Information Technology Reference
In-Depth Information
5.3 SENSITIVITY FUNCTION
The features of the sensitivity function will be displayed by the continuation of example
mixer5.bkp through example mixer5s.bkp. The Sensitivity function is located under
the setup menu Model Analysis Tools and when selected initiates the Sensitivity Data
Browser. When New is selected, a Sensitivity ID such as S-1 is assigned. This initiates
a display that facilitates the association of a Fortran-accessible variable with a variable
within the process. It is imperative that this process be started by selecting the New
button, which generates the displays shown in Figure 5.3. The variable xetoh, which is
user selected, represents the mole fraction of ethanol in output stream 4 of the example.
Figure 5.4 shows the assignment of the process variable to the Fortran variable. For
this example, a Fortran expression will be created to calculate the fraction of alcohols
in stream 4. For this purpose it will be necessary to create three additional Fortran-
accessible variables (fmoh, fetoh, and f4), the flow rates of methanol and ethanol in
stream 4, and the total flow of stream 4.
Selection of the tab Vary in the Sensitivity input Data Browser brings up Figure 5.5,
which defines the range of trial values (the independent variable) that stream 2 should
use in seeking for a value that would produce an approximate solution to the desired
target of ethanol mole fraction in stream 4 of 0.5.
Selection of the tab Tabulate permits the assignment of any defined Fortran variables
or legitimate Fortran expression to the column of a table on which the results of the
Sensitivity study will be presented. Note that column 3 contains an expression for the
calculation of the fraction of alcohols leaving the mixer. Tabular and plotted results are
displayed in Figure 5.6. One can see that the flow rate required to produce a 0.5 mole
fraction of ethanol is bracketed between a stream 2 flow of 100 and 300 mol/hr,
and from the plot
the solution is approximately 225 mol/hr. Note that
the mole
Figure 5.3
Creation of a Fortran-accesible variable.
