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Polyethylene quality control in an industrial scale fluidized bed reactor
, Article Indian Journal of Chemical Technology ; Volume 25, Issue 1 , January , 2018 , Pages 21-30 ; 0971457X (ISSN) ; Shahrokhi, M ; Sharif University of Technology
National Institute of Science Communication and Information Resources (NISCAIR)
2018
Abstract
Polymer quality control in an industrial scale polyethylene fluidized bed reactor has been addressed. Since online measurements of polymer properties (melt index and density) are not available, they must be controlled indirectly via other available measurements. In the present paper, two algebraic equations correlating polyethylene melt index and density with the measureable concentrations of chemical components are obtained. Having the desired polyethylene properties and using these correlations, desired concentrations of chemical components are calculated and used via corresponding control loops. By using the infrequently available polyethylene property measurements, the correlation...
Energetic and exergetic performance enhancement of heat exchangers via simultaneous use of nanofluid and magnetic swirling flow: A two-phase approach
, Article Thermal Science and Engineering Progress ; Volume 20 , 2020 ; Rostamzadeh, H ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
A high-efficient method has been considered for simultaneously improving the hydrothermal and exergetic performance of heat exchangers. Two-phase Eulerian model is employed in a 3-D numerical study to precisely study the hydrothermal and entropic behaviors of Fe3O4/water ferrofluid, under the effect of a magnetic field inducer. The findings reveal that employing the magnetic field can improve the energetic and exergetic performance by generating a swirling flow in the heat exchanger. The pressure drop and entropy generation minimization are also achieved by the induced flow in comparison with other passive techniques due to the lack of any additional obstacle in the flow path. Results show...
Control of a fluidized bed polyethylene reactor
, Article Iranian Journal of Chemistry and Chemical Engineering ; Volume 27, Issue 3 , September and October , 2008 , Pages 87-101 ; 10219986 (ISSN) ; Shahrokhi, M ; Mirzaei, A ; Sharif University of Technology
2008
Abstract
In present paper, dynamic behavior and control of a fluidized bed reactor for polyethylene production has been considered. A double active sites model for Ziegler-Natta catalysts is used for simulation of polymerization reaction. Hydrodynamic behavior of the bed is modeled using a two phase model including bubble and emulsion phases in which bubble phase has plug flow pattern with differentially variable velocity and size through the bed and emulsion phase has the CSTR flow pattern. The reactor model is validated using industrial data. Conventional PID controllers with anti-windup are considered for control purposes. It has been shown that the control system has satisfactory performances...
Characterization of Mechanical Properties of Polymer Nanocomposites with Spherical Inhomogeneities
, M.Sc. Thesis Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Bagheri, Reza (Supervisor)
Abstract
The improved properties of nanocomposites are not achievable with conventional composites. Scale effect is one the most important parameters in the physical and mechanical properties of polymeric nanocomposites. One of the physical phenomena, which can be related to the scale effect, is the very large interface between the nanoparticles and the polymeric matrices. Motional behavior and conformation of polymeric chains change near the nanoparticles surfaces. Due to high interface of the nanoparticles with the polymeric matrices the amount of these types of changes in the polymeric chains are so large that can change the physical and mechanical properties of polymeric nanocomposites. In this...
Considering the Environmental Effect on the Performance of Vertical Axis
Wind Turbines (VAWT)
,
M.Sc. Thesis
Sharif University of Technology
;
Sattari, Sorna
(Supervisor)
;
Boroushaki, Mehrdad
(Supervisor)
Abstract
This project aims to investigate environmental effect –such as dust and rain- on the performance of a vertical axis wind turbine (VAWT). However, those issues are frequently investigated in the horizontal axis wind turbines, but this subject has not been studied in vertical axis wind turbines. Impact of rain or dust particles on the turbine blades can change the turbine performance. So consideration of the impact of environmental factors on the performance of wind turbines is very important. Vertical axis wind turbines, particularly the straight bladed VAWT are widely used in wind power generation in agricultural and rural lighting and the use of this type of turbines is increasing...
Modeling of dislocation density and strength on rheoforged A356 alloy during multi-directional forging
, Article Computational Materials Science ; Vol. 81 , 2014 , pp. 284-289 ; Saei, M ; Kazeminezhad, M ; Dodangeh, A ; Sharif University of Technology
Abstract
In this study, a hybrid model is presented to predict the dislocation density and strength evolution of the rheoforged non-dendritic A356 alloy during multi-directional forging. Regarding the characteristics of non-dendritic A356 alloy, combination of Shear Lag and Nes models is used for the eutectic structure, and Nes model is used for the α-Al globular phase. The aspect ratio variations of Si particles in eutectic structure during 3 passes of multi-directional forging do not change the model predictions, significantly. Model predictions on shear stress are in good agreement with experimental results of shear punch test
Mechanical properties and structure of solvent processed novolac resin/layered silicate: Development of interphase region
, Article RSC Advances ; Volume 5, Issue 98 , Jun , 2015 , Pages 80875-80883 ; 20462069 (ISSN) ; Shojaei, A ; Sharif University of Technology
Royal Society of Chemistry
2015
Abstract
Composites of phenol-formaldehyde (PF) resin with Closite Na+ and Closite 30B up to 20 wt% loadings were prepared by solution mixing. Tensile testing showed that both pristine and organically modified clays increased considerably the mechanical properties of PF resin at 2.5 wt% loading followed by marginal improvement or even sacrificed properties at high loadings. DMA and DSC analyses suggested development of a highly crosslinked and well adhered interphase around silicate layers. A novel three-phase model considering the interphase region was proposed to predict composite modulus. The model was successfully employed to correlate morphological characteristics and mechanical properties of...
