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fluid-dynamics
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Toward design and fabrication of wind-driven vehicles: Procedure to optimize the threshold of driving forces
, Article Applied Mathematical Modelling ; Volume 37, Issue 1-2 , 2013 , Pages 50-61 ; 0307904X (ISSN) ; Rad, M ; Sharif University of Technology
2013
Abstract
Wind energy has been continuously considered as a green, available, and economical alternative source of energy. For centuries, the transformed wind energy to drag-force has been used for transportation in watercrafts. With improvement of aerodynamics, the airfoil was invented to create and use a higher magnitude aerodynamic force, lift-force, in order to elevate airplanes. Later, the lift-force was horizontally applied as the thrust force in land/water wind-crafts. Whereas in airplanes horizontal airfoils (wing) create a vertical lift-force, installed vertical airfoils (wing-sail) produce a horizontal lift-force in wind-crafts. Therefore, this force can be used as thrust (driving) force in...
Drop profile analysis tensiometry under highly dynamic conditions
, Article Colloids and Surfaces A: Physicochemical and Engineering Aspects ; Volume 413 , 2012 , Pages 292-297 ; 09277757 (ISSN) ; Bastani, D ; Javadi, A ; Kovalchuk, V. I ; Kovalchuk, N. M ; Makievski, A. V ; Bonaccurso, E ; Miller, R ; Sharif University of Technology
2012
Abstract
Profile analysis tensiometry (PAT) is presently the most frequently used technique for measuring surface tensions of liquids. The basis of this methodology is however an equilibrium force balance as given by the Gauss-Laplace equation. Therefore, its application under dynamic conditions, i.e. for growing drops or bubbles, is questionable. We discuss the limits of the applicability of PAT under dynamic conditions by using a growing drop configuration equipped with a high speed video camera. The systems studied are the water/air and water/hexane interface. The obtained "dynamic" drop profiles are analyzed by fitting the classical Gauss-Laplace equation. The results are additionally compared...
Mold filling simulation in the injection molding process with openFOAM software for non-isothermal newtonian fluid
, Article Proceedings of the 2nd IASTED Asian Conference on Modelling, Identification, and Control, AsiaMIC 2012 ; 2012 , Pages 291-296 ; 9780889869110 (ISBN) ; Vafaeipour, M ; Etemadi, H ; Dabbaghian, A ; Bardestani, R ; Dehghan, M ; Sharif University of Technology
2012
Abstract
Injection molding is one of the most important manufacturing processes for mass production of complex plastic parts. In this study, mold filling is simulated by using the OpenFOAM software for Non- isothermal Newtonian fluid. The OpenFOAM is an open source software that is used in Computational Fluid Dynamics (CFD) tools. The studied mold shape has a rectangular structure with a gate for Newtonian fluid injection. The simulation carried out at non-isothermal conditions and two-dimensional flow is considered. The velocity, shear stress and temperature changes in different parts of the mold are critically studied. We show that vortex formation plays an important role on changes of shear stress...
Improvement and experimental validation of a multi-zone model for combustion and NO emissions in CNG fueled spark ignition engine
, Article Journal of Mechanical Science and Technology ; Volume 26, Issue 4 , 2012 , Pages 1205-1212 ; 1738494X (ISSN) ; Hannani, S. K ; Ebrahimi, R ; Sharif University of Technology
2012
Abstract
This article reports the experimental and theoretical results for a spark ignition engine working with compressed natural gas as a fuel. The theoretical part of this work uses a zero-dimensional, multi-zone combustion model in order to predict nitric oxide (NO) emission in a spark ignition (SI) engine. The basic concept of the model is the division of the burned gas into several distinct zones for taking into account the temperature stratification of the burned mixture during combustion. This is especially important for accurate NO emissions predictions, since NO formation is strongly temperature dependent. During combustion, 12 products are obtained by chemical equilibrium via Gibbs energy...
Mathematical modeling of a slurry reactor for DME direct synthesis from syngas
, Article Journal of Natural Gas Chemistry ; Volume 21, Issue 2 , March , 2012 , Pages 148-157 ; 10039953 (ISSN) ; Kazemeini, M ; Fattahi, M ; Sharif University of Technology
2012
Abstract
In this paper, an axial dispersion mathematical model is developed to simulate a three-phase slurry bubble column reactor for direct synthesis of dimethyl ether (DME) from syngas. This large-scale reactor is modeled using mass and energy balances, catalyst sedimentation and single-bubble as well as two-bubbles class flow hydrodynamics. A comparison between the two hydrodynamic models through pilot plant experimental data from the literature shows that heterogeneous two-bubbles flow model is in better agreement with the experimental data than homogeneous single-bubble gas flow model. Also, by investigating the heterogeneous gas flow and axial dispersion model for small bubbles as well as the...
