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Breakup of droplets in micro and nanofluidic T-junctions
, Article Journal of Applied Fluid Mechanics ; Volume 6, Issue 1 , 2013 , Pages 81-86 ; 17353572 (ISSN) ; Moosavi, A ; Sharif University of Technology
2013
Abstract
We employ numerical simulations to investigate the breakup of droplets in micro- and nanoscale T junctions, which are used to produce small droplets from a large droplet. For this purpose a Volume f Fluid (VOF) based method is used and for verifying the reliability of the numerical outcomes, the results are compared with the available experimental and analytical results. Our results reveal that breakup time and breakup length of the droplets play important roles in handling these systems optimally. Our results also indicate that for nanoscale Tjunctions by increasing the capillary number the performance increases while for the micro-scale systems there is a specific capillary number for...
Study of droplet behaviour along a pulsed liquid-liquid extraction column in the presence of nanoparticles
, Article Canadian Journal of Chemical Engineering ; Volume 91, Issue 3 , 2013 , Pages 506-515 ; 00084034 (ISSN) ; Bahmanyar, A ; Molavi, H ; Bastani, D ; Mozdianfard, M. R ; Bahmanyar, H ; Sharif University of Technology
2013
Abstract
In this article, droplet size and its distribution along a pulsed liquid-liquid extraction column, is studied where SiO2 nanoparticles with concentrations of 0.01, 0.05 and 0.1vol.% and different hydrophobicities are applied to the dispersed phase. Using ultrasonication, nanoparticles were dispersed in kerosene as the base fluid. Nanofluids' stability was ensured using a UV-vis spectrophotometer. Some 22,000 droplets were measured by photographic technique and results were compared with systems containing no-nanoparticles (Water-Acetic acid-Kerosene). Addition of nanoparticles changed the droplet shape from ellipsoidal to spherical. Also, there was a marked influence on droplet breakage and...
Experimental investigation of rheological and morphological properties of water in crude oil emulsions stabilized by a lipophilic surfactant
, Article Journal of Dispersion Science and Technology ; Volume 34, Issue 3 , Feb , 2013 , Pages 356-368 ; 01932691 (ISSN) ; Ramazani, S. A. A ; Taghikhani, V ; Ghotbi, C ; Sharif University of Technology
2013
Abstract
Rheological behavior of two crude oils and their surfactant-stabilized emulsions with initial droplet sizes ranging from 0.5 to 75 μm were investigated at various temperatures under steady and dynamic shear testing conditions. In order to evaluate the morphology and Stability of emulsions, microscopic analysis was carried out over three months and average diameter and size distribution of dispersed droplets were determined. The water content and surfactant concentration ranged from 10 to 60% vol/vol and 0.1 to 10% wt/vol, respectively. The results indicated that the rheological properties and the physical structure and stability of emulsions were significantly influenced by the water content...
Numerical investigation of cone angle effect on the flow field and separation efficiency of deoiling hydrocyclones
, Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 49, Issue 2 , February , 2013 , Pages 247-260 ; 09477411 (ISSN) ; Maddahian, R ; Farhanieh, B ; Sharif University of Technology
2013
Abstract
In this study, the effect of cone angle on the flow field and separation efficiency of deoiling hydrocyclones is investigated taking advantage of large eddy simulation. The dynamic Smagorinsky is employed to determine the residual stress tensor of the continuous phase. The method of Lagrangian particle tracking with an optimized search algorithm (closest cell) is applied to evaluate the separation efficiency of deoiling hydrocyclone. Simulations are performed on a 35-mm deoiling hydrocyclone with the three different cone angles of 6, 10 and 20 degree. The numerical results revealed that the changes in the cone angle would affect the velocity and pressure distribution inside hydrocyclone, and...
