Search for: drop-breakup
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    Droplet breakup in an asymmetric microfluidic T junction

    , Article European Physical Journal E ; Volume 34, Issue 8 , 2011 ; 12928941 (ISSN) Bedram, A ; Moosavi, A ; Sharif University of Technology
    Breakup of non-uniform droplets in an asymmetric T junction consisting of an inlet channel and two different-size outlet channels has been investigated numerically. Also, an analytical approach in the limit of the lubrication approximation has been extended to provide some analytical relations to study the system and verify the numerical results. Parameters that are important in the performance of the system have been determined and discussed. Our results indicate that smaller droplets can be produced by increasing the capillary number. As the geometry becomes symmetric the pressure drop decreases. Our results also reveal that the breakup time and the pressure drop for this system are... 

    Analytical relations for long-droplet breakup in asymmetric T junctions

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 91, Issue 5 , May , 2015 ; 15393755 (ISSN) Bedram, A ; Moosavi, A ; Hannani, S. K ; Sharif University of Technology
    American Physical Society  2015
    We develop accurate analytical relations for the droplet volume ratio, droplet length during breakup process, and pressure drop of asymmetric T junctions with a valve in each of the branches for producing unequal-sized droplets. An important advantage of this system is that after manufacturing the system, the size of the generated droplets can be changed simply by adjusting the valves. The results indicate that if the valve ratio is smaller than 0.65, the system enters a nonbreakup regime. Also the pressure drop does not depend on the time and decreases by increasing the valve ratio, namely, opening the degree of valve 1 to valve 2. In addition, the results reveal that by decreasing... 

    Formation and breakup patterns of falling droplets

    , Article Numerical Heat Transfer; Part A: Applications ; Volume 68, Issue 9 , Jun , 2015 , Pages 1023-1030 ; 10407782 (ISSN) Sharafatmandjoor, S ; Taeibi Rahni, M ; Azwadi Che Sidik, N ; Sharif University of Technology
    Taylor and Francis Ltd  2015
    Some interface front patterns of falling droplets are studied via direct numerical solution of the full Navier-Stokes equations governing the system of droplets and the ambient surrounding media as a single-fluid model. We focus on the mutual interactions of the effects of characterizing nondimensional parameters on the formation and break-up of large cylindrical droplets. The investigation of droplet cross sections and deformation angles shows that for moderate values of the Atwood number, increasing the Eötvös number explicitly increases the deformation rate in formation and breakup phenomena. Otherwise, increasing the Ohnesorge number basically amplifies the viscous effects  

    A Lagrangian-extended finite-element method in modeling large-plasticity deformations and contact problems

    , Article International Journal of Mechanical Sciences ; Volume 51, Issue 5 , 2009 , Pages 384-401 ; 00207403 (ISSN) Khoei, A. R ; Biabanaki, S. O. R ; Anahid, M ; Sharif University of Technology
    In this paper, a Lagrangian-extended finite-element (FE) method is presented in modeling large-plasticity deformations and contact problems. The technique is used to model arbitrary interfaces in two-dimensional (2D)/three-dimensional (3D) large deformations. The material interfaces are represented independent of the FE mesh and the process is accomplished by integrating enriched elements with a larger number of Gauss points, whose positions are fixed in the element. The large elasto-plastic deformation formulation is employed within the eXtended Finite-Element Method (X-FEM) framework to simulate the nonlinear behavior of materials. The interface between two bodies is modeled by using the... 

    Numerical modeling of instability and breakup of elliptical liquid jets

    , Article AIAA Journal ; Volume 58, Issue 6 , June , 2020 , Pages 2442-2449 Morad, M. R ; Nasiri, M ; Amini, G ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2020
    Numerical simulations are performed to provide an in-depth insight into the effect of instabilities on liquid jets discharging from elliptical orifices. The axis-switching phenomenon and breakup are simulated and characterized under the effect of disturbances imposed at the nozzle exit. The simulations are based on the volume of fluid approach and an adaptive meshing. A range of orifice aspect ratios from 1 to 4 at the Rayleigh breakup regime is considered. The evolution of the jet cross section and axis switching under the influence of disturbances is compared with that of nonperturbed elliptical jets. It is found that the axis-switching repetition and breakup length exponentially decrease... 

    Electrowetting induced droplet generation in T-junctions

    , Article Journal of Heat Transfer ; Volume 143, Issue 5 , 2021 ; 00221481 (ISSN) Merdasi, A ; Moosavi, A ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2021
    In this study, droplet generation in a T-junction fluidic channel device was studied by using electrowetting actuation with the consideration of different droplet forming regimes. For this purpose, 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. It was shown that there was a good agreement between obtained data and other work during the process of droplet generation in the absence of electrowetting actuation which results in the decrease in the size of the droplet with increasing the velocity ratios. In the shearing regime, the effectiveness of electrowetting on... 

    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
    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... 

    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... 

