Study of an air-lift system,Part II: Heat transfer in co-current,vertical two-phase,non-boiling flows

Heat transfer at the inner wall for co-current vertical air-water mixture flow has been investigated in a 161.5 mm diameter pumping tube of an air-lift system. The experimental heat transfer coefficients were found to be significantly higher than those calculated from a single liquid phase correlation for the same liquid flow rate. The enhancement of heat transfer was found to be related to the flow pattern. A decrease of the heat transfer coefficient was observed in the transition region from slug flow to churn flow. Hydrodynamic and heat transfer models have been used to describe heat transfer during the slug flow regime and a correlation is proposed for the heat transfer coefficient in the liquid plug behind the gas bubble.     

Distance-Dependent Electronic Interactions Across DNA Base Pairs: Charge Transport,Exciton Coupling,and Energy Transfer

The π-stacked bases of B-DNA constitute a helical ruler present nowhere else in nature. When two chromophores are placed at the ends of a base-pair domain with fixed orientations of their transition dipole moments, insertion of an additional base pair between the chromophores increases the distance between the chromophores by ca. 3.4 Å and the angle between their transition dipoles by ca. 36°. The consequences of these changes on the dynamics and efficiency of photoinduced charge transport and upon exciton-coupled circular dichroism and fluorescence resonance energy transfer are discussed.     

AIRLIFT REACTORS: CHARACTERISTICS, APPLICATIONS AND DESIGN CONSIDERATIONS

Bioreactors of the airlift type are a promising design for aerobic fermentations. The basic knowledge required for understanding and predicting the performance of these reactors is only now beginning to emerge. In this review we present our observations and those of other investigators in an attempt to build up a coherent picture of airlift devices. All the major aspects—mixing and hydrodynamics, mass and heat transfer—in these reactors are considered. Comparisons between bubble columns and airlift systems are made where analogies, similarities and/or differences between them provide insight into airlift systems. Throughout, the areas of particular concern and those in need of further research in this field are mentioned. Extensive work on all forms of airlift reactors, particularly in non-Newtonian media—homogeneous and suspensions—remains to be done. Current knowledge does not permit airlift reactor design with a high degree of confidence. However, the technical feasibility of all types of fermentations—plant cell, tissue culture, bacterial, fungal, and those utilizing yeasts—in airlift vessels has been demonstrated.     

Mechanistic Modeling of Pollutant Removal,Temperature, and Evaporation in Chemical Air Scrubbers

Chemical air scrubbers reduce the concentration of water‐soluble components such as ammonia from the outgoing ventilation air through absorption in water, followed by chemical conversions and removal of the end products. A mechanistic model for a countercurrent air scrubber was set up. Mass balances for ammonia, hydrogen sulfide, nitrous oxide, and methane were implemented, as well as the water mass balance and heat balances. The model was validated against experimental data from a conventional fattening pig housing facility. The effect of influent characteristics, design parameters, and control handles on the removal efficiency, the temperature profile, and the water evaporation rate were investigated through simulation. The model was able to describe the behavior of a countercurrent chemical air scrubber.     

PREDICTION OF LIQUID-PHASE MASS-TRANSFER COEFFICIENTS IN MULTICOMPONENT ION EXCHANGE: COMPARISON OF MATRIX, FILM-MODEL, AND EFFECTIVE-DIFFUSIVITY METHODS

Several methods are evaluated for predicting or correlating liquid-phase mass-transfer coefficients in multicomponent ion exchange. Comparisons are made of methods based on matrix generalizations of binary results, methods using the film-model relation between multicomponent fluxes and binary mass-transfer coefficients, and effective-diffusivity methods. It was determined that methods based on the film model give results in good agreement with matrix generalization methods and, where comparisons can be made, both of these methods give results in good agreement with exact calculations. Effective-diffusivity methods were found to be less reliable. The film-model methods developed in this study are analogous to methods commonly used in nonelectrolyte systems.     

Substituent effects of iron porphyrins: Structural, kinetic, and theoretical studies

Substituent effects of iron porphyrin complexes on the structures and kinetic processes have been examined for the first time. Basing on the premise that iron porphyrin is functional analogous to heme, a series of iron porphyrin derivatives bearing different substituents at the meso positions of the corrole ring are investigated as to their electrochemistry, the relationships among the electron transfer (ET) processes, their structures, and orbital energies. The good coherence between the experiment and theory indicates that the ET rate can be accelerated when electron-donating substituents are introduced to the iron porphyrin ring. Finally, the implications of the results are discussed in the influence of stability of iron porphyrin complexes on the ability to carry molecular oxygen, which may suggest it possible to dominate the biological activity of heme by selecting the appropriate substituents to iron porphyrin ring.     

