Chemical storage of solar energy—kinetics of heterogeneous NH3 and H2SO4 reactions II. Process and reactor design

An important energy recovery step in the ammonium hydrogen sulfate (AHS) cycle is the recombination reaction producing NH₄HSO₄. It has been determined that the optimum way to accomplish this, and prevent side reactions, is by the heterogeneous gas-liquid reaction of H₂SO₄ and NH₃. A mathematical model is presented and applied to the two reaction zones and a method of numerical solution is discussed. Three horizontal pilot-scale configurations, 0.17 × 10⁶ to 4.2 × 10⁶ kJ/h energy release, are discussed and sizing is presented. The most important conclusion from the work is that the energy can be released most effectively by carrying out the reaction in a double pipe tubular reactor operating in the annular flow regime with both gas and liquid in turbulent flow.     

Chemical surface treatment of ultrahigh molecular weight polyethylene for improved adhesion to methacrylate resins

Ultrahigh molecular weight polyethylene (UHMWPE) has high yield strength and modulus, but is nonpolar and chemically inert. For it to be used as an effective reinforcing agent for composites, methods to make the UHMWPE wettable or capable of reaction with the matrix are critical. In the current work, Spectra 900? (UHMWPE) fibers were surface modified by swelling in p‐xylene with: (1) methylmethacrylate (MMA) monomer; (2) PMMA; (3) camphorquinone (CQ); (4) 3‐methacryloxypropyltrichlorosilane (Cl‐MPS); (5) trimethoxysilyl modified polyethylene, N‐(triethoxysilylpropyl)‐dansylamide (fluorescent silane), or octadecyltrimethoxy silane (OMS), followed by hydrolysis and reaction with Cl‐MPS; and (6) by coating with SiO₂ films followed by reaction with MPS. These modifiers were used to improve wettability and provide sites for chemical interactions with the resin matrix. Beads of resin [60/40 BisGMA‐TEGMA (bis‐phenol A bis‐(2‐hydroxypropyl) methacrylate and tri(ethylene glycol) dimethacrylate)] were light‐cured around the treated fibers and the improvement in adhesion was tested by microbond shear strength (τ) tests. The improvements were comparable to those reported by acid etching and plasma treatments. The OMS, fluorescent silane, and SiO₂/Cl‐MPS treatments yielded the best results, that is fourfold increases in τ compared with untreated fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1564–1572, 2005     

FLOW GENERATED BY PITCHED BLADE TURBINES II: SIMULATION USING κ-ε MODEL

Experimental data on average velocity and turbulence intensity generated by pitched blade downflow turbines (PTD) were presented in Part I of this paper. Part II presents the results of the simulation of flow generated by PTD

The standard κ-ε model along with the boundary conditions developed in the Part 1 have been employed to predict the flow generated by PTD in cylindrical baffled vessel. This part describes the new software FIAT (Flow In Agitated Tanks) for the prediction of three dimensional flow in stirred tanks. The basis of this software has been described adequately. The influence of grid size, impeller boundary conditions and values of model parameters on the predicted flow have been analysed. The model predictions successfully reproduce the three dimensionality and the other essential characteristics of the flow. The model can be used to improve the overall understanding about the relative distribution of turbulence by PTD in the agitated tank     

Rotary Cement Kiln Simulator (RoCKS): Integrated modeling of pre-heater, calciner, kiln and clinker cooler

This paper presents an integrated reaction engineering based mathematical model for clinker formation in cement industry. Separate models for pre-heater, calciner, rotary kiln and cooler were initially developed and coupled together to build an integrated simulator. Appropriate models for simulating gas-solid contact and heat transfer in pre-heaters were developed. Calciner was modeled by considering simultaneous combustion of coal particles and calcination of raw meal. Complex heat transfer and reactions (solid-solid, gas-solid and homogeneous reactions in gas phase) in rotary kiln were modeled using three sub-models coupled to each other. Solid-solid reactions in the bed region of the kiln were modeled using pseudo-homogeneous approximation. Melting of solids in the bed and formation of coating within the kiln were accounted. Clinker cooler was simulated by developing a two-dimensional model to capture cross-flow heat transfer between air and hot clinkers. The individual models were coupled with each other via mass and energy communication through common boundaries. The coupled model equations were solved iteratively. The model predictions agree well with the observations and experience from cement industry. The model was used to gain better understanding of influence of operating conditions on energy consumption in cement plant. Several ways for reducing energy consumption were computationally investigated. The integrated model, the developed software RoCKS (for Rotary Cement Kiln Simulator) and results presented here will be useful for enhancing our understanding and for enhancing the performance of clinker manufacturing.     

