Spiral coil heat exchange
 

Hi, I'm new to Fluent and trying to model a spiral coil (with cold water flowing through it) inside an enclosure with hot air flowing normal to the coil. I have made the geometry and mesh but I am unsure about the boundary conditions to use. I was hoping to use coupled boundary conditions however this option doesn't appear and it says I need to state a wall temperature or flux. I have also tried merging the coil and enclosure in geometry however this removes the water fluid zone in Fluent. Does anyone know how to model this? (I am trying to find the average nusselt number on the inside and outside of the spiral coil and the temperature of the water around the coil).

Sorry if this is in the wrong section, I wasn't sure if it would come under meshing or Fluent.

Thanks in advance :)