Coarsening dynamics of nanodroplets on topographically structured substrates
, Article Journal of Physics Condensed Matter ; Volume 25, Issue 4 , 2013 ; 09538984 (ISSN) ; Moosavi, A ; Sharif University of Technology
2013
Abstract
Employing a biharmonic boundary integral method with linear elements, coarsening dynamics of nanodroplets on topographical step heterogeneity is investigated. It is shown that the step height and droplet configuration have an influential effect on the dynamics. Increasing the step height slows down the process while locating the droplets close to the step boosts the coarsening rate. Considering a slip boundary condition enhances the dynamics and reveals a transition in the droplet migration direction. Our results reveal that increasing the surface wettability weakens the dynamics. Various types of the disjoining pressure over the step are also considered and their effects on the coarsening...
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) ; Moosavi, A ; Sharif University of Technology
2012
Abstract
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
On the motion of Newtonian and non-Newtonian liquid drops
, Article Scientia Iranica ; Volume 19, Issue 5 , 2012 , Pages 1265-1278 ; 10263098 (ISSN) ; Maleki, A ; Firoozabadi, B ; Afshin, H ; Sharif University of Technology
2012
Abstract
In the present study, the motion of Newtonian and non-Newtonian liquid drops has been investigated experimentally. In order to investigate the effect of bulk fluid on drops, we have used water and air, as two fluids with different properties, and various industrial and biological applications. Image processing is utilized to analyze the images obtained by a high speed camera. The research has been separated into two parts. The first part has been devoted to the experiments in which air is the bulk fluid, and the second is related to the experiment carried out in water. The range of Reynolds number is, approximately, 50
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) ; Sharif University of Technology
2012
Abstract
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 new method to control heat and mass transfer to work piece in a GMAW process
, Article Journal of Process Control ; Volume 22, Issue 6 , 2012 , Pages 1087-1102 ; 09591524 (ISSN) ; Haeri, M ; Sharif University of Technology
2012
Abstract
It is proposed to employ melting rate, heat input, and detaching droplet diameter as controlled variables to control heat and mass transfer to work piece in a gas metal arc welding process. A two-layer architecture with cascade configuration of PI and MPC controllers is implemented to incorporate existing constraints on the process variables, improve transient behavior of the closed-loop responses and reduce interaction level. Computer simulation results are presented to indicate usefulness of the proposed controlled variables selection and applying two-layer control architecture to control heat and mass transfer to work piece
The effects of SiO 2 and K 2O on glass forming ability and structure of CaOTiO 2P 2O 5 glass system
, Article Ceramics International ; Volume 38, Issue 4 , 2012 , Pages 3281-3290 ; 02728842 (ISSN) ; Nemati, A ; Eftekhari Yekta, B ; Hamnabard, Z ; Sharif University of Technology
2012
Abstract
The effects of SiO 2 and K 2O were investigated on the glass forming ability (GFA) and structural characteristics of CaOTiO 2P 2O 5 system. Differential thermal analyzer (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR and 31P magic angle spinning NMR methods were applied for characterizations of the system. Unwanted crystallization in the initial three components base glass composition was observed by adding SiO 2 and crystalline phases such as TiP 2O 7, rutile (TiO 2) and cristobalite (SiO 2) were formed in it. The results showed that K 2O prevents crystallization of glasses and promotes the formation of glass. FT-IR and X-ray diffraction showed that the addition...
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) ; 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...
Determination of 2,4-D in environmental samples by three phases directly suspended LPME combined with HPLC-UV
, Article Analytical Methods ; Volume 3, Issue 10 , 2011 , Pages 2261-2267 ; 17599660 (ISSN) ; Roshan, S ; Asgharinezhad, A. A ; Najafi, E ; Abedi, H ; Tavassoli, N ; Lotfi Zadeh Zhad, H. R ; Sharif University of Technology
Abstract
Experimental design of directly suspended droplet liquid-liquid-liquid microextraction has been used to determine residue of 2,4-D, in environmental water samples. A free suspended droplet of 5.5 μL of receiving phase is delivered to the top-center position of 1-Octanol, which is an immiscible organic solvent, floating on the top of a 2.5 mL aqueous sample while being agitated by a stirring bar to create a mild vortex at the center of the vial. Central composite rotatable design has been used for studying the effect of the parameters, the factors interacting with each other and finding the optimum condition. The chromatographic separation was accomplished on a shim-Pak C18 column using a...
