TRISECT
The
calculation of phase boundaries of triangular sections through
multicomponent systems at fixed temperatures and pressures
This
application is used for calculating horizontal sections through
multicomponent phase diagrams for fixed temperatures and pressures but
with varying (constrained) compositions based on a triangular section.
Graphical output is produced as the calculations proceed showing the
phase boundaries calculated by MTDATA.
Two different algorithms for calculating these sections are available
within MTDATA. In the first algorithm (TRISECT),
the graph displayed consists of a series of discrete points ie not
joined up. Options are available to perform more calculations within a
given area and to label individual phase fields. Following
the calculations it is possible to arrange for a graph to be plotted
with all the calculated points joined up.
In
the second algorithm (NEW_TRISECT), the calculation follows each line
on the phase diagram across the phase
diagram using the concept of zero phase fraction. Again options are
available to label individual phase fields.
Before
asking for the isopleth to be calculated it is necessary to define a
datafile, to classify any phases required to be absent or identified as
giving rise to miscibility gaps and to specify the temperature and
pressure. Also the range
of compositions must be defined by setting three compositon groups
and specifying the number of compositions to be examined between
them. All this can be set up using the normal APPLICATION commands
within
MTDATA.
The
application is designed for a multicomponent system (ie with at least
three components). The following example, however, is for a three
component system. In this case the ternary section is identical to an
ordinary ternary diagram. To calculate sections in higher order systems
it is necessary simply
to add more components to the composition groups.
set 'A' 0.9998 0.0001 0.0001 !
set
'B' 0.0001 0.9998 0.0001 !
set
'C' 0.0001 0.0001 0.9998 !
The
density of calculations is set through use of the user variable
"number_of_steps".
set user_v(number_of_steps)
30 !
and
the corners of the diagram assigned to the composition groups.
set user_v(group_lower_left)
'A' !
set
user_v(group_top) 'B' !
set
user_v(group_lower_right) 'C' !
Extra
calculations to be carried out in regions where phase boundaries meet.
This can be turned off
using the "refine" user variable. By default this variable is set to 1.
However if extra calculations
are not required the change can be initiated with:
set user_v(refine) = 0 !
