Search for: thermal-conductivity
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    Application GMDH artificial neural network for modeling of Al2O3/water and Al2O3/Ethylene glycol thermal conductivity

    , Article International Journal of Heat and Technology ; Volume 36, Issue 3 , 2018 , Pages 773-782 ; 03928764 (ISSN) Ahmadi, M. H ; Hajizadeh, F ; Rahimzadeh, M ; Shafii, M. B ; Chamkha, A. J ; Lorenzini, G ; Ghasempour, R ; Sharif University of Technology
    International Information and Engineering Technology Association  2018
    Thermal conductivity of nanofluids depends on several parameters including temperature, concentration, and size of nanoparticles. Most of the proposed models utilized concentration and temperature as influential factors in their modeling. In this study, group method of data handling (GMDH) artificial neural networks is applied in order to model the dependency of thermal conductivity on the mentioned factors. Firstly, temperature and concentration considered as inputs and a model is represented. Afterwards, the size of nanoparticles is added to the input variables and the results are compared. Based on obtained results, GMDH is an appropriate method to predict thermal conductivity of the... 

    A review of thermal conductivity of various nanofluids

    , Article Journal of Molecular Liquids ; Volume 265 , 2018 , Pages 181-188 ; 01677322 (ISSN) Ahmadi, M. H ; Mirlohi, A ; Alhuyi Nazari, M ; Ghasempour, R ; Sharif University of Technology
    In the present paper, several experimental and theoretical studies conducted on the thermal conductivity of nanofluids are represented and investigated. Based on the reviewed studies, various factors affect thermal conductivity of nanofluids such as temperature, the shape of nanoparticles, concentration and etc. Results indicated the increase in temperature and concentration of nanoparticles usually leads to the higher thermal conductivity of nanofluids. In addition, it is concluded that there are some novel approaches in order to obtain nanofluids with more appropriate thermal properties including using binary fluids as the base fluid or utilizing hybrid nanofluids. © 2018 Elsevier B.V  

    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
    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... 

    Heat transfer analysis of a porously covered heated square cylinder, using a hybrid Navier-Stokes-lattice Boltzmann numerical method

    , Article International Journal of Thermal Sciences ; Volume 91 , May , 2015 , Pages 59-75 ; 12900729 (ISSN) Salimi, M. R ; Taeibi Rahni, M ; Jam, F ; Sharif University of Technology
    Elsevier Masson SAS  2015
    In this work, two-dimensional laminar flow and heat transfer across a heated square cylinder, covered by a porous layer in a plane channel have been numerically investigated. The flow and thermal fields inside the porous layer were simulated using BrinkmaneForchmeyer extended Darcy model. Simulations were performed in different Reynolds numbers (Re = 60, 120, 160, and 200), porosities (ω = 0.7, 0.87, and 0.96), solid to fluid thermal conductivity ratios (λR = 10, 200, and 2000) and blockage ratios (BR = 0.5, 0.25 and 0.125). The effects of the mentioned parameters on pressure drop and heat transfer rate were investigated in detail. Also, the contribution of each side of the central squared... 

    Calculation of confined phonon spectrum in narrow silicon nanowires using the valence force field method

    , Article Journal of Electronic Materials ; Volume 42, Issue 7 , 2013 , Pages 2091-2097 ; 03615235 (ISSN) Karamitaheri, H ; Neophytou, N ; Taheri, M. K ; Faez, R ; Kosina, H ; Sharif University of Technology
    We study the effect of confinement on the phonon properties of ultra-narrow silicon nanowires of side sizes of 1 nm to 10 nm. We use the modified valence force field (MVFF) method to compute the phononic dispersion and extract the density of states, the transmission function, the sound velocity, the ballistic thermal conductance and boundary-scattering-limited diffusive thermal conductivity. We find that the phononic dispersion and the ballistic thermal conductance are functions of the geometrical features of the structures, i.e., the transport orientation and confinement dimension. The phonon group velocity and thermal conductance can vary by a factor of two depending on the geometrical... 

