Determination of vapor pressure/molecular weight correlations from droplet evaporation data

A rapid method is presented for the determination of vapor pressure/molecular weight correlations for homologous hydrocarbon mixtures. By comparing droplet evaporation data to discretized theoretical continuum mass flux rates which employ two parameter exponential vapor pressure/molecular weight correlations, best fit pressure correlation parameters are determined. The present technique is applied to the multicomponent oil mixture, 100 pale oil, which is modeled as a fifteen component system. Postulating the mixture is thermodynamically ideal, best fit pressure correlations are determined which result in less than 5% error between theory and experiment. It is shown the hydrocarbon vapor pressure calculated from the derived pressure correlation is in satisfactory agreement with pressures calculated from distillation data and the Clausius Clapeyron relation.     

方形微通道内流动凝结时气液相界面演进过程的数值模拟

基于VOF模型,模拟了R32在水力直径为50 μm的方形微通道内流动凝结时的气液两相流型演进过程,模拟涉及的流型包括环状流、喷射流、泡状流和收缩泡状流。模拟结果显示,由于沿通道周向气液界面存在曲率差异,凝结液内部存在表面张力导致的横向压力梯度,驱使凝结液流向通道壁面拐角处,减薄通道壁面中部液膜厚度。基于势能最小原理,解释了表面张力与界面黏性力主导的喷射流形成机理。小质量流率时,喷射流诱发环状流上游气液界面波动,界面波动在界面黏性力的作用下逐渐生长。这与大质量流率时,流向下游并逐渐生长的界面波动导致流型转换的机理不同。     

Design equations for multicomponent gas absorption

The recently developed linearized theory of multicomponent mass transfer^{(1, 2, 3, 4)} is applied to the case of gas absorption in a plate column. Matrix generalizations of the well-known binary design equations are obtained using the diagonalizing procedure of Toor⁽¹⁾. The results demonstrate that the theory provides a general framework for the direct incorporation of diffusional and thermodynamic interaction effects into design procedures for multicomponent systems.     

Electrosorption from multicomponent liquid systems—II. General equations for surface pressure,electrosorption isotherm and surface charge density

The general equations for electrosorption isotherms, surface pressure and excess surface charge density for the case of organic electrosorption from a multicomponent liquid system have been presented. Some implications of the obtained results in the physical interpretation have been discussed. Derived equations are expressed in the terms of excess electrochemical Gibbs energy of mixing function, ΔḠ^E, in a multicomponent surface solution. No specific mathematical form for this function is needed in this theory. In this way some of the constraints and physical limitations, inherent in adsorption modelling, are relieved, giving one more degree of freedom in testing various adsorption models. Additionally, some of the consequences of a priori decisions in adsorption modelling are indicated. The theory is based upon explicit defined standard states and the importance of the rigor in this matter for the interpretation and understanding of experimental results has also been shown. Finally the general conclusions regarding the form of dependence of excess surface charge densities on the surface concentrations in a multicomponent system, at the potential of the maximum of ΔḠ^E, are deduced.     

Viscous dissipation effects on turbulent heat transfer in pipes with uniform wall heat flux

An analysis is made of the turbulent Graetz problem with viscous energy dissipation effects in pipes with uniform wall beat flux. The effects of viscous dissipation on fully developed Nusselt numbers are studied for fluids with Prandtl numbers 1, 10, 10², 10³ for Reynolds numbers between 5 × 10³ and 5 × 10⁵ with both cooling and heating conditions at the pipe wall. The viscous dissipation effects on convective turbulent heat transfer in arctic hot oil pipelines are discussed.     

Viscous flow effects in the periodic pressure cycling of gas-phase catalytic reactions

The previous study of Hamer and Cormack[1], on the increased effectiveness of gas phase catalytic reactions under conditions of oscillating external pressure, is extended to include viscous flow effects. For this purpose, the full, time dependent equations of viscous flow, diffusion and chemical reaction for a first order, isothermal reaction in a porous catalyst are solved numerically.The inclusion of viscous effects results in a new dimensionless parameter, N. It is shown that in general the catalyst effectiveness factor is smaller for smaller N. It is concluded, however, that even though viscous effects might be very important for extremely low permeability catalysts, viscous effects can be neglected for operating conditions such that N > 1. For one example cited this corresponds to a permeability of 0.2 millidarcy.     

