Almost all the program modules require a certain amount of information about the pressure and temperature-dependent properties of the medium being used in the process. CONVAL® is capable to determine the process specific data for an immense number of fluids in the context of a calculation module.
Basically available in CONVAL®
The substance database contains a variety of pure substances and mixtures with their specific material constants and measured values. Temperature and pressure dependent values will be calculated by the approximation procedure using the basic substance database. The data can be corrected manually if you have proved operating data. In this case, the substance calculation is deactivated and the relevant icons - Calculated or Looked up/Default - are locked with a red cross. You can restore the original data and reactivate the substance calculation by clicking on these icons.
Mixtures for liquid or gas compositions of arbitrary fluids can be defined in CONVAL®. For this it is possible to specify the fluid components in mole percent. If the selected medium or mixture is based on the thermodynamic database the behavior will be determined by equations of state. In other cases, approximations are used.
CONVAL® can calculate pressure and temperature-dependent properties according to various methods. Three different calculation methods for process data are offered at present.
Approximation is a very useful option if no special calculation methods, such as the steam table (IAPWS 97) for water, are available.
CONVAL® integrates an extensible property database containing around 800 substances and their physical constants, which can be taken as a basis for pressure and temperature-dependent calculations of the substance properties.
The boiling pressure pv of a liquid can be calculated, for example, in its state at a temperature t1, or the boiling temperature tv of this liquid in its state at a pressure p1, in accordance with Riedel's correlation (error < 10%).
Alternatively, it is possible to calculate the real gas factors Z1 and Zn, and thus also the specific gas densities. This calculation is based on Newton and Raphson's correlations and on publications by Dranchuk, Purvis, Robinson and Takacs.
The operating density of liquids is calculated with the help of the physical constants stored in the database according to mathematical approximation methods described by R. W. Hankinson and G. H. Thomson. In conjunction with other authors these methods are also referred to as the COSTALD correlation. The error is < 1% for the majority of applications and only exceeds 5% under a very limited number of boundary conditions.
Approximation methods are also available for calculating the isentropic exponent, the sound velocity, etc.
If neither properties for approximation equations nor special calculation methods such as the steam table (IAPWS 97) for water are available, CONVAL® can interpolate the information it needs on the basis of measured values.
CONVAL® integrates an extensible property database containing around 200 substances (thermal oils, for instance), for which operating data is available in the form of measured values.
Curves of the operating density, dynamic viscosity, boiling temperature, specific heat capacity, thermal conductivity and isentropic exponent can be entered here for liquids.
Curves of the specific heat capacity, thermal conductivity and isentropic exponent can be entered additionally for gases.
The calculation capabilities of CONVAL® are extended and enhanced by the optional thermodynamic package. Beside higher accuracy and the extended area of application (low temperatures, high pressures, area of the critical point) an option has been created which enables the calculation of additional substance properties (Joule-Thomson-Effect, entropy, enthalpy etc.). In sum this leads to an increased result accuracy and additional calculation capabilities inside the different calculation modules.
The thermodynamic module is composed of three components:
The program FLUIDCAL for the calculation of thermodynamic properties from equations of state (fundamental equations in the form of the Helmholtz free energy) in research and for technical applications. This program enables the user to calculate more than 25 thermodynamic properties of more than 70 substances. For a large number of substances the most common transport properties can also be calculated.
REFPROP is an acronym for REFerence fluid PROPerties describing a program which calculates the thermodynamic and transport properties of industrially important fluids and their mixtures. The program embeds pure substances and predefined or user defined fluid mixtures and represents the substance calculation with the highest accuracy in this context.
Calculation of mixtures according to GERG 2008. The GERG-2008 equation is valid in the gas phase, in the liquid phase, in the supercritical region and for the vapor-liquid equilibrium.