    Thermally conductive rubber-based composite friction materials for railroad brakes - Thermal conduction characteristics

    , Article Composites Science and Technology ; Volume 67, Issue 13 , 2007 , Pages 2665-2674 ; 02663538 (ISSN) Shojaei, A ; Fahimian, M ; Derakhshandeh, B ; Sharif University of Technology
    This study deals with the thermal conductivity of rubber-based composite friction materials used in railroad vehicles. Based on a commercially available railroad friction material, called here base material (BM), various friction materials containing different thermally conductive fillers (Cu, brass, Al, Al2O3 and talc) are fabricated and then their thermal conductivities are measured at various contents of the fillers. Addition of the thermally conductive fillers causes an increase in thermal conductivity of the friction material from 0.48 up to 5.8 W/m K, depending on the type and content of the filler. In addition, the experimental results reveal that the thermal conductivity of the... 

    Effect of porosity variation in determination of stagnant and dispersion thermal conductivities in the resin transfer molding process

    , Article Heat Transfer Research ; Volume 43, Issue 7 , 2012 , Pages 651-667 ; 10642285 (ISSN) Nouri Boroujerdi, A ; Rabani, R ; Kermani, M. J ; Sharif University of Technology
    A numerical analysis for determination of the stagnant and dispersion thermal conductivities in the Resin Transfer Molding (RTM) process is presented. A solution was obtained for the momentum and energy equations, which are used in this study and which represent the Brinkman- Forchheimer-extended Darcy model, and one-temperature energy equation. Subject to the appropriate boundary conditions, the governing equations are solved by the finite volume method on a collocated grid. In order to satisfy the pressure-velocity coupling in the solution, the SIMPLE algorithm was used and for determining the mass flux flowing past the cell faces, the Rhie-Chow interpolation was applied. Both constant and... 

    Investigation and modeling of the thermal conductivity of PP/clay nanocomposites and PP/MWCNT nanocomposites

    , Article E-Polymers ; Dec , 2010 ; 16187229 (ISSN) Shahryar Nejad, S ; Golzary, A ; Sharif University of Technology
    In this study, polypropylene/clay nanocomposites were prepared by melt blending method and their thermal conductivity and the thermal conductivity of polypropylene/multi-wall carbon nanotube (MWCNT) nanocomposites were investigated and modeled. It is found that the thermal conductivity of the PP/Clay and PP/MWCNT nanocomposites is increased with increasing temperature. The thermal conductivity of the nanocomposites is improved due to incorporation of nanoclay and MWCNT compared with pure PP matrix  

    Copper oxide nano-fluid stabilized by ionic liquid for enhancing thermal conductivity of reservoir formation: Applicable for thermal enhanced oil recovery processes

    , Article Chemical Industry and Chemical Engineering Quarterly ; Volume 22, Issue 2 , 2016 , Pages 211-225 ; 14519372 (ISSN) Barahoei, M ; Hezave, A. Z ; Sabbaghi, S ; Ayatollahi, S ; Sharif University of Technology
    CI and CEQ  2016
    Since oil reservoirs are limited and energy demand is increasing, seeking for high efficient EOR processes or enhancing the efficiency of current proposed EOR methods for producing trapped oil from reservoirs are highly investigated. As a way out, it is possible to couple the EOR and nanotechnology to utilize the efficiency of both methods together. Regarding this possibility, in the present study, in the first stage of investigation stable and uniform water-based solution of nano-sized particles of copper oxide with different concentrations (0.01–0.05 M) were prepared and then injected into the core samples. In the first stage, the effects of different surfactants with respect to their... 

    Investigation of a new mean temperature-dependent potential energy function for methane and its use for the prediction of transport properties

    , Article Molecular Physics ; Volume 105, Issue 10 , 2007 , Pages 1453-1463 ; 00268976 (ISSN) Nahaly, M ; Parsafar, G. A ; Goharshadi, E. K ; Sharif University of Technology
    In this work an improved mean potential energy function for the interaction of an isolated pair of methane is obtained, from which the non-equilibrium properties of methane at zero pressure limit are calculated, accurately. The potential energy function of 21 different fixed orientations of (CH4)2 dimer has been obtained via the coupled cluster method. In order to obtain a mean potential energy function, the Boltzmann-average of the obtained potentials of the selected fixed orientations has been used. Unlike the full potential energy surface with the angle-dependent, the parameters of the mean potential are found to be temperature-dependent. The mean potential energy function is fitted well... 

