Investigation in thermal endurance of polyesterimide used in electrical machines

The purpose of this investigation is to evaluate thermal lifetime of polyesterimide using Weibull statistics. Thermal aging was performed on twisted pair specimens of copper wire insulated by a polyesterimide layer. The study shows that breakdown voltage varies versus aging time. Its increase is allotted to a crosslinking inducing a diminution of mean‐free path of charge carriers leading thereby to a mobility decrease, whereas its decrease is attributed to the viscosity diminution expressing a weakening of molecular bonds and a mobility increase of charge carriers. Shape parameter changes in function of aging time. Its increase is ascribed to an arrangement of the molecular structure, whereas its decrease is due to an augmentation in the size of defects. The thermal endurance graph is a straight line indicating that the degradation is governed by a first‐order chemical reaction. Activation energy and temperature index were determined. The degradation is governed by the dissolution of copper into the polymer and accelerates its degradation occurring at the polyesterimide–copper interface. Oxygen can diffuse into the insulation and attack copper resulting in the formation of copper oxide. The degradation is caused by the scission of imide and ester bonds. The process is followed by a change in color and a presence of cracks. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Boundary Effects in Flow in Annular Porous Media

An analytical method for flow calculations in an annular porous media bounded by a solid outer wall and subject to a countercurrent flow in its inner boundary is presented. The analysis is rigorous and makes it possible to evaluate the effect of the boundaries in the transport capacity of porous channels. The mathematical model is applicable to wicks, such as those found in heat pipes. The paper explores the conditions, that is. the value of critical parameters, under which boundary effects are not negligible and should be taken into account in wick design.     

煤焦油中脱除喹啉不溶物技术的研究进展

煤焦油是一种制备高附加值碳材料的理想原料,然而其深加工利用受到内部高含量喹啉不溶物(QI)的影响。为此,本文介绍了煤焦油的组成和性质,简述了煤焦油中QI的组成、来源和其对煤焦油加工利用的危害,综合对比分析了煤焦油净化分离常用的几种方法。热过滤法分离效率虽然满足工业需求,但工业成本较高;重力沉降法操作简单,但分离效率低;离心分离法分离效率高,但处理量小,难以满足工业化应用;蒸馏处理法分离效率高,但原料利用率低;溶剂萃取法容易操作,但溶剂需求量大;改质法效果明显,但成本较高;静电分离法能量消耗低,但静电分离最佳条件变动性较大;联合处理法分离效率较高,应用前景广阔,可以作为一种净化分离的科学有效方法,并可以作为一种净化分离技术的发展趋势。     

Autowave processes in a heterogeneous medium with chemical reactions in a gaseous phase and in a catalyst bed

A mathematical model is constructed for autowave processes in a heterogeneous medium with chemical reactions in a gaseous phase and in a catalyst bed. The model accounts for the changes in the interphase heat and mass transfer and thermal conductivity coefficients of the catalyst bed as a function of the system parameters. The phase trajectories of the dynamic system are investigated using qualitative and numerical analyses, and an effective technique for searching for a physically comprehensive autowave solution of the problem is proposed. The mathematical model of hybrid autowaves is tested in a cycle of numerical calculations, and the influence of the system parameters on the main technological characteristics of the autowave processes is analyzed.     

Numerical study of shock-wave diffraction in variable-section channels in gas suspensions

The problem of shock-wave transition past a backward-facing step in a gas suspension is solved. The calculation method is tested on a similar problem for a pure gas, and good agreement with available experimental and numerical results is reached. The effect of shock-wave intensity, mass load factor of particles in the mixture, and particle size on the flow structure in the gas suspension is determined. It is shown that the greatest difference between the flow pattern in a two-phase mixture and the corresponding flow in a pure gas is observed in the range of times when the characteristic sizes of the structures being formed are commensurable with the scale of the relaxation zones. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 85–95, January–February, 2008.     

