AN EMPIRICAL VIRIAL-LIKE CUBIC EQUATION OF STATE FOR PHASE EQUILIBRIUM CALCULATIONS

An empirical cubic equation of state(EOS) was obtained by truncating the virial expansion in reciprocal of molar volume after the third term. The constants of the EOS was generalized in terms of critical temperature, critical pressure and Pitzer's acentric factor. In pure component applications the EOS exhibited a performance comparable to Peng-Robinson (1976) EOS in the reduced temperature range of 0.5 to 1. The present EOS tends to predict better saturation liquid volumes at reduced temperatures below 0.8, and better estimations for second virial coefficient at high reduced temperatures. The EOS was successfully employed for vapor liquid equilibrium calculations for some mixtures of normal or slightly polar fluids with traditional one binary parameter mixing rule at moderately high pressures. At low reduced temperatures, where conventional one adjustable parameter applications of the cubic equations compare unfavorably with dual methods based on excess Gibbs energy functions for the liquid phase, a new two constant mixing rule introduced by Stryjek and Vera (1986) was employed for the present equation of state.Publisher's Versio

EVALUATION OF SECOND VIRIAL COEFFICIENTS FROM SATURATION DATA

A data reduction technique is introduced for the evaluation of second virial coefficients of gases at subcritical temperatures. The method makes use of the vapor-liquid equilibrium data, i.e., temperature, saturation pressure, liquid and vapor molar volumes and can be used to obtain second virial coefficients of a wide variety of fluids including polar, associating and quantum gases. The calculated second virial coefficients are in good agreement with their counterparts from literature, which are obtained from gas compressibility data by traditional data reduction methods

VAPOR-LIQUID-EQUILIBRIUM OF POLYMER-SOLUTIONS USING A CUBIC EQUATION OF STATE

A recently proposed mixing rule has been combined with a cubic equation of state to correlate the vapor-liquid equilibria of various polymer + solvent and solvent + long chain hydrocarbon mixtures. We find that the two-parameter version of this model can correlate the solvent partial pressure in concentrated polymer solutions with high accuracy over a range of temperatures and pressures with temperature-independent parameters. For the solvent + long chain hydrocarbon systems, for which accurate vapor-phase concentrations are also important, the model is best used as a three-parameter correlation. Advantages of this approach are that it extends the application of cubic equations of state to polymer + solvent systems in a simple fashion and that generally only temperature-independent parameters are required which allow for accurate interpolation and extrapolation of available data

DETERMINATION OF THE RELAXATION SPECTRUM FROM OSCILLATORY SHEAR DATA

In order to use either a linear or nonlinear model of viscoelasticity to calculate the stress response of a material to various deformations, it is usually necessary to have available an explicit equation for the linear relaxation modulus G(t). The most popular procedure is to use the data from a small-amplitude oscillatory shear experiment to determine the parameters of a generalized Maxwell model. However, this is an ill-posed problem and is not at all a straightforward curve-fitting operation. We compare three procedures for determining a set of relaxation times and discrete moduli that can then be used as empirical fitting parameters in fluid mechanics computations. These are linear regression, with and without regularization, and nonlinear regression. Nonlinear regression is found to give a good fit of the data with a minimum number of parameters

A SIMPLE PROCEDURE FOR ASSESSING THE PROTECTIVE EFFECT OF TRANSPARENT POLYMER-FILMS USED FOR PACKAGING FOODS CONTAINING LIGHT-SENSITIVE NUTRIENTS

Sensitive components of foods may undergo degradation reactions when subjected to light. The packaging of the food may slow down such reactions by absorbing and reflecting a fraction of the incident light. Riboflavin is a typical light-sensitive nutrient and undergoes first-order degradation when subjected to light. Rate constants of this reaction were evaluated under 25W, 60W, 100W and 200W white light bulbs at pH = 8, at 20 +/- 1-degrees-C, with no light shielding or by shielding the light with a single fold of high density polyethylene or two folds of low density polyethylene films. Numerical values of the reaction rate constants were proportional to the light source power and varied with the number of polymer films. The proportionality constant was regarded as the 'protection index' of the specific film. The results implied that the smaller the protection index of the film the smaller was the degradation reaction rate constant. Although this study was done by employing two different kinds of polymer films and one light-sensitive chemical only, this approach may be employed for comparing the packaging efficiency of polymers used for wrapping foods containing light-sensitive components

EFFECT OF DIFFUSION RESISTANCES ON SELECTIVITY IN BIDISPERSED POROUS CATALYSTS

Particle-pellet approach was used for the analysis of selectivity in a consecutive reaction scheme. It was illustrated that the ratio of macro and micropore diffusion resistance (α) has a significant effect on selectivity especially for intermediate values of particle Thiele modulus. Increase of this ratio and increase of particle Thiele modulus yield lower selectivities for the intermediate product