Sharif Digital Repository

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... 

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.... 

In the present study a through comparison has been made between different free surface modeling methods. Methods for improving the current schemes are analyzed and studied. Among different proposed methods and based on the current in-house CFD solver’s limitations and capabilities, the Flux-Blending Strategy has been used for interface capturing in the framework of the Finite Volume Method (FVM). The proposed scheme has been coupled with other algorithms for improving the capabilities and functionality of the general computational fluid dynamic software, NUMELS, in order to simulate fluid flows with sharp interface.
The improved interface capturing scheme uses the continuous switching... 

In this research, droplet motion in symmetric and asymmetric junctions in micro and nano scales was investigated. Droplets motion in symmetric and asymmetric junctions have many applications in many industries such as chemical and pharmacy. In this research symmetric T-junction in micro and nano sizes was simulated numerically in 2D and 3D formes. Also asymmetric T-junction (with unequal width branches) was simulated numerically in two cases, 2D and 3D. In the asymmetric T-junction, also an analyrical theory was developed. Numerical simulation was performed by using VOF techniqe and analytical theory was developed by thin film theory. For verifying the accuracy of numerical solution, grid... 

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... 

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... 

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... 

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... 

Dense underflows are continuous currents that move down-slope due to their density being heavier than that of the ambient water. This difference between the dense fluid and environment fluid can be due to temperature difference, chemical materials, solved materials or suspend solid particles. In these currents, the effect of buoyancy force is produced by this difference density. In this research, many experiments performed in different flow rates, slopes and concentrations to understand the current structure and turbulence specification of the salt solution density currents and particle-laden density currents. Acoustic Doppler Velocimeter is used to measure the velocity fluctuations. 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... 

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,...