Scale effects in fluidized multiphase reactors

It is shown that the two-phase model for bubbling gas—solid fluidized beds can be extended to bubble column slurry reactors operating in the heterogeneous flow regime by proper definition of the ‘dilute’ and ‘dense’ phases. The ‘dilute’ phase in a bubble column slurry reactor is to be identified with the fast-rising ‘large’ bubbles. The ‘dense’ phase consists of the slurry phase in which ‘small’ bubbles are finely dispersed. With the aid of extensive experimental data obtained in columns of 0.1, 0.19 and 0.38 m diameter it is shown that the rise velocity of the ‘dilute’ phase for gas—solid fluid beds and slurry reactors show analogous scale dependencies and can be modelled in a similar manner. It is also demonstrated that fluidized multiphase reactors can be modelled in a common manner using Computational Fluid Dynamics (CFD) within the Eulerian framework. It is concluded that CFD is an invaluable tool for scaling up of fluidized multiphase reactors.     

Various size effects in fracture of concrete

The paper reports the results of a series of three-point bend test on pre-cracked cement mortar and concrete beams. The tests are performed with a view to studying the influence of pre-crack, aggregate and specimen sizes on the fracture of concrete. A simple formula based on the experimental data is proposed to account for all the three size dependent effects. Other parameters having a significant influence on the fracture of concrete are also pointed out.     

The influence of fiber wetting in resin transfer molding: Scale effects

Resin transfer molding (RTM) has become a popular technique for fabrication of composite parts. During the mold filling stage, the resin is forced to flow into pore spaces between tow filaments and the between the tows themselves. Voids trapped in the composite during the filling stage are believed to be the consequence of the non‐uniform micro‐flows inside fiber bundles and macro‐flows between them. Thus, to minimize the void formation, the processing parameters should be determined to generate a uniform front. In this case, the flow inside tows is driven by both the injection pressure and the capillarity forces and matches the flow outside the tows, which is driven only by pressure. To control such a flow, both viscous and capillarity flows have to be known at all scales of the fibrous structure. For this purpose, the wetting effects at the different scales (ranging from the individual tow to the multi‐layers reinforcements) are investigated. Original experiments are carried out to visualize micro‐flows and to measure the capillarity flow rates. Wicking effects are quantified in terms of the overall and local effective permeabilities. A new parameter that accounts for interactions between flows splitting in macro‐ and micro‐flows is introduced. Practical ways to reduce voids entrapment are also discussed.     

Densification effects on the fracture in fused silica under Vickers indentation

This study investigates the effects of densification on the deformation and fracture in fused silica under Vickers indentation by both the finite element analysis (FEA) and experimental tests. A refined elliptical constitutive model was used, which enables us to investigate the effects of the evolution of yield stress under pure shear and elastic properties with densification. The densification distribution was predicted and compared with experiments. The plastic deformation and indentation stress fields were used to analyze the initiation and morphology of various crack types. The formation mechanism of borderline cracks was revealed for the first time. This study reveals that the asymmetry of the densification distribution and elastic-plastic boundary significantly influences the cracking behavior. Under the Vickers indentation, conical cracks have the largest penetration depth. When these cracks emerge from a region far from the impression, they extend with constant radii to form circles on the sample surface. Otherwise, they tend to be initiated at the centers of the indenter-material contact edges before propagating towards the impression corners with increasing radii. Therefore, the borderline cracks consisting of successive partial conical cracks can form at a low load and makes them the first type of crack to appear.     

Oxidation effects on CTE and thermal shock fracture initiation in polycrystalline graphites

The coefficient of thermal expansion (CTE) was measured as a function of oxidation for three commercial fine-grained graphites derived from petroleum cokes and coal tar pitches and fabricated by extrusion, undirectional molding, and isostatic molding. The CTE was observed to vary with the crystallite size and the preferred orientation and to decrease as much as 20% with increasing oxidation. This CTE decrease was attributed to an increase of the accommodation by Mrozowski cracks enlarged by the oxidation process. Effects on thermal shock fracture initiation were examined by estimating changes in the thermal shock resistance parameter, R. It is concluded that in spite of the continuous decrease in CTE, changes in R with oxidation are not continuous for these graphites. The complexity is a consequence of the different extents to which graphite oxidation affects CTE, strength and the Young's elastic modulus.     

