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    Simulation of Rapid Formation of Multicellular Spheroids in Double-emulsion Droplets with Controllable Microenvironment

    , M.Sc. Thesis Sharif University of Technology Talakoob Shirazi, Shahriar (Author) ; Moosavi, Ali (Supervisor) ; Sadrhosseini, Hani (Supervisor)
    Abstract
    This study is aimed at simulation of double emulsion formation in a microfluidic double flow focusing device which consists of two cross-junctions connected serially. The water in oil (w/o) emulsions are produced in the first junction. In the second junction, water in oil emulsions are encapsulated by an outer aqueous phase to generate water in oil in water (w/o/w) double emulsions. Water in oil emulsions are formed in hydrophobic channels and water in oil in water double emulsions are formed in hydrophilic channels. A three phase numerical model, based on the VOF-CSF method, is developed for simulating the process of double emulsion formation. An adaptive mesh refinement technique is... 

    Numerical Simulation of Electrospray with Presence of Cone-Jet

    , M.Sc. Thesis Sharif University of Technology Ghate Ghushchi, Mehran (Author) ; Morad, Mohammad Reza (Supervisor)
    Abstract
    In this work, the cone-jet mode of electrospray is simulated by a two phase solver in OpenFoam software. For this aim firstly, breakup of a liquid jet is examined without applying any electric potential to the injecting capillary and results are compared with other works to evaluate the two phase solver. Next with applying electric potential, the whole evolution of cone-jet in time is simulated. One of the most important issues in this mode is the minimum potential that needs to form a stable cone-jet in different flow rates. These minimum voltages are obtained in various flow rates and compared with other experimental and computational works. Result shows that with increasing flow rate the... 

    Numerical Simulation of Magneto Mercury Reciprocating Micropump

    , M.Sc. Thesis Sharif University of Technology Mehrabi, Ali (Author) ; Shafii, Mohammad Behshad (Supervisor)
    Abstract
    In this investigation Magneto Mercury Reciprocating Micrpump (MMRM) the combination of Magneto-Hydrodynamic and Reciprocating micropumps has been analyzed. To achieve the analytical and numerical solution of one-tank and three-tank MMRM, the momentum, continuity, volume fraction and magnetohydrodynamic equations have been presented. The dimensionless analytical solution of one-phase and two-phase three dimensional MHD flow in the condition of using constant current and potential electrical source, has been offered.
    The boundary between mercury and air has been tracked via VOF method in OpenFOAM software. VOF equation has been solved by explicit method with variable time step and maximum... 

    The investigation of natural super-cavitation flow behind three-dimensional cavitators: Full cavitation model

    , Article Applied Mathematical Modelling ; Volume 45 , 2016 , Pages 165-178 ; 0307904X (ISSN) Kadivar, E ; Kadivar, Erfan ; Javadi, K ; Javadpour, S. M ; Sharif University of Technology
    Elsevier Inc 
    Abstract
    In this study, natural super-cavitating flow around three different conical cavitators with wedge angles of 30°, 45° and 60° is investigated. We apply the k−ϵ turbulence model and the volume of fluid (VOF) technique to numerically study the three-dimensional cavitating flow around the cavitators. The turbulence approach is coupled with a mass transfer model which is implemented into the finite-volume package. Simulations are performed for different cavitation numbers. Finally, the effects of some important parameters such as the cavitation index, inlet velocity, Froude number and wedge angle of cavitators on the geometrical characteristics of the super-cavities are discussed. Our numerical... 

    Experimental and Numerical Study on Particle-Laden Flows

    , Ph.D. Dissertation Sharif University of Technology Afshin, Hossein (Author) ; Firoozabadi, Bahar (Supervisor) ; Rad, Manouchehr (Supervisor)
    Abstract
    Dense underflows are continuous currents that move down-slope due to their density being heavier than that of the ambient water. This difference between the dense fluid and environment fluid can be due to temperature difference, chemical materials, solved materials or suspend solid particles. In these currents, the effect of buoyancy force is produced by this difference density. In this research, many experiments performed in different flow rates, slopes and concentrations to understand the current structure and turbulence specification of the salt solution density currents and particle-laden density currents. Acoustic Doppler Velocimeter is used to measure the velocity fluctuations. The... 

