[FRIAM] [EXT] Swirlies redux

[John Kennison]

Hi Nick,

My theory would be that in order to drain the upper bottle, the best route for the water is to move along a cyclical path.  And the best path follows a preferred rotation, say clockwise or counterclockwise.  If you start the rotation along the preferred rotation, then the bottle drains more quickly. But if you start the rotation in the opposite of the preferred rotation, the bottle takes more time to drain.


--John


________________________________
From: Friam <friam-bounces at redfish.com> on behalf of Nicholas Thompson <thompnickson2 at gmail.com>
Sent: Friday, August 4, 2023 10:05 PM
To: The Friday Morning Applied Complexity Coffee Group <friam at redfish.com>
Subject: [EXT] [FRIAM] Swirlies redux


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 ENGLISH MAJORS SHOULD NOT BE ALLOWED TO TALK about fluid dynamics.

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?

Nick
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