Consider a body with fins on its outer surface, with air flowing around it. 
The heat transfer rate depends on 
* Shape and geometry of the external surface
* Surface area of the body
* Velocity of the wind (or any fluid in other cases)
* Temperature of surroundings
Modelling of the fins in this case involves, experimenting on this physical model and optimizing the number of fins and fin pitch for maximum performance.
One of the experimentally obtained equations for heat transfer coefficient for the fin surface for low wind velocities is:
where
k= Fin surface heat transfer coefficient [W/mK ]
a=fin length [mm]
v=wind velocity [km/h]
θ=fin pitch [mm]
Another equation for high fluid velocities, obtained from experiments conducted by Gibson, is
where
k=Fin surface heat transfer coefficient[W/mK ]
a=Fin length[mm]
θ=Fin pitch[mm]
v=Wind velocity[km/h]
A more accurate equation for fin surface heat transfer coefficient is:
where
k (avg)= Fin surface heat transfer coefficient[W/mK ]
θ=Fin pitch[mm]
v=Wind velocity[km/h]
All these equations can be used to evaluate average heat transfer coefficient for various fin designs.