Overall Performance Evaluation and Functional Analysis of Egyptian Starch Manufacturing Plants

The present paper outlines the approach and principal results of a full-fledged performance evaluation and functional analysis program conducted at the Egyptian Starch and Glucose Company that has been wholly documented elsewhere [12]. The ultimate goal of the program is to come up with well-defined and appropriate courses of action to improve products quality, plant productivity and overall economy. The paper also reports the results of additional computer work that has been undertaken to enhance the applicability of the results. The adopted methodology for applying the developed computer material balance (MASSBAL) in the evaluation program and in analysing the impacts of stepwise improvements in the individual plant sectors of concern is also presented.     

CFD analysis of pollutant dispersion around buildings: Effect of cell geometry

The choice of the best mesh in terms of cost, time and accuracy of computational solutions in the CFD industry is a challenging topic and a subject of some controversy. Generating meshes based on hexahedral elements requires significant time and effort, however, these meshes are claimed to produce high quality solutions. Meshes that employ tetrahedral elements can be constructed much faster in complex geometries, but may increase the levels of numerical diffusion. The objective of this study is to better establish quantitative assessment of the influence of cell geometry in the computational mesh on the CFD results of pollutant dispersion around buildings in order to help modelers to choose the most effective mesh type for their applications. In order to achieve this objective, two widely used mesh styles, i.e., hexahedral-based and tetrahedral-based meshes, are considered in the simulation of this flow problem. Quantitative grid convergence was calculated based on a grid convergence index (GCI). The mesh style was found to have an observable effect on the calculated pollutant concentrations. For instance, the hexahedral-based mesh was observed to have GCI values that were in an order of magnitude below the tetrahedral-based mesh values for all resolutions considered, even in the very fine tetrahedral-based mesh. Furthermore, the GCI value, and hence the truncation error, remains high compared to conventional hexahedral cases. The study recommends taking special care when employing an unstructured tetrahedral-based mesh to ensure that the mesh is fine enough and any numerical errors should be documented for selected variables reported analogous to experimental uncertainty in order to assess the quality of the numerical solution.     

On the electrochemical behaviour of the anodic oxide film on tungsten in HCOOH and CH3COOH solutions

The electrochemical behaviour of the anodic oxide film on tungsten during, or after, interruption of current flow was studied in HCOOH and CH₃COOH solutions by galvanostatic and capacitance techniques. The results show the conditions under which enhancement of film growth occurs as revealed from its formation and dissolution characteristics. The results also show the possibility of the electrochemical oxidation of formic acid by the thick oxide film on tungsten. The importance of this electrocatalytic process is the occurrence of the oxidation process without appreciable oxygen evolution. The galvanostatic oxidation of tungsten in HCOOH as a reducing agent can be considered as a novel method for the preparation of a class of oxides; oxidation with simultaneous partial reduction.     

Inhibition of the corrosion of steel by acid dihydrazides

The corrosion inhibitory properties of homologous series of acid dihydrazides were studied. Gasometry, potentiodynamic polarization and impedance measurements were recorded for mild steel specimens immersed in 1.0 M H₂SO₄ or a mixture of 1.0 M H₂SO₄ + 1.0 M Na₂SO₄ having the same ionic strength with a pH range from zero to 7. Effect of presence of different concentrations of oxalic, malonic, succinic or pimelic dihydrazide on the corrosion rate of steel in the above solutions were investigated. The results indicated that the protection efficiency of the acid dihydrazides increased with the increase of the number of the methylene groups in the acid dihydrazide molecule. The results are discussed on the basis of the change of each, of the electron density of the donating atoms, of the inhibitor molecules, and the orientation of the inhibitor at the metal surface with the molecular structure of the inhibitor.     

Normal Transmission of S-Wave Across Parallel Fractures with Coulomb Slip Behavior

When an elastic wave propagates through a rock mass, its amplitude is attenuated and velocity is slowed due to the presence of fractures. During wave propagation, if the shear stress at a fracture interface reaches the fracture shear strength, the fracture will experience a large shear displacement. This paper presents a study of the normal transmission of S-waves across parallel fractures with Coulomb slip behavior. In our theoretical formulation, the method of characteristics combined with the Coulomb slip model is used to develop a set of recurrence equations with respect to particle velocities and shear stress. These equations are then solved numerically. In a comparison with the theoretical study, numerical modeling using the universal distinct element code (UDEC) has been conducted. A general agreement between UDEC modeling and theoretical analysis is achieved. The magnitude of the transmission coefficient is calculated as a function of shear stress ratio, nondimensional fracture spacing, normalized shear stiffness, and number of fractures. The study shows that the shear stress ratio is the most important factor influencing wave transmission, and the influence of other factors becomes more apparent when the shear stress ratio is small.     

Transmission ratio （Tn） in the radian direction normal to joints in 2-D compressional wave propagation in rock masses

The transmission ratio along the radian direction normal to the joints was studied in the Universal Distinct Element Code （UDEC）. The variation of the transmission ratio with the ratio of joint spacing to wavelength was generalized into a general curve, which was determined by two critical points. The relationship between the two critical points and the affecting factors, quantity of joints and the normalized normal stiffness of joints, were obtained. A prediction model of the transmission ratio in the radian direction normal to the joints was proposed. The proposed model was applied to a field explosion test. The estimated values of the peak particle velocity from the prediction model were compared with the field records. The comparisons showed that the prediction model of the transmission ratio in the direction normal to the joints in the process of 2-D compressional wave propagation through multiple parallel joints is reliable.     

Morphologies of anodic oxide films deduced from dissolution studies

Study of the chemical stripping of anodic oxide films on hafnium, zirconium, tungsten and aluminium has led to the deduction of the morphology of the respective oxides. Away from the boundary region hafnium oxide is a compact, smooth, homogenous and crystalline oxide. Zirconium oxide has a superficial disorder layer which constitutes about 17% of the entire film. Tungsten oxide deposits are composed of two defective partial layers the outer one being more disordered. Aluminium oxide is a porous film. A schematic representation of each film had been presented.     

Electrochemical behaviour of surface zirconium oxides in the presence of some electroactive species

The open circuit potential, capacitance and resistance techniques were used to investigate the behaviour of two types of surface zirconium oxides in pure 0.5 N H₂SO₄ and in the presence of additives of K₂CrO₄, KI, FeSO₄ and HCOOH.

The air-formed preimmersion oxide film grows in all solutions following a logarithmic rate law. Depending on the nature of the additive the oxide grows directly by oxidation of the surface by the oxidizing additive (K₂CrO₄) or indirectly by mediating the oxidation by atmospheric oxygen in the presence of reducing additives.

Anodically formed zirconium oxide films dissolve in all solutions. The results of impedance measurements indicate that adsorption of HCOOH activates the oxide surface owing, possibly, to its hydrophilic nature while iodide adsorption diminishes the reactivity of active sites (probably oxygen vacanies) where the dissolution process is initiated.     

Effect of chemically modified waste rubber powder as a filler in natural rubber vulcanizates

Waste rubber powder (RP) was subjected to chemical modification by using different concentrations of oxidizing agents such as nitric acid and 30% hydrogen peroxide solution. This treatment leads to introducing some functional groups onto the surface of RP. The chemically modified RP was incorporated in natural rubber mixes either alone or in combination with carbon black (HAF). The physicomechanical properties of NR vulcanizates obtained were studied and compared to NR vulcanizates filled with untreated RP. It was found that the chemically modified RP improves tensile strength and aging resistance of NR vulcanizates compared with untreated RP. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 30–36, 2004