جستجوی مقالات مرتبط با کلیدواژه « فشار بخار » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

The Flory-Huggins interaction parameter (χ) is a crucial factor affecting the miscibility and morphology of components in polymer mixtures and their final properties and applications. The reliable measurement of the interaction parameter is worthwhile in fundamental understanding and quantitative determination of structure-performance relation and finally in practical applications of polymers in different fields. Different methods are used for evaluation of this parameter. In this study, six semi-experimental methods are reviewed: measurement of melting point depression, equilibrium swelling, contact angle, phase separation points, vapor pressure, and inverse gas chromatography. In these methods, equilibrium melting temperatures of pure polymer and its mixtures, degree of equilibrium swelling of the cross-linked polymer in the presence of swelling agent, surface energy of components in the polymeric mixtures, equilibrium components composition in the two-phase system, the ratio of partial vapor pressure of solvent to its saturated one and retention volume are experimentally measured, respectively. Then a proper equation is fitted on the data and the interaction parameter is obtained. In some methods, such as measurement of contact angle, only a positive interaction parameter at temperature of the test is obtained. But in some others, such as measurement of melting point depression, there is no constraint for the sign of interaction parameter. In addition, some methods can determine the composition dependency of the interaction parameter, such as determination of phase separation points.

Hydrogen molecule consists of two states: ortho and para hydrogen which are in equilibrium at a certain ratio in any temperature. The conversion process in the catalytic beds takes place in order to prevent a slow exothermic conversion of ortho to para hydrogen in the liquid hydrogen storage tanks and to avoid evaporation of liquid hydrogen. Ortho and para hydrogen differs in physical properties such as thermal conductivity, vapor pressure, enthalpy, as well as Raman spectroscopy, nuclear magnetic resonance and gas chromatography. The percentages of para hydrogen content can be determined in each stage of hydrogen liquefaction process using such differences in these properties. Given the importance of determining the amount of para hydrogen in the quality control test of produced liquefied hydrogen, various percentage measurement methods based on differences in the physical properties of para hydrogen content has been expressed in this paper. As the surveys shows, the thermal conductivity is the most applicable method to determine the percentage of para hydrogen.