[Stoves] Rolling Boil

Sat Nov 3 20:39:48 EDT 2007

Dear friend,

It seems that you skipped over my point.

The definition you listed (in my observation) leaves too much to be  
defined by the operator.
Quoting your post: "Just passing on the info that in South African  
standards the term used to
describe 'boiling' is 'rolling boil' and this is defined in the
'Definitions' section of a standard as:

"the condition when boiling once vigorous convection is attained" ---  
end quote

The part that is too ambiguous is "once vigorous convection is attained"

Is that the point when the vigorous bubbles suddenly rise from the  
middle of the pot where the most heat is usually felt?  Is it when  
the whole water is vigorously jumping around?  Is it when the bubbles  
are vigorously moving from the sides towards the middle?  Or from the  
middle towards the sides?

Whereas "The point when the temperature of the local boiling point is  
reached" is quite precise and leaves almost no room for operator  
manipulation.

The WBT states that one should start with cold water and record that  
temperature  although I don't believe it needs to be 80o temp  
difference.  In Saipina the ambient water might be 23oC and the  
boiling point 96.  That doesn't give us 80 DeltaT

Sorry about the spanish, but should be able to get the skinny of what  
its referring to.
Mediciones Prueba de poder calor’fico alto inicio fr’oPrueba de poder  
calor’fico alto inicio calientePrueba de hervido
   InicialFinalInicioFinalInicialFinal
DatosUnitValorSimb.ValorSimb.ValorSimb.ValorSimb.ValorSimb.ValorSimb.
Tiempomin0tci14.3tcf0thi16.4thf0tsi45tsf
Peso del combustibleg3000fci2090fcf3000fhi2146fhf2158fsi1488fsf
Temperatura del agua olla 1ûC23T1ci95.5T1cf24.3T1hi95T1hf95.8T1si93T1sf
Temperatura del agua olla 2ûC23T2ci96T2cf24.3T2hi96T2hf95.9T2si93T2sf
Peso de olla 1 con aguag5425P1ci5185P1cf5425P1hi5187P1hf5189P1si4261P1sf
Peso de olla 2 con aguag5410P2ci5146P2cf5410P2hi5122P2hf5164P2si4208P2sf
Peso del contenedor + cenizasg  372cc  358ch  344cs

PRUEBA DE PODER CALORIFICO ALTOPRUEBA DE PODER CALORIFICO BAJO
  Inicio fr’oInicio caliente
C‡lculos/resultadosUnidValorSimb.ValorSimb.C‡lculos/ 
resultadosUnidValorSimb
Combustible consumidog910fcm854fhmCombustible consumido durante la  
fase de hervidog670fsm
Cambio a cenizas durante la fase de pruebag100Dcc86DchCambio a  
cenizas durante la fase de pruebag-14Dcs
Equivalente de combustible seco  
consumidog669.1034709fcd639.6971035fhdEquivalente de combustible seco  
consumidog624.0761819fsd
Agua vaporizada en las ollasg504Wcv526WhvAgua vaporizadag1884Wsv
Masa efectiva de agua hervidag9463.39726Wcr9407.584379WhrAgua  
restante final de la olla 1g-163846Wsr
Tiempo de ebullici—n de la olla 1min14.3Dtc16.4DthTiempo de  
ebullici—nmin45Dts
Eficiencia tŽrmica - 0.347426335Hc0.262885789HhEficiencia tŽrmica  
-0.376399302Hs
Rango de combustible consumidog/min46.79045251rch39.00592094rhbRango  
de combustible consumidog/min13.8683596rsb
Consumo espec’fico de combustibleg/ 
g0.070704363SCc0.067998019SChConsumo espec’fico de combustibleg/ 
g-0.003808919SCs
Temperatura corregida por el consumo
de combustible espec’fico g/ 
liter0.036445548SCtc0.035813563SCthPotencia del fuegowatts4160.507879FPs
Potencia del fuegowatts14037.13575FPc11701.77628FPhRango de rechazo -  
2.812583613TDR
Eficiencia tŽrmica promedio - 32.89038088%

Of course in the case of the Kitchen test, the local operator would  
then use the SANS method.

abrazos
David

On Nov 3, 2007, at 2:45 PM, Crispin Pemberton-Pigott wrote:

> Dear David
>
>> I [think] the SA method leaves to much to
>> the tester to decide.
>
> Actually if you try it, the different in time between (say) 100 C  
> and a
> rolling boil is very short for a lot of stoves.  It is longer if  
> the lid is
> off, of course.  If the pot is going to have a rolling boil it has  
> to be
> seen, which is an issue in my view because the lid should be glass  
> or off
> which will give a different time-to-boil.  It so happens that the  
> ethanol
> stove protocol calls for a 225mm diameter pot to have only 1 litre  
> of water
> in it which is very little.  There is no mention of a lid so I  
> think I will
> suggest adding that.  Ethanol stoves are famous for being low  
> powered and
> they should definitely be used with the lid on.
>
> The idea is that the test should prove that the stove supplies a  
> minimum
> quantum of heat.  Stoves that are not powerful enough to 'cook'  
> will not be
> allowed.  The power required is quite small but still, it assumes that
> watchmen's stoves as seen in Senegal are not needed. They are tiny  
> charcoal
> JIKO's about 4 inches in diameter.  The SANS Ethanol stove standard  
> does not
> foresee this, nor for the hyper-efficient stoves of the future.
>
>> In this case, I believe the WBT protocols are more precise.
>
> I think the idea of using the local boiling point is OK  Asking  
> someone when
> a pot is boiling they will probably look and say it is when there  
> is the
> rolling circulation the SANS talks about.
>
>> It seems from your post that you too agree that this method gives
>> better and more comparable data.
>
> I want to be sure that we agree on several conceptual things.  I  
> have been
> involved in writing a few stove testing protocols and you would be  
> surprised
> at how different they are from the ones we use.  There is no general
> agreement within this group on testing, but we are more in  
> agreement than
> the ones used by governments.  The process for writing them is more
> consultative and people have to pitch up concrete wording, not
> philosophising which is of course disciplining!
>
> I favour the temperature measuring method for the reason that  
> people in
> remote places can check the data and make new calculations based on  
> the raw
> data to test other ideas.
>
> For your region, I ask that you ensure that your test data is  
> corrected for
> the need to measure a temperature rise in the pot that is the same as
> whatever protocol you are rating the stove with (from another  
> place).  By
> this I mean that you need to either start with colder water, or make
> mathematical adjustments for the lower boiling temperature at  
> altitude.  The
> correction method should be shown so it can be checked and used by  
> others.
>
> If you use 75 or 80 degrees of water temperature rise (I favour 80)  
> for the
> boiling portion of the test, it doesn't matter much what the  
> boiling point
> is, and you will be able to make legitimate comparisons across the  
> globe if
> you are using the same protocol.
>
> Best regards
> Crispin
>
> "It was Winston Churchill who first wrote, "We make a living by  
> what we get,
> but we make a life by what we give" "
> http://www.uwalumni.com/home/onwisconsin/archives/fall2007/ 
> siftingmakealife.
> aspx
>
> As Harold Blake Walker wrote, "We make a living by what we get, but  
> we make
> a life by what we give."
> http://www.profam.org/docs/jah/thc_jah_submission.htm
>
> See?  There isn't even agreement on that!
>
>
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David Whitfield
lists.cedesol at gmail.com
-------------------------------

"We make a living by what we get... we make a life by what we give."  
- unknown author

David Whitfield V.

Executive Director

CEDESOL Foundation

Alternative Education, Renewable Energy, Social Equality

http://www.cedesol.org

SKYPE - solar1bol