摘要 :
Latex films have been produced through evaporation of aqueous dispersions containing polymeric particles. These films have a cellular structure: The cell cores are made of hydrophobic polymers, and the cell walls are made of carbo...
展开
Latex films have been produced through evaporation of aqueous dispersions containing polymeric particles. These films have a cellular structure: The cell cores are made of hydrophobic polymers, and the cell walls are made of carboxylic monomers that are copolymerized with the core polymers. The mechanical properties of these films are determined by the state of the cell walls. In humid environments, the cell walls take up water and lose their cohesive strength; consequently the films become brittle. The possibility of reinforcing the films through interdiffusion of core polymers across the cell walls was examined. Annealing the films at temperatures where these polymers are mobile produced extensive interdiffusion of low molar mass polymers across the cell walls. This had no effect on the mechanical properties of the films. Annealing at temperatures that caused fragmentation of cell walls produced interdiffusion of high molar mass polymers. At this stage the films became resistant to humidity. [References: 22]
收起
摘要 :
In previous studies, the adsorption kinetics of asphaltenes at the water?oil interface were interpreted utilizing a Langmuir equation of state (EOS) based on droplet expansion experiments.~(1?3) Long-term adsorption kinetics follo...
展开
In previous studies, the adsorption kinetics of asphaltenes at the water?oil interface were interpreted utilizing a Langmuir equation of state (EOS) based on droplet expansion experiments.~(1?3) Long-term adsorption kinetics followed random sequential adsorption (RSA) theory predictions, asymptotically reaching ～85% limiting surface coverage, which is similar to limiting random 2D close packing of disks. To extend this work beyond this slow adsorption process, we performed rapid contractions and contraction?expansions of asphaltene-laden interfaces using the pendant drop experiment to emulate a Langmuir trough. This simulates the rapid increase in interfacial asphaltene concentration that occurs during coalescence events. For the contraction of droplets aged in asphaltene solutions, deviation from the EOS consistently occurs at a surface pressure value ～21 mN/m corresponding to a surface coverage ～80%. At this point droplets lose the shape required for validity of the Laplace?Young equation, indicating solidlike surface behavior. On further contraction wrinkles appear, which disappear when the droplet is held at constant volume. Surface pressure also decreases down to an equilibrium value near that measured for slow adsorption experiments. This behavior appears to be due to a transition to a glassy interface on contraction past the packing limit, followed by relaxation toward equilibrium by desorption at constant volume. This hypothesis is supported by cycling experiments around the close-packed limit where the transition to and from a solidlike state appears to be both fast and reversible, with little hysteresis. Also, the soft glass rheology model of Sollich is shown to capture previously reported shear behavior during adsorption. The results suggest that the mechanism by which asphaltenes stabilize water-in-oil emulsions is by blocking coalescence due to rapid formation of a glassy interface, in turn caused by interfacial asphaltenes rapidly increasing in concentration beyond the glass transition point.
收起
摘要 :
Several processes involve two immiscible liquid phases where the drops of the dispersed phase are surrounded by a continuous phase. The drops coalesce for joining their mother phase. This phenomenon occurs in many industrial mixin...
展开
Several processes involve two immiscible liquid phases where the drops of the dispersed phase are surrounded by a continuous phase. The drops coalesce for joining their mother phase. This phenomenon occurs in many industrial mixing, separation, as well as in environmental processes. This paper is focused on the problem of the coalescence of a single drop at the interface with its mother phase. An original model characterizing the mechanism of coalescence is proposed and then validated by comparison with experimental data both from the literature and from the authors.
收起
摘要 :
In the churn-turbulent bubbly flow regime with highly nonuniform bubble size distributions, bubble breakage and coalescence are important processes because they govern the bubble size distribution and consequently directly affect ...
展开
In the churn-turbulent bubbly flow regime with highly nonuniform bubble size distributions, bubble breakage and coalescence are important processes because they govern the bubble size distribution and consequently directly affect the interfacial mass, momentum, and heat transfer fluxes through the renewal bubble surfaces. At present, accurate prediction of bubble size distributions of dispersed gas–liquid flows by use of the population balance (PB) equation is a difficult task. The modeling of bubble breakup and coalescence rates is very complex and is based on the knowledge of collision and breakup frequencies, breakage daughter size distributions, and probability of coalescence. In this work, we focus on the coalescence phenomenon. The coalescence models are still on an empirical level and the mechanisms are not fully understood. This motivates the analysis of the suitability of the coalescence closures for the prediction of experimental data obtained from coalescence dominated gas–liquid flows. For this task, a cross-sectional averaged combined multifluid-PB model is adopted. Based on different theories for the coalescence efficiency, the simulation results show a similar trend in the prediction of the experimental data. Good prediction of the Sauter mean diameter is achieved although the shape of the bubble size distribution is not completely reproduced. The second aim of this work is to review the PB framework. Here, focus is placed on the coalescence term and the combined multifluid-PB model based on kinetic theory approach.
收起
摘要 :
The purpose of this study was to determine the effects of the properties of different binders on the granular agglomeration mechanism for the fabrication of pharmaceuticals. The raw materials included calcium carbonate powders wit...