    Implementing the Appropriate Numerical Method for Modeling the Two-Phase Flow in Upriser Pipe of Airlift Pump

    , M.Sc. Thesis Sharif University of Technology Moezzi Najafabadi, Mahsa (Author) ; Saeedi, Mohammad Hassan (Supervisor) ; Kazemzadeh Hannani, Siamak (Supervisor)
    Abstract
    Airlift pumps are devices for lifting liquid phase incorporating the gas phase to be injected in the bottom of the liquid column. Gas-liquid two-phase flow being the main part of the flow through these systems, flowing in vertical pipes of airlift pumps has different regimes namely bubbly, slug, churn and annular. Generally these regimes appear starting from bubbly to annular from bottom to top of the upriser pipe. Gas/liquid multiphase flows occur in a wide range of natural and man-made situations such as boiling heat transfer, cloud cavitation, bubble columns and reactors in the chemical industry, cooling circuits of power plants, spraying of liquid fuel and paint, emulsions, rain, bubbles... 

    Numerical Modeling of Drop Formation and Deformation using the Finite Volume Method

    , M.Sc. Thesis Sharif University of Technology Sadat Salehi, Moloud (Author) ; Firoozabadi, Bahar (Supervisor) ; Afshin, Hossein (Co-Advisor)
    Abstract
    Drop formation from the tip of a nozzle and its motion in bulk fluid is an interesting and practical process which has widely turned researchers’ attention. Investigation into the governing physics and effective parameters on formation, deformation and motion of a drop increases the efficiency of the related industrial processes. Thus in the present study, in order to simulate this process, full Navier-Stokes equations solved by the Volume of Fluid (VOF) method in an axisymmetric domain using Fluent software as the solver. In this research, the effects of Weber number (the proportion of inertial force to surface tension force) and Ohnesorge number (which refers to the proportion of viscous... 

    Numerical Simulation of Forced Impregnation in a Thick Capillary Tube

    , M.Sc. Thesis Sharif University of Technology Safavi, Mohammad (Author) ; Mousavi, Ali (Supervisor)
    Abstract
    Drop penetration into the capillary tube, as a classical problem, has been studied over 100 years. But there are a few studies that investigate forced impregnation of capillary tubes, which has major application in coating, inkjet printing and rain drop penetration into the soil, have been made. A comprehensive numerical investigation on millimeter droplet impact dynamics on a thick capillary tube with micrometer sized pore is conducted and validated against experimental data. This work is extended to oblique impact of drops into pores and normal impact on nanoscaled pores. We apply the finite volume numerical method to solve the time-dependent governing equations of continuity, momentum in... 

    Simulation of Mass Transfer from Droplet in a Two Phase Liquid-liquid Extraction System

    , M.Sc. Thesis Sharif University of Technology Fahim Alavi, Morteza (Author) ; Afshin, Hossein (Supervisor) ; Firoozabadi, Bahar (Co-Advisor)
    Abstract
    Mass transfer of a drop moving in a bulk fluid is an interesting subject which has attracted a lot of attention. Understanding effective parameters in this process would be helpful in order to increase the efficiency of the industrial processes related to mass transfer. In this research, the deformation and mas transfer of a moving drop was studied numerically. Navier-Stokes equations and concentration equation were solved separately with a VOF method in an axisymmetric domain using Fluent software. Comparision between numerical results and former experimental results proves the accuracy of the modelling in both fields of deformation and mass transfer. Moreover, effects of the physical... 

    Simulation of Behavior of a Single Cavitating Bubble Near Solid Boundariesby solvingTwophase Navier-Stokes Equations with a Central Difference Finite Volume Method

    , M.Sc. Thesis Sharif University of Technology Mortezazadeh Dorostkar, Mohammad (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In the present work, the deformation and collapse of a single cavitating bubble near solid boundaries is simulated by solving the preconditioned, homogenous, multiphaseNavier-Stokes equations. Up to now, all studies in the literature performed by the volume of fluid (VOF)approach to capture the bubble surface have been based on the pressure-based category in which the flow variables are calculated through solving the Poisson equation. Here, the density-based category is applied and the solution methodology is based on the artificial compressibility approach. The compressible form of the Navier-Stokes equations is applied inside the bubble and the liquid phase is assumed to be incompressible.... 

