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Total 261 records

    The study of growth and coagulation of titania nanoparticles by chemical vapor synthesis

    , Article Journal of Nuclear Science and Technology ; No.53 , 2010 , pp. 20-29 Rahiminezhad-Soltani, M ; Saberyan, K ; Shahri, F ; Simchi, A. (Abdolreza) ; Sharif Univesity of Technology
    Abstract
    Chemical Vapor Synthesis route was used for synthesis of titanium dioxide (TiO2) nanoparticles in hot-walled reactor at 800degreeC using TiCl4 as precursor. The effect of processing parameters e.g., temperature and amount of precursor on phase structure, size, purity, coagulation and agglomeration of nanoparticles were investigated in this respect. Also, the H2O effects on the size, crystallinity, phase transformation and purity of nanoparticles were studied. Comprehensive experimental observations were confirmed by transmission electron microscopy, X-ray diffraction analysis and thermal gravimetric-differential thermal analysis results. The obtained results showed that by increasing the... 

    The study of magnetic field implementation on cylinder quenched in boiling ferro-fluid

    , Article Applied Thermal Engineering ; Volume 64, Issue 1-2 , March , 2014 , Pages 331-338 ; ISSN: 13594311 Habibi Khoshmehr, H ; Saboonchi, A ; Shafii, M. B ; Jahani, N ; Sharif University of Technology
    Abstract
    It has been shown that nanofluids in different investigations increase or decrease heat transfer rate in boiling phenomenon. The present study examined the effects of ferro-fluid concentrations and magnetic field implementation on the fluid throughout the boiling process. Obtained are the quenching curve and boiling curve on specified surface roughness in both water and ferro-fluid with two different concentrations. A silver cylinder with Aspect ratio of 10, and surface roughness of 689 nm was heated up to 350 C and then was overwhelmed in the fluid under study. Temperatures were measured by a thermocouple which installed in the center of the cylinder. The test was carried out 5 times. The... 

    Investigating the rheological properties of nanofluids of water/hybrid nanostructure of spherical silica/MWCNT

    , Article Thermochimica Acta ; Volume 578 , 20 February , 2014 , Pages 53-58 ; ISSN: 00406031 Baghbanzadeh, M ; Rashidi, A ; Soleimanisalim, A. H ; Rashtchian, D ; Sharif University of Technology
    Abstract
    Regarding the importance of rheological properties of water based drilling fluids, the effects of silica nanospheres, multiwall carbon nanotubes (MWCNTs) and two types of their hybrid, i.e. H1 (80 wt.% silica nanosphere/20 wt.% MWCNT) and H2 (50 wt.% silica nanosphere/50 wt.% MWCNT) on the viscosity and density of distilled water were investigated. According to the results, viscosity and density of the nanofluids increased with the concentration, while they were reduced by increasing the temperature. At high concentrations, the least increase in the viscosity of distilled water by adding the nanomaterials is related to H2 (8.2% increase at 1.0 wt.%). Likewise, the optimum operating... 

    Nanofluidic transport inside carbon nanotubes

    , Article Journal of Physics D: Applied Physics ; Volume 47, Issue 6 , 12 February , 2014 ; ISSN: 00223727 Moghimi Kheirabadi, A ; Moosavi, A ; Akbarzadeh, A. M ; Sharif University of Technology
    Abstract
    Using non-equilibrium molecular dynamics simulations, we investigate the effects of nanotube size, mean flow velocity, ion concentration and temperature of an electrolyte water solution on shearing stress and nominal viscosity. It is shown that the distributed electric field arising from the electrolyte water solution has significant influences on fluid properties. Also, the temperature of the solution, which causes thermal movement, affects nanofluidic transport in nanoenvironments. The nominal viscosity and shearing stress increases as the tube diameter increases. When the temperature of solution increases or ion concentration decreases, the shearing stress and nominal viscosity increase.... 

    Mixed-convection flow of Al2O3-H2O nanofluid in a channel partially filled with porous metal foam: Experimental and numerical study

    , Article Experimental Thermal and Fluid Science ; Vol. 53 , February , 2014 , pp. 49-56 ; ISSN: 08941777 Hajipour, M ; Molaei Dehkordi, A ; Sharif University of Technology
    Abstract
    Mixed-convection flow of nanofluids inside a vertical rectangular channel partially filled with open-cell metal foam and subject to a constant wall-heat flux was investigated experimentally and numerically. Al2O3-water nanofluids with different concentrations were prepared and their stability was examined using UV-Vis spectroscopy. Dynamic light scattering method was used to determine particle size distribution of the nanofluid feedstock. The outlet temperature and pressure drop were measured for different nanofluid flow rates (i.e., Reynolds number values). In the numerical section, a two-dimensional volume-averaged form of the governing equations was used. The velocity and temperature... 

