Go to the composition field and add a .v to the end of feed as shown. This will designate that we want the feed's vapour composition, rather than its bulk composition. The phase descriptors are:
These are not case sensitive, so they can be entered in upper case if you wish.
Note the phase envelope can only be used for two phase fluids.
While on this page, also add a quality of .95 to the Qualities field, also as shown. Note you can separate the qualities with spaces or commas or both as desired.
Normally you can probably ignore the Start Pressure field and leave it at its default value of 500 kPa. A quality curve calculation starts on the dew point side and this is the pressure it starts from. If you want the dew point side of the curve to start at a lower pressure, you can reduce this value, but be aware that some compositions may start to predict a second liquid phase at colder temperatures. The phase envelope cannot handle multiple liquid phases and will quit at that point with an error message. Any quality lines already calculated will be displayed though. Although it will almost always contain a constant, this is actually a formula field (which will be discussed in the next tutorial section).
Tap the Done button at the top right to see the vapour phase envelope.