    Numerical Simulation of Secondary Sedimentation Tanks to Increase the Efficiency

    , M.Sc. Thesis Sharif University of Technology Lak, Behzad (Author) ; Firoozabadi, Bahar (Supervisor) ; Afshin, Hossein (Supervisor)
    Abstract
    Sedimentation tanks are one of the important and costly stages of water treatment process in which remained particles from previous stages settle down due to gravity force. In this research, the hydrodynamics of secondary settling tanks without and in the presence of particles is numerically investigated using VOF method in order to simulate the interphase using RNG k-ε for turbulence modelling. The simulations are performed by means of open-source code OpenFoam, and the code is developed to model particles in the flow. The calculated velocity profiles using VOF method show a reasonable agreement with the experimental data. Comparing the concentration profiles with experiments shows the... 

    Separation of Metal Ions-based Microfluidic Platform for Liquid-liquid Extraction

    , M.Sc. Thesis Sharif University of Technology Foroozan, Peyman (Author) ; Mohammadi, Ali Asghar (Supervisor) ; Karimi Sabet, Javad (Co-Advisor)
    Abstract
    Continuous separation processes in microfluidic devices experienced a steep rise in attention during the last two decades. Among the different separation processes, liquid-liquid extraction especially benefits from the short molecular diffusion distance and large specific interfacial area, as these are advantageous for effective mass transport. In the present study, glass-based microfluidic devices have been fabricated utilizing laser ablation and wet chemical etching methods then experiments and numerical simulation were carried out to investigate hydrodynamic behavior of fluid flow in Y-junction microfluidic. In order to achieve phase separation at the end of the microchannel, a phase... 

    , M.Sc. Thesis Sharif University of Technology Nazari, Fatemeh (Author) ; Shamsaei, Abolfazl (Supervisor)
    Abstract
    Entrance of air to close water conduits occurs in many ways. This phenomenon makes displeasing effects on water transport structures. Two-phase flows in closed conduits are studied experimentally, numerically and theoretically. Even after decades, due to the complexity of the subject, these studies still require development and reformation. Numerical and theoretical two-phase models are often limited to a special regime of flow."Volume Of Fluid"(VOF) is a model for non-mixing two-phase flows. "Fluent" software uses this model in this field of flows. Volume of fluid is used successfully in some problems like dam break or rising bubbles. Main disadvantage of this model is distribution of the... 

    Hydrodynamics of fingering instability in the presence of a magnetic field

    , Article Fluid Dynamics Research ; Volume 48, Issue 5 , 2016 ; 01695983 (ISSN) Mostaghimi, P ; Ashouri, M ; Ebrahimi, B ; Sharif University of Technology
    Institute of Physics Publishing 
    Abstract
    The hydrodynamics of two immiscible fluids in a rectangular Hele-Shaw cell under the influence of a magnetic field is studied, both theoretically and numerically. A linear stability analysis is conducted to determine the effect of magnetic fields on the formation of viscous fingers. As a result, an analytical solution is found to calculate the growth rate of perturbations. For numerical simulation of the two-phase flow, the interfacial tension is treated as a body force using the continuum surface force model and the interface tracking is performed by the volume of fluid method. The variations of the width and growth rate of fingers in an unstable displacement versus Hartmann number, a... 

    Numerical investigation of droplets breakup in a microfluidic T-junction

    , Article Applied Mechanics and Materials ; Volume 110-116 , 2012 , Pages 3269-3277 ; 16609336 (ISSN) ; 9783037852620 (ISBN) Bedram, A ; Moosavi, A ; Int. Assoc. Comput. Sci. Inf. Technol. (IACSIT) ; Sharif University of Technology
    2012
    Abstract
    A Volume of Fluid (VOF) method is used to stdy the breakup of droplets in T-junction geometries. Symmetric T-junctions, which are used to produce equal size droplets and have many applications in pharmacy and chemical industries, are considered. Two important factors namely "breakup time" and "breakup length" that can improve the performance of these systems have been introduced. In addition a novel system which consists of an asymmetric T-junction is proposed to produce unequal size droplets. The effects of the channel width ratio and the capillary number on the size and length of the generated droplets and also the time of the generation have been studied and discussed. For simulation the... 