Heat transfer and pressure drop characteristics of nanofluid in unsteady squeezing flow between rotating porous disks considering the effects of thermophoresis and Brownian motion
, Article Advanced Powder Technology ; Volume 27, Issue 2 , Volume 27, Issue 2 , 2016 , Pages 564-574 ; 09218831 (ISSN) ; Tamim, H ; Sharif University of Technology
Elsevier B.V
2016
Abstract
In this study, the unsteady three dimensional nanofluid flow, heat and mass transfer in a rotating system in the presence of an externally applied uniform vertical magnetic field is investigated. This study has different applications in rotating magneto-hydrodynamic (MHD) energy generators for new space systems and also thermal conversion mechanisms for nuclear propulsion space vehicles. The important effects of Brownian motion and thermophoresis have been included in the model of nanofluid. The governing equations are non-dimensionalized using geometrical and physical flow field-dependent parameters. The velocity profiles in radial, tangential and axial directions, pressure gradient,...
Numerical Study of Spray Formation in Slinger Injection
, M.Sc. Thesis Sharif University of Technology ; Farshchi, Mohammad (Supervisor)
Abstract
In this M.S. dissertation numerical study of slinger fuel distributer has been studied. This type of atomizer has been used in mini turbojets like Teledyne CAE.
The main purpose of this work was obtaining spray structure of slinger atomizers. This goal was achieved by implementing a UDF code in FLUENT® software to model the primary atomization that include variation of fluid from exit of slinger disk bores till formation of primary droplet. In FLUENT® the DPM method and its ability to utilizing Lagrangian approaches have been used. The result of this model is validated by the data from experimental test that can be found in Articles. This is the first time that spray structure of slinger...
The main purpose of this work was obtaining spray structure of slinger atomizers. This goal was achieved by implementing a UDF code in FLUENT® software to model the primary atomization that include variation of fluid from exit of slinger disk bores till formation of primary droplet. In FLUENT® the DPM method and its ability to utilizing Lagrangian approaches have been used. The result of this model is validated by the data from experimental test that can be found in Articles. This is the first time that spray structure of slinger...
Investigation of the interphase effects on the mechanical behavior of carbon nanotube polymer composites by multiscale modeling
, Article Journal of Applied Polymer Science ; Volume 117, Issue 1 , March , 2010 , Pages 361-367 ; 00218995 (ISSN) ; Naghdabadi, R ; Sharif University of Technology
2010
Abstract
In this article, a multiscale modeling procedure is implemented to study the effect of interphase on the Young's modulus of CNT/polymer composites. For this purpose, a three-phase RVE is introduced which consists of three components, i.e., a carbon nanotube, an interphase layer, and an outer polymer matrix. The nanotube is modeled at the atomistic scale using molecular structural mechanics. Moreover, three-dimensional elements are employed to model the interphase layer and polymer matrix. The nanotube and polymer matrix are assumed to be bonded by van der Waals interactions based on the Lennard-Jones potential at the interface. Using this Molecular Structural Mechanics/Finite Element...
CFD Modeling of Ammonia Release and Water Curtain for Mitigation
,
M.Sc. Thesis
Sharif University of Technology
;
Rashtchian, Davoud
(Supervisor)
Abstract
The release of toxic materials causes tragic accidents every year. There are various techniques in order to mitigate the release effect of these materials such as Application of air jets, steam curtains and water curtains. This study presents numerical calculations to reproduce the continuous ammonia release dispersion with and without the mitigating influence of a downwind water curtain using computational fluid dynamic (CFD) software ANSYS Fluent 15.0. The RNG model coupled with Lagrangian discrete phase model (DPM) was used to simulate the dilution effectiveness of the water curtain system. The ammonia absorption was taken into account by means of user-defined functions (UDF). The...
Three Dimensional Numerical Simulation of Slinger Combustor
, M.Sc. Thesis Sharif University of Technology ; Farshchi, Mohammad (Supervisor)
Abstract
Annular combustion chambers used in small turbine motors which incorporate centrifugal (rotary) injectors for injecting fuel, are known as Slinger combustion chambers. The Slinger injector works in such a way that fuel enters from an inner tube in motor shaft and exits with high pressure from the holes on the cylinder connected to the shaft. Because of the high centrifugal force, the fuel is sprayed with high quality after entering the combustion chamber. Type and angle of spray, fuel-air mixing type, combustion phenomena and flame stability makes this different than other annular combustion chambers. The process of combustion in the Slinger chamber of YJ402 motor is numerically simulated in...
