Numerical study of the performance of multistage Scaba 6SRGT impellers for the agitation of yield stress fluids in cylindrical tanks

The 3-D flow fields and power consumption in a vessel stirred by multistage Scaba 6SRGT impeller have been investigated. The Xanthan gum solutions in water were used, which have a shear thinning behavior with yield stress. This study was carried out with the help of a CFD package(CFX 13.0, Ansys Inc.) which is based on the finite volume method to solve the momentum equations. The effects of stirring rate, fluid rheology, impeller number, impeller location and vessel size on the performance of such stirred system are presented. To validate the CFD model, our predicted results have been compared with other literature data and a satisfactory agreement has been found.     

Phase behavior of binary blends of PP/PP‐g‐AA: limitations of the conventional characterization techniques

In this study, miscibility/immiscibility issues of a binary blend consisting of polypropylene (PP) and acrylic acid grafted polypropylene (PP‐g‐AA) were investigated using rheometry, DSC, dynamic mechanical and thermal analysis (DMTA), AFM and time‐of‐flight secondary‐ion mass spectrometry (ToF‐SIMS). Phase separation analysis of such blend systems is a challenge and complex due to chemically similar components as well as the low value of acrylic acid groups in the graft copolymer. Thus, it is crucial to determine if the present blend shows some degree of miscibility or develops co‐continuous morphology between the components. The analysis of rheometrical, DSC and DMTA results indicated no sensitivity of these classical techniques for detecting the miscibility or immiscibility of such a system. However, AFM data effectively detected dispersed‐phase domains corresponding to the PP‐g‐AA rich phase. The results, for the first time, indicated that the start of phase separation occurs at a critical copolymer concentration between 2 and 5 wt%. Furthermore it was observed that, as the PP‐g‐AA content increases, the size and continuity of the dispersed phase increase and reach a highly continuous morphology. Additionally, ToF‐SIMS chemical imaging was carried out to aid in the interpretation of the AFM data. © 2016 Society of Chemical Industry     

Multidentate Cyclohexylphosphonic Acid as Corrosion Inhibitor for Structural Steel in 3.5% NaCl Solution: An Experimental and Computational Study

Protection of Metals and Physical Chemistry of Surfaces - The inhibition effect of cyclohexylphosphonic acid (CHPA) on the corrosion of structural steel (EN 10027) in 3.5% sodium chloride solution...     

Advanced Process Simulation of Solidification and Melting

At some stage in the production of every metal part or product, the metal material has been melted and solidified to form the primary or final shape as well as the as-cast structure. Quantitative prediction and control of solidification and melting has been, and remains, the most critical issue in the metallurgical industry. Example questions currently raised by the Austrian metallurgical industry, which is one of the key economic sectors of this country, are as follows: in thin-slab casting, how does the solid shell form and interact with turbulent flow? How can the electro-slag-remelting (ESR) process be better understood and controlled (stabilized)? How can metallurgical imperfections (macrosegregation, porosity, non-metallic inclusion, surface crack, etc.) in castings be predicted and minimized? Therefore, a Christian-Doppler laboratory—Advanced Process Simulation of Solidification and Melting was established in July 2011 with the final goal to address the questions mentioned above. This article reports on some progresses.     

Process Simulation for the Metallurgical Industry: New Insights into Invisible Phenomena

In order to demonstrate how advanced process simulation can help to understand metallurgical process details and thus to improve industrial productivity, a number of examples are shown and discussed. The paper covers recent simulation results gained at the Chair of Simulation and Modeling of Metallurgical Processes, namely (i) the flow and shell formation in thin slap casting of steel, (ii) multiphase flow and magneto-hydrodynamic during Electro-Slag-Remelting, (iii) mold filling, surface wave dissipation and solidification during horizontal centrifugal casting of rolls, and (iv) forced and natural convection during electro-refining of copper in an industrial-size tankhouse cell.     

Microstructure and properties of porous nanocomposite films: effects of composition and process parameters

Porous nanocomposite films based on polypropylene (PP) and titanium dioxide (TiO₂) nanoparticles were prepared by melt extrusion followed by uniaxial stretching. The effects of drawing temperature, extension rate, stretching ratio and composition of the base films on the final properties and microstructure of the stretched films were studied. Water vapor permeability (WVP) results showed a significant decrease in permeability of the films stretched at temperatures higher than 60 °C. Porosity, pore size and water vapor transmission rate in the porous nanocomposite films had a direct relation with nanoparticle content, extension rate and stretching ratio. Study of the morphology of the stretched films, using SEM, revealed that the pores form due to PP/TiO₂ interfacial debonding at low stretching ratios. Higher stretching ratios cause an enlargement of the pores and the formation of a PP fibril structure parallel to the stretching direction. Quantification of dye adsorption revealed that the quantity of adsorbed dye increased with porosity and surface area of the pores. © 2014 Society of Chemical Industry     

Stabilization of Discrete-Time Nonlinear Switching Systems

This paper presents sufficient conditions for the stabilization of saturated switching nonlinear discrete- time systems. The type of nonlinearity is the so-called Lur’e type. Less conservative stability regions are obtained. This fact is shown upon a numerical example.     

Analytical 2D modeling for potential distribution and threshold voltage of the short channel fully depleted cylindrical/surrounding gate MOSFET

A two-dimensional analytical model for fully depleted cylindrical/surrounding gate MOSFET is presented. We used the evanescent mode analysis to solve the 2D Poisson's equation and to deduce analytically the surface potential and threshold voltage expressions of this device. Comparison with the other models reveals a good agreement.     

Analytical V TH and S models for (DMG–GC–stack) surrounding-gate MOSFET

This article presents an analytical model of surface potential, threshold voltage and subthreshold swing for a new structure of surrounding-gate MOSFET by combining dual-material gate, graded channel and gate stack. By comparison with published results, it is shown that the new MOSFET structure can improve the immunity of CMOS-based devices in the nanoscale regime against short-channel effects.