Transport Phenomena in Nano and Micro ScalesTransport Phenomena in Nano and Micro Scales
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Tue, 27 Jun 2017 21:46:07 +0100FeedCreatorTransport Phenomena in Nano and Micro Scales
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Feed provided by Transport Phenomena in Nano and Micro Scales. Click to visit.A modified variable physical properties model, for analyzing nanofluids flow and heat transfer ...
http://tpnms.usb.ac.ir/article_3207_430.html
In this paper, the problem of laminar nanofluid flow which results from the nonlinear stretching of a flat sheet is investigated numerically. In this paper, a modified variable physical properties model for analyzing nanofluids flow and heat transfer is introduced. In this model, the effective viscosity, density, and thermal conductivity of the solid-liquid mixture (nanofluids) which are commonly utilized in the homogenous single-phase model, are locally combined with the prevalent single-phase model. A numerical similarity solution is considered which depends on the local Prandtl number, local Brownian motion number, local Lewis number, and local thermophoresis number. The results are compared to the prevalent single-phase model. This comparison depicts that the prevalent single-phase model has a considerable deviation for predicting the behavior of nanofluids flow especially in dimensionless temperature and nanoparticle volume fraction. In addition the effect of the governing parameters such as Prandtl number, the Brownian motion number, the thermophoresis parameter, the Lewis number, and etc. on the velocity, temperature, and volume fraction distribution and the dimensionless heat and mass transfer rates are examined.Fri, 09 Jun 2017 19:30:00 +0100Synthesis and characterization of magnetic γ- Fe2O3 nanoparticles: Thermal cooling enhancement ...
http://tpnms.usb.ac.ir/article_3208_430.html
Nano-size maghemite (γ-Fe2O3) particles were prepared in one step using ultrasound radiation. The obtained nanoparticles were characterized by SEM, TEM , XRD, FTIR, and VSM. The results revealed that the synthesized nanoparticles were spherical, mono-dispersed and uniform. Furthermore, the crystalline structure of nanoparticles endorsed by X-ray diffraction study. The FTIR spectra have provided information on the structure of the surface of nanoparticles. TEM analysis showed that the average particle size of the γ -Fe2O3 are about 15 nm. The formed nanoparticles exhibited unique magnetic behavior with magnetic saturation values of~68 emu/g. By utilizing properties of synthetic γ -Fe2O3 nanoparticles, a three-dimensional incompressible nanofluid flow in a confined sinusoidal converging jet in turbulent flow regime was numerically investigated. Results were obtained for the flow structure at different Reynolds numbers for steady asymmetric jet development at various values of the duct-to-jet width ratio (aspect ratio),different amplitudes and different volume fractions of nanoparticles. The results showed that by increasing the Reynolds number, aspect ratio, amplitude and volume fraction of γ -Fe2O3 nanoparticles, the averaged Nusselt number will increase.Fri, 09 Jun 2017 19:30:00 +0100Improvement of Thermal Conductivity Properties of Drilling Fluid by CuO Nanofluid
http://tpnms.usb.ac.ir/article_3209_430.html
In a recent decade, application of nanofluid as a candidate for heat transfer medium has gaining an increasing attention due to its unique advantages. In the light of its unique advantages, it has been utilized in different industries such as oil and gas industries. In this work aims at improving thermal conductivity of the water-based drilling fluid by using the CuO nanofluid additive. CuO nanoparticle is synthesized by precipitation method and CuO nanofluid was produced to use as an additive to drilling fluid. Scanning electron microscope, x-ray diffraction, dynamic light scatering, sedimentation test and zeta-potential are used to characterize nanoparticle and nanofluid. The result indicated that the size of synthesized nanoparticles and nanofluid were about 4 nm and 34 nm, respectively. Finally CuO nanofluid added into drilling fluid to measure the improvement of drilling fluid thermal conductivity. The result shows that the nanofluid concentration in the range of 0.1 to 0.3 vol% is able to enhance the thermal conductivity of drilling fluid to 29 % and decrease the temperature gradient more than twice compare with the base drilling fluid.Fri, 09 Jun 2017 19:30:00 +0100Numerical simulation of nanofluid flow over diamond-shaped elements in tandem in laminar and ...
