hello,
since it is a computer software I dont think it will influence the computation time, you can try some segments and see how the pressure drop changes till there is no significant change.
if it is a non-compressible fluid the no of segments will not affect the total pressure drop.
if it is a compressible or two phase flow I'll try segments that give a DP per segment that is not greater than 10% of the inlet pressure to the segment, but here again since it is a computer program you can shorten the segments to get a more accurate result.
regards,
roker