    Corrigendum: partial replacement of copper slag with treated crumb rubber aggregates in alkali-activated slag mortar” (construction and building materials (2020) 256, (S0950061820314732), (10.1016/j.conbuildmat.2020.119468))

    , Article Construction and Building Materials ; Volume 283 , 2021 ; 09500618 (ISSN) Ameri, F ; Shoaei, P ; Reza Musaeei, H ; Zareei, A. R ; Chee Ban, C ; Sharif University of Technology
    Elsevier Ltd  2021
    The authors regret that there was an error in the SEM image presented in Fig. 4(c) of the previously print version of the article. Please refer to the corrected SEM image as presented here. It is noteworthy that this change does not affect any of the conclusions. The authors would like to apologise for any inconvenience caused. © 2021 Elsevier Ltd  

    Modelling the work-roll temperature variation at unsteady state condition

    , Article Modelling and Simulation in Materials Science and Engineering ; Volume 11, Issue 2 , 2003 , Pages 179-194 ; 09650393 (ISSN) Serajzadeh, S ; Mucciardi, F ; Sharif University of Technology
    In this paper, the unsteady state heat transfer equations with time dependent boundary conditions are coupled with a two-dimensional finite element method to predict the work-roll temperature distribution during the continuous hot slab rolling process. To achieve an accurate temperature field, the effects of various factors including the thermal relationship of the work-roll and the metal slab, the idling work-roll revolutions, the rolling speed, the slab/roll interfacial heat transfer coefficient, and the magnitude of the thickness reduction of the slab at each deformation pass are taken into account. Comparisons between the predicted and published experimental results are used to... 

    Graphene-based antidots for thermoelectric applications

    , Article Journal of the Electrochemical Society ; Volume 158, Issue 12 , 2011 , Pages K213-K216 ; 00134651 (ISSN) Karamitaheri, H ; Pourfath, M ; Pazoki, M ; Faez, R ; Kosina, H ; Sharif University of Technology
    The low temperature thermoelectric properties of hydrogen-passivated graphene-based antidot lattices are theoretically investigated. Calculations are performed using density functional theory in conjunction with the Landauer formula to obtain the ballistic transport coefficients. Antidot lattices with hexagonal, triangular and rectangular antidot shapes are studied. Methods to reduce the thermal conductance and to increase the thermoelectric power factor of such structures are studied. Our results indicate that triangular antidot lattices have the smallest thermal conductance due to longer boundaries, the smallest distance between the neighboring antidots, and the armchair edges. This... 

    Geometrical effects on the thermoelectric properties of ballistic graphene antidot lattices

    , Article Journal of Applied Physics ; Volume 110, Issue 5 , 2011 ; 00218979 (ISSN) Karamitaheri, H ; Pourfath, M ; Faez, R ; Kosina, H ; Sharif University of Technology
    The thermoelectric properties of graphene-based antidot lattices are theoretically investigated. A third nearest-neighbor tight-binding model and a fourth nearest-neighbor force constant model are employed to study the electronic and phononic band structures of graphene antidot lattices with circular, rectangular, hexagonal, and triangular antidot shapes. Ballistic transport models are used to evaluate transport coefficients. Methods to reduce the thermal conductance and to increase the thermoelectric power factor of such structures are studied. Our results indicate that triangular antidot lattices have the smallest thermal conductance due to longer boundaries and the smallest distance... 

    An experimental study on the effect of ultrasonication on thermal conductivity of ferrofluid loaded with carbon nanotubes

    , Article Thermochimica Acta ; Volume 617 , October , 2015 , Pages 102-110 ; 00406031 (ISSN) Shahsavar, A ; Salimpour, M. R ; Saghafian, M ; Shafii, M. B ; Sharif University of Technology
    Elsevier  2015
    Nanofluids containing Fe3O4 and carbon nanotubes nanoparticles emulsified and dispersed using gum arabic (GA) and tetramethylammonium hydroxide (TMAH) were made and characterized for potential use as heat transfer fluids. Due to the interaction between the TMAH and GA molecules, the magnetic nanoparticles and CNTs were physically adsorbed. This paper reports an experimental work on the effect of ultrasonication on thermal conductivity of this aqueous suspension. The characterization and surface morphology of the dried samples were studied by using XRD and TEM measurements. Experiments were conducted in the magnetic nanoparticles mass concentration range 0.494-2.428%,... 

    Experimental and numerical investigation of the thermal performance of a novel sintered-wick heat pipe

    , Article Applied Thermal Engineering ; Volume 94 , 2016 , Pages 59-75 ; 13594311 (ISSN) Khalili, M ; Shafii, M. B ; Sharif University of Technology
    Elsevier Ltd 
    Thermal performance of a novel sintered wick heat pipe was investigated in this study. Two types of sintered wick heat pipes were fabricated and tested at different filling ratios of water, and their thermal resistances in different modes were compared. In the first type, wick was sintered annularly (conventional type), and in the other one (novel type of sintered wick) it was sintered only in one third of cross-section. Results showed that dry-out occurs at higher heat input by an increase in the filling ratio. Moreover, the best filling ratio is 20% for both heat pipes. Thermal resistances of the partly sintered wick heat pipe are approximately 28%, 17% and 47% lower than those of the... 

