μ‐Consortium: Aufbau einer mobilen Anlage für die Aus‐ und Weiterbildung in der Mikroverfahrenstechnik

A mobile plant for practical training was developed as part of the project μ‐Consortium to integrate micro process engineering into teaching. Lab experiments in the fields of mixing and homogenous reactions, heterogeneous reactions, heat transfer and particle synthesis were worked out to impart knowledge of different process‐engineering operations.     

Fabrication of Composite Sewing Thread Using Polyester Microfibres

New technology for manufacture of composite sewing thread using hollow spindles was developed. The manufacturing process for production of sewing thread of 21 tex × 2 structure was optimized, and the optimum values of the basic process parameters were found: first twist of 720–750 tw./m, second twist of 550–570 tw./m. Industrial testing of this sewing thread showed that it has good sewing properties and provides for quality joining of clothing parts.__________Translated from Khimicheskie Volokna, No. 2, pp. 62–64, March–April, 2005.     

Hot-spot combustion of heterogeneous condensed mixtures. Thermal percolation

A model of combustion of heterogeneous condensed mixtures composed of reactive particles separated by an inert heat-conducting substance is considered. Propagation of the reaction in a one-dimensional periodic system of point reaction cells connected by inert thermal bridges is examined. The burning rate is determined as a function of the basic parameters of the system, and stability of the steady combustion mode is studied. It is shown that there exists a range of parameters in which the reaction propagates in an unstable manner. Combustion of the system in the instability domain is examined. It is shown that the reaction propagation loses its stability many times as the adiabatic temperature of the system decreases; in this case, the existing unsteady mode is replaced by another, more complicated mode, and the alteration of the regimes in the examined systems always proceeds as a period-doubling bifurcation. Beginning from a certain value of adiabatic temperature, the reaction-propagation process becomes stochastic. In the systems examined, there exists an ultimate adiabatic temperature, below which self-sustained propagation of the reaction in the system becomes impossible.Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 1, pp. 41–54, January–February, 2005.     

Molecular dynamics study on the viscosity of glass-forming systems near and below the glass transition temperature

Temperature-dependent viscosity is critical to decipher two profound questions in condensed matter physics, namely the glass transition and the relaxation of amorphous solids. However, direct measurement of viscosity over a large temperature range is extremely difficult. Here, using classical molecular dynamics (MD) simulations, we report a novel method to calculate the equilibrium viscosity of supercooled liquid both above and below the glass transition temperature (T_g) and to estimate the nonequilibrium viscosity of glass down to room temperature. Based on the shoving model, we derived an analytical formula showing that the shear viscosity in logarithmic scale changes linearly with the shear-induced variation in shear modulus or potential energy of the glass-forming system. The shear viscosity as a function of steady-state potential energy of liquid under different shear strain rates can be directly calculated in MD simulations; together with its equilibrium potential energy, one can extrapolate the zero-strain-rate equilibrium viscosity. We verified the proposed model by reliably calculating equilibrium viscosity near T_g of four glass-forming systems (Kob–Andersen system, silica, Cu_45.5Zr_45.5Al₉, and silicon) with different fragilities. Furthermore, our model can estimate the nonequilibrium viscosity of glass below T_g; the upper-bound nonequilibrium viscosity of amorphous silica and silicon at room temperature are calculated to be ~10³² and 10²⁵ Pa·s, respectively.     

System Approach to Analysis of the Role of the Synthesis Components and Stability of the MCM-41 Mesostructured Silicate Material

