Detailed Modeling of Gas Flow in Liquid Steel: Bubble Size Distribution and Voidage Calculation

Although the role of gas purging in liquid steel systems is well recognized, it has yet to be adequately analyzed. One key aspect of this process is the prediction of gas voidage in the bath, which has been studied in great detail beginning with water modeling in the early days and using advanced multiphase models more recently. Still, there are significant unresolved issues with gas purging systems. When gas is introduced through a nozzle at high flow rate, a jet may form which is undesirable. The break‐up of this jet into bubbles is a separate topic of research. The more common practice in the steel industry is to use porous plugs for gas injection. Gas entry through a porous plug can be characterized by the stretched bubble regime, and the laws of coalescence and fragmentation used to analyze bubble column reactors are generally applicable. Calculation of the bubble size distribution is important for two reasons. First, the voidage distribution in the bath is significantly modified by the injection system and flow rates used, primarily due to changes in flow regime and bubble dynamics (collision, break‐up, coalescence). Second, the voidage distribution directly determines the buoyancy, that influences the physical mixing process, and the specific‐area‐density, that influences surface reactions (for example, decarburization, desulfurization and nitrogen pick‐up). In this paper, a numerical study is presented that combines a bubble dynamics model with an Eulerian multiphase model. The results of the simulation are compared with the experimental data from Anagbo and Brimacombe (1990). Relevant discussion and reviews will be presented to distinguish the differences of this detailed bubble dynamics model with the uniform bubble diameter approximations reported in various recent studies.     

Synthesis,characterization, and antimicrobial properties of novel quaternary amine methacrylate copolymers

A novel amine methacrylate monomer trimethylolpropane trimethacrylate–piperazine–ethyleneglycol dimethacrylate (TMPTMA‐PPZ‐EGDMA) was synthesized by amination of trimethylolpropane trimethacrylate (TMPTMA) with excess of piperazine (PPZ) followed by reaction with ethyleneglycol dimethacrylate (EGDMA). Copolymerization of TMPTMA‐PPZ‐EGDMA with 2‐hydroxyethyl methacrylate (HEMA) was carried out by free radical polymerization using ammonium persulfate (APS) and N,N,N′,N′‐tetramethyl ethylenediamine (TEMED) as a redox initiator. The copolymers obtained were then quaternized with 1‐iodooctane. The monomers were characterized by FTIR and ¹H NMR spectral studies. The molecular weights and polydispersity values of the monomers were determined with gel permeation chromatography. Quaternized copolymers containing more than 20% amine methacrylate monomer showed microporosity in the range of 9.9–10.4 μm. The antibacterial activity of the quaternized copolymers against Escherichia coli and Staphylococcus aureus was studied using UV–vis spectrophotometer and scanning electron microscopy. Quaternized copolymers showed broad‐spectrum contact‐killing antibacterial properties without releasing any active agent as checked by iodide selective ion meter. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Characterization of poly(vinyl alcohol) grafted with acrylic acid and methylmethacrylate using a Ce(IV) glucose redox system

Poly(vinyl alcohol) (PVA) is a well-known biomedical polymer and is biocompatible. Methylmethacrylate and acrylic acid monomers were grafted onto PVA using a Ce(IV)–glucose redox system at three different temperatures (35, 45, and 55°C) under nitrogen atmosphere. More than 80% grafting could be achieved in the process. The grafted PVA was characterized through infrared spectra, thermal decomposition studies [thermogravimetric analysis (TGA) and decomposition thermal grafting (DTG)], differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The thermal stability and other properties of grafted PVA related to medical applications was found to be better than those of ungrafted PVA. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 677–683, 1999     

Numerical modelling framework of continuous salt precipitation from super-critical water

Salt separation at super-critical condition is a promising technology to separate dissolved salts from water by utilizing sharp changes in thermal and physical properties of water close to its critical point in a tube in tube separator. To capture flow complexity and geometric asymmetry, a three-dimensional CFD model of salt separator is developed in Fluent ver 16. Simulation results are compared and validated with experimental work by Schubert et al. [19]. The axial temperature profiles predicted by model at different wall temperature are well in agreement with the reported data [19]. The model provides insight to axial and radial flow field, temperature gradients, and so on within the salt separator. The blurred boundary between super-critical and sub-critical regions is captured by accounting sharp changes in physical properties of water close to critical temperature and pressure. Sensitivity of key process parameters (e.g., vessel wall temperature, feed pre-heat temperature, flow rates and forced cooling in cold region) was carried out to check effect of operating parameters on deviation in performance of salt separator. No pre-heat feed condition (25°C) is best since it ensures no salt deposition in dip tube without affecting the salt separator performance. Optimum wall temperature lies between 390°C to 470°C to avoid salt deposition and maintain desired temperature gradient between hot and cold section. The modelling framework will aid in efficient design and scale up of salt separator.     