Modeling of Sorption Dynamics in Transition Metal Ion–Weak-Base Ion Exchanger Systems in Terms of Surface Complexation Theory

A model is constructed for sorption dynamics in multicomponent ion-exchange systems with a weak-base ion exchanger. The model is based on computer-solved nonlinear material balances and internal-diffusion kinetic equations. The multicomponent equilibria involving a weak-base ion exchanger are described in terms of surface complexation theory. According to this theory, the fixed amino groups of the ion exchanger (Lewis bases) and sorbate anions form complexes with metal cations (Lewis acids). These complexes are located in different Stern layers at different distances from the surface. Sorption dynamics models are considered for the frontal ion-exchange chromatographic separation of the H⁺/A/B/X (A, B; = Cu²⁺, Zn²⁺, Ni²⁺, Cd²⁺; X = Cl^–, SO ₄ ^2– ) systems on the amino-containing weak-base ion exchangers Purolite A-109 and Fuji PEI-CS-07. Frontal ion-exchange chromatograms are compared for a number of multicomponent systems.     

The cross-flow filtration of an unstable β-lactam antibiotic fermentation broth

A ceramic cross-flow filter has been evaluated in a recycle loop connected to a bioreactor containing a viscous Streptomyces sp. broth. Because of the instability of the antibiotics formed, it would be advantageous to extract them continuously as they are produced. The performance of the filter, under conditions of high viscosity and suspended solids, has been calculated. Resistance to filtrate flux, distribution of the antibiotic and sterilisability within the system were also examined. An initial flux at a cross-flow velocity of 4 ms^?1 gave readings of 162 litres m^?2 h^?1, which dropped to 131 litres m^?1 h^?1 on subsequent runs because of ‘bedding-in’. Fluxes were improved by an increase of cross-flow velocity and, for short periods, by applying pressure. They were reduced by anti-foam agents and the gradual build-up of particle polarisation layers. Loop sterilisation and removal of the antibiotic in the filtrate stream were excellent.     

The effect of thermal diffusion in multicomponent gas absorption

The contribution of thermal diffusion to interfacial mass transfer rates is examined in multicomponent gas absorption systems. Each interfacial flux is expressed as the product of the isothermal expression corresponding to the bulk temperature of the liquid and a dimensionless correction factor that includes the pure heat effects in multicomponent absorption and the contributions of thermal diffusion. It is shown that when the influence of thermal diffusion is to increase the interfacial mass flux, it is opposite to the heat effect and that the two effects may cancel within a realistic range of values of the thermal diffusion coefficient. A monotonic trend to greater significance of thermal diffusion with the number of components being absorbed is illustrated. This trend is shown to be very rapid for the more dilute species in the mixture. Examples based on the absorption of propane, n-pentane, and n-hexane by paraffin oil are treated. The error induced in the correction factor for the flux of n-pentane by neglecting thermal diffusion when adding propane and n-hexane is less than 6·1 per cent, but the corresponding result for propane is 59·2 per cent for a thermal diffusion coefficient of 1· X 10⁻⁷ g/(cm sec °K) for each species.     

Performance analysis of an integrated tangential microfilter‐fermenter

A specially designed bioreactor including an axial microfilter for cell retention was evaluated for continuous‐flow operation with selected liquid media as controls and in aerobic cultivations of Saccharomyces yeasts. In the initial tests, performance characteristics such as filtration rates and cell accumulation were assessed as a function of filter rotational speed, operating pressure, cultivation time and microfilter type (i.e. membrane or porous metal). The bioreactor did not perform satisfactorily when viscous extracellular polymer was present in the liquid. In the continuous‐flow culture enabling cell retention, Saccharomyces cerevisiae yeast cell concentrations were enhanced by as much as 16‐fold over ordinary batch growth. Concomitant filtration rates were stable over operating times of up to 130 h and hence were independent of the cell concentration. The maximum steady‐state flux was enhanced at rotational speeds up to 400‐700 rpm ranging from 22 to 42 L m^?2 h^?1. Higher rotation rates offered no further improvements. The maximum stabilized flux was independent of operating pressure. Pressure increases caused momentary flux improvements, which rapidly declined and eventually restabilized. Copyright © 2006 Society of Chemical Industry     

A core-shell structured diffusion-bubbling membrane for efficient oxygen separation: Formation and transport properties