    Effect of carbon nanotube dispersion and network formation on thermal conductivity of thermoplastic polyurethane/carbon nanotube nanocomposites

    , Article Polymer Engineering and Science ; Volume 56, Issue 4 , 2016 , Pages 394-407 ; 00323888 (ISSN) Pircheraghi, G ; Powell, T ; Solouki Bonab, V ; Manas Zloczower, I ; Sharif University of Technology
    Carbon nanotubes (CNTs) were dispersed without any solvent in poly(tetramethylene ether glycol), (PTMEG) well above its melting point by ultrasonication in the pulse mode and different times. The polyol/CNT suspensions were used to prepare in situ polymerized thermoplastic polyurethane TPU/CNT nanocomposites with the CNT concentration of ∼ 0.05 vol%, much below the CNT geometrical percolation threshold calculated at 0.43 vol%. Results of rotational rheological measurements and ultraviolet-visible (UV-Vis) spectroscopy analysis revealed improvement in the nanoscale CNT dispersion with sonication time. Moreover, the optical microscopic images and sedimentation behavior for these samples... 

    Thermal conductivity, viscosity, and electrical conductivity of iron oxide with a cloud fractal structure

    , Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 53, Issue 4 , 2017 , Pages 1343-1354 ; 09477411 (ISSN) Jamilpanah, P ; Pahlavanzadeh, H ; Kheradmand, A ; Sharif University of Technology
    Springer Verlag  2017
    In the present study, nanoscale iron oxide was synthesized using a hydrothermal method; XRD analysis revealed that all the produced crystals are iron oxide. FESEM microscopic imaging showed that particles are on the scale of nano and their morphology is cloud fractal. To study the laboratory properties of thermal conductivity, viscosity, and electrical conductivity of the nanoparticles, they were dispersed in ethylene glycol-based fluid and the nanofluid was in a two-step synthesis during this process. The experiments were carried out with a weight fraction between 0 and 2 % at temperatures between 25 and 45 °C. According to the results of the experiments, increasing the density of... 

    A numerical investigation on natural convection heat transfer in annular-finned concentric horizontal annulus using nanofluids: a parametric study

    , Article Heat Transfer Engineering ; 2020 Ashouri, M ; Zarei, M. M ; Hakkaki Fard, A ; Sharif University of Technology
    Taylor and Francis Ltd  2020
    Natural convection heat transfer in a concentric horizontal annulus with annular fins is numerically studied. Due to the low thermal conductivity of water, CuO-water and Al2O3-water nanofluids were used as heat transfer fluids. The effect of three different parameters, including fin spacing, fin eccentricity, and fin thickness at different fin diameters and Rayleigh number range of 104 to 9 (Formula presented.) 105, were studied. The obtained results revealed that Al2O3-water nanofluid has the highest heat transfer rate. The calculated heat transfer rates for Al2O3-water nanofluid for Rayleigh numbers of 9 (Formula presented.) 105, 105, and 104 were respectively up to 12.1%, 26.2%, and 31.6%... 

    Role of thermal conduction in single-bubble cavitation

    , Article Physics Letters, Section A: General, Atomic and Solid State Physics ; Volume 372, Issue 8 , 2008 , Pages 1283-1287 ; 03759601 (ISSN) Moshaii, A ; Rezaei Nasirabad, R ; Imani, Kh ; Silatani, M ; Sadighi Bonabi, R ; Sharif University of Technology
    Elsevier  2008
    Effect of thermal conduction on radiation from a single cavitating bubble has been studied in a hydrochemical framework including variation of heat conductivity of noble gases up to 2500 K. Results of numerical simulation show that thermal conductivity plays an important role in determining ultimate cavitation temperature. Higher thermal conductivity of lighter noble gases causes to more thermal dissipation during the bubble collapse, leading to a lower peak temperature. Moreover, at the same driving conditions, radius of light emitting region is greater for heavier noble bubbles. Therefore, sonoluminescence radiation is more intensive from heavier noble gases. Phase diagrams of...