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    Numerical simulation of heat transfer in mixed electroosmotic pressure-driven flow in straight microchannels

    , Article Journal of Thermal Science and Engineering Applications ; Volume 8, Issue 2 , 2016 ; 19485085 (ISSN) Shamloo, A ; Merdasi, A ; Vatankhah, P ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2016
    Abstract
    This paper investigates two-dimensional, time-independent elecroosmotic pressuredriven flow generated by a direct current electric potential with asymmetrical and symmetrical zeta potential distributions along the microchannel walls. Fluid flow through the horizontal microchannel is simulated using a numerical method. Two different cases are proposed to study the effect of electric potential on the flow field. First, negative electric potential is applied on the microchannel walls. In this case, large segments with negative electric potential are initially placed on the first half of the microchannel walls with two different arrangements. Afterward, smaller segments with negative electric... 

    Droplet-based flows in serpentine microchannels: chemical reactions and secondary flows

    , Article International Journal of Multiphase Flow ; Volume 97 , 2017 , Pages 186-196 ; 03019322 (ISSN) Madadelahi, M ; Shamloo, A ; Sharif University of Technology
    Abstract
    Mixing is an essential operation in many microfluidic devices. Droplet-based micromixers utilize droplets for mixing enhancement. In the present study, a novel three-dimensional simulation is conducted which has the ability to capture not only the mixing process, but also the chemical reactions inside liquid droplets. This two-phase model is used for simulating the reacting flow inside a serpentine microchannel and explores the effects of droplet size and reaction rate on the production and consumption of species in droplets. It is observed that the chemical reaction in each droplet, begins from its front area. Furthermore, it is shown that the production of species does not depend on water... 

    Parametric study on mixing process in an in-plane spiral micromixer utilizing chaotic advection

    , Article Analytica Chimica Acta ; Volume 1022 , 2018 , Pages 96-105 ; 00032670 (ISSN) Vatankhah, P ; Shamloo, A ; Sharif University of Technology
    Abstract
    Recent advances in the field of microfabrication have made the application of high-throughput microfluidics feasible. Mixing which is an essential part of any miniaturized standalone system remains the key challenge. This paper proposes a geometrically simple micromixer for efficient mixing for high-throughput microfluidic devices. The proposed micromixer utilizes a curved microchannel (spiral microchannel) to induce chaotic advection and enhance the mixing process. It is shown that the spiral microchannel is more efficient in comparison to a straight microchannel, mixing wise. The pressure drop in the spiral microchannel is only slightly higher than that in the straight microchannel. It is... 

    High throughput solution exchange of microparticles using magnetophoresis in curved microchannels

    , Article 21st International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2017, 22 October 2017 through 26 October 2017 ; 2020 , Pages 1324-1325 Bayat, P ; Zareian, S ; Rezai, P ; The Chemical and Biological Microsystems Society (CBMS) ; Sharif University of Technology
    Chemical and Biological Microsystems Society  2020
    Abstract
    A novel method involving focusing of magnetic particles at the inner wall of a curved microchannel and secondary Dean flow-based exchange of their fluid was investigated. Solution exchange occurred in a hybrid microchip at very high throughput and with unprecedented solution exchange and particle isolation efficiencies of 99.2% and 90%, respectively. © 17CBMS-0001  

    CFD Modeling of a LNG Microchannel Heat Exchanger

    , M.Sc. Thesis Sharif University of Technology Mahdian, Ehsan (Author) ; Farhadi, Fathollah (Supervisor)
    Abstract
    In the present work, the possibility of using a cross flow microchannel heat exchanger in cryogenic service for natural gas liquefaction has been numerically investigated using 3D computational fluid dynamics approach. Microchannels of rectangular and triangular cross section with a hydraulic diameter of 0.667 and 0.472 mm respectively have been constructed in Gambit and Fluent is used as the solver of numerical simulations.For solver’s equations validation, the existing experimental data on flow of water through rectangular microchannels has been modeled by CFD. Comparison of CFD results with experimental data shows a good agreement.Both models are constructed of three distinct layers. In... 

