Short and long term particle release from surfaces under the influence of gas flow

Preliminary measurement of particle reentrainment from 5 mm i.d. and 3 m long stainless steel tubes show two distinct regimes of concentration decay with time.

In the regime (t < few minutes) the concentration n(t) is proportional to t^−a with a > 1 being a function of flow rate and particle size. The ST regime appears to correspond to particle release by shear flow in the region where F = (adhesion force)/(removal force) 1.

The concentration decay is described by the desorption model of Wen and Kasper, where n(t) is proportional to (1/t) exp (−t/T). The LT regime appears to include the release of relatively strongly adhering particles where F > 1 up to about F = 5 or 6 (Wen and Kasper, 1989) which is classically forbidden and explained only in the model Reeks et al. (1988).     

Effect of long term humid aging on plastics

The warm humidity resistance of more than thirty plastic formulations has been evaluated in a program which aged specimens for periods ranging from 10 months to 3 years. Both thermoset and thermoplastic products were included in this study. All of these materials can be used in high humidity at moderate temperatures for short periods of time except where water absorption lowers the glass transition temperature enough to cause distortion. Several of these commercial products exhibit good long term resistance to humidity at temperatures approaching 100°C. However, some are degraded by long term exposure to warm humidity. This hydrolysis effect can result in useful lifetimes which are considerably shorter than would be expected from projections which are based on conventional dry oven aging tests. This broad data base provides a basis for selecting plastics for use in warm, humid environments.     

Short term isothermal aging of epoxy resin and epoxy-carbon fiber composites

Short term isothermal aging of a neat epoxy resin and one ply epoxy-carbon fiber composite has been performed. The glass transition temperature, T_g of the neat epoxy resin aged at 204°C increased with aging time. The weight loss of the neat epoxy resin due to aging increased with aging temperature and aging time. The weight loss of the epoxy–carbon fiber composite during aging was slightly less than that of the neat resin. SEM microscopy showed the presence of voids and pores on the surface of the composite due to loss of low molecular weight volatiles. The amount and the size of the voids formed during aging increased with aging temperature and time.     

Very large cathode current and long term stability of vacuum sealed tubes with engrafted-carbon-nanotube emitters

For the future commercial applications of carbon nanotubes (CNTs) in high power vacuum microwave amplifiers or compact X-ray tubes, we have attempted to fabricate engrafted CNT field emitters on a metallic substrate using both screen printing and chemical vapor deposition. Cobalt nano-grains are doped in the printed CNT paste and act as the catalyst for the engrafted growth of CNTs by the cold wall chemical vapor deposition. Stable cathode current (~ 30 mA) from a small area (~ 1.5 mm²) of engrafted CNT emitters was measured in a vacuum-sealed diode tube. High current density (> 1.6A/cm²) has also gotten in the vacuum sealed tube in which the emitters spread about 0.78 mm² after an aging process that lasts more than 12 h in DC mode with the water cooling of the anode.     

The short and long term performance of polymers in different environments

The behaviour of polymeric solids in contact with different environments is considered. A thermodynamic viewpoint is adopted and worked out in terms of chemical reactions, physical processes and the interaction between the two. It is shown that chemical attack alone does not normally cause serious loss of physical properties, but that a combination of chemical and physical (or physico-chemical) interactions between polymer and environment can lead to rapid deterioration. An understanding of these processes, and their synergistic effects, is essential in designing against environmental failure.     

Short term flexural creep behavior of wood-fiber/polypropylene composites

Short term flexural creep tests were conducted to investigate the creep behavior of wood-fiber polypropylene composites. Three experimental parameters were selected: the addition of a wetting agent, temperature, and wood-fiber concentration. All creep curves are presented in terms of relative creep as a percentage of instantaneous (initial) strain. The creep power law model was used to accurately fit the creep data. The addition of a wetting agent greatly reduced the creep at high stress, but had little effect at a lower stress level. The extent of relative creep increased with increasing temperature. It was found that the slope of the power law model was directly proportional to the temperature. The addition of wood-fibers into pure polymer greatly improved the creep resistance of the matrix polymer. The relative creep of the composites decreased with an increase in wood-fiber concentration. However, the composite showed relatively large creep compared with that of solid wood. It was found that both the time exponent and slope of the power law model were inversely related to wood-fiber concentration. The flexural modulus of the composites also had an inverse relationship with the time exponent.     

