[CFDJonas]

Hello everyone again,

I'm trying to switch to the stiff chemistry solver, thus my understanding is I have to swtich from DEFINE_VR_RATE to DEFINE_NET_REACTION_RATE (or DEFINE_CHEM_STEP). My problem is, when I hook the DEFINE_NET_REACTION_RATE the solver interrups even before going into the UDF once, because of a "Non-physical Specific Heat = 0.000000e+00". Even when I set the rate for each species to zero/or have a Message output in the first line of this UDF, nothing happens.

I also tried to achieve my goal by using the DEFINE_CHEM_STEP but then I have to assign new mass fracs. This is a little bit inconvinient as my rates are molar rates. However I managed to get some kind of result by calculating the concentration, calculating the rate, and then adding up the rate*CURRENT_TIMESTEP to the last concentration and then convert back to a mass fraction. However this does not deliver correct results (the CURRENT_TIMESTEP is always 1 so this multiplication is kinda weird to me).

Does anybody have a little bit of experience about chemistry using the stiff chemistry solver? I really don't know how to approach this problem.

[study_CFD]

Have you solved it? I have a similar problem