[Stoves] Specific heat capacity/ Stove preformance data

Tue Aug 13 12:48:07 CDT 2013

Dear Lanny

You perform a minimum of 4 tests - one to get the char and three to perform
real life cycle tests. If the stove can't use any of the remaining fuel,
chuck it and treat it as lost in the ashes. That might include small stick
and partially burned wood in some stoves.

The mass of water is not important - the procedure is the same. It should be
in a pot suited to the stove. You will get a different answer for each pot
size. In Indonesia (the WB CSI project) there will be a minimum heat per sq
cm requirement for the pot. That means you can't claim to be able to cook a
100 litre pot on a 1 kW stove because no one will accept a product that
slow. The target is presently 2 Watts per sq cm based on the area of the
bottom of the pot.

The testing is of the performance of the whole system. You should include
the mass of the pot and its material in the heat transferred. The Indian
efficiency test (based on a good British Standard) does this in an
interesting way.

Mass of pot 3500 g
Specific heat of the material 0.91
Joules per degree = 3500 x 0.91 = 3185

Divide by the specific heat of water

3185/4.186 = 761

The pot heats and cools with exactly the same amount of energy as 761 g of
water.

Simply add 761 to whatever mass of water you have and presto - you have an
accurate thermal mass of the heated portion of the system.

If you had 20 litres in that pot, you calculation of thermal efficiency
(across some range of water temperature) would be 

20,000 + 761 = 20761 grams of water (equivalent) x change in temperature x
4.186 = Joules absorbed.

Then using your fuel type and the method described earlier, determine the
mass of new fuel needed to conduct one or three replications. You can
average the three fuel masses (first) then calculate the energy content of
the average fuel energy. There are other ways but pick a method. This is
good: all three amounts of heat gained divided by the total heat available
in the three fires - that is the best and most precise.

Heat gained / heat available in the raw fuel is the system efficiency, for
example 0.31 or 31%.

Note that you don't have to boil the water to get a system efficiency
number. It is much easier to heat the water from 25-70 but no more so you
don't have to worry about water evaporating. Use a lid so you do not
introduce the water IR radiation error and transient wind taking away the
supersaturated layer of air above the water surface (water droplets leave
without being evaporated).

That is what to do if you want the overall thermal efficiency. That number
is directly related to the raw fuel that will be used each time because it
is calculated from the raw fuel consumed. If the char cannot be recycled
into the next fire it is a loss, don't worry about it.

On the other hand. the fuel needed to boil that same water does not depend
on calculating the heat involved in the water because 'boiling' is an
arbitrary concept - do what you like. Just divide the raw fuel mass needed
each time by the total number of litres you put in to begin with. If the
final volume is less, it was still boiled or it would not be missing.

Even with simple equipment, done carefully, you should be able to reproduce
the thermal efficiency within 2% and the fuel for boiling within 3-4%.
Remember that in order to make comparisons between stoves in different
countries report the numbers as following:

Thermal efficiency: xx% (including the pot mass) when using yyyy Fuel type
Energy consumption: xx MJ per litre boiled when using yyyy Fuel type

The 'boiling' temperature change is usually 'normalised' to represent a
particular temperature range, sometimes 15.6-212 F, 20-100 C, 25-100 C and
so on. A report would have to say which temperature range it was normalised
to.

Changing the fuel might change both numbers - never assume anything so
report it all.

Regards
Crispin

-----Original Message-----
From: Lanny Henson [mailto:lannych at bellsouth.net] 
Sent: Tuesday, August 13, 2013 12:26 PM
To: crispinpigott at gmail.com; Discussion of biomass cooking stoves
Subject: Re: [Stoves] Specific heat capacity/ Stove preformance data

>Then use as your triplicate three tests like that in a row. There is 
>month need to measure the char mass until the very end

Crispin, Sarbagya
Is that 3 sets of  3 test or 3 test total?
How much water should be tested in a 40 liter/60/80/100 liter pot? 35 liters
is about all you can cook in a 40 Qt? would about 90% full ok? that would be
36 liters in a 40 liter pot.
Sarbagya, how much are you using?
Lanny