国内离子膜电解法与金属阳极隔膜电解法烧碱将在相当长的时期内共存

关于选择烧碱生产工艺的问题,作者阐述了如下观点:离子膜法是电解法烧碱生产工艺的发展方向,金属阳极隔膜法最终将被离子膜法取代;但由于历史、投资、设备更新、经济效益、市场需求等方面的原因,国内金属阳极隔膜法和离子膜法电解工艺将在今后相当长的一段时期内共存.     

长期搁置碳钢管的化学清洗及预膜处理工艺介绍

介绍了长期搁置碳钢管的化学清洗,以及在总Fe含量较高的水环境中的钝化预膜处理工艺。该工艺的实施取得了良好的化学清洗和钝化预膜效果,控制了碳钢管的腐蚀趋势;同时节约了用水、降低了清洗成本。     

The effect of annealing on the short and long term behavior of PEEK

Summary Short and long-term tensile tests have been done on injection-moulded poly-ether-etherketone (PEEK) in order to assess the effect of annealing on its mechanical behavior. In addition to the behavior reported before, namely increases in yield and drawing stress, the annealed specimens exhibit a distinct work hardening behavior in the beginning of the drawing phase at temperatures between 80°C and 160°C. Subsequent creep tests show that the annealing treatment also influences greatly the long-term static properties of PEEK with creep rates after annealing being considerably below those recorded on the standard injection.DSC thermograms of the samples annealed for more than 20 minutes exhibit similar curves as those reported before, two endothermic peaks: a major peak at 340°C and a minor one at 260°C which is 10 K higher than the annealing temperature.The experimental results support that a type of secondary crystallites grow in the material by the annealing treatment. The existance of those secondary crystallites enhances the mechanical properties of PEEK.     

Strength development due to long term sulfation and carbonation/sulfation phenomena

CFBC boilers firing high sulfur, low ash fuels can produce deposits consisting of almost pure CaSO₄. Test work has shown that if sorbents or bed materials are sulfated for long times (several days or more), they develop compositions similar to those deposits. Sulfation increases with temperature from 650°;C to 900°C, and strength increases continuously in the temperature range of 650°C to 950°C. When sulfation occurs under conditions where CaCO₃ is stable, the overall strength of the deposit increases but the degree of sulfation diminishes. Finally, this work suggests that pellet tests using crushed and calcined sorbents can give misleading information and should be used with caution to study the phenomena described here.     

分布式并行算法在长周期原油混输调度中的应用

为了有效求解长周期原油混输调度问题,提出了基于事件树的分布式并行算法。该方法把原油混输调度问题分解为码头调度子问题和厂区调度子问题,采用基于事件树的建模方法,并根据两个子问题的求解顺序提出了原油混输调度问题的分布式并行算法。本方法采用主从式并行结构,主节点把求解码头调度子问题所需的原油质量要求信息发送到各从节点,然后各从节点把与质量要求信息对应的码头调度最优解返回给主节点,通过综合比较两个子问题的解,从而得出最优的调度方案。实例计算表明,该并行算法可以有效减少问题的求解时间,特别是对不同常减压对原油质量要求不同时的长周期调度（如4周）问题,采用串行算法在48 h内都无法得到可行解,而采用此算法用3台计算机可以在25 h内得到最优解。     

