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Implications of inertia for hydroelastic instability of Herschel-Bulkley fluids in plane poiseuille flow

Jafargholinejad S., Najafi M.

Journal of Theoretical and Applied Mechanics

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2018

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Vol. 56 nr 4

1205--1216

EN

This study investigates the effects of inertia on the hydroelastic instability of a pressure- -driven Herschel-Bulkley fluid passing through a two-dimensional channel lined with a polymeric coating. The no-viscous hyperelastic polymeric coating is assumed to follow the two-constant Mooney-Rivlin model. In this work, analytical basic solutions are determined for both the polymeric gel and the fluid at very low Reynolds numbers. Next, the basic solutions are subjected to infinitesimally-small, normal-mode perturbations. After eliminating the nonlinear terms, two 4-th order differential equations are obtained. The equations with appropriate boundary conditions are then numerically solved using the shooting method. The results of the solution show that the inertia terms in the perturbed equations destabilize the pressure-driven Herschel-Bulkley fluid flow. The investigation reveals that the elastic parameter has a stabilizing effect on the flow. Also, based on the obtained results, the yield stress, depending on the power-law index, has a stabilizing or destabilizing effect on the flow. Since in this work the inertia terms are included in the pertinent governing equations, therefore, the results of this study are much more realistic and reliable than previous works in which inertia terms were absent. In addition, unlike the previous works, the present study considers both the shear-thinning and shear-thickening types of fluids. Hence, the results of this work embrace all the fluids which obey the Herschel-Bulkley model.

2

Inclination angle implications for fluid flow and mixed convection in complex geometry enclosure-meshless numerical analyses

Najafi M., Nikfar M., Arefmanesh A.

Journal of Theoretical and Applied Mechanics

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2015

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Vol. 53 nr 3

519--530

EN

The meshless local Petrov-Galerkin (MLPG) method is extended to analyze the mixed convection and fluid flow in an inclined two-dimensional lid-driven cavity. The enclosure considered comprises two insulated vertical walls and a wavy bottom wall which is subjected to a higher constant temperature than its top counterpart, the sliding lid. For the proposed scheme, the stream function formulation with a weighting function of unity is employed. The simulation results reveal that the local Nusselt number increases with a clockwise increase in the inclination angle. Also, a decrease in the aspect ratio results in an increase in the hot wavy wall average Nusselt number.

3

Template Assisted Growth of Molybdenum Oxide Nanocrystals Through Hydrothermal Process

Farzaneh F., Najafi M.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 9

1523-1528

EN

Rod shaped MoO3 nanocrystals were prepared from ammonium heptamolybdate tetra - hydrate (AHM) and ethylene diamine (en) as template agent in water via a hydrothermal process at 180 graduate C. The prepared nanocrystals were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The range size of nanorods are from a few nanometers (nm) to micrometers in length and 50 to 200 nm in diameter. It was also found that nanostructures of varied dimensionality such as plates and helical plates are formed using citric acid (CA), and starch as template respectively.

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Electrocatalytic Behavior of a Carbon Paste Electrode Modified with Iron(III)tetracyanophenylporphyrin Chloride Towards Dioxygen Reduction

Shamsipur M., Najafi M., Milani Hosseini M. R., Sharghi H.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 6

1173-1183

EN

The electrochemical behavior and ability of a carbon paste electrode modified with iron(III)tetracyanophenylporphyrin chloride (FeTCPP-Cl) as a potential electrocatalyst for the reduction of dioxygen to hydrogen peroxide was investigated using cyclic voltammetry (CV), dou ble-potential step chronoamperometry, and hydrodynamic voltammetry at the rotating disk electrode. The modified electrode showed an excellent electrocatalytic behavior, with respect to reduction of dioxygen in acidic aqueous solu - tions with an overpotential of 750 mV lower than that at the blank carbon paste electrode. Some kinetic parameters for the process were determined from the RDE voltammetry experiments using the Koutecky-Levich plot analysis. Based on the results obtained, a mechanism of the electrocatalysis was proposed.