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... 

In this work, the cone-jet mode of electrospray is simulated by a two phase solver in OpenFoam software. For this aim firstly, breakup of a liquid jet is examined without applying any electric potential to the injecting capillary and results are compared with other works to evaluate the two phase solver. Next with applying electric potential, the whole evolution of cone-jet in time is simulated. One of the most important issues in this mode is the minimum potential that needs to form a stable cone-jet in different flow rates. These minimum voltages are obtained in various flow rates and compared with other experimental and computational works. Result shows that with increasing flow rate the... 

In this investigation Magneto Mercury Reciprocating Micrpump (MMRM) the combination of Magneto-Hydrodynamic and Reciprocating micropumps has been analyzed. To achieve the analytical and numerical solution of one-tank and three-tank MMRM, the momentum, continuity, volume fraction and magnetohydrodynamic equations have been presented. The dimensionless analytical solution of one-phase and two-phase three dimensional MHD flow in the condition of using constant current and potential electrical source, has been offered.
The boundary between mercury and air has been tracked via VOF method in OpenFOAM software. VOF equation has been solved by explicit method with variable time step and maximum... 

Drop penetration into the capillary tube, as a classical problem, has been studied over 100 years. But there are a few studies that investigate forced impregnation of capillary tubes, which has major application in coating, inkjet printing and rain drop penetration into the soil, have been made. A comprehensive numerical investigation on millimeter droplet impact dynamics on a thick capillary tube with micrometer sized pore is conducted and validated against experimental data. This work is extended to oblique impact of drops into pores and normal impact on nanoscaled pores. We apply the finite volume numerical method to solve the time-dependent governing equations of continuity, momentum in... 

Continuous separation processes in microfluidic devices experienced a steep rise in attention during the last two decades. Among the different separation processes, liquid-liquid extraction especially benefits from the short molecular diffusion distance and large specific interfacial area, as these are advantageous for effective mass transport. In the present study, glass-based microfluidic devices have been fabricated utilizing laser ablation and wet chemical etching methods then experiments and numerical simulation were carried out to investigate hydrodynamic behavior of fluid flow in Y-junction microfluidic. In order to achieve phase separation at the end of the microchannel, a phase... 

Entrance of air to close water conduits occurs in many ways. This phenomenon makes displeasing effects on water transport structures. Two-phase flows in closed conduits are studied experimentally, numerically and theoretically. Even after decades, due to the complexity of the subject, these studies still require development and reformation. Numerical and theoretical two-phase models are often limited to a special regime of flow."Volume Of Fluid"(VOF) is a model for non-mixing two-phase flows. "Fluent" software uses this model in this field of flows. Volume of fluid is used successfully in some problems like dam break or rising bubbles. Main disadvantage of this model is distribution of the... 

Airlift pumps are devices for lifting liquid phase incorporating the gas phase to be injected in the bottom of the liquid column. Gas-liquid two-phase flow being the main part of the flow through these systems, flowing in vertical pipes of airlift pumps has different regimes namely bubbly, slug, churn and annular. Generally these regimes appear starting from bubbly to annular from bottom to top of the upriser pipe. Gas/liquid multiphase flows occur in a wide range of natural and man-made situations such as boiling heat transfer, cloud cavitation, bubble columns and reactors in the chemical industry, cooling circuits of power plants, spraying of liquid fuel and paint, emulsions, rain, bubbles... 

Drop formation from the tip of a nozzle and its motion in bulk fluid is an interesting and practical process which has widely turned researchers’ attention. Investigation into the governing physics and effective parameters on formation, deformation and motion of a drop increases the efficiency of the related industrial processes. Thus in the present study, in order to simulate this process, full Navier-Stokes equations solved by the Volume of Fluid (VOF) method in an axisymmetric domain using Fluent software as the solver. In this research, the effects of Weber number (the proportion of inertial force to surface tension force) and Ohnesorge number (which refers to the proportion of viscous... 

Mass transfer of a drop moving in a bulk fluid is an interesting subject which has attracted a lot of attention. Understanding effective parameters in this process would be helpful in order to increase the efficiency of the industrial processes related to mass transfer. In this research, the deformation and mas transfer of a moving drop was studied numerically. Navier-Stokes equations and concentration equation were solved separately with a VOF method in an axisymmetric domain using Fluent software. Comparision between numerical results and former experimental results proves the accuracy of the modelling in both fields of deformation and mass transfer. Moreover, effects of the physical... 

One of the key features of multiphase flow applications is the creation of as little liquid droplets as possible. For example, it is important to use combustion to burn liquid fuels in combustion chambers, fuel-air mixing and complete evaporation of fuel. Liquid fuel should be converted into small droplets and then mixed with air quickly and evaporated. This challenge has been investigated using injectors of various designs and is still being investigated. One of the injectors used is injectors where both gas and liquid are injected into the injector and supplemented with each other. These injectors are referred to as focal injectors, in which gas flows through a typical orifice to...