Hello. The task is to calculate cooling of a resonator. I want to know if the cooling tube should be a solid (just setting the faces of the solid as openings or lids.. ) or it should represent a pipe as in real life and should be filled with another solid (water).

I need to understand how to set the fluid domain, lids and opening correctly.

As a result I want to see the difference of the water temperature of the inlet and outlet (water passing along the heated resonator). Thank you.