Hello I'm a new user with comsol but i know my way around,
I need to solve a heating problem in a closed space.

In order to do so I'm using comsol multiphysics - incompressible naviar stokes and convection and conduction.

After defining the geometry, boundary and subdomains I solved the heat only and then the whole problem, I got an error something like sqrt(-1).
see file at http://rapidshare.com/files/361389700/didnt_work.mph

Where did I go wrong?

And another question:
If I'm trying to use a fan and I want to set the boundary I have only velocity boundary that fits,
But I need to enter a source (Q) to the equation so how do I do it?

I'm attaching the file that i made

Thanx!!!!!!!