Determination of Binary Diffusion Coefficients of Gases Using Holographic Interferometry in a Loschmidt Cell

A measuring system for the determination of binary diffusion coefficients of gases has been developed. The lower and upper half cells of the Loschmidt diffusion cell are fixed, one upon the other, contrary to the usual shearing cells. A sliding component between the half cells is moved to connect them and to start the diffusion. The concentration changes due to diffusion are determined by the optical method of real-time holographic interferometry. In this way the concentration is obtained as a function of time and location resulting from the analysis of the interference pattern. The data are evaluated by using the integrated diffusion equation for the closed-tube technique. First, measurements on the system argon-propane have been successfully performed at 1 bar and at room temperature. The results show an uncertainty of 1 per cent and are in good agreement with data by Wakeham and Slater (1974). Furthermore, refractive index measurements on the pure gases, argon and propane, as a function of gas density have been performed and evaluated to derive values of the first refractivity virial coefficient.     

Theory of Membrane Separation of Binary Gas Mixtures

A general approach to the solution of the problem on convective mass transfer in the process of separation of binary gas mixtures in the channels of membrane units is proposed. An integral equation for the main separation parameter -- the rate of flow of a binary mixture component through a membrane -- has been obtained.     

A New Method of Frozen-fringe Holographic Interferometry Using Thermoplastic Recording Media

A new technique is described which confers the advantage of a permanent holographic frozen fringe record on live fringe holographic interferometry. The exact form of the frozen fringe record is known in advance and all information about fringe localization is retained. Some of the applications and implications of such a technique are discussed.     

Study on the Interaction Coefficients in PR Equation with vdW Mixing Rules for HFC and HC Binary Mixtures

The Peng-Robinson equation of state with the van der Waals mixing rules was used to correlate vapor–liquid equilibrium (VLE) data for HFC/HC, HFC/HFC, and HC/HC binary mixtures. The interaction parameter k _ij was obtained for every binary mixture. It was assumed that k _ij has contributions from the two components, and each component has its own constant contribution factor k _i for the mixture, and the values of k _ij indicate the degree in difference of properties between the two components. Therefore, the interaction parameters k _ij is proposed as: k _ij  = k _i  − k _j . The values of the mixing factor k _i for Hydrofluorocarbons (HFCs) and Hydrocarbons (HCs), including propane, isobutane, n-butane, R23, R32, R125, R143a, R134a, R152a, R227ea R236fa, R236ea, and R245fa, were obtained by least-square fitting. In total, 39 refrigerant binary mixtures were analyzed on the basis of this method, and the results showed good agreement with experimental data. The overall average absolute deviations of pressure and vapor mole fraction are 1.3 % and 0.0089, respectively.     

物理靶上自由飞流场全息干涉诊断

在马赫数为15的条件下,采用激光全息干涉技术在物理靶上拍摄到直径12mm的球标模自 由飞流场全息干涉图和阴影照片。通过干涉照片获得了流场中六个截面的密度分布曲线,同时从阴影照片上测量出弓形激波的归一化脱体距离为0.046。将实验照片与计算流场干涉图进行比较,二者的激波位置、条纹变化量及条纹连接基本一致。     

Experimental Research on Thermocapillary-Buoyancy Migration Interaction of Axisymmetric Two Drops by Using Digital Holographic Interferometry

The migration and interaction of axisymmetric two drops in a vertical temperature gradient is investigated experimentally on the ground. A silicon oil is used as the continuous phase, and a water-ethanol mixture is used as the drop phase, respectively. The migration and interaction of two drops, under the combined effects of buoyancy and thermocapillary, is recorded by a digital holographic interferometry measurement in the experiment to analyse the velocities and temperature distribution of the drops. As a result, when two drops migrate together, the drop affects the other drop by perturbing the temperature field around itself. For the leading drop, the velocity is faster than the one of the isolated drop, and the maximum of the interfacial temperature distribution is larger than the one of the isolated drop. For the trailing drop, the velocity is slower than the one of the isolated drop, and the maximum of the interfacial temperature distribution is less than the one of the isolated drop. The influence of the dimensionless initial distance between the drop centres to the drop migration is discussed in detail in this study.     

