Buoyancy driven Flow of a Second-Grade Nanofluid flow Taking into Account the Arrhenius Activation Energy and Elastic Deformation:Models and Numerical Results

The buoyancy driven flow of a second-grade nanofluid in the presence of a binary chemical reaction is analyzed in the context of a model based on the balance equations for mass,species concentration,momentum and energy.The elastic properties of the considered fluid are taken into account.The two-dimensional slip flow of such non-Newtonian fluid over a porous flat material which is stretched vertically upwards is considered.The role played by the activation energy is accounted for through an exponent form modified Arrhenius function added to the Buongiorno model for the nanofluid concentration.The effects of thermal radiation are also examined.A similarity transformations is used to turn the problem based on partial differential equations into a system of ordinary differential equations.The resulting system is solved using a fourth order RK and shooting methods.The velocity profile,temperature profile,concentration profile,local skin friction,local Nusselt number and local Sherwood number are reported for several circumstances.The influence of the chemical reaction on the properties of the concentration and momentum boundary layers is critically discussed.

Transfer of electrons on scratched iron surfaces:Photoelectron emission and X-ray photoelectron spectroscopy studies

We report the activation energy, ΔEa, for the quantum yield in thermally assisted photoelectron emission(TAPE) under 210-nm-wavelength light irradiation, and the associated X-ray photoelectron spectroscopy(XPS) results. Samples were cleaned only in acetone and scratched in air, water, methanol, ethanol, acetone, benzene, and cyclohexane. Glow curves, describing the temperature dependence of photoelectron emission(PE) quantum yield(emitted electrons/photon), Y, were obtained. A simple method of determining ΔEa using Y, called YGC, at seven temperatures up to 353 °C, for the same Y glow curve, was proposed. The ΔEa obtained using this method was almost the same as that obtained from Y for seven stationary temperatures(YST). For scratched samples, the TAPE was measured over two cycles of temperature increase and subsequent decrease(Up1, Down1 and Up2, Down2 scans) in the 25–339 °C range, and ΔE_a was obtained from YGC. The Arrhenius plot was approximated by a straight line, although a convex swelling peak appeared in the Up1 scan. ΔE_(aUp1) was in the 0.212–0.035 eV range, depending on the environment in which scratching was performed; ΔE_(aUp1) for water was much higher than that for acetone. This was explained in terms of the mode of the acid–base interaction between the liquid molecules and the hydroxyl group of Fe–OH. The values of ΔE_(aDown1), ΔEa Up2, and ΔE_(aDown2) were in the 0.038–0.012 eV range. The total count of electrons emitted during the Up1 and Up2 scans was found to decrease with increasing ΔE_(aUp1) and ΔE_(aUp2), respectively. ΔE_(aUp2) was found to increase with increasing presence of the FeO component in the analyzed Fe oxides. The convex swelling peak was attributed to the removal of carbon materials from the scratched surface and the effect of the increased electron density of the surface hydroxyl group of FeOH under the light irradiation.

Influence of N-type doping on the oxidation rate in n-type 6H-SiC

The doping dependence of dry thermal oxidation rates in n-type 6H-SiC was studied. The oxidation temperature ranged from 1050 to 1150℃ and the nitrogen doping concentration ranged from 9.53× 10^16, 1.44× 10^17, to 2.68×10^18 cm ^3. By combining the modified deal-grove model and Arrhenius equation, the linear and parabolic rate constants, and their corresponding activation energies were extracted. The results show that： higher temperature corresponded to thicker oxides; dry thermal oxidation rate in n-type 6H-SiC depended on the doping concentration; both linear-rate-constant and parabolic-rate-constant increased with the doping concentration; the parabolic activation energy increased from 0.082 to 0.104 e V, both linear and parabolic activation energies increasing with the doping concentration; and, the parabolic pre-exponential factor increased from 2.6 ×10^4 to 2.7 ×10^5nm^2/s, both linear and parabolic pre-exponential factor increasing with doping concentration. Moreover, the experiment also illustrated that it is unreasonable to use a variation of the Arrhenius activation energy to explain the doping dependence of thermal oxidation on SiC.