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    Experimental Study of Microbubbles Generation as a Contrast Agent in Blood, to Determine the Blood Flow by Echo-PIV Method

    , M.Sc. Thesis Sharif University of Technology Salari, Alinaghi (Author) ; Shafiee, Behshad (Supervisor)
    Abstract
    Today microbubbles are broadly used as ultrasound contrast agents. These bubbles enhance the image resolution of B-mode pictures. Flow focusing in microchannels could provide us the goal of one-size bubbles generation. Microbubbles could use as tracers in Echo_PIV method to determine the velocity profile in main body vessels such as carotid. In this paper we introduce a new production method to fabricate a low-cost microchannel for preparing Microbubble contrast agents (less than 50 microns) by using some surface active agents and a viscosity enhancing material to obtain appropriate Microbubbles with desired life time and stability for any in vitro infusion for velocity measurement. By... 

    Electroosmotic Flow in Microchannels

    , M.Sc. Thesis Sharif University of Technology Lesani, Mostafa (Author) ; Saeedi, Mohammad Saeed (Supervisor)
    Abstract
    The present study examines both Direct Current (DC) and Alternating Current (AC) electroosmotic flows in a parallel plate microchannel. The method consists of a central finite difference scheme for spatial terms and a forward difference scheme for the temporal term. Asymmetric boundary conditions are assumed for Poison-Boltzmann equation used to determine the electric double layer (EDL) potential distribution. The potential distribution is then used to evaluate the velocity distribution for both DC and AC electroosmotic flows. The velocity distributions are obtained by applying slip boundary conditions on the walls to account for probable hydrophobicity of the surfaces. After determining the... 

    Modeling and Simulation of Tansport Phenomena in Irregular Microchannels

    , M.Sc. Thesis Sharif University of Technology Nikouei, Maryam Sadat (Author) ; Molaie Dehkordi, Asghar (Supervisor)
    Abstract
    In this article, the problem of mixed convection in vertical rectangular microchannels for both regular fluids and nanofluids have been solved, using the CFD technique in the entrance regions of momentum and heat transfer taking in account the influences of viscous heating, inertial force and sleep conditions. In case of nanofluid flow, both the Brownian and thermophoresis molecular transfer mechanisms were considered.The predicted results were validated using fully developed distributions of velocity and temperature. Furthermore, the influences of mixed convection parameter (Gr/Re) and Kn number values on distributions of velocity and temperature through the entrance and fully-developed... 

    Phase Extraction in Segmented Flow

    , M.Sc. Thesis Sharif University of Technology Amini, Mohammad (Author) ; Moosavi, Ali (Supervisor)
    Abstract
    The formation of droplets at a T-junction in a micro channel network is primarily influenced by the pressure difference across the interface in the squeezing regime. Accurate measurements of droplet velocity and pressure profiles are difficult to obtain experimentally, yet these are the basic parameters required. Droplet micro fluidics has shown great potential for biological assays, chemical reactions and polymer emulsions. High stability allows the droplets to work as stable and isolated reactors that open up for parallel and serial reactions where each droplet can be screened individually. The purpose was to fabricate such systems, establish stable droplet generation where droplet volumes... 

    Simulation of Fluid Flow on Superhydrophobic Surfaces

    , M.Sc. Thesis Sharif University of Technology Abdollahzadeh, Mohammad Javad (Author) ; Moosavi, Ali (Supervisor)
    Abstract
    Today, with rapid developments and advances in science and technology, different ways have been studied to reduce energy consumption in various industries. Reducing the drag force and thus reducing the friction force is one of these methods which has many applications (e. g, in submarine construction industries). Creating some microgrooves in the microchannels is one of the most effective methods in order to reduce the friction force in microchannels that has recently been studied. In this method the air is trapped within the microgrooves and when the fluid (e. g, water) enters the channel passes over the trapped air within these microgrooves instead of touching the channel walls (solid... 

    Design and Fabrication of a Ferrofluidic Miniature Pump

    , Ph.D. Dissertation Sharif University of Technology Ashouri, Majid (Author) ; Shafii, Mohammad Behshad (Supervisor) ; Moosavi, Ali (Supervisor)
    Abstract
    This thesis presents the prototype design and fabrication of magnetically actuated miniature pumps which utilize self-sealing capability of ferrofluid-covered permanent magnets in both pumping and valving mechanisms. The contactless external actuation feature of the design enables integration of the pump with other PMMA-based microfluidic systems with low cost and disposability. The body of the 1st fabricated prototype pump consists of three nozzle/diffuser elements and two pumping chambers connected to the ends of a flat-wall pumping cylinder. A cylindrical permanent magnet placed inside the pumping cylinder acts as a piston which reciprocates by using an external magnetic actuator driven... 