The formation of a mesostructured silicate material of the MCM-41 type is studied. The influence of the replacement of components in a reaction medium is investigated experimentally. Analysis of the results obtained and the data available in the literature suggests that the process under investigation is based on the approximate stoichiometric supramolecular interaction between [Si₄O_{4 + x} (OH)_{9 − x} ]^{−(1 + x)} silicate polyanions and C₁₆H₃₃(CH₃)₃N⁺ cetyltrimethylammonium cations with the formation of supramolecular aggregates, which condense to a mesostructured organosilicate composite. A further evolution of the product involves hydrolysis of the inner surface and the polymerization of the inorganic component. It is demonstrated that the properties of the product are determined, to a large extent, by the components of the reaction medium, which control the relative reaction rates in the process. The inference is made that an alcohol-ammonia medium is the most optimum for alkaline synthesis. This medium provides good preparation of the initial components for the reaction and the high rate of hydrolysis of pore walls, minimizes the osmotic effects during hydrothermal treatment, and, eventually, favors the formation of a highly structured hydrothermally stable material.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Kirik, Belousov, Parfenov, Vershinina.     

Numerical Study of Hybrid Combustion Waves in Vehicles of Complicated Geometry

A mathematical model is proposed for numerical studies of hybrid combustion waves in cylindrical and spherical vehicles. A code based on the previously developed algorithm is written, and a large series of numerical computations is performed. For different flow rates of the gas, various characteristics of the process are considered, such as the position of the stationary point, maximum temperature of the gas, gas velocity at the stationary point, width of the combustion zone, etc. Transitional regimes with a varied flow rate of the gas are modeled.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 3, pp. 52–57, May–June, 2005.     

Measurement of polydispersity of ultra-narrow polymer fractions by thermal field-flow fractionation

In this paper we demonstrate that the polydispersity µ = M?_w/M?_N of narrow polymer fractions can be readily obtained by measuring band broadening and its velocity dependence in a thermal field–flow fractionation (thermal FFF) system. The thermal FFF method is shown to be more accurate than size exclusion chromatography for the determination of polymer polydispersities due to the simpler band dispersion function and the higher selectivity inherent to the technique. The polydispersities of a series of four narrow polystyrene samples prepared by anionic polymerization were consequently determined by thermal FFF and found to be much smaller (1.003–1.006) than the ceiling values (1.06) suggested by the suppliers. As part of this investigation, an experimental study of band dispersion in thermal FFF is used to examine current theory. The data show nonequilibrium to be the dominant factor, whereas relaxation effects are insignificant at lower flow rates and can be subdued at higher flow rates. A high correlation between nonequilibrium theory and experiment allows for the estimation of diffusion coefficients from plate height–velocity data.     

Stability of a CFSTR with two consecutive reactions by the Liapunov direct method

The stability of a continuous flow stirred tank reactor with two consecutive reactionsA → B → C is studied with the direct method of Liapunov. Krasovskii’s method with the identity matrix is used to obtain a Liapunov function in the analysis of the system with single or multiple steady states. The results show that this method is mathematically conservative as expected. From the viewpoint of practical stability, however, this method predicts the regions of stability adequately.     

Evaluation of published kinetic models for tert-amyl ethyl ether synthesis

The published kinetic models for liquid phase synthesis of tert-amyl ethyl ether (TAEE) by addition of ethanol to isoamylenes on acidic ion exchange resins were evaluated by comparison with own experimental data. Fixed bed and batch reactor experiments were carried out in liquid phase on Amberlyst-35 ion exchange resin as catalyst. Among the published kinetic models, our experimental data fits the best with the model published by [J.A. Linnekoski, A.O. Krause, L.K. Rihko, Kinetics of the heterogeneously catalyzed formation of tert-amyl ethyl ether, Ind. Eng. Chem. Res. 36 (1997) 310–316.]. In the simulation study for the fixed bed reactor experiments, the influences of axial mixing, liquid–solid mass transfer and internal diffusion steps on the overall process kinetics were theoretically evaluated. The results evidenced that on the working temperature domain, significant kinetic limitations by internal diffusion can appear for catalyst pellets size over 1 mm. The external mass transfer step has a weak influence on the process kinetics and can be important only at lower limit of the flow rates domain. Our computations evidenced also a negligible influence of the axial mixing on the reactants conversion in the experimental fixed bed reactor, on the working domain investigated.     

