Unsteady mass transfer around spheroidal drops in potential flow

Unsteady mass transfer in the continuous phase around spheroidal drops in potential flow and at high Peclet numbers has been theoretically studied. Analytical solutions for the concentration profile, the molar flux, the concentration boundary layer thickness, and the time to reach steady state are presented. The solution to the problem was obtained by the useful equations derived by Favelukis and Mudunuri for axisymmetric drops of revolution, with the only requirements being the shape of the drop and the tangential velocity at the surface of the drop. The solution suggests that, as the eccentricity increases, the total quantity of material transferred to or from the drop decreases (for prolate spheroids) and increases (for oblate spheroids). It was also determined that when the dimensionless time is greater than 2, then steady state is in practice obtained, with prolate drops attain steady-state conditions faster than oblate drops.     

The vaporization of small binary drops on a flat plate at maximum heat flux

The vaporization times of small (12 mg.) drops of a binary liquid on a flat plate were measured in the maximum (critical) heat flux region of boiling heat transfer. The binary system studied was water-1-pentanol, the mixture previously shown by other workers to exhibit the most pronounced concentration effect on critical heat flux. Evaporation curves are reported in the critical region for pure water, pure pentanol and a number of mixtures in the concentration range 1.0 to 2.5 weight % pentanol in water. It was confirmed that drop lifetimes can be obtained in the critical heat flux region by comparatively simple techniques and that there is a concentration effect on drop lifetime that is very similar to that observed during critical heat flux boiling studies. A minimum drop lifetime is observed at 1.8 weight % pentanol in water, the same concentration at which maximum critical heat fluxes were obtained in pool boiling studies at one atmosphere by S. J. D. Van Stralen and co-workers.     

Model development for multicomponent mass transfer with rapid chemical reactions in a small drop

Multicomponent mass transfer accompanied by instantaneous chemical reactions in a small drop has been modeled and simulated for the case where two different solutes diffuse from a continuous phase into the drop and react rapidly with a third reactant in the drop. The computational results obtained by Galerkin’s finite element method are reported in terms of concentration profiles, the locations of reaction front, the cumulative mass flux, and the enhancement factor. The effects of physical parameters, such as diffusivities of the solutes and the reactant, the interfacial concentration of solutes, and the relative amount of the reactant, on the calculated quantities are discussed.     

Unsteady mass transfer around axisymmetric drops of revolution in variable diffusion coefficient liquids

Unsteady mass transfer in the continuous phase around axisymmetric drops of revolution at high Peclet numbers has been theoretically studied. The liquid is a binary system, having a variable diffusion coefficient, which depends on the solute concentration. The solution to the problem was obtained by extending the theory of Favelukis and Mudunuri, developed for a constant diffusion coefficient liquid. The procedure consists of transforming the differential mass balance, for a binary system, into a partial differential equation which has an analytical solution, and an ordinary differential equation that needs to be solved numerically. Solutions to a large number of problems can be immediately obtained with the only requirements being the shape of the drop, the tangential velocity at the surface of the drop and an expression for the variable diffusion coefficient liquid. An approximate analytical solution is also suggested which is in excellent agreement with the numerical results.     

Steady flow simulation of a polymer‐diluent solution through an abrupt axisymmetric contraction using internally consistent rheological scaling

In this work, a new methodology is developed that describes the viscoelastic scaling of a polymer‐physical foaming agent (PFA) solution in a detailed and internally consistent manner. The approach is new in that while previous researchers have largely focused on scaling down experimentally obtained high pressure polymer‐PFA solution viscosity data onto a master curve for the viscosity of the undiluted polymer melt at a reference temperature and atmospheric pressure, we have generated the shear viscosity data required for our simulations by systematically scaling up the viscosity values obtained from measurements on a pure polymer melt to the desired temperature, pressure, and concentration values characterizing the flow. Simulations have been run for the flow of a polymer‐PFA solution through an extrusion foaming die with an abrupt axisymmetric contraction and good qualitative agreement is obtained with experimental pressure drop measurements obtained previously in our laboratory. The pressure drop rates and temperature rise rates have been estimated at the surface of incipient nucleation. Because of the short residence times in the die for the microcellular foaming process, approximating the flow through the die as a single phase flow in our simulations still gives useful insights into the dynamics of the flow. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

喷雾场多参数层析算法的仿真效验与实验测量

根据层析技术原理,对喷雾雾滴粒径和浓度的空间分布开展了研究,并编制了喷雾粒径和浓度层析计算程序.对给定粒径和浓度空间分布的喷雾场,根据脉动法测量原理在计算机上仿真了雾滴粒径和浓度的线投影值,根据仿真的投影值重建了雾滴粒径和浓度的空间分布,重建结果与给定的分布结果完全吻合.在喷雾实验台上用光脉动法装置测量了喷雾雾滴粒径和浓度的线投影值,并用编制的程序对喷雾雾滴粒径和浓度的空间分布进行了层析计算.     

