Flash and Phase Separation

Suppose you put some water in an open pan on the stove, initially at room temperature. The partial pressure of water in the air (at equilibrium) will equal the vapor pressure of water at that temperature. Now heat the pan. The vapor pressure increases, since it 

Introduction to Cheniieol Engineering Computing, by Bruce A. Finlayson Copyright 2006 John Wiley Sons. Inc. 

There is another scenario that, unfortunately, is purely imaginary. In that scenario, as the temperature increases, chemical one evaporates completely when the temperature reaches its boiling point. As the temperature increases further, the boiling point for the second chemical is reached, and it aU evaporates. You wish it did happen this way Despite the fact that in real life the separation of the two chemicals is never complete in either liquid or vapor phase, it is still a useful phenomenon and forms the basis for distillation. 

This chapter looks first at equations governing an isothermal flash, and then shows how you can predict the thermodynamic quantities you need to solve the isothermal flash problem. The problems are all sets of algebraic equations, and you can solve these problems using Excel and MATLAB . The chapter then addresses more complicated vapor-liquid separations, but now using Aspen Plus because of its large database. 

The members of the set Kj are called A -vahies, and they can be predicted from thermodynamics, as shown below. For now, though, assume that you know their values. 

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