5 replies to this topic

[J_Leo]

Hello,

 

I couldn't find a place to input the atmospheric pressure. I think the dedault should be 14.69psia. For some project sites, the atm pressure is quite different from this number. Where to set the atm pressure in HYSYS/Unisim?

 

Thank you.

 

Best regards,

Leo

[Ajay S. Satpute]

Leo,

A query to AspenTech Support provided below solution;

"
Problem Statement:

How do I change or customize the units/unit set for my simulation?

 

Solution:

Units can be found by selecting Tools | Preferences, and looking under Units on the Variables tab. The default unit sets Field, SI and Euro SI appear as black and are thus unmodifiable. To create a custom unit set, select one of these to use as a base, and select the "Clone" button.

This will create a duplicate unit set (with default name NewUser) which can be modified. The variables in the list appear as blue and are modifiable. To change the unit for any given variable, select the unit with your mouse and choose an alternate unit from the dropdown list at the top of the view.

For custom units which are not included in Hysys (such as gauge pressure with a different reference pressure for atmospheric), you can select the unit with your mouse and select the Add button. This will allow you to specify a multiplier for the default Hysys internal unit and an offset.

Supposing you wish to create a custom pressure unit which uses 12 psia as a reference pressure, you would take the following steps:
•select the menu choice Tools | Preferences
•select Units on the Variables tab
•ensure that you are using a user created unit set
•highlight the units for the variable Pressure
•select the Add button

psig_user*= .1450 *kPa + -12

It is important to note that standard conditions will not change. That is, variables such as standard density and standard liquid volume flow will still be reported referring to Hysys internal standard conditions, which are either (15 C, 1 atm) or (60 F, 1 atm).

"

Regards.

Ajay

[Zauberberg]

You can avoid all the trouble with atmospheric pressure if you use absolute pressure units (i.e. psia or kPaa instead of psig or kPag).

[J_Leo]

Alay,
Thank you very much! Actually I am using unisim right now. I will give it a try following your method. I talked to the support group for Unisim, a guy told me he was not aware of it.

Leo

[J_Leo]

Zauberberg,
We seldom report pressure in absolute values except vapor pressure.
Leo

[Zauberberg]

You don't need to report in absolute pressure figures. What I was saying is that you can easily run all simulations by using absolute pressure and then subtract 12 psia from the results to obtain the gauge pressure. Whatever works the best for you.