Sharif Digital Repository

The use of stepped weirs dates back at least 3500 years. In this research, the hydrodynamics of gabion stepped weirs have been investigated as a three-dimensional simulation of two-phase flow air-water using Flow3D software and the method of computational fluid dynamics (CFD) analysis. In order to solve the Reynolds-Averaged Navier-Stokes (RANS) equations, the RNG turbulence model (k-ε) was used and the free surface elevation of fluid was determined by the volume of fluid (VOF) method. The experimental results of Wutrish and Chanson (2014) over gabion stepped weirs are used to validate the numerical model simulations. Gabion stepped weirs with steps of 3, 7.5, and 10 cm in height, as well as... 

In this study, the factors affecting cavitation in the crest of an ogee spillway were investigated. One of the factors affecting the occurrence of cavitation on the ogee crest is the ratio of the head to the design head. As the head ratio increases, the probability of cavitation on the crest increases. The value of the head is also an effective parameter for the occurrence of cavitation. The spillway crest curve is also one of the factors affecting the occurrence of cavitation on the ogee-crested spillways. In this study, the ogee crested spillway that consists of three circular arcs upstream has been investigated. 5 different head ratios have been used. For this study, OpenFOAM software,... 

The scarcity of potable water is one of the world's challenges. In the Middle East, this crisis is even worse and as a consequence, the most aggregation of desalination plants has been constructed in this area. However, brine effluent discharged from these plants entails serious environmental issues. Despite the extensive studies about the investigation of dilution and the area which faces the brine discharges as submerge jets, there are a few experimental investigations with a focus on the injecting brine discharge into the shallow environment. Whereas the Persian Gulf's coastal environment is shallow. Moreover, there is a huge construction of desalination held in this area. Accordingly,... 

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... 

The drop motion in fluid and the mass transfer is one of the most interesting and favorite topics that has attracted the attention of many researchers. Knowing the functions of the factors affecting the deformation and the process of mass transfer and the effects of the addition of the surfactant, improve the efficiency of the related industrial processes.In this regard, the present study examines how the shape and speed of a moving Newtonian drop in a Newtonian fluid, the mass transfer of soluble material from inside the drop to the surrounding fluid and also the study of the effect of surfactant on the dynamics of moving droplet is studied numerically. During the drop movement, the... 

Oil/water separation is an important field, not only for scientific research, but also for environmental, economic, and social issues. On the one hand, oily wastewater, resulting from industries such as steel, aluminum, food, textile, leather, petrochemical and metal finishing, has become the most common pollutant all over the world. On the other hand, frequent oil spill accidents are of great concern since the discharge can lead not only to serious environmental pollution, but also a great loss of energy.
In crude oil removing water is necessary due to reducing corrosion, increasing thermal values of fuels obtained from crude oil, preventing catalists from destruction by water and... 

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... 

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... 

Sedimentation tanks are one of the important and costly stages of water treatment process in which remained particles from previous stages settle down due to gravity force. In this research, the hydrodynamics of secondary settling tanks without and in the presence of particles is numerically investigated using VOF method in order to simulate the interphase using RNG k-ε for turbulence modelling. The simulations are performed by means of open-source code OpenFoam, and the code is developed to model particles in the flow. The calculated velocity profiles using VOF method show a reasonable agreement with the experimental data. Comparing the concentration profiles with experiments shows the... 

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... 

The stirred tank is one of the oldest device that widely used in different industrial. a special kind of stirred tank that clled bioreactor refer to any device which supplies required biological, biochemical and biomechanical engineered product. Since the aim of bioreactor is produce of desired biological product, it is essential to accurate monitoring internal and external transfer of nutrient, heat transfer, fluid velocity, Strain stress and medium PH. good design and application of bioreactor depend on product, organism, conditions for produce desired product and scale of produce. also cost of capital and function cost are important in bioreactor design. one of the most important... 

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... 

In the present work, the deformation and collapse of a single cavitating bubble near solid boundaries is simulated by solving the preconditioned, homogenous, multiphaseNavier-Stokes equations. Up to now, all studies in the literature performed by the volume of fluid (VOF)approach to capture the bubble surface have been based on the pressure-based category in which the flow variables are calculated through solving the Poisson equation. Here, the density-based category is applied and the solution methodology is based on the artificial compressibility approach. The compressible form of the Navier-Stokes equations is applied inside the bubble and the liquid phase is assumed to be incompressible.... 

A bioreactor can refer to any device or system constructed on engineering basis and has an active biological medium. This medium includes aerobic and non-aerobic reactions in which organisms and the theire produced substances have the main role. One of the applications of bioreactors is to provide an appropriate medium for animal and plant cell culture and growth. Nowadays many biological processes in high volume scales are carried out in stirred tank bioreactors. In these bioreactors oxygen transfer is usually increased by increasing turbulence which is necessary for mixing nutrients and keeping the homogeneity of the medium. However, there are some limitations for increasing the stirring... 

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... 

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... 

Mesoscopic hydrodynamic equations are solved employing a VOF based method to investigate the equilibrium shape of nanodroplets positioned over various topographic geometries of the supporting substrate for three-dimensional systems. By taking into account liquid-liquid and liquid-solid interactions a complex distribution for inter-molecular forces over the substrates (the disjoining pressure) is observed. In this research we show that motion of nanodroplets not only caused by contact angle difference in drplets two sides, but also depend on disjoining pressure parameters.Geometries with increasing complexities, from wedges to three dimensional edges and wedges, were explored with the main... 

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... 

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...