Modeling of operation of a solid-propellant pulse aerosol generator during extinguishing of methane-air mixture ignition in coal mine drifts

Operation of a pulse aerosol system of extinguishing fires caused by ignition of a methane-air mixture in drifts and coalfaces of coal mines is modeled. A computational experiment shows that such a system can cut off the shock wave propagating over the coal mine drift filled by a combustible methane-air mixture, suppress burning, and protect people and equipment in the mine from the shock wave action.     

Modeling of ignition of a solid-propellant plate by a low-temperature plasma jet

A problem of ignition of a semi-infinite solid-propellant plate by a low-temperature plasma jet formed in an igniter under a high-power electric discharge is considered. Particular attention is paid to formation and evolution of zones of forced gasification of the fuel under the action of a heat flux from the plasma to the propellant. The locations of these zones are determined by satisfying two conditions: the propellant surface reaches the gasification temperature and the heat flux exceeds a certain “threshold” value. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 23–28, January–February, 2007.     

提升管内细长颗粒流化运动的气固多向耦合模型的构建

细长颗粒气固两相流研究已成为气固两相流研究的重点问题之一。而各种细长颗粒在流场中的受力、运动模型构建以及细长颗粒/流场间的耦合关系的构建是细长颗粒两相流数值模拟研究的难点之一。在已经基于刚体动力学原理构建了细长粒子气固两相流单向耦合模型的基础上,结合基于κ-ε模型的球形粒子-流场气固间耦合关联式,并改进细长颗粒间碰撞模型,从而构建了细长颗粒气固两相流动多向耦合数值模拟平台。并且采用此平台对某一实际流化床内的细长粒子气固两相流场进行了数值模拟研究。研究表明,不同时间细长颗粒在流场内的停留位置具有较强的随机性;细长颗粒在流化运动过程中伴随有较明显的取向选择性;细长颗粒的存在会导致当地流场的速度、压强均有较为明显的下降。     

Modeling of equilibrium combustion of kerosene by a mixture of gaseous hydrocarbons

It is demonstrated that the composition and parameters of state of the gas formed in the course of equilibrium combustion of aviation kerosene in air can be modeled by means of determining the same quantities for a certain mixture of hydrocarbon fuels. The latter can be a mixture of identical amounts of methane and acetylene. The equilibrium composition calculated for the model mixture exactly coincides with the composition of kerosene combustion products for identical values of pressure (or density), temperature, and oxidizer-to-fuel ratio. Combustion of kerosene and the model mixture in a constant-pressure (or constant-density) mode can ensure satisfactory agreement between the temperatures of the final products and their compositions if air with a lower-than-normal fraction of oxygen is used as an oxidizer. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 3–7, July–August, 2007.     

Modeling drop breakage using the full energy spectrum and a specific realization of turbulence anisotropy

The assumption of homogeneous isotropic turbulence when modeling drop breakage in industrially relevant geometries is questionable. We describe the development of an anisotropic breakage model, where the anisotropy is introduced via the inclusion of a perturbed turbulence spectrum. The selection of the perturbed spectrum is itself motivated by our previous large-eddy simulations of high-pressure homogenizers. The model redistributes energy from small to large scales, and assumes that the anisotropic part of the Reynolds stresses is confined to the energy-containing range. The second-order structure function arising from the perturbed spectrum is used in the standard framework of Coulaloglou and Tavlarides to calculate breakage frequency. While the base model exhibits non-monotonic behavior (by predicting a maximum value for a certain drop size), the effect of anisotropy is shown to increase breakage frequency in length scales larger than this peak, thereby reducing non-monotonicity. This effect is more pronounced for small turbulence Reynolds numbers.     

Modeling of a process for removal of metal ions by electromigration and electrodeposition

A mathematical model for the removal of impurities of the metal ions of Fe, Ni, and Cu from hard chromium plating solution by electromigration and subsequent electrodeposition has been developed and presented. Experimental data for the metal removal at 45°C and constant cell voltage using o‐phosphoric acid as the catholyte are presented. Up to 36% iron and 29% nickel removal is obtained over about 25 h. The copper removal rate is observed to be approximately four times greater than the rate of nickel removal. The experimental data were found to closely match results predicted from the model developed. The inherent model parameters such as mobility, diffusivity, mass transfer coefficient and metal deposition rate constants were estimated. The calculated values of these parameters are found to be in good agreement with the published data.     

