Leo,
A query to AspenTech Support provided below solution;
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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).
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Regards.
Ajay