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    The level set modeling of droplet dynamic in fluid-fluid interaction

    , Article 39th AIAA Fluid Dynamics Conference, 22 June 2009 through 25 June 2009, San Antonio, TX ; 2009 ; 9781563479755 (ISBN) Darbandi, M ; Mazaheri, I ; Dehkordi, A. M ; Schneider, G. E ; Sharif University of Technology
    In this work, we present a level set method to simulate steady and unsteady mass transfer from a single droplet moving in a second phase fluid under buoyant force. We initially use level set to determine the interface between the two phases, where the shape of drop forms. Next, we extend this method to solve a unique mass transfer equation for the entire solution domain without considering the discontinuity appeared at the interface. We use a finite element method incorporated with the characteristic-based split (CBS) algorithm to implement axi-symmetric mass transfer equations on a stationary Eulerian grid. Of course, the convection-diffusion modeling of mass transfer is different from the... 

    The effect of brine salinity on water-in-oil emulsion stability through droplet size distribution analysis: A case study

    , Article Journal of Dispersion Science and Technology ; 2017 , Pages 1-13 ; 01932691 (ISSN) Maaref, S ; Ayatollahi, S ; Sharif University of Technology
    Water-in-oil emulsion usually forms during waterflooding in some heavy oil reservoirs. The composition and salinity of the injected water critically affect the w/o emulsion droplet size distribution, which control the emulsion stability and emulsion flow in porous media. The aim of the present work is to assess the effect of different sea water salinities on w/o emulsion stability through microscopic imaging. Therefore, w/o emulsions were prepared with different sea water samples, which were synthesized to resemble Persian Gulf, Mediterranean, Red Sea, and North Sea water samples. The results showed that log-normal distribution function predicts very well the experimental data to track the... 

    Experimental investigation of two phase flow in horizontal wells: Flow regime assessment and pressure drop analysis

    , Article Experimental Thermal and Fluid Science ; Volume 88 , 2017 , Pages 55-64 ; 08941777 (ISSN) Shams, R ; Tavakoli, A ; Shad, S ; Sharif University of Technology
    Elsevier Inc  2017
    Multiphase flow is fundamental to different fields of engineering and science including petroleum engineering. In oil and gas, flow of multiple phases inside wells is a common phenomenon. In such conditions, petroleum engineers deal with different design and operational difficulties due to complexities involved in flow of multiple phases inside a well. Unlike flow of gas and liquid inside a well, the liquid-liquid flow inside a horizontal well has received rather less attention. This study is aimed at experimentally investigating multiphase flow in a horizontal well by using a 12 m length and 30 mm diameter well made of Plexiglas. Despite the importance of defining pattern transition... 

    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... 

    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... 

    Simulation of Microcapsule Formation for Cell Encapsulation Application

    , M.Sc. Thesis Sharif University of Technology Yaghoobi, Mohammad (Author) ; Saeedi, Mohammad Saeed (Supervisor) ; Kazemzadeh Hanani, Siamak (Co-Advisor)
    Co-culture of different cells is necessary for cancer spheroid formation in preclinical drug tests. It is possible to produce thousands of micro-droplets containing different cells, i.e. microcapsules, in a short time, using droplet microfluidics. However the homogeneity of the cell numbers in the droplets has remained as an unsolved problem.Despite the large amount of experimental efforts to reduce the number of undesirable microcapsules, no one tried to utilize the ease of computer aided simulation for investigating different parameters. In this study, we develop a novel method for capturing cell encapsulation using CFD simulations. The effect of the cell suspension inhomogeneity and... 

    Numerical Simulation of Non-Newtonian Droplet Formation under External Electric Field in a Microfluidic Device

    , M.Sc. Thesis Sharif University of Technology Amiri, Nasir (Author) ; Moosavi, Ali (Supervisor) ; Kazemzadeh Hannani, Siamak (Supervisor)
    Droplet formation and breakup processes are one of the important steps in many microfluidic devices with a wide range of biological and chemical applications. The purpose of this study is numerical simulation of non-Newtonian droplet formation under the influence of electric field in a microfluidic system. The innovation aspect of this project is the use of non-Newtonian fluid in this process, which, despite many applications in real issues, has been less studied, and in most of the previous researches, Newtonian fluid assumption has been used to simplify the solving. Also, simultaneously, the effects of an external electric field on this process were also studied. Carboxymethyl cellulose... 

