Heterogeneous Reaction PFR Bug

Discusses use of COCO, the process simulation and modelling software suite from AmsterCHEM, downloadable from http://www.cocosimulator.org

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Heterogeneous Reaction PFR Bug

Postby antoinetonee » 31 October 2022, 07:05

Hi all,

I'm encountering a persistent problem in the simulation of heterogeneous reaction in PFR. The simulation file is attached. Similar to that in a previous thread, I put max(0,X("component name")) to avoid the value in question from getting below zero. Instead, the simulation gives error message as follows:

Unit "PFR_NTA": calculate failed for unit PFR_NTA: Failed to obtain reactionRate for reaction NTA_N2: Failed to calculate reactionRate: CalcReactionProps failed using property package NTA_NH3: Failed to obtain fraction for phase Vapor: no values set for fraction, phase Vapor

What's wrong with my simulation? Why does all the sudden it failed to calculate the fraction (the reactions are entirely in vapor phase, so I suppose this error shouldn't be there in the first place)? Thanks in advance.
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Re: Heterogeneous Reaction PFR Bug

Postby jasper » 01 November 2022, 09:59

You can see the reason if you calculate the unit (which fails) and go to the Profiles report:

Screenshot 2022-11-01 103957.jpg
Screenshot 2022-11-01 103957.jpg (156.55 KiB) Viewed 11805 times

Your integration fails and pushes values to NaN, which is CAPE-OPEN-ese for numbers are not available. At first glance, I suspect your problem is 0^-0.5 for X["Carbon monoxide"] dropping to zero. Zero to the power of a positive number is defined, but zero to the power of a negative number is not.
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Re: Heterogeneous Reaction PFR Bug

Postby antoinetonee » 30 November 2022, 06:50

Apologies for the very late response. Thanks for the answer, I've also found and fixed the faulty rate equation.
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