences of viscous heating and inertial force. In this regard, various types of vi...

A comprehensive mathematical model has been developed for the simulation of simultaneous chemical absorption of carbon dioxide and hydrogen sulfide by means of Monoethanolamine (MEA) aqueous solution in hollow fiber membrane reactors is described. In this regard, a perfect model considering the entrance regions of momentum, energy, and mass transfe...

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 sc...

A novel phenomenological discrete bubble model was developed and tested for prediction of the hydrodynamic behavior of the dense phase of a 3D gas-solid cylindrical fluidized bed. The mirror image technique was applied to take into account the effects of the bed wall. The simulation results were validated against experimental data reported in the l...

In this article, a new method for solving multidimensional population balance (PB) equations for agglomeration is presented. First, discretized 2-dimensional PB (DPB) is derived and by applying probability approach, this method is extended to n-dimensional PB. The discretization of size intervals is in the form of v(j) = 2j-iv(i) and the volume bas...

A targeted research on the oxidative desulfurization of kerosene with a total sulfur content of 1,600 ppmw was conducted with hydrogen peroxide and formic acid. The influences of various operating parameters, including reaction temperature, hydrogen peroxide/sulfur molar ratio (O/S), and formic acid/sulfur molar ratio (Acid/S), on the desulfurizati...

In this article, the problem of simultaneous heat, mass, and momentum transfer in the developing region of tubular reactors with homogeneous chemical reaction and laminar power-law fluid flow under unsteady-state conditions has been solved. In this regard, the general governing equations were solved using finite-difference method and analyzed caref...

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 th...

In this article, the digital image analysis (DIA) technique has been used to study the bubble size and bubble size distribution evolution in a pseudo-two-dimensional gas–solid fluidized bed. In addition, a numerical discrete bubble model (DBM) based on the bubble–bubble interactions was developed and the model predictions were compared with the exp...

Heterogeneous solid catalysts comprising CaO and ZrO2 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 influen...

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 por...

A discrete bubble model has been developed taking into account multiple bubble-bubble interactions and a delayed coalescence method. The obtained simulation results were compared with experimental data reported in literature. The simulation results predicted by the developed model indicate clearly that the multiple interactions of bubbles lead to m...

In industrial gas-liquid processes, the liquid feed is not clean but there are various kinds of contaminants in the feed entering the contactors. In this regard, a new type of two-impinging-streams reactor (TISR) was tested through the sodium sulfite solution as the liquid phase and air as the gas phase, in the presence and absence of various types...

In this paper, combined forced and natural convection in a vertical channel containing both porous and viscous regions taking into account the influences of inertial force and viscous dissipation has been studied. In this regard, fully developed fluid flow in the porous region was modeled using the Brinkman-Forchheimer extended Darcy model. To solv...

In this article, the problem of combined forced and natural convection in a vertical porous channel for both regular fluids and nanofluids has been solved by perturbation and numerical methods, taking into account the influences of viscous heating and inertial force. In this regard, various types of viscous dissipation models, including the Darcy m...

The theory of mass transfer accompanied by chemical reaction for gas−liquid systems was used to measure the effective interfacial area (a) and the overall volumetric mass-transfer coefficient (kLa) in a new two impinging streams reactor (TISR), which is characterized by a high-intensity mixing chamber equipped with two two-phase nozzles directed to...

Mass-transfer rates to and from drops in liquid−liquid extraction processes are often reduced by the presence of contaminants. To design an industrial extractor, it is essential to consider this contamination effect in a quantitative manner. To achieve this goal, an experimental investigation was conducted on the mass transfer into single drops for...

A compartment model was developed to describe the flow pattern of gas within the dense zone of a tapered membrane-assisted fluidized-bed reactor (TMAFBR), in the bubbling mode of operation for steam reforming of methane under wall heat flux. The parameters of the developed model (i.e., number of compartments for the bubble and emulsion phases) were...

An experimental study was conducted on the desulfurization of non-hydrotreated kerosene with oxidation followed by liquid–liquid extraction. Various types of solvents including acetonitrile, methanol, and ethanol have been examined in the extraction of oxidized sulfur-containing compounds of kerosene. The performance of these solvents has been care...

A novel type of four-impinging-jets reactor (FIJR) has been proposed and tested successfully for the oxidative desulfurization of kerosene as a typical light fuel oil. The FIJR is characterized by a high-intensity mixing chamber located at the bottom of the reactor and equipped with four impinging jets. The influences of various operating and desig...

The desulfurization of non-hydrotreated gas oil using oxidation followed by liquid/liquid extraction has been studied. The solvent extraction of oxidized sulfur-containing compounds of gas oil was carried out by utilizing various types of solvents, including acetonitrile, methanol, and 96 vol.-% ethanol. The performance of these solvents was carefu...

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-stat...

In industrial liquid-liquid extraction processes, the feed is not clean liquid but there are various kinds of contaminants in the feed entering the extractors. In this regard, a two-impinging-jets contacting device (TIJCD) was tested through the standard test system recommended by the European Federation of Chemical Engineering (EFCE), namely tolue...

The catalytic wet peroxide oxidation (CWPO) of phenol with activated carbon (AC) as the catalyst has been successfully tested in a novel type of two-impinging-jets reactor (TIJR). The TIJR is characterized by a high-intensity reaction chamber, which is separated by a perforated plate from other parts of the reactor. The perforated plate was used as...

