[nagimov]

Hey guys,
I have the following problem:
Cold helium flow (5 K / 3000 Pa) flowing in inner steel tube.
Warm (300 K / 1 atm) air is surrounding outer tube.
Vacuum insulation with low-pressure helium (1 Pa) is located between outer tube and inner tube. The length of double pipe system is 10 meters.
The problem is just to solve this double pipe heat exchanger case.
I created fluent case (see link for picture http://ngm.me/1eu5f) and I am getting some strange results: outlet He temperature and minimal shield temperature does not depend from He pressure in vacuum insulation. This takes place independently from radiation model.
Can anyone help to find the error?
P.S. I used embedded NIST real-gas model for helium.
Thanks!