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"Restriction" rapidly diminishes the "area available for transit". One large pipe is best if what you want is Flow, related to viscosity and demand, etc. It really isn't critical the cross-section, but the available gross area.
Several small pipes can perform as well as one big one. Introducing another variable, Ice, changes everything. The small openings pack first, but may remain open if demand is, say, Idle or flight idle. Increasing demand may be the same as further restricting the cross section with constant flow. I don't have any more information than anyone else, and quite possibly less than some, but the bypass, while preventing a case that Boeing proposes, eliminates heat exchange. The GE has a recirc feature that may make the ice more susceptible to transit, eg forestalling refreeze.
If the Fuel is VERY cold, it may cool the Oil too much, also a bad thing.
While it's interesting to discuss these problems, my basic concern is the same as Phil Gollins. I'm a convert to ETOPS and have high expectations, I'm no engineer, but I dislike the lack of information forthcoming from the authority. So far, I like Boeing's approach better than the other's.
Last edited by airfoilmod; 6th Mar 2009 at 20:19.