The Experimental Study of Temperature Dependence of Binary Diffusion Coefficients of Gases at Different Pressures

An experimental study of the temperature dependence of the binary diffusion coefficients (BDCs) was conducted for five binary mixtures of gases: $\mathrm{H}_{2}{-}\mathrm{N}_{2}, \mathrm{H}_{2}{-}\mathrm{CO}, \mathrm{H}_{2}{-}\mathrm{CH}_{4}, \mathrm{H}_{2}{-}\mathrm{C}_{2}\mathrm{H}_{6}$ , and $\mathrm{H}_{2}{-}\mathrm{C}_{3}\mathrm{H}_{8}$ . Measurements were carried out with the use of a steady-flow method in the temperature range from 250 K to 900 K and the pressure range from 0.1 MPa to 15 MPa. The determination of the BDCs is based on analysis of the volume fraction of the diffusing gas in the gas flow. The experimental data were compared with the results of calculations by the proposed formula evaluated within the framework of the elementary kinetic theory. The obtained results exhibit considerably good agreement with the experimental data within the experimental error. The results of investigations of the temperature dependence of the BDCs show that this dependence can be fitted with a power law only at atmospheric pressure.     

Diffusion in Gas Mixtures Containing the Components of the Synthesis of Ammonia

The diffusional process in certain multicomponent gas mixtures that contain the components of the synthesis of ammonia is investigated experimentally as a function of pressure. The effective coefficients of diffusion and the matrices of the coefficients of multicomponent diffusion are determined. The dependence of the coefficients on the pressure is shown. A comparison of the experimental and calculated data shows their good agreement.     

Phase Behaviors of Binary Hard-Sphere Mixtures Using Simple Analytical Equations of State

Recently, we have proposed a unified analytical equation of state (EOS) for solid–liquid–vapor states of matter, and have examined the thermodynamic properties of argon, carbon dioxide, and methane, as well as binary mixtures of methane and carbon dioxide. Also it has been demonstrated that the EOS can be applied for the solid–fluid transition of hard spheres, by eliminating the attractive part of the EOS. The present work is an extension of the earlier calculations for identical hard spheres, and here we examine the phase behavior of binary hard-sphere mixtures. The hard-sphere EOS employed in this study is

Self-Diffusion and Binary Maxwell–Stefan Diffusion Coefficients of Quadrupolar Real Fluids from Molecular Simulation

Self- and binary Maxwell–Stefan (MS) diffusion coefficients were determined by equilibrium molecular dynamics simulations with the Green–Kubo method. This study covers self-diffusion coefficients at liquid states for eight pure fluids, i.e., F₂, N₂, CO₂, CS₂, C₂H₆, C₂H₄, C₂H₂, and SF₆ as well as MS diffusion coefficients for three binary mixtures N₂+CO₂, N₂+C₂H₆, and CO₂+C₂H₆. The fluids were modeled by the two-center Lennard–Jones plus point-quadrupole pair potential, with parameters taken from previous work of our group which were determined solely on the basis of vapor–liquid equilibrium data. Self-diffusion coefficients are predicted with a statistical uncertainty less than 1%, and they agree within 2–28% with the experimental data. The correction of the simulation data due to the finite size of the system increases the value of the self-diffusion coefficient typically by 10%. If this correction is considered, better agreement with the experimental data can be expected for most of the studied fluids. MS diffusion coefficients for three binary mixtures were also predicted; their statistical uncertainty is about 10%. These results were used to test three empirical equations to estimate MS diffusion coefficients in binary mixtures, i.e., the equations of Caldwell and Babb, of Darken, and of Vignes. The equations of Caldwell and Babb and of Vignes show qualitatively different behavior of the MS diffusion coefficient than that observed in the simulations. In agreement with previous work, the best results are obtained in all cases with the equation of Darken.     

