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Numerical Investigation of Droplet Generation in a Microfluidic Flow-Focusing Junction Aiming High-Throughput Droplet Generation
, M.Sc. Thesis Sharif University of Technology ; Taghipoor, Mojtaba (Supervisor) ; Hosseini, Vahid (Supervisor)
Abstract
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...
The Numerical Simulation of Droplet Generation and its Control Using Electrowetting Method in Microfluidic Devices
, M.Sc. Thesis Sharif University of Technology ; Moosavi, Ali (Supervisor) ; Shafii, Mohammad Behshad (Supervisor)
Abstract
In this research, two important mechanisms were discussed including droplet generation and jumping mechanisms using electro wetting-on-dielectric. For these purposes, the finite element method (FEM) was used to solve the unsteady Naiver-Stokes equation. In addition, the level set method was applied to capture the interface between two phases. In the current study, first, droplet generation in a T-junction fluidic channel device was studied through using electro wetting actuation. The efficacy of electro wetting on the droplet generation frequency as well as droplet diameter is visible in a T-junction fluidic channel since after applying voltages, specified with non-dimensional electro...
Experimental and Numerical Study of The Production of Alginate Microgels and Cancer Spheroids by Droplet-Based Microfluidic
, M.Sc. Thesis Sharif University of Technology ; Shamloo, Amir (Supervisor) ; Kazemzadeh Hannani, Siamak (Supervisor)
Abstract
Significant advances in biotechnology have led to the emergence of a cost-effective way with less ethical issues to study disease, organ functions, tumors, and their response to drugs besides studying on animals. Microfluidic devices and organ on a chip (tumor on a chip) were introduced to remove those obstacles. Organ on a chip is a powerful tool for studying different types of tissues and simulating diseases, especially cancers, for biological and medical applications. Organ (tumor) on a chip is considered as a smaller scale of the real organ or tumor and it causes to the real-time study of tissues and their functions more accurately. In this study, to fabricate a droplet-based...
Experimental and Numerical Investigation on the Splitting of Microdroplets in Symmetrical and Asymmetrical T Junctions Using Magnetic Fields
, Ph.D. Dissertation Sharif University of Technology ; Shafii, Mohammad Behashad (Supervisor) ; Kazemzadeh Hannani, Siamak (Co-Supervisor)
Abstract
Ferrofluids are used in various fields such as drug delivery systems, heat transfer, biotechnology and separation processes. In this study, the splitting of ferrofluid microdroplets in symmetric and asymmetric T-junctions in the presence of a magnetic field has been investigated numerically and experimentally. These studies have shown that the creation of an asymmetric magnetic field can either affect the phenomenon of ferrofluid microdroplet breakup or the volume of microdroplets that are created after breaking and leaving each branch. Furthermore, more control can be applied to the phenomenon of microdroplet breakup. In the numerical study, the ferrofluid microdroplet breakup at different...
Numerical Study of SARS-CoV-2 Virus Dispersion in Hospital Wards
, M.Sc. Thesis Sharif University of Technology ; Abdekhodaie, Mohammad Jafar (Supervisor)
Abstract
The ongoing Covid-19 pandemic has driven our attention to a simulation of virus dispersion to complete our understanding of airborne transmission. A myriad of studies have shown that respiratory diseases such as MERS, SARS, and COVID-19 can be transmitted by virus-laden droplets released during coughs, sneezing, and normal breathing. To mitigate and prevent the spread of such infectious diseases, investigation of the transmission routes is of great importance. This study has been fueled to harness the CFD tool to simulate the virus-laden droplets dispersion in hospitals inwards. Because of the limitations intertwined with experimental works such as the risk of infection of experimenters, and...
The Study of Nanoparticles on the Droplets Hydrodynamics
, M.Sc. Thesis Sharif University of Technology ; Bastani, Dariush (Supervisor)
Abstract
Liquid-liquid extraction is one of the common chemical processes in the industry which its application is increasing day by day. Taking trend of increase of energy resources, chemical materials and industrial system into account, the necessity use of least energy consumption and material for achieving highest output and purity of products in different industries is attracted researches and industerialists.In this research we have studied the effect of presence of nano particles on both disperses and continuous liquids phases on hydrodynamic of deoplets specially their investigated system in this project was watter, toluene and acetone, and chosen nanoparticles wer carbon nanotubes and TiO2....
