input variables

[thubelihle]

Hi. l notice l can't vary number of stages as an independent parameter using the COCO parametric study. Same applies for the heat exchanger outlet temperature can not be specified as an independent variable to vary on the parametric studies. Thanks

[jasper]

You can vary many things - but they have to be input parameters. To make the number of stages an input parameter, you have to tell ChemSep to do so.

Untitled.png (26.19 KiB) Viewed 17644 times

[jasper]

The heat exchanger outlet temperature is only an input parameter if the heat exchanger has Type = Temperature

[thubelihle]

Hi. l notice l can't vary number of stages as an independent parameter using the COCO parametric study. Same applies for the heat exchanger outlet temperature can not be specified as an independent variable to vary on the parametric studies. thanks. The bottoms flowrate is one of specifications and l exposed it as an input parameter, but does not converge using a controller

[thubelihle]

I even try to put a value of 0.6 for bottoms flowrate but l try to solve it automatically changes this value

[jasper]

The number of stages is an integer parameter - only real valued parameters can be controlled (otherwise the solver would need to solve for an integer value). For a parametric study the same holds at the moment, only real values can be modified.

Not clear on which heat exchanger outlet temperature you mean - can you attach an example?

The problem with the bottoms flowrate is of a complely different nature - something went wrong with the unit of measure. The document contains

<dimension parameter="bottoms flowrate">
<dimension>
<quantity name="Amount">1</quantity>
<quantity name="Time">-1</quantity>
<quantity name="LightIntensity">inf</quantity>
</dimension>
<flags>OnlyMole</flags>
<select dimension="Amount">mol</select>
<select dimension="LightIntensity">cd</select>
<select dimension="Time">s</select>
</dimension>

and subsequently all unit conversions on this value are nonsensical. Unfortunately fixing the issue requires editing the xml, as COFE is rather persistent in remembering unit of measure preferences.

I am attaching the repaired version, but I would like to investigate how this issue came to be - where did you get this column from?

Luyben_edited.fsd

Corrected file

(33.75 KiB) Downloaded 909 times

Thanks.

[thubelihle]

It’s from Distillation design n control by Luyben 2nd edition example on chapter 3. Thanks

[thubelihle]

hi jasper, attached is the distillation column with a controller. it does not converge but looking at the specification, the set point is reached, but still it gives the error message . thank you for your help.

[jasper]

The same problem is present again - did you use your document or my corrected Luyben_edited as a starting point for this one?

[thubelihle]

yes l just did and l am facing the same issue. thank you, see attachment.