Flash invoice

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A flash calculation makes it possible to determine the composition of the liquid and vapor phase for a mixture of chemical substances for which only its gross composition (proportions of the substance ) is known. It is used, for example, to calculate the flash evaporation .

In addition to the amount of substance, input values ​​are also pressure and temperature; output values ​​are the amounts of substance in the vapor or liquid that are in equilibrium . The observed phase equilibria are in this case in addition to the vapor-liquid equilibrium (VLE) and liquid-liquid equilibria (LLE), thereby it is determined whether an in the liquid phase miscibility gap is formed. If the LLE is not observed, a 2-phase flash is used, and if the LLE is taken into account, a 3-phase flash .

Flash calculations are based on models that establish a correlation between pressure, temperature and the compositions of vapor and liquid. For this purpose, activity coefficient models such as NRTL are often used, but also mixing rules combined with equations of state .

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  • Hans Dieter Baehr, Stephan Kabelac: Thermodynamics: Basics and technical applications. ISBN 978-3642005558 .