Development of Rational Technology for Manufacture of Arselon Sewing Thread

The effect of the twist value on the basic physicomechanical indexes of Arselon sewing thread of 29 tex × 4 structure was examined. Polynomial models that adequately reflect the dependence of the optimization criteria on the twist were obtained. The analysis of these models allowed establishing the optimum twisting parameters for Arselon sewing thread.__________Translated from Khimicheskie Volokna, No. 2, pp. 30–31, March–April, 2005.     

Calculation of binodal lines for a multicomponent mixture by the homotopy method

Equations are proposed for binodal lines of a multicomponent mixture in the T-P and P-V planes. A numerical method for solving the equations of the thermodynamics model is described, which is based on the homotopy method and uses the physical parameters of the system, in particular, temperature and pressure, as parameters of continuation of solution. Calculation results illustrating the features of the phase states of binary and multicomponent mixtures are presented.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 1, 2005, pp. 88–94.Original Russian Text Copyright © 2005 by Yermakova, Sazhina, Anikeev.     

Optimization of the Structure of Cord-Braiding Articles

The basic physicomechanical properties of cord made of polyamide complex fibres for different load structures and different manufacturing speeds on a cord-braiding machine are investigated. The optimum structure and production technology for cords made of synthetic fibres that ensure a high breaking load and minimum relative elongation at break of the cords under the effect of a constant load are determined.__________Translated from Khimicheskie Volokna, No. 1, pp. 48–49, January–February, 2005.     

Method for Calculating Pressure Losses in an Upward Cocurrent Flow

In an upward cocurrent gas-liquid flow in a vertical tube, the dependence of the pressure gradient on the gas velocity is known to be extremal. At a certain gas velocity w = w ₀, the pressure gradient takes the minimal value ϕ = ϕ₀. It is also known that stable modes of upward cocurrent flow, which are of the greatest practical importance for adsorption processes, occur at w ≥ w ₀. By analyzing a large body of primary experimental data obtained by various researchers over a wide parameter range, corrections are made to a known relation between the pressure gradient and the gas velocity in a column. An algorithm for calculating the pressure loss is developed.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 3, 2005, pp. 319–326.Original Russian Text Copyright © 2005 by Novozhilov, Kutepov.     

Prediction of thermal degradation of thermoprotective materials on the basis of their composition and properties of components

Thermal decomposition of thermoprotective materials based on phenolformaldehyde resin and carbon cloth with different contents of components is studied. Physical and mathematical models for the process are proposed. It is shown that the mass loss in carbon fiber reinforced plastics is determined by thermal degradation of the components and can be described by a generic kinetic scheme with a given set of thermokinetic constants. The mass loss of materials can be predicted by solving a system of ordinary differential equations taking into account the mass ratio of the components in the composite material.Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 1, pp. 66–72, January–February, 2005.     

Mathematical simulation of heterogeneous detonation of coal dust in oxygen with allowance for the ignition stage

A consistent physicomathematical model that describes ignition and detonation combustion of a gas suspension of coal-dust particles is developed. The model is based on the concepts of the two-velocity two-temperature continuum of mechanics of heterogeneous media with allowance for reduced reactions of pyrolysis, combustion of volatiles, and combustion of the coke residue. The model is verified with the use of available experimental data on the dependence of the detonation velocity on the initial concentration of the discrete phase and the dependence of the ignition delay on the Mach number of the incident shock wave. An analysis of ignition of the gas suspension of bituminous coal in shock waves shows that the stage of ignition proceeds under conditions of both temperature and velocity nonequilibrium. The influence of particle heating due to stagnation temperature on devolatilization dynamics and ignition delay is established. Examples of computed flow structures behind shock and detonation waves with allowance for the ignition stage are presented.Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 1, pp. 89–99, January–February, 2005.     

