Counterflow in 2d Axisymmetrical problem
 

I have a simple counter flow problem with metal wall in between and conjugate heat transfer.

The problem is that Fluent is unable to solve 2D axisymmetric with counterflow.

I am not getting convergance at all.

Does anyone have experience with 2D axisymmetric in counter flow ?

I don't think that fluent is, in general, unable to simulate such a flow.
Give some detail information about your setup, maybe we can figure it out.

The problem is simple enough.
There is a 25mm rad pipe with air flowing from left to right.
It has 10mm thickness and made of steel.
There is an outer pipe of 50mm rad with water flowing from right to left.

If I model the flow with air/air. It runs very well. If I use air/water, there is no convergance.

The air is at say 500K and the water is at 700K. Velocity for air is 5m/s and for water is 0.1 m/s

You can use any values, I am interested in the concept of counter flow with different species.

I think the problem in your case is the large difference between the timescales of heat transfer in the different species.
Not only is this a conjugate heat transfer problem (because of the solid wall), in addition you are using different fluids, one with a small heat storage capacity (air) and one with a high storage capacity (water).

You will need to apply a high timescale factor for the solid and the water to obtain convergence.
Actually this is the procedure in CFX, but there must be something similar in Fluent.
I am sure you will find it if you search for conjugate heat transfer.