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    Numerical Modeling of Fuel Droplet Vaporization in Gas Phase at Supercritical Conditions

    , M.Sc. Thesis Sharif University of Technology Rajabi Matin, Zahra (Author) ; Hejranfar, Kazem (Supervisor)
    The study of evaporation of fuel droplet and determination of the rate of vaporization are important in designing combustion chambers. For achieving high performance of a combustor, the evaporation of fuel droplets takes place within a high pressure environment. At these conditions, the use of low-pressure models is not appropriate and many effects that are assumed negligible at low ambient pressures become very important. For example, the solubility of the ambient gas into the liquid phase is increased by increasing the ambient pressure. In addition, the ideal gas assumption is not valid for these conditions and one should use an appropriate equation of state (EOS) that can predict the... 

    Simulation of Droplet Formation and Detachment, Using Lattice Boltzmann Method

    , M.Sc. Thesis Sharif University of Technology Haghshenas, Majid (Author) ; Taeibi Rahni, Mohammad (Supervisor)
    The phenomena of formation and detachment of droplets are of fundamental importance in studying two-phase flows, such as spraying processes, ink jet printing, emulosin, etc. Droplets are formed under the effects of surface tension forces. After formation, forces like gravity detach the droplet from the rest of the fluid. Recent advancements in computational fluid dynamics and computers have made it feasible to have advancement in simulation of complex flows, including two-phase phenomenon. On the other hand, the lattice Boltzmann method (LBM) has been developed into an alternative and promising numerical scheme for simulating multi-component fluid flows.
    In this project, formation and... 

    Analytical and Numerical Study of Dynamics of Wettability Driven Droplets in Smooth And Corrugated Channels

    , M.Sc. Thesis Sharif University of Technology Esmaili, Ehsan (Author) ; Moosavi, Ali (Supervisor)
    We studied dynamics of droplets inside channels under surface forces created by chemicalsteps on the channel walls. A multi-component Shan-Chen lattice Boltzmann method isused for this purpose.The effects of parameters such as the channel height, viscosity anddensity ratios on the results were investigated for homogeneous and grooved substrates. Alsoan analytical solution was developed for droplets under chemical heterogeneities in channels with smooth surfaces. The solution considers a general condition, namely, asymmetry of the contact angles on the top and bottom walls, the viscosity of the gas as the second fluid and the effect of the channel height. Then using Shan-Chen lattice... 

    Topological Defects in Confined Nematics by Planar Anchoring

    , M.Sc. Thesis Sharif University of Technology Seyed Nejad, Reza (Author) ; Ejtehadi, Mohammad Reza (Supervisor) ; Mozaffari, Mohammad Reza (Supervisor)
    Confining nematic liquid crystal between two curved boundary conditions while the nematic molecules have a degenerate planar anchoring leads to complex and beautiful textures of molecular disparagement(defect) in the bulk and on the surfaces. Such the liquid crystal shells are made with double-emulsion techniques in microfluidic devices have provided applications for micro-scale colloidal linkers.In this work, we have numerically minimized the elastic energy in one-constant approximation in present of Fournier’s degenerate surface potential with finite element method. The nematic shell is confined between two spherical surfaces that we have studied the final energies and their related... 

    Numerical Simulation of Forced Impregnation in a Thick Capillary Tube

    , M.Sc. Thesis Sharif University of Technology Safavi, Mohammad (Author) ; Mousavi, Ali (Supervisor)
    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 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)
    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... 

    Electric-field-induced Response of Charged Droplets in Uncharged Hydrogels

    , M.Sc. Thesis Sharif University of Technology Maghsoudnia, Abolfazl (Author) ; Mohammadi, Ali Asghar (Supervisor)
    The electric field induced response of a charged droplet in an uncharged gel is calculated theoretically. For modeling, the gel is considered as a soft porous solid that is saturated with a Newtonian electrolyte and modeled as a continuum that contains 3 phases: a porous, soft and compressible solid, an incompressible Newtonian fluid and the ions inside fluid. Droplet is modeled as a charged incompressible Newtonian fluid immiscible with the gel. The droplet-gel interface is considered as a surface with electrostatic potential ζ . After obtaining governing equations, they solved by using perturbation methodology and linear superposition. Boundary conditions, especially at the droplet-gel... 

