Connections between solids in Flow Simulation

Hi,

i am trying to simulate a water cooled element (see attached sketch)

Solid 1 is a heat source, Solid 2 is made of a different material and the connection between these 2 is not ideal. Water is flowing (direction: through the paper) and the air is still. So it's the water that cools the whole system. the simulation itself is going good.

But i would like to add a thermal contact resistance between Solid1 and Solid 2. But i can't find how to do this.

Is it possible that i have to swap to a different kind of simulation to do this?

Hopefully someone can help because i have been searching for a solution for a while now.

Thanks in advance.