[Stoves] briquette air feed

Kobus Venter ventfory at iafrica.com
Thu Jan 6 09:32:28 CST 2011


Crispin,

It's taken 6 years for people to crit on it, well better late than 
never.  Just being cynical here:-) .  I appreciate your comments and 
will follow your lead on WBT.  I used to assume the charcoal burning 
phase was the low power phase, i.e. when the flame goes out you enter 
the glowing ember stage, especially in the core of the briquette.  No 
visible flame results in poor heat transfer hence the low power output 
and efficiency.  Looking forward to proper, universally accepted WBT 
procedures or should that be looking forward to applying a new 
universally accepted WBT in the correct manner.

-- 
Kobus Venter
Vuthisa
www.vuthisa.com


On 2011/01/06 01:51, Crispin Pemberton-Pigott wrote:
> Dear Kobus
>
> Thanks for the link to your un-popular report which should now get a read or
> three....
>
> http://www.bioenergylists.org/stovesdoc/Stanley/BriqGassstove.htm
>
> Sorry for the major digression, but:
>
> I want to comment on the reported efficiency of low power. I have serious
> doubts that the need to reform the test reporting is being fully gripped
> here.
>
> It is great that you have a (meaningful) thermal efficiency based on the
> heating and boiling of water but seriously folks, we have to stop reporting
> the thermal efficiency of simmering calculated on that basis. It is simply
> not true that the same stove has an efficiency of 3% on low power.
>
> Think about it: you have a stove with a thermal efficiency of 35% on high
> power and when going to low, the reported efficiency drops to 3%. That is
> simply impossible save under very special circumstances. It is much more
> likely that the efficiency is 50% or higher.  65% is not uncommon at low
> power.
>
> Because the METHOD of doing the calculation is the problem, not the stove or
> the efficiency, we have to get to grips with this misrepresentation of lower
> power because people take this 'low power efficiency' and average it with
> the 'high power efficiency' to get some meaningless number that
> misrepresents what is happening with the stove.
>
> I would really appreciate Aprovecho getting engaged on this subject because
> their long term support for the reporting of 'efficiency' on low power is a
> long term source of this enduring confusion. Is this going to be carried
> into the new WBT 4? Will we have to wait for WBT 5 to correct it?
>
> Quite coincidentally Nat at Iowa State and I were talking about this earlier
> today. We as stovers are not going to be taken seriously in the world of
> thermal engineering if we can't get past these basic errors of science and
> math. Missing water during simmering does not allow one to calculate the
> thermal efficiency of a stove.
>
> Determining the efficiency of low power operation includes calculating the
> heat transferred to the pot, not the amount of water than happens to be
> missing with its own arbitrary definitions.
>
> Rok, that stove is not 3% efficient at low power. It is probably 10 times
> that. Maybe 20 times.
>
> Now, what can we doing about this? Stovers will converge on Washington to
> assist/advise the DoE next week and we have to talk more sense than this if
> we want to be taken seriously by those from the Energy field who have
> nothing invested in the stove enthusiasts and its strange measures.
> Stonewalling or hiding will not solve the problem.
>
> We need better methods.
>
> Regards
> Crispin





More information about the Stoves mailing list