    Open-loop pulsating heat pipes charged with magnetic nanofluids: powerful candidates for future electronic coolers

    , Article Nanoscale and Microscale Thermophysical Engineering ; Volume 18, Issue 1 , 2014 , Pages 18-38 ; ISSN: 15567265 Mohammadi, M ; Taslimifar, M ; Haghayegh, S ; Hannani, S. K ; Shafii, M. B ; Saidi, M. H ; Afshin, H ; Sharif University of Technology
    Abstract
    The present research proposes an effective method to enhance the heat transport capability of conventional electronic coolers and improve their thermal management. Pulsating heat pipes (PHPs) are outstanding heat transfer devices in the field of electronic cooling. In the present study, two sets of open-loop pulsating heat pipes (OLPHPs) for two different magnetic nanofluids (with and without surfactant) were fabricated and their thermal performance was experimentally investigated. Effects of working fluid (water and two types of magnetic nanofluids), heating power, charging ratio, nanofluid concentration, inclination angle, application of a magnetic field, and magnet location are described.... 

    Modified Buongiorno's model for fully developed mixed convection flow of nanofluids in a vertical annular pipe

    , Article Computers and Fluids ; Vol. 89 , 2014 , pp. 124-132 ; ISSN: 00457930 Malvandi, A ; Moshizi, S. A ; Soltani, E. G ; Ganji, D. D ; Sharif University of Technology
    Abstract
    This paper deals with the mixed convective heat transfer of nanofluids through a concentric vertical annulus. Because of the non-adherence of the fluid-solid interface in the presence of nanoparticle migrations, known as slip condition, the Navier's slip boundary condition was considered at the pipe walls. The employed model for nanofluid includes the modified two-component four-equation non-homogeneous equilibrium model that fully accounts for the effects of nanoparticles volume fraction distribution. Assuming the fully developed flow and heat transfer, the basic partial differential equations including continuity, momentum, and energy equations have been reduced to two-point ordinary... 

    Enhanced heavy oil recovery in sandstone cores using TiO2 nanofluids

    , Article Energy and Fuels ; Vol. 28, issue. 1 , 2014 , pp. 423-430 ; ISSN: 08870624 Ehtesabi, H ; Ahadian, M. M ; Taghikhani, V ; Ghazanfari, M. H ; Sharif University of Technology
    Abstract
    Anatase and amorphous TiO2 nanoparticles were used to improve recovery of heavy oil from sandstone cores. Before performing core floods, the stability of nanoparticles at different salinities was tested using ζ potential and ultraviolet-visible (UV-vis) methods. While water recovered only 49% of the oil in the core flood experiments, 0.01% anatase structure solution recovered 80% of the oil after injecting two pore volumes at optimum conditions. To understand the mechanism responsible for improved recovery, contact angle measurements were performed on the rock surface before and after treatment with the nanoparticle solution. Contact angle measurements showed that the rock wettability... 

    Experimental investigation of thermal resistance of a ferrofluidic closed-loop pulsating heat pipe

    , Article Heat Transfer Engineering ; Vol. 35, issue. 1 , 2014 , pp. 25-33 ; ISSN: 01457632 Mohammadi, M ; Mohammadi, M ; Ghahremani, A. R ; Shafii, M. B ; Mohammadi, N ; Sharif University of Technology
    Abstract
    For the present article, a pulsating heat pipe (PHP) is fabricated and tested experimentally by bending a copper tube. The effects of working fluid, heat input, charging ratio, inclination angle, magnets location, and ferrofluid (magnetic nanofluid) volumetric concentration have been investigated on the thermal performance of this PHP. Experimental results show that using ferrofluid as a working fluid improves the thermal performance of the PHP significantly. Moreover, applying a magnetic field on a ferrofluidic PHP reduces its thermal resistance. By changing the inclination angle of the PHP from vertical mode to angles close to the horizontal mode, the present PHP has a constant and... 

    Modeling and CFD simulation of a mixed-convection flow of regular fluids and nanofluids in vertical porous and regular channels

    , Article Heat Transfer - Asian Research ; Vol. 43, issue. 3 , May , 2014 , pp. 243-269 ; ISSN: 1523-1496 Hashemi Amrei, S. M. H ; Dehkordi, A. M ; Sharif University of Technology
    Abstract
    In this article, the problem of combined forced and free convection in vertical porous and regular channels for both regular fluids and nanofluids has been solved using the CFD technique in the entrance regions of momentum and heat transfer taking into account the influences of viscous heating and inertial force. In this regard, various types of viscous dissipation models reported in the literature such as the Darcy model, the power of the drag force model, and the clear fluid-compatible model were applied. In the case of nanofluid flow, both the Brownian and thermophoresis molecular transfer mechanisms were considered. The dimensionless distributions of velocity, temperature, and the volume... 

