فهرست مطالب

  • Volume:2 Issue:1, 2014
  • تاریخ انتشار: 1393/01/10
  • تعداد عناوین: 7
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  • H. Safikhani, A. Abbassi, S. Ghanami Pages 1-13
    In the present study, Computational Fluid Dynamics (CFD) techniques and Artificial Neural Networks (ANN) are used to predict the pressure drop value (Δp) of Al2O3-water nanofluid in flat tubes. Δp is predicted taking into account five input variables: tube flattening (H), inlet volumetric flow rate (Qi), wall heat flux (qnw), nanoparticle volume fraction (Φ) and nanoparticle diameter (dp). The required output data for training the ANN are taken from the results of numerical simulations. The numerical simulations of nanofluid are performed using two phase mixture model by FORTRAN programming language. The flow regime and the wall boundary conditions are assumed to be laminar and constant heat flux respectively. The ANN results are compared with the numerical simulated one and excellent agreement is observed. To view the accuracy of ANN model, statistical measures R2, RMSE and MAPE are used and it is seen that the ANN model has high accuracy in predicting the (Δp) values.
    Keywords: Nanofluid, ANN, Pressure drop, Mixture model, GMDH
  • M. Jafari, M. Farhadi, K. Sedighi Pages 14-28
    The effects of Single Walled Carbon Nanotube (SWCNT) on mixed convection in a cavity are investigated numerically. The problem is studied for different Richardson numbers (0.1-10), volume fractions of nanotubes (0-1%), and aspect ratio of the cavity (0.5-2.5) when the Grashof number is equal to 103. The volume fraction of added nanotubes to Water as base fluid are lowers than 1% to make dilute suspensions. The Study presents a numerical treatment based on LBM to model convection heat transfer of Carbon nanotube based nanofluids. A theoretical model is used for effective thermal conductivity of the nanofluid containing Carbon nanotubes. This model covers different phenomena of energy transport in nanofluids. Also, an analytical model is applied for effective viscosity of the nanofluid which includes the Brownian effect and other physical properties of nanofluids. Results show that adding a low value of SWCNT to the base fluid led to significant enhancement of convection heat transfer. Make a comparison between the obtained results and other published papers shows that Carbon nanotubes enhances the rate of convection heat transfer better than other nanoparticles.
    Keywords: Lattice Boltzmann Method, Single Walled Carbon Nanotube (SWCNT), Effective Thermal Conductivity, lid, driven cavity, Nusselt number, Richardson number, Mixed convection, Effective Viscosity
  • A. Zare Ghadi, M. Sadegh Valipour Pages 29-42
    In the present research mixed convection flow through a copper-water nanofluid in a driven cavity in the presence of magnetic field is investigated numerically. The cavity is heated from top and cooled from bottom while its two vertical walls are insulated. The governing equations including continuity, N-S and energy equations are solved over a staggered grid system. The study is conducted for Grashof number103 to 105, Hartmann number 0 to 100 and volume fraction number 0 to 5% while Reynolds number is fixed at 100. Hamilton–Crosser and Brinkman models have estimated effective thermal conductivity and effective viscosity of nanofluid, respectively. It is observed that magnetic field has unconstructive effect on heat transfer process whereas nanoparticles increase heat transfer rate.
    Keywords: Mixed convection, Nanofluid, MHD flow, lid, driven cavity
  • F. Haghighatju, H. Hashemipour Rafsanjani Pages 43-47
    Three activated carbons are synthesized in a rotary reactor at different activation times. The adsorption isotherms of the samples are measured The pore size distribution of the samples is determined using combined Saito and Foley method, BJH method. An average potential function has been determined inside the cylindrical pores. The effect of activation time on the pore size distribution samples was investigated. In the micropore size range, as the reaction started, the SF method show the initial micropore was generated. As the activation reaction progress, the micropore volume is developed and widened and therefore area under the PSD curve is increased. Improving the reaction, the pore overlapping was carried out and this occurrence causes decreasing in micropore volume. In the mesopore size range, mesopore volume is increased as the reaction progress. It is acceptable because both developing and overlapping of pores causes improvement of mesopore (and macropore) volume
    Keywords: pore size distribution, SF, BJH, micropore, activated carbon
  • H. Khorasanizadeh, M.M. Fakhari, S. P. Ghaffari Pages 48-64
    In this study, the natural convection heat transfer of variable properties Al2O3-EG-water nanofluid in a differentially heated rectangular cavity has been investigated numerically. The governing equations, for a Newtonian fluid, have been solved numerically with a finite volume approach. The influences of the pertinent parameters such as Ra in the range of 103-107 and volume fraction of nanoparticles from 0 to 0.04 on heat transfer characteristics have been studied. The results verified by making overall comparison with some existing experimental results have shown that for Ra=103, for which conduction heat transfer is dominant, the average Nusselt number increases as volume fraction of nanoparticles increases, but for higher Ra numbers in contradiction with the constant properties cases it decreases. This reduction, which is associated with increased viscosity, is more severe at Ra of 104 compared to higher Ra numbers such that the least deterioration in heat transfer occurs for Ra=107. This is due to the fact that as Ra increases, the Brownian motion enhances; thus conductivity improves and becomes more important than viscosity increase. An scale analysis, performed to clarify the contradictory reports in the literature on the natural convection heat transfer enhancement or deterioration of nanofluids, showed that different kinds of evaluating the base fluid Rayleigh number has led to such a difference.
    Keywords: Nanofluid, Variable properties, Natural convection, Ethylene Glycol, Nusselt number, Enclosure
  • A. Fattahi, M. Alizadeh Pages 65-77
    Double-diffusive mixed convection in a lid-driven square enclosure filled with Al2O3-water is numerically investigated. Two-dimensional nonlinear governing equations are discretized using the control volume method and hybrid scheme. The equations are solved using SIMPLER algorithm. The results are displayed in the form of streamlines, isotherms, and iso-concentrations when the Richardson number varies between 0.01 and 100, the Lewis number changes from 0.1 to 10, the buoyancy ratio ranges between 0 and 5,the volume fractions of nanoparticles differs from 0 to 0.06 and the source location moves from the top toward bottom of the left wall. Moreover, the variation of average Nusselt and Sherwood number are illustrated. It is observed that heat transfer enhances as nanoparticles volume fraction increases, while mass transfer reduces. Additionally, by increasing the buoyancy ratio, both heat and mass transfer are increased.
    Keywords: Mixed convection, Double, diffusion, Variable properties, Al2O3, water nanofluid
  • B. Zahed, T.Fanaei, A. Behzadmehr, H.Ateshi Pages 78-85
    Chemical Vapor Deposition (CVD) is one of the most popular methods for producing Carbon Nanotubes (CNTs). The growth rate of CNTs based on CVD technique is investigated by using a numerical model based on finite volume method. Inlet gas mixture, including xylene as carbon source and mixture of argon and hydrogen as carrier gas enters into a horizontal CVD reactor at atmospheric pressure. In this article the operating pressure variations are studied as the effective parameter on CNT growth rate and length uniformity.
    Keywords: Carbon Nanotube, Chemical Vapor Deposition, Operating Pressure