The difference in resistance due to the higher element temperature would be very small and so amount of heat available would only change very minimally.
Yeah, it would certainly see a small change in the heat available.
They are now. The "bulky insulation" was for adding to cylinders that had none.
Yebbut... if the resistance rises due to the element getting hot, it would take longer to dissipate the 100kW you originally proposed, and power might fall from 100kW to 50kW, in which case it would take 2 seconds to dissipate the same amount of energy. But the efficiency would still remain the same. All the energy would end up in the water, and bearing in mind we're only talking 3kW max for most domestic water cylinder heaters, I can't see it being improved on in any way that makes a difference. Possibly for very high power flash heaters, if such things exist, but not domestic stuff.
Not the same at all. As has been said in this thread many times, all the heat from the element goes into the water, whether you put it in slowly or quickly. The only factor relating to efficiency is the external insulation on the tank. If it's poorly insulated, more heat will be lost with slow heating than fast heating, so less efficient, but that wasn't what the OP was asking about IIRC.
AFAIK the resistance is very little affected by temperature - just as well, reaaly, as a 3kW element that has low resistance at cold...!
For kettles, the "concealed" (I think of it as remote) element will run hotter than the immersed type. The area of the element is very low and there might be an advantage to having a physically larger one to transfer the same rate of heat at a lower temperature. The plate at the bottom of the kettle gets very hot I'd guess, judging by the colour. It might also spread the scale to a thinner layer(?).
Correct.
I was thankful for the loft tank when we were without supply for about 18 hours a few weeks ago.
Chris
Mate, it's blatantly obvious you really aren't wired suitably to be able to join in such conversations so please don't bother.
No one is talking about actually re-designing anything, this was a 'just wondering' discussion for those able to 'just wonder'.
May I suggest an early new years resolution for you. Put me back in your killfile and that way you don't have to read what I write and I don't have to deal with your stalking and harassment.
Cheers, T i m
Ok.
Sure, but I think within the bounds of a 'just wondering' thread, the fact that it *would* change would be worthy of note (even if then discarded on real world grounds). ;-)
Cheers, T i m
Yeahbut that was the point, it only got the 1 second, no compensation for 'other variables'?
No, quite, we are all pretty sure that is the case, including me. ;-)
Ok.
Yes, like I said ('it's not a closed system' but the point I was trying to make was the 'slippage' when the heat transfer process is pushed past a particular point). Similarly, if you overcharge a battery the surplus energy often gets dissipated in heat (or liberated as a gas as the battery 'boils off')?
So, extreme example ... an element that was so hot that it formed a layer of steam round it all the time. Would all the energy still end up in the water as heat or isn't that energy being used to convert water to a vapour that would then be lost up the overflow pipe?
How much hotter does a kettle of water get if the thermostat gets stuck on and the water continues boiling? If it doesn't get any hotter, where / how is that surplus energy being dissipated?
Quite.
Cheers, T i m
Depends on the design of the system. If the container was deep and narrow, and the heater near the bottom, the steam would condense back to water, thus giving up its latent heat of evaporation to the water, before it got to the surface. If the container was wide and shallow and the heater near the surface, then yes, steam would probably be lost and the system would be inefficient, unless of course generating steam was the objective.
If a thermostat in a kettle sticks on, the kettle eventually boils dry, but doesn't get any hotter than 100C until all the water has evaporated. The surplus energy is carried away by the latent heat of evaporation in converting water at 100C to steam at 100C, i.e. 2257 kJ/kg, or 0.627 kWh per litre, near enough.
Understood.
Quite. ;-)
Agreed (and previously). My point was there are times where you could 'overheat' (too fast or max temperature) something and the energy not end up where you hoped it might. I concede that is way outside the RW application here though. ;-)
Cheers, T i m
It also gets quite noisy (in these kind of kettles) needing frequent de-scaling, although no visible scale build-up and in a soft(ish) area.
A larger (surface area) element at lower temperature may result in slightly less scaling. It should not make much difference to the recovery time though since the limit is usually the rate of heat input.
TNP, You have to remember little Timmy only has half a brain.
Didn't you pay any attention at all in your science lessons? At normal atmospheric pressure water boils at 100 degrees - period.
It can't get any hotter than 100C at sea-level pressures until all the water has boiled away. The extra energy being put in is what is needed to boil the water off - quite a lot of energy is needed for that purpose.
Ok.
Understood ... the fact that it might make *some* difference though (then) could be of interest to some. ;-)
Cheers, T i m
Bert dribbled pointlessly re thermal fins:
"Collapsible to get them through the small hole."
Bwhahahaha ...
Yeah, well done 'bert'! ;-)
Cheers, T i m
Yup ....
No? Really? Fancy that!
Another left brainer failing to understand a rhetorical statement.
The point (that whooshed you) was to suggest that you *could* continue to put energy into a system without actually increasing (say) the temperature because the surplus energy was being liberated elsewhere.
Try to keep up OM. ;-)
Cheers, T i m
Quite, so, *if* an element was kettling and *if* that energy wasn't being recovered before escaping the closed system, then increasing the surface area of the element might improve the situation.
Loads of 'ifs' there of course but still a potential answer to a 'just wondering' type question. ;-)
Cheers, T i m
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