Creating fluid flow source within a meshed body
 

Hello, I am modeling a twin screw reactor and well what i have to do is to model the reactor with some particle inside which after following reaction gives out gasses. I am working with the particle insertion but in the mean time i tried to work with the idea that on course of time gasses will evolve from the system. Is there a way to do so? I tried to make some 1d sketches inside the body so that it can have boundary condition of velocity or mass inlet but when we mesh its taken to be a part of the part body. I want to place certain inlet with heated air coming out, along with air coming in from the actual inlet of the combustion chamber.
Any one did anything similar?