[Stoves] Conceptioal Errors and possible pitfals.

[Ron]

Crispin 

   In your three-sentence final paragraph, the first two sentences seem to contradict each other.

   Can you give an example of a metric which is invalidated?

Ron


On May 7, 2013, at 1:35 PM, "Crispin Pemberton-Pigott" <crispinpigott at gmail.com> wrote:

> Dear Paul
>  
> I think there are excellent questions. I think we have a responsibility to ‘bring the group’ along on this because there are a lot of people reading the list who are able to do the calculations.
>  
> It is through these thought experiments that we find out whether or not the metrics being used are valid (or not).
>  
> It would be more helpful to know the heat transfer efficiency at low power than that turns out to be invalid. Getting the low power efficiency is easy to find out, though not by simmering a pot.
>  
> To give you a brief answer regarding heat transfer, the quantity of heat transferred during simmering is not affected by the volume of water in the pot (unless there is nearly none left). Heat transfer is a relationship between the pot and the stove, not what is in the pot. This fact invalidates several WBT metrics.
>  
> Regards
> Crispin
>  
>  
>  
>  
> From: Paul Anderson [mailto:psanders at ilstu.edu] 
> Sent: Tuesday, May 07, 2013 12:39 PM
> To: Discussion of biomass cooking stoves
> Cc: Crispin Pemberton-Pigott; Jim Jetter; Tami bond
> Subject: Re: [Stoves] Conceptioal Errors and possible pitfals.
>  
> Dear all,
> 
> Further thoughts about just one of Crispin's examples below:
> >    3.  How about giving us ONE paragraph in 4.2.2  to look at  - and with especially new language on how you would change that paragraph?  Even if that has to be a year or two from now.
> 
> Crispin wrote:
> 
> How is this:
> 
> I give you 5 litres of water in a pot and ask you to bring it to a boil.
> 
> You put it in a fire and bring it to what we agree is ‘a boil’ by which time 100 cc has evaporated.
> 
> I ask you how many litres of water you have just boiled.
> 
> What is your answer?
> 
> That is an example of a conceptual difference. The WBT says you boiled 4.9. An engineering will say you boiled 5.0.
> 
> Is this cognitive dissonance or conceptual error?
> 
> And take this to the simmer stage, which typically is for 45 minutes in the WBT.   If the pot has not lid (and it does not have a lid in the official testing), additional water will be boiled away.   Assume two cases, one with a very low fire and one with very high fire (a common result of not having much of a turn-down ratio on powerful stoves).  
> 
> In the low fire case, assume that there are still 4.5 liters in the pot.
> In the high fire case, assume that there are only 3 liters in the pot.
> 
> In the final minutes, the difference in the amount of water in the two pots is 1.5 liters, which is 33% of 4.5 liters and 50% of 3 liters.   So, are you actually "simmering" 5 or 4.5 or 3 liters?   And how much actual ENERGY is needed to accomplish that task if the amounts of water are so different?   
> 
> And which stove has the "advantage" (that is, looks the best in the reported results) depending on what number(s) are used in the analyses?    (Will someone please do the math using the formulae, just changing the number of liters from 5 to 4.5 to 3 so that we can see the impact.)   This is hypothetical, but educational.     
> 
> I think that this is the type of stuff that Erin was mentioning about issues not well understood.  If you have the answer WITHOUT doing the 6 calculations, then you are quite special.   But I will still ask you to give me the numbers.
> 
>            Topic                 Stove type                              Results  5 L            4.5 L           3 L                    Comments:
>                                     (L or H heat)                           
> 
> Results of      
> A.   Efficiency???       for LOW heat stove:        ________           ______      _______          _______..........
> 
> B.           dito                   HIGH                                     ________           ______      _______          _______..........
> 
> 
> C.  Result ???            for LOW heat stove:        ________           ______      _______          _______..........
> 
> D.           dito                   HIGH                                   ________           ______      _______          _______..........
> 
> And more???
> 
> Sorry, I do not know the answers, and I am not qualified to do the calculations.  But I would like to know the results.   Maybe more than one "result" is correct and should be reported in the results of the stove testing?  If this is meaningless, I want to know why.
> 
> Note:   If the results of the above are NOT of interest to you, then perhaps none of the discussion about testing protocols is of interest to you.   All of us will be grateful for these types of questions being resolved.
> 
> Paul
> 
> 
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