The newly developed core-shell structured molten oxide membranes with fast combined diffusion-bubbling oxygen mass transfer and theoretically infinite selectivity are of technological interest because of their high separation efficiency. In this article, a core-shell structured molten V₂O₅–Cu₂O- based diffusion-bubbling membrane was prepared by one-step thermal treatment of initial CuO–25 wt.% Cu₅V₂O₁₀ ceramic composite in a chemical field (under an oxygen partial pressure difference across the composite) above copper vanadate peritectic transformation temperature (816°C). Oxygen fluxes through the membrane were measured at 830°C, using either gas mixtures (O₂ + N₂) with different oxygen concentrations or air as feed gas at the shell of the membrane and helium (He) as sweep gas. Oxygen flux through the membrane with a shell thickness of 0.15–0.61 mm was 3.8·10^–8–1.4·10^–7 mol/cm²/s under an oxygen partial pressure difference of 0.1 –0.75 atm, respectively. The effect of oxygen partial pressure on the thickness of the membrane shell is found. The relationship between membrane shell thickness, oxygen partial pressure difference across the membrane, and oxygen permeation flux through the membrane is established. Oxygen permeation flux through the dual-phase MIEC membrane shell is described in terms of the diffusion model. Oxygen permeation flux through the membrane core is described both within the framework of the stationary model and nonstationary model for uniform (the membrane thickness is much larger than the characteristic distance of bubble dynamic relaxation) and accelerated (the membrane thickness is comparable to the characteristic distance of bubble dynamic relaxation) bubble motion in a viscous oxide melt, respectively.     

Modeling of the Sorption Dynamics in Multicomponent Ion-Exchange Systems with Consideration of Complexation Reactions on the Basis of the Surface Complexation Theory

The sorption dynamics in multicomponent ion-exchange systems with consideration of complexation reactions in solution is theoretically described by solving (on a computer) nonlinear material balance equations and kinetic equations of internal diffusion. Equilibria in multicomponent ion-exchange systems are characterized using the surface complexation theory. According to this theory, fixed groups of an ion exchanger and counterions form complexes located in different layers (Stern layers) at different distances from the surface. These layers constitute a circuit of series-connected capacitors. The fundamental advantage of such an approach is the fact that equilibria in multicomponent systems can be described in terms of a set of parameters obtained for binary systems. Additional account is taken of complexation reactions in the solution in the space between sorbent grains in an ion-exchange column. The H⁺–A–B three-component metal-ion exchange in various systems (A, B = Zn²⁺, Co²⁺, Ni²⁺, Cd²⁺, Ca²⁺, and Na⁺) is studied. Comparison is made between the results of numerical calculations of the characteristics of the H⁺–A ^{n +}–B ^{n +} ion exchange in multicomponent systems containing metal ions with and without consideration of chemical reactions.     

On the dynamics of distillation processes—I: The simple distillation of multicomponent non-reacting,homogeneous liquid mixtures

The mathematical theory of multicomponent simple distillation processes is presented. Through the analysis it is possible to deduce the characteristics of this inherently dynamical process. It is shown that every azeotropic point and pure component vertex corresponds to a singular point and that both elementary and non-elementary singular points may arise. It is further shown that the temperature and pressure surfaces are naturally occurring Liapounov functions for this system. The latter part of the paper is concerned with design methods. Rayleigh's design equation is shown not to extend to multicomponent mixtures and an alternative procedure is presented.     

Selective reduction of nitrogen oxides by hydrocarbons on hydrotalcite Co and Ni catalysts

Hydrotalcitelike Co-Al and Ni-Al catalysts of different compositions (with the atomic ratio M ²⁺/Al³⁺ = 0.5–3.0) were studied in the reaction of selective reduction of NO by propane, propylene, and n-decane in the presence of O₂. The higher activity of the catalysts with M ²⁺/Al³⁺ = 0.5 is connected with high dispersity of Ni or Co cations stabilized by a significant amount of Al³⁺ ions. Propylene was shown to be the most efficient reducing agent for nitrogen oxide. The highest degree of conversion to the extent of 90–99% was attained at 400 and 420–440°C for Ni-Al and Co-Al samples, respectively. When propane and decane were used as reducing agents, the conversion of both catalysts was characterized by the volcano-shaped dependence on temperature due to the fact that the catalyst took part in the concurrent reaction of hydrocarbon (reducing agent) oxidation. Hydrotalcitelike materials are promising representatives of inexpensive bi- and multicomponent systems. The design strategy for new active catalysts for processes of purification of gas exhausts from NO _x , that are stable in the presence of water and sulfur oxides, may be based on usage of hydrotalcites with modified ions introduced into them.     

