HYDRODYNAMIC EFFECTS IN THE PHASE SEPARATION OF BINARY POLYMER MIXTURES

The phenomenon of phase separation by spinodal decomposition was studied for polymer blends made by compositional quenching. The modified Cahn-Hilliard theory of phase separation was extended to include hydrodynamics, with a volumetric body force, due to concentration gradients, that induced convective flows. This force influenced the morphology and the growth rate of the average domain size. Unlike the conventional treatment of flows driven by surface tension, the velocity and pressure fields were treated as continuous functions of spatial position.

Numerical solutions for the phase separation in a binary mixture were obtained for a three-dimensional system with periodic boundary conditions. For near critical quenches with similar volume fractions for the two components, cocontinuity was destroyed by the hydrodynamics, giving discrete domains. The breakup in interconnectivity is believed to be a universal phenomenon. The domain growth rate followed a power law, r → τⁿ. The growth exponent depended on the dimensionless viscosity group, ξ = (R_g T/v_s) (Km/μD_AB) and ranged from n = 0.32 ± 0.006 for ξ J = 0 (no hydrodynamic effects) to n ∼ 1 for ξ = 1. For off-critical quenches in which a dispersed phase would be formed by diffusion alone, the scaling exponent showed little enhancement. The simulations accurately predicted the particle size formed in the early stages of spinodal decomposition.     

丙酮-正丙醇和丙酮-正丁醇二元混合物的密度和超额体积

使用DMA-55型精密数字密度计测定丙酮-正丙酮和丙酮-正丁醇两个二元混合物在25℃,30℃和35℃三个温度下的密度数据,关联得出密度与组成和温度的关系式。还计算了三个温度下混合物的超额体积,并用六参数Redlich-Kister方程进行关联。     

AN EXPERIMENTAL STUDY OF SOLIDIFICATION OF BINARY MIXTURES WITH DOUBLE-DIFFUSIVE CONVECTION IN THE LIQUID

An experimental study is reported of solidification of ammonium chloride-water solutions inside a rectangular enclosure. The phase-change and convection processes are studied through shadowgraph and flow visualization as well as temperature and concentration measurements. A number of different initial and boundary conditions are utilized in the experiments in order to obtain a representative data base of the system behavior. It is found that the solidification process induces a variety of double-diffusive convection phenomena in the liquid, including layers, plumes, and stable stratifications. The convection processes influence considerably the local solidification rates and can cause remelting in parts of the system. It is emphasized that many of the physical phenomena identified through the present experiments are expected to be of considerable importance in actual casting processes involving metallic alloys. Consequently, careful consideration must be given to these phenomena when developing more realistic models of solidification processes. The present experiments should serve as a data base for both qualitative and quantitative validation of such models.     

SURFACE TENSION EFFECTS IN THE SEDIMENTATION OF COAL PARTICLES IN VARIOUS LIQUID MIXTURES

The sedimentation volume, V_sed, of coal particles in mixtures of pairs of non-polar and more polar organic liquid combinations as well as in aqueous solutions was determined at 20°C.

The liquid combinations were chosen such that the surface tension, γ_SV, of the coal particles fell between the surface tensions, γ_LV, of the two liquids. A constant mass of a given coal sample was suspended in constant volumes of liquid mixtures of different concentrations.

It was found that the sedimentation volume changed with varying composition of the liquid mixtures, as did the surface tension. A maximum or a minimum occurred in V_sed when the surface tension of the suspending liquid was equal to that of the coal particles, i.e. when γ_LV = γ_SV. Maxima occurred in more polar and minima in the non-polar or less polar liquid mixtures. The position of the extrema, and hence the surface tension, γ_sv, of the particles, was found to change with particle size, in agreement with findings from other independent techniques.

It was found that the surface tension of coal, γ_sv, depends on the surrounding liquid, i.e. coal is hydrophobic in organic and hydrophilic in aqueous media, again in agreement with the results from other techniques.     

