**Options** - The first step when running a case is to select the desired
conditions on the Options page:

The figure above shows the Options tab where the user chooses the vapor-liquid equilibrium model, the
physical properties models, and other parameters such as **Units** and **Decimal
Places**.

**Equilibrium** - FlashCalc currently offers four different
methods for calculating vapor-liquid
equilibrium using :

- 1. Vapor Pressure Equations
- 2. Redlich-Kwong Equation of State
- 3. Soave-Redlich-Kwong Equation of State
- 4. Peng-Robinson Equation of State

**kij Parameters** - The program contains common interaction parameters
(kij’s) for the
SRK and PR equations of state, or the user can enter the parameters if known.
The user needs to either select the default values or enter his own values
for each case after selecting components. More on kij
parameters later in the tour.

**Flash Stream Flows** - This options controls the format
of units in the material balance grid displayed for flash
calculations. An example is shown later in this tour on the Properties
page discussion.

**Calculations** - Two proprietary convergence procedures give the maximum possible
reliability and range. When solving equilibrium problems two loops must be converged. One
loop solves for the phase compositions while the other solves for temperature, pressure or
fraction vapor. Typically the composition loop is the outer loop. The user has the
option to choose either loops. This allows the program to solve cases involving wide
boiling mixtures and cases very close to the critical point, which previously would not
converge to a solution.

**Volume/Density, Enthalpy/Heat Capacity, **and** Entropy**
- The various physical properties can be calculated using an
equation of state or one of several user selectable empirical models.

**Controls** - The Display Tool Tips option activates tips
such as the "SRK and PR Interaction Parameters" shown above when the
mouse hovers over the kij Parameters button.

**Diagram Options** - Controls appearance of graphs shown later in
the tour.