Sharif Digital Repository

A droplet placed on the boundary of two solids with different wettabilities will move to the more wettable part. This is a well-known phenomenon and has been extensively used in a variety of processes and applications ranging from biological systems and ink jet printing to the commercial lab-on-a-chip. Because of its importance, many studies are conducted around this phenomenon. The difference between the equilibrium contact angles of the droplet on the two parts gives rise to an interfacial driving force which moves the droplet. Such a motion is not continuous as the droplet slides to the more wettable area, the driving force diminishes and consequently the droplet stops. A non-stop motion... 

Hydrophobic and superhydrophobic surfaces find many applications in different fields of science. The aerospace industry is one such field that can take the advantage of superhydrophobicity for anti-icing coatings. In order to make hydrophobic and superhydrophobic surfaces on hydrophilic materials, two-step process is usually need, at first, making a rough surface and then modifying it with hydrophobic coatings with low surface free energy. In this research, we have used glancing angle deposition (GLAD) RF sputtering technique to fabricate Teflon coated tungsten on glass substrate for obtaining hydrophobic surface. GLAD approach is a method to grow structures such as nanorods and zigzag... 

During production from gas condensate reservoirs, reservoir pressure decreses to lower than dew point pressure of the reservoir fluid. Consequently, condensates will form in near wellbore regions, which significantly decrease well productivity. One of the remediations that is recently proposed for solving this problem is wettability alteration of near wellbore region to gas wetting condition. In comparison to other methods, it provides a better permanency, which is its key advantage. The main purpose of this thesis is, quantitative, qualitative and modeling study of wettability alteration of rock to gas wetting condition and verification of modeling rsults for a reservoir rock sample. Also,... 

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... 

Although using solar energies have some limitations, such as low efficiency, require a large space and high starting cost, they are one of the most attractive source of energies. The reasons that cause efficiency of the solar panels decrease are contamination of dust particles on them and formation of water droplet on solar panel surface due to humidity of the air. Also, a solar panel can absorb only 25% of incident light and the others are reflected by the cover glass. Therefore, fabrication of a self-cleaning surface that can inhibit the aggregation of dust particles and also transparent that doesn’t reflect the incident light is crucial.In this work, we aim to obtain a transparent,... 

Liquid-Liquid coalescers are devices used for increasing the droplet size of the dispersed phase in continuous phase flow such as water droplets in oil flow. The scope of this work is a literature study on the coalescence phenomenon and CFD modeling in general. A mathematical model for simulating coalescence of water droplets in continuous oil flow by the use of different commercial coalescers. The basis for the model are plate-type coalescer and swirl-based coalescer. So, the simulations are done by Eulerian-Lagrangian method. Different aspects of the performance of the coalescers are studied on the rate of coalescence such as impact of changing droplet’s inlet diameters, impact of the... 

First by reviewing some built micropumps, the importance of rotary magnetohydrodynamic micropump has been highlighted. Then some information about the performance and rules applied to these specific micropumps has been provided. Based on the research, the necessity of using transient flow relations for analyzing the procedure of these micropumps would become crucial. The next step would be extracting the information out of dimensionlessrelations of magnetohydrodynamic theory and dimension less equations of momentum in transientsingle-phase fluid flow which is moved by theoverall Lorentzforce in between 2 parallel surfaces. It would be done in two state of using constantcurrent source and... 

Flows in porous media exist in many practical and research fields including water flow in soil, transport of pollution in soil, oil recovery engineering, and etc. Studying the multi-phase flows seems being too complex due to the interactions between fluids or between fluid and media in the porous media, wetting tendency of fluids, intrinsic permeability of the porous media, tortuosity of the flow’s path and etc. Hence, the field and laboratory studies of multi-phase flows is difficult, if not impossible. While numerical methods can handle many of these complexities, many of them are unable to simulate the micro-scale flows. On contrary, Lattice Boltzmann has no such shortcomings and even is... 