http://tpnms.usb.ac.ir/article_3210_430.html
In this paper, the Al2O3-water nanofluid flow in laminar and turbulent flows inside tubes fitted with diamond-shaped turbulators is numerically modeled. The nanofluid flow is modeled by employing a two-phase mixture method and applying the constant heat flux boundary condition at tube walls. In the results, the effects of different parameters such as the geometry of turbulators, volume fraction and diameter of nanoparticles, etc. on the flow field in the tubes have been investigated. The obtained results indicate that, with the reduction of tail length ratio (TR) and increase of vertex angle of turbulators (θ), the heat transfer coefficient as well as the wall shear stress increase. Similarly, with the reduction of TR and increase of θ, the amount of secondary flows, vortices and the turbulent kinetic energy increase. Moreover, the increase in the volume fraction of nanoparticles and the reduction of nanoparticles diameter lead to the increase of the heat transfer coefficient and wall shear stress.Wed, 31 May 2017 19:30:00 +0100Lattice Boltzmann method for MHD natural convection of CuO/water nanofluid in a wavy-walled ...
http://tpnms.usb.ac.ir/article_3211_430.html
In this paper, natural convection heat transfer of CuO-water Nanofluid within a wavy-walled cavity and subjected to a uniform magnetic field is examined by adopting the lattice Boltzmann model. The left wavy wall is heated sinusoidal, while the right flat wall is maintained at the constant temperature of Tc. The top and the bottom horizontal walls are smooth and insulated against heat and mass. The influence of pertinent parameters such as solid volume fraction of nanoparticles (φ), Rayleigh number (Ra), Hartmann number (Ha) and phase deviation of sinusoidal boundary condition (Φ) are investigated on flow and heat transfer fields. Results show that the heat transfer decreases with the increase of the Hartmann number, but it increases by the increment of Rayleigh number and nanoparticle volume fraction. The magnetic field augments the effect produced by the presence of nanoparticles at Ra = 104 and 105 in contrast with Ra = 103. Moreover, the greatest effects of nanoparticles are observed for different values of the phase deviation with an increase in Rayleigh number. This study can, provide useful insight for enhancing the MHD natural convection heat transfer performance within wavy-walled cavity and sinusoidal temperature distribution.Fri, 09 Jun 2017 19:30:00 +0100Numerical Simulation of Laminar Convective Heat Transfer and Pressure Drop of Water Based-Al2O3 ...
http://tpnms.usb.ac.ir/article_3214_430.html
The convective heat transfer and pressure drop of water based Al2O3 nanofluid in a horizontal tube subject to constant wall temperature condition is investigated by computational fluid dynamic (CFD) method. The Al2O3 nanofluid at five volume concentration of 0.1, 0.5, 1.0, 1.5 and 2 % are applied as a non Newtonian power law and Newtonian fluid with experimentally measured properties of density, viscosity, thermal conductivity and specific heat capacity. The power law fluid determines the heat transfer coefficient and pressure drop better than that of the Newtonian fluid. The experimentally measured viscosity is used as consistency index and the flow behavior index (n) is computed in various Reynolds number and nanoparticle concentrations in order to minimize the difference between the experimental and computational results. It is revealed that n is a function of nanoparticle concentration and independent of nanofluid velocity and Al2O3 nanofluid behaves as a shear thickening fluid for n>1. Both the experimental and computational results show an increase in the heat transfer coefficient and pressure drop with an increase in the nanofluid concentration. By using the experimental data a correlation for the average Nusselt number estimation based on the dimensionless number (Re and Pr) and nanoparticles concentration (φ) is obtained. The results of this correlation introduce a 1.162 % average absolute deviation.Fri, 09 Jun 2017 19:30:00 +0100Effects of Plasma Discharge Parameters on the Nano-Particles Formation in the PECVD Reactor
http://tpnms.usb.ac.ir/article_3219_430.html
In this paper, the effects of plasma discharge parameters on the nano particles formation process in a plasma enhanced chemical vapor deposition (PECVD) reactor using a model based on equations of ionization kinetics for different active species are studied. A radio frequency applied electric field causes ionization inside the reactor and consequently different reaction schemically active species are formed. The reactions leading to production of nano-particles include negative and positive ion, neutrals and radicals.
The dependency of the background gas temperature, frequency and amplitude of applied electric field as the main plasma discharge parameters on the avalanche time constant, nano-particles formation and their growth rate is verified. Silane and hydrogen gases are considered as background species. It was observed that the growth rate at higher frequencies and lower temperatures is higher. It was seen that increase in the applied voltage peak amplitude affects charged and radical particles fairly similar to the applied voltage frequency.Fri, 09 Jun 2017 19:30:00 +0100