Syntheses, characterization, and energy transfer properties of benzothiadiazole-based hyperbranched polyfluorenes

A series of benzothiadiazole-based (BT) hyperbranched polyfluorene copolymers with various branching degrees (5-40%) were designed and synthesized. TGA and film annealing tests showed the substantial thermal stability of these highly branched polymers. The optical performance of the polymers in solutions and as films, and their electrochemical properties were characterized. The energy transfer (ET) processes in these hyperbranched conjugated polymers, both in solutions and in the solid state, were also investigated. With the change of the solution concentration and the branching degree, the energy transfer efficiency of the polymers varied in solutions and the main photoluminescence (PL) peaks changed from blue to green region. As films, only green light emitted from BT units. In addition, the PL efficiency of the films decreased dramatically with the increase of branching degrees. All these features demonstrated that highly branched structure would effectively impede the intra- and interchain energy migration, especially in solutions, and remarkably influence the ET process in the solid state, which resulted in low PL efficiency.     

Modeling of Gas‐Solid Reactions: Kinetics,Mass and Heat Transfer,and Evolution of the Pore Structure

Mathematical models for simulating heterogeneous gas‐solid reactions must describe a complex set of physicochemical and thermal phenomena. These include the chemical reaction itself, at an interface whose area varies during the conversion, the transport of gaseous species by diffusion in the pores of the solid, whose size and number generally change in the course of reaction, diffusional transport in the layer of solid product, the evolution or consumption of heat by the reaction and its transport in the porous solid, etc. The present paper gives details of the equations employed to model each of these processes. Some computed results illustrate how increasingly sophisticated recent models describe the gradual obstruction of pores during reactions, such as the sulfation of lime, or the thermal effects related to the exothermic nature of the oxidation of zinc sulfide.     

非热平衡多孔介质内反应与传热传质耦合过程

采用局部热不平衡假设,对发生强吸热化学反应的多孔介质体系建立了反应与传热、传质耦合问题的数学模型,采用Ergun-Forchheimer-Brinkman方程描述多孔介质中的流体流动.运用交替方向隐式(ADI)方法对模型离散求解,并采用文献中的实验数据对模型进行验证.计算了不同条件下颗粒物料层内气体和固体骨架的温度场、产物气体浓度场以及固体转化率分布,以得到多孔介质体系内固有化学反应时的传热、传质规律.结果表明,不能忽略固体骨架与流体间的温度差.入口渗流速度、入口气体温度以及固体颗粒尺寸是影响系统反应特性的重要参数.研究结果对具有强吸热反应的固定床反应器的设计和运行具有一定的参考作用.     

Ce3+/Tb3+-coactived NaMgBO3 phosphors toward versatile applications in white LED,FED, and optical anti-counterfeiting

Ce³⁺/Tb³⁺ co-doped NaMgBO₃ phosphors were successfully synthesized by solid-state method. Under 381 nm excitation, the cyan emission owing to the 5d → 4f of Ce³⁺ ions and green emissions arising from the ⁵D₄ → ⁷F_J (J = 6, 5, 4, and 3) transitions of Tb³⁺ ions were seen in all the phosphors. Through theoretical analysis, one knows that the energy transfer from Ce³⁺ to Tb³⁺ ions with high efficiency of 83.74% was contributed by dipole–dipole transition. Furthermore, the internal quantum efficiency of NaMgBO₃:0.01Ce³⁺,0.03Tb³⁺ phosphor was 54.28%. Compared with that of at 303 K, the emission intensity of the developed products at 423 K still kept 73%, revealing the splendid thermal stability of the studied phosphors. Through utilizing the resultant phosphors as cyan-green components, the fabricated white-LED device exhibited an excellent correlated color temperature of 2785 K, high color-rendering index of 85.73, suitable luminance efficiency of 25.00 lm/W, and appropriate color coordinate of (0.4279, 0.3617). Aside from the superior photoluminescence, the synthesized phosphors also exhibited excellent cathode-luminescence properties which were sensitive to the current and accelerating voltage. Furthermore, the NaMgBO₃:0.01Ce³⁺,0.03Tb³⁺ phosphors with multi-mode emissions were promising candidates for optical anti-counterfeiting. All the results indicated that the Ce³⁺/Tb³⁺ co-doped NaMgBO₃ phosphors were potential multi-platforms toward white-LED, field emission displays, and optical anti-counterfeiting applications.     

