Looking for a little help. I am designing a sort of recooperator. Basically it is a twin tube counterflow helical heat exchanger. There are two streams on N2 entering on oppisite sides, one hot stream (250psi & 533K) and one cold stream (250-psi & 297K).

Issue:

I have played around with different settings and I can't get the flow trajectory of the temperature fluids to not have a "gap" in the middle of the helix. Basicall the simulator shows nothing in the middle, no color, no lines, nothing. I am running the simulation again this morning with the convergence on Goals turned off to see if this is the issue.

I will post a picture if I get the same result with the "gap". Any thoughts on a setting I am over looking? Thanks.