Modeling of the Wet Compression System in Transient Behavior of the Industrial Gas Turbine
, Ph.D. Dissertation Sharif University of Technology ; Saeedi, Mohammad Hassan (Supervisor)
Abstract
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...
Simulating of Droplet Formation and Calculation of Interfacial Tension by Microfluidic Method
, M.Sc. Thesis Sharif University of Technology ; Mohammadi, Ali Asghar (Supervisor)
Abstract
Emulsions are the intermittent dispersion of liquid droplets that have many applications such as polymerization, dyeing, cosmetics, food industry, etc. Droplets can be created in a variety of ways, but the most important point in emulsification and the greatest efficiency of its applications is when the formed droplets are uniform. In the emulsification process, there is a key parameter called interfacial tension, which affects the behavior of the formed droplets, such as their stability and morphology, and its precise measurement is very effective in the quality control of the mentioned applications. Be. In this research, droplet formation in microfluidic systems due to uniform droplet...
Numerical Simulation to Improve the Efficiency of a Combined Cycle Incorporating a J-Class Gas Turbine Equipped with a Water Fogging System at Its Inlet
, M.Sc. Thesis Sharif University of Technology ; Darbandi, Masoud (Supervisor)
Abstract
One way to increase the power and efficiency of the gas turbines is to cool their incoming air. There are different methods to cool down the inlet air. One of the most widely used and suitable method is spraying or fogging the water droplets into the air at the gas turbine air inlet. In this research and for the first time, the effect of fogging system on the performance of a combined cycle incorporated with a J-class gas turbine (M-501J) is investigated using the computational fluid dynamics (CFD). There are so many parameters, which affect the amount of achieved efficiency. A few of them includes the average temperature and humidity at the outlet, the evaporation efficiency of the water...
Numerical Simulation of the Impact of a Drop with a Flat Surface in a Cross Flow, Using LBM
, M.Sc. Thesis Sharif University of Technology ; Taebi Rahni, Mohammad (Supervisor)
Abstract
In this research, numerical simulation of the impact of a drop on a flat surface with oblique velocity has been performed, using two-phase model of Lattice Boltzmann Method (conservative phase-field). During impact, it is important to investigate two-dimensional drop dynamics and to evaluate the effectiveness of the numerical method used. The model used here restores conservative phase field and preserves mass both locally and globally. In addition, to calculate the slope of the phase field, it calls the center points without engaging finite difference calculations. This makes it efficient for running parallel computations. A fixed dry and hard surface is considered and the drop impacts it...
Simulation, Design, and Fabrication of a Droplet-Based Microfluidic Device to Study The Role of Tumor Microenvironment and Drug Effects on the Behavior of Multicellular Tumor Spheroids
, Ph.D. Dissertation Sharif University of Technology ; Shamloo, Amir (Supervisor) ; Kazemzadeh Hannani, Siamak (Supervisor)
Abstract
Despite the extensive research conducted so far to treat cancer, this disease is still one of the main causes of death worldwide. The results of recent studies reveal the importance of the tumor microenvironment in the growth, proliferation, and invasion of the primary tumor. Most common models in cancer research, such as 2-dimensional in vitro models and xenografts, do not have sufficient ability to mimic the interaction of tumors with human stromal tissue. Therefore, the implementation of 3-dimensional in vitro models with the ability to replicate tumor microenvironments is essential. In this study, a microfluidic platform has been introduced to create parallel models of the tumor...
Electric-field-induced Response of Charged Droplets in Uncharged Hydrogels
, M.Sc. Thesis Sharif University of Technology ; Mohammadi, Ali Asghar (Supervisor)
Abstract
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...
Experimental and Theoretical Investigation of Microdroplet Breakup at Asymmetric T Junctions
, M.Sc. Thesis Sharif University of Technology ; Behshad Shafii, Mohammad (Supervisor)
Abstract
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
Simultaneous Impact of Multiple Boiling Droplets on a Molten Phase Change Material as a Direct-Contact Solidification Method
, M.Sc. Thesis Sharif University of Technology ; Shafii, Mohammad Behshad (Supervisor)
Abstract
Encompassing an interaction between the phase change material (PCM) and the droplets of a heat transfer fluid, the direct contact (DC) method provides a state-of-the-art solution for the meager melting and solidification rates of PCMs. In the DC procedure, when impinging on the molten PCM pool, droplets evaporate, solidifying the portion of the PCM. For the first time, the impact of single and simultaneous double ethanol droplets, having an average diameter of 2.68 mm, on the molten paraffin wax has been scrutinized exhaustively. Experiments have been carried out through high-speed imaging for various Weber numbers ranging from 179 to 464, pool temperatures from 70 to 95°C, and horizontal...