    Design and Fabrication of a Microfluidic Digital PCR

    , M.Sc. Thesis Sharif University of Technology Bahrami, Mohammad Amin (Author) ; Saeedi, Mohammad Saeed (Supervisor) ; Firouzabadi, Bahar (Supervisor)
    Polymerase chain reaction, abbreviated as PCR, is a method of amplifying the number of copies of a desired DNA sequence through special protocols. The rapid advance of microfluidic devices and the emerging concept of digital microfluidics has resulted into the development of digital droplet PCR (ddPCR) systems with their significant uses in the detection of rare mutations, cancer diagnosis, and surveillance. In this study, an integrated ddPCR microfluidic chip alongside its thermoelectric thermal cycler and optical analysis systems have been designed, fabricated and their performance has been tested and evaluated. It was shown that the effect of master mold’s surface quality, the material of... 

    Experimental Study of Droplet Formation in Surfactant Solution

    , M.Sc. Thesis Sharif University of Technology Niknezhad, Mahdi (Author) ; Firoozabadi, Bahar (Supervisor) ; Afshin, Hossein (Co-Advisor)
    Surfactants are materials that reduces surface tension, and this property has provided a wide range of applications for them. Most of the surfactants reduce surface tensions at the interface of two fluids. The pharmaceutical and food industries, detergents, cosmetics, agricultural pesticides, dye production and oil extraction are among these applications.In this study, the formation of droplets in the presence of three types of surfactants SDS, CTAB and Tween 20 has been investigated. To evaluate the droplet behavior in the presence of specific surfactants, various parameters such as formation time of the droplet, the diameter and length of the droplet formed, the diameter and length of the... 

    Numerical Simulation of Self-propelled Droplet over a Surface with Surface Tension Gradient

    , M.Sc. Thesis Sharif University of Technology Zolfi, Hamid Reza (Author) ; Javadi, Khodayar (Supervisor)
    Ice accretion may cause malfunction or serious performance degradation in outdoor facilities and structures, such as aircraft, ship, locks and dams, offshore platforms, solar panels, wind turbines, power transmission towers and lines, and sports facilities, leading to huge economic loss or even loss of human lives. Icephobic materials, typically applied in the form of coatings, have received growing attention in the last decade. This work focuses on surfaces with a surface tension gradient which has icephobic properties. various surface tension gradients such as linear, exponential, cycloid and parabola have been imposed on a surface in order to achieve the shortest time for a droplet to... 

    Numerical Investigation of Droplet Generation in a Microfluidic Flow-Focusing Junction Aiming High-Throughput Droplet Generation

    , M.Sc. Thesis Sharif University of Technology Mardani Boldaji, Fatemeh (Author) ; Taghipoor, Mojtaba (Supervisor) ; Hosseini, Vahid (Supervisor)
    Droplet microfluidic platform generates monodisperse droplets in a desired size through immiscible multiphase flows inside microchannels. Droplets are individual reactor and can be used for bio(chemical) analyses. Also, for materials fabrication, droplet microfluidics offers a versatile platform for generation of nano- or micro-sized particles and microcapsules that are widely used in drug delivery. In addition to the monodispersity, high-throughput generation is also necessary in many applications. Therefore, droplets must be formed in stable regimes (dripping and squeezing) in the highest possible frequency. In this study, the flow-focusing geometry, which is the most common geometry in... 

    Modeling of the Wet Compression System in Transient Behavior of the Industrial Gas Turbine

    , Ph.D. Dissertation Sharif University of Technology Keshavarz Mohammadian, Poorya (Author) ; Saeedi, Mohammad Hassan (Supervisor)
    In general, the output power of the gas turbines decreases as the ambient temperature increases. One of the ways to deal with such a performance loss is to use a wet compression system, which reduces the air temperature rise throughout the compressor. In this system, the water droplets are injected into the compressor inlet and evaporated throughout the stages. As a result, the work of the compressor decreases, and the power and efficiency of the whole engine increase. Most of the researchers in this field have tried to develop mathematical models to investigate the effects of this system on compressor and gas turbine performance in steady-state conditions. However, it is necessary to... 

    Late-stage evolution of thin liquid coating films over step topographies

    , Article Advanced Materials Research ; Volume 569 , 2012 , Pages 560-563 ; 10226680 (ISSN) ; 9783037854808 (ISBN) Asgari, M ; Moosavi, A ; Sharif University of Technology
    Mesoscopic hydrodynamic equations are solved to investigate late-stage evolution of thin liquid films over step topographies. Different geometrical parameters including step height and initial position and configuration of resultant masses of dewetting (droplets) are probed to find their effects on the mass evolution of the system. Our results indicate that increasing the step height and locating the droplets close to the step enhance the dynamics and accelerate smaller droplet collapse  

    Coarsening dynamics of dewetting nanodroplets on chemically patterned substrates

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 86, Issue 1 , July , 2012 ; 15393755 (ISSN) Moosavi, A ; Sharif University of Technology
    Mesoscopic hydrodynamic equations are solved to investigate coarsening dynamics of two interacting nanodroplets on chemically patterned substrates. The effects of different parameters such as the surface chemical pattern, the slip length, the profile of the disjoining pressure, the size of the droplets, and the contact angles on the coarsening are studied. Our results reveal that the presence of a chemical heterogeneity can enhance or weaken the coarsening dynamics depending on the pattern type and positions of the droplets on the substrate. Also increasing the contact angles to values larger than a critical value may qualitatively change the coarsening process, and the profile of the... 