Droplet breakup in an asymmetric microfluidic T junction
, Article European Physical Journal E ; Volume 34, Issue 8 , 2011 ; 12928941 (ISSN) ; Moosavi, A ; Sharif University of Technology
2011
Abstract
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...
Dynamics of nanodroplets on wettability gradient surfaces
, Article Journal of Physics Condensed Matter ; Volume 23, Issue 8 , February , 2011 ; 09538984 (ISSN) ; Mohammadi, A ; Sharif University of Technology
2011
Abstract
A lubrication model is used to study the dynamics of nanoscale droplets on wettability gradient surfaces. The effects of the gradient size, size of the nanodroplets and the slip on the dynamics have been studied. Our results indicate that the position of the center of mass of the droplets can be well described in terms of a third-order polynomial function of the time of the motion for all the cases considered. By increasing the size of the droplets the dynamics increases. It is also shown that the slip can considerably enhance the dynamics. The results have been compared with the results obtained using theoretical models and molecular dynamics simulations
Effect of RE elements on the microstructural evolution of as cast and SIMA processed Mg-4Al alloy
, Article Journal of Alloys and Compounds ; Volume 509, Issue 5 , February , 2011 , Pages 1567-1572 ; 09258388 (ISSN) ; Khomamizadeh, F ; Sharif University of Technology
2011
Abstract
In the present article, the effect of Rare Earth elements on the microstructural development of as cast and semisolid Mg-4Al alloy produced by SIMA process is studied. Investigation conducted by metallographic observation, scanning electron microscope and quantitative metallographic methods. Results showed that alloy's dendrites turn into larger fully dendritic shape with sharp and narrow arms from equiaxed rosette type as the amount of RE elements increased from 0 through 4%. The effect of RE elements on the microstructure of the treated-alloys was detectable through elimination of vast number of intragranular liquid droplets as well as by decreasing kinetic of microstructural changes. It...
Formation of liquid bridges between porous matrix blocks
, Article AIChE Journal ; Volume 57, Issue 2 , 2011 , Pages 286-298 ; 00011541 (ISSN) ; Hassanzadeh, H ; Sharif University of Technology
2011
Abstract
It is widely accepted that, in fluid flow and transport in fractured porous media, there exists some degree of block-to-block interaction that may lead to capillary continuity. The formation of liquid bridges causing interaction between blocks will affect oil recovery from naturally fractured reservoirs. However, the accurate modeling of the growth and detachment of liquid bridges that may cause capillary continuity between matrix blocks remains a controversial topic. In an attempt to improve our understanding of the problem, a mechanistic model is developed in this work for the formation of liquid bridges between porous blocks. The proposed model considers growth and detachment of pendant...
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) ; Moosavi, A ; Kazemzadeh Hannani, S ; Sharif University of Technology
Springer New York LLC
2015
Abstract
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 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) ; Moosavi, A ; Hannani, S. K ; Sharif University of Technology
American Physical Society
2015
Abstract
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...
Transport in droplet-hydrogel composites: response to external stimuli
, Article Colloid and Polymer Science ; Volume 293, Issue 3 , March , 2015 , Pages 941-962 ; 0303402X (ISSN) ; Sharif University of Technology
Springer Verlag
2015
Abstract
Determination of effective transport properties of droplet-hydrogel composites is essential for various applications. The transport of ions through a droplet-hydrogel composite subjected to an electric field is theoretically studied as an initial step toward quantifying the effective transport properties of droplet-hydrogel composites. A three-phase electrokinetic model is used to derive the microscale characteristics of the polyelectrolyte hydrogel, and the droplet is considered an incompressible Newtonian fluid. The droplet-hydrogel interface is modeled as a surface, which encloses the interior fluid. The surface has the thickness of zero and the electrostatic potential ζ. Standard...
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) ; Taeibi Rahni, M ; Azwadi Che Sidik, N ; Sharif University of Technology
Taylor and Francis Ltd
2015
Abstract
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