Modeling of nonisothermal film blowing process for non‐Newtonian fluids by using variational principles

In this work, nonisothermal film blowing process analysis for non‐Newtonian polymer melts has been performed theoretically by using minimum energy approach and the obtained predictions were compared with both, theoretical and experimental data (internal bubble pressure, take‐up force, bubble shape, velocity and temperature profiles) taken from the open literature. For this purpose, recently proposed generalized Newtonian model depending on three principal invariants of the deformation rate tensor, D, and its absolute defined as $\sqrt {D \cdot D}$ has been used. It has been found that film blowing model predictions are in very good agreement with the corresponding experimental data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

顶燃式热风炉燃烧过程的数值模拟

针对目前国内原料磨热风炉结构形式和特点,采用CFD(Computational Fluid Dynamics)技术数值研究该热风炉内的燃烧过程。基于初始设计方案的模拟结果,提出优化改进方案,然后再次进行数值模拟研究,最后得到较为合理的流场分布,为该热风炉的工程设计提供了重要的理论指导。     

蓄热段长度对流向变换催化燃烧反应器性能影响的模型研究

在建立低浓度挥发性有机化合物VOCs催化燃烧流向变换反应器一维非均相模型的基础上,编写Matlab程序对模型进行求解。分析在不同的表观气速下,反应器蓄热段长度对反应器性能的影响,着重研究大气速条件下反应器的最佳床层结构比例。计算结果表明,不同的蓄热段长度对反应器性能有很大影响。对于直径0.2 m的反应器,小气速条件下,反应器内最高温度随着蓄热段长度的增大而降低,大气速条件下则相反。在表观气速为0.15 m·s^-1和床层结构比例为1.2~2.0条件下,反应器能达到最佳操作状态。     

Modeling of the volatile organic compounds biodegradation process in the trickle-bed bioreactor—Analysis of the model parametric sensitivity

Mathematical models of the process of air purification from hydrophobic (styrene) or hydrophilic (vinyl acetate, VA) compounds carried out in a co-current trickle-bed bioreactor were presented. These models were marked as TSM (two-substrate model), OSM (one-substrate model) and AOSM (approximate one-substrate model). The experimental database was exploited to validate the TSM which approximated very well the experimental data; the mean percentage error of RE prediction did not exceed 3% for styrene and 4.1% for VA. For the tested systems, TSM was only sensitive to the changes in biomass dry density X_b and effective diffusion coefficient D_j,ef values. The percentage relative error of the state variable computed using OSM/AOSM in relation to the value obtained from TSM was the quantitative criterion for comparison of the results obtained using different mathematical models of the process. It was shown that the simplified models describe the process investigated with satisfactory accuracy.     

Can simulation technology enable a paradigm shift in process control?: Modeling for the rest of us

Commercial process simulation software makes it easy for experts to develop very complex models with thousands of equations. But how well are these models used? Remember the admonition of Box [Box, G. E. P. (1979). Robustness in scientific model building. In R. L. Launer & G. N. Wilkinson (Eds.), Robustness in statistics (pp. 201–236). New York: Academic Press], “All models are wrong, but some are useful”. Are case runs just captured in a report and then filed away? Is the expert the only one who can run additional cases? We believe that process dynamics simulation should be ubiquitous in chemical engineering practice and education. Undergraduate engineers should experience unit operations through a virtual process simulator. In industry, engineers must be able to quickly build dynamic models to study operability and design control strategies. We feel that DuPont has undergone a paradigm shift where engineers are much more likely to use dynamic simulation as part of their day-to-day work. This paper illustrates some of the features that process dynamic simulators need to enable this paradigm shift.     

Modeling of the free flight region of a cyclone transferred arc plasma reactor

The Plasmacan cyclone transferred arc plasma furnace seems ideally suited for the treatment of fine refractory powders to produce a consolidated liquid product. In this furnace, particles are pneumatically injected tangentially near the wall of a cylindrical sleeve while an arc is struck along the central axis of the sleeve. A simple model has been developed to examine the behaviour of the injected particles in the entrance region of the furnace up to the point where the particles reach their melting point and form the molten film. Three-dimensional equations of particle motion are solved to compute particle trajectories, given gas temperature and velocity fields in the furnace. The location of the first appearance of the molten film is computed under a variety of operating conditions for a laboratory scale furnace.     

Modeling the kinetics of a photochemical water treatment process by means of artificial neural networks

We have investigated the kinetics of the degradation of 2,4-dimethyl aniline (2,4-xylidine), chosen as a model pollutant, by the photochemically enhanced Fenton reaction. This process, which may be efficiently applied to the treatment of industrial waste waters, involves a series of complex reactions leading eventually to the mineralization of the organic pollutant. A model based on artificial neural networks has been developed for fitting the experimental data obtained in a laboratory batch reactor. The model can describe the evolution of the pollutant concentration during irradiation time under various conditions. It has been used for simulating the behavior of the reaction system in sensitivity studies aimed at optimizing the amounts of reactants employed in the process — an iron(II) salt and hydrogen peroxide. The results show that the process is much more sensitive to the iron(II) salt concentration than to the hydrogen peroxide concentration, a favorable condition in terms of economic feasibility.     

