# مقالههای Ahmad Ramazani S.A

**توجه:**محتویات این صفحه به صورت خودکار پردازش شده و مقالههای نویسندگانی با تشابه اسمی، همگی در بخش یکسان نمایش داده میشوند.

##### ۱NUMERICAL INVESTIGATION OF NORMAL STRESS DIFFERENCE AND VISCOSITY USING OF DYNAMICAL MODELS IN SLIT DIE

اطلاعات انتشار:
دوازدهمین کنگره ملی مهندسی شیمی ایران،
سال ۱۳۸۷

تعداد صفحات:
۷

In this paper, the flow behavior of Leonov–Like conformational rheological model, which has root in the generalized Poisson bracket formalism based on the conformation tensor, have been studied in the slit die flow. Prediction of the normal stress differences

during the flow of these fluids lets us to follow and calculate relaxation dependent phenomena such as die swell. The model predictions have been compared for the two families of mobility expressions. The Study of the model prediction sensitivity to its mobility term shows that model predictions can cover a wide range of rheological behaviors generally observed for polymer melts and solutions in the circular die flow.<\div>

during the flow of these fluids lets us to follow and calculate relaxation dependent phenomena such as die swell. The model predictions have been compared for the two families of mobility expressions. The Study of the model prediction sensitivity to its mobility term shows that model predictions can cover a wide range of rheological behaviors generally observed for polymer melts and solutions in the circular die flow.<\div>

##### ۲Simulation of Viscoelastic Fluid Flow in Micropore with Dead End

اطلاعات انتشار:
هجدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۹

تعداد صفحات:
۶

The flow characteristics of a nonlinear viscoelastic fluid in porous pores in reservoir with the dead ends are simulated numerically to find effects of fluids and flow character on the replacement ability of flooding fluid with dead oil in the dead ends. The contours of velocity and stream function and shear stress and pressure are drawn and micro–scale sweep efficiency is calculated qualitatively. The Oldroyd–B model has been used to describe the rheological properties of polymer solution. A finite–volume–based numerical approach has been used to solve the equations of motion and fluid constitutive equation for the steady, isothermal and incompressible fluid past through a two–dimensional micropore. The streamline plots showing the flow dynamic at different Reynolds and Debora numbers are presented graphically. The presented results show that the viscoelastic nature of the displacing polymer fluids can considerably improve the displacement efficiency in pores compared to the Newtonian and generalized Newtonian fluids which must be due to contribution of the normal forces. This conclusion could be very important in selecting polymer fluids and designing polymer flooding operation conditions.<\div>

##### ۳Three–Dimensional Simulation of mold filling of viscoelastic fluids using finite volume method

اطلاعات انتشار:
کنفرانس بین المللی فرآورش پلیمرها،
سال ۱۳۹۰

تعداد صفحات:
۴

In this research, three dimensional molds filling of polymeric resins has been considered using finite volume scheme. Two–phase model concerning two–phase fluid including Viscoelastic and Newtonian (Air) was applied in mold. Giesekus model was used for a solution of viscoelastic fluid. The viscosity of polymer fluid was assumed 1.2 Pa.s which is about 1000 times greater than water viscosity. The applied pressure difference was considered 8000 Pa. To improve the pressure distribution in the mold, two symmetrical vents on either side of the mold. Obtained results for velocity and pressure distribution are qualitatively in agreement with experimental data presented in literature. Die–swell phenomenon for Viscoelastic fluid was observed at mold entrance. When vent was not embedded, due to increase of pressure in the cavity, an upward force would be applied to the fluid which result in. When the vent is fitted, there is no upward force and the inputted fluid will be gain a greater velocity. Better results were achieved by changing the size and position of vents at different points of mold . Doing several mold filling simulation and investigation the pressure, velocity and alpha profiles. The governing equations of the flow are solved by means of the Open Source code Open FOAM<\div>

