Sir, the reference Paper upon which I am working have mentioned that..The receiver is considered symmetric about its vertical axis. Therefore only a half section of receiver has been considered for numerical modelling.nNow the Boundary conditions used by the Author are;n1) The fluid flow have a uniform velocity at the receiver inlet..here I have no problem.n2) Zero pressure gradient condition is employed across the outlet boundary..no problem.n3) The top half periphery of the receiver is subjected to some radiation Flux..no issue.n4) The bottom half periphery of the receiver is subjected to Some radiation Flux multiplied by a concentration ratio...In this only I have a Doubt Sir. If the Geometry is symmetric about the base plane, so it should not be a Wall type. It should be of Symmetry type. But, if am changing it to symmetry type, then i am unable to apply any boundary condition.nAlthough in the reference Paper, they have clearly mentioned that..Symmetry boundary conditions are applied for the receivernplease sir, guide me !!nThanks&Regards,nRishikesh Kumarn