CFD models in the development of electrical waste recycling technologies

Nowadays electrical waste (EW) recycling has become a practical way to provide raw material for new devices. Computer parts such as memory, motherboard or other parts contain large amount of metals from which the recovery of precious metals and copper represents the highest economical potential. With a proper chemical treatment these metals can be efficiently extracted and separated from the actual waste. For this task a specially designed leaching reactor, equipped with a perforated rotating drum, was used. This work is aimed at investigating if computational fluid dynamics (CFD) tools can be efficiently applied to model the chemical reactor used to dissolve the metals from the EW. First a hybrid CFD-compartment approach was developed to describe the dissolution process in the leaching reactor while the CFD models were used to model the hydrodynamics of the process. Based on the detailed model containing momentum and component mass balance the developed simulator could be used to enhance the performance of the existing reactor system. For the modelling studies COMSOL Multiphysics was used as CFD software.     

Numerical assessment of steam ejector efficiencies using CFD

Ejector efficiencies for the primary nozzle, suction, mixing and diffuser were determined for the first time, according to their definitions, using an axi-symmetric CFD model. Water was considered as working fluid and the operating conditions were selected in a range that would be suitable for an air-conditioner powered by solar thermal energy. Ejector performance was estimated for different nozzle throat to constant section area ratios. The results indicated the existence of an optimal ratio, depending on operating conditions. Ejector efficiencies were calculated for different operating conditions. It was found that while nozzle efficiency can be considered as constant, the efficiencies related to the suction, mixing and diffuser sections of the ejector depend on operating conditions.     

Flexible ceramic-reinforced polyurethane composite coatings on synthetic fibres: Process of continuous liquid film coating and its influence on the coating thickness

A concept for the realisation of composite layers on the surface of synthetic fibres by continuous liquid film coating of spread roving or monofilaments with a slurry containing ceramic particles and a polymeric binder is successfully demonstrated. Polyamide 6 monofilaments were coated with alumina particles and a polyurethane elastomer based binder system to achieve higher abrasion resistance. Under frictional load, the coating is abraded in small units consisting of some particles and the surrounding polyurethane matrix, which predetermines it to be used as sacrificial layer. The slurries showed shear thinning behaviour. Increasing the content of the rheological agent (carboxymethylcellulose [CMC]) led to an exponential increase of the viscosity, which therefore can be tailored by varying the CMC content. An increase of fibre radius, slurry viscosity or withdrawal speed led to an increase of the coating thickness, which is in accordance to published results of Newtonian or non-Newtonian coating fluids.     

Applying process design software for capacity increase and revamp of distillation units

The paper presents the results of feasibility study for increase of crude processing capacity and improves of energy efficiency of crude oil distillation units. Results introduce that boosting up the distillation capacity was solved while keeping the flexibility of units for processing different type crude oils. Analysis of heat exchanger network resulted significant reduction in fuel consumption and in CO₂ emission (93 × 10⁶ GJ year⁻¹ and 3,030 tCO₂ year⁻¹, respectively). Modification of furnace of one of the distillation units showed 63 GJ kt_crude⁻¹ saving in energy and 4.5 tCO₂ kt_crude⁻¹ decrease in emission.     

Focusing of electromagnetic radiation by hyperboloidal and ellipsoidal lenses

A solution to the problem of plane electromagnetic waves focused by an ellipsoidal or a hyperboloidal lens is derived from the Stratton-Chu integral by solving a boundary-value problem. The current method is more rigorous than those hitherto published in the literature. Results show that for linearly polarized incident illumination and in the vicinity of the focus, the distribution of the time-averaged electric energy density is almost fully transverse electric.     

Focusing of electromagnetic waves by paraboloid mirrors. II. Numerical results

We present results of numerical computations obtained from a theory described in Part 1 of our current investigations [J. Opt. Soc. Am. A 17, 2081 (2000)]. We show that a segment of a paraboloid mirror produces an intensity distribution identical to that of a high-aperture lens. It is shown that when the convergence angle of the paraboloid is increased beyond the pi/2 limit, the lateral resolution in the direction orthogonal to the incident polarization improves, whereas in the other direction the resolution worsens. Numerical results show that paraboloid mirrors of high convergence angle exhibit dispersion; that is, when the focal length is altered by a quarter of the wavelength the intensity in the focus changes from its maximum to its minimum value. A focal shift is observed that, in the case of a paraboloid of low convergence angle is identical to the Fresnel shift. However, a focal shift is also observed at large convergence angles.     

