The changes are likely to alter the domain temperature field. That could be something in the porous zone, but it depends what you're doing with the film model. With a complex system you either need to know what's going to happen before turning the solver on, or build up how complex it is. The former comes with experience, the latter is how you get that experience! Turn off EWF and see what happens. The look at the flow & temperature to see what the EWF is going to do: evaporate, condense, flash etc.
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