Natural convection effects on heat transfer to power-law fluids flowing under turbulent conditions in vertical pipes

A theoretical analysis of the effect of buoyancy on the heat transfer to non-Newtonian power-law fluids for upward flow in vertical pipes under turbulent conditions has been presented. A criteria for limiting the reduction in heat transfer to less than 5% has been developed for varying pseudoplasticity index. The equation for quantitative evaluation of the natural convection effect on the forced convection has been suggested to be applicable for upward as well as downward flow of the power-law fluids by a change in the sign of the controlling term.     

Separation of nickel from copper in ammoniacal/ammonium carbonate solution using ACORGA M5640 by selective stripping

Separation of nickel from copper in ammoniacal/ammonium carbonate solution using ACORGA M5640 by selective stripping was carried out. The influence of equilibration time, equilibrium pH and extractant concentration on the extraction of both the metals was studied. It was found that the copper extraction equilibrium was reached in a shorter time than the nickel extraction equilibrium. Nickel extraction decreases above an equilibrium pH of 9.0, while the extraction of copper remains unaffected by the changes in the equilibrium pH range of 7–10. Co-extraction, ammonia scrubbing and the selective stripping of copper and nickel were performed for a solution containing 3 g/l each of copper and nickel and 60 g/l ammonium carbonate. The extraction and the percentage stripping of copper and nickel were almost quantitative.     

Study of mutagenic pollution in Bombay

Airborne suspended particulate matter (SPM) from seven areas in and around Bombay city were collected over glass fibre filters (0.8 μm porosity). The chemicals from the SPM were extracted in dimethylsulfoxide and distilled water and were further tested for mutagenicity by Ames' test using five mutants of Salmonella typhimurium. Of the seven areas studied, only four exhibited mutagenicity, which was confirmed by dose—response assays using the mutant strain TA 100. The very high mutagenicity observed in central Bombay correlates with the higher incidence of respiratory tract diseases in the resident population.     

Graphene-based environmental barriers

Many environmental technologies rely on containment by engineered barriers that inhibit the release or transport of toxicants. Graphene is a new, atomically thin, two-dimensional sheet material, whose aspect ratio, chemical resistance, flexibility, and impermeability make it a promising candidate for inclusion in a next generation of engineered barriers. Here we show that ultrathin graphene oxide (GO) films can serve as effective barriers for both liquid and vapor permeants. First, GO deposition on porous substrates is shown to block convective flow at much lower mass loadings than other carbon nanomaterials, and can achieve hydraulic conductivities of 5 × 10(-12) cm/s or lower. Second we show that ultrathin GO films of only 20-nm thickness coated on polyethylene films reduce their vapor permeability by 90% using elemental mercury as a model vapor toxicant. The barrier performance of GO in this thin-film configuration is much better than the Nielsen model limit, which describes ideal behavior of flake-like fillers uniformly imbedded in a polymer. The Hg barrier performance of GO films is found to be sensitive to residual water in the films, which is consistent with molecular dynamics (MD) simulations that show lateral diffusion of Hg atoms in graphene interlayer spaces that have been expanded by hydration.     

Coherent states and the suppression of Bose-Einstein condensation in restricted geometries

A coherent state formalism involving density-phase variables is used to show that for the ideal Bose gas the suppression of Bose condensation in restricted geometries is due to thermal fluctuations of the superfluid velocity potential. The phase factor correlation function has the same form in one, two, and three dimensions as that obtained by Rice for superconductors, with the thermal wavelength setting the scale in this case.     

Estimation of the melt rheology of polymer waste from melt flow index

The need for recycling of polymeric waste has been well recogmized as a result of the escalating prices of the petrochemical feedstocks and the growing awareness to curtail solid waste that causes environmental pollution. During processing, the molecular weight of the polymer is reduced due to thermal and shear degradation. Since the melt rheology of the processed material is sensitive to the changes in molecular structure, knowledge of the complete flow curve depicting the variation of melt viscosity with shear rate at processing temperatures is a useful tool for assessing the reprocessibility of waste material and for specifying the conditions of reprocessing. In the present paper, an effective method is proposed to generate the melt flow curves of polymer waste from knowledge of its melt flow index. The method makes use of a master curve that can be obtained by plotting the available viscosity data in terms of modified functions based on the melt flow index. The master curves characteristic of the particular generic resin type are presented for low-density polyethylene, polypropylene and polystyrene.     

Role of Chain Entanglements in the Electrospinning of Wheat Protein-Poly(Vinyl Alcohol) Blends

The aim of this investigation was to determine if the rapid solvent removal evaporation that occurs during electrospinning enabled the gluten protein and poly(vinyl alcohol) (PVOH) chains to remain at least partially entangled in the final product. Natural and synthetic biopolymer blends are known to phase separate in the melt. Differential scanning calorimetry (DSC) was used to test our hypothesis, which we achieved by systematically comparing the thermal profiles of the nonwoven fibrous sheets comprising: 1) 100% commercial wheat gluten, 2) 100% PVOH, and 3) the (75/25) wheat gluten/PVOH blend. The DSC scans of the two PVOH-containing, nonwoven fibrous sheets exhibited differences in the characteristics and positions of the melting peaks (T_m) of the PVOH crystalline phase, while the DSC scans of the nonwoven fibrous sheets comprising either 100% commercial wheat gluten or the wheat gluten/PVOH blend yielded neither a measurable glass transition temperature (T_g) nor a T_m. Energy dispersive spectroscopy (EDS) was used to compare the elemental compositions of the individual fibers with the compositions of the spherical domains found in the nonwoven fibrous mats. These scans revealed that the mineral matter found in commercial wheat gluten (roughly 1% by weight) had phase-separated from the bulk gluten protein as a result of electrospinning.     

Stability of tri-taper journal bearings under dynamic load using a non-linear transient method

Stability of a tri-taper journal bearing which is subjected to steady, periodic and variable rotating loads is studied theoretically using a non-linear transient approach. The hydrodynamic forces are initially obtained by solving the Reynolds equation, satisfying the Reynolds boundary conditions. Further, the transient behavior of rotor bearing system is predicted by substituting these hydrodynamic forces in the equations of motion and then solving them by fourth order Runge Kutta method. Stability of the rotor bearing system is determined from the journal locus. Comparative studies predict that the dynamic performance is superior for a bearing with high ramp size and aspect ratio.     

Comparative examination of adhesive and cohesive properties of fluorinated coatings on stone/tile surfaces

A NanoScratch methodology was used to evaluate the relative adhesive and cohesive strength of fluorinated poly(methyl methacrylate-co-methacrylic acid) and fluorinated phosphate coatings on stone and tile surfaces. In general, all coatings showed ability to bind to the stone and tile surfaces, and polymer-based coatings expressed stronger adhesion compared to a small-molecule fluorinated phosphate coating. Also, anionic fluorinated polymers containing methacrylic acid (MAA) residues in the ammonium carboxylate form adhered more strongly compared to corresponding acidic polymer counterparts. In addition, anionic fluorinated polymers, shown to adhere more strongly to granite than marble, possibly due to strong Lewis acid-base interaction between carboxylate and aluminosilicates. Conversely, the fluorinated polymers, bearing the MAA side-chains in their free-acid form, bound more strongly to marble via possible Brønsted acid-base interactions between carboxylic acid and calcium carbonate. Lastly, in most cases, comparable fracture thresholds were observed for the same coating material on different substrates. This was expected since fracture threshold is a measure of the mechanical strength of the coating material, independent of the substrate difference.