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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
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...
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...
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) ; Mozafari, A. A ; Saidi, M. H ; Ghafourian, A ; Sharif University of Technology
2010
Abstract
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...
Designing of a static frequency observer for GMAW process in the globular transfer mode
, Article ICCAS 2010 - International Conference on Control, Automation and Systems, 27 October 2010 through 30 October 2010, Gyeonggi-do ; 2010 , Pages 286-289 ; 9781424474530 (ISBN) ; Haeri, M ; Doodman Tipi, A. R ; Sharif University of Technology
2010
Abstract
In the welding process, droplet detachment regularity is important for a good welding quality. The frequency of detachment is one of influential indices for assessing the quality of GMAW in the globular transfer mode. In this paper, a relationship is estimated for measuring droplet detachment frequency in the globular GMAW. The droplet detachment frequency is estimated with a curve fitting by the least squares error (LSE) method. By using short time frequency transform (STFT) we can extract the frequency contents from the mass of drop that is one of the states in the welding model
Simulation of SO2 absorption in a venturi scrubber
, Article Chemical Engineering Communications ; Volume 197, Issue 7 , Feb , 2010 , Pages 934-952 ; 00986445 (ISSN) ; Mohebbi, A ; Taheri, A ; Sharif University of Technology
2010
Abstract
In this study, a three-dimensional mathematical model, based on a nonuniform droplet concentration distribution, has been developed to simulate gas absorption in a venturi scrubber. The mass transfer process was illustrated by assuming the liquid phase as a combination of droplets and film. The flow, just as the annular two-phase flow, includes a flow of liquid film layer on the walls and a flow of gas and liquid drops in the core. Peclet number was determined using experimental data reported by Viswanathan et al. (1984) for distribution of droplets across the cross section of the scrubber. The mathematical model for gas absorption was justified by comparing the theoretical predictions with...
Globular structure of M2 high speed steel by thermomechanical treatment in the semisolid state
, Article Steel Research International ; Volume 81, Issue 5 , May , 2010 , Pages 381-386 ; 16113683 (ISSN) ; Aashuri, H ; Sharif University of Technology
2010
Abstract
The globular structure of M2 high speed steel in the rolled - annealed and as cast conditions was investigated in the semisolid state. Metallographic observations resulted in globular austenite particles that were surrounded by a liquid phase. Dissolution of various carbides in the austenite phase at semisolid temperatures led to grain boundary liquation and formation of near-spherical solid grains in a liquid matrix. Therefore, at the semisolid state, the solid particles were free from carbides. MC-type and M6C-type eutectic carbides re-precipitated at the grain boundaries during cooling of the samples from the semisolid temperature. The variation of shape factor versus holding time and...