Sharif Digital Repository

This is a theoretical study on heat and mass transfer in electrokinetically driven microfluidic devices with particular consideration to the lab-on-a-chip (LOC) applications. Special attention is given to disclose the effects of the fluid rheology and the aspect ratio of the rectangular geometry on the surface reaction kinetics and the temperature rise due to the Joule heating. Along this line, two different viscoelastic constitutive equations namely PTT and FENE-P models along with the power-law viscosity model are being considered. The secondary aims also include exploring the influences of the fluid properties variations throughout the channel cross section on the hydrodynamic and thermal... 

In the study of heat transfer in micro-channels, free and force convections are two limit cases and these two methods of heat transfer are combined together generally, so to achieve the most accurate informations about the flow field they should be considered in combination. In the first part of the thesis the fully developed slip flow mixed convection in vertical micro-ducts of arbitrary shapes is investigated.Uniform axial heat flux and uniform peripheral wall temperature (H1) is considered. The method considered is analytical-numerical in which the governing equations and three of the boundary conditions are exactly satisfied but the remaining slip boundary condition on the duct wall... 

In this thesis, two-phase flow modeling in two-dimensional micro channel with liquid injection from wall is studied. Two models as "separated flow model" and "two-phase mixture flow" is developed. The separated flow model considers gas and liquid flow in separated films of flow with an interface between the phases. The two-phase mixture flow considers equivalent fluid mixture from gas and liquid with local modification in density and viscosity. Governing equations include continuity and momentum solved with control volume method. SIMPLE algorithm's been used to pressure-velocity linked equations. Velocity and pressure profiles plotted for mentioned models at a given situations. By comparing... 

Microfluidics is a field of science that studies micron-scale characteristics of fluids. In this scale fluids show fascinating behavior far beyond our expectation compared to their large-scale counterparts. One of such peculiar behavior is the mixing of two different liquids flowing inside a microchannel. Due to low Reynolds number, the flow inside such a channel would be dominated by laminar behavior. In this regime mixing of the fluids is only mediated by molecular diffusion which is a rather slow process. In the current thesis, we utilized the rotating ability of optical tweezers to construct an active micromixer for Microfluidics. In order to do this we used birefringent microbeads. The... 

EOR (oil enhanced recovery) is very important as oil is a nonrenewable resource. Depending on the characteristics of the rock formation, primary production can result in the recovery of up to 20% of the oil originally in the rock. This means that at least 80% of the oil may remain in the rock unless additional technology is used to increase the recovery. Before finding best way to do for EOR, scientists must study properties of different porous media that oil is trapped between its grains. Most of research and studies investigate networks of porous media but this work focused on oil movement through a pore space in porous media lonely not in network by waterflooding. Studying a pore space is... 

The purpose of this research is the synthesis of nanoparticles using micro fluid glass.The microfluidic glassy building is studied. Glass microfluidic microchannels making hydrophobic the continuing experiments carried out so that the water droplets in the organic phase and at the end of nanoparticles should be synthesized. Tests hydrophobic microchannels and water droplets in the organic phase was formed. In order to ensure an escape water contact angle and FTIR micro-channel test is taken and to avoid the droplets merged with each of surfactant SDS was used. In the end, DLS and FESEM nanoparticles synthesized using the tests have been evaluated and the concentrations of reactants and flow... 

The microfluidic fuel cell or laminar flow-based fuel cell is a membrane-less fuel cell which typically consists of two electrodes mounted within a T- or Y-shaped microchannel. Aqueous fuel and oxidant are introduced from the two inlets of the channel and flow together side-by-side toward the end of the channel. The Reynolds number in the microchannel is low, and hence viscous forces are dominant over the inertial forces. This causes the anolyte and catholyte form a co-laminar flow inside the microchannel which is required to maintain the separation of the fuel and oxidant and limit the reactions to the appropriate electrodes. In this work, a comprehensive numerical model of the microfluidic... 

The integrated development of small-scale electronic and mechanical systems has drawn attention, since they lead to increase in speed and decrease in volume of industry dimensions in the manufacturing sector. That is why microelectromechanical systems are highly considered. MEMS are widely used in Microfluidic systems that can be used in medicine, biology and drug injection. Due to the fact that consistent fluid velocity is necessary in biological applications, electroosmotic flow is more important than ever. To investigate the behavior of biofluids, Newtonian models cannot be used and it is required to use models that predict the behavior of these fluids accurately. In this research... 

The effect of using backpressure of air injection in a microchannel on internal flow pressure drop were investigated in this study. Multiphase flows are commonly encountered in gas and oil industries. Flow fields in production operations are often complex and include multiphase flows of gas and liquid. Previously, because of their complex nature, these flow patterns have been mostly investigated only experimentally and empirical correlations based on the experimental data. From another point of view, it is almost impossible to experimentally realize all the flow conditions for each of the flow patterns. Nowadays computer facilities provide the tool to construct and use large-scale... 

With the advancement of the industry, microscale devices use due to its unique characteristics. On the other hand, it is essential to find ways to reduce drag inside microchannels because of The importance of energy. One of the methods is to optimize the contact surface using structured geometric surfaces. These hydrophobic surfaces reduce drag by trapping the air in roughness and creating a two-phase flow. The purpose of this project is to reduce the drag within the microchannel using structured geometric surfaces for non-Newtonian and multiphase flows. In most previous studies, with simplification, Newtonian and two-phase flows have been investigated. While most industrial fluids show... 

This research concerns investigating the behavior of two-phase flow in the inlet and outlet of the microchannels.Both the droplet based and the continuous microfluidics are considered. For the continuous system whenthe minor fluid enters the microchannel, due to ratio of viscosity of two fluids, viscous folding occurs.Viscous folding phenomena is similar to the buckling phenomena in solids.This means that the viscosity of the fluid, which is applied to two sides of the fluid layer, causes folding the fluid layer and changing the shape of it. For the study we employ a VOF based numerical routine. In order to verify numerical results, the grid and the time step independenciesare checked. In... 

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... 

In recent years, desulfurization has received much attention due to its devastating environmental effects. The existence of sulfur compounds has effects such as corrosion, poisoning of catalysts, reduction of heat of combustion and reduction of price. Sulfur compounds in hydrocarbon fuels also produce sulfur oxides caused by combustion then they enter the atmosphere, and cause acid rain. Acid rain dissolves building materials, poisons lakes, and destroys forests. Therefore, removing sulfur or converting it to less harmful substances is one of the most important processes in refineries. The method studied in this research is the use of adsorption desulfurization method by microchannel which... 

When the fluid passes through the microchannel, some energy is lost due to drag force and pressure drop. One of the methods used in the last few decades to optimize energy consumption is creating superhydrophobic surfaces in microchannels. These surfaces, with their features such as increasing the contact angle and reducing the contact angle hysteresis, can reduce energy loss, which is due to the presence of unevenness on the surface, and by trapping air and creating a two-phase flow, they reduce the drag force. On the other hand, the air trapped inside these irregularities will also affect the heat transfer of the passing fluid in the microchannel, which by creating resistance in the...