Application of silicon-germanium in the fabrication of ultra-shallow extension junctions for sub-100 nm PMOSFETs

This work summarizes the results of several experiments to investigate the potential applications of Silicon-Germanium alloy in the fabrication of shallow source/drain (S/D) extension Junctions for deep submicron PMOS transistors. Two approaches were used for the fabrication of p/sup +/-Si/sub 1-x/Ge/sub x//n-Si heterojunctions. In the first approach, high dose Ge ion implantation followed by boron implantation into Si was used to form very shallow p/sup +/-Si/sub 1-x/Ge/sub x//n-Si junctions (x/spl les/0.2). In the second approach, thin Ge films were deposited onto Si substrates by conventional low pressure chemical vapor deposition. This was followed by boron implantation into the Ge and thermal annealing to co-diffuse Ge and B atoms into Si and form p/sup +//n heterojunctions. The electrical characteristics of the heterojunction diodes were comparable to those of conventional Si (homo) junctions. Secondary ion mass spectrometry (SIMS) concentration-depth profiles indicate that dopant segregation in the Si/sub 1-x/Ge/sub x/ regions resulted in the formation of ultra-shallow and abrupt junctions that could be used as S/D extensions for sub-100 nm CMOS generations. PMOS transistors fabricated using these techniques exhibit superior short-channel performance compared to control devices, for physical gate lengths down to 60 nm.     

Hysteresis in cloud heights during solid suspension in stirred tank reactor: Experiments and CFD simulations

Solid suspension in stirred tank reactor is widely used in process industries for catalytic reactions, dissolution of solids, crystallization, and so on. Suspension quality is a key issue in design and operation of stirred reactor and its determination is not straight forward. Cloud height measurements of solid suspension provide a relatively simple way to quantify quality of suspension. In this work, experiments were carried out to quantify variation of cloud heights with impeller speed and particle characteristics. These measurements were carried out using visual observations, image analysis, and ultrasound velocity profiler techniques. The obtained data demonstrated the existence of hysteresis in cloud heights with respect to impeller speed. Apart from possible applications in reducing power required for achieving desired solid suspension quality, the existence of hysteresis also provides a new way to evaluate computational fluid dynamics (CFD) simulations of solid–liquid flows in stirred vessels. An attempt was made to capture observed hysteresis in cloud heights in CFD simulations. The simulated results were compared with the experimental data. The presented models and results (experimental and computational) will be useful for simulating complex solid–liquid flows in stirred reactors. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

On the producibility of composite position tolerance specifications for patterns of holes

A composite position tolerance verification algorithm is embedded in a simulation program to explore the producibility of three composite position tolerance variants for patterns of holes. The influence of some selective design and manufacturing variables on producibility is simulated and evaluated. It is shown that design variables such as specification variant, material condition modifier and number of holes in the pattern have a significant influence on producibility. The influence of manufacturing variables such as orientation error and numerical control path programming in the presence of axis reversal error are also simulated and discussed. Detailed graphs of these effects are presented and discussed.     

Modeling of bubble column slurry reactor for reductive alkylation of p-phenylenediamine

A bubble column slurry reactor (BCSR) model has been developed for the reductive alkylation of p-phenylenediamine (PPDA) with methyl ethyl ketone (MEK) to N,N^′-di-secondary-alkyl-p-phenylenediamine (Di-amine). This particular reaction system is commercially relevant and involves a combination of parallel and consecutive reactions comprising equilibrium non-catalytic (homogeneous) and catalytic (heterogeneous) steps. The proposed model is based on the ‘mixing cell approach’. In this work the mixing cell approach has been extended by including a liquid backflow stream from all but the bottommost mixing cell. The model incorporates the contributions of gas-liquid and liquid-solid mass transfer, heat effects, and complex multistep reaction kinetics. CFD model is used to estimate the extent of backflow among mixing cells and its dependence on operating parameters. The effect of gas and liquid velocities, catalyst loading, inlet PPDA concentration, and temperature on the conversion, selectivity, global rate of hydrogenation, and temperature rise is discussed. The comparison of the current approach with the traditional mixing cell model is discussed. The BCSR model presented here will be useful to provide guidelines for designing and improving overall performance of bubble column reactors.     

SIMULATION OF FLOWS IN STIRRED VESSELS AGITATED BY DUAL RUSHTON IMPELLERS USING COMPUTATIONAL SNAPSHOT APPROACH

Flow in baffled stirred vessels involves interactions between flow around rotating impeller blades and stationary baffles. When more than one impeller is used (which is quite common in practice), the flow complexity is greatly increased, especially when there is an interaction between two impellers. The extent of interaction depends on relative distances between the two impellers and clearance from the vessel bottom. In this paper we have simulated flow generated by two Rushton (disc) impellers. A computational snapshot approach was used to simulate single-phase flow experiments carried out by Rutherford et al. (1996). The computational model was mapped on the commercial CFD code FLUENT (Fluent Inc., USA). The simulated results were analyzed in detail to understand flow around impellers and interaction between impellers. The model predictions were verified using the data of Rutherford et al. (1996). The results presented in this paper have significant implications for applications of computational fluid mixing tools for designing multiple impeller stirred reactors.