    Investigation of heat transfer enhancement in a microchannel heat sink with the aid of internal fins: a metamodel approach

    , Article Computer Aided Chemical Engineering ; Volume 48 , 2020 , Pages 85-90 Hosseinpour, V ; Kazemeini, M ; Sharif University of Technology
    Elsevier B.V  2020
    Abstract
    Heat transfer enhancement with microchannel tools has been increased in recent year. In this study effect of geometric parameters as well as Reynolds number have been studied with experimental design approach. A metamodel was generated in this study for pressure drop and average Nusselt number passed all statistical tests. Order of an individual effect upon a response has been evaluated and interaction effects have been determined. Numerical results indicated that heat transfer increased significantly with inserting pyramidal micro fins. © 2020 Elsevier B.V  

    An analytical solution for thermally fully developed combined pressure - electroosmotically driven flow in microchannels

    , Article International Journal of Heat and Mass Transfer ; Volume 50, Issue 5-6 , 2007 , Pages 1087-1096 ; 00179310 (ISSN) Qazi Zade, A ; Taghizadeh Manzari, M ; Hannani, S. K ; Sharif University of Technology
    2007
    Abstract
    An analytical solution is presented to study the heat transfer characteristics of the combined pressure - electroosmotically driven flow in planar microchannels. The physical model includes the Joule heating effect to predict the convective heat transfer coefficient in two dimensional microchannels. The velocity field, which is a function of external electrical field, electroosmotic mobility, fluid viscosity and the pressure gradient, is obtained by solving the hydrodynamically fully-developed laminar Navier-Stokes equations considering the electrokinetic body force for low wall zeta potentials. Then, assuming a thermally fully-developed flow, the temperature distribution and the Nusselt... 

    Developing consistent inlet boundary conditions to study the entrance zone in microchannels

    , Article Journal of Thermophysics and Heat Transfer ; Volume 21, Issue 3 , 2007 , Pages 596-607 ; 08878722 (ISSN) Darbandi, M ; Vakilipour, S ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2007
    Abstract
    One important point in microflow study is the correct consideration of the Knudsen layer. In addition to the many complexities behind numerical simulation of the Knudsen layer near the solid walls, there are serious uncertainties at the microchannel inlet (the point at which the flow enters the microdomain). One major difficulty is the appearance of two singularities at the two corners of the inlet section. They seriously affect the solution in the entrance region of microchannels in which the lengths are comparable with the lengths of their hydrodynamic developing zones. Although the macro inlet flow problem has been largely investigated, there has been little attempt to study the issue in... 

    The effect of the time dependent pressure difference on bubble dynamics in microchannels

    , Article 4th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2006, Limerick, 19 June 2006 through 21 June 2006 ; Volume 2006 A , 2006 , Pages 83-88 ; 0791847608 (ISBN); 9780791847602 (ISBN) Keikhaee, A ; Rouhani, S ; Saboohi, Y ; Sharif University of Technology
    American Society of Mechanical Engineers  2006
    Abstract
    The physical processes responsible for bubble formation in microchannels are not well understood and lack fundamental understanding. Experimental results are not exactly in agreement with each other and there are no definite theories to explain the possible effects of different parameters. Among different parameters the microchannel hydraulic diameter can affect the bubble formation mechanism in microchannels strongly. In this paper the effect of the time dependent pressure difference between inside and outside of the bubble on bubble dynamics in microchannels have been investigated. The source of this time dependency can be the emergence of bubble embryos which produces a density... 