ESTIMATION OF CRITICAL PROPERTIES OF BINARY MIXTURES USING GROUP CONTRIBUTION METHODS

A new method for estimating critical temperature (T_c), critical pressure (P_c), and critical volume (V_c), of both nonpolar and polar binary mixtures displaying continuous critical loci is proposed. The methodology is based on the group contribution concept for estimation of critical constants of pure compounds, and the combining rule concept for estimation of mixture properties. Lydersen group contribution method is used to demonstrate the application of this methodology. The combining rules are formulated and their adjustable parameters are determined using 43 nonpolar and polar binary mixtures including 417 data points for (T_c), 390 data points for (P_c), and 219 data points for (V_c), respectively. The method is then evaluated with 15 independently selected binary mixtures containing hydrocarbons, alcohols, ethers, amine, carbon dioxide, nitrous oxide, sulfur dioxide, chloroform, and hydrogen sulfide. The average deviations of the estimated (T_c), (P_c), (V_c) are 1.60%, 7.26%, and 3.64%, respectively. The present procedure does not require experimentally adjusted interaction parameters for estimation of the critical properties of a given binary mixture.     

A SIMPLE CALCULATION OF THE PRESSURE AND LIQUID MOLE FRACTION AT THE VLE OF ETHANE/LIGHT HYDROCARBON BINARY MIXTURES

An analytical expression for the calculation of the pressure and liquid mole fraction at the VLE of ethane/light hydrocarbon binary mixtures is proposed. The model is based on a simple analytical expression for the vapor pressure of pure non-polar fluids, which, for a given temperature, only requires as input the values of the Lennard-Jones molecular parameters and the acentric factor. A properly modified Lorentz-Berthelot mixing rule is used, the interaction parameters being given as simple functions of the temperature and composition with eight constants for each binary mixture. The model is shown to reproduce accurately and simply the pressure (for a given liquid mole fraction) or the liquid composition (for a given pressure) of six ethane + hydrocarbon systems at different temperatures.     

EFFECTIVE THERMAL CONDUCTIVITY OF BINARY MIXTURES AT HIGH SOLID TO GAS CONDUCTIVITY RATIOS

The effective thermal conductivity of single size and binary mixtures of packed particle beds with stagnant gas at high solid/gas conductivity ratios is determined by a deterministic, unit cell approach. The model results are shown to be in good agreement with experimental data for various gas pressures and solid to gas thermal conductivity ratios up to 1300. A set of correlations for effective conductivity of binary mixtures as a function of gas pressure and particle size is derived. The effect of particle swelling on the effective conductivity of binary mixtures is studied by performing a parametric study of the contact area between the particles     

POOL BOILING OF BINARY MIXTURES

Nucleate pool boiling heat transfer coefficients for pure water, pure n-propanol and eight of their mixtures including the azeotrope were measured by using a horizontal electrically heated stainless steel tube of 3.35 mm O.D. and 9.8 cm long as heating element. This binary system was chosen for the reason that it is suitable for simultaneous investigation of the mass diffusion effect (the F effect), the effect of slowing down in bubble growth rate caused by the exhaustion of the volatile component near the vapor-liquid interface, the Marangoni effect (the M effect), the effect of surface tension gradient caused by the evaporation of the component of lower surface tension, and the dynamic surface effect (the Y effect), the effect of surface tension gradient caused by the stretching of vapor-liquid interface, on the boiling heat transfer rate in mixture. It is concluded that the mass diffusion effect can qualitatively account for the experimental results of the system. The discrepancy between the experimental data and the theoretical prediction by considering the F effect is due to taking no account of the intercorrelated effects of M and Y.

The effect of interfacial properties such as surface tension and contact angle on boiling heat transfer rate and the incipience of boiling were also evaluated.     

SOLUBILITY OF ANTHRACENE IN BINARY ALKANE + 2-PROPOXYETHANOL SOLVENT MIXTURES

Experimental solubilities are reported for anthracene dissolved in six binary mixtures containing 2-propoxyethanol with n-hexane, n-heptane, n-octane, cyclohexane, methylcyclohex-ane, 2,2,4-trimethylpentane and tert-butylcyclohexane at 298.15 K. Results of these measurements are used to test a mathematical representation based upon the combined Nearly Ideal Binary Solvent (NIBS)/Redlich-Kister model. For the seven systems studied, the model was found to provide an accurate mathematical representation of the experimental results, with an overall average absolute deviation between measured and calculated values being on the order of 0.5 per cent or less.     