----- Original Message -----
From: "Crispin Pemberton-Pigott" <crispinpigott at gmail.com>
To: "Stoves" <stoves at lists.bioenergylists.org>
Sent: Tuesday, August 13, 2013 8:30 AM
Subject: Re: [Stoves] Specific heat capacity/ Stove preformance data

> Dear Sarbagya
>
> Thanks for that clarification.
>
> Please run a test that uses the leftover char from a previous run. That 
> represents reality. Then see if you get about the same amount of char 
> remaining the second time.
>
> Let's assume you do.
>
> Then use as your triplicate three tests like that in a row. There is month

> need to measure the char mass until the very end.
>
> The 'fuel consumption' is the amount of new raw fuel needed for each 
> replication.
>
> The char is always fed into the subsequent fire.
>
> The energy available in the raw fuel is the energy consumption. It has to 
> be compensated for moisture or course.
>
> Testing in this manner is 1) easier than a WBT, 2) more accurate than a 
> WBT, 3) closer to actual behaviour and 4) automatically deals correctly 
> with the char energy is it is removed from the process either because it 
> can't burn in the same stove or because it was withdrawn for other 
> purposes. As long as there is no excessive char accumulation in subsequent

> tests you don't even have to weigh it or worry about its actual heat 
> content. Either a stove can burn it or it can't and the 'consumption' is 
> the raw fuel that has to be added for each replication - only.
>
> I am interested to know the difference in numbers if you do this.
>
> You should of course divide the fuel energy by the number of litres of 
> water boiled based on the initial mass, not the final mass because missing

> water was of boiled (evaporated). The effect is a few %. Always express 
> the efficiency in terms of energy in and energy transferred (work done).
>
> Regards
> Crispin
> From BB9900
>
> -----Original Message-----
> From: "Sarbagya R. Tuladhar" <sarbagya007 at gmail.com>
> Date: Tue, 13 Aug 2013 17:44:45
> To: <crispinpigott at gmail.com>; Discussion of biomass cooking 
> stoves<stoves at lists.bioenergylists.org>
> Subject: Re: [Stoves] Specific heat capacity/ Stove preformance data
>
> Hi Crispin,
>
> Yes, the charcoal remaining is subtracted from the initial amount of wood 
> used.
>
> The stove even though can burn that char (we have done that numerous 
> times) however for lab tests we throw it away and start with a fresh 
> batch. The consistency in the tests are hence maintained. The wood species

> we use for our purpose is Casuarina with an energy value of 20,790 kJ/kg.
>
> Cheers
>
> Sarbagya
>
> On 13/08/2013, at 5:13 PM, Crispin Pemberton-Pigott wrote:
>
>> Dear Sarbagya
>>
>> Are you deducting charcoal remaining as 'wood not consumed' in that 
>> calculation?
>>
>> If you are, can the stove burn that char on the next run or is it thrown 
>> away?
>>
>> Please everyone note that we can't tell the real energy efficiency if we 
>> do not know the heat content of the mass of fuel. It is most helpful if 
>> the reported figure is 'the energy needed to perform the task' not the 
>> mass of fuel. We don't all use the same fuel - in fact we can all use 
>> different fuels if we report energy instead of mass.
>>
>> Thanks
>> Crispin
>> From BB9900
>>
>> -----Original Message-----
>> From: "Sarbagya R. Tuladhar" <sarbagya007 at gmail.com>
>> Sender: "Stoves" <stoves-bounces at lists.bioenergylists.org>
>> Date: Tue, 13 Aug 2013 14:02:30
>> To: Discussion of biomass cooking stoves<stoves at lists.bioenergylists.org>
>> Reply-To: Discussion of biomass cooking stoves
>> <stoves at lists.bioenergylists.org>
>> Subject: Re: [Stoves] Specific heat capacity/ Stove preformance data
>>
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