Efficient Binary Tomographic Reconstruction

Tomographic reconstruction of a binary image from few projections is considered. A novel heuristic algorithm is proposed, the central element of which is a nonlinear transformation ψ(p)=log(p/(1?p)) of the probability p that a pixel of the sought image be 1-valued. It consists of backprojections based on ψ(p) and iterative corrections. Application of this algorithm to a series of artificial test cases leads to exact binary reconstructions, (i.e., recovery of the binary image for each single pixel) from the knowledge of projection data over a few directions. Images up to 10⁶ pixels are reconstructed in a few seconds. A series of test cases is performed for comparison with previous methods, showing a better efficiency and reduced computation times.     

An Investigation of Error Sources in Computational Fluid Dynamics Modelling of a Co-current Spray Dryer

The paper is focused on identifying error sources in computational fluid dynamics(CFD) predictions of a spray drying process. Seven groups of drying and atomisation parameters were selected for analysis and 13 simulation trials were performed. The theoretical results were compared with experimental data and sensitivity of the simulation results to the analysed factors was determined. The following parameters affecting the accuracy of CFD spray modelling were found: gas turbulence model, particle dispersion, atomising air, initial parameters of atomisation and heat losses to the environment. A major difference in the errors committed during modelling of spray drying process for fine and coarse sprays was observed.     

Unsteady radiative heat transfer within a suspension of ZnO particles undergoing thermal dissociation

An emitting, absorbing, and anisotropically scattering plain medium containing a suspension of ZnO particles is considered, in which the particles are directly exposed to high-flux irradiation and undergo shrinkage during their endothermic dissociation into Zn(g) and O₂ at above 2100 K. The unsteady energy equation that links the rate of radiative heat transfer to the rate of the chemical reaction is formulated and solved numerically by the finite volume technique and the explicit Euler time-integration scheme. The path-length Monte Carlo method is applied for modeling the radiative transfer within the suspension using the absorption/scattering coefficients and the scattering phase function obtained from the Mie theory. It is found that the particle suspension can be heated rapidly from its initial 300 K to over 1800 K in less than 0.1 s, resulting in a more uniform temperature profile as the reaction progresses, particles shrink, and the suspension becomes optically thinner. The chemical conversion increases with decreasing initial particle diameter and volume fraction due to the efficient radiative absorption.     

Ionic liquids as electrolytes

Salts having a low melting point are liquid at room temperature, or even below, and form a new class of liquids usually called room temperature ionic liquids (RTIL). Information about RTILs can be found in the literature with such key words as: room temperature molten salt, low-temperature molten salt, ambient-temperature molten salt, liquid organic salt or simply ionic liquid. Their physicochemical properties are the same as high temperature ionic liquids, but the practical aspects of their maintenance or handling are different enough to merit a distinction. The class of ionic liquids, based on tetraalkylammonium cation and chloroaluminate anion, has been extensively studied since late 1970s of the XX century, following the works of Osteryoung. Systematic research on the application of chloroaluminate ionic liquids as solvents was performed in 1980s. However, ionic liquids based on aluminium halides are moisture sensitive. During the last decade an increasing number of new ionic liquids have been prepared and used as solvents. The general aim of this paper was to review the physical and chemical properties of RTILs from the point of view of their possible application as electrolytes in electrochemical processes and devices. The following points are discussed: melting and freezing, conductivity, viscosity, temperature dependence of conductivity, transport and transference numbers, electrochemical stability, possible application in aluminium electroplating, lithium batteries and in electrochemical capacitors.     

Carbon materials and catalytic wet air oxidation of organic pollutants in wastewater

The use of carbon materials as catalytic support or direct catalyst in catalytic wet air oxidation (WAO) of organic pollutants is reviewed. The discussion covers important engineering aspects including the characterisation, activity and stability of carbon catalysts, process performance, reaction kinetics and reactor modelling. Recommendations for further research in catalytic WAO are outlined.     

Einige fragen der tunneltheorie der wasserstoffüberspannung—II. Die temperaturabhängigkeit der stromdichte und die beträge der quanteneffekte

The dimensions of the potential barrier involved in hydrogen and deuterium evolution on mercury are computed from the experimental values of the effective activation energies on the assumption that the barrier has a parabolic shape. The ratio of the pre-exponential factors and the isotopic separation factor obtained theoretically in this manner are in good agreement with experimental data. The calculation shows that the tunnel effect plays a substantial but still moderate role in the case under study. Comparison with the results of an earlier derivation based on Eckart's potential function allows the determination of the most probable shape of the true barrier. The usually assumed dimensions are shown to be incorrect.

Résumé

On calcule les dimensions de la barrière de potentiel pour le dégagement d'hydrogène et de deutérium sur le mercure en partant des valeurs expérimentales de l'énergie d'activation et en supposant que la barrière a une forme parabolique. Le rapport des facteurs préexponentiels et le facteur de séparation isotopique ainsi obtenus théoriquement sont en accord avec les données expérimentales. Le calcul montre que l'effet tunnel ne peut être négligé mais qu'il ne joue cependant qu'un rôle moyen dans le cas étudié. La comparaison avec les résultats d'une dérivation précédente partant de la fonction de potentiel d'Eckart permet de déterminer la forme la plus probable de la barrière de potentiel. Il est montré que les valeurs habituellement admises pour les dimensions de cette barrière ne sont pas correctes.     

An analysis of thermal warpage in injection molded flat parts due to unbalanced cooling

To illustrate the potential effect of unbalanced cooling on warpage of flat parts, a simplified two-part analysis is presented. First a computational model for amorphous polymers cooling in an injection molding cavity is presented. The simulation is a finite difference solution of the one-dimensional, transient heat conduction equation with constant material properties. Plastic and mold temperature profiles are calculated through the cooling cycle and the transients from cycle to cycle are included. Temperatures are predicted for both sides of the mold allowing asymmetrical cooling to be analyzed. The model is verified analytically and is in agreement with published data. Secondly, a simplified method of predicting the thermal warpage of a fiat part from calculated temperature profiles is discussed and illustrated. The relative effects on calculated part warpage of asymmetric mold geometry and cooling fluid temperature are predicted with this analysis method. The sensitivity of warpage to these design factors is illustrated for an example part.     

The effect of molecular structure on the gas transmission rates of aromatic polyimides

A series of high-molecular weight condensation polyimides was evaluated to determine the effect of polymer molecular structure on the transmission rate of oxygen, carbon dioxide, and water vapor. The polyimide films were prepared from either 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) or pyromellitic dianhydride (PMDA) with various diamines. The study shows that molecular structure had a strong influence on gas transmission rates with results for some films varying three orders of magnitude from that of other polyimide films. In general, the BTDA series of polyimides had overall lower gas transmission rates than the PMDA-derived series. Polymers prepared with meta-oriented diamines characteristically displayed lower gas transmission than those prepared with para-oriented diamines.     

Selective separation of yttrium from rare earth elements by ion interaction chromatography. Analytical and larger scale applications

ABSTRACT

New ion interaction chromatographic (IIC) method employing Kromasil 100 C₁₈ column and tetra-n-butylammonium hydroxide (TBAOH) as an ion interaction reagent (IIR) is able to separate yttrium from Rare Earth Elements (REE) as anionic complexes with nitrilotriacetic acid (NTA). New method for the chromatographic determination of Y in REE mixture was devised and validated by the analysis of the certified reference material (CRM). Potential possibilities of the new chromatographic system for larger scale applications including macro-micro events were demonstrated.