Willis Water Heating System

[EFLImpudence]

Had not seen your latest post when written.

Ok, in this simple loop if we could engineer it, do you think the lower density white part (either a bubble or lighter water would try to rise (and/or the other side would try to fall because of gravity) causing a circulation of the water and if continuously replenished it would maintain that circulation?

 

[Harry Bloomfield]

I've never really thought about it but, as you imply, warmer water can only rise ('within the water which is there') if cooler water can fall ('within the water which is there'), which is what would usually happen, even in a pretty small pipe. However, if a situation arose in which the pipe were "small enough to prevent convection" (which, I guess, would, at the extreme, probably would be the case with a 'capillary tube'), I can but presume that the warmer water would just be 'stuck' at the bottom, because it couldn't 'rise' (in the way you seem to be envisaging) if cooler water could not correspondingly 'fall.

John, how do you think an hot air balloon works? Heated air rises through the rest of the cooler air, capture that hot air in a balloon, then hot air plus balloon will rise. Likewise, the water will move upwards, drawing cooler water behind it. The only place it can go is into the top of the cylinder, assisted by the cold water being removed at the bottom of the cylinder.

 

[JohnW2]

John, how do you think an hot air balloon works? Heated air rises through the rest of the cooler air, capture that hot air in a balloon, then hot air plus balloon will rise.

Sure, but that's because the balloon is 'within the atmosphere' and contains air which is warmer (hence less dense) than the surrounding atmosphere, and hence rises through the (cooler, more dense) atmosphere - that's 'buoyancy'. If it reached the (hypothetical) 'top of the atmosphere', it would obviously stop rising, since there would be no atmosphere above within which it could be 'buoyant'. The crucial point is that 'rising due to buoyancy' can only happen within the existing mass of gas (or liquid, in terms of what we are discussing)

Likewise, the water will move upwards, drawing cooler water behind it.

As above, I can't see how that can/could happen. 'Rising' (due to buoyancy resulting from differential densities) can only happen within the existing mass of water - the water cannot just 'move up' ouside of the existing mass of water ('drawing more water in').

Kind Regards, John

 

[EFLImpudence]

What would happen if the balloon were in a big vertical tube?

 

[JohnW2]

Had not seen your latest post when written.

Ok, in this simple loop if we could engineer it, do you think the lower density white part (either a bubble or lighter water would try to rise (and/or the other side would try to fall because of gravity) causing a circulation of the water and if continuously replenished it would maintain that circulation?

View attachment 234862

No. The bubble of air, lighter water or whatever would rise to the top and then stay there, wouldn't it? I can't see what would make it go down the 'other arm' (despite being 'buoyant' within that arm), resulting in 'circulation', can you?

Apart from anything else, if there were 'circulation' then (particularly if it were an air bubble), I think you might have invented a 'perpetual motion machine'

Kind Regards, John

 

[JohnW2]

What would happen if the balloon were in a big vertical tube?

Provided the tube were big enough to allow displaced air to slip down beside the balloon, I would not expect the tube to make any significant difference.

If the balloon were 'a tight {'air-tight'} fit' in the tube, and the top of the tube were 'closed', then the balloon would obviously not be able to rise very much at all, because of considerations of pressure. It would stop rising when the increased pressure in the tube above the balloon became equal to the buoyancy ('lift') due to the warmer, lower density, air within the balloon.

Kind Regards, John

 

[EFLImpudence]

No. The bubble of air, lighter water or whatever would rise to the top and then stay there, wouldn't it? I can't see what would make it go down the 'other arm' (despite being 'buoyant' within that arm), resulting in 'circulation', can you?

...because it is replaced with new hotter water at the original position

Apart from anything else, if there were 'circulation' then (particularly if it were an air bubble), I think you might have invented a 'perpetual motion machine'

Not really, it is being driven by the element using power.

 

[EFLImpudence]

Look at my diagram the other way round.

Instead of a 'bubble' of lighter material, on the other side is now a heavier weight.
Do you think this weight will fall:

a. only if water can pass the sides of the weight, or
b. if water cannot pass, it will stay where it is, or
c. if water cannot pass, it will still fall by 'rotating' the water?