    Temperature rise in electroosmotic flow of typical non-newtonian biofluids through rectangular microchannels

    , Article Journal of Heat Transfer ; Volume 136, Issue 3 , March , 2014 ; ISSN: 00221481 Yavari, H ; Sadeghi, A ; Saidi, M. H ; Chakraborty, S ; Sharif University of Technology
    Abstract
    Electroosmosis is the main mechanism for flow generation in lab-on-a-chip (LOC) devices. The temperature rise due to the Joule heating phenomenon, associated with the electroosmosis, may be detrimental for samples being considered in LOCs. Hence, a complete understanding of the heat transfer physics associated with the electroosmotic flow is of high importance in design and active control of LOCs. The objective of the present study is to estimate the temperature rise and the thermal entry length in electroosmotic flow through rectangular microchannels, having potential applications in LOC devices. Along this line, the power-law rheological model is used to account for non-Newtonian behavior... 

    Buoyancy effects on gaseous slip flow in a vertical rectangular microchannel

    , Article Microfluidics and Nanofluidics ; Vol. 16, issue. 1-2 , 2014 , pp. 207-224 ; ISSN: 16134982 Sadeghi, M ; Sadeghi, A ; Saidi, M. H ; Sharif University of Technology
    Abstract
    Consideration is given to the buoyancy effects on the fully developed gaseous slip flow in a vertical rectangular microduct. Two different cases of the thermal boundary conditions are considered, namely uniform temperature at two facing duct walls with different temperatures and adiabatic other walls (case A) and uniform heat flux at two walls and uniform temperature at other walls (case B). The rarefaction effects are treated using the firstorder slip boundary conditions. By means of finite Fourier transform method, analytical solutions are obtained for the velocity and temperature distributions as well as the Poiseuille number. Furthermore, the threshold value of the mixed convection... 

    Joule heating effects in electrokinetically driven flow through rectangular microchannels: An analytical approach

    , Article Nanoscale and Microscale Thermophysical Engineering ; Volume 17, Issue 3 , 2013 , Pages 173-193 ; 15567265 (ISSN) Sadeghi, A ; Kazemi, Y ; Saidi, M. H ; Sharif University of Technology
    2013
    Abstract
    This is a theoretical study dealing with mixed electroosmotic and pressure-driven flow of a Newtonian liquid in a rectangular microchannel. Both and thermal boundary conditions are considered and the Debye-Hückel linearization is invoked. The governing equations are made dimensionless assuming fully developed conditions and then analytically solved using an infinite series solution. The governing factors are found to be the dimensionless Debye-Hückel parameter, velocity scale ratio, dimensionless Joule heating parameter, and channel aspect ratio. The results indicate that the Nusselt number is an increasing function of the channel aspect ratio, whereas the opposite is true for the velocity... 

    An experimental review on microbubble generation to be used in echo-particle image velocimetry method to determine the pipe flow velocity

    , Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 135, Issue 3 , Feb , 2013 , Paper No: FE-12-1217 ; 00982202 (ISSN) Salari, A ; Shafii, M. B ; Shirani, S ; Sharif University of Technology
    2013
    Abstract
    Microbubbles are broadly used as ultrasound contrast agents. In this paper we use a low-cost flow focusing microchannel fabrication method for preparing microbubble contrast agents by using some surface active agents and a viscosity enhancing material to obtain appropriate microbubbles with desired lifetime and stability for any in vitro infusion for velocity measurement. All the five parameters that govern the bubble size extract and some efforts are done to achieve the smallest bubbles by adding suitable surfactant concentrations. By using these microbubbles for the echo-particle image velocimetry method, we experimentally determine the velocity field of steady state and pulsatile pipe... 

    Forced convective heat transfer in parallel flow multilayer microchannels

    , Article Journal of Heat Transfer ; Volume 129, Issue 9 , 2007 , Pages 1230-1236 ; 00221481 (ISSN) Saidi, M. H ; Hajiaghaee Khiabani , R ; Sharif University of Technology
    2007
    Abstract
    In this paper, the effect of increasing the number of layers on improving the thermal performance of microchannel heat sinks is studied. In this way, both numerical and analytical methods are utilized. The analytical method is based on the porous medium assumption. Here, the modified Darcy equation and the energy balance equations are used. The method has led to an analytical expression presenting the average dimensionless temperature field in the multilayer microchannel heat sink. The effects of different parameters such as aspect ratio, porosity, channel width, and the solid properties on the thermal resistance are described. The results for single layer and multilayer heat sinks are... 

