problem meshing two interacting volumes
 

my case is a pipe passing thourgh a box. I want to model the propagation of radiaton inside the box and model flow in the pipe but i need also propagation of radiation in the pipe. I made a hole into the box that means there is face in contact with the outwall of the pipe. I have a problem merging those two faces hoping to get radiatoion disptribution of radiation into the pipe but have a boundary so that when I model water only inside the pipe. Does any body have an idea? When I tried Fluent only modeled each volume separately I am not getting the radiation to pass though pipe wall even though it is transparent.