Advances in calculating thermally induced stresses in nonlinear viscoelastic materials

Temperature change can build up tensile stresses into thermoplastic materials, if their thermal expansion is hindered. This paper describes how to calculate those stresses. Because thermoplastic materials are time dependent with respect to temperature and strain, a nonlinear viscoelastic material model is necessary for the prediction of thermal stresses. This paper presents a numerical model that is able to predict thermally induced stresses in dependency on the load history. The calibration as well as the numerical procedures are described. The model is evaluated with a semicrystalline high density polyethylene (HDPE). Finally, a simulation of a screwed joint reveals the importance of this modeling for a more effective use of thermoplastics in the future.     

Zur Berechnung der Partikelabscheidung in ZyklonenA model for particle separation in cyclones

In the present paper a new model is developed for cyclone design. This is based upon results of recent experimental and theoretical studies on gas flow and particle collection in cyclones. Particle transport is interpreted as a process, in which a random particle motion due to flow turbulence is superimposed on a mean motion. The particle flux within the cyclone is calculated using a simple flow model. In this model the separation chamber is divided into four characteristic regions. The model covers all important design parameters and requires little computational effort. Calculated grade efficiencies are in good agreement with the experimental results.     

The Freundlich isotherm in studying adsorption in oil processing

The objective of this review is to discuss the history of the use of the Freundlich isotherm in investigating adsorption processing of vegetable oils and to evaluate its current value in adsorption studies. The Freundlich isotherm was originally developed to explain the adsorption of a single solute from solution. However, a similar adsorption pattern has been observed when studying a more complex system of adsorption of vegetable oil pigments onto bleaching clay during commercial bleaching of vegetable oils. The Freundlich isotherm has been useful for decades in finding the commercial value of adsorbents as long as a narrow experimental interval of adsorbate is used. More recent studies have shown that a complex series of interactions controls the adsorption process. While the isotherm summarizes these interactions, investigating them is vital to understand the physicochemical factors involved during adsorption. Statistical modeling and spectroscopy are useful in understanding the vegetable oil bleaching/refining process as a multiple-component adsorption system.     

The role of desalination in bridging the water gap in Jordan

The water resources of Jordan have always been scarce. The demand for water in the country exceeds the available resources and the gap between the water supply and demand is continuously increasing. Furthermore, the quality of water resources has dramatically deteriorated in recent years, which prevented the utilization of some resources. To secure the economic sustainability of the country, it is important at this stage to consider non-conventional water resources, such as sea and brackish water desalination. This study examines the water resources of Jordan, projected water demand, and the gap between the demand and supply based on two scenarios. The possibility of closing this gap by water desalination was investigated. Both sea and brackish water desalination were considered. The analysis revealed that seawater desalination process is economically infeasible for domestic water uses at this stage. This is attributed to that Jordan is not an oil producing country and the location of sea shoreline in Aqaba is on the Red Sea, away from the consumption centers. However, seawater desalination may be a viable option for tourist and industrial enterprises that will be established as a result of the new Law of Aqaba Free Zone. The most convenient and realistic option for Jordan in the short term, is the desalination of brackish water by reverse osmosis (RO). The brackish water with total dissolved solids between 2000-10000 mg/l is available from many aquifers and springs of the country. The study concluded that Jordan is facing a severe water crisis. Until recently, the water planners have not given the water desalination the required attention as a potential source of water supply. Taking into account the progress that is being achieved in the field of desalination technology, Jordan has to consider the desalination option more seriously and to start building a national capacity in the field of water desalination. It was emphasized that desalination is not a substitute to traditional water resources, it is rather a supplementary source that can contribute in bridging the water gap of the country.     

Mass transfer in a film flowing over semipermeable surfaces in microfiltration-desorption apparatuses

Desorption of dissolved water and gases during the purification of organic liquids in microfiltration-desorption apparatuses is simulated. The problem of desorption from a liquid film of variable thickness flowing over a microfiltration membrane is solved, and its numerical and approximate analytical solutions are presented. The problem of desorption from a film running down an impermeable surface in additional purification system is also solved, and its analytical solution is presented. The solutions are used to determine the generalized variables controlling the extent of desorption. The conditions ensuring high purification efficiencies are found.     

