Like a lot of mysteries in science, the BN effect was introduced as one type of phenomena when it was really something else.
The way a problem is originally presented often determines how long or if it will be solved. That is often the most important part of the solution according to Einstein and others.
This _mindset_ led everyone astray for a long time. I looked at the BN effect very casually shortly before -- but not after -- I started working on particle bed displacers in free cylinder "salt shaker" Stirlings and I wondered if it might have to do with larger particles having a higher Reynolds number.
I was originally misled too.
The BN effect and the particle displacer were like skew lines in my mind. I may have thought about mixing various size particles in the displacer but I never thought about the BN effect issue, even though I had recently looked at it. I never thought that there might or might not be a nexus.
What triggered the solution was the BN effect being raised as an issue in the particle bed displacer _after_ I had spent so much time trying to deal with the assymetry of the particle displacer cycle.
The assymetry issue occupied so much of my mind it dislodged the old prejudices that got the BN effect off to a bad start.
Supposing a lot of empirical fields are like that? Supposing continuum mechanics, for example, was somehow misintroduced and that's why Newton messed up his lift equation and why they are still coming up with considerable advances in a field where everything should have been well settled years ago?
After Phelps made that spectacular victory back in March everyone was diagraming his stroke to determine the success of his swimming style. Phelps probably just tried a lot of different things to determine what worked. That's just the way things seem to get done in fluid mechanics.
In fields like structures or mechanics you will never be upstaged by some empiricist.