SOLUBILITY OF ANTHRACENE IN BINARY ALKANE + 2-METHOXYETHYL ETHER SOLVENT MIXTURES

Experimental solubilities are reported for anthracene dissolved in six binary mixtures containing 2-methoxyethyl ether with n-hexane, n-heptane, n-octane, cyclohexane, methyl-cyclohexane and 2,2,4-trimethylpentane at 298.15 K. Results of these measurements are used to test a mathematical representation based upon the combined Nearly Ideal Binary Solvent (NIBS)/Redlich-Kister model. For the six systems studied, the model was found to provide an accurate mathematical representation of the experimental results, with an overall average absolute deviation between measured and calculated values being on the order of 0.4 per cent or less.     

二元液体混合物非理想吸附平衡数据的预测

根据气相吸附和液相吸附的热力学一致性条件 ,从溶液理论、表面热力学出发并结合相交换模型 ,提出从气相吸附平衡数据预测二元液体混合物吸附平衡的模型 ,模型中仅含 4个未知参数 .应用该模型对二元液体吸附体系进行了预测 ,结果与实验数据相当吻合     

A TRANSPORT MODEL FOR REVERSE OSMOSIS SEPARATION OF BINARY ORGANIC LIQUID MIXTURES

A set of transport equations was derived for the separation of the binary mixtures of organic solvents on the basis of the surface force-pore flow (SFPF) model. These equations enable the quantitative prediction of the membrane performance data under a given set of operating conditions together with the information on the membrane pore size, interaction forces working between the solution components and the membrane material, and the activity and the molecular radii of solution components. The usefulness of such transport equations is shown for the system ethyl alcohol-heptane-cellulose membrane and some other separation systems.     

运用醋酸纤维素丁酯和芳香聚酰胺膜的二元有机液体混合物的反渗透法分离

本文运用实验室制备的醋酸纤维素丁酯膜和芳香聚酰胺膜系统研究并证实了反渗透技术用于分离液体有机混合物的适用性,并用液相色谱法则量了上述二种膜材料的优先吸附性能。研究发现:反渗透枝术能够应用于液体有机混合物的分离。通过考虑进料液中每一个组分的优先吸附特性和斯托克斯半径,能够预测出二元混合物中哪一组分会在膜透过液中得到浓缩。     

PREDICTION OF PHASE EQUILIBRIA IN BINARY MIXTURES USING AN IMPROVED EQUATION OF STATE AND A THEORETICALLY CONSISTENT MIXING RULE

Prediction of thermodynamic properties and phase equilibria in fluid mixtures using a simple cubic equation of state is still a challenging problem. In this paper, we have predicted vapor/ liquid phase equilibria of several binary fluid mixtures using our previously developed improved Peng-Robinson equation of state and a theoretically consistent mixing rule. Our mixing rule combines the mixing rule of Wong-Sandier with a physically based combination rule. Mixtures are composed of nonpolar, nonassociating polar and associating polar fluids. Comparisons of theoretical predictions with experimental data show a very good performance of our approach in describing vapor/liquid phase equilibria of several mixtures, namely, carbon dioxide/ propane, ethane/hexane, butane/methanol, benzene/methanol, acetone/methanol, methanol/ ethanol, methanol/1-butanol, methanol/water and ethanol/water.     

ADSORPTION OF AUTOMOTIVE PAINT SOLVENTS ON ACTIVATED CARBON: III. EQUILIBRIUM ADSORPTION OF BINARY MIXTURES

The use of activated carbon adsorption systems to remove volatile organic compounds released during automobile paint spray operations has received considerable attention in the past few years. In this paper, adsorption equilibria of eight automotive paint solvent pairs on activated carbon are presented. The data were obtained at total vapor concentrations of 365 ppm by volume, typical of those found in automobile assembly plant spraybooth exhaust air. Correlations of the data using two different modifications of the Polanyi adsorption potential theory in order to accommodate multicomponent equilibria are also presented and discussed. The correlations evaluated predict equilibrium compositions reasonably well for some binary mixtures. However, neither of the methods evaluated appeared to be satisfactory to correlate the equilibrium composition of all of the vapor pairs studied. A possible explanation for this behavior is that very small errors in the data available for the adsorption of pure components result in substantial changes in the predicted binary mixture compositions.     