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... 

Titanium nano-oxide (TiO2) coatings have been used for self-cleaning, antimicrobial, and dust-proof designs. The degree of wetting of a solid surface with water in humid air depends on how the surface tension of the existing phases relates. The ratio between these tensions estimates the contact angle between a drop of water and the surface on which it is placed. A contact angle above 150 º is essential for surface overflow. In this study, 18 different combinations of titanium oxide and FAS, PDMS and PMS nanoparticles were obtained with a static contact angle of 165 to 150 º and a dynamic contact angle of 7 º.1 to 4.5 º. Following the measurement of water droplet slip speed on a sloping... 

In recent years, there have been a tremendous research performed in the field of sestems containing small scales. However, besides all advantages of such systems, microfluidic systems have extraordinary difficulties and pumping liquid drops as part of some of these systems has been very important issue. An approach related to flow control is use of surface acoustic waves (SAW), which is known as acoustofluidic device. So far, most researches have only qualitatively investigated acoustic flux phenomenon. On the other hand, computational research is ongoing more emphasizing on accuracy, optimization, and obtaining more detailed physical understanding of SAW applications. Investigation of the... 

It is aimed in this study to numerically investigate the effect of contact angle on the heat transfer coefficient in oil-water two-phase flow. For this purpose, the finite element method (FEM) is used to solve the unsteady Navier-Stokes and energy equations. The level set method is also used to capture the interface between the phases. In the first part of the study, two-phase flow of the water and calibration oil is considered in a T-junction geometry at contact angles of 5°, 40°, and 75°. It is observed that the flow patterns formed in the microchannel depend on the initial flow condition which results in the hysteresis phenomenon. Investigating the effect of wall contact angle on the... 

Recently, the researchers try to identify the application of nanofluids for wettability alteration. Changing the wettability of reservoirs, which gas injects to them, to gas wet can lead to enhanced oil recovery. Although several studies have been conducted to introduce proper nanofluids for altering the wettability of reservoirs to gas wet, there is not enough study to investigate the application of nanocomposites for wettability alteration of carbonate reservoirs. In this study, 20 nanoparticles with different compositional structures were synthesized, and then various nanofluids were prepared for the experimental survey. Also, the potential of these nanofluids for wettability alteration... 

With rising oil prices and predictions about the future of hydrocarbon reserves, issues of enhanced oil recovery and optimal production of existing reservoirs are of particular importance. In this study, molecular dynamics simulation was used to study the absorption of silica nanoparticles with surface groups at the interface of water and decane. The effect of surface chemistry of silica nanoparticles on the interface properties of water-decane with changing the surface groups was simulated. The initial surface factor of nanoparticle is hydroxyl (OH), which is called a hydrophilic surface agent. Nanoparticles were modified by methyl and ethyl surface agents to increase the hydrophobicity and... 

Today, increasing the productivity of reservoirs is more important than in the past, while the use of nanoparticles to change the wettability of rock and increase the recovery factor from the reservoir has been considered by many researchers. Despite previous studies on the use of nanoparticles to change the wettability of rock to gas-wet, the use of nanocomposites with super gas-wet at high temperature and pressure in the crude oil-gas system has rarely been considered. In this research, several nanocomposites with different structures have been synthesized in the laboratory and nanofluids with different formulations have been used to coat the rock thin sections and measure droplet contact... 

Wettability is the cause of many interactions today and is definitely effective in almost all processes where liquid and solid phases are in contact. Wetting controls by surface engineering can accelerate the process in the industry or improve the quality of daily life. Therefore, the fabrication of complex surfaces with a specific purpose and different wettability has attracted the attention of researchers. In this thesis, silica nanoparticles were synthesized to create roughness and reduce contact between surfaces and liquids at first. Then, using chemical compounds to reduce the surface energy, a transparent (94.20%) superhydrophobic and oleophobic coating was created on the glass. The...