pressure drop: radiator or porous jump

luigi

I'm modeling lots of small channels connected at the ends by common volumes. For my purposes I don't need the behavior in the individual channels, just the overall flow area. So I combined them into one pipe with the correct flow area. But i want to account for the pressure drop that the fluid would experience through the little channels. How would I do this?

So far I've split my pipe into axial section and I plan on applying either a porous jump or radiator boundary condition at the interfaces of these axial sections. Are there any tips on what values i would use for the coefficients? If I've found that the pressure drop reduces by a factor of 4 for the big pipe, how could I use that for the coefficients?

Or could I use the radiator boundary condition, and for the heat transfer inputs just insert "0" in all the inputs? would that work, because the pressure part seems easier since it is just a factor?

thanks a lot