فهرست مطالب

  • Volume:9 Issue:4, 2013
  • تاریخ انتشار: 1392/10/06
  • تعداد عناوین: 7
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  • M. Tajik Jamal-Abadi*, A. H. Zamzamian Pages 177-184
    Common heat transfer fluids such as water, ethylene glycol, and engine oil have limited heat transfer capabilities due to their low heat transfer properties. Nanofluids are suspensions of nanoparticles in base fluids, a new challenge for thermal sciences provided by nanotechnology. In this study, we are to optimize and report the effects of various parameters such as the ratio of the thermal conductivity of nanoparticles to that of a base fluid, volume fraction, nanoparticle size, and temperature on the effective thermal conductivity of nanofluids using nonlinear optimization methods and artificial neural network. The results for nonlinear optimization methods show that Thermal conductivity of nanofluid enhanced by 32 percent. For the modeling of the Thermal conductivity of nanofluid, the feed-forward back-propagation ANN is employed. Result showed the maximum enhancement of 42 percent for thermal conductivity and this method is more acceptable since excellent agreement between the predictions and the experimental data is obtained with a MAE (mean absolute error) of 0.30%.
    Keywords: Al2O3 nanofluid, Thermal conductivity, Nonlinear optimization, Neural networks
  • M. Hashemiravan, A. S. Mazloom*, N. Farhadyar Pages 185-192
    In this study, blueberry essential oil as a core material was microencapsulated with Inulin and β-cyclodextrin at a ratio of 1:5 (core: wall). Oil in water nano-emulsions were prepared by ultrasonic liquid processors and then transformed to encapsulate powder in spray dryer. Dried powder was stored at 4 ˚C in refrigerator for determining moisture, encapsulation efficiency and morphology properties of encapsulated powders by Scanning electron microscopy. Results showed that the best encapsulation efficiency was found where Inulin was used as wall material. Also, on the basis of observations with Scanning electron microscopy, it was indicated that particles size varied from the range of 140 nm to 20 μm. Accordingly, there is a direct relation between emulsion droplet size and surface blueberry content which affects the oxidation. On the other hand, there is a revise relationship between the emulsion droplet size and encapsulation efficiency.
    Keywords: Blueberry, Nano, emulsion, Ultrasound, Spray dryer, Inulin, β Cyclodextrin
  • A. Banisharif, S. Hakim Elahi, A. Anaraki Firooz, A. A. Khodadadi*, Y. Mortazavi Pages 193-202
    TiO2 /Fe3O4 nanocomposites with various TiO2:Fe3O4 ratios were synthesized by an ultrasonic-assisted deposition-precipitation method and their UV-light decolorization of Congo dye and magnetic separation were investigated. The nanocomposite samples were characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), surface area analayzer (BET) and Fourier transform infrared spectroscopy (FTIR). The effect of TiO2 /Fe3O4 ratio on the photocatalytic activity and magnetic property of the nanocomposites was studied by comparing their decolorization curves and magnetism in the presence of magnet, respectively. The results revealed that the decolorization efficiency and the chemical oxygen demand (COD) removal of TiO2 /Fe3O4 nanocomposite with the ratio of 24/1 reached about 95% and 50%, respectively, within 60 min at room temperature. However, this sample showed the least magnetism. The TiO2 /Fe3O4 nanocomposites with the ratio of 16/1 showed the optimum magnetism and hotodecolorization activity. Also, the ability of synthesized nanocomposites in holding the adsorbed Congo red dye on their surface was investigated.
    Keywords: TiO2, Fe3O4 nanocomposite, Ultrasonic, assisted deposition, precipitation method, Photocatalytic activity, Congo red
  • Maryam Ranjbar, Mostafa Yousefi, Robabeh Nozari, Shabnam Sheshmani Pages 203-212
    In this investigation, we report facile synthesis of cadmium(II)-thioacetamide nanocomposites in the presence and absence of polyvinyl alcohol under ultrasonic irradiations, using cadmium acetate dihydrate (Cd(CH3COO)2.2H2O), potassium iodide (KI), thioacetamide (TAA, CH3CSNH2), and polyvinyl alcohol (PVA) as the starting materials. Results show that in the presence of polyvinyl alcohol sizes of the particles reduce. Characterization of the compounds was carried out by determination of melting point, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared (FT-IR) spectroscopy, 1H-NMR spectroscopy and thermogravimetric-differential thermal analyses (TG/DTA). The thermal decomposition of the polymeric nanocomposite, Cd-thioacetamide/PVA in an autoclave under critical condition led to the formation of spherical cadmium sulfide nanoparticles with an average particle size of about 20 nm. The X-ray diffraction pattern at room temperature revealed that highly pure and crystallized CdS with hexagonal structure were obtained. The sonochemical method resulted in a significant reduction of reaction time, reaction temperature and particle size of the products.
