total pressure in CFX
 

I use CFX 5.7. I model the flow in the geometry which consists of two body: the circular collector with the vertical chimney connected in the middle of the collector. There is the volumetric heat source in the collector. The collector perimeter is openned, then the heated air flows from the perimeter towards the vertical chimney. When I model this system, I used the boundary conditions like one example I read, but cannot recognize which example now. I specify the Open boundary condition with zero total pressure and 380K at the perimeter of the collector. At the chimney outlet, Outlet boundary condition with averaged zero static pressure is specified. The remaining surfaces is set to adiabatic wall. The results seem reasonable. However someone suggest me that if the total pressure in CFX is defined as conventional, the air flows from the location with low total pressure to the higher total pressure, which cannot be possible without the pump. Do anyone have the explanation? Thank you very much for your kind consideration.

Atit