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Hello, my name is Sergio and I have been learning Comsol via the tutorials; I managed to finish the tutorial of Displacement Ventilation succesfully. Now I'm trying to build a model based on the latter, I built it , but when I compute it the program encounters the following problem:

Failed to evaluate variable.

- Variable: nitf1.rho
- Geometry:1
-Domain:1
-Feature:Stationary Solver 1(sol1/s1)
-Error:Failed to evaluate variable

In a recent Forum I read that nitf1.rho is used so one automatically uses the correct density for the given temperature, so this variable is a density function, I assume. My question is, since the air´s density I want to model is .92 kg/m3, and Im going to add a volume force to my model, in the displacement ventilation tutorial the indication says to specify the vector F in z as -g_const*nitf1.rho .

What units does nitf1.rho have?

If i want to add the volume force with my constant density value, do i type -g_const*.92 ?

Thank you very much for your time !