    Numerical Simulation of the Effect of Ultrasound and Bubble Dynamic for the Application of Gas Embolotherapy Technique

    , M.Sc. Thesis Sharif University of Technology Salajeghe, Roozbeh (Author) ; Saeedi, Mohammad Saeed (Supervisor)
    Gas embolotherapy is a therapeutic method which is a suitable replacement for traditional embolotherapy techniques. This method is especially applicable for vascularized tumors which cannot be treated using other tumor treatments. In Gas embolotherapy technique, droplets made of Perfluorocarbon, whose evaporation temperature is below body temperature are injected into blood stream. The size of this droplets is chosen so that they can freely circulate in human vasculature and finally reach the specified target. At the target point, an ultrasound transducer is focused which causes the droplets to evaporate and turn into bubbles. During the evaporation process, bubbles expand volumetrically to... 

    Defects Structure in Nematic Shell with Oblate Ellipsoidal Core

    , M.Sc. Thesis Sharif University of Technology Jamshidi, MohammadHossein (Author) ; Ejtehadi, MohammadReza (Supervisor) ; Mozaffari, MohammadReza (Supervisor)
    Nematic liquid crystal shells (droplets) containing cores have attracted considerable attention in recent years. Defect structures that form in such systems do not emerge in the bulk.These shells which could be created using double emulsion techniques in the laboratory have provided applications in microscale optical structures.In the past just boundary conditions and bulk parameters were noticed but recently the geometry of the core is considered likewise.In this work oblate ellipsoid cores are examined numerically using finite-element method. The boundary conditions in studied systems are perpendicular in outer surface of droplet and planar in the vicinity of the core. First by minimizing... 

    Experimental Analysis of Surface Temperature and Geometry Effects for Drop Impact on Solid Surfaces

    , Ph.D. Dissertation Sharif University of Technology Jowkar, Saeed (Author) ; Morad, Mohammad Reza (Supervisor)
    When a liquid drop impacts on a hot non-flat surface the curvature of the surface and its geometrical characteristics transmute the physical regimes and their boundary compared to a flat surface impact. The present experimental study is focused on water drop impingement on the mimetic solid semi-cylindrical convex and concave hot surfaces. The thermal versus inertia map of generated regimes is obtained, while some well-known regimes associated with a flat surface are not observed for the present non-flat impacts. The maximum spreading of the droplet is measured at different surface temperatures and impact Weber numbers for the case of droplet impingement on the convex surface. In directrix... 

    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)
    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... 

    Experimental Investigation of Mass Transfer by Droplet Using Image Processing

    , M.Sc. Thesis Sharif University of Technology Babak, Pirooz Hashemi (Author) ; Firoozabadi, Bahar (Supervisor) ; Afshin, Hossein ($item.subfieldsMap.e)
    Wide and varied aspects of droplet motion due to its increasing application in various fields has attracted much attention. Analysis of mass transfer from the liquid drop into the other fluid, such as complex and intriguing problems in fluid mechanics, which is very important. Many experimental and numerical studies have been carried out in this case that the evelopment of laboratory equipment and software, are rapidly growing.
    In this study, given the importance of this issue, experimental study on mass transfer in fluid systems solution droplet liquid - liquid extraction, have been considered. Different methods have been discussed to date. In the present study, using image processing... 

    Numerical and Analytical Investigation of Unequal Size Droplets Generation Process in Micro and Nano Channels

    , Ph.D. Dissertation Sharif University of Technology Bedram, Ahmad (Author) ; Moosavi, Ali (Supervisor) ; Kazemzadeh Hannani, Siamak (Co-Advisor)
    In this paper, we introduced two methods for producing unequal sized droplet from an initial one that don’t have the disadvantages of the available methods. We developed a comprehensive analytical theory for the T-junction with valve method. Also the geometry was simulated using a VOF algorithm and a comparison was performed between numerical and analytical results and very good agreement was observed. The accuracy of numerical results was confirmed by doing the grid independency and time step independency and comparing the results with two analytical benchmarks. We derived accurate analytical relations for calculating the droplet volume ratio, droplet length (L1, L2 and Lwhole) and pressure... 

    CFD-Modeling and Simulation of Droplets Evaporation With a Size Distribution Function

    , M.Sc. Thesis Sharif University of Technology Pirhadi, Zahra (Author) ; Farhadi, Fatollah (Supervisor)
    Injecting several droplets with a known size distribution function in the hot gas environment makes droplets smaller because of evaporation or reaction. Droplets lifetime specification is important in vapor-liquid interactive processes such as chemical or process industries. In previous works, different approximate semi-empirical methods are developed to specify droplets lifetime without considering their size distribution. In this work, governing equations is studiedconsidering a size distribution function for droplets. There is not any analytical method for solving this set of equations, so numerical methods using CFD packages such as Fluent, are applicable in these cases. In this study,... 