    Integration of spatial fuzzy clustering with level set for segmentation of 2-D angiogram

    , Article IECBES 2014, Conference Proceedings - 2014 IEEE Conference on Biomedical Engineering and Sciences: "Miri, Where Engineering in Medicine and Biology and Humanity Meet", 8 December 2014 through 10 December 2014 ; December , 2015 , Pages 309-314 ; 9781479940844 (ISBN) Ghalehnovi, M ; Zahedi, E ; Fatemizadeh, E ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Coronary angiography is a vital instrument to detect the prevailing of vascular diseases, and accurate vascular segmentation acts a crucial role for proper quantitative analysis of the vascular tree morphological features. Level set methods are popular for segmenting the coronary arteries, but their performance is related to suitable start-up and optimum setting of regulating parameters, essentially done manually. This research presents a novel fuzzy level set procedure with the objective of segmentation of the coronary artery tree in 2-D X-ray angiography as automatically. It is clever to clearly develop from the early segmentation with spatial fuzzy grouping. The adjusting parameters of... 

    Liquid jet trajectory and droplet path influenced by combined cross flow and electric fields

    , Article Chemical Engineering Science ; Volume 181 , 18 May , 2018 , Pages 114-121 ; 00092509 (ISSN) Rajabi, A ; Morad, M. R ; Rahbari, N ; Pejman Sereshkeh, S. R ; Razavi, M ; Sharif University of Technology
    Elsevier Ltd  2018
    This study investigates an ethanol liquid jet subjected to combination of an air crossflow and a normal electric field. The results on the liquid jet trajectory and subsequent droplets flight paths are presented. The liquid jet trajectory was found as a function of two non-dimensional quantities; the liquid jet to the crossflow momentum ratio and the electroinertial number. The electroinertial number is defined as the ratio between the liquid jet specific momentum and the electric force. A correlation is introduced for the jet trajectory in low crossflow speeds and electric field intensities. The same two quantities control the detached droplets flight paths. Satellite droplets flight angles... 

    Ferrofluid droplet formation from a nozzle using alternating magnetic field with different magnetic coil positions

    , Article Journal of Magnetism and Magnetic Materials ; Volume 498 , 2020 Favakeh, A ; Bijarchi, M. A ; Shafii, M. B ; Sharif University of Technology
    Elsevier B.V  2020
    Ferrofluid has been used in many fields, such as microfluidics, droplet formation, and heat transfer, due to its potential to be attracted in the presence of a magnetic field. Droplet formation, itself, has many applications such as emulsions, 3D micro-printers, MEMS, and electro-sprays. In this study, the mechanism of ferrofluid droplet formation from the nozzle in the presence of an alternating magnetic field was investigated. The magnetic coil was fixed at different angles with respect to gravity and the effect of the alternating magnetic field and the angle of the magnetic coil axis with respect to gravity on the produced droplet volume, satellite droplet, and droplet formation frequency... 

    Axis-switching and breakup of rectangular liquid jets

    , Article International Journal of Multiphase Flow ; Volume 126 , May , 2020 Morad, M. R ; Nasiri, M ; Amini, G ; Sharif University of Technology
    Elsevier Ltd  2020
    The behavior of low-speed liquid jets emerging from rectangular orifices into a quiescent air is studied numerically. After ejection, the rectangular cross-section transforms into an elliptical form along the jet and while axis-switching includes elliptical cross-sections only, the rectangular shape never establishes again. The optimum wavenumber, corresponding to the most dominant wave, is found to be greater in orifices with higher aspect ratios and, as a result, breakup length of the jet will be shorter. The breakup length decreases exponentially with the initial amplitude of disturbances. Moreover, it is observed that the form of final breakup leads to elimination of the satellite... 

    Ferrofluid droplet breakup process and neck evolution under steady and pulse-width modulated magnetic fields

    , Article Journal of Molecular Liquids ; Volume 343 , 2021 ; 01677322 (ISSN) Bijarchi, M.A ; Favakeh, A ; Mohammadi, K ; Akbari, A ; Shafii, M. B ; Sharif University of Technology
    Elsevier B.V  2021
    Numerous applications in engineering and biotechnology have attracted the attention of many researchers to the analysis of underlying physical phenomena during the droplet pinch-off. In this study, the neck evolution during the formation of a ferrofluid droplet from a capillary is investigated under two types of magnetic field for a drop-on-demand system. The two types are steady and Pulse-Width Modulated (PWM) magnetic fields. First, under steady magnetic field, the necking process is studied for different values of magnetic Bond number and various angles between magnetic coil centerline and gravity. Subsequently, self-similar behavior in the vicinity of the detachment moment is observed.... 

    Breakup of microdroplets in asymmetric T junctions

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 87, Issue 5 , 2013 ; 15393755 (ISSN) Samie, M ; Salari, A ; Shafii, M. B ; Sharif University of Technology
    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  

    Simulation of buoyant bubble motion in viscous flows employing lattice Boltzmann and level set methods

    , Article Scientia Iranica ; Volume 18, Issue 2 B , 2011 , Pages 231-240 ; 10263098 (ISSN) Mehravaran, M ; Hannani, S. K ; Sharif University of Technology
    Recently, a hybrid Lattice Boltzmann Level Set Method (LBLSM) for two-phase incompressible fluids with large density differences, in cases of negligible or a priori known pressure gradients, has been proposed. In the present work, the mentioned LBLSM method is extended to take into account pressure gradient effects. The lattice Boltzmann method is used for calculating velocities, the interface is captured by the level set function, and the surface tension is replaced by an equivalent body force. The method can be applied to simulate two-phase fluid flows with density ratios up to 1000 and viscosity ratios up to 100. In order to validate the method, the evolution and merging of rising bubbles... 

