Modeling granular materials as compressible nonlinear fluids: Heat transfer boundary value problems

We discuss three boundary value problems in the flow and heat transfer analysis in flowing granular materials: (i) the flow down an inclined plane with radiation effects at the free surface; (ii) the natural convection flow between two heated vertical walls; (iii) the shearing motion between two horizontal flat plates with heat conduction. It is assumed that the material behaves like a continuum, similar to a compressible nonlinear fluid where the effects of density gradients are incorporated in the stress tensor. For a fully developed flow the equations are simplified to a system of three nonlinear ordinary differential equations. The equations are made dimensionless and a parametric study is performed where the effects of various dimensionless numbers representing the effects of heat conduction, viscous dissipation, radiation, and so forth are presented

A highly N-doped carbon phase "dressing" of macroscopic supports for catalytic applications

© The Royal Society of Chemistry 2015. The straightforward "dressing" of macroscopically shaped supports (i.e. β-SiC and α-Al2O3) with a mesoporous and highly nitrogen-doped carbon-phase starting from food-processing raw materials is described. The as-prepared composites serve as highly efficient and selective metal-free catalysts for promoting industrial key-processes at the heart of renewable energy technology and environmental protection

Synthesis and Characterization of Nanocomposites Using the Nanoscale Laser Soldering in Liquid Technique

Abstract We have synthesized Au/CuO and Au/ZnO nanocomposites using the laser soldering technique. The process was carried out by irradiating a solution containing Au-CuO and Au-ZnO nanoparticles using 532 nm laser pulses of 0.1 J/cm 2 continuously for 20 minutes. The beam was focused using a 75 mm focal lens and the laser power near the focal region was estimated to be about 2.4 x 10 12 W/m 2 . Their UV-VIS absorption and transmission were observed and the results indicated that the bandgap energies of the Au/CuO and Au/ZnO are significantly lower than those of pure CuO and ZnO. A theoretical model was developed and the calculation showed that the soldering process was due to the laser melting of the gold nanoparticles and the molten gold got soldered to the ZnO as well as CuO nanoparticles nearby

Remarks on Constitutive Modeling of Nanofluids

We discuss briefly the constitutive modeling of the stress tensor for nanofluids. In particular, we look at the viscosity of nanofluids containing multiwalled carbon nanotubes (MWCNTs) stabilized by cationic chitosan. MWCNTs can be used either to enhance or reduce the fluid base viscosity depending on their weight fractions. By assuming that MWCNT nanofluids behave as generalized second-grade fluid where the viscosity coefficient depends upon the rate of deformation, a theoretical model is developed. A simplified version of this model, similar to the traditional power-law model, is used in this study. It is observed that the theoretical results agree well with the experimental data

Use Of Laser-Induced Spark For Studying Ignition Stability And Unburned Hydrogen Escaping From Laminar Diluted Hydrogen Diffusion Jet Flames

Ignition and unburned hydrogen escaping from hydrogen jet diffusion flames diluted with nitrogen up to 70% were experimentally studied. The successful ignition locations were about 2/3 of the flame length above the jet exit for undiluted flames and moved much closer to the exit for diluted flames. For higher levels of dilution or higher flow rates, there existed a region within which a diluted hydrogen diffusion flame can be ignited and burns with a stable liftoff height. This is contrary to previous findings that pure and diluted hydrogen jet diffusion cannot achieve a stable lifted flame configuration. With liftoff, the flame is noisy and short with significant amount of unburned hydrogen escaping into the product gases. If ignition is initiated below this region, the flame propagates upstream quickly and attaches to the burner rim. Results from measurements of unburned hydrogen in the combustion products showed that the amount of unburned hydrogen increased as the nitrogen dilution level was increased. Thus, hydrogen diffusion flame diluted with nitrogen cannot burn completely

Modeling The Effect Of Particle Size On The Activation Energy And Ignition Temperature Of Metallic Nanoparticles

The present work reports a simple theoretical model to calculate the effect of the particle size on the activation energy and the ignition temperature of metallic nanoparticles. The activation energy was deduced from the particle cohesive energy and the ignition temperature was calculated using the condition that the heat generated by the combustion reactions is sufficient to counterbalance the particle heat loss to the surrounding. Heat loss was assumed to be in the transient regime and the combustion heat generation was calculated using the simplest Arrhenius-type model. Using aluminum as an example, the results showed that for particles of sizes larger than 50 nm, increasing the particle size had a little effect on the number of the surface atoms, the activation energy and the ignition temperature. As the particle size decreases the number of the surface atoms increases and the corresponding activation energy, Ed/E∞ and the ignition temperature decrease. As the particle size decreased to about 5 nm and smaller, the activation energy could reduce to 20% or 50% of the bulk value and an ignition temperature as low as 800 K was obtained from the calculation depending on the ratio of the coordination number

Synthesis Of Cation-Exchanged Laponite Suspensions By Laser Ablation Of Microsized-Metal Particles In Liquid

Laser ablation in the liquid technique has been used to synthesize cation-exchanged laponite suspensions. In summary, laser ablation of the microsize-metal powder (Co, Al, and Cu) dispersed in an aqueous solution containing deionized water laponite crystals was carried out using laser beam generated by a single-mode, Q-switched NdYag laser operating at 532 nm with a pulse duration of 5.5 ns and 10 Hz repetition rate. Laser fluence was 0.265 J/cm2 for all tests. For all samples, the mass fraction of laponite was 1%. General observations of the prepared samples indicated that an aqueous suspension of 1 wt% laponite retained its free flowing liquid phase characteristics even after aging for several weeks. When bivalent cationic metals (Cu, Co, Al) were ablated in it for about 1 h, even with a small amount of the metal (0.025% and 0.050%) were generated, the suspension became highly viscous and behaved as a shear-thinning and thixotropic material. That is, the suspension gelled strongly when it was allowed to rest. The gels, however, could easily be reverted to a low viscosity liquid with simple shaking. Information from TEM and XRD analysis indicated that such a solgel transformation might be due to the charge exchange between the cationic species produced during the laser ablation and the sodium ions in the interlayers of the clay sheets