    Analysis of fluid flow in cylindrical microchannels subjected to uniform wall injection

    , Article 3rd ASME Integrated Nanosystems Conference - Design, Synthesis, and Applications, Pasadena, CA, 22 September 2004 through 24 September 2004 ; 2004 , Pages 139-146 ; 0791841774 (ISBN); 9780791841778 (ISBN) Layeghi, M ; ASME Nanotechnology Institute ; Sharif University of Technology
    American Society of Mechanical Engineers  2004
    Abstract
    Analytical analysis of fluid flow in cylindrical microchannels subjected to uniform wall injection at various Reynolds numbers is presented. The classical Navier-Stokes equations are used in the present study. Mathematically, using an appropriate change of variable, Navier-Stokes equations are transformed to a set of nonlinear ordinary differential equations. The governing equations are solved analytically using series solution method. The presented analytical results can be used for the prediction of velocity profiles and pressure drops in the cylindrical micro channels. The results are validated against available data in the literature and have shown good agreement. Copyright © 2004 by... 

    High frequency oscillatory flow in micro channels

    , Article Colloids and Surfaces A: Physicochemical and Engineering Aspects ; Vol. 460 , 2014 , pp. 355-360 ; ISSN: 09277757 Karbaschi, M ; Javadi, A ; Bastani, D ; Miller, R ; Sharif University of Technology
    Abstract
    This paper deals with computational and experimental studies on the oscillatory flow at high frequencies up to 100. Hz performed with the Oscillating Drop and Bubble Analyzer (ODBA) setup based on the capillary pressure technique. The CFD results are validated considering pressure amplitude experimental data. The simulated results of phase shift between the generated oscillatory flow and the consequent pressure amplitudes show also good agreement with the experimental data. In absence of any compressibility and viscoelasticity effects and assumptions, a complex velocity field during oscillation is the main reason for the observation of a phase shift. The results of velocity profiles at the... 

    Gaseous slip flow mixed convection in vertical microducts with constant axial energy input

    , Article Journal of Heat Transfer ; Vol. 136, issue. 3 , 2014 ; ISSN: 00221481 Sadeghi, A ; Baghani, M ; Saidi, M. H ; Sharif University of Technology
    Abstract
    The present investigation is devoted to the fully developed slip flow mixed convection in vertical microducts of two different cross sections, namely, polygon, with circle as a limiting case, and rectangle. The two axially constant heat flux boundary conditions of H1 and H2 are considered in the analysis. The velocity and temperature discontinuities at the boundary are incorporated into the solutions using the first-order slip boundary conditions. The method considered is mainly analytical in which the governing equations in cylindrical coordinates along with the symmetry conditions and finiteness of the flow parameter at the origin are exactly satisfied. The first-order slip boundary... 

    Pressure effects on electroosmotic flow of power-law fluids in rectangular microchannels

    , Article Theoretical and Computational Fluid Dynamics ; Vol. 28, issue. 4 , 2014 , pp. 409-426 ; ISSN: 09354964 Vakili, M. A ; Sadeghi, A ; Saidi, M. H ; Sharif University of Technology
    Abstract
    In this paper, the fully developed electroosmotic flow of power-law fluids in rectangular microchannels in the presence of pressure gradient is analyzed. The electrical potential and momentum equations are numerically solved through a finite difference procedure for a non-uniform grid. A complete parametric study reveals that the pressure effects are more pronounced at higher values of the channel aspect ratio and smaller values of the flow behavior index. The Poiseuille number is found to be an increasing function of the channel aspect ratio for pressure assisted flow and a decreasing function of this parameter for pressure opposed flow. It is also observed that the Poiseuille number is... 

    Two-phase flow in microchannels with a bounding porous medium

    , Article ASME 2011 9th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2011, 19 June 2011 through 22 June 2011 ; Volume 1 , June , 2011 , Pages 263-268 ; 9780791844632 (ISBN) Nouri Borujerdi, A ; Sharif University of Technology
    2011
    Abstract
    This paper investigates numerical simulation of one-dimensional homogeneous adiabatic gas-liquid two-phase flow in a rectangular microchannel with one boundary porous wall under the assumption of hydrophobic condition. Gas enters the microchannel with a uniform velocity and liquid is injected through the porous side wall. The present approach is to simulate water injection effects and developing mechanism of two-phase flow. The modeling and solution of the conservation equations provide pressure drop, vapor quality, void fraction and tow-phase mixture velocity for different water injection rates. The results show that velocity and pressure drop significantly perturbed when the water... 