    Numerical simulation of collision between two droplets in the T-shaped microchannel with lattice Boltzmann method

    , Article AIP Advances ; Volume 6, Issue 11 , 2016 ; 21583226 (ISSN) Merdasi, A ; Ebrahimi, S ; Moosavi, A ; Shafii, M. B ; Kowsary, F ; Sharif University of Technology
    American Institute of Physics Inc 
    In this study, the Lattice Boltzmann Method (LBM) is used to investigate the deformation of two droplets within microfluidic T-junctions (MFTD). In order to increase the accuracy the two immiscible fluids are modeled using the He-Chen-Zhang model. First, this model is applied to ensure that the surface tension effect existing between the droplets and the continuous fluid is properly implemented in the model. Then the collision and merging of the two droplets within the intersection of a T-shaped microchannel is investigated. For generating droplet formation the effects of relevant dimensionless parameters such as the Reynolds, the Weber numbers as well as a collision parameter affecting the... 

    Droplet dynamics in rotating flows

    , Article Advances in Colloid and Interface Science ; Volume 236 , 2016 , Pages 63-82 ; 00018686 (ISSN) Maneshian, B ; Javadi, K ; Taeibi Rahni, M ; Miller, R ; Sharif University of Technology
    Elsevier B.V  2016
    This paper deals with investigations of droplet dynamics in rotating flows. In many previous studies droplet dynamics was analyzed in simple unidirectional flows. To fill this gap, the focus of this study is an overview on investigations of droplet dynamics in a complex rotating flow. A Lattice Boltzmann Method with high potential in simulation of two-phase unsteady flows is applied to simulate the physics of the problem in a lid-driven cavity. In spite of its simple geometry, there is a complex rotating flow field containing different vortices and shear regions. The Reynolds number based on the cavity length scale and the upper wall velocity, ReL, is considered to be 1000. We discuss here... 

    Drop formation from a capillary tube: comparison of different bulk fluid on newtonian drops and formation of newtonian and non-newtonian drops in air using image processing

    , Article International Journal of Heat and Mass Transfer ; Volume 124 , 2018 , Pages 912-919 ; 00179310 (ISSN) Nazari, A ; Zadkazemi Derakhshi, A ; Nazari, A ; Firoozabadi, B ; Sharif University of Technology
    The formation of water drops as a Newtonian fluid and formation of a shear-thinning non-Newtonian fluid, Carboxyl Methyl Cellulose (CMC) from a capillary into different bulk fluids are experimentally investigated. A high speed camera is used to visualize the images of the drops and an image-processing code employed to determine the drop properties from each image. It was found that the properties of the water drops when they are drooped into the liquids bulk fluids such as toluene and n-hexane are almost the same while they differed substantially when they were drooped into the air bulk fluid. It is shown that during the formation of water drop in all three kinds of bulk fluids, the drop... 

    Simulation of a falling droplet in a vertical channel with rectangular obstacles

    , Article European Journal of Mechanics, B/Fluids ; Volume 68 , March-April , 2018 , Pages 108-117 ; 09977546 (ISSN) Merdasi, A ; Ebrahimi, S ; Moosavi, A ; Shafii, M. B ; Kowsary, F ; Sharif University of Technology
    Elsevier Ltd  2018
    Droplet microfluidic systems have attracted a large amount of research due to their numerous applications in biomedical micro-devices and drug discovery/delivery platforms. One of the most important problems in such systems is to investigate deformation, coalescence, and breakup of droplets within the channel. The present study demonstrates numerical simulation of a falling droplet subject to gravitational force in a channel with embedded rectangular obstacles. The lattice Boltzmann method incorporated using He–Chen–Zhang method for two phase flow is employed. Two rectangular obstacles with inverse aspect ratios are introduced to investigate the mechanism of breakup and deformation of the... 

    Careful parameter study to enhance the effect of injecting heavy fuel oil into a crossflow using numerical approaches

    , Article ASME 2018 5th Joint US-European Fluids Engineering Division Summer Meeting, FEDSM 2018, 15 July 2018 through 20 July 2018 ; Volume 2 , July , 2018 ; 08888116 (ISSN) ; 9780791851562 (ISBN) Darbandi, M ; Fatin, A ; Schneider, G.E ; Fluids Engineering Division ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2018
    The flow and spray parameters can have noticeable roles in heavy fuel oil (HFO) spray finesse. As known, the interaction between droplets and cross flow should be considered carefully in many different industrial applications such as the process burners and gas turbine combustors. So, it would be so important to investigate the effect of injecting HFO into a crossflow more subtly. In this work, the effects of various flow and spray parameters on the droplet breakup and dispersion parameters are investigated numerically using the finite-volume-element method. The numerical method consists of a number of different models to predict the droplets breakup and their dispersion into a cross flow...