[FRIAM] Swirlies redux

Nicholas Thompson thompnickson2 at gmail.com
Fri Aug 4 22:05:25 EDT 2023

Ok, folks. I apologize to those of you who are fed up with my kitchen
physics, but there has been a bit of a development in that saga that I want
to share with those few of you who aren’t.   Years ago, I came home for the
summer with my ears ringing with the notion that structures are formed to
dissipate gradients.  Please set aside any teleological implications of
this statement and ask the question in its most neutral form:  Do the
structures that sometimes form as a gradient is dissipated dissipate it
more quickly once the structure has been formed.   Or, as I came to
interpret it, does facilitating the formation of such a structure speed the
dissipation of the gradient.

I was the family dishwasher at the time.  I deplore washing dishes, but I
love messing around with warm soapy water, and so I started to experiment
with starting the vortex that forms *after* you pull the plug out of the
sink *before* I pulled the plug.  Quickly, it became apparent that
facilitating the vortex formation in that way GREATLY SLOWED the emptying
of the sink.  Triumphally, I wrote Steve on Friam only to be greeted by a
torrent of scatological raillery, so intense and so persistent from the
fluid dynamicists on the list that I never heard from Steve. The burden of
this raillery I have distilled into Roberts Rule of Order:  DEFROCKED

More than a decade later, I am back in Massachusetts, washing dishes at the
same sink, and the question occurred to me again. I raised it finally with
Steve, and he generously sent me the little two-bottle toy, where you flip
it over and the water drains from one bottle to the other.  As it drains,
it forms a vortex in the draining bottle, and the occurrence of the vortex
greatly *increases* the speed of the draining.  Finally, if one facilitates
the formation of the vortex by rotating the bottle a bit, the bottle drains
even more quickly.  Thus, the result is entirely different, especially if
one substitutes two large pop bottles for the ones included in the kit.

At the risk of bringing another round of raillery down on my head, I opine
that the difference has something to do with the fact that two bottle
situation is more of a closed system than the sink situation.  The test
would be to saw the bottom off both bottles and demonstrate that
vortex-formation now slows drainage.

It will be a while, though, before I can get two extra bottles to destroy.

Does anybody care to make a prediction and offer an explanation why the
results should be different in the two cases?

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