Sharif Digital Repository

Loess as a subcategory of collapsible soils is a well-known aeolian deposit generally characterized as a highly-porous medium with relatively low natural density and water content and a high percentage of fine-grained particles. Such collapsible soil sustains large stresses under a dry condition with natural water content. However, it can experience high and relatively sudden decreases in its volume once it reaches a certain water content under a certain load and therefore, the natural condition of the soil might not be suitable for construction if the possibility of the exposure of the soil to excessive water exists during the lifetime of the project. This research presents the utilization... 

Mixing in droplets is an essential task in a variety of microfluidic systems. Inspired by electrokinetic mixing, electric field-induced hydrodynamic flow inside a charged droplet embedded in an unbounded polyelectrolyte hydrogel is investigated theoretically. In this study, the polyelectrolyte hydrogel is modeled as a soft, and electrically charged porous solid saturated with a salted Newtonian fluid, and the droplet is considered an incompressible Newtonian fluid. The droplet-hydrogel interface is modeled as a surface, which is located at the plane of shear, with the electrostatic potential ζ. The fluid inside the droplet attains a finite velocity owing to hydrodynamic coupling with the... 

The high reactivity of the carbonate rocks at various pH makes it difficult to evaluate the wettability, hence to find the recovery mechanisms behind modified waterflood in carbonate reservoirs. More recently, the streaming potential measurement is introduced as a method of electrokinetic phenomena more relevant to the subsurface systems. Regarding few experimental studies and in order to improve our understanding on streaming potential measurement, the electrokinetic studies on quartz and calcite surface were conducted as a function of pH in the range of 1.5–11.5 using an in-house novel setup of streaming potential measurement. High sensitivity of streaming potential coupling coefficient to... 

Identifying tumor cells from a pool of other cells has always been an appealing topic for different purposes. The objective of this study is to discriminate circulating tumor cells (CTCs) from blood cells for diagnostic purposes in a novel microfluidic device using two active methods: magnetophoresis and dielectrophoresis. The most specific feature of this device is the differentiation of CTCs without labeling them in order to achieve a more reliable and less complicated method. This device was analyzed and evaluated using finite element method. Four cell lines are separated in this device containing red blood cells, platelets, white blood cells, and CTCs. Primarily, red blood cells and... 

In recent years there have been many efforts to develop a hydrogen energy system in Iran. For instance, the Iranian fuel cell steering committee conducted a project and determined some targets to implement hydrogen in different sectors, especially transportation. In this paper, the costs of building stations and the levelized cost of hydrogen for two types of stations, SMR and electrolysis, with various sizes and capacity factors have been investigated. Also, in the case of electrolysis, hydrogen cost sensitivity to the price of electricity has been examined. According to the cost analysis conducted here, it is understandable that hydrogen costs ($/kg) vary considerably based on station... 

The dispersion of a neutral solute band by electrokinetic flow in polyelectrolyte layer (PEL)-grafted rectangular/slit microchannels is theoretically studied. The flow is assumed to be both steady and fully developed and a first-order irreversible reaction is considered at the wall to account for probable surface adsorption of solutes. Considering low electric potentials, analytical solutions are obtained for electric potential, fluid velocity and solute concentration. Special solutions are also obtained for the case without wall adsorption. To track the dispersion properties of the solute band, the generalized dispersion model is adopted by considering the exchange, the convection and the... 

In order to decrease CO 2 emission into the atmosphere and develop renewable energy sources for carbon capture, an integrated system is considered for co-production of electricity and methanol. In this research, methanol synthesis unit through captured CO 2 from fossil fuel power plant and produced H 2 from water electrolysis unit by wind renewable energy is developed. An oxy-fuel combustion carbon capture method is considered in large scale Matiant power plant based on utilization of oxygen from water electrolysis unit. Technical and economical analysis of the proposed system shows that when the price of natural gas is 7.8US$/GJ, the total CO 2 avoided cost is 93US$/(tonne of CO 2) and... 

This paper presents an analysis of the combined electro-osmotic and pressure-driven axial flows of viscoelastic fluids in a rectangular microchannel with arbitrary aspect ratios. The rheological behavior of the fluid is described by the complete form of Phan-Thien–Tanner (PTT) model with the Gordon–Schowalter convected derivative which covers the upper convected Maxwell, Johnson–Segalman and FENE-P models. Our numerical simulation is based on the computation of 2D Poisson–Boltzmann, Cauchy momentum and PTT constitutive equations. The solution of these governing nonlinear coupled set of equations is obtained by using the second-order central finite difference method in a non-uniform grid... 

Models play an important role in fuel cell design and development. One of the critical problems to overcome in the proton exchange membrane (PEM) fuel cells is the water management. In this work a steady state, two-dimensional, isothermal model in a single PEM fuel cell using individual computational fluid dynamics code was presented. Special attention was devoted to the water transport through the membrane which is assumed to be combined effect of diffusion, electro-osmotic drag and convection. The effect of current density variation distribution on the water content (λ) in membrane/electrode assembly (MEA) was determined. In this work the membrane heat conductivity is considered as a...