[banerji]

My case: I have a pipe passing through a box, the box just contains air. I there is a source of radiation on one wall of the box which propagates into the box and it should also pass through the wall of the pipe to interact with the fluid in the pipe. I meshed the pipe and the box around it separately. and I do not know what to do so that radiation can pass through the wall of the pipe but water not go into the box. How would I make the two meshed two interact. I tried to unite 2 faces diving the meshed but gambit shows error.