Propagation of detonation waves in gas suspensions in channels with a backward-facing step

Propagation of heterogeneous detonation in a mixture of oxygen and fine aluminum particles in a plane channel with a backward-facing step is studied numerically. The plane detonation regime is taken as the initial flow in the narrow part of the channel. Possible scenarios of evolution of this flow after its passage to the expanded part of the channel are analyzed. The effect of the particle size and channel geometry on detonation propagation/failure is found. Cellular detonation is formed in the wide part of the channel, with a subsequent change in the cell size in the course of establishment of a steady propagation regime. The cell size in steady regimes is invariant with respect to the flow formation process.     

Equipment development in solvent extraction

Any solvent extraction system must ultimately involve mixing and phase separation. The mixer-settler, which is the chief subject of this paper, has several advantages. It can be readily scaled up to handle large flow rates, and there is a great deal of practical experience in using it. There are also a number of areas where it can be modified to give improved operation. The mixer is an ideal area to apply the knowledge of chemical reactor fundamentals. The stage efficiencies to which we commonly refer can also be viewed primarily as mixer efficiencies. It would be a logical matter to consider increasing the degree of chemical reaction by using mixers in series within each stage. The physical phenomena taking place within the settler become clear with investigation. The assumption that plug flow predominates in any settler is probably at variance with actual facts. The control of the flow of the dispersion in the settler is a factor which should serve to make settlers smaller and more efficient. Solvent extraction equipment is undergoing constant scrutiny and improvement. The conventional mixer still needs additional basic studies, but it may some day be replaced by some other basic method of imparting mechanical energy and flow. It is likely that the gravity settler may be replaced by a device using a more intense force field, such as electrostatic or centrifugal forces.     

Surface crack in tension or in bending – A reassessment of the Newman and Raju formula in respect to fracture toughness measurements in brittle materials

The Newman and Raju formula for the stress intensity factor of a semi-elliptical surface crack loaded in uniaxial tension or in bending has been developed about 30 years ago using an FE-analysis for several geometric parameters and fitting an empirical equation to the data points. The Poisson's ratio analyzed was 0.3.In this paper a reassessment of the Newman and Raju formula is made, where all relevant geometric parameters of crack and specimen and the Poisson's ratio are considered. The deviations of the old formula from the new results are up to 21%, if the full range of Poisson's ratio is taken into account. Furthermore the influence of the crack-surface intersection angle is discussed.The results of this work are important for more precise fracture toughness measurements in brittle materials and give a practical guidance for appropriate specimen preparation for fracture toughness measurements, which is also considered here.     

Systematic staging in chemical reactor design

The foundation and implementation of a method for systematic reactor design is described. The reactor path is sectioned into stages where each stage is designed so as to optimize an overall objective. This is a further development of a previously proposed method for designing chemical reactors (Hillestad, 2004, Hillestad, 2005). Reactants pass through a series basic operations or functions to form the desired products. The basic operations are represented by design functions on the path volume. The design functions are fluid mixing (dispersion), distribution of extra feed points, distribution of heat transfer area and coolant temperature, catalyst dilution distribution and more. The conceptual reactor design problem is solved as an optimal control problem. A direct method is applied where both the design functions and the state variables are discretized. The realization of the optimization is a staged process string of multi-functional units. A kinetic model of the gas phase methanol synthesis is used as an example. By applying the method on the model, a staged reactor design with less heat transfer area and higher production is possible.     