Measurement of the Diffusion Coefficient of Miscible Fluids Using Both Interferometry and Wiener's Method

Measurements of the diffusion coefficient of two miscible liquids are reported. The liquids are various combinations of pure silicone oils and those to which small amounts of solvents are added to control the difference in density between the fluids. The liquids were placed in a quartz cell such that the interface is initially horizontal. As the fluids diffuse, the profile of the index of refraction near the interface is time dependent and is related to the local concentration of the diffusing fluids. The concentration gradient profile was measured by a shearing interferometer incorporating a Wollaston prism, as well as Wiener's method. In the latter technique, a 45° light sheet was passed through the test cell, and the local deflection of the light beam was measured. The average diffusion coefficient was obtained by analysis of the measured concentration gradient profile, assuming that the diffusion process is one-dimensional and is characterized by a constant value of the diffusion coefficient.     

Prediction of Critical Properties of Binary Mixtures Using the PRSV-2 Equation of State

The aim of this work is to test the value of the Peng–Robinson–Stryjek–Vera (PRSV-2) equation of state for predicting the critical behavior of binary mixtures. A procedure adopted by Heidemann and Khalil, based on the Helmholtz free energy, has been followed. The resulting two complex nonlinear equations have been solved simultaneously for the critical temperature and volume, while the critical pressure is calculated from the PRSV-2 equation of state itself. Three forms of binary-interaction parameters have been tried: the zero-type, conventional one-parameter type, and Margules two-parameter type. The optimum values of the binary interaction parameters, based on minimizing the sum of the squares of the relative errors between predicted and experimental critical temperatures, have been calculated for 20 polar and nonpolar systems. The Margules two-parameter type gives the best results, but its mathematical derivation is cumbersome and it requires more computation time. The standard and the average of the absolute relative deviations in critical properties are included. The predicted critical temperatures and pressures agree well with the experimental results, and are always better than those predicted by the group-contribution method. The deviations in the predicted critical volumes using any of the tested binary-interaction parameter types are relatively large compared to those using the group-contribution method.     

求解一类变系数对流扩散方程的GER方法

本文将并行算法中的GER方法推广到一类变系数对流扩散方程的求解问题,获得了其相应的稳定性条件。数值实验结果表明了该问题并行解法的可行性。     

Predicting the High-Pressure Phase Equilibria of Binary Mixtures of n-Alkanes Using the SAFT-VR Approach

The phase behavior of selected alkane binary mixtures is studied using SAFT-VR, a version of the statistical associating fluid theory for potentials of variable attractive range (SAFT). We treat the n-alkane molecules as chains formed from united-atom hard-sphere segments with square-well potentials of variable range to describe the attractive interactions. We use a simple relationship between the number of carbon atoms in the n-alkane molecule and the number of segments in the united atom chains in order to predict the phase behavior of n-butane with other n-alkanes. The calculated vapor pressures and saturated liquid densities of the pure components are fitted to experimental data from the triple point to the critical point. These optimized parameters are rescaled by the respective experimental critical points and used to determine the critical lines and phase behavior of the mixtures. We use the Lorentz-Berthelot combining rule for the unlike interactions. We predict the phase behavior of n-butane + n-alkane binary mixtures, concentrating mainly on the critical region. The gas-liquid critical lines predicted by SAFT-VR for the n-alkane mixtures are in excellent agreement with the experimental data, and improve significantly on the results obtained with the simpler SAFT-HS approach where the attractive interactions are treated at the mean-field level.     

Analysis of the Thermal Conductivity Coefficients for Gas Mixtures: Application of the Modified Enskog Theory

The method for the calculation of transport coefficients for mixtures of high-density simple gases, which is a generalization of the modified Enskog theory for pure (individual) gases, is used in a simplified form suggested by the author. The simplification is derived using the perturbation method. Computer codes are compiled for performing an analysis of the coefficients of viscosity and thermal conductivity for multicomponent mixtures of high-density gases. The results of calculation of the thermal conductivity coefficient of a nitrogen–carbon dioxide mixture are compared with relevant experimental data: the deviation does not exceed 7% in the experimentally treated region of states.