Electrochemical studies of the pitting corrosion of tin in citric acid solution containing Cl

The electrochemical behavior of a tin electrode in citric acid solutions of different concentrations was studied by electrochemical techniques. The E/I curves showed that the anodic behavior of tin exhibits active/passive transition. Passivation is due to the formation of Sn(OH)₄ and/or SnO₂ film on the electrode surface. Addition of NaCl to citric acid solution, enhances the active dissolution of tin and tends to breakdown the passivity at a certain breakdown potential. Cyclic voltammetry and galvanostatic measurements allow the pitting potential (E_pit) and the repassivation potential (E_rp) to be determined. Potentiostatic measurements showed that the overall anodic processes can be described by three stages. The first stage corresponds to the nucleation and growth of a passive oxide layer. The second stages involve pit nucleation and growth and third stage involve repassivation. The impedance spectrum of pure Sn is found to consist of three intersecting capacitive semicircles at the high and medium frequencies with an inductive loop at low frequencies. The capacitive semicircles occurring at the high and medium frequency are due to the dielectric properties of surface oxide film and dissolution of underlying metal, respectively. The inductive loop at low frequencies results from Cl⁻ adsorption at the pitting region. By increasing the potential the pitting corrosion and the fractal dimension of surface due to pitting increase.     

Centrifuge study into the effect of liquefaction extent on permanent settlement and seismic response of shallow foundations

Centrifuge experiments were conducted to investigate how the liquefaction extent affects the seismic and post-seismic settlement of shallow foundations resting on saturated sand. Two rigid foundations with different bearing pressures were placed on the ground surface in a model container. Multiple input motions were applied to achieve different extents of soil liquefaction. The results indicate that foundation settlement can be divided into three distinct phases: (I) during shaking, (II) during the time period after shaking has ceased and before soil reconsolidation in the shallowest layers has taken place, and (III) during soil reconsolidation. Contrary to the free-field ground, most of the total settlement of the foundations occurred before soil reconsolidation, i.e., during Phases I and II. The volumetric strain during these phases was not significant as opposed to the shear strain produced by the foundation surcharge. It was demonstrated that foundation settlement is not necessarily proportional to the liquefied depth of the sand. The extent of the liquefaction in the sand medium mostly affected the post-seismic settlement of the foundations, while the co-seismic settlement was relatively the same for both foundations. The response of the foundations was significantly influenced by the liquefaction extent, whereas the foundations did not experience large accelerations when the soil profile was entirely liquefied. However, the foundations tolerated large settlement under severe liquefaction conditions. The results of this study highlight the role of the liquefaction extent on co-seismic and post-seismic settlement as well as the seismic response of shallow foundations.     

Second law based modeling to optimum design of high capacity pulse tube refrigerators

The optimum design of a high capacity double inlet pulse tube refrigerator based on second law of thermodynamics has been presented in this paper. Second law is applied to calculate the work loss in the regenerator and to optimize the cryocooler performance. To investigate the behavior of the pulse tube refrigerator, mass and energy balance equations are applied to several control volumes of the cryocooler cycle. A complete system of conservation equations is employed to solve the regenerator analytically. The proposed model reports the cooling capacity of 110 W at 80 K cold end temperature at frequency of 50 Hz, orifice conductance of 0.4 and double inlet coefficient of 0.6, with 2.4 kW net power delivered to the gas. In this case, the entropy generation in the gas phase is dominant which is contributing more than 85% of the total lost work in the regenerator. The optimum thermal efficiency of 99.1% was achieved at a proper mesh number. However, the second law efficiency is reported to have an inverse behavior at this mesh number.     

Numerical Modeling of Fluid Flow and Thermal Behavior of Different Nanofluids on a Rotating Disk

The thermal and velocity profiles of various nanofluid systems on a rotating disk are simulated. Finite difference method, the orthogonal collocation method, and the differential quadrature method (DQM) of numerical approaches are used to solve the governing equations and are compared to determine the faster and more accurate solution procedure. Five nanoparticles Al, Al₂O₃, Cu, CuO, and TiO₂ solved in three base fluids water, ethylene glycol, and engine oil are considered to be used on the disk at different volume fractions. A new general algorithm is presented for solving equations of a rotating‐disk problem quickly and accurately and it is found that the DQM method is the best approach for this numerical simulation. Heat transfer performance of a rotating disk would be much better enhanced with water based Al nanofluid. A wide range of results for different base–fluid combinations with nanoparticles is presented with untransformed 3D results and effects of the variation of different parameters provides comprehensive insight and prevents inaccurate deductions.     