Optimization strategies and impact of low oil price on long term SAGD projects

Steam assisted gravity drainage (SAGD) has been known as a commercially proven high ultimate recovery process for bitumen and heavy crudes. It is an energy intensive process, which is economical when oil price is above certain value. When the oil price goes below the economic threshold of project, steam injection can be decreased or completely stopped for a certain period of time, and can resume thereafter when the condition alters. The objective of this study is to provide comprehensive information about the effect of steam injection interruptions on thermal project performance. An optimization strategy for the SAGD process, in cases where steam injection interruption occurs, is discussed using actual reservoir models of different geological formations. An economical model is used to evaluate operating strategy effect on the net present value (NPV) of the project. The parameters, like shut-in period, initial steam injection period, etc, are optimized for Athabasca type oil sand reservoirs. The results show several key mechanisms exist in the life cycle of the SAGD process that must be included to reflect the field scale behaviour; otherwise, the mechanistic simplicity of the models could lead to directional and semi-quantitative conclusions. Among the mechanisms, temperature effect on basic petrophysical properties of reservoir rocks was found to have an important role in the oil recovery, and considerably impacts the results of optimization. When the steam injection is interrupted, an optimum shut-in period can be determined to maximize the oil recovery. The optimum length of steam injection interruption depends on the initial steam injection period.     

技术创新 管理细化 实现装置长周期运行

结合本装置已连续运行 90 0多天的实际经验 ,从技术创新和管理细化两个方面探讨了如何保证老装置的长周期运行     

On the nonlinear characterization of the long term behavior of polymeric materials

In the linear viscoelastic range the long term behavior of viscoelastic materials—such as polymers—can be described by using exponential series with a limited number of terms for the approximation of the relaxation modulus or of the creep compliance. This procedure can be extended to the nonlinear viscoelastic range by multiplying the linear parameters of the material by certain nonlinearity factors, which depend upon the level of the applied loading. Application of this method to stress relaxation data of several polymers has shown that nonlinearity factors can be approximated as linear functions of the applied constant strain. From creep tests, on the other hand, one can observe that the immediate strain response to the suddenly applied stress is linear elastic even in the nonlinear viscoelastic range of the investigated polymer. The computation of the linear viscoelastic material parameters as well as of the nonlinearity factors is conducted numerically by using least squares techniques. Good agreement between computed results and experimental data can be observed in the presented examples.     

Current and long term considerations for the application of reverse osmosis technology in Israel

In the past two decades desalting technology has been selectively used to solve water shortage and water quality problems in the more arid regions of Israel.The multi-year experience gained in design, construction and operation with a variety of technologies for desalting of various brackish and seawater feeds will be of great value in coping with the severe problems of water shortage and water quality in Israel.The multi-year research and development program prepared by Mekorot Water Co., aimed to add 50 million m³ per year of desalted water at six sites in Israel using advanced reverse osmosis technology, will also contribute to further improving the economics of desalting saline water.     

Short term essential fatty acid deficiency in rats. Influence of dietary carbohydrates

The effects of long term (8–14 wk) essential fatty acid (EFA)-deprived diets in rats are well documented. In the present study, we compared, in weanling rats, the effect of a short term (two wk) hydrogenated coconut oil, EFA-deprived, diet (D) with that of a corn oil, EFA-adequate, diet (A), using either sucrose (SU) or starch (ST) as carbohydrate. After two wk, rats fed the sucrose/hydrogenated coconut oil diet developed some characteristic features of EFA deprivation: slower growth rate, decreases in linoleic and arachidonic acid of plasma phospholipids and an increase in n−9 eicosatrienoic acid of plasma phospholipids. When rats ate the starch/hydrogenated coconut oil diet, there was a similar decrease in linoleic acid of plasma phospholipids, but only a small effect on growth rate and no change in the arachidonic acid content of plasma phospholipids. EFA deprivation and sucrose had opposite effects on plasma triglyceride (TG) levels: deprivation induced a decrease, whereas the sucrose induced an increase in very low density lipoprotein (VLDL) triglycerides. The observed decrease in plasma triglyceride during EFA deporivation might result from an activation of lipoprotein lipase during the early stages of deprivation.     

Application of time-temperature superposition principle to long term engineering properties of plastic materials

Time-temperature equivalence was used to predict the long term engineering behavior of highly crystalline ethylene-butene copolymers. The long term behavior (greater than 1000 hrs.) was accurately predicted from tests of short duration (30 hrs.). This time-temperature principle was applied to stress-relaxation and creep at stresses, strains and temperatures normally encountered in engineering practices. It was also used to solve a design problem involving the creep deformation of metal plastic laminates. Long term tests were performed to confirm the predicted results. This technique was not applicable to rubber modified polystyrene because of an unexpected transition at 88°F.