define the fluid volume
 

hi, i am trying to solve a reactor problam, in the middle of the reactor there is some elements that act like a porous surfaces. i am realy beginer and i have some realy simple questions. first i think i should define the fluid volume and the porous elements volume, do i right or should i define the walls volume too(their is some walls in the middle of the reactor) ? , second, should i cut the volume of the porous elements from the fluid volume(its will cut the continous of the fluid) ? my think was to model the fluid volume meshing it and export it to fluent do i right ? or maybe its more complicated.