Aspen Hysys tricks

Finding if u fall in the supercritical region in Aspen Hysys

1) it will itself say that "A temperature stream is not found at requested condition" 
2) Press cntl + U to see the critical pressure and temperature
2) Look at the envelope curve

BUUBLE POINT / BOILING POINT / VP

setting vapour fraction = 0 or 0.00000001 gives u the vapour pressure at that temperature
It also gives u the bubble point since first bubble or boiling point  is formed at that point

DEW POINT

Alternatively setting vf = 0.99999999 or vf = 1 sets dews point 

VP and OP  VP > OP = Flashing 
VP = OP  = boiling 
VP < OP = Trying to boil

vapour pressure greater than operating pressure (for a multicomponent mixtures) just means that the liquid is flashing (Vapor-liquid mixture).



VP and Tmp. and Molecular weight
VP decreases with molecular weight and increases with temperature

PV  = NRT 
PV X Molecular Mass = mass RT 

Also for a a biggher moecular harder to break the bonds

• Hydrocarbon dewpoint calculations are very sensitive to trace amounts of heavier hydrocarbons. 
• The hydrocarbon dewpoint for an analysis which shows an amount of "C7+" can have a very different dewpoint depending on whether the heaviest component is assumed to be (e.g.) n-C7 or n-C10.
• One should be aware of the maximum pressure for the phase envelope (cricondenbar). In the supercritical (dense phase) region, the concept of a dewpoint is not applicable. However, it should be noted that HYSYS may apply a vapour fraction of 0 or 1 in the supercritical region as an indication of which correlations are being used for the stream.