DPM approach for spray drying
 

Dear All,
I am trying to do a DPM modeling for the flow dynamics of particles and air inside a spray dryer using ANSYS Fluent. My confusion might be under rated but I am stuck with it since a week now. The model apparently seems easy and might also be but I am confused about few things. I have attached a picture of the geometry as well as geometry file if someone wants to look into it.
Firstly, I am confused about the negative volume (fluid extraction) inside the spray dryer body. Should I use certain operations like fill or enclosure in order to model the flow dynamics or does assigning the body as Fluid body is enough?
Secondly as there an outlet pipe inside the dryer, I am not very sure how to proceed with this? Should the pipe be as a solid body or a fluid body? And should I use certain Boolean operations for the pipe like subtract or not? For now all the bodies I have kept as frozen.
I would be very grateful if anyone could give an insight to this problem. I merely need an advice or a guidance to what path or necessary steps I should follow that align with my problem. I look forward to helpful responses. Thank you very much.
I have attached two pictures one from Design Modeler, and other to see Boundry conditions in Fluent.
Kind regards,
Umair Jamil