Fiber length distribution effects on the fracture of short-fiber composites

The effect of fiber geometry on the fracture behavior of short glass fiber-reinforced nylons was examined. In particular a comparison was made between conventional short-fiber composites (with feedstock made by an extrusion process) and the newer pultruded feedstock materials which have longer fiber length distributions but larger fiber diameters. The toughness of the material was measured over a wide range of loading rates, from impact conditions, using Kc and Gc type tests, to long term, slow crack growth tests. The moisture content of the materials was varied from dry to saturated. It was found that there was little difference in fracture toughness when the materials were dry. However, when moist, the longer fiber material showed significant improvements over the conventional short-fiber-reinforced material. This behavior is explained in terms of the changes in fiber geometry.     

Rate effects for mixed-mode fracture of plastically-deforming,adhesively-bonded structures

Mixed-mode fracture of an adhesively-bonded structure made from a commercial adhesive and a dual-phase steel has been studied under different rates. Since mixed-mode fracture occurs along the interface between the steel and the adhesive, the cohesive parameters for the interface were required. The mode-II interfacial properties were deduced in earlier work. In this paper the mode-I interfacial toughness and the mode-I interfacial strength were determined at different rates. The mode-I interfacial strength was not affected by rate up to crack velocities at levels associated with impact conditions, and was essentially identical to the cohesive strength appropriate for crack growth within the adhesive layer. The mode-I toughness was reduced by about 40% when the crack propagated along the interface rather than within the adhesive. Furthermore, transitions to a brittle mode of failure occurred in a stochastic fashion, and were associated with a drop in interfacial toughness by a factor of about five. The mode-I interfacial parameters were combined with the previously-determined mode-II interfacial parameters within a cohesive-zone model to analyze the mixed-mode fracture of the joints which exhibited both quasi-static and unstable fracture. The mixed-mode model and the associated cohesive parameters for both quasi-static and unstable crack propagation provide bounds for predicting the behavior of the bonded joints under various rates of loading, up to the impact conditions that could be appropriate for automotive design.     

Scale effects upon morphology development during mix melting of multiphase polymer blends in ZSK extruders

Replicate experiments were performed on ZSK-30 and ZSK-40 split barrel extruders concerning structure developments from PS-PE pellet blends during the melting process. PS is the minor phase. PE grades were choosen to accommodate viscous and thin matrix phase viscosities. The large extruder displays a more diverse cross channel structure and retarded phase development for some blends. Inferior dispersion is especially obvious in the larger extruder when processing low viscosity matrix blends. Similar phase development occurs in the extruders for high viscosity matrix blends.     

The effects of eccentricities on the fracture of off-axis fiber composites

Finite element analyses were performed to investigate theoretically the effects of in-plane and out-of-plane eccentricities, bending or twisting, and thickness nonuniformity on the axial stress and strain variations across the width of off-axis specimens. The results are compared with measured data and are also used to assess the effects of these eccentricities on the fracture stress of off-axis fiber composites. Guidelines for detecting and minimizing the presence of eccentricities are described.     

Microstructure effects on fracture failure mechanism of CrAl/CrAlN coating

In this work, the Metal-rich phase Chromium Aluminum (CrAl)/Ceramic phase Chromium Aluminum Nitride (CrAlN) multi-layer coatings were prepared by Arc Ion Plating (AIP). The micro-structure and phase composition of CrAl/CrAlN multi-layer coatings were characterized, and the microstructure, mechanical properties, residual stress and fracture toughness of the coating were emphatically analyzed. It has been found out that the residual stress of the multi-layer coating was only ?0.932 ± 0.065 GPa, which was significantly lower than that of the mono-layer coating for ?1.569 ± 0.093 GPa. At the same time, it was also found that the preferred growth orientation of the coating changed from a mono-layer (111) to a multi-layer (200) crystal plane. The hardness of the multi-layer (22.74 ± 0.57 GPa) is slightly lower than that of the mono-layer (24.92 ± 0.5 GPa), and the adhesion strength (46.2 ± 3.8 N) is obviously higher than that of the mono-layer (37.4 ± 2.4 N), and the fracture toughness is also higher (8.7 ± 0.8 MPa m^1/2). In addition, the mechanism of crack initiation and propagation in stress-induced coatings was studied in detail on the basis of the structure of micro-nano CrAl/CrAlN multi-layer coatings.     

