Sharif Digital Repository

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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...