Structural changes in melts of butadiene–styrene and isoprene–styrene block polymer-based pressure-sensitive adhesives

Rheological and small angle x-ray scattering (SAXS) measurements show that typical pressure sensitive adhesives prepared from block polymers of butadiene or isoprene with styrene maintain the domain structure of the block polymer well beyond the polystyrene domain T_g, but form homogeneous melts above a critical temperature, T_c. For the examples investigated, T_c lies some 20°C below the usual hot melt processing temperature. The extremely high resistance to creep of the adhesives at service temperatures is explained as being the result of viscous flow with the domain structure in a state of dynamic equilibrium, in which polystyrene blocks are detached from domains and reattached to others. A transition between nonequilibrium and equilibrium domain structures is revealed clearly by SAXS for one of the block polymers used in this work.     

AC impedance spectroscopy as a technique for investigating corrosion of iron in hot flowing Bayer liquors

The flow-induced corrosion of iron, in spent Bayer liquor at high temperatures, was investigated using a rotating cylinder electrode (RCE) in an autoclave facility. A temperature range of 100–230 °C and equivalent pipe velocities in the range 0.84–3 m s^–1 were used. AC impedance technique was applied to monitor in situ the entire corrosion process. Corrosion rates measured by a.c. impedance expressed as average 1/R _p were in good agreement with those obtained by weight loss measurements. The results suggest that a.c. impedance is a suitable method to monitor the corrosion process of steels exposed to flowing Bayer liquor at higher temperatures.     

A General Nonequilibrium Multicomponent Adsorption Model: Numerical Solution

Abstract

A comprehensive mathematical model has been developed to describe the process of multicomponent adsorption from a well-stirred bath. Both internal and external diffusional resistances were included in the physical model. A nonlinear Fritz-Schluender isotherm was used to describe the adsorption equilibrium. An infinite bath, one-component, non-equilibrium model was compared with an equilibrium model. A numerical solution for a binary system in an infinite bath was obtained. The numerical solution for a two-component model in a stirred finite bath was shown to satisfactorily match previously published experimental data. Its extension to an n-component system was shown. It was shown that the solution of nonequilibrium model is easier and more efficient than that of the equilibrium model. The nonequilibrium model is especially advantageous for a large number of solutes.     

Microwave Radiation from Combustion of an Iron-Aluminum Thermite Mixture

Nonequilibrium microwave radiation from the combustion wave of the Fe₂O₃-Al powder system in the frequency range of 3.4–37.5 GHz was recorded. It is found that the radiation power is proportional to the free-surface area of the reaction products and is 4–7 orders of magnitude higher than the thermal-radiation level in the same wavelength interval. A possible mechanism of the electromagnetic emission is the Bremsstrahlung of the mobile electrons released by the condensed-phase surface.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 4, pp. 132–135, July–August, 2005.     

Oxide crystals for electro-optic <Emphasis Type="Italic">Q</Emphasis>-switching of lasers

A new generation of oxide crystals is emerging for electro-optic Q-switching or control of high-power pulsed lasers. Unlike the acousto-optic Q-switches in which the total turn-off time is limited by the duration of sound wave propagation (110–220 ns/mm) across the beam diameter, the electro-optic devices provide a short (<10 ns) response needed for minimum losses. Extinction ratios of better than 100 : 1 for electro-optic crystals ensure their reliable hold-off. By contrast, acousto-optic devices are characterized by single-pass dynamic losses of approximately 40%, which hinders their use in high-gain lasers. The basic principles of electro-optic Pockels cells are discussed. The performance characteristics of Q-switching for traditional electro-optic materials [deuterated potassium dihydrogen phosphate (DKDP), lithium niobate (LNB)] and other new electro-optic crystals, such as barium metaborate (BBO) and crystals belonging to the langasite (LGS) and potassium titanyl phosphate (KTP) families, are reviewed comparatively. Particular emphasis is placed on KTP-type electro-optic crystals, primarily on rubidium titanyl phosphate RbTiOPO₄ (RTP), which stand out in their ability to provide Q-switching at extremely high frequencies or repetition rates up to 200 kHz. The use of both X- and Y-oriented double crystals as Q-switches in order to combine large electro-optic coefficients and low quarter-wave hold-off voltages with excellent thermal stability of the device is considered.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Roth, Tseitlin, Angert.