##### ۴Solving the Undesirable Polymerization Problem in the Industrial Unit of Styrene Production

اطلاعات انتشار:
کنفرانس بین المللی فرآورش پلیمرها،
سال ۱۳۹۰

تعداد صفحات:
۷

There are several common methods to produce the styrene monomer in the industrial units, including the ethylbenzene (EB) adiabatic dehydrogenation, the ethylbenzene isothermal dehydrogenation, simultaneously styrene producing and propylene oxidation, membranous process for the ethylbenzene dehydrogenation, and the ethylbenzene dehydrogenation and oxidation using carbon dioxide. Styrene production unit in Iranian Petrochemical Complex has used the ethylbenzene (EB) adiabatic dehydrogenation process to prepare the styrene monomer where undesirably styrene polymer is formed by applied process conditions. According to solve this problem, there are two solutions: 1) changing difference applied process conditions; 2) using polymerization inhibitors. In this study, the production process is modified by investigation of polymerization conditions, and operation conditions are optimized using mathematical kinetic models in accordance with Hougen–Watson method (as non–porous Model). Besides, all kinds of the polymerization inhibitors are investigated to select the best ones for the employed operation conditions. The obtained results depict that residence time in the heat exchangers and separation vessel should be reduced, and organic–aqueous separator should be modified by other stabilization approaches instead of using mesh grid method. Furthermore, the operation conditions such as selectivity, feed temperature, and flowrate ratio profiles for the main components based on a new presented catalyst are optimized to diminish the possibility of polymerization formation.<\div>

##### ۵Manufacturing of polypropylene\silica nanocomposites using in–situ polymerization and investigation of product properties

اطلاعات انتشار:
کنفرانس بین المللی فرآورش پلیمرها،
سال ۱۳۹۰

تعداد صفحات:
۴

In this research polypropylene\silica nanocomposites with different concentrations of fumed silica were prepared via in situ polymerization method using bi–supported Ziegler–Natta catalyst and their properties was investigated. Fumed silica and magnesium ethoxide were used as supports of TiCl4. Preparation of catalyst and polymerization process have been done in slurry phase and under argon atmosphere using triisobutylaluminum as the cocatalyst. Scanning Electron Microscopy (SEM) images also certified very good dispersion of fumed silica throughout PP matrix. The crystalline structures of prepared nanocomposites were characterized by differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) was used to characterize the thermal properties. Structural study was carried out using FTIR and GPC techniques. Meanwhile, the rheological tests of samples have been taken.In addition to tests for describe nanocomposites's properties, effect of different factor e.g polymerization time, monomer pressure and [Al]\[Ti] were studied. Moreover, prepared nanocomposites in this method have superior thermal and morphological properties in comparison with those of similar nanocomposites prepared with other methods<\div>

##### ۶Modeling and Simulation of Generalized Newtonian and Viscoelastic Fluid Flows in Screw Turning Extruder in the Presence of Leakage Flow Using OpenFOAM Software

اطلاعات انتشار:
کنفرانس بین المللی فرآورش پلیمرها،
سال ۱۳۹۰

تعداد صفحات:
۸

This manuscript presents a simulation of viscoelastic and generalized Newtonian fluid flows in a single screw extruder (SSE) considering that the extruder screw is turning instead of its barrel, which normally was considered in most simulations as an assumption. A three dimensional finite–volume scheme is used to solve momentum and the fluid constitutive equations. The really geometrical mesh of the channel is generated to investigate pressure, velocity, shear stress, and normal stress changes. The simulation is done considering the condition of existence and absence of leakage flow, and results are compared. The simulations concern incompressible flow of the Carreau–Yasuda generalized Newtonian and Phan–Thien\Tanner (PTT) viscoelastic fluids. The obtained results are shown in contour and vector form based on special position onto the axial flow. Numerical results demonstrate the influence of boundary conditions (fixed and mobile barrel assumption and omitted leakage assumption) and rheological properties on the flow characteristics in considered geometry. The results show that screw moving as realistic conditions instead of the mobile barrel assumption in single extruder have significant effects on pressure, stress, and velocity profiles comparing to results obtained from simulation with the assumption of fixed barrel boundary that currently is used to model extruder flows. Presented results show that the pressure profile and flow fields change upon changing the assumption of the static boundary. The simulations also predict the different pressure profile and flow characteristics for the generalized Newtonian and viscoelastic fluids.<\div>

