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Mass conservation violation in a stirred reactor

Posted Mar 18, 2026, 12:01 p.m. EDT Computational Fluid Dynamics (CFD), Chemical Reaction Engineering, Mesh Version 6.2 0 Replies

Onur Can Boy

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Hi,

I would like to simulate a stirred reactor for an aqueous reaction. The stirrer is a huge plate, and the reaction occurs on the surface of this plate. For the flow regime, first, I solve the Frozen Rotor problem. Then, I use the Frozen Rotor solution as the initial condition for a time-dependent study. To study mixing and reaction, I use the flow field obtained from the time-dependent simulation, and I solve another time-dependent study

I am considering an irreversible reaction, for example: A → B. At some point, the concentration of A starts to accumulate inside the reactor, while the concentration of B begins to decrease (which is physically impossible). The trends appear to be very symmetrical. If I disable the reaction, the concentrations becomes stable. There is no accumulation in this case.

I asked ChatGPT about possible reasons for this behavior. I have tried changing the mesh density, adjusting the time steps, and switching the convective term to conservative form (which led to a numerical instability/explosion), and none of these worked for me.

Therefore, I would like to ask whether you have encountered this type of problem before, and what the possible causes or solutions might be.

Thank you for your time and support.

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