1 reply to this topic

[Kat]

Hi all,
I have a warning message when I start running Pro II. I simulate an airplant with 2 different thermodynamic set, one without binary coefficient and one with the binary coeffient. There is one stream going from column A with thermodynamic set 1 to column B with thermodynamic set 2. The warning message is "the thermodynamic set for this stream will be the same as the thermodynamic set for unit 2 (column B ) ".
As I understood, Pro II set the thermodynamic of a connecting stream as the same as the thermodynamic set of the downstream unit. Then it will generates the warning message when the thermodynamic set of the upstream unit is not the same as the set of the downstream unit.
1. How to fix this problem?
2. Is it necessary to have no warning messages, no errors before I start running simulation?
Thanks

Edited by Kat, 03 November 2010 - 05:15 PM.

[abhi_agrawa]

Kat,

Simulation with multiple thermodynamic method sets require special attention. Please remember that the enthalpy reported by the simulation software is actually the enthalpy difference with respect to a particular state, at which the enthalpy is zero. This reference point is different for different method sets. Therefore, to make the enthalpy consistent, in PRO-II it needs to be "RESET" from the originating method to the destination method set. For the same use the RESET block available in PRO-II.

Few tips on how to do the Enthalpy reset:

1. Do not conserve the enthalpy (even though PRO-II allows this, it defeats the very purpose of Reset block). In PRO-II, pressure is kept same across the reset block, conserve the vapor fraction if two-phase, else conserve temperature.

2. Try to reset enthalpy of the stream when the same is in single phase. When the vapor fraction is conserved, the temperature may change. Keep a watch.

Your problem is that the stream from column A is generated in method set A, whereas the column B is solved using method set B. PRO-II gives you a warning to check as the heat balance around Column B is based on a (incorrect?) inlet enthalpy basis.

While it is not essential that you remove all warning messages from your simulation, you should analyze the warnings to check if there is anything that may cause your answer to be widely different.

Hope this help you,
-abhishek