using porous instead of fins
 

hey guys
I want to simulate a heat exchanger (simple pipe with fins) under external flows.
because of mesh problems I cant simulate all of the fins so I thought maybe its possible to use porous zone instead of fins, my question is am I right?

and if its possible I don't have any ideas about porous inputs!
I found these in forums but I don't know how to use them, I don't have any particles


Rv = [150*(1-e)^2/phi^2*D^2*e^3]


Ri = [2*1.75*(1-e)/phi*D*e^3]


Nomenclature:
Rv: Viscous resistance
Ri: Inertial resistance
mu: Viscosity
rho: Density
e: Porosity of the medium
phi: Sphericity of the particles making the medium (can assume 0.75)
D: Diameter of particles making the medium
v: Average velocity