One pot,two step sequence converting atom transfer radical polymerization directly to radical trap-assisted atom transfer radical coupling

Monobrominated polystyrene (PStBr) chains were prepared using standard atom transfer radical polymerization (ATRP) procedures at 80 °C in THF, with monomer conversions allowed to proceed to approximately 40%. At this time, additional copper catalyst, reducing agent, and ligand were added to the unpurified reaction mixture, and the reaction was allowed to proceed at 50 °C in an atom transfer radical coupling (ATRC) phase. During this phase, polymerization continued to occur as well as coupling; expected due to the substantial amount of residual monomer remaining. This was confirmed using gel permeation chromatography (GPC), which showed increases in molecular weight not matching a simple doubling of the PStBr formed during ATRP, and an increase in monomer conversion after the second phase. When the radical trap 2-methyl-2-nitrosopropane (MNP) was added to the ATRC phase, no further monomer conversion occurred and the resulting product showed a doubling of peak molecular weight (M_p), consistent with a radical trap-assisted ATRC (RTA-ATRC) reaction.     

搅拌槽内气－液体系的分散、传质和传热

综述了搅拌槽内气－液体系分散、传质和传热特性，比较了搅拌器类型、通气方式和多级搅拌器对混合性能的影响。对文献中观点的分歧进行了探讨，由此得到两个传质系数关联式，并揭示出给热系数随操作条件变化的机理。     

Polymerization of styrene and cyclization to macrocyclic polystyrene in a one-pot,two-step sequence

Dibrominated polystyrene (BrPStBr) was produced by atom transfer radical polymerization (ATRP) at 80 °C, using the bifunctional initiator benzal bromide to afford the telechelic precursor. The ATRP reaction was stopped around 40% monomer conversion and directly converted into an radical trap-assisted atom transfer radical coupling (RTA-ATRC) reaction by lowering the temperature to 50 °C, and adding the radical trap 2-methyl-2-nitrosopropane (MNP) along with additional catalyst, reducing agent, and ligand to match ATRC-type reaction conditions. In an attempt to induce intramolecular coupling, rather than solely intermolecular coupling and elongation, the total reaction volume was increased by the addition of varying amounts of THF. Cyclization, along with intermolecular coupling and elongation, occurred in all cases, with the extent of ring closure a function of the total reaction volume. The cyclic portion of the coupled product was found to have a 〈G〉 value around 0.8 by GPC analysis, consistent with the reduction in hydrodynamic volume of a cyclic polymer compared to its linear analog. Analysis of the sequence by ¹H NMR confirmed that propagation was suppressed nearly completely during the RTA-ATRC phase, with percent monomer conversion remaining constant after the ATRP phase.     

Complex-radical terpolymerization of styrene, maleic anhydride, and N-vinyl pyrrolidone via γ-ray radiation: Synthesis, characterization, and micellization

Radical terpolymerization of donor–acceptor monomers, i.e. styrene (St), maleic anhydride (MA) and N-vinyl pyrrolidone (NVP) were carried out in methyl ethyl ketone(MEK) under γ-ray radiation at room temperature. Constants of copolymerization, complex formation, and some kinetic parameters for the monomer systems were studied by UV, ¹H NMR, Kelen-Tüdöş and Fineman-Ross methods, respectively. Obtained results show that terpolymerization proceeded mainly through ‘complex’ mechanisms in the state of near-binary copolymerization of StMA and MANVP complexes. The homo-polymerization of St and NVP and the copolymerization between St and NVP could hardly be occurred. The possible reason is the effect of protection from radiation by styrene with its aryl-ring structure and/or the much larger reactivity of the complex copolymerization between the donor–acceptor monomers. The terpolymer self-assembles into micelles in aqueous solution. Polymeric micelles, composed of chains of St–MA and MA–NVP with equal molar ratio, displayed narrow size distribution of about 120 nm. The critical association concentration of micelles was determined to be around 3 mg/L.     