Mass-transfer effects on droplet phenomena and extraction column hydrodynamics revisited

The effect of solute mass transfer between the two liquid phases on the drop size distribution and holdup profiles of the dispersed phase in a multistage extraction column is experimentally investigated in this article. Experimental results of the drop size distribution, dispersed-phase volume fraction (holdup), and concentration profiles are obtained for both directions of mass transfer. The drop size distribution is measured by a photomicrographic technique, the holdup profile is measured by an ultrasonic technique, and the concentration profiles are measured by refraction index measurements. A strong influence of the mass-transfer direction on drop size and holdup has been found. The results are in qualitative agreement with the observations of other investigators. Mass transfer of butyric acid from toluene (dispersed) to water (continuous) produced larger drop sizes and lower values of the dispersed-phase holdup than for the equilibrated toluene—water system. For mass transfer of butyric acid from water (continuous) to toluene (dispersed) smaller drop sizes and higher holdup values are observed than for the equilibrated toluene-water system. This behavior significantly affects the performance of the extractor and indicates the necessity for more studies to determine the physics of the phenomenon and to model these processes appropriately.     

锌离子浓度对磷化性能的影响

以钢铁和铝及铝合金为基材,研究了锌离子浓度对酸度、磷化转化膜的外观、钢铁件硫酸铜点滴时间、铝件氢氧化钠点滴时间的影响,最终获得了致密、耐腐蚀的铝及铝合金磷化膜。     

Pressure drop prediction in hydraulic transport of bi-dispersed particles of coal and copper ore in pipeline

Hydraulic transport studies with coal and copper ore have been carried out in a 0.0254 m and a 0.019 m diameter pipeline to observe the effect of solids concentration, surface characteristics and particle size distribution on pressure drop. The coarse coal showed a lower pressure drop than the fines at any velocity of suspension, whereas copper ore, exhibited the opposite trend. It has been observed, that the pressure drop for hydraulic transportation of bi-dispersed particles is a minimum at certain weight proportions of coarse to fines, as compared to that for the transportation of either of the single size. Based on the experimental results, an empirical expression was developed for the prediction of pressure gradient.     

The effect of coalescence on drop size distribution in an agitated liquid-liquid dispersion

A procedure involving high speed cine photography and novel optical probes has been used to study droplet interaction phenomena in liquid-liquid dispersions. Coalescence and breakup events were observed and the rate of coalescence was measured at various positions in a stirred tank for dispersions of methylisobutylketone in water. For the conditions studied, drop breakup occurred near the impeller and droplet coalescence predominated at other locations, as expected. However, the extent of this behavior was unexpected. Beyond distances from the impeller region of order of only $\text{1}\text{6}$ the impeller diameter, breakup was virtually nonexistent. Outside the impeller region, extensive coalescence measurements showed (1) collisions between droplets are extremely inefficient for this chemically equilibrated system—at most 10% of collisions result in a coalescence, (2) only binary coalescence occurs even at the highest dispersed phase concentration investigated, (3) coalescence rate shows little preference on drop size, and (4) the coalescence rate is directly proportional to turbulence level; that is, the highest coalescence rates occur closest to the impeller. On the basis of these measurements, drop balance methods and a circulation path model were used to relate the drop size distribution at various locations in the region where coalescence predominates. In this case good agreement was obtained between measured and predicted drop size distributions.     

两段循环流化床吸附有机气体实验

以Ambersorb 600为吸附剂,甲苯为吸附质,在两级循环流化床吸附装置内进行了吸附特性的实验. 采用PGM-7600型VOCs分析仪测量甲苯的浓度,得到两段循环流化床的压力和空隙率分布及浓度随床高的分布;研究了气体进口浓度和表观气速对吸附效率的影响. 在实验条件下吸附装置效率为95%~98%.     

Model development for diffusion with instantaneous chemical reactions in a spherical multicomponent drop

Diffusion accompanied by instantaneous chemical reactions in a multicomponent drop is modeled. The developed model is then simulated for the case of absorption of one solute from a continuous phase into the drop, followed by fast reactions with two different reactants existing in the drop. The results of the model are obtained by using Galerkin’s finite element method and represented by unsteady concentration profiles of all components in the drop, the reaction front positions, and the cumulative mass flux and the enhancement factor of the diffusing solute. The effects of the system parameters, such as diffusivities of the solute and the reactants, the relative amount of the reactants in the drop, and the interfacial concentration of the solute, on the calculated quantities are evaluated.     

EVAPORATION,DROP SIZE DISTRIBUTION AND ENTROPY GENERATION CHARACTERISTICS OF A LIQUID SPRAY CONTAINING DISSOLVED SOLIDS IN A CONVECTIVE MEDIUM

Theoretical studies have been made through a unified nondimenslonal numerical model to evaluate the evaporation, drop size distribution and entropy generation characteristics of an atomized spray of liquid containing dissolved solids in a uniform stream of gas at high temperature. The influence of pertinent input parameters, namely, the initial concentration, initial Reynolds number of the spray and the ratio of ambient to initial drop temperature on the evaporation, drop size distribution and entropy generation histories of the spray with its down stream distance have been established.     