Electrodeposition of Al,Mn, and Al–Mn Alloy on aluminum electrodes from molten salt (AlCl<Subscript>3</Subscript>–NaCl–KCl)

Electrochemical deposition of aluminum and manganese from basic and acidic molten AlCl₃–NaCl–KCl mixture on an aluminum electrode at 180 °C was studied by the methods of voltammetry, and potential and current transient. The deposition of aluminum was found to proceed via a nucleation/growth mechanism in basic melt, while the deposition of manganese was found to be diffusion controlled in basic melt. The diffusion coefficient of Mn²⁺ ions in basic melt, as derived by voltammetry was in agreement with the deductions of transient methods. Analysis of the chronoamperograms indicates that the deposition of manganese on Al was controlled by 3D diffusion controlled nucleation and growth. The processes are manifested as peaks on a decaying chronoamperogram. Non-linear fitting methods were applied to obtain the kinetic parameters from theoretical formulae proposed to describe this system. It is also found that under more cathodic potentials, the saturation number density of the manganese nuclei and also the efficiency of use of the available surface nucleation sites increased.     

VARIATIONS IN PETROPHYSICAL PROPERTIES OF UPPER PALAEOZOIC MIXED CARBONATE AND NON‐CARBONATE DEPOSITS,SPITSBERGEN, SVALBARD ARCHIPELAGO

The Late Carboniferous – Early Permian Gipsdalen Group and the Early to Late Permian Templefjorden Group are known hydrocarbon plays in the Arctic region, e.g. on the Finnmark Platform, Loppa High and Sverdrup Basin. Time‐equivalent deposits crop out on the island of Spitsbergen and consist of mixed carbonate and non‐carbonate (primarily siliciclastic, siliceous, organic‐carbon rich and clayey) sediments deposited in continental to deep‐marine settings. In rock samples (n = 73) collected from five outcrop locations on Spitsbergen, thin‐section analysis showed the presence of ten microfacies types ranging from claystones and spiculitic cherts to rudstones and dolostones. Petrophysical and textural properties of the samples were measured to evaluate the link with the acoustic (P‐ and S‐wave) velocities of these generally tight rocks, which have an average porosity of about 2%. Variations in acoustic velocity measurements primarily depend on variations in mineralogical composition (silica versus carbonate) and, to a lesser extent, on variations in porosity and bulk density. Pore networks in the sediments are dominated by microporosity and (micro)cracks, followed by interparticle porosity. Recrystallization effects and pore shape variations show a lesser effect on the P‐wave velocity. Clay content does not exceed 12.7% and also has a secondary impact on the acoustic velocities. Defining which textural and physical parameters control the acoustic properties of these carbonate and non‐carbonate sedimentary rocks will help with the interpretation of the seismic response of equivalent deposits in the subsurface.     

Performance analysis of a tubular solid oxide fuel cell with an indirect internal reformer

A 2‐D steady‐state mathematical model of a tubular solid oxide fuel cell with indirect internal reforming (IIR‐SOFC) has been developed to examine the chemical and electrochemical processes and the effect of different operating parameters on the cell performance. The conservation equations for energy, mass, momentum as well as the electrochemical equations are solved simultaneously employing numerical techniques. A co‐flow configuration is considered for gas streams in the air and fuel channels. The heat radiation between the preheater and reformer surface is incorporated into the model and local heat transfer coefficients are determined throughout the channels. The model predictions have been compared with the data available in the literature. The model was used to study the effect of various operating conditions on the cell performance. Numerical results indicate that as the cell operating pressure increases, the reforming reaction extends to a larger portion of the cell and the maximum temperature move away from the cell inlet. As a result, a more uniform temperature prevails in the solid structure which reduces thermal stresses. Also, at higher excess air, the rate of heat transfer to the air stream is augmented and the average cell temperature is decreased. Copyright © 2010 John Wiley & Sons, Ltd.