Electrochemical corrosion behavior of amorphous carbon nitride thin films

The corrosion behavior along with biocompatibility and mechanical properties plays an important role in determining of biomedical implants feasibility. Diamond-like carbon seems to be the promising material in which all these three requirements can be achieved. In this study nitrogen doped amorphous carbon (a-C:N) films were deposited on silicon and medical CoCrMo alloy substrates by vacuum glow discharge sputtering technique using different deposition conditions from graphite target. Potentiodynamic polarization tests were employed to assess the corrosion performances of the films at room temperature in 0.89 wt. % NaCl solution. The influence of substrate bias on the electrochemical corrosion behavior was investigated. The highest value off E_corr for CoCrMo substrate was measured on the coating deposited with substrate bias around −0.6 kV. The shift of E_corr to more positive values was about 350 mV.     

Mechanically Versus Thermally Generated Quantum Turbulence of 4He Superflow

An experiment on thermally driven ⁴He superflow (Chagovets and Skrbek in Phys. Rev. Lett. 100:215302, 2008; J. Low Temp. Phys. 153:162, 2008) yielded very different steady state turbulence properties from a nominally identical recent realisation where the helium fountain drive was replaced by bellows. Here we argue that differences are most likely not due to fundamental reasons, but to incorrect velocity calculation in the fountain drive version. We show by a combination of direct velocity measurements and indirect analysis that the real velocity is significantly lower than predicted, and one main reason for this is unaccounted heat spent to enhance helium evaporation. The velocity correction brings the two experiments in reasonable agreement. We also suggest that the transition to a new state of superfluid turbulence claimed in Refs. (Chagovets and Skrbek in Phys. Rev. Lett. 100:215302, 2008; J. Low Temp. Phys. 153:162, 2008) may be a spurious effect of an observed nonlinearity occurring between fountain heat current and superflow velocity.     

Biocompatibility study of three distinct carbon pastes for application as electrode material in neural stimulations and recordings

Neural interfaces hold great promise for research and treatment of a wide variety of neurological diseases. Medical electrodes are designed to interface with the nervous system and provide control signals for neural prostheses. We fabricated previously a hook-up neural electrode. Here we investigate the in vitro cytotoxicity of three commercial carbon pastes used for printing the conductor tracks of this electrode. At first, the carbon pastes were characterized with respect to their microstructure and chemical composition. SEM images showed a grainy texture that is associated to the carbon/graphite microparticles dispersed by the polymeric binder. All the three pastes contained in major proportions carbon and in different proportions other elements. The surface roughness analysis evidenced differences in the smoothness of the carbon paste surfaces. Sterilization procedures did not alter the microstructure or surface morphology of the pastes. Finally, cell viability based on -(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test and fluorescence staining experiments proved non-cytotoxicity and suitability of the studied carbon pastes as electrode material for measuring neural activity during surgeries (up to a certain time period).     

Absorption and fluorescence spectroscopic study on complexation of Oxazine 1 Dye by calix[8]arenesulfonate

It has been established by combined absorption and fluorescence measurements that the cationic dye Oxazine 1 (OX) and the polyvalent anionic host calix[8]arenesulfonate (SCA8) form two complexes in simultaneous reactions: OX + SCA8 <--> OX.SCA8 (1), and OX.SCA8 + OX <--> OX(2).SCA8 (2). The equilibrium constants for the two reactions, as functions of the ionic strength (I), and the absorption and fluorescence spectra of the two complex species have been determined by a least-squares fitting method from the experimental data. The variations of the binding constants with the ionic strength could be described on the basis of Debye-Huckel theory. The equilibrium constants are large; their values extrapolated to I = 0 are K(1) = 5.5 x 10(6) M(-1) and K(2) = 4.4 x 10(5) M(-1). The fluorescence of OX undergoes a strong static quenching upon complexation. These results indicate that the complexes are held together by strong electrostatic forces. The addition of non-fluorescent tetramethylammonium chloride to OX-SCA8 mixtures results in a dramatic fluorescent enhancement, which demonstrates the potential applicability of this supramolecular system in fluorescence assays.