The effects of stress cracking on the fracture toughness of polycarbonate

The growth of crazes from a sharp crack in extruded polycarbonate sheets immersed in ethanol was measured. Below a critical level of the stress intensity factor craze growth was controlled by solvent diffusion through the end of the notch and fracture was prevented by craze arrest. Above a critical level, growth was controlled by either end diffusion or a combination of end diffusion and diffusion through the faces of the extruded sheet, and in both cases the final result was brittle fracture. The effects of annealing and quenching was studied at various sheet thicknesses. In thin specimens annealing and/or quenching had a significant effect on crack growth rate, which was predictable in terms of the state of stress. As the specimen thickness increased, causing a transition from plane stress to plane strain conditions, the previous thermal history had a diminishing effect on craze growth rate. The effects of thermal history and thickness on the fracture toughness of polycarbonate was also investigated. It was found that thickness was the more important variable and that at a ½ in. thickness the effects of thermal history were statistically insignificant. The effect of ethanol exposure on fracture toughness was studied. It was found that exposure to solvent initially caused an increase in k_IC with time to a maximum value, followed by a substantial decrease with time which eventually led to brittle fracture. This behavior was explained as a competition between plasticization of the crack tip and coalescence of crazes to form microcracks.     

The effects of physical aging on the brittle fracture behavior of polymers

The effects of physical aging on the failure behavior of a typical brittle polymer, polystyrene, have been studied. Properties examined were creep rupture lifetimes, fatigue lifetimes, and environmental stress cracking in ethanol. Fractured samples were examined both optically and by scanning electron microscopy to determine the degree of crazing. It was found that a longer physical aging time produced shorter lifetimes in all cases. The main reason for this is the reduction in craze strength caused by a reduced toughness due to physical aging. A long aging time was found to delay craze formation, but once formed, these crazes were much less stable than those formed with a short aging time. The effects of aging are important on failure prediction criteria and on testing methodologies, and the implications are discussed.     

Substrate constraint and adhesive thickness effects on fracture toughness of adhesive joints

The adhesive thickness effect on fracture behaviour of adhesive joints has been studied using the boundary effect model recently developed for specimen size effect on fracture properties of concrete, and the essential work of fracture model for ligament (uncracked region) effect on largescale yield of bulk metals and polymers. The leading common mechanism responsible for the nonlinear elastic fracture mechanics behaviours, such as adhesive thickness effect of adhesive joints, specimen size effect of brittle heterogeneous materials and notch dependence of deeply notched metal and polymer specimens, is discussed. These two fracture mechanics models show that the height variation of a fracture process zone (FPZ) or a plastic zone is directly responsible for any change in fracture energy measurements such as the specific fracture energy G _f and the critical strain energy release rate G _c. Both models show that G _f is rapidly reduced when the crack-tip approaches the back-face boundary of a specimen because only a limited FPZ or plastic zone height h _FPZ can be developed in the boundary region. In the case of a thin adhesive joint, the development of a plastic zone height is limited by the thickness of the adhesive sandwiched between the upper and lower adherends or substrates. Consequently, a linear relationship between the adhesive joint toughness and adhesive thickness is established. Test results on adhesive joints from the literature are analysed and compared with the new adhesive joint failure model based on the two well-established fracture mechanics models developed for other material systems.     