Two phase modal analysis of nonlinear sloshing in a rectangular container
, Article Ocean Engineering ; Volume 38, Issue 11-12 , August , 2011 , Pages 1277-1282 ; 00298018 (ISSN) ; Firouz Abadi, R. D ; Ghasemi, M ; Sharif University of Technology
2011
Abstract
Sloshing, or liquid free surface oscillation, in containers has many important applications in a variety of engineering fields. The modal method can be used to solve linear sloshing problems and is the most efficient reduced order method that has been used during the previous decade. In the present article, the modal method is used to solve a nonlinear sloshing problem. The method is based on a potential flow solution that implements a two-phase analysis on sloshing in a rectangular container. According to this method, the solution to the mass conservation equation, with a nonpenetration condition at the tank walls, results in velocity potential expansion; this is similar to the mode shapes...
The effect of source motion on contaminant distribution in the cleanrooms
, Article Energy and Buildings ; Volume 43, Issue 4 , April , 2011 , Pages 966-970 ; 03787788 (ISSN) ; Sajadi, B ; Molaeimanesh, G. R ; Sharif University of Technology
2011
Abstract
In the recent decades, cleanrooms have found growing applications in broad range of industries such as pharmacy and microelectronics. Concerns about negative effects of the contaminant exposure on the human health and product quality motivate many researchers towards understanding of the airflow and contaminant distribution though these environments. With an improvement in computational capacity of the computers, computational fluid dynamics (CFD) technique has become a powerful tool to study the engineering problems including indoor air quality (IAQ). In this research, indoor airflow in a full-scale cleanroom is investigated numerically using Eulerian-Eulerian approach. To evaluate the...
Hydrodynamic characteristics of gas-solid tapered fluidized beds: Experimental studies and empirical models
, Article Powder Technology ; Volume 283 , October , 2015 , Pages 355-367 ; 00325910 (ISSN) ; Farhadi, F ; Bahramian, A ; Sharif University of Technology
Elsevier
2015
Abstract
Understanding the hydrodynamic behavior of tapered fluidized beds is essential for accurate design and better operation in these fluid-solid contactors. Minimum fluidization velocity, minimum velocity of full fluidization, maximum pressure drop and bed expansion ratio are more important hydrodynamic characteristics in tapered fluidized beds. In this study, based on experimental data, dimensional analysis has been used to develop dimensionless correlations for predicting hydrodynamic characteristics of Geldart B particles in tapered fluidized bed. The effects of bed geometry, static bed height, particle density, size, and sphericity and also interparticle forces on hydrodynamic behavior of...
Two phase gas-liquid bubbly flow modeling in vertical mini pipe
, Article 2010 14th International Heat Transfer Conference, IHTC 14, 8 August 2010 through 13 August 2010 ; Volume 3 , 2010 , Pages 947-956 ; 9780791849385 (ISBN) ; Karabi, H ; Khorsandi, S ; Saidi, M. H ; Heat Transfer Division ; Sharif University of Technology
Abstract
Studies on two-phase flow in small scale pipes have become more important, because of the application of mini-scale devices in several engineering fields including, high heat-flux compact heat exchangers, and cooling systems of various types of equipment. In a mini pipe the behavior of two phase flow is not the same as flow in conventional pipes. The difference is caused by different effective forces; for e. g. inside a mini pipe capillary forces are more important in comparison with gravitational forces. This paper is devoted to numerical simulation of gas-liquid two phase flow in a vertical mini pipe. Prediction of bubble shape and the effects of gas and liquid velocities on flow...
Two-dimensional numerical investigation of a micro combustor
, Article Scientia Iranica ; Volume 17, Issue 6 B , December , 2010 , Pages 433-442 ; 10263098 (ISSN) ; Saidi, M. S ; Saidi, M. H ; Shafii, M. B ; Sharif University of Technology
2010
Abstract
In this paper, a two-dimensional numerical approach is used to study the effect of micro combustor height, mass flow rate and external convection heat transfer coefficient on the temperature and species mass fraction profiles. A premixed mixture of H2-Air with a multi-step chemistry is used. The transient gas phase energy and species conservation equations result in an Advection-Diffusion-Reaction system that leads to two stiff systems of PDEs. In the present work, the computational domain is solved through the Strang splitting method, which is suitable for a nonlinear stiff system of PDEs. A revised boundary condition for the velocity equation is applied and its effect on the flow...