    Numerical investigation of a stepped planing hull in calm water

    , Article Ocean Engineering ; Volume 94 , January , 2015 , Pages 103-110 ; 00298018 (ISSN) Lotfi, P ; Ashrafizaadeh, M ; Esfahan, R. K ; Sharif University of Technology
    Elsevier Ltd  2015
    Abstract
    Stepped planing hulls enable the feasibility of running at relatively low Drag-Lift ratio by means of achieving more optimal trim angle at high speeds. Currently, there is no precise method to analyze these hulls over the full range of operating speeds. In this study, a three-dimensional computational fluid dynamics (CFD) model using volume of fluid (VOF) approach is presented for examining the characteristics of a planing hull having one transverse step. A procedure is presented to transform a series of fixed-position simulations into a free to heave and pitch simulation. Resistance, lift, running draft, dynamic trim angle, and wetted area are compared with available experimental data and... 

    Comparison and Improving of Free Surface Modeling Methods In Moving Grids

    , M.Sc. Thesis Sharif University of Technology Jeddi, Reza (Author) ; Seif, Mohammad Saeed (Supervisor) ; Nouri Borujerdi, Ali (Supervisor)
    Abstract
    In the present study a through comparison has been made between different free surface modeling methods. Methods for improving the current schemes are analyzed and studied. Among different proposed methods and based on the current in-house CFD solver’s limitations and capabilities, the Flux-Blending Strategy has been used for interface capturing in the framework of the Finite Volume Method (FVM). The proposed scheme has been coupled with other algorithms for improving the capabilities and functionality of the general computational fluid dynamic software, NUMELS, in order to simulate fluid flows with sharp interface.
    The improved interface capturing scheme uses the continuous switching... 

    Numerical Investigation of Motion of Droplets in Micro and Nanochannels

    , M.Sc. Thesis Sharif University of Technology Bedram, Ahmad (Author) ; Moosavi, Ali (Supervisor)
    Abstract
    In this research, droplet motion in symmetric and asymmetric junctions in micro and nano scales was investigated. Droplets motion in symmetric and asymmetric junctions have many applications in many industries such as chemical and pharmacy. In this research symmetric T-junction in micro and nano sizes was simulated numerically in 2D and 3D formes. Also asymmetric T-junction (with unequal width branches) was simulated numerically in two cases, 2D and 3D. In the asymmetric T-junction, also an analyrical theory was developed. Numerical simulation was performed by using VOF techniqe and analytical theory was developed by thin film theory. For verifying the accuracy of numerical solution, grid... 

    Three Dimensional Simulation of Morphology of Nanodroplets Near and on Structured Substrates

    , M.Sc. Thesis Sharif University of Technology Vahid, Afshin (Author) ; Moosavi, Ali (Supervisor)
    Abstract
    Mesoscopic hydrodynamic equations are solved employing a VOF based method to investigate the equilibrium shape of nanodroplets positioned over various topographic geometries of the supporting substrate for three-dimensional systems. By taking into account liquid-liquid and liquid-solid interactions a complex distribution for inter-molecular forces over the substrates (the disjoining pressure) is observed. In this research we show that motion of nanodroplets not only caused by contact angle difference in drplets two sides, but also depend on disjoining pressure parameters.Geometries with increasing complexities, from wedges to three dimensional edges and wedges, were explored with the main... 

    Numerical Simulation of Shaking Bioreactors for Cell Culture

    , M.Sc. Thesis Sharif University of Technology Ghahremannezhad, Ali (Author) ; Saidi, Mohammad Said (Supervisor)
    Abstract
    A bioreactor can refer to any device or system constructed on engineering basis and has an active biological medium. This medium includes aerobic and non-aerobic reactions in which organisms and the theire produced substances have the main role. One of the applications of bioreactors is to provide an appropriate medium for animal and plant cell culture and growth. Nowadays many biological processes in high volume scales are carried out in stirred tank bioreactors. In these bioreactors oxygen transfer is usually increased by increasing turbulence which is necessary for mixing nutrients and keeping the homogeneity of the medium. However, there are some limitations for increasing the stirring...