    Keywords: Nanocomposite, Sonochemical method, Thioacetamide, Cadmium sulfide nanoparticles
  • A. Ghaee*, M. Shariaty-Niassar, J. Barzin, A. F. Ismail Pages 213-220
    Chitosan/polyethersulfone (CS/PES) composite membrane was prepared from casting chitosan solution on polyethersulfone substrate membrane. The Substrate membrane was prepared by phaseinversion technique using polyethersulfone (PES) and dimethylacetamide (DMAc) as solvent with and without the addition of polyvinylpyrrolidone (PVP) as pore-forming agent. The effects of the composition of the casting solution on membrane morphology and water permeation were investigated. The membrane prepared from 15 wt % PES with 2.25 wt % PVP demonstrated better water permeability compared to other compositions. CS/PES composite membrane flux and retention were 5.2 lit/m2hr and 76.15%, respectively. The mean pore size of the composite membrane was calculated as 0.99 nm.
    Keywords: Chitosan, Composite membrane, Molecular weight cut off, Nanofiltration, Thermal analysis
  • R. Mohammadinejad*, Sh. Pourseyedi, A. Baghizadeh, Sh. Ranjbar, G. A. Mansoori Pages 221-226
    Green synthesis of nanoparticles, as fundamental building blocks of nanotechnology, has recently attracted considerable attention. Silver nanoparticles have unique physiochemical, biological and environmental properties which make them useful in a wide range of applications. In the present paper we report our research results on biosynthesis of silver nanoparticles from silver precursor using milk thistle plant (Silybum marianum) seed extract. The resulting synthesized Ag nanoparticles (AgNPs) were characterized with UV– visible spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Our measurements showed that S. marianum seed extract can mediate facile and eco-friendly biosynthesis of colloidal spherical silver nanoparticles (AgNPs) of size range 1–25 nm. The colloidal AgNPs were formed at room temperature and were observed to be highly stable even after 6 months.
    Keywords: milk, thistle plant, Silver nanoparticles, Silybum marianum, stable colloids, UV–vis spectroscopy, XRD, TEM
  • A. H. Javid, M. Gorannevis, F. Moattar, A. Mashinchian Moradi, P. Saeeidi* Pages 227-234
    Air Pollution has always been a major problem in metropolises. Volatile organic compounds are one of the major pollutants that are caused by incomplete combustion of fuels in vehicles and gasoline evaporation, especially in fueling stations. Removing these pollutants through traditional methods has always been considered. The paper investigates and studies chemical adsorption behavior of benzene on single-walled carbon nanotubes (9, 9) and (7, 7) in the gas phase by the Gaussian 09 program and using quantum chemical calculations and density functional theory method (DFT). First, carbon nanotubes were generated by a nanotube modeler, and then benzene was passed through the inside and outside of the nanotubes. After that, the absorption energies were calculated using the B3LYP calculation method and 6-31G basic set at different time intervals. Next, the amount of structure energy for carbon nanotube and benzene was separately calculated by the Gaussian 09 program. Using the existing equations, the absorption energy at different time intervals was obtained as follows: For 0.5, 1, 1.5, and 2 angstrom outside the nanotube (7, 7), 14.25, 11.22, 3.32, and 0.78 electron volts (eV); for the nanotube (9, 9), -776.34, -807.12, 817.16, and -844.62 electron volts (eV); for the inside of the nanotube (7, 7), 14.66, 7.76, 7.30, and 7.27 electron volts (eV); and for the nanotube (9, 9), -813.69, -813.9, -816.68, and -819.33 electron volts (eV), respectively. As the results show, when the diameter of the nanotube increases, the energy absorption decreases. Therefore, the carbon nanotube (7, 7), which hasa smaller diameter than the carbon nanotube (9, 9), will be more effective in absorbing and removing benzene from the air.
    Keywords: Air pollution, Carbon nanotubes, Volatile organic Compounds, Benzene