A fluid-structure interaction model for stability analysis of shells conveying fluid
, Article Journal of Fluids and Structures ; Volume 26, Issue 5 , July , 2010 , Pages 747-763 ; 08899746 (ISSN) ; Noorian, M. A ; Haddadpour, H ; Sharif University of Technology
2010
Abstract
In this paper, a fluid-structure interaction model for stability analysis of shells conveying fluid is developed. This model is developed for shells of arbitrary geometry and structure and is based on incompressible potential flow. The boundary element method is applied to model the potential flow. The fluid dynamics model is derived by using an inflow/outflow model along with the impermeability condition at the fluid-shell interface. This model is applied to obtain the flow modes and eigenvalues, which are used for the modal representation of the flow field in the shell. Based on the mode shapes and natural frequencies of the shell obtained from an FEM model, the modal analysis technique is...
Analysis of laminar flow in the entrance region of parallel plate microchannels for slip flow
, Article Proceedings of the 7th International Conference on Nanochannels, Microchannels, and Minichannels 2009, ICNMM2009, 22 June 2009 through 24 June 2009, Pohang ; Issue PART A , 2009 , Pages 345-352 ; 9780791843499 (ISBN) ; Asgarshamsi, A ; Saidi, M. H ; Sharif University of Technology
Abstract
Microscale fluid dynamics has received intensive interest due to the emergence of microelectromechanical systems (MEMS) technology. Fluid flow in microdevices has some characteristics which one of them is rarefaction effect related with gas flow. In this work, the steady state laminar rarefied gas flow in the entrance region of parallel plate microchannels is investigated by the integral method with slip flow conditions at solid surface. The effects of Knudsen number on friction factor and Nusselt number are presented in graphical form as well as analytical form. Also the effect of Knudsen number on hydrodynamic entry length is presented. The results show that as Knudsen number increases the...
CFD-DEM simulation of the hole cleaning process in a deviated well drilling: the effects of particle shape
, Article Particuology ; Volume 25 , 2016 , Pages 72-82 ; 16742001 (ISSN) ; Behzad, M ; Rajabi, M ; Sharif University of Technology
Abstract
We investigate the effect of particle shape on the transportation mechanism in well-drilling using a three-dimensional model that couples computational fluid dynamics (CFD) with the discrete element method (DEM). This numerical method allows us to incorporate the fluid-particle interactions (drag force, contact force, Saffman lift force, Magnus lift force, buoyancy force) using momentum exchange and the non-Newtonian behavior of the fluid. The interactions of particle-particle, particle-wall, and particle-drill pipe are taken into account with the Hertz-Mindlin model. We compare the transport of spheres with non-spherical particles (non-smooth sphere, disc, and cubic) constructed via the...
Application of the splitting approach to solve population balance equations in chemical processes
, Article Chemical Engineering and Technology ; Volume 32, Issue 12 , 2009 , Pages 1894-1900 ; 09307516 (ISSN) ; Baghaei, A ; Sarrafi, A ; Sharif University of Technology
Abstract
Different processes in chemical industries deal with particles and multiphase flow. In such processes, particle or bubble size distribution (PSD) influences the final product quality and also process design. On the other hand, solutions to the dominant hydrodynamic and thermo-kinetic equations ignoring these distributions will make it impossible to accurately simulate these processes. Solutions to population balance equations (PBE's) are needed to attain the PSD. One of the most common methods for the solution of a PBE is the classes method (CM). However, as this method requires a large number of classes to give a reasonable result, it needs a huge amount of calculations and time. To...
Simulation of the effects of oxygen carriers and scaffold geometry on oxygen distribution and cell growth in a channeled scaffold for engineering myocardium
, Article Mathematical Biosciences ; Volume 294 , 2017 , Pages 160-171 ; 00255564 (ISSN) ; Mashayekhan, S ; Bastani, D ; Sharif University of Technology
Abstract
This study proposes a mathematical model to evaluate the impact of oxygen carriers and scaffold geometry on oxygen distribution and cell growth in a 3D cardiac construct using computational fluid dynamics (CFD). Flow equations, oxygen balance equation and cell balance equation were solved using special initial and boundary conditions. The modeling results revealed that 55% increase in cardiac cell density occurred by using 6.4% perfluorocarbon oxygen carrier (PFC) compared to pure culture medium without PFC supplementation. Moreover, the effects of the scaffold geometry on cell density were examined by changing the channel numbers and the construct length. A 30% increase in the average cells...