    Entropy generation in thermally developing laminar forced convection through a slit microchannel

    , Article ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels Collocated with 3rd Joint US-European Fluids Engineering Summer Meeting, ICNMM2010, 1 August 2010 through 5 August 2010, Montreal, QC ; Issue PARTS A AND B , 2010 , Pages 515-526 ; 9780791854501 (ISBN) Sadeghi, A ; Baghani, M ; Saidi, M. H ; Sharif University of Technology
    2010
    Abstract
    The issue of entropy generation in laminar forced convection of a Newtonian fluid through a slit microchannel is analytically investigated by taking the viscous dissipation effect, the slip velocity and the temperature jump at the wall into account. Flow is considered to be hydrodynamically fully developed but thermally developing. The energy equation is solved by means of integral transform. The results demonstrate that to increase Knudsen number is to decrease entropy generation, while the effect of increasing values of Brinkman number and the group parameter is to increase entropy generation. Also it is disclosed that in the thermal entrance region the average entropy generation number... 

    Second law analysis of slip flow forced convection through a parallel plate microchannel

    , Article Nanoscale and Microscale Thermophysical Engineering ; Volume 14, Issue 4 , 2010 , Pages 209-228 ; 15567265 (ISSN) Sadeghi, A ; Saidi, M. H ; Sharif University of Technology
    Abstract
    In the present work, the second law of thermodynamics analysis has been carried out for steady-state fully developed laminar gas flow in a parallel plate microchannel with asymmetrically heated walls. The rarefaction effects as well as viscous heating effects are taken into consideration. Closed-form expressions are obtained for velocity and temperature distributions and entropy generation rates. The results demonstrate that increasing values of the wall heat fluxes ratio result in greater entropy generation for positive Brinkman numbers, whereas the opposite is true for negative values of Brinkman. However, the effect of the wall heat fluxes ratio on entropy generation becomes insignificant... 

    Numerical modeling of ureagenesis in a microfluidic channel mimicking a liver lobule

    , Article 2015 22nd Iranian Conference on Biomedical Engineering, ICBME 2015, 25 November 2015 through 28 November 2015 ; 2015 , Pages 54-59 ; 9781467393515 (ISBN) Sharifi, F ; Firoozabadi, B ; Saidi, M. S ; Firoozbakhsh, K ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Abstract
    Ammonia detoxification is one of the main functions of the liver results in production of urea. In this study ammonia elimination and urea production was simulated in a microchannel mimicking the hepatic porto central axis. Navier- Stockes equations along with convection equations were solved for the related species in the entire domain. Since the Reynolds number was small (~1) the fluid flow regime was laminar. Urea cycle was modeled regarding its four main enzymes. Twelve rate equations were also solved in order to obtain the concentration of each metabolites participating in urea cycle. Concentration of the urea reached its maximum ca. 1.2e-5 M at the end of the channel which is in good... 

    Experimental investigation of slip velocity and settling distribution of micro-particles in converging–diverging microchannel

    , Article Microsystem Technologies ; 2016 , Pages 1-10 ; 09467076 (ISSN) Shirinzadeh, F ; Saidi, M. H ; Davari, A ; Sharif University of Technology
    Springer Verlag  2016
    Abstract
    An experimental test bed based on single particle tracking techniques is employed in order to investigate the velocity domain, slip velocity, and settling distribution of micro-particles in low-Reynolds number poiseuille flow in converging–diverging microchannel. Three-dimensional velocity domain of particles are studied in the presence of walls and compared with the particle-free fluid. The results show that the velocity of particles moving near the side walls of microchannel decreases about 30 % compared to those moving at the centerline. Furthermore, the effects of converging–diverging geometry on sedimentation of micro-particles are considered. The results show an average decrease of... 