Numerical Simulation of Non-Newtonian Droplet Formation under External Electric Field in a Microfluidic Device
, M.Sc. Thesis Sharif University of Technology ; Moosavi, Ali (Supervisor) ; Kazemzadeh Hannani, Siamak (Supervisor)
Abstract
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...
Investigation of the Spray Pattern in the Air Flow Induced by Coaxial Rotors Used for Pesticide Spraying
, M.Sc. Thesis Sharif University of Technology ; Morad, Mohammad Reza (Supervisor) ; Hejranfar, Kazem (Supervisor)
Abstract
The production of agricultural products is one of the most important human economic activities. The issue of mechanized and optimal use of pesticides is vital for human health and the environment, and the use of helicopters makes this possible. Although spray-based systems in helicopters are one of the most effective ways to produce agricultural products, it is still unclear how droplet movement in aerial spraying is affected by the complex downwash flow created by rotors. Modeling agricultural air spray to identify the spray trend of droplets in the air stream, downwash flows, and consequent vortices has attracted more attention as a result of the development of computational fluid...
Evaluation of chemicals interaction with heavy crude oil through water/oil emulsion and interfacial tension study
, Article Energy and Fuels ; Vol. 27, issue. 10 , September , 2013 , p. 5852-5860 ; ISSN: 08870624 ; Masihi, M ; Ayatollahi, S ; Sharif University of Technology
Abstract
A newly-designed surfactant was formulated to tolerate the harsh conditions of oil reservoirs, including high salinity of the formation brine and temperature. The specific emulsion and interfacial tension (IFT) behavior of this new surface active agent were investigated by performing emulsion stability tests, emulsion size analysis, and IFT behavior in the presence of four different types of alkalis. Image processing was utilized to analyze the droplet size distribution using microscopic images of the samples. The results show that depending on the composition of the mixtures, the optimum phase region and interfacial tension behavior change considerably. Solutions containing a higher...
Numerical study on the oscillation of a transient bubble near a confined free surface for droplet generation
, Article Theoretical and Computational Fluid Dynamics ; Vol. 28, issue. 4 , 2014 , p. 449-472 ; Shervani-Tabar, M.T ; Taeibi-Rahni, M ; Dadvand, A ; Sharif University of Technology
Abstract
In the present work, the oscillation of a spark-created bubble near a confined water-air interface and the ensuing droplet generation and ejection are studied numerically using the boundary element method. The interface is accorded by the top opening of either one of the following symmetrical configurations, which are distinguished by the value of angle between their vertical symmetry axis and lateral wall (i.e., θ): (i) a centrally perforated horizontal flat plate (θ = 90°) and (ii) vertically placed cylinder (θ = 0°), nozzle (θ > 0°) and diffuser (θ < 0°). Furthermore, the influences of the effective parameters such as the strength parameter (i.e., the intensity of local energy input), the...
Morphology of nanodroplets on structured surfaces
, Article Journal of Physics D: Applied Physics ; Volume 46, Issue 21 , May , 2013 ; 00223727 (ISSN) ; Moosavi, A ; Sharif University of Technology
2013
Abstract
We report different morphologies of nanodroplets over various topographical features of the supporting substrates. The effects of different parameters such as the profile of the disjoining pressure, droplet size and the geometrical parameters are studied and discussed. Also, the effects of a coating layer on the surface of the substrate are determined. It is demonstrated that the nanodroplets at some positions are not stable and gradually move to more stable positions so that the system has less energy. For grooves this results in a series of morphology diagrams of the nanodroplets over the grooves as a function of the grooves' width and the liquid volume
Breakup of microdroplets in asymmetric T junctions
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 87, Issue 5 , 2013 ; 15393755 (ISSN) ; Salari, A ; Shafii, M. B ; Sharif University of Technology
2013
Abstract
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-sized 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. An 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 (present and previous) and the experiments