Pulsatile blood flow in total cavopulmonary connection: a comparison between Y-shaped and T-shaped geometry
, Article Medical and Biological Engineering and Computing ; Volume 55, Issue 2 , 2017 , Pages 213-224 ; 01400118 (ISSN) ; Firoozabadi, B ; Saidi, M. S ; Monjezi, M ; Navabi Shirazi, M. A ; Malakan Rad, E ; Sharif University of Technology
Springer Verlag
2017
Abstract
Single-ventricle anomaly is a hereditary heart disease that is characterized by anatomical malformations. The main consequence of this malformation is desaturated blood flow, which without proper treatment increases the risk of death. The classical treatment is based on a three-stage palliative procedure which should begin from the first few days of patient’s life. The final stage is known as Fontan procedure, in which inferior vena cava is directly connected to pulmonary arteries without going through the ventricle. This connection is called total cavopulmonary connection (TCPC). After surgery, the single ventricle supplies adequate and saturated systemic blood flow to the body; however,...
Numerical study of hydrogen-air combustion characteristics in a novel micro-thermophotovoltaic power generator
, Article Applied Energy ; Volume 199 , 2017 , Pages 382-399 ; 03062619 (ISSN) ; Saidi, M. H ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
In the present work, a micro combustor for thermophotovoltaic (TPV) devices is proposed which is included a U-shaped microtube in a box with a secondary fluid in space between U-shaped microtube and box walls. By utilizing the three-dimensional CFD model, combustion characteristics of the premixed lean hydrogen-air mixture in the present micro combustor are studied numerically with detailed chemistry and transport taking into account heat transfer through the wall. The results show that the establishment of secondary flows and better preheating in the curved tubes is caused the flammability limits to be at least four times in comparison with straight tubes. Combustion characteristics are...
Parallelized numerical modeling of the interaction of a solid object with immiscible incompressible two-phase fluid flow
, Article Engineering Computations (Swansea, Wales) ; Volume 34, Issue 3 , 2017 , Pages 709-724 ; 02644401 (ISSN) ; Nikbakhti, R ; Ghasemi, A ; Hedayati, F ; Malvandi, A ; Sharif University of Technology
Abstract
Purpose - A numerical method is developed to capture the interaction of solid object with two-phase flow with high density ratios. The current computational tool would be the first step of accurate modeling of wave energy converters in which the immense energy of the ocean can be extracted at low cost. Design/methodology/approach - The full two-dimensional Navier-Stokes equations are discretized on a regular structured grid, and the two-step projection method along with multi-processing (OpenMP) is used to efficiently solve the flow equations. The level set and the immersed boundary methods are used to capture the free surface of a fluid and a solid object, respectively. The full...
Simulation of a density current turbulent flow employing different RANS models: a comparison study
, Article Scientia Iranica ; Volume 16, Issue 1 , 2009 , Pages 53-63 ; 10263098 (ISSN) ; Firoozabadi, B ; Sharif University of Technology
2009
Abstract
The accuracy of Reynolds Averaged Navier-Stokes (RANS) turbulence models to predict the behavior of 2-D density currents has been examined. In this work, a steady density current is simulated by the k - ε, k - ε RNG, two-layer k - ε and modified v̄2 - f model, all of which are compared with the experimental data. Density currents, with a uniform velocity and concentration, enter a channel via a sluice gate into a lighter ambient fluid and move forward down-slope. The eddy-viscosity concept cannot accurately simulate this flow because of two stress production structures found within it. Results show that all isotropic models have a weak outcome on this current, but by improving the ability of...
Transient forced convection with viscous dissipation to power-law fluids in thermal entrance region of circular ducts with constant wall heat flux
, Article Energy Conversion and Management ; Volume 50, Issue 4 , 2009 , Pages 1062-1068 ; 01968904 (ISSN) ; Mohammadi, A. A ; Sharif University of Technology
2009
Abstract
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 energy equation was solved by using a finite difference method, whereas the steady state thermal energy equation without wall heat flux was solved analytically as the initial condition of the former. The effects of the power-law index and wall heat flux on the local Nusselt number and thermal entrance length were investigated. Moreover, the local...