展开
The purpose of this study was to determine the effects of the properties of different binders on the granular agglomeration mechanism for the fabrication of pharmaceuticals. The raw materials included calcium carbonate powders with an average particle size of 32-75 μm and four different grades (4000, 6000, 8000 and 10,000) of polyethylene glycol (PEG) used as binders. The raw material was mixed with the binder in a high shear mixer. The surface structure of the granules was analyzed by low vacuum scanning electron microscope (LV-SEM) examination. Three major agglomeration mechanisms are discussed in this study: nucleation, consolidation and coalescence. The results showed that the agglomeration growth rate increased with increasing binder viscosity during the nucleation stage, but the exact opposite phenomenon occurred in the consolidation stage. Observation of the granular surfaces showed the surfaces to be full of fine powder in the nucleation stage, but PEG crystals appeared on the surface in the consolidation stage. During the coalescence stage, the granules grew quickly due to collisions and the surface structures of the granules became full of binders, as can be seen from the LV-SEM photographs.
收起
摘要 :
Consider a binary family tree starting with one ancestor where each individual in any generation gives rise to two individuals in the next. In such a tree there will be 2n individuals in the nth generation. Now choose two of these...
展开
Consider a binary family tree starting with one ancestor where each individual in any generation gives rise to two individuals in the next. In such a tree there will be 2n individuals in the nth generation. Now choose two of these 2n individuals of the nth generation at random and trace their lines of descent back in time till they meet, i.e. coalesce, and call that generation number χ n, the coalescence time. Then χ n is a random variable such that the probability χ n is less than k (for k ≥ 1) equals which is approximately (1 . b–k) which for n large. In particular, for any k ≥ 0, the probability that χ n equals k converges to b–k(1 . b–1). That is, for n large, coalescence of two randomly chosen individuals from the nth generation occurs in the remote past. This suggests that if the tree was generated by some random mechanism as long as it is growing rapidly, coalescence should occur in the remote past. It turns out that this need not hold if the growth is too rapid. In fact, the following result holds.
收起
摘要 :
In this paper,a mechanical coalescer is tested to coalesce the oil droplets in the oil-in-water (O/W) emulsions.The coalescence of the O/W emulsions through fibrous and granular beds is studied.More specifically,the pressure drop ...
展开
In this paper,a mechanical coalescer is tested to coalesce the oil droplets in the oil-in-water (O/W) emulsions.The coalescence of the O/W emulsions through fibrous and granular beds is studied.More specifically,the pressure drop across the coalescing beds is successfully predicted by using the Carman-Kozeny equation for the single-phase flow.A geometric method for the fibrous beds and an experimental method for the granular beds are used to determine the Kozeny constant,respectively.For the two-phase flow,the pressure drop is slightly increased as compared with that for the single-phase flow.In addition,the effects of flow rate,inlet oil concentration,length of the coalescing bed and fiber size on the coalescence performance are examined.In the parametric studies,first,it has been found that the overall coalescence efficiency is not a monotonous function of flow rate in the granular beds.The coalescence efficiency is higher at some intermediate superficial velocities.Secondly,the higher the inlet oil concentration is,the lower the overall coalescence efficiency is.Thirdly,the coalescence performance is insensitive to the length of the granular bed tested in this study.It has also been found that the coalescence performance is better for a fibrous bed packed with smaller fibers.
收起
摘要 :
An experimental approach on propagation and coalescence of pre-existing cracks (fractures) in marble samples under compression is carried out. Two types of newborn cracks are observed: wing (tensile) cracks and secondary (shear) c...
展开
An experimental approach on propagation and coalescence of pre-existing cracks (fractures) in marble samples under compression is carried out. Two types of newborn cracks are observed: wing (tensile) cracks and secondary (shear) cracks. Both types of cracks initiate from the tips of the fractures and propagate in a stable manner. Wing cracks initiate at an angle with the fractures and tend to propagate towards the direction of the most compressive stress. Secondary cracks, however, initiate in a direction quasi-coplanar to the fractures and also parallel to the wing cracks but in the opposite direction. The orientations and geometries of fractures can decide which kind of wing cracks and secondary cracks will be produced. The interactions between fractures strongly affect the initiation and propagation of wing cracks and secondary cracks, and make examples' failure patterns thoroughly different. The initial fracture angles of wing cracks range among 52degrees-68degrees, which are lower than the results (about 77degrees) of previous experiments on molding materials. In addition, the characters of acoustic emission (AE) of pre-cracked marble samples are also studied. For some rock samples, a secondary peak value phenomenon of AE counts is observed. For the samples with zigzag fractures, the accumulated AE counts at the moment of failure occupy almost half of the summation of whole load processes. This reveals that the failure of materials with zigzag fractures is more unexpected. (C) 2004 Published by Elsevier Ltd.
收起
摘要 :
An experiment is presented which succeeds for the first time in stimulating the formation of coarse plates of bainite by the coalescence of identically oriented individual platelets. Transformation under the influence of a tensile...
展开
An experiment is presented which succeeds for the first time in stimulating the formation of coarse plates of bainite by the coalescence of identically oriented individual platelets. Transformation under the influence of a tensile stress dramatically promotes the formation of the coalesced bainite by increasing the probability of growing parallel platelets in close proximity. Whereas the coarse plates are detrimental to toughness, the result serves to validate the mechanism of coalescence, which has been discussed extensively in the literature.
收起
摘要 :
This paper presents a literature review on the mechanisms and models of coalescence of fluid particles. For the mechanisms, five categories are summarized, namely, turbulence fluctuation, viscous shear stress, capture in turbulent...
展开
This paper presents a literature review on the mechanisms and models of coalescence of fluid particles. For the mechanisms, five categories are summarized, namely, turbulence fluctuation, viscous shear stress, capture in turbulent eddies, buoyancy and wake interaction. The models for collision frequency and coalescence efficiency as well as contact and drainage times available in literature are reviewed thoroughly. The development and limitation of the existing models are studied and possible improvements are proposed.
收起
原文获取