Fair enough, but I didn't think that's what EFLI was talking about, since he has been talking about the need to 'draw more water in' to replace water that has 'gone somewhere' - which obviously would not be necessary in the case of the glass of water.
Exactly - and, as I've said, much the same could be achieved with the same (tedious) "... continually planned in advance, or via an extensive program." with a cylinder and a couple of immersions (upper one for low volumes and lower one for large volumes). The only difference is that, as bernard mentioned, the immersion method involves hot water rising from an immersion partially mixing with cooler water (which, at least for modest volumes, is not the case with Willis), but with two immersions to choose from, I really don't think that would be much of an issue.
How can it not be necessary? How can some water go somewhere if none replaces it?
It can't - that's why, unlike Harry (or yourself), I personally wouldn't say that any water had "gone" anywhere. Harry was talking about the 'tall glass experiment' I mentioned and, although hot water had 'risen up' from bottom to the top of the glass (and other water had fallen from top to lower), no water had 'gone' anywhere. The volume of water in the glass was unchanged, so no 'replacement' was required; two 'bits of water' had simply 'swapped places'.
As said, this is all about words. We have to accept that you and I have different understandings of "circulate". To me, it means 'to continuously go around and around (a circuit/loop) in 'circles' " - as in CH, car cooling, refrigerator, the human blood "circulation" etc. - and I would not use the word to refer to movement of a fraction of 'one circuit' (of a circuit/loop). To you, it seems to mean any movement, however little, within a circuit/loop, even if a lot less than 'one circuit'. I think we have to live with that difference between us.
I think that (at last!) I now more-or-less understand how the system works.
Seemingly about 4.5 litres/5 minutes (0.9 litres/minute) for a 3 kW Willis. That corresponds pretty well to 'energy calculations'. Your suggested 35L in 10 mins would not work for a 3 kW heater - that would imply that I could heat my 140 L cylinder in just 40 mins whereas, in reality, with a 3 kW immersion it takes about 2.5 hours. I previously posted the following, which you will find more-or-less identically for many products ...
Not "without water moving around", but nor with what I would call 'circulation'. Heated water will rise out of the Willis at the rate of about 0.9 L/minute. That hot water, necessarily 'at the top' of the loop/circuit (since it is hot that all other water) 'pushes down' ('gravity', if you wish) on the water in the cylinder, causing 0.9 L/min of cold water to exit the bottom of the cylinder and return to the Willis - what you call 'drawing in' more cold water. After 10-15 minutes, 9 - 13.5 litres (per above quote, not your "35L") of hot water will be at the top of the cylinder and, of course (since its an essentially 'closed' system (give or take the expansion pipe, to which nothing happens), the same volume of cold water will have "moved" from bottom of cylinder to Willis. If it were a 140L cylinder, then this would effectively mean that about 10% of 'one circuit' of what you would call 'circulation' had occurred in 15 minutes.
As above, our figures differ - per the one's I've cited, it would be 0.9 L/min - but only until a total of 9-14 L (<10% of contents of a 140 L cylinder) had 'flowed'.
It would certainly eventually heat the whole cylinder, with (if there were no heat losses) 'water movement' simply being a scaled-up version of the figures above - and eventually a total of approaching one 'circuit' of what you would call 'circulation'.
As I've said, what matters to me is that I have come to understand how the Willis system works, and I'm not particularly interested in a discussion about the 'words', and nor do I find that useful. On the contrary, it was all the talk (hence my thinking) about 'convection' and 'circulation' that resulted it in it taking be so long to come to an understanding of the Willis system.
Very wise
This thread which I started was very interesting and intriguing until, after the intrigue had been resolved, it turned into a series of exchanges about 'words'!
Very wise
I thought you had 'bowed out'Note :- I did not concede that you were correct in your misunderstanding of convection currents
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