##### ۷Mold Filling Simulation in the Injection Molding Process with OpenFOAM Software

اطلاعات انتشار:
کنفرانس بین المللی فرآورش پلیمرها،
سال ۱۳۹۰

تعداد صفحات:
۴

Viscoelastic fluids play significant roles in many industries, including food and polymeric petrochemical and forming industries. The rheological response of viscoelastic fluids is quite complex, including combination of viscous and elastic effects. In this study, mold filling of Oldroyd–B and linear PTT viscoelastic fluids are simulated by the OpenFOAM software. The OpenFOAM is a finite volume based open source software that has been used in Computational Fluid Dynamics (CFD) successfully. The studied mold has a rectangular structure with a gate for fluids injection. The simulation is carrying out at isothermal conditions and flow considered two dimensional. The velocity, shear stress and first normal stress difference changes in different points of the mold are critically studied. The simulation results indicate that maximum velocity decreases along the mold length. Maximum velocity and maximum first normal stress difference increase as injection rate increases. In addition, maximum shear stress and first normal stress difference occur in the inlet of mold and changes of shear stress and first normal stress difference are linear along the mold length. Shear stress changes at the inlet are completely different compared to regions far from the inlet, where the highest values of elongation rate are found<\div>

##### ۸Numerical simulation of the expansion flow of some viscoelastic fluids

اطلاعات انتشار:
چهاردهمین کنگره ملی مهندسی شیمی ایران،
سال ۱۳۹۱

تعداد صفحات:
۵

Numerical simulation of flow of Oldroyd–B, linear Phan–Thien–Tanner (L–PTT) and finitely extensible Nonlinear Elastic (FENE–P) viscoelastic fluids in a sudden expansion geometry with expansion ratio M\N=3.Have been done in two dimensional Cartesian coordinates. The governing equations in transient and fully developed regions were solved using open source software called OpenFOAM. This software used finite volume methods for resolution of partial differential equation of flow system. The flow pattern, including velocityprofiles, shear and normal stresses in some horizontal and vertical sections are presented. In addition, effect offlow dynamics and fluid types on flow and vortex patterns in transient and fully developed regions are presented and discussed the presented results show that existences of vortices cause to create inverse velocity and negative tension in expansion regions of the channel. Furthermore the stagnant zone can be observed at expansion region close to wall<\div>

##### ۹Investigation of Screw Turning and Barrel Turning Boundaries in Single Screw Extruders by OpenFOAM cfd Software

اطلاعات انتشار:
هفتمین کنگره ملی مهندسی شیمی،
سال ۱۳۹۰

تعداد صفحات:
۱۴

This study presents CFD modeling of Newtonian, generalized–Newtonian and viscoelastic fluidflows in an extruder concerning screw turning (as realistic boundary) and barrel turning (as classical boundary) to compare modern extrusion modeling vs. classical extrusion modeling in which normally barrel turns.A three dimensional finite–volume scheme is used to solve momentum and fluid constitutive equations by a generated hex grid for the convective–type terms to discrete the equations and solve the set of governing equations. The simulations concern incompressible fluids obeying different constitutive equations: Newtonian fluid, generalized–Newtonian fluid with shear–thinning properties (Carreau–Yasuda model), and viscoelastic differential fluid, the Phan– Thien\Tanner model (PTT). The post–processing are done in contour and vector form based on channel depth onto the axial flow. Considering screw moving boundary in the extruder has significant effects on pressure, stress, and velocity behaviors comparing to the obtained results from the assumption of the turning barrel boundary that currently is used to model the extrusion process. Numerical results demonstrate that the pressure and velocity profiles are opposite in the two mentioned assumptions and viscoelastic properties cause effectively to change flow behavior in the spiral direction. Furthermore, the major variables of flow are influenced by Newtonian, viscoelastic and generalized–Newtonian models in volume control output.<\div>

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