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Undefined variable error in Chemistry module

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Hi, I'm modeling a heterogeneous surface reaction with the Chemistry module. For a reaction A(g) + S(ads) <=> A(ads) (where S denotes a surface site), the rate expression for A(g) must be equal to the change in the number of moles of A(ads) divided by the reactor volume. So since the concentration of A(ads) is constant over the catalyst surface, the rate expression for A(g) should be the rate expression for A(ads) divided by the distance from the catalyst surface to the bulk solution, which is 0.01 cm. So my rate expression for A(ads) is chem.r_1 and the rate expression for A(g) is -chem.r_1/0.01 cm. On computing the reaction, I have the following error message:

Undefined variable. -Variable: comp1.cS_surf -Geometry: geom1 -Domain: 1 Failed to evaluate Jacobian of expression. -Expression: dvol_spatial* comp1.tds.reac1.R_cCO2 Failued to evalute Jacobian of expression. -Expression: (comp1.tds.react1.R_cCO2test* (comp1.cCO2))* (dvolspatial)

The error message will go away on changing the rate expression for A(g) to a constant value. Any thoughts on what may be causing this issue?


0 Replies Last Post Mar 25, 2020, 2:32 p.m. EDT
COMSOL Moderator

Hello Kelsey Levine

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