DWSIM exothermic reaction (NH3 synthesis) is cooling in plug flow reactor
Simulate chemical processes using advanced thermodynamic models
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Hi
Word of introduction: I'm new to DWSIM and my English is my second tong.
Like WTF is going on. I've created reactor based on 1979 paper (and some other data as rules of thumb from other papers like 'catalyst void') and everything looks and feels right until I run simulation and exothermic reaction of creating ammonia is sucking all energy until the stream reaches 25deg.C
This is my formula:
exp(33.8776-(19654.2874/T))x(0.0049xR2xR1^3-P1^2)
P1^1.1xR1^1.35
(I've change multiply sign for x because site architecture is messing with formula)
and below is graph from my reactor. And to wrap this up: anything that I could change I was messing around in order of magnitude and nothing was yielding any results
Last edit: Eryk Łopata 2025-05-14
To me, this term seems incorrect: exp(33.8776 − 19654.2874 / T)
The equation appears to be numerically unstable: as T → low, the exponential term increases rapidly, which accelerates the reaction, consumes the reactants faster, and drives ammonia formation — but the heat release seems either poorly implemented or completely ignored.
It’s also unclear whether the user may have accidentally swapped reactants and products (i.e., reversed the stoichiometry), or if the reaction enthalpy (ΔH) is actually correct.
From the start, the simulation behaves as if the reaction were endothermic, which contradicts the well-known fact that ammonia synthesis is highly exothermic.
If possible, please attach the simulation file so I can take a closer look. It would help greatly in diagnosing whether the issue lies in the reaction kinetics or thermodynamic setup.
Also, I noticed expressions like P1\^2 being used. It's unclear whether this is meant to represent a division, an exponentiation, or if it's just an improvised notation (\ do not exist!). If this is intended as a power term, make sure the syntax is compatible with the simulation environment | scripting formula.
Sorry,
I seems that if I paste my formula directly somehow the division sign is added. I've corrected it
Above I've corrected formula and I've added simulation file. The paper that I was using is below. To make it easier for myself I've hard writhed equilibrium constant of reaction as 0.0049 after exponentiation
Last edit: Eryk Łopata 2025-05-15