On Sun, 08 Jul 2007 09:59:47 +0100, "Dave Plowman (News)"
wrote:

In article ,
Spurious Response wrote:
no, they radiate less total energy because they take 1/3 the time and
radiated power is no different to a 1kW unit, since that depends
entirely on water temp and kettle shape & finish.


Sorry, but the difference in time heating 4 quarts of water in a 1kW
vat is NOT 3 times that of the 3kW unit.

There are constraints. The water has to still be there when you are
done.

If it takes a 1kW unit to heat it to boil in ten minutes, there is no
way in hell a 3kW unit will do it in three.

It is NOT linear, chucko.

Go on then Einstein, show the maths to prove this.


Basic inline water heaters prove it. If it were so much faster, we
would have 3kW inline water heaters. As it stands, that it not the case.

Sure, as you increase power, you get more work done. But you also lose
more of that heat as well.

What it really comes down to is the diameter (and length) of the coil.

Since both 1kW as well as 3kW coils BOTH reach temperatures far above
the boiling temp of water, it would seem to me that you would foresee
some point at which there are diminishing returns from the amount of
energy one dumps into those coils over the return of heat imparted into
the water.

I'd bet that a larger diameter coil will heat the water faster than a
smaller diameter coil, for any given equal wattage, and the reason is
that the coil surface area is so much larger, yet it's surface temp is
very much the same.

So to me, the ideal heater for water would be one that does the job
with the least amount of energy in a reasonable time.