    Effect of nanofluid treatment on water sensitive formation to investigate water shock phenomenon, an experimental study

    , Article Journal of Dispersion Science and Technology ; Volume 35, Issue 7 , 21 May 2014 , Pages 889-897 Habibi, A ; Heidari, M. A ; Al-Hadrami, H ; Al-Ajmi, A ; Al-Wahaibi, Y ; Ayatollahi, S ; Sharif University of Technology
    Abstract
    Permeability reduction in porous media as a result of frail and tenuous fine particles migration would decrease the productivity index in the subterranean reservoirs. During reservoir stimulation by injecting fluids into the reservoir, as the salinity condition of the formation brine changes, fine particles initiate the triggering process. In this study, MgO-based nanofluid as a fines fixation agent was stably prepared based on the particle size distribution and characterized through transmission electron microscopy analysis. Afterward, several core flooding tests were performed using Berea sandstone cores to study the effect of nanofluid injection on fines fixation in the water shock... 

    Numerical investigation of nanofluid mixed-convection flow in the entrance region of a vertical channel partially filled with porous medium

    , Article Heat Transfer - Asian Research ; Vol. 43, issue. 7 , November , 2014 , p. 607-627 Hajipour, M ; Dehkordi, A. M ; Jamshidi, S ; Sharif University of Technology
    Abstract
    In this article, transient two-dimensional mixed convection of nanofluids in the entrance region of a vertical channel has been studied carefully. The geometry under consideration consisted of a parallel-plate channel partly filled with a porous medium with a constant wall temperature. In the free flow region, the two-dimensional flow field has been governed by the Navier-Stokes equations. The general formulation of the momentum equations accounting for the inertial and the viscous effects in the presence of a porous medium has been used. Viscous dissipation effects have also been incorporated in the thermal energy equation. Effects of Brownian diffusion and thermophoresis have also been... 

    The quenching of silver rod in boiling carbon nano tube-water nanofluid

    , Article International Journal of Thermal Sciences ; Volume 75 , 2014 , Pages 95-104 ; ISSN: 12900729 Habibi Khoshmehr, H ; Saboonchi, A ; Shafii, M. B ; Sharif University of Technology
    Abstract
    It is well established that nanofluids increase or decrease heat transfer in boiling phenomenon. The study acquired Quenching curve and boiling curve in two different surface roughnesses in two fluids: deionized water and the nanofluid MWCNT-water with four different concentrations. The cylinder was made of silver and two surface roughnesses of 129 and 690 nm. It was heated up and soaked in the fluid mentioned above. Temperature was recorded by a drilled to install thermocouple. The experiment was replicated in five times. To calculate the heat transfer quotient, assuming the cylinder to be thermally homogeneous, the Lumped capacity method was applied. The obtained results during quenching... 

    Reduction of fine migration in different pH and salinity conditions using nanofluid

    , Article SPE - European Formation Damage Conference, Proceedings, EFDC ; Volume 2 , 2013 , Pages 737-743 ; 9781627486101 (ISBN) Asset, Y ; Pourafshary, P ; Ayatollahi, S ; Sharif University of Technology
    2013
    Abstract
    Movement and transportation of fine particles in formations leads to clogging the pores and reduction in permeability. This type of formation damage is stronglycontingent upon water salinity and ionic conditions in the formation. The main parameters which control the particle release are the interactions and forces between particles and porous medium surfaces. Changing salinity which leads to pH alteration, affects these interactions and subsequently the fine migration process. Hence, pH and salinity variations should be considered to study and evaluate the portion of fine migration in formation damage. The principal challenge in this research therefore, is to try to change the surface... 

    Remedial effects of metal oxide nanoparticles to treat suspension transport in saturated porous media

    , Article SPE - European Formation Damage Conference, Proceedings, EFDC ; Volume 1 , 2013 , Pages 478-488 ; 9781627486101 (ISBN) Arab, D ; Pourafshary, P ; Ayatollahi, S ; Habibi, A ; Sharif University of Technology
    2013
    Abstract
    Hydrocarbon production decline as a result of formation damage caused by fines migration has been widely observed in laboratory corefloods and natural flows in porous media. Permeability impairment due to fines migration is explained by different capture mechanisms of already released particles at some pore sites. Preventing detachment of in-situ particles from the rock surface during enhanced oil recovery (EOR) agent injection into the porous media has been reported recently. In this experimental study, the effect of five types of metal oxide nanoparticles; γ-AI2O3, ZnO, CuO, MgO and SiO: to adsorb the fine particles existing in the flowing suspension has been investigated. In each test,... 

