Willis Heating System

[JohnW2]

Do you accept, that a heating radiator on one wall, will cause the air to rise above it, makes it way across the ceiling, then fall down the far wall - the traditional theory of how a radiator in a room behaves?

Indeed, I do accept that.

However, as things are, I'm far less able to accept that a radiator mounted high up on the wall of a tall room would result in appreciable heating of the room below the level of the radiator - and that particularly if the radiator had aTRV (hence my belief that the location of the stat in a Willis system is crucal).

 

[Harry Bloomfield]

However, as things are, I'm far less able to accept that a radiator mounted high up on the wall of a tall room would result in appreciable heating of the room below the level of the radiator

The air circulates - rises from the radiator, across the ceiling, down the far wall, along the floor, and back to the radiator. Exactly the way the Willis, circulates water. Where the stat is located, in the Willis system, will make minimal difference to it's operation, due to the rapid movement of the water.

 

[JohnW2]

The air circulates - rises from the radiator, across the ceiling, down the far wall, along the floor, and back to the radiator. Exactly the way the Willis, circulates water.

I'm afraid I just don't get it. .... Air will only 'rise from the radiator' so long as the air above the radiator is colder than that air heated by the radiator. Once the air above the radiator is up to that temp, there is no reason for any further 'rising'.

"Hot air rises" is an over-simplification. Air which is hotter than that above it will rise, but if the air above it is just as hot, there will be no 'rising', no matter how 'hot' the air.

Where the stat is located, in the Willis system, will make minimal difference to it's operation, due to the rapid movement of the water.

That's surely nonsense, whether in relation to the Willis system (above or level with the cylinder), an internal immersion in a cylinder or the radiator mounted high up a wall, isn't it? In all cases, if a thermostat local to the heating source switches off the heating as soon as the local air is 'up to temp', then there will surely be no appreciable heating of water or air below that location (of heating source and stat), will there?

 

[Harry Bloomfield]

I'm afraid I just don't get it. .... Air will only 'rise from the radiator' so long as the air above the radiator is colder than that air heated by the radiator. Once the air above the radiator is up to that temp, there is no reason for any further 'rising'.

Which ignores the fact, that the rising air around the radiator - will always be hotter. The air at the ceiling can never get to that temperature, that the convection currents can ever come to a stop. Likewise, the Willis.

 

[JohnW2]

Which ignores the fact, that the rising air around the radiator - will always be hotter. The air at the ceiling can never get to that temperature, that the convection currents can ever come to a stop.

Literally true, but the temp of the air above a high radiator would fairly quickly get mighty close to that of air which was newly-heated by the rad, such that density differences, and hence 'buoyancy', would presumably be minimal, hence only slow and slight 'rising' at most, wouldn't it?

Likewise, the Willis.

Even worse with a Willis, since the only thing 'above' the heater is then small column of water in a short length of relatively small-bore pipe. The temp of water in that pipe would very quickly rise to that at the top of the Willis heater, at which point any 'rising' would essentially grind to a halt, wouldn't it? Furthermore, as I wrote, if there were a stat in the Willis, it would quite rapidly put a stop to any rising, unless it was set to a frighteningly high temp, wouldn't it?

 

[Harry Bloomfield]

Literally true, but the temp of the air above a high radiator would fairly quickly get mighty close to that of air which was newly-heated by the rad, such that density differences, and hence 'buoyancy', would presumably be minimal, hence only slow and slight 'rising' at most, wouldn't it?

No!

Even worse with a Willis, since the only thing 'above' the heater is then small column of water in a short length of relatively small-bore pipe. The temp of water in that pipe would very quickly rise to that at the top of the Willis heater, at which point any 'rising' would essentially grind to a halt, wouldn't it? Furthermore, as I wrote, if there were a stat in the Willis, it would quite rapidly put a stop to any rising, unless it was set to a frighteningly high temp, wouldn't it?

And again - No! Otherwise the Willis would not work at all, and absolutely no one would buy one.

 

[JohnW2]

No!

That doesn't really help me to understand.

And again - No! Otherwise the Willis would not work at all, and absolutely no one would buy one.

Again, that doesn't really help me. You rather remind me of that maths teacher I recently mentioned, since you are effectively repeatedly telling me that "it works because it works", which doesn't help me at all with my "how/why?"questions.

When a Willis heater is first switched on ('from cold'), I would imagine that the initial 'rising up of heated water" will be pretty rapid. Do you really not believe that the temp of water in the small pipe immediately above the heater will rapidly come to be the same as the temp of the water at the very top of the Willis heater (maybe just a centimetre or so away)?

 

[Harry Bloomfield]

That doesn't really help me to understand.

Again, that doesn't really help me. You rather remind me of that maths teacher I recently mentioned, since you are effectively repeatedly telling me that "it works because it works", which doesn't help me at all with my "how/why?"questions.

John - With all due respect, the principle has been explained to you numerous times, by several posters, in numerous ways.

 

[JohnW2]

John - With all due respect, the principle has been explained to you numerous times, by several posters, in numerous ways.

There have certainly been numerous attempts to 'explain the principle' to me but, so far, none which I can fully understand in terms of the Physics involved.

Your recent point, that, since people buy them, they must work to at least some extent, is obviously valid but that merely reinforces my belief (which I have been stating from the very start) that I must be missing something. I like to think that I am not particularly 'uneducated' or 'unintelligent' and, for what it's worth, I've got a lot of bits of paper and 'letters after my name' which give some degree of support to that view ... so it's probably not just a case of my 'being daft/ignorant'

The problem has been that, whilst people have been asserting and re-asserting their pre-conceptions of 'the explanation' no-one has yet said anything new which helps me to understand the principles, and most people have 'sided-stepped' my questions aimed at helping me to understand their thinking/beliefs. For example, you have not yet answered my recent question ....

..... When a Willis heater is first switched on ('from cold'), I would imagine that the initial 'rising up of heated water" will be pretty rapid. Do you really not believe that the temp of water in the small pipe immediately above the heater will rapidly come to be the same as the temp of the water at the very top of the Willis heater (maybe just a centimetre or so away)?

Your answer to that question, if I had one, might help me to at least understand 'where you are coming from'!