[B_R_Khan]

Hi,

I am doing 2D and 3D analysis of counter current concentric tube heat exchanger
Cold water is flowing from outer tube while hot oil is flowing from inner tube
I used mesh interface at the place of inner wall between water and oil
However I am not getting different temperatures at inlet and outlet for both 2D and 3D analysis (see pictures for reference). I am getting a small strip of temperature variation around interface but the temperature for inlet and outlet remains same for both water and oil. I have not used multiphase in this problem as both are liquid fluids. Tried it for cold and hot water, changed inlet velocity, changed boundary conditions but still same profile comes in the end.
Can anyone explain why is that so?

P.S: Attached pictures show 2D analysis done without symmetry and 3D analysis done with quater symmetry.