3D Modeling of the Elastic-Plastic Behavior of Thin Aeronautical Adhesive Films Suited for a Wide Range of Tensile/Compression-Shear Loads

Adhesive bonding is an interesting structural assembling technique for weight saving in modern commercial aircraft, in which the use of composites materials is increasing. In order to meet both optimization and respect of safety conception constraints, the development of accurate numerical strategies is required. Thus, improvement in the experimental characterization and in the design of reliable numerical tools for bonded assemblies is necessary. This paper presents the characterization of the elastic-plastic behaviour of four aeronautical adhesive films, consisting of two epoxy-based resins supported by two types of carrier. The characterization over a wide range of monotonic proportional tensile-shear loads is performed using a modified Arcan test device designed to strongly limit the influence of edge effects. Moreover, to obtain an accurate definition of the initial elastic limit of the adhesives, further experimental tests have been performed using a pressure vessel especially designed to study the influence of the hydrostatic stress. Inverse identification techniques using finite element analysis have been used to identify the material parameters of an elastic-plastic model based on the experimental results (the load-displacement curves). Results underline the potential of such a model to represent the non-linear behaviour of ductile adhesives under tensile/compression-shear proportional monotonic loads.     

Modeling the Regeneration of a Polymeric Resin Column Saturated with Ethanol by Air Purge and External Heating

In this work, the regeneration of a polymeric resin column saturated with ethanol with air purge and external heating has been studied. A theoretical model is proposed for describing the mass and heat transfers in the system, and it has been validated with experimental data. This model can be used for simulating the regeneration step in a concentration-thermal swing adsorption process for fuel-grade ethanol production. The model has been used to analyze the process dynamic behavior, and to compare the performance of the regeneration step using external heating and hot air purge.     

Modeling of kinetics for the enzymatic hydrolysis of sunflower oil in a high-pressure reactor

This study presents a mathematical model for characterizing the Michaelis-Menten type of sunflower oil hydrolysis, catalyzed by the lipase preparation Lipolase 100T (Novozymes Ays, Bagsvaerd, Denmark). Supercritical carbon dioxide was used as a solvent for this reaction. Computer modeling of the kinetics was done for the enzymatic hydrolysis of sunflower oil in a high-pressure reactor using the MicroMath Scientist^® program (Micro-Math Research, St. Louis, MO). On the basis of the experimental results, we presumed the reaction was reversible. The suitability of the model was confirmed statistically with Student's t-test. Good agreement was found between the experimental and calculated values for the concentrations of oleic and linoleic acids.     

Steered molecular dynamics simulation of the detaching process of two parallel surfaces glued together by a single polyethylene chain

The detaching process of two parallel surfaces glued together by a single polyethylene chain in vacuo was investigated with a steered molecular dynamics method. Various statistical properties were analyzed in detail, including the mean‐square end‐to‐end distance; parallel and perpendicular mean‐square radii of gyration; shape factor; segment density distribution; average percentages of the microstructure of the chain of the tail, train, bridge, and loop; average surface adsorption energy; average total energy; and average pulling force (〈f〉). All these properties depended strongly on the pulling velocity (v). There existed a peak in the curve of 〈f〉 as a function of the detaching distance. Further, the relation between the maximum value of 〈f〉 and v showed three distinctive regions: a region of weak dependence at v < 10^?2 Å/ps, a region of strong dependence at 10^?2 Å/ps < v < 6.50 Å/ps, and a region of weak dependence at v > 6.50 Å/ps. These investigations may provide some insight into the microcosmic principle of the failure process of polymeric adhesives. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of defect states in the optical and magnetic properties of nanocrystalline NiO synthesised in a single step by an aerosol process

Nanocrystalline nickel oxide (NiO) was successfully synthesised as a phase-pure product from an inorganic precursor through a “single-pot”, gas-phase synthesis method, nebulised spray pyrolysis (NSP). Functional properties such as magnetic behaviour, luminescence and band gap were studied and compared with the properties of NiO powder synthesised by a conventional reverse co-precipitation process (RCP) which also needed an additional calcination step. Although NiO crystallised in the cubic (rocksalt) form, Rietveld analysis of X-ray diffraction data revealed the synthesised nanopowders to be in a distorted cubic (rocksalt) or monoclinic form. This distortion resulted from the antiferromagnetic exchange interaction energy and increased magnetic surface anisotropy, as seen from the bond lengths determined from Fourier transform infra-red (FTIR) studies. Raman spectroscopy also confirmed the distortion in the structure indicated by the presence of a first order phonon peak. The band gap decreased in case of both the powders and was attributed to the shallow donor or acceptor levels created due to the presence of defect states as determined from photoluminescence studies. The NSP powders also exhibited a dependence on the excitation wavelength during emission luminescence. A mixed antiferromagnetic and ferromagnetic behaviour was observed in the NSP powders and the susceptibility of each was deconvoluted through low and high field magnetometry studies. Further, the nanopowders from both the processes showed “core-shell” magnetism, with paramagnetic behaviour in the shell and antiferromagnetism in the core. The thicknesses of the core and shell were also determined.