[Stoves] Test report of metal chulah

[Saloop T S]

Respected Sir,
          Thank you sir for your valuable comments. I promise you that I
will take necessary actions you have mentioned, from the next test onwards.
Thank you once again for your valuable time.
Happy New year...
On Jan 1, 2015 4:09 AM, "Crispin Pemberton-Pigott" <
crispinpigott at outlook.com> wrote:

> Dear Saloop
>
>
>
> I have look again at the formulas used for calculating the efficiency and
> you should be careful in drawing conclusions about the stove and its
> various forms until you have corrected the calculations.
>
>
>
> This formula (copied below) does *not* give the correct efficiency value.
> Because you are interpreting the calculated results to make conclusions
> about the design, it is really important that you use a slightly modified
> test method and correct the formula.
>
>
>
>
>
> There are two problems with this formula.
>
> The first is that you have counted the heat gained by the water before it
> started boiling. No problem. Then you evaporated water, no problem.  Later
> the water cooled and some of it evaporated. That is a problem.  The heat
> driving that evaporation did not come from the fire (which is out) but from
> the cooling of the water. Energy was transformed from hot water into hot
> steam at a conversion rate of at least 540 kCal/kg (more, if the
> temperature at the time was below the boiling point).
>
>
>
> I mentioned this problem before.
>
>
>
> Here is your formula broken down:
>
>
>
> {2 (99.8-31.5)                     [I left out the x1]
>
>
>
> That is: water mass times Delta T. The result is the enthalpy change in
> the water.
>
>
>
> +(0.58 x 540}
>
>
>
> That is: the enthalpy change from water to steam for 0.58 kg of water.
>
>
>
> However you note that the test was finished and the water mass missing was
> measured at the end of a cooling period. Is that correct? Your description
> does not state explicitly that the water mass was determined at the end of
> the gasifier experiment, though it does say so for the Chula experiment.
> If so there is a problem.
>
>
>
> You have not calculated the change in enthalpy for the pot cooling between
> flame out and the time when you determined the mass of water evaporated.
> This change in enthalpy is negative, not positive and is missing from the
> formula.
>
>
>
> It is the same as the first portion but with a negative number:
>
>
>
> {? (36-99.8)     [in the case of Test 1]
>
>
>
> {? (36-99.8)         What number should be in place of the '?'. It should
> be the final mass.
>
>
>
> 1.134 (36-99.8)
>
> = 1.134 x -63.8
>
> = -72.34 Kcal heat lost from the hot water and turned into evaporation and
> the heating of the local environment directly from the pot surface (which
> is an unknown value).
>
>
>
> Thus the reasonably correct total heat gained number is:
>
>
>
> {2 (99.8-31.5) - 1.134 (36-99.8) + (0.58 x 540}
>
>
>
> Water heating - water cooling + total water evaporated.
>
>
>
> Second problem with the calculation:
>
> You have allowed the pot to cool long after the fire has been removed from
> under it. The pot loses heat into the air, not only from evaporation. You
> do not know the amount of heat gained by the pot and water that was
> subsequently lost to the surrounding air. You do not know how much heat was
> lost from the pot when the water temperature was rising and or when it was
> boiling. Letting the pot cool for so long has allowed a large amount of
> heat to be lost from the pot 'uncounted' meaning, counting the lost heat
> that was not turned into evaporation. The longer the wait (without fire)
> the greater the unknown and the greater the error and the less confidence
> we can have in the final number.
>
>
>
> To correct this you need to know the mass of the water at the moment when
> the gasification stops and stop the experiment at that time. You have
> recorded the time, and the temperature, but not the water mass remaining.
> If you know the mass of water remaining when the gasification is completed,
> you can get a pretty good figure for the cold start system efficiency.
>
>
>
>
>
> There are two problems with the test procedure.
>
> The first is that it is not clear what 'efficiency' you are trying to
> determine. An efficiency is a ratio and there are many ratios that can be
> reported.  As I read the description, it seems to me you want to know the
> system efficiency, that is, the % of useful heat available in the fuel that
> is detected in the pot.
>
>
>
> It would be a very unusual cook who was 'cooking' while the pot reduced in
> temperature to 36 C. I think this is a reasonable assumption. So if you
> could report the mass of water either when the flame goes out or after it
> cools to 95 C (whether the flame is out or not -  otherwise known as the
> Chinese Method) you can use the extended formula above that accounts for
> the enthalpy of cooling.
>
>
>
> To get the best answer, record the mass of water when the gasification is
> finished, or when water drops to 95 C (you decide and report which you have
> done).
>
>
>
> The second problem with the procedure is that the pot was allowed to cool
> while sitting on the stove which allows some of the heat retained by the
> stove body to be transferred to the pot. This can be quite misleading when
> trying to determine whether or not the change in architecture is affecting
> the performance. The cooling energy calculation has such large unknowns in
> it that decisions about results may be misguided because of something
> taking place long after the real cooking has stopped. That should be
> avoided.
>
>
>
> Regarding the secondary air inlets, my previous comments still apply. I
> won't repeat them here.  The number of holes it too large and the diameter
> too small to impel the air into the centre of the gas chamber.
>
>
>
> I agree with all Julien's comments. I believe a better seal between the
> riser and the body would prevent hot air which is now rising past the
> outside of the riser and into the flaming area at the top edge of the
> riser.  That air is surely cooling the flame and pot surface and
> interfering with the transfer of heat to the pot.
>
>
>
> Regards
>
> Crispin
>
>
>
> Respected sir,
>         Please find the resized documents attached with this mail. It has
> been sized down to 800 KB. Hope it is possible to post it.
>
> Thanking you,
>
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