فهرست مطالب

  • Volume:7 Issue:3, 2011
  • تاریخ انتشار: 1390/07/14
  • تعداد عناوین: 7
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  • S. Zeinali Heris*, Taofik H. Nassan Nassan, S. H. Noie Pages 111-120
    Sometimes the need for non-circular ducts arises in many heat transfer applications because of lower pressure drop of non-circular cross section such as square duct compared to circular tube, particularly in compact heat. But square cross section has poor heat transfer performance and it is expected that using a nanofluid as a new heat transfer media may improve the heat transfer performance of this kind of duct. In this work, a nanofluid of CuO nanoparticles and distilled water has been prepared and its heat transfer characteristics have been studied through square cupric duct in laminar flow under uniform heat flux. Experiments revealed that a remarkable enhancement in heat transfer coefficient is achieved compared to the base fluid. Moreover, it has been reported that heat transfer coefficient enhances with increasing nanofluid flow rate as well as concentration of nanoparticles in the nanofluid especially at high flow rates. So, ultimate enhancement of 20.7% in Nu achieved at 1.5% volume concentration of CuO/water nanofluid. The basic reason for lower heat transfer rate of square ducts is existence of a static section for some part of fluid near corners of square duct and the results indicated that the presence of nanoparticles decrease this unmoved static section which consequently increase the heat transfer from the duct wall to the nanofluid.
    Keywords: Heat transfer enhancement, Square duct, Nanofluid, Uniform heat flux
  • S. H. Mahboobi*, A. Meghdari, N. Jalili, F. Amiri Pages 121-126
    Based on the fact the manipulation of fine nanoclusters calls for more precise modeling, the aim of this paper is to conduct an atomistic investigation for interaction analysis of particle-substrate system for pushing and positioning purposes. In the present research, 2D molecular dynamics simulations have been used to investigate such behaviors. Performing the planar simulations can provide a fairly acceptable qualitative tool for our purpose while the computation time is reduced extremely in comparison to 3D simulations. To perform this study, Nose-Hoover dynamics and Sutton-Chen interatomic potential are used to investigate the behavior of the aforementioned system. Pushing of Au clusters on Au substrate has been chosen as illustrative examples. Dependency of the aforementioned behavior on temperature has been investigated. Higher temperature affects the pushing success level considerably. In addition, the simulation was performed for Ag cluster as well to compare the performance to one for Au cluster.
    Keywords: Molecular dynamics, Transition Metals, Nano, clusters, Nano, scale manipulation
  • A. Doustgani, E. Vasheghani-Farahani*, M. Soleimani, S. Hashemi-Najafabadi Pages 127-132
    Nanofibrous scaffolds produced by electrospinning have attracted much attention, recently. Aligned and random nanofibrous scaffolds of poly (vinyl alcohol) (PVA), poly (ε-caprolactone) (PCL) and nanohydroxyapatite (nHA) were fabricated by electrospinning method in this study. The composite nanofibrous scaffolds were subjected to detailed analysis. Morphological investigations revealed that the prepared nanofibers have uniform morphology and the average fiber diameters of aligned and random scaffolds were 135.5 and 290 nm, respectively. The obtained scaffolds have a porous structure with porosity of 88 and 76 % for random and aligned nanofibers, respectively. Furthermore, FTIR analysis demonstrated that there were strong intramolecular interactions between the molecules of PVA/PCL/nHA. On the other hand, mechanical characterizations show that aligning the nanofibers, could significantly improve the rigidity of the resultant biocomposite nanofibrous scaffolds. The results indicate that aligned scaffolds are suitable for tissue engineering applications.
    Keywords: Electrospinnig, Nanofibrous scaffold, poly (vinyl alcohol), Poly (ε, caprolactone)
  • H. Mohammadi Kamrava*, M. Barati Pages 133-136
    In this paper we investigate the effect of a random transverse field, distributed according to a trimodal distribution, on the phase diagram and magnetic properties of a two-dimensional lattice (square with z=4), ferromagnetic Ising system consisting of magnetic atoms with spin-1. This study is done using the effectivefield theory (EFT) with correlations method. The equations are derived using a probability distribution method based on the use of exact Van der Waerden identities. We present our numerical results, such as the phase diagrams, the thermal variations of the transverse magnetization, the internal energy, the magnetic specific heat as a function of different values of p, the concentration of the random transverse field. As a result, the critical values of transverse field, temperature and concentration were obtained for the square lattice.
    Keywords: Transverse Ising model, Effective, field theory, Phase transition, Surface magnetic properties
  • S. Basir Jafari, R. Malekfar*, S. E. Khadem Pages 137-142
    In this paper, the radial breathing mode (RBM) frequencies of multi-walled carbon nanotubes (MWCNTs) are obtained based on the multiple-elastic thin shell model. For this purpose, MWCNT is considered as a multiple concentric elastic thin cylindrical shells, which are coupled through van der Waals (vdW) forces between two adjacent tubes. Lennard-Jones potential is used to calculate the vdW forces between adjacent tubes. The RBM frequencies of MWCNTs predicted by the present shell model are in excellent agreement with the available experimental and atomistic results with relative errors less than 2.5%. The results emphasize the utility of multiple-elastic thin shell theory for modelling the RBM vibrational behaviour of MWCNTs.
    Keywords: Lennard, Jones potential, Multi, walled carbon nanotube, Multiple, elastic thin shell model, Radial
  • J. Davoodi*, H. Alizade Pages 143-146
    In this study, we have investigated radius dependence of hydrogen storage within armchair (n,n) single walled carbon nanotubes (SWCNT) in a square arrays. To this aim, we have employed equilibrium molecular dynamics (MD) simulation. Our simulations results reveal that radius of carbon nanotubes are an important and influent factor in hydrogen distribution inside carbon nanotubes and consequently in amount of hydrogen stored in carbon nanotube array. Moreover, our results show that the SWCNTs with radius smaller than (5, 5) SWCNTs, do not have the ability of adsorption and storage of hydrogen inside themselves.
    Keywords: Hydrogen storage, Carbon nanotube, Molecular dynamics simulation
  • M. Ranjbar*, S. H. Mahmoudi Najafi, N. Shahsavan, M. Yousefi Pages 147-152
    The study describes the synthesis and characterization of zinc(II) minoxidil nanocomposite (1). The reaction between zinc(II) acetate, minoxidil, {C9H15N5O=minoxidil=(2,4-diamino-6-piperidine-1-yl) pyrimidine N-oxide)} as a ligand and KI as bridging agent, in methanol at 60°C leads to the formation of nano-sized Zn(II) minoxidil nanocomposite, 1. Characterization of (1) was carried out by elemental analysis, FTIR, scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDAX), and gel-permeation chromatography analysis (GPC). The result showed that nanocomposite (1) has polymeric structure with spherical morphology and particle size of about 77 nm. Wurtzite (hexagonal) nanocrystals of zinc oxide were prepared from decomposition of the coordination polymer (1) at 400°C. Characterization of zinc oxide nanocrystals was performed by FTIR spectroscopy, scanning electron microscopy (SEM), EDAX and X-ray powder diffraction XRD. The results showed that the product has spherical morphology with particle size of about 34 nm.
    Keywords: Minoxidil, Zinc oxide, Nanocrystals, thermal gradient method