多微通道内两相流动阻力特性及气泡行为

采用去离子水作为实验工质,对14条水力直径为187.5 μm的平行矩形微通道内两相流动阻力特性及气泡行为进行可视化实验。研究发现,当质量流速一定时,随着热通量增大,汽相逐渐增多,平行多微通道内压降相应增加;当热通量一定时,随着质量流速减小,压降出现先减小后增大的趋势,该曲线中的最低点被认为是静态流动不稳定性起始点（OFI点）。结合可视化图像并利用气泡动力学理论对4种不同的汽相行为特征进行分析,发现汽核受限、倒流等堵塞流道现象的出现导致系统阻力增大,压降增加。通过压降实验值与Kim & Mudawar关系式在不同质量流速下进行比较发现,Kim & Mudawar关系式仅能对本实验压降变化趋势进行预估,而无法对压降数值进行有效预测。     

丁烯氧化脱氢钼铋系催化剂:晶相之间的协同效应

钼铋系催化剂以其优良的性能一直以来都是丁烯氧化脱氢研究和应用的热点。本文简述了已有研究中对钼铋系催化剂及改性后的多组分催化剂的晶相结构及其与反应性能间关系的研究进展。指出在钼铋催化剂中,有较多晶格缺陷的α-Bi₂(MoO₄)₃提供吸附位,氧流动性较强的γ-Bi₂MoO₆提供晶格氧,二者的协同作用提高了催化剂的活性。而在改性后的多组分钼铋系催化剂中,添加的组分与钼铋元素结合生成新的晶相,产生了更多的晶格缺陷及氧供体,从而提升了催化性能。对于钼铋系催化剂进一步改进的方向,本文认为在添加组分的方法基础上,还可以从催化剂表面结构方面入手,进行进一步的深入探究。     

Catalytic conversion of urea to biuret: A catalyst screening study

Biuret was synthesized from urea in a batch reactor using various homogeneous and heterogeneous catalysts, with the aim of searching for efficient catalyst in converting non-catalytic reaction to catalytic reaction. For this purpose, zeolite, heteropolyacid, organic acid and base, multicomponent bismuth molybdate, and multicomponent bismuth molybdate-alumina mixed catalysts were tested. It was revealed that the performance of catalytic reaction was better than that of non-catalytic reaction in the synthesis of biuret from urea. Among the homogeneous acid and base catalysts tested, thionyl chloride (SOCl₂) showed the best catalytic performance. Among the heterogeneous catalysts tested, on the other hand, a mixed catalyst comprising multicomponent bismuth molybdate (Co₈Fe₃Bi₁Mo₁₂O₅₀) and alumina showed the best catalytic performance.     

Multicomponent sorption kinetics of hydrocarbons in activated carbon: Simultaneous desorption and displacement

Binary desorption and displacement kinetics of ethane and propane in Ajax activated carbon are studied in this paper to further understand the multicomponent adsorption of light hydrocarbons onto activated carbon. The experimental data are collected using a differential adsorption bed over a range of temperatures, bulk concentration combinations, particle sizes and shapes. A macropore, surface and micropore diffusion (MSMD) model recently proposed by Hu and Do (Chem Eng Sci (1993) 48 1317) is used in the analysis of experimental data. This model takes into account the concentration dependency of the surface diffusivity. Both diffusions of free and adsorbed species are allowed for in the theory. The adsorbed species are assumed to diffuse in the particle as well as in the microparticle (grain) coordinates. An imaginary gas-phase concentration concept is used to calculate the local diffusion flux of the adsorbed species inside the microparticle. The local multicomponent adsorption equilibrium at any point within the particle is calculated using the ideal adsorbed solution theory (IAST), with the single-component adsorption equilibrium data described by a Unilan equation.     

Reverse osmosis performance of organosilica membranes and comparison with the pervaporation and gas permeation properties

Hybrid organosilica membranes were successfully prepared using bis(triethoxysilyl)ethane (BTESE) and applied to reverse osmosis (RO) desalination. The organosilica membrane calcined at 300^°C almost completely rejected salts and neutral solutes with low‐molecular‐weight. Increasing the operating pressure led to an increase in water flux and salt rejection, while the flux and rejection decreased as salt concentration increased. The water permeation mechanism differed from the viscous flow mechanism. Observed activation energies for permeation were larger for membranes with a smaller pore size, and were considerably larger than the activation energy for water viscosity. The organosilica membranes exhibited exceptional hydrothermal stability in temperature cycles up to 90^°C. The applicability of the generalized solution‐diffusion (SD) model to RO and pervaporation (PV) desalination processes were examined, and the quantitative differences in water permeance were accurately predicted by the application of generalized transport equations. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1298–1307, 2013     

微通道内低沸点工质流动沸腾压降特性

在压力为0.5～1.7 MPa,质量流量为381～2291 kg·m^-2·s^-1,干度为0～1.0的工况范围内试验研究微尺度通道内低沸点混合工质R32/R134a的流动沸腾压降性能,同时对两相流流型进行可视化观察。微尺度通道内径为1.92 mm,0.86 mm和0.5 mm相似文献