[Stoves] Efficiency of clean fuel

[AJH]

On Tue, 1 Jan 2008 21:45:05 +0200, Philip Lloyd wrote:

>I don't recall a proposition that "an electric hob transfers 40% of the
>thermal power into the pot." 

Thanks for pointing that out, it was my mistake, you did indeed say
80% efficiency from hob to pot and the 40% was for a "thermal cook
stove"
>
>What we have measured is an 80+/-1% efficiency of transferring electrical
>energy received by the hob into thermal energy in the pot.  This efficiency
>was measured with a voltmeter and wattmeter on the electrical feed to the
>stove, and the mass of water turned to steam during boiling, at close to sea
>level.

When I first came to the list this type of simple water loss
calculation is what we used to get a figure of merit per kg of fuel
burned, if all other things remain the same then it should be a decent
enough comparator between and electric and a gas hob.

Did you start a rolling boil and then measure the electricity used
from that point? Perhaps someone with a gas hob can do something
similar. I think I have a butane stove that I could try.


> The hob was a simple resistance element coiled into a spiral, such as
>is widely available as a cheap cooking device, and drew about 0.9kW at peak
>power.  The pot was a simple, flat-bottomed aluminum pot.
>
>For a power station at 37% thermal efficiency, and losing 8% of the
>electrical energy in transmission and distribution, that works out as 27.2%
>overall efficiency from heat energy supplied at the power station to heat
>energy into the pot, which is better than most.

Yes and as I said to Sharon one of the reasons it is good is that
there is no mass flow to carry away sensible heat. Now gas won't be
far behind as it can be burned near stoichiometrically and the flue
gas can be rejected at a low temperature, I wonder whether a coal or
charcoal stove will be better as these will have less losses from
discarding the latent heat of steam. Of course the charcoal might be
penalised if the heat losses during production aren't recovered in
some way.
>
>Hope that clarifies things!
>
>Happy New Year.

Happy new year Philip