    A novel method for producing unequal sized droplets in micro- and nanofluidic channels

    , Article European Physical Journal E ; Volume 38, Issue 9 , September , 2015 ; 12928941 (ISSN) Bedram, A ; Moosavi, A ; Kazemzadeh Hannani, S ; Sharif University of Technology
    Springer New York LLC  2015
    Abstract: We propose a novel method for producing unequal sized droplets through breakup of droplets. This method does not have the disadvantages of the available methods and also reduces the dependence of the droplets volume ratio on the inlet velocity of the system by up to 26 percent. The employed method for investigating the proposed system relies on 3D numerical simulation using the VOF algorithm and the results have been obtained with various valve ratios for both the micro- and nanoscale. The results indicate that the droplet length during the breakup process increases linearly with time. The droplet length at the nanoscale is smaller than that at the micro scale. It has been shown... 

    Analytical solution of chamber effective length in the axial engine

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE), 12 November 2010 through 18 November 2010, Vancouver, BC ; Volume 7, Issue PARTS A AND B , 2010 , Pages 1095-1102 ; 9780791844441 (ISBN) Dehghani, S. R ; Mozafari, A. A ; Saidi, M. H ; Ghafourian, A ; Sharif University of Technology
    this research chamber effective length, which is the minimum chamber length required for complete combustion, for a dilute monopropellant spray, constant area, one dimensional and fixed volume engine is analytically predicted. A new evaporation rate in the form of dk +1 relation, instead of d 2 law, is introduced. In case of controlling the vaporization by radiative heat transfer, k is equal to zero, and when molecular processes control the vaporization, k will be equal to unity and in some cases the vaporization data need the value of k greater than one to fit properly to related equation. Development of this approach can be used in design of combustion chambers with optimum length and with... 

    Control of droplet detachment frequency in a GMAW process by a hybrid model predictive control

    , Article Journal of Dynamic Systems, Measurement and Control, Transactions of the ASME ; Volume 140, Issue 11 , 2018 ; 00220434 (ISSN) Sartipizadeh, H ; Haeri, M ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2018
    Efficient control of a gas metal arc welding (GMAW) process enables one to obtain high quality products as a consequence of achieving a high quality weld. Although control of the droplet detachment frequency in the welding process would play a great role in improving the welding quality, measuring this variable is difficult and expensive. In this paper, we attempt to control the frequency of droplet detachments without directly measuring it. To this end, we utilize the hybrid property of the GMAW process to indirectly control the frequency. Specifically, a mixed logical dynamical (MLD) model is obtained by considering the hybrid act of the process during droplet detachment. Then, a nonlinear... 

    Multi-objective optimization approach toward conceptual design of gas turbine combustor

    , Article Applied Thermal Engineering ; Volume 148 , 2019 , Pages 1210-1223 ; 13594311 (ISSN) Saboohi, Z ; Ommi, F ; Akbari, M ; Sharif University of Technology
    Elsevier Ltd  2019
    This paper focused on the conceptual design of a conventional gas turbine combustor via the multi-objective optimization approach. The suggested method integrated the design and estimation of the performance of the combustion chamber. The geometry and performance parameters could be found by applying the design tool. According to the level of available information in the primary phases of the design process, a chemical reactor network approach for modeling the combustion was chosen; thus, the droplet evaporation of the liquid fuel and unmixedness of the fuel-air mixture in the primary zone was modeled. The results obtained from the design tool for the two annular combustors were compared... 

    Swirl intensity as a control mechanism for methane purification in supersonic gas separators

    , Article Journal of Natural Gas Science and Engineering ; Volume 83 , 2020 Ghorbanian, K ; Amini Magham, M ; Sharif University of Technology
    Elsevier B.V  2020
    Supersonic gas separator is proposed for methane purification. One-dimensional analysis is performed to examine the design aspects associated with the converging-diverging nozzle and the liquid separation chamber. The results indicate that at low swirl intensities, the separation chamber length is about 100 times of the nozzle throat. Increasing the swirl intensity would lower this length sharply and it will be less than 10 for swirl intensity of unity which is equivalent to a swirl angle of 45°. In addition, a sensitivity analysis of the separator performance to the inlet conditions like the temperature, pressure, and composition of the mixture is carried out. It is observed that increasing...