heat exchanger
 

I want to modell a straight bundle heat exchanger using CFX. It consits of about 3000 indipendent pipes. Therefore I want to use a porous media with directional loss. The porosity is easy to calculate but I am not sure about the pressure loss in the pipes. Is the pressure loss over the whole bundel equal to the pressure loss of one bundle (simply parallel pipes) or does the pressure loss sum up (3000 x pressure loss of one pipe). Or should I use the summed up fluid flow cross-sections and use this to calculate an effective pressure loss of an "effective pipe"?

Thanks in advance