The oxidative desulfurization of a real refinery feedstock (i.e., non-hydrotreated kerosene with total sulfur mass content of 0.16%) with a mixture of hydrogen peroxide and acetic acid was studied. The influences of various operating parameters including reaction temperature (T), acid to sulfur molar ratio (nacid/nS), and oxidant to sulfur molar ra...

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 Na2SO4, respectively, into the chamber of spinning disk reactor, where a liquid−liquid reaction took place to form BaSO4. The influences of various operating an...

In this work, we present a level set method to simulate steady and unsteady mass transfer from a single droplet moving in a second phase fluid under buoyant force. We initially use level set to determine the interface between the two phases, where the shape of drop forms. Next, we extend this method to solve a unique mass transfer equation for the...

A numerical investigation 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 taking into account the effect of viscous dissipation but neglecting the effect of axial conduction. In this regard, the unsteady state thermal energ...

We present the kinetic parameters and equilibrium constant of the enzymatic glucose−fructose isomerization reaction with an immobilized glucose isomerase (IGI), Sweetzyme IT, using a batch stirred-tank reactor following the procedure developed by Dehkordi et al. ( AIChE J. 2008, 54, 1333). The model predictions were compared with the experimental d...

Novel type of two-impinging-jets loop reactor (TIJLR) has been proposed and tested successfully for the solid−liquid catalytic reactions. The TIJLR was tested using the catalytic reaction of isomerization of d-glucose to d-fructose by immobilized glucose isomerase catalyst as a typical model system of solid−liquid catalytic reactions. The TIJLR is...

An experimental investigation was conducted on the oxidative desulfurization of model sulfur compounds such as dibenzothiophene and benzothiophene in toluene as a simulated light fuel oil with a mixture of hydrogen peroxide as the oxidant and various acids as the catalyst. The influences of various parameters including reaction temperature (T), aci...

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 el...

The catalytic wet peroxide oxidation (CWPO) of phenol was studied in a batch system using a commercial activated carbon supplied by Jacobi Co. ( Sweden, type of AquaSorb 101). The influences of various operating parameters including the initial pH of solution, temperature, catalyst loading, and the addition modes of hydrogen peroxide on the fracti...

The kinetics and equilibrium of isomerization reaction of D-glucose to D-fructose have been investigated using a commercial immobilized glucose isomerase (IGI), Sweetzyme type IT®, in a batch stirred-tank reactor. The batch experimental data were used to model the reaction kinetics using the well-known Michaelis–Menten rate expression. The kinetic...

The mass transfer coefficients of single drops in liquid-liquid extraction systems were studied using a single drop apparatus both with and without packing. The chemical system of n-butanol-succinic acid-water and the Structured Packing (SMV.350Y) were used in the liquid-liquid extraction. Based on the experimental results obtained for both mass tr...

This paper deals with the modeling and simulation of binary liquid-phase adsorption of methyl mercaptan and hydrogen sulfide from a liquid butane stream by zeolite molecular sieve 13X in a fixed bed. The model equations account for the effect of axial dispersion and the inter- and intraparticle mass-transfer resistances at isothermal operating cond...

The prediction of mass-transfer rates into and from moving drops in the liquid−liquid systems has usually used the well-known Whitman two-film theory approach. According to the latter, the total resistance to mass transfer resides on each side of the interface and is described by the individual film mass-transfer coefficients for the continuous and...

A two impinging-jets contacting device (TIJCD) for liquid–liquid extraction processes was proposed and tested through the standard test system recommended by the European Federation of Chemical Engineering (EFCE), toluene–acetone–water, as a typical example of liquid–liquid extraction processes. The results obtained for the overall volumetric mass...

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...

The theory of mass transfer accompanied by chemical reaction for the pseudo-first-order heterogeneous liquid–liquid reactions was used to measure the effective interfacial area in a novel two-impinging-jets reactor (TIJR), which is characterized by a small reactor volume equipped with two simple nozzles directed toward each other. Aqueous and organ...

The theory of mass transfer accompanied by chemical reaction for the pseudo-first-order heterogeneous liquid−liquid reactions was employed to measure the effective interfacial area in an air-driven two-impinging-streams reactor (ADTISR) with spray nozzles. Experiments have also been conducted on the physical extraction of n-butyl formate into disti...

A novel two-impinging-jets reactor (TIJR) for metals extraction was proposed and tested through solvent extraction of copper by means of a weak extractant with moderately slow chemical kinetics such as LIX 84, as a typical example of hydrometallurgical solvent extraction processes. The results obtained for the extraction and stripping rates of copp...

An air-operated two-impinging-streams reactor (AOTISR) was employed as a heterogeneous chemical reactor to carry out the extraction of copper by means of 2-hydroxy-5-nonylacetophenone oxime, LIX 84 (15% v/v), diluted with kerosene and the stripping of the loaded solvent by means of sulfuric acid of an appropriate concentration. The effects of the a...

Liquid–liquid extraction of the recommended test system, cumene–iso butyric acid–water (CBW) as a typical example of liquid–liquid extraction processes has been carried out in a new two-opposed-jets contacting device (TOJCD). The experimental results clearly indicate that TOJCD provides much higher overall volumetric (capacity) mass transfer coeffi...

Extraction of succinic acid by means of normal butanol from its aqueous solutions (BSW), acetic acid by means of distilled water from kerosene (WAK) and iodine by means of kerosene from its aqueous solution (KIW) have been investigated in an air-operated two impinging streams extractor (AOTISE) with spray nozzles. The effects of air flow rate, solu...