Non-isothermal pipe flow in Comsol

Hi all,

I am trying to figure out the theoretical background of this module since, instead of using a 3D pipe flow model, it cuts down to 1D pipe flow.

1. Does it mean this module essentially equal to solving partial differential equations under given boundary conditions? If this is the case, what's the difference between this and 3D model, or, what's the limitation of this module?

2. Can't show the velocity/temperature profile along the cross section, but the mean velocity?

3. Can it evaluate log mean temperature, which depends on the velocity?

Thanks!