细胞微包囊的研究进展

利用异体细胞是代谢类组织工程的研究热点，但异体细胞引起的免疫排斥反应是一个重要的限制因素。通过细胞微包裹，可以消除这种不期望的反应发生。本文介绍了机械，静电制备微包囊的方法以及细胞微包囊法在镇痛，人工胰岛，肝，肾等方面的应用，同时展望了细胞微包囊在生命科学领域中的应用前景。     

Flow Compartments in Viscoelastic Fluids Using Radial Impellers in Stirred Tanks

The influence of viscoelastic flow properties on fluid dynamics using radial impellers is investigated. The use of transparent model fluids allows for the optical measurement of general flow behavior with a fluorescence dying technique. By varying viscoelastic flow properties, size of agitators and rotational frequency, the impact of these parameters on fluid dynamics is analyzed. Toroidally shaped, cavern‐like flow compartments form around the agitators in all fluids in specific rotational frequency ranges, preventing an efficient mixing. By balancing elastic with centrifugal forces, a simple model is developed with which compartment sizes can be predicted with good accuracy. The results indicate a good suitability of the elasticity number as a scale‐up criterion.     

Vitamin D-Bestimmung in Margarine

Determination of Vitamin D in Margarine The very low Vitamin D content of margarine necessitates for its quantitative determination a very elaborate working up of the sample. After cold saponification and extraction of the unsaponifiables a preliminary purification is carried out on an Aluminium-oxide-Digitonin/Celite column. The other impurities are eliminated by HPLC on an adsorption column and by collecting the Vitamin D fraction. The final analysis is done by HPLC on a reversed phase system which allows a separation of Vitamin D₂ and D₃. Whichever D-Vitamin is not contained in the sample is used as an internal standard.     

In-plant microfouling in desalination

Microfouling of solid surfaces exposed to sea water by primary film forming bacteria is a phenomenon reasonably well known. Microfouling is believed to serve as a percursor to marine macrofouling and corrosion, significantly reduce the efficiency of condenser-heat exchangers, and cause a reduction in efficiency of performance of reverse osmosis membranes. The complex poorly understood microfouling-corrosion process has caused a huge and continuing cost to the desalination industry.Microfouling in desalination is a process in which the rate of increase of the mass of surface film is dependent in large part on the specific character of the environment, most particularly the physical, chemical and biological condition of the intake sea water. The microfouling process occurs in four stages: (1) Chemical Conditioning, (2) Attachment and Colonization by bacteria, (5) Colonization by other microorganisms, and (4) Accumulation. The attachment of bacteria to surfaces is mediated by a glycoprotein polymer. This adhesion-inducing polymeric material has been recovered from filtered sea water, marine bacteria, and algal cultures. The glycoprotein is active in exceedingly low concentration and has been shown to adhere very effectively to solid surfaces.While microfouling is a known phenomenon in reverse osmosis, its role in accelerating corrosion as well as causing a decrease in the overall heat transfer coefficient in distillation has still not been fully studied. Sucessful control of microbial fouling will follow when a complete understanding of the process has been achieved.     

Frill-like defect in glazes in the context of synergism

The behavior of the glaze layer deposited on a ceramic sample is considered from the standpoint of nonequilibrium thermodynamics beginning with the moment of slip deposition up to the birth of the melt. The significance of a combined approach to the study of this process is demonstrated and methods for the control of the macrostructure of the coating thus formed are proposed.     

Phenol oxidation in supercritical water in a well-stirred continuous reactor

A well-stirred reactor for phenol and acetic acid oxidation in supercritical water is considered. A mathematical model of an adiabatic reactor is formulated. A numerical algorithm for solving the model equations using the homotopy method is developed. The model takes into account specific features of processes under supercritical conditions, namely, the changes in the thermodynamic properties (enthalpy, heat capacity, and critical parameters) of mixtures with a change in pressure and temperature. The thermodynamic properties are calculated by methods of nonideal thermodynamics. It is shown that there is a multiplicity of steady-state solutions at various reactor performances. The results of numerical analysis of the effect of the inlet flow temperature, the amount of methanol (fuel) fed, and the total pressure on the reactor performance are presented.