粒度对煤粒燃烧和热解影响的理论分析

在化学热力学和动力学理论中引入表面项,并由此来分析和讨论粒度对煤颗粒燃烧和热解反应的影响规律.研究结果表明,煤颗粒的粒度对其燃烧和热解反应的热力学性质和动力学参数有明显的影响,粒度越小,影响越大;减小煤颗粒的粒径,化学反应的吉布斯函数差减小,煤颗粒燃烧和热解的趋势增大,使着火温度和热解温度降低,自燃容易发生;并且减小煤颗粒的粒径,其摩尔表面能增大,导致其燃烧和热解的表观活化能降低和速率常数增大,使煤颗粒的燃烧和热解速率加快,使转化率、燃尽度和热解度增加.     

EFFECTS OF INTERPARTICLE INTERACTIONS ON STABILITY, AGGREGATION AND SEDIMENTATION IN COLLOIDAL SUSPENSIONS

Relations between interparticle effective interactions, structure formation, stability and sedimentation for a colloidal system are presented in this paper. For a binary mixture of large and small particles, the potential of the mean forces between large particles is obtained from the Ornstein-Zernike equation. We incorporated the small particles in our numerical simulations by using this potential of the mean force as the interparticle effective interaction. Our numerical results reveal the phenomenon of strong particle aggregation due to the attractive depletion force exerted by small particles. In the absence of the effect of gravity, this aggregation can result in flocculation and the formation of particle clusters thereby forming “void” structures, while under the influence of gravity, the aggregation can greatly affect the sedimentation rates. An analytical expression relating the aggregation number to the sedimentation velocity is presented. Our sedimentation experiments with a bidisperse latex suspension as well as clay particle dispersions show both the destabilizing and stabilizing effects of small particles, which are in qualitative agreement with our theoretical predictions.     

CALCULATION OF VAPOR-LIQUID EQUILIBRIA AND SATURATED LIQUID VOLUMES FOR WATER-AMMONIA MIXTURES

The approach of using T, at ΔZ= Z^s _vZ^{s L} = 0.5 for a balanced representation of saturated volumes (V^{s L} and V^{s Vs L}( of pure components has been extended from non-polar fluids to water and ammonia. For the mixtures of these two compounds, the average absolute percentage deviation in the calculated V ^{s L} values is less than 2% without affecting the representation of vapor-liquid equilibrium values.     

蒽在烷烃和丁醇二元混合溶剂中的溶解度

本文报告了在２５℃下，蒽溶于丁醇及正己烷、正庚烷、正辛烷、环己烷、甲基环己烷和２，２，４－三甲基戊烷六种二元溶剂混合物中的实验溶解度。实验结果可以用近似理想的二元溶剂（ＮＩＢＳ）／Ｒｅｄｌｉｃｈ－Ｋｉｓｔｅｒ方程和修改后的Ｗｉｌｓｏｎ模型来关联。用于系统研究，ＮＩＢＳ／Ｒｅｄｌｉｃｈ－Ｋｉｓｔｅｒ及修改后的Ｗｉｌｓｏｎ方程提供了很好的数学表达式，实验值和计算值的偏差在±１．５％之内。     

PREDICTION OF THERMAL PRESSURE COEFFICIENTS AND INTERNAL PRESSURE IN BINARY LIQUID MIXTURES

1 INTRODUCTIONThe internal pressure of liquids plays an important role in study on liquids and solu-tions.Internal pressure may serve as a measurement for the intermolecular force.Furthermore,internal pressure is capable of giving indications on entropy changes withthe changes in volume during mixing,as can be seen from the following thermodynamicrelationship: