Influence Of Activity Coefficients Research Articles

Thermodynamics of Aluminum Deoxidization Equilibria in GCr18Mo Bearing-Steel

Based on the predecessors of thermodynamic data, the relationship between aluminum contents and oxygen contents of the aluminum deoxidization reaction was calculated. And the influence of activity coefficient to the reaction equilibrium in bearing-steel is analyzed. First-order and second-order interaction coefficients were used to calculate and draw the equilibrium curves, respectively. The effects of different temperature and different interaction parameters on the deoxidization equilibrium curves were studied. And through the curve the influence of the change of aluminum contents to the activity can be known. The trend of the curve with first-order interaction parameters is consistent with the curve with first-order and second-order interaction parameters at the low Al concentration region. And the oxygen contents of curve with first-order interaction parameters are higher than the other curve at the high Al concentration region

Surface Tension and Interfacial Tension of Binary Organic Liquid Mixtures

The pendant drop method, combined with efficient temperature control of the measuring cell, allows high precision measurements of both surface tension and interfacial tension. The surface tensions and liquid densities of mixtures of cyclohexane + heptane, cyclohexane + propanone, and toluene + propanone have been determined at a normal pressure of 1 bar over the temperature range from 287 K to 317 K. The surface tension data could be parametrized with a cubic polynomial. Gibbs excess surface concentrations are derived from our experimental data, and the influence of activity coefficients is discussed. The high precision pendant drop apparatus allows accurate measurements of the interfacial tension in systems with liquid−liquid phase separation. In binary mixtures of heptane + N,N-dimethylformamide, heptane + N-methyl-2-pyrrolidone, and decane + N,N-dimethylformamide, the interfacial tension was measured over a wide temperature range close to the critical solution point. The densities of the corresponding ...

Surface Tension of Pure Liquids and Binary Liquid Mixtures

The pendant drop method, combined with efficient temperature control of the measuring cell, allows high precision in surface tension measurements. The surface tensions of heptane, toluene, N,N-dimethylformamide, cyclohexane, N-methyl-2-pyrrolidone, and propanone were measured as a function of temperature using the pendant drop method. The results were compared with literature data. The surface tension and density of toluene + heptane and N,N-dimethylformamide + toluene at atmospheric pressure were measured over a temperature range. Gibbs excess surface concentrations are derived from the experimental surface tensions, and the influence of activity coefficients is discussed.

Refrigeration with electrolytic and immiscible liquid–liquid systems

Due to environmental concerns, new refrigerants are urgently needed to meet the refrigeration needs in the coming century. Two novel absorption refrigeration systems are considered herewith (1) the mixed-solvent electrolytes, and (2) mixtures exhibiting liquid–liquid immiscible phase separations as working fluids. When properly designed, they can avoid the global warming and ozone depletion pitfalls usually associated with the chlorofluorcarbon refrigerants. Electrolytic systems such as water–lithium bromide–ethylene glycol, and ammonia–sodium thiocyanate mixtures can serve as cooling media in an absorption refrigeration cycle with salts as absorbents and water (or ammonia) as refrigerants. The cycle efficiency (expressed in terms of the coefficient of performance—COP) plays a major role in determining their economical viability. In this paper, we study the desirable molecular characteristics that the salt systems should possess in order to yield high COP. We set out to answer the questions: how do we select and screen electrolytic mixtures as working fluids? and what molecular properties impact on design and efficiency? We shall apply an accurate theory, namely, the mean-spherical approach (MSA) to electrolytes to model the activities of the salt solutions. The results are checked with available data to ascertain its accuracy. Predictions can then be made on the performance of electrolytic working fluids in applications such as air-conditioning and refrigeration. Next, for mixtures of chemical solvents that form liquid–liquid immiscibility gaps, a Maxwell cycle can be constructed to generate refrigeration. In order for this class of solvents to work, a number of practical and thermodynamic considerations must be satisfied. We examine several functional criteria that are needed to operate the cycle: the first is concerned with the free energy-of-mixing behavior; the second, the pattern of the immiscibility gaps; and the last, most importantly, the influence of activity coefficients on absorption. This type of refrigeration, not yet commercially developed, promises to be highly economical due to hardware savings (elimination of the condenser), and energy savings (no need to supply the latent heats of evaporation).

Density functional theory: Structure and interfacial properties of binary mixtures

AbstractBased on Density Functional Theory (DFT) of inhomogeneous fluid mixtures we model the liquid‐vapour interface of some binary mixtures. Attractive contributions to the Helmholtz free energy are treated by a mean‐field approximation (MF). The local density approximation (LDA) is applied to the repulsive reference system described by a hard sphere equation of state. A cut‐off and shifted Lennard‐Jones‐12‐6 potential divided according to the WCA‐prescription is used as interaction pair potential. Binary Lennard‐Jones parameter are introduced and fitted to experimental liquid‐vapour compositions to describe interactions between different species. The calculations give good results in the case of simple fluid mixtures like Ar‐N2 and CO‐N2. Similar results are obtained for the nonpolar mixture n‐heptane‐toluene. The predicted surface tensions γ agree very well with experimental data. Computed partial density profiles clearly show the enrichment of the component with the lower surface tension in the interphase. The relative Gibbs surface excess concentration is calculated from partial density profiles and compared with experimental values. The influence of activity coefficients on Gibbs adsorption is discussed.