how do i make a perfectly insulating wall?
 

i would like to make a perfectly (or almost perfectly) insulating wall between 2 fluids in my energy analysis. ive made the geometry and meshed it and now im up to setup.

should i make a custom solid material and apply it to the wall? if so, what should the properties be?

obviously thermal conductivity would be as low as possible (can i make it 0?) but what about density and specific heat?

Is your interface between fluids needed for anything else? You could just remove the interface so that the two are no longer coupled. You also might just be able to change the boundary condition type from coupled to heat flux and set the heat flux equal to zero.

Setting k=0 will likely cause the solution to blow up, but if you wanted to do something like this, you should also set the wall thickness to a really large number. Either way, I don't recommend hacking the solid properties of the thin wall / thermal resistance model when there is a more direct approach.

Thanks for your advice but I'm a bit embarrassed to say that I don't understand what you mean (I'm new to Fluent). I've attached screenshots of my geometry and mesh. I hope it makes my question clearer.

You should have 1 cell zone for each fluid. If you have 2 fluids, you should have 2 cell zones.

These cell zones are distinct and they communicate via interfaces. If you do not put an interface, then the two fluids cannot communicate and there is no connecting physics between them.

Both the fuel inlet and coflow inlet fluids in this simulation is air, but at different temperatures and velocities. This is the base case as I first want to see temperature and velocity profiles. Do i still need an interface?