On Sun, 25 Dec 2016 11:09:21 +0000, Chris Hogg wrote:

snip

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?

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.

Understood.

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.

Quite. ;-)


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?

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.

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