Heat transfer and pressure drop characteristics of nanofluid in unsteady squeezing flow between rotating porous disks considering the effects of thermophoresis and Brownian motion
, Article Advanced Powder Technology ; Volume 27, Issue 2 , March , 2016 , Pages 564–574 ; 09218831 (ISSN) ; Tamim, H ; Sharif University of Technology
Elsevier
2016
Abstract
In this study, the unsteady three dimensional nanofluid flow, heat and mass transfer in a rotating system in the presence of an externally applied uniform vertical magnetic field is investigated. This study has different applications in rotating magneto-hydrodynamic (MHD) energy generators for new space systems and also thermal conversion mechanisms for nuclear propulsion space vehicles. The important effects of Brownian motion and thermophoresis have been included in the model of nanofluid. The governing equations are non-dimensionalized using geometrical and physical flow field-dependent parameters. The velocity profiles in radial, tangential and axial directions, pressure gradient,...
Numerical study of forced convective heat transfer of nanofluids: comparison of different approaches
, Article International Communications in Heat and Mass Transfer ; Volume 37, Issue 1 , 2010 , Pages 74-78 ; 07351933 (ISSN) ; Saboohi, Y ; Rashidi, A. M ; Sharif University of Technology
Abstract
Forced convective of a nanofluid that consists of water and Al2O3 in horizontal tubes has been studied numerically. Computed results were validated with existing well established correlation. Two-phase Eulerian model has been implemented for the first time to study such a flow field. A single-phase model and two-phase mixture model formulations were also used for comparison. The comparison of calculated results with experimental values shows that the mixture model is more precise. It is illustrated that the single-phase model and the two-phase Eulerian model underestimates the Nusselt number. Effects of nanoparticles concentration on the thermal parameters are also discussed
Modeling and simulation of barite deposition in an annulus space of a well using CFD
, Article Journal of Petroleum Science and Engineering ; Volume 161 , 2018 , Pages 476-496 ; 09204105 (ISSN) ; Shad, S ; Beagom Mokhtari Hosseini, Z ; Sharif University of Technology
Elsevier B.V
2018
Abstract
In drilling industry, barite particles settling and barite sag as a major problem can potentially impose significant operational issues. Static conditions, in which well undergoes an extended shut-in period, could occur during different drilling and completion operations such fishing operation, tripping, and logging. Despite its importance, such phenomenon is not well understood yet. To avoid issues related to barite settlement and barite sag, a good understanding of the impact of different drilling parameters on barite settlement and sag phenomenon is required. Recently, the mathematical formulation and modeling of settlement and sag processes have gained more attention. In order to better...
A simple three-phase model for distributed static series compensator (DSSC) in Newton power flow
, Article 2009 Asia-Pacific Power and Energy Engineering Conference, APPEEC 2009, Wuhan, 27 March 2009 through 31 March 2009 ; 2009 ; 21574839 (ISSN); 9781424424870 (ISBN) ; Mokhtari, H ; Wuhan University; IEEE Power and Energy Society; Chinese Society for Electrical Engineering; Scientific Research Publishing ; Sharif University of Technology
2009
Abstract
Load flow problems have always been an important issue in power system analysis and require proper modeling of system components. In this regard Flexible AC Transmission System (FACTS) controllers are modern devices that their modeling specially the series type is a challenging topic. This paper describes a three-phase model for Distributed Static Series Compensator (DSSC) based on extending the Static Synchronous Series Compensator (SSSC) model in Newton power flow. To extend the SSSC model the following two differences must be considered; three completely independent phases and the existence of several modules in a DSSC system. Simulation results on the IEEE 30-bus system and a five bus...
The effect of hematocrit and nanoparticles diameter on hemodynamic parameters and drug delivery in abdominal aortic aneurysm with consideration of blood pulsatile flow
, Article Computer Methods and Programs in Biomedicine ; Volume 195 , October , 2020 ; Nasiri Sadr, A ; Kaffash, E ; Goudarzi, S ; Golab, E ; Karimipour, A ; Sharif University of Technology
Elsevier Ireland Ltd
2020
Abstract
Background and Objective: The present article has simulated to investigate the efficient hemodynamic parameters, the drug persistence, and drug distribution on an abdominal aortic aneurysm. Methods: Blood as a non-Newtonian fluid enters the artery acting as a real pulse waveform; its behavior is dependent on hematocrit and strain rate. In this simulation of computational fluid dynamic, magnetic nanoparticles of iron oxide which were in advance coated with the drug, are injected into the artery during a cardiac cycle. A two-phase model was applied to investigate the distribution of these carriers. Results: The results are presented for different hematocrits and the nanoparticle diameter. It...