Helium3 in low Temp -real gas
 

Hello
I m running some simulations with He3 gas. it is a long tube (10 m) A=14.5 cm^2 filled with this gas. the temp of this tube is 2K BUT at the both ends of this tube I apply 70K . The tube is closed . when i run simulations with temp of the ends=20K and pressure inside =0.085 bar i had really good results. but now running the model with new boundary conditions (70K at the ends, 2K in the tube -15mbar ) the results are not so good. I m using the k-e turbulence model.
I used as heat transfer the Thermal energy and things get better. I noticed that at the ends the Reynolds number is very low. ~100. something is wrong.
It looks like there is very little gas at the ends and goes really fast ~100m/s.
any suggestion if I was clear enough? i tried also other turbulence models for low Reynolds number (sst etc ) but with no success.
thank you

What is driving the flow?

He3
 

In the 10m tube there is always a heat load of 2K while at the ends a thermal load of 70 K is applied. so I think the answer to your question if i m not wrong is the buoyancy and the convection.

This is so far out of my area of expertise that I have no idea what to expect from this flow. What is the Rayliegh number? Is the flow really turbulent?

Do you want steady state or transient results?