Synthesis, spectroscopic, and electrochemical properties of two dyads consisted of tetrathiafulvalene and carbazole

Two donor-σ-acceptor molecules containing tetrathiafulvalene (TTF) and carbazole moieties were synthesized by the reaction of 9-(4-bromo-butyl)-carbazole (1) with 2,6-bis(hexylthio)-3-(2-cyanoethylthio)-7- (methylthio)-tetrathiafulvalene (2) or 2,6-bis(2-cyanoethylthio)-3, 7-bis(methylthio)tetrathiafulvalene (3) in the presence of CsOH·H2O, respectively. The structures of the molecules were characterized by ¹H NMR, ¹³C NMR, MS, and elemental analyses. They showed negligible intramolecular charge-transfer interaction in their ground states as indicated by their UV-Vis spectroscopics and cyclic voltammetry results. Compared with carbazole, their fluorescence was strongly quenched, which implied that a photo induced electron transfer (PET) interaction between TTF and carbazole moieties occurred.     

环流反应器的流动、混合与传递特性

由于环流反应器内存在定向循环,与鼓泡塔反应器相比,其混合性能大幅提升,已广泛应用于许多工业过程,如发酵、反应器结晶等工业过程,近年来成为国内外学者研究的热点。针对环流反应器内操作条件下的流动形态、流体力学（包括相含率分布、循环液速、混合时间以及离集指数等）及传质/传热特性,总结了其最新研究进展,分析了相含率尤其是固含率变化对反应器中关键参数如循环液速和化学反应速率的影响,展望了从机理上研究相互耦合的多相流动、传质/传热和化学反应规律,为进一步推动其工业应用提供参考。     

Some novel polymer-supported optically active phase transfer catalysts: 2. Use in displacement,reduction, epoxidation and addition reactions

The performance of 27 novel polymer-supported chiral phase transfer catalysts in a range of phase separated reactions has been studied. The later include a number of displacement reactions, sodium borohydride reductions of prochiral ketones, the epoxidation of chalcone, the addition of nitromethane to chalcone and the addition of thiophenol to cyclohexenone. Some of the reactions were performed under liquid/liquid conditions and others using solid/liquid. No systematic difference emerged between these. In general many of the catalysts provided fast reactions and good chemical yields of products. However, in no case was any significant enantiomeric excess achieved. The latter observation is discussed in the light of the reported behaviour of analogous non-supported catalytic systems, and suggestions proposed to explain these differences.     

Dissolution of a solid sphere in an unbounded, stagnant liquid

An exact analytical solution is obtained for the transient dissolution of solid spheres in a diffusion-controlled environment. This result provides a useful reference point for drug testing in humans. The dimensionless solution is expressed in terms of a single parameter, which accounts for solubility, bulk flow, and stagnant fluid composition. A simple, explicit and exact expression was found to predict time-to-complete dissolution (TCD). An approximate solution was also found which tracks the exact case for low solubility conditions.     

Nano titanium oxide organosol: Synthesis,characterization, and application for electrorheological fluid

A liquid–liquid phase transfer method was employed to prepare novel nano titanium oxide/silicone oil organosol. First, titanium oxide nanoparticles were synthesized in aqueous phase and then modified with several surfactants. It is found that only sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulphate (SDS) can cap nanoparticles and then nanoparticles could be transferred into organic phase by the phase transfer method. The transfer process was certified by the rapid change of color for the aqueous and organic phase. Other surfactants including hexadecyltrimethyl ammonium bromide (CTAB) and oleic acid were unable to ensure the phase transfer in the organic phase. The procedure was also verified by high‐resolution transmission electron microscopy (HRTEM), particle size analyzer, UV–vis, etc. The results also showed the narrow size distribution of the nanoparticles. The mechanism of phase transfer is also discussed for different surfactant. Because of its good antisedimentation and high electrorheological effect, organosol is a novel path for the design and application of electrorheological fluid. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Sulfur addition to aldimines: thioamides,not thiaziridines,as products; revision of an old report

The reaction of 4-(phenylimino)butan-2-ol with ammonium polysulfide in refluxing EtOH yields 3-hydroxy-N-phenylbutanethioamide as the only isolated product. The structure has been established by single-crystal X-ray diffraction. Treatment of N-benzylidenamines with ammonium polysulfide has proven a general method for the preparation of thiobenzamides.