 

[Harry Bloomfield]

Sure, but that's because the balloon is 'within the atmosphere' and contains air which is warmer (hence less dense) than the surrounding atmosphere, and hence rises through the (cooler, more dense) atmosphere - that's 'buoyancy'. If it reached the (hypothetical) 'top of the atmosphere', it would obviously stop rising, since there would be no atmosphere above within which it could be 'buoyant'. The crucial point is that 'rising due to buoyancy' can only happen within the existing mass of gas (or liquid, in terms of what we are discussing)

So the hot water will rise out of the Willis and having no where else open to it, it will cool slightly and fall down into the top of cylinder. Of course it will draw cool water in at the bottom from the cylinder as part of that flowing process - there will be a circular flow around the circuit.

 

[JohnW2]

...because it is replaced with new hotter water at the original position

Ah, I took your diagram too literally (no heat source) particularly because I took (probably incorrectly) your mention of 'bubble' to mean an 'air bubble'.

However, I think this may well be a "Eureka! Moment"!

I think that we (certainly I) have probably totally confused ourselves with all the talk about 'convection' and, in particular, "circulation around convection loops", because I now don't think that has really got anything to do with it.

Referring to your diagram, if one continues to heat water at the position of your 'lower density white part', then all the newly heated water would rise up that arm of the 'loop', progressively increasing the amount of hot water at the top of the loop (in both arms). Although the heated water in 'the other arm' of the loop would still be 'at the top' of the water in that arm (and could not fall 'by convection', since the water below it was cooler), the bottom of that region of hot water in that 'other arm' would gradually be 'forced down' by the increasing amount of hot water - despite the fact that convection/buoyancy was keeping uit above the cooler water below.

Given that, in the actual situation we are discussing, that 'other arm of the loop' is the cylinder then, yes, this appears to be (at long last) an explanation of how the cylinder gradually fills with heated water from top downwards. QED!

Put another way, this is absolutely nothing to do with convection or 'circulation in loops' but is merely a consequence of the fact that as progressively more hot water is created and 'rises' to the top of the 'loop', this increased amount of hot water has risen to the top of both 'arms' of the loop, one of which 'top arms of the loop' is the upper part of the cylinder. The important thing (per all the confusions) is that nothing is 'circulating' - the hot water is simply staying at the top of the loop (both 'arms') just as it should - and all the talk about 'water rising and causing more to be drawn in' has really just confused the issue even more!

Phew! Unless I've got this wrong, it's fairly satisfying to have at last 'got there' (since we all know that, because it 'works', there had to be an explanation!). I may award myself a drink!

Kind Regards, John

 

[JohnW2]

Look at my diagram the other way round.

No need - I think I have just 'got there' - see recent post

Kind Regards, John

 

[JohnW2]

So the hot water will rise out of the Willis and having no where else open to it, it will cool slightly and fall down into the top of cylinder. Of course it will draw cool water in at the bottom from the cylinder as part of that flowing process - there will be a circular flow around the circuit.

As I've just written, I think that I have 'got there', but I think that we have probably all confused ourselves (certainly me) with all the talk about convection, 'circulation' and 'drawing water in'.

Kind Regards, John

 

[Harry Bloomfield]

Can I suggest a little experiment with some plastic pipe as per EFL's diagram? Fill the pipe up with water, but add some coloured dye at one end, join the two ends, formed in a vertical loop, then warm up one side, where the dye is. The dye will rise up over the top of the loop, and fall at the cooler side.

 

[Harry Bloomfield]

As I've just written, I think that I have 'got there', but I think that we have probably all confused ourselves (certainly me) with all the talk about convection, 'circulation' and 'drawing water in'.

Kind Regards, John

Phew

It is certainly convection, convection currents in water.

Next problem - when hot water is drawn, what stops it drawing hot water from both the cylinder and cooler water through the Willis?

 

[bernardgreen]

Mr Willis has a lot to answer for......