X-ray diffraction,calorimetric, and spectroscopic studies of lithium borate glass activated with various oxide admixtures based on europium

Lithium borate glass activated with europium oxide, europium borate, and europium molybdate has been obtained by melt quenching. It has been found that by excitation with UV light of λ_ex = 365 nm, the highest luminescence intensity is observed in the samples activated with europium molybdate. The extreme europium molybdate concentration at which a sharp drop in the glass optical quality starts is measured. The thermal regions of stability are determined and the thermophysical characteristics (jumps of the thermal capacity in the glass-transition point and thermal effects of crystallization) for lithium borate glass doped with various oxides based on europium are calculated.     

EVAPORATION, DROP SIZE DISTRIBUTION AND ENTROPY GENERATION CHARACTERISTICS OF A LIQUID SPRAY CONTAINING DISSOLVED SOLIDS IN A CONVECTIVE MEDIUM

Theoretical studies have been made through a unified nondimenslonal numerical model to evaluate the evaporation, drop size distribution and entropy generation characteristics of an atomized spray of liquid containing dissolved solids in a uniform stream of gas at high temperature. The influence of pertinent input parameters, namely, the initial concentration, initial Reynolds number of the spray and the ratio of ambient to initial drop temperature on the evaporation, drop size distribution and entropy generation histories of the spray with its down stream distance have been established.     

冷轧薄钢板磷化发蓝问题的原因及对策

冷轧薄钢板在使用时出现三种形态的磷化发蓝缺陷；点状，条状及整个磷化面蓝色，其原因主要有以下几种，钢板的化学活性高，催化剂的浓度高以及磷化段入口处磷化液流量小等，通过作相应的调整，获得了合格的磷化膜。     

High flux mass transfer: Comparison of liquid-liquid extraction column and drop (Handlos-Baron) model predictions with rotating disc contactor performance

High flux mass transfer measurements have been made in a rotating disc contactor and the results compared with model predicted results. Extraction column and drop model equations for single solute transfer were modified to include the influence of the interphase convective, or drift, flux, previously neglected. The Handlos-Baron drop model was utilized and found to predict the correct trends with changes in drop size. Continuous phase axial dispersion measurements were carried out by pulse tracer injection and by concentration profile measurements at low flux, when simultaneous measurements were made of the continuous phase mass transfer coefficient. When these values were used in the high flux model, high flux extraction efficiencies were accurately predicted but concentration profiles were not.     

袋式过滤器过滤初期阶段滤袋压力特性的实验研究

针对袋式过滤器过滤初期阶段的压力特性,选用高密度聚乙烯粉料进行了实验分析,主要考察过滤速度和入口浓度对滤袋压降的影响。实验结果表明,在过滤初期阶段滤袋的压降上升趋势很明显,这种压降的增大主要来自于残余压降;滞留在滤料内的粉尘改变了滤料内部的流道结构,从而导致了滤袋残余压降的不断升高;过滤速度和入口浓度的增加均可使残余压降增大。最后通过压降组成的分析,提出了滤袋总压降的计算模型。     

Reduction of dicarbonyl compounds on a mercury electrode—I. Reduction mechanism of diacetyl

A polarographic and kinetic study of the reduction of diacetyl has been carried out in the 0 < pH < 10 range in buffered aqueous solutions.The effect of pH, the diacetyl concentration, the height of the mercury column, the drop time, and temperature on the limiting current is studied. A discussion of the obtained results and the data reported in the literature is made.The Tafel slopes and reaction orders with the respect to diacetyl and H⁺ ion are obtained for the first reduction wave at potentials corresponding to the foot of the polarographic wave, and a reaction mechanism according to the experimental data is proposed in this zone of potentials.     

Behavior of an organic solvent drop during the supercritical extraction of emulsions

The behavior of a drop of dichloromethane in water in contact with CO₂ at high pressure has been investigated with the purpose of analyzing the phenomena that takes place during the supercritical fluid extraction of emulsions process. Experiments have been performed with and without a solute (β‐carotene) and a surfactant (n‐octenylsuccinic anhydride‐modified starch) dissolved in the drop, and the evolution of the drop volume as well as of the interfacial tension between the drop and the aqueous phase has been measured. Additionally, a mathematical model has been developed that allows describing the mass transfer. Results show that the drop undergoes swelling and shrinking processes due to diffusion of CO₂ into the drop and dichloromethane out of the drop. CO₂ concentration in the drop can be as high as 0.9 (molar fraction). Emulsion drops behave as miniature gas antisolvent precipitators and many particles are formed inside the drop. The interfacial tension between the drop and the aqueous phase increases during the process, therefore destabilizing the emulsion. © 2009 American Institute of Chemical Engineers AIChE J, 2010