Investigations on performance of PEDOT:PSS/V2O5 hybrid symmetric supercapacitor with redox electrolyte

Nanocomposites of PEDOT:PSS with V₂O₅ nanoparticles are synthesized by simple physical mixing of the two with different weight percentages of the latter and their performance as supercapacitor electrode materials is verified. Best performance is obtained for an optimum weight percent of 16.8% of V₂O₅. The specific capacitance and specific energy of the composite with 16.8% V₂O₅ increases by more than two fold, with increase in specific power, as compared to that of pristine PEDOT:PSS device. This is attributed to increase in conductivity brought about by the presence of V₂O₅ nanoparticles, easier transportation and intimate contact of electrolyte ions with the nanolayers of V₂O₅ due to the intercalation of PEDOT:PSS between the layers, and additional redox reactions due to various oxidation states of vanadium element, besides redox electrolyte effects. This is further confirmed by the reduced ESR of the composite device as compared to that of pristine PEDOT:PSS device.     

Improvement in dry sliding wear resistance of Al-17Si-5Cu alloy after an enhanced heat treatment process

To improve the wear resistance of cast Al-17Si-5Cu alloy (AR alloy), isothermal heat treatment is employed to modify the morphology of Si particles (particularly eutectic Si particles). Furthermore, wear behaviour of heat-treated alloy (HT alloy) along with AR alloy is studied using a pin-on-disc tribometer. Worn surfaces are then characterised using scanning electron microscope. The result reveals considerable microstructural modifications after the heat treatment. Accordingly, higher hardness value in HT alloy is obtained compared with AR alloy. The overall wear rate for HT alloy is found to be significantly lower compared with AR alloy at all the applied loads, indicating remarkable improvement in wear resistance. Eutectic Si particles become from acicular/rod-like to spherical/equiaxed morphology (aspect ratio close to 1) on heat treatment, resulting in good bonding with the matrix. Thus, they remain intact during wear and being harder, providing resistance to wear. Moreover, the increased hardness on heat treatment causes further resistance to wear. Therefore, the combined effect of intact harder Si particles on the wearing surface and higher hardness results in superior wear behavior in HT alloy at all loads compared with AR alloy.     

Design of Three bit ADC and DAC Using Spatial Wave-function Switched SWSFETs

The spatial wave-function switched field effect transistor (SWSFET) has two or three low band-gap quantum well channels inside the substrate of the semiconductor. The applied voltage at the gate region of the SWSFET, switches the charge carrier concentration in different channels from the source to the drain region. The switching of the electron wave function in different channels can be explained by the device model of the SWSFET. A circuit model of a SWSFET is developed in the Berkeley Short Channel IGFET Model (BSIM) 4.0.0. The design of a three bit analog-to-digital converter (ADC) and digital-to-analog converter (DAC) using SWSFET is explained in this work. Advanced circuit design using fewer SWSFETs will reduce the device count in future analog and digital circuit design.     

Implementation of Six Bit ADC and DAC Using Quantum Dot Gate Non-Volatile Memory

This paper presents the implementation of six-bit analog to digital converters (ADCs) and digital-to-analog converters (DACs) using quantum dot gate non-volatile memory (QDNVM). The charge accumulation in the gate region varies the threshold voltage of QDNVM which can be used as a reference voltage source in a comparator circuit. A simplified comparator circuit can be implemented using the quantum dot gate non-volatile memory (QDNVM). In this work, we discuss the use of QDNVM based comparators in designing 6-bit Analog-to-Digital Converters (ADCs) and Digital-to-Analog Converters (DACs).     

Three-State Quantum Dot Gate FETs Using ZnS-ZnMgS Lattice-Matched Gate Insulator on Silicon

This paper presents the three-state behavior of quantum dot gate field-effect transistors (FETs). GeO _x -cladded Ge quantum dots (QDs) are site-specifically self-assembled over lattice-matched ZnS-ZnMgS high-κ gate insulator layers grown by metalorganic chemical vapor deposition (MOCVD) on silicon substrates. A model of three-state behavior manifested in the transfer characteristics due to the quantum dot gate is also presented. The model is based on the transfer of carriers from the inversion channel to two layers of cladded GeO _x -Ge quantum dots.