    Thermal conductivity of mixed nanofluids under controlled pH conditions

    , Article International Journal of Thermal Sciences ; Volume 74 , 2013 , Pages 63-71 ; 12900729 (ISSN) Iranidokht, V ; Hamian, S ; Mohammadi, N ; Shafii, M. B ; Sharif University of Technology
    2013
    Abstract
    Just a few investigations have been conducted to study the mixed nanofluids(MNs), which contain more than one type of nanoparticles, despite considerable advances in the field of nanofluids thermal conductivity. In present research, by combining different volume fractions of various nanoparticles, the variation of mixed nanofluids thermal conductivity was considered. The mentioned nanofluids have different fabrication cost. First, the effect of each specific nanoparticle presence in the base fluid on the thermal conductivity of nanofluid was surveyed both experimentally and theoretically. Then, the thermal conductivities of two MNs, one consisted of a metallic nanoparticle (high thermal... 

    Promising technology for electronic cooling: Nanofluidic micro pulsating heat pipes

    , Article Journal of Electronic Packaging, Transactions of the ASME ; Volume 135, Issue 2 , 2013 ; 10437398 (ISSN) Jahani, K ; Mohammadi, M ; Shafii, M. B ; Shiee, Z ; Sharif University of Technology
    2013
    Abstract
    Currently, the thermal management of microelectromechanical systems (MEMS) has become a challenge. In the present research, a micro pulsating heat pipe (MPHP) with a hydraulic diameter of 508 lm, is experimented. The thermal performance of the MPHP in both the transient and steady conditions, the effects of the working fluid (water, silver nanofluid, and ferrofluid), heating power (4, 8, 12, 16, 20, 24, and 28 W), charging ratio (20, 40, 60, and 80%), inclination angle (0 deg, 25 deg, 45 deg, 75 deg, and 90 deg relative to horizontal axis), and the application of magnetic field, are investigated and thoroughly discussed. The experimental results show that the optimum charging ratio for water... 

    Analysis of nanoparticles migration on natural convective heat transfer of nanofluids

    , Article International Journal of Thermal Sciences ; Volume 68 , June , 2013 , Pages 79-93 ; 12900729 (ISSN) Pakravan, H. A ; Yaghoubi, M ; Sharif University of Technology
    2013
    Abstract
    Both experimental and numerical studies are unanimous for enhancing Nusselt number for forced convection of nanofluids with slight difference, but there is inconsistency for natural convection heat transfer of nanofluids. In this paper attempt is made to study the effects of nanoparticles migration on the natural convection behavior of nanofluids. For analysis, a mixture model is used by including important phenomena such as Brownian motion and thermophoresis effects. These two mechanisms are taken into account to compute the slip velocities between the base fluid and nanoparticles. The governing equations are solved numerically and good agreements are observed in comparison with... 

    Study of droplet behaviour along a pulsed liquid-liquid extraction column in the presence of nanoparticles

    , Article Canadian Journal of Chemical Engineering ; Volume 91, Issue 3 , 2013 , Pages 506-515 ; 00084034 (ISSN) Khoobi, N ; Bahmanyar, A ; Molavi, H ; Bastani, D ; Mozdianfard, M. R ; Bahmanyar, H ; Sharif University of Technology
    2013
    Abstract
    In this article, droplet size and its distribution along a pulsed liquid-liquid extraction column, is studied where SiO2 nanoparticles with concentrations of 0.01, 0.05 and 0.1vol.% and different hydrophobicities are applied to the dispersed phase. Using ultrasonication, nanoparticles were dispersed in kerosene as the base fluid. Nanofluids' stability was ensured using a UV-vis spectrophotometer. Some 22,000 droplets were measured by photographic technique and results were compared with systems containing no-nanoparticles (Water-Acetic acid-Kerosene). Addition of nanoparticles changed the droplet shape from ellipsoidal to spherical. Also, there was a marked influence on droplet breakage and... 

    Synthesis of spherical silica/multiwall carbon nanotubes hybrid nanostructures and investigation of thermal conductivity of related nanofluids

    , Article Thermochimica Acta ; Volume 549 , 2012 , Pages 87-94 ; 00406031 (ISSN) Baghbanzadeh, M ; Rashidi, A ; Rashtchian, D ; Lotfi, R ; Amrollahi, A ; Sharif University of Technology
    2012
    Abstract
    In this study, a hybrid of silica nanosphere/multiwall carbon nanotube (MWCNT) has been synthesized by wet chemical method at room temperature. The effect of MWCNTs, silica nanospheres and hybrid nanostructures (80% silica nanosphere/20% MWCNT and 50% silica nanosphere/50% MWCNT) on the thermal conductivity of distilled water has been investigated. SDBS was used as the dispersant to stabilize nanomaterials in the aqueous suspension and its concentration was 1.5 times of the concentration of nanomaterials. As results show, by increasing the concentration of nanomaterials, effective thermal conductivity of nanofluids increased. The most and the least enhancement in the effective thermal...