    Experimental investigation of slip velocity and settling distribution of micro-particles in converging–diverging microchannel

    , Article Microsystem Technologies ; Volume 23, Issue 8 , 2017 , Pages 3361-3370 ; 09467076 (ISSN) Shirinzadeh, F ; Saidi, M. H ; Davari, A ; Sharif University of Technology
    Springer Verlag  2017
    Abstract
    An experimental test bed based on single particle tracking techniques is employed in order to investigate the velocity domain, slip velocity, and settling distribution of micro-particles in low-Reynolds number poiseuille flow in converging–diverging microchannel. Three-dimensional velocity domain of particles are studied in the presence of walls and compared with the particle-free fluid. The results show that the velocity of particles moving near the side walls of microchannel decreases about 30 % compared to those moving at the centerline. Furthermore, the effects of converging–diverging geometry on sedimentation of micro-particles are considered. The results show an average decrease of... 

    Analyzing mixing quality in a curved centrifugal micromixer through numerical simulation

    , Article Chemical Engineering and Processing: Process Intensification ; Volume 116 , 2017 , Pages 9-16 ; 02552701 (ISSN) Shamloo, A ; Vatankhah, P ; Akbari, A ; Sharif University of Technology
    Elsevier B.V  2017
    Abstract
    The Lab On a CD (LOCD), also known as Centrifugal Microfluidics, has evolved into a sophisticated platform for performing biomedical assays due to its marvelous miniaturization and accurate simulation of biological reactions. Among the numerous applications of the LOCD is fluid mixing. In this paper a centrifugal, serpentine micromixer is simulated and reformed toward better mixing performance. The micromixer was chosen to be curved as a curved design was found to be thrice as functional and compact as a rectilinear design, mixing-wise. The two angular velocity and opening radius parameters were originally hypothesized to affect mixing performance. Effect of angular velocity was studied over... 

    Developing a Parallel DSMC Algorithm for Simulating Flow in Micro-Nano Propulsion Systems

    , M.Sc. Thesis Sharif University of Technology Mirjalili, Vahid (Author) ; Darbandi, Masoud (Supervisor)
    Abstract
    With the rapid development of mico-nano propulsion systems in micro-spacecrafts and micro-sattelites, precise investigation of flow field in these devices has become necessary. Micro propulsion systems usually have a thrust in order of mili Newton, and they can be used for maneuvers of spacecrafts with mass of less than 10 kg. Micro propulsion systems are usually classified according to their thrust generation mechanism to different classes like cold gas, and chemical propulsion systems. Cold gas micro propulsion systems obtain their energy from thermodynamic expansion of gas and not by combustion. If the flow fiel dimensionare comparable to mean free path, rarefaction effects are observed... 

    Experimental Study on Two-Phase Flow Characteristics in Micro-Channels

    , M.Sc. Thesis Sharif University of Technology Yavari, Hadi (Author) ; Nouri, Ali (Supervisor)
    Abstract
    The present study provids an experimental investigation on two-pase flow characteristics in microchannels. Experiment were conducted with a mixture of air and water in horizontal circular pyrex channel with 400µm inner diameter. The pressure drop and flow rates of the liquid and gas were measured using new method and images of the flow patterns recorded by high shutter speed camera. The gas and liquid superficial velocity ranges were 0.025-12.5m/s and 0.016-3.6m/s, respectively. The flow pattern map is developed from the observed flow patterns based on phases superficial velocity as wel as We numbers of liquid and gas phases. The flow pattern map is compared with those of larger channels.... 

    Experimental Investigation of Nano Particle Effect on Heat Transfer in a Micro Heat Exchanger

    , M.Sc. Thesis Sharif University of Technology Jafarpoor Chekab, Hamideh (Author) ; Shafii, Mohammad Behshad (Supervisor) ; Saidi, Mohammad Hassan (Supervisor) ; Saeedi, Mohammad Saeed (Supervisor)
    Abstract
    Modern microelectronic systems generate a large amount of heat which must be transferred out of the system without excessive temperature rise. Conventional forced air convection and microchannel cooling plates have reached their performance limits Nanofiuids are proposed as an innovative way to solve the problem. A nanofiuid is nanoscale solid particles dispersed in a traditional heat transfer liquid. Some studies show an anomalous increase in the thermal conductivity for stationary nanofiuids. However, there are only few previous studies on the convection heat transfer rate and viscosity of nanofiuids. Both convection and stationary measurements of the thermal conductivity are widely... 

    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...