Liquid phases physical property computation

The complexity of the physical properties of liquid water is largely determined by the presence of a three-dimensional hydrogen bond (HB) network [1]. The HB s undergo continuous transformations that occur on ultrafast timescales. The molecular vibrations are especially sensitive to the presence of the HB network. For example, the spectrum of the OH-stretch vibrational mode is substantially broadened and shifted towards lower frequencies if the OH-group is involved in the HB. Therefore, the microscopic structure and the dynamics of water are expected to manifest themselves in the IR vibrational spectrum, and, therefore, can be studied by methods of ultrafast infrared spectroscopy. It has been shown in a number of ultrafast spectroscopic experiments and computer simulations that dephasing dynamics of the OH-stretch vibrations of water molecules in the liquid phase occurs on sub-picosecond timescales [2-14],... 

The physical property monitors of ASPEN provide very complete flexibility in computing physical properties. Quite often a user may need to compute a property in one area of a process with high accuracy, which is expensive in computer time, and then compromise the accuracy in another area, in order to save computer time. In ASPEN, the user can do this by specifying the method or "property route", as it is called. The property route is the detailed specification of how to calculate one of the ten major properties for a given vapor, liquid, or solid phase of a pure component or mixture. Properties that can be calculated are enthalpy, entropy, free energy, molar volume, equilibrium ratio, fugacity coefficient, viscosity, thermal conductivity, diffusion coefficient, and thermal conductivity. 

Although the new estimates of the liquid-phase mole fractions satisfy the mole fraction summation equation, the values given above clearly are physically impossible. Since negative mole fractions may cause problems computing physical properties it is advisable to reset them so that they are positive. We proceed with the values... 

The unprecedented progress in computer technology and in computer science has had a tremendous impact on computational molecular physics and chemistry. Methods, algorithms, and software for performing molecular structure calculations have been developed to predict molecular properties and processes with high accuracy [1-3]. Notably, almost all these methods are applicable only for the isolated molecules thus corresponding to the gas phase at low pressure and temperature. Most chemical processes, in particular biochemical reactions in vivo and in vitro, and industrial processes of great impact take place, however, in condensed (liquid) phase. 

By far the most important application of liquid crystals is display devices. Liquid crystal displays (LCDs) are used in watches, calculators, and laptop computer screens, and for instrumentation in cars, ships, and airplanes. Several types of LCDs exist. In general their value is due to the fact that the orientation of the molecules in a nematic phase substance can be altered by the application of an external electric field, and that liquid crystals are anisotropic fluids, that is, fluids whose physical properties depend on the direction of measurement. It is not pure liquid crystalline compounds that are used in LCDs, but liquid crystal mixtures having optimized properties. 

The following properties of the system are considered (i) two liquid-phase streams enter the heat exchange in a countercurrent set-up (ii) the heat exchanger is operated at isobaric conditions (m) both liquid streams are assumed behave ideally, (iv) both streams have equal physical properties, excluding heat capacity, which are temperature independent (v) heat transfer due to conduction is the only source of entropy production and (m) the driving force for heat transfer is computed between outlet conditions. 

Computational fluid dynamics (CFD) approach has become a standard tool for analyzing various situations where fluid flow has an effect on the studied processes. Numerous studies using CFD for chemical process industry have also been reported. Mostly, they have been simple cases as the system is non-reacting, contains only one phase (liquid or gas), or physical properties are assumed constant. When we are dealing with multiphase systems like gas-liquid or liquid-liquid systems we must take into account some phenomena which are not of importance for one-phase systems. The vapor-liquid or liquid-liquid equilibrium is one of these that are needed in order to model the system. In addition to that, mass and heat transfer between the phases must generally be taken into account. Also, the two-phase characteristics of fluid flow need to be taken into consideration in the CFD models. 

The gas-liquid phase behavior described by the van der Waals theory is considered simple . In this sense it is a reference distinguishing simple from complex . We emphasize that this refers to the qualitative description rather than to the quantitative prediction of fluid properties. Other phenomenological equations of state may be better in this respect, but it is the physical insight which here is important to us. Because of this we compute a number of other thermophysical quantities in terms of t, p, and/or v. 

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