Poll: Heating Concepts

[EFLImpudence]

.... If you are suggesting that an unpumped back boiler on an upper floor could successfully heat the water in a cylinder on a lower floor, then I would probably have as much difficulty in understanding that as I do in understanding how a Willis heater can heat water below its level.

I am not saying that, no one has, but what if the pipes went up even higher and then came back down to the cylinder, would that not set up a current?
However, why would anyone fit a Willis where it is not supposed to go?

Anyway - stop wriggling.

 

[JohnW2]

No. You need to concentrate on the water that is being pushed/drawn into the Willis' bottom tube, where it comes from and its temperature compared to an immersion element inside the cylinder.

All true, so long as at least some of the water in the cylinder above the level of the Willis remains 'cold', since the hydrostatic pressure difference on the two 'sides' (cylinder on one side and Willis+pipes on the other side), due to the different densities, will result in cold water from the bottom of the cylinder being 'pushed up' into the Willis, hence perpetuating a 'circulation'.

However, once that process has progressed to the stage illustrated below, the pressures on the two sides have equalised, so there is no longer any 'pushing' of cold water into the Willis - hence 'circulation' ceases. I would say that in the absence of any thermostats, the heated water would then get hottter and hotter (until it boiled), whilst sitting on top of the essentially cold water (heated, eventually, only by a little conduction).

Can you propose any way in which your 'process' can proceed any further from the stage below (other than by conduction) hence heating the water in the lowerparts of the cylinder?

 

[EFLImpudence]

However, once that process has progressed to the stage illustrated below, the pressures on the two sides have equalised, so there is no longer any 'pushing' of cold water into the Willis - hence 'circulation' ceases.

Only if you turn off the element.

I would say that in the absence of any thermostats, the heated water would then get hottter and hotter (until it boiled), whilst sitting on top of the essentially cold water (heated, eventually, only by a little conduction).

Why, in that unlikely situation will the hotter and hotter water not be less dense than the less hot water in the cylinder?

Can you propose any way in which your 'process' can proceed any further from the stage below (other than by conduction) hence heating the water in the lowerparts of the cylinder?

Yes - by turning on the element and by continued heating of the water in the Willis

 

[Harry Bloomfield]

That's just words. I need to understand how it is that it "acts in some respects as a pump".

John - I have explained the principle, numerous times. Heated water rises, exits via the top pipe, and is drawn in via the lower one.

Well, I find it hard to see that a 'Willis heater" in the middle of the cylinder would be materially different from a standard immersion in the same place, don't you?

I have already suggested that idea, as an alternative to the side mounted Willis, and yes, it would behave just like a Willis.

 

[JohnW2]

.

 

[Harry Bloomfield]

Can you propose any way in which your 'process' can proceed any further from the stage below (other than by conduction) hence heating the water in the lowerparts of the cylinder?

While ever the water at the upper part of the Willis, is hotter than the water at the top of the main cylider - then the flow, and circulation will continue to take place.

 

[JohnW2]

Why, in that unlikely situation will the hotter and hotter water not be less dense than the less hot water in the cylinder?

OK - but when thigs have reached the stage I illustrated, the temp difference, hence density difference,, is surely going to be very small,, so also will the pressure difference be very small. Circulation will therefore not 'cease' (as I had suggested) but I would expect it to considerably slow, wouldn't you?

In any event, I was talking about a hypothetical, and unrealistic, situation in which there were no thermostats. In practice, there obviously would be a thermostat, which takes me back to the fact that its location is crucial. As far as I can make out, all of the Willis heaters use standard 11" immersions with their standard associated thermostats. If that's the case, then most of this discussion becomes moot, since the heater will be turned off as soon as water at its level is 'up to temp'', wouldn't it?

 

[JohnW2]

John - I have explained the principle, numerous times. Heated water rises, exits via the top pipe, and is drawn in via the lower one.

Indeed - so long as the average temp in the Willis+pipes is higher, hence the average density lower, than in the full height of the cylinder

I have already suggested that idea, as an alternative to the side mounted Willis, and yes, it would behave just like a Willis.

If (as EFLI has seemingly agreed with me) a 'bare' Willis heater inside the cylinder would be no different from an internal immersion at the same location (after all, essentially the same thing) then what you say must mean that it is the pipes attached to the Willis which make a difference, and I'm still having difficulty with that concept ...

... as I wrote before, I would expect heated water coming out of the top of the Willis to rise 'to the top' whether there is a pipe or not. As for the 'bottom pipe, the 'pressure difference' (which drives the circulation) would surely actually be greater at the lower inlet to the Willis than at the end of an attached pipe close to the bottom of the cylinder - so I would have expected addition of that pipe to actual 'impair' circulation. Asalways, what am I missing?