    Numerical Investigation of Formation and Growth of Steam Condensing Droplets on Nanostructured Superhydrophobic Surface Using Lattice Boltzmann Method

    , M.Sc. Thesis Sharif University of Technology Ashrafi Habibabadi, Amir (Author) ; Moosavi, Ali (Supervisor)
    Condensation is one of the main processes in environment and engineering systems, including thermal power plants, desalination systems and air conditioners. Thus, improvement of its performance can lead to decrease of energy consumption and the resulting air pollutions. Recently, using nanotechnology and new coating methods, there have been great researches on stable superhydrophobic surfaces and using theme as condensing surfaces which because of jumping droplet phenomena can increase condensation performance. Because of the great influence of wetting and structure properties of surfaces on condensation, in this study nucleation and growth of condensing droplets on smooth and structured... 

    CFD Simulation of Dispersed Drops in Contact with Different Coalescers for Liquid-Liquid Separation

    , M.Sc. Thesis Sharif University of Technology Mehdizadeh Chelebari, Yasin (Author) ; Farhadi, Fathollah (Supervisor)
    Liquid-Liquid coalescers are devices used for increasing the droplet size of the dispersed phase in continuous phase flow such as water droplets in oil flow. The scope of this work is a literature study on the coalescence phenomenon and CFD modeling in general. A mathematical model for simulating coalescence of water droplets in continuous oil flow by the use of different commercial coalescers. The basis for the model are plate-type coalescer and swirl-based coalescer. So, the simulations are done by Eulerian-Lagrangian method. Different aspects of the performance of the coalescers are studied on the rate of coalescence such as impact of changing droplet’s inlet diameters, impact of the... 

    Develoment of Droplet Velocimetry Method Using Shadowgrapy

    , M.Sc. Thesis Sharif University of Technology Abbasi Zarrin, Fatemeh (Author) ; Kebriaee, Azadeh (Supervisor)
    Injection of liquid fuel in the cross-flowing air provides a means of higher penetration, rapid mixing of liquid fuel and air, and is encountered in many engineering applications. Air-breathing propulsion systems (e.g. gas turbine combustors, ramjets, and scramjets), liquid rocket engines,cooling sprays for turbine blades, and injection of fuel in the afterburners are examples of such applications. The identification of microscopic characteristics is one of the basic methods of atomizer examination, which has not been taken into account due to inadequate experimental equipment. In the present study, droplet mono-frame velocimetry and size distribution of secondary atomization in a pressure... 

    Experimental Investigation of Surfactant Effects on Drop Formation of Shear-thinning Liquids

    , M.Sc. Thesis Sharif University of Technology Dastyar, Peyman (Author) ; Firoozabadi, Bahar (Supervisor) ; Afshin, Hossein (Supervisor)
    In this research, the characteristics of non-Newtonian, shear-thinning drop formation containing surfactant from a needle are investigated experimentally. The ambient fluid is air and all experiments have been conducted in a constant flow rate of drop phase fluid. Images of forming drop are taken using a high-speed camera and by processing them, important parameters in drop formation such as length of drop, minimum neck thickness, formation time and the size of satellite drops have been studied. Three non-Newtonian and three Newtonian fluids are considered in a way that the initial viscosity of non-Newtonian fluids would be equal to the viscosity of their corresponding Newtonian fluids.... 

    Numerical Study of Spray Impingement to Solid Wall

    , M.Sc. Thesis Sharif University of Technology Abbasi Chenari, Fatemeh (Author) ; Morad, Mohammad Reza (Supervisor) ; Jahannama, Mohammad Reza (Co-Supervisor)
    Spray-wall impingement is one of the phenomenon that associated in different subject such as spray cooling, combustion chamber and gas turbine. With the impingement of spray to the wall, liquid film begins to form. Wall film characteristics is still an important subject to study. Due to the various stages of liquid film formation from injection of spray till spray-wall impingement, the investigation of this phenomenon is far more complicated. This paper is meant to provide detailed data on spray-wall impingement and wall film formation physics with the help of computational analysis of OpenFOAM . A Lagrangian-Eulerian method based on discrete phase model (DPM) was employed to model... 

    Experimental and Theoretical Investigation of Microdroplet Breakup at Asymmetric T Junctions

    , M.Sc. Thesis Sharif University of Technology Samie, Milad (Author) ; Behshad Shafii, Mohammad (Supervisor)
    Symmetric T junctions have been used widely in microfluidics to generate equal-sized microdroplets, which are applicable in drug delivery systems. A newly proposed method for generating unequal-size microdroplets at a T junction is investigated theoretically and experimentally. Asymmetric T junctions with branches of identical lengths and different cross-sections are utilized for this aim. A novel equation for the critical breakup of droplets at asymmetric T junctions and one for determining the breakup point of droplets are developed. A good agreement was observed between the theories (novel and previous) and the experiments