4 replies to this topic

[ari]

dear all,
i found something unusual ( weird ) when i tried to calculate heat of vaporization ( Hv ) using Hysys ( hysys 3.0.1 and 3.2 version ). when i plot Hv vs Temp, hysys show a constant value, it mean that Hv is not depend on temperature, but depend on pressure ( the graphic build using databook facility in hysys ),
when i calculate it by using aspen, pro ii or chemcad, the simulation result show that Hv depend on temperature not pressure
please give any reason or answer ?

[gvdlans]

The heat of vaporization is the amount of heat required to convert a unit mass of a liquid at its boiling point into vapor without an increase in temperature.

So if you fix the pressure the temperature cannot be varied since that is the boiling point of the liquid at that fixed pressure. The heat of vaporization should definitely vary with pressure (lower heat of vaporization at higher pressures, heat of vaporization becomes zero at the critical pressure).

So maybe following is the case: where you say that as per Aspen etc. Hv varies with temperature you actually mean that Hv varies with boiling temperature (and therefore with the system pressure).

[Zauberberg]

Hello Ari,

Similar question has been raised at Eng-Tips forum recently, you might want to look for some really nice explanations:

http://www.eng-tips....d=187927&page=1

[smalawi]

hi,

the heat of vaporization is estimated deferantly for pure compoents and mixturs. for pure compontents its simple. for water the heat of vaporization as can be seen in the phase diagrams gives and dont need explaning here.

for mixturs and specificly hydrocarbon oils the thermodynamic package is a critical slection.

every simulation software is deferent and results are not the same. for hysys using PR EOS/ LK or GS gives significant deveation in results, which in heavy oils and VDU simualtions are critical.

also at high pressures the choise is important. one has to know that the deviation varies and what equation to use

[Mohit]

Hello Ari/Smalawi,

Can you please tell me how to calculate heat of vaporization of pure componet and mixtures in Aspen Plus.

I am new to Aspen plus and have no idea where can I find it.

Any help would be appreciated.

Thank You.

Mohit