三元复合驱结垢及化学防垢剂研究进展

介绍了大庆三元复合驱生产过程中油田垢的产生过程、危害和组成,简单阐述化学防垢剂的防垢机理,同时总结了近年来国内外化学防垢剂的研究进展与应用现状,客观评价各种防垢剂在使用过程中的优点和存在的不足,最后对化学防垢剂的发展进行展望。     

HPMA和EDTMPS复合有机阻垢剂的阻垢性能

对水解聚马来酸酐（HPMA）和乙二胺四亚甲叉膦酸钠（EDTMPS）的复配物阻垢性能进行研究。考察阻垢剂添加量、pH值、Ca^2＋浓度、HCO3^-浓度、恒温时间对阻垢率的影响。实验发现,当HPMA和EDTMPS质量配比为3：1,总加入量为10mg／L时效果最佳,阻垢率达98％。复配物阻垢性能受时间的影响较小,受Ca^2＋浓度的影响较大。     

Scale esterase

Body scales of the silk mothAntheraea polyphemus contain an esterase which can degrade the female sex pheromone of this species. This esterase, which appears to be stabilized to the scale cuticle, is present in both sexes, but is species specific. The enzyme may play a significant role in the behaviors associated with sex-pheromone attraction, helping to filter out stimulus noise by degrading adsorbed pheromone, thus preventing adsoptive body surfaces from becoming uncontrolled pheromone sources.     

考虑二次梯度项影响的变形均质地层中有限导流垂直裂缝井压力动态分析

考虑应力敏感地层中介质的变形,同时考虑二次梯度项和井筒储集的影响,建立了变形均质地层中有限导流垂直裂缝井双线性模型,模型采用方法获得了无限大地层的数值解,形成新的理论图版,利用这些图版对模型中的有关参数进行敏感性分析,这些结果可用于实际试井分析。     

Temperature and loading rate effects in the mode II interlaminar fracture behavior of carbon fiber reinforced PEEK

The combined effect of varying loading rate and test temperature on the mode II interlaminar fracture properties of AS4/carbon fiber reinforced PEEK has been investigated. End notch flexure tests have shown that this thermoplastic‐based composite system offers a very high value of interlaminar fracture toughness at room temperature. Increasing the test temperature leads to a reduction in the mode II interlaminar fracture toughness of the composite, with the value at 150°C being approximately one half of the room temperature value. In contrast, increasing the crosshead displacement rate has been shown to increase the value of G_IIc by up to 25%. A more detailed understanding of the effect of varying temperature and loading rate on the failure mechanisms occurring at the crack tip of these interlaminar fracture specimens has been achieved using the double end notch flexure (DENF) geometry. Here, extensive plastic flow within the crack tip region was observed in all specimens. It is believed that the rate sensitivity of G_IIc reflects the rate‐dependent characteristics of the thermoplastic resin.     

阻垢剂作用机理研究进展

本文回顾了阻垢剂的发展历程 ,并对阻垢性能研究与评价方法、阻垢剂对成垢盐沉积抑制作用的研究状况以及阻垢作用机理作了综述 ,在此基础上提出了有待进一步研究的几个问题。     

Scale reduction in saline water conversion

Distillation of sea water and other naturally occurring saline waters gives rise to the formation of scale deposits, causing a reduction in capacity or efficiency, or both.Several methods suggested to reduce the amount of potential scale have met with only partial success. Recently, it was found that the addition of small amounts of polymeric materials of selected molecular weight range to the sea water feed, had a remarkable effect in reducing the adverse effects of scale formation on the heat transfer surfaces.The work reported here was carried out in an attempt to establish the optimum dosage of these organic polymers (sodium polyacrylate and sodium polymethacrylate)in saline water feed, by experiments with a single effect evaporator.For batch type operations, using a synthetic sea water of 7,000 ppm total hardness as CaCO₃ and a pH of 7.5, sodium polyacrylate at a 4 ppm concentration, gave 98% scale reduction. Molecular weight of the polymer being tested was 125,000. Similar experiments with sodium polymethacrylate, molecular weight 8,000 to 10,000, with rather concentrated feed (10,400 ppm total hardness) indicated it to be effective at 100 ppm concentration. Scale reduction in this case was 92%.Three different molecular weights of each polymer were investigated for their effectiveness. Sodium polymethacrylate, having a molecular weight of 4,500, was found to be most effective as a scale preventive additive. In the case of sodium polyacrylate, both a lower molecular weight of 84,500 and a higher one of 190,000 were found to be almost equally effective. However, a molecular weight of 125,000 gave very poor results. Scale reduction was found to be only 17.1%, as compared to 69.2%, obtained with the other homologue.