    Experimental investigation of drag and lift forces on microparticles in low reynolds number poiseuille flow in microchannel

    , Article Journal of Dispersion Science and Technology ; Volume 37, Issue 12 , 2016 , Pages 1767-1777 ; 01932691 (ISSN) Razaghi, R ; Saidi, M. H ; Sharif University of Technology
    Taylor and Francis Inc 
    Abstract
    In this paper, the hydrodynamic drag and lift forces on microparticles in a dilute suspension in low Reynolds number Poiseuille flow in a microchannel is experimentally investigated using microscopic image analysis. An effective technique is applied to manipulate single-particle tracking in order to determine the velocity field and hydrodynamic forces on microparticles with diameter-to-channel height ratio of 0.1 (Formula presented.) in microchannels. The results show that there is a distance near the walls of the channel in which the hydrodynamic coupling between the particles and channel walls is considerable. Also, the magnitude of drag force that is imposed on the particles with... 

    Transportation and Settling Distribution of Microparticles in Low-Reynolds-Number Poiseuille Flow in Microchannel

    , Article Journal of Dispersion Science and Technology ; Volume 37, Issue 4 , 2016 , Pages 582-594 ; 01932691 (ISSN) Razaghi, R ; Saidi, M. H ; Sharif University of Technology
    Taylor and Francis Inc 
    Abstract
    In this article, velocity field and settling distribution of microparticles in a dilute suspension in low-Reynolds-number Poiseuille flow in a microchannel is experimentally investigated using microscopic image analysis. An effective technique is applied to manipulate single-particle tracking in order to determine the controlling parameters on transportation and settling of microparticles in microchannels. The results show that the velocities of dispersed phase are affected by the hydrodynamic properties, and this velocity deviation can be significant when the hydrodynamic coupling between particles and channel walls is considerable. Increasing the Reynolds number would result in decrease in... 

    Spiral microchannel with stair-like cross section for size-based particle separation

    , Article Microfluidics and Nanofluidics ; Volume 21, Issue 7 , 2017 ; 16134982 (ISSN) Ghadami, S ; Kowsari Esfahan, R ; Saidi, M. S ; Firoozbakhsh, K ; Sharif University of Technology
    Springer Verlag  2017
    Abstract
    Particle separation has a variety of applications in biology, chemistry and industry. Among them, circulating tumor cells (CTCs) separation has drawn significant attention to itself due to its high impact on both cancer diagnosis and therapeutics. In recent years, there has been growing interest in using inertial microfluidics to separate micro/nano particles based on their sizes. This technique offers label-free, high-throughput and efficient separation and can be easily fabricated. However, further improvements are needed for potential clinical applications. In this study, a novel inertial separation technique using spiral microchannel having stair-like cross section is introduced. The... 

    An optimized procedure to develop a 3-dimensional microfluidic hydrogel with parallel transport networks

    , Article International Journal for Numerical Methods in Biomedical Engineering ; 2018 ; 20407939 (ISSN) Jafarkhani, M ; Salehi, Z ; Shokrgozar, M. A ; Mashayekhan, S ; Sharif University of Technology
    Wiley-Blackwell  2018
    Abstract
    The development of microfluidic hydrogels is an attractive method to generate continuous perfusion, induce vascularization, increase solute delivery, and ultimately improve cell viability. However, the transport processes in many in vitro studies still have not been realized completely. To address this problem, we have developed a microchanneled hydrogel with different collagen type I concentrations of 1, 2, and 3 wt% and assessed its physical properties and obtained diffusion coefficient of nutrient within the hydrogel. It is well known that microchannel geometry has critical role in maintaining stable perfusion rate. Therefore, in this study, a computational modeling was applied to... 

    Solute dispersion by electroosmotic flow through soft microchannels

    , Article Sensors and Actuators, B: Chemical ; Volume 255, Part 3 , February , 2018 , Pages 3585-3600 ; 09254005 (ISSN) Hoshyargar, V ; Khorami, A ; Ashrafizadeh, S. N ; Sadeghi, A ; Sharif University of Technology
    Elsevier B.V  2018
    Abstract
    We study the hydrodynamic dispersion (HD) by electroosmotic flow in soft microchannels. Considering a fully developed flow in a slit microchannel of low surface potential and adopting the Taylor dispersion theory, we derive analytical solutions for the solute concentration field and the effective dispersion coefficient. We also conduct numerical analyses to broaden the paper's scope to high surface potentials and to specify a criterion for the validity of the Debye-Hückel linearization in soft microconduits as well as to investigate the broadening of an analyte band from the time of injection. It is demonstrated that the effective dispersion coefficient of a neutral solute band is generally...