[Stoves] Thermal efficiency

Dean Still deankstill at gmail.com
Mon Oct 14 14:08:35 CDT 2013 

Hi Frank,

We test stoves several times a day here at the lab usually following an
iterative design process to improve performance and decrease emissions of
CO and PM. As far as I can tell, boiling and simmering water and tracking
fuel use and emissions works OK but the real measure is using the CCT with
real cooks, making their favorite food under the emission hood. Then we're
a lot closer to seeing actual performance compared to the traditional
stove. The CCT gets the lab into the field and the field into the lab which
gets us closer to predictive data.

Best,

Dean


On Mon, Oct 14, 2013 at 9:38 AM, Frank Shields <frank at compostlab.com> wrote:

> *Hi Dean,*
>
> * *
>
> *Anything as close to real world I am in favor of. So I agree about using
> the water boiling test as-is. *
>
> * *
>
> *But I do like the design of the method Alex described that included all
> the necessary checks that make for a good, repeatable test. Well designed.
> I may use it here for measuring heat increase in cubic meter size,
> self-heating compost bins with compost-char experiments. Thinking a coil of
> water filled tubing would work better getting a more representative reading
> than a thermometer stuck in the center.   *
>
> * *
>
> *And maybe someday I will actually get to test some stoves.*
>
> * *
>
> *Regards*
>
> * *
>
> *Frank*
>
> * *
>
> * *
>
> *Frank Shields*
>
> *Control Laboratories; Inc.*
>
> *42 Hangar Way*
>
> *Watsonville, CA  95076*
>
> *(831) 724-5422 tel*
>
> *(831) 724-3188 fax*
>
> *frank at biocharlab.com*
>
> *www.controllabs.com*
>
> * *
>
> * *
>
> * *
>
> * *
>
> * *
>
> * *
>
> * *
>
> * *
>
> * *
>
> * *
>
> * *
>
> *From:* Stoves [mailto:stoves-bounces at lists.bioenergylists.org] *On
> Behalf Of *Dean Still
> *Sent:* Sunday, October 13, 2013 3:38 PM
> *To:* Discussion of biomass cooking stoves
> *Subject:* Re: [Stoves] Thermal efficiency****
>
> ** **
>
> Hi Frank and Alex,****
>
> ** **
>
> Boiling 2.5 or 5 liters of water in a pot shows if the stove is capable of
> doing one of the tasks which are often needed for cooking food. It's
> important information. Boiling and simmering are both frequently needed
> when cooking. The WBT published by VITA was patterned after actual cooking
> tasks for good reasons.****
>
> ** **
>
> Best,****
>
> ** **
>
> Dean****
>
> ** **
>
> On Sun, Oct 13, 2013 at 12:43 PM, Frank Shields <frank at compostlab.com>
> wrote:****
>
> *Dear Alex,*****
>
> * *****
>
> *I like it. Easy to calibrate a flow meter with a stop watch and
> volumetric flask and both temperature meters calibrated using the same
> temperature water to make sure they read the same. So we can all be on the
> same page using different equipment in different parts of the world. *****
>
> * *****
>
> *So one thermometer is set, say 30c higher than the other and we plot the
> flow of water?  Perhaps bucket filling with water on a balance being
> plotted? Or flow gauge? *****
>
> * *****
>
> *Thanks*****
>
> * *****
>
> *Frank*****
>
> * *****
>
> * *****
>
> *Frank Shields*****
>
> *Control Laboratories; Inc.*****
>
> *42 Hangar Way*****
>
> *Watsonville, CA  95076*****
>
> *(831) 724-5422 tel*****
>
> *(831) 724-3188 fax*****
>
> *frank at biocharlab.com*****
>
> *www.controllabs.com*****
>
> * *****
>
> * *****
>
> * *****
>
> *From:* Stoves [mailto:stoves-bounces at lists.bioenergylists.org] *On
> Behalf Of *Alex English
> *Sent:* Sunday, October 13, 2013 10:54 AM
> *To:* Discussion of biomass cooking stoves
> *Subject:* Re: [Stoves] Thermal efficiency****
>
>  ****
>
> Crispin,
>
> On the heat transfer side there are clearly a lot of variables. Get rid of
> them like we do with boilers. Use a sealed pot with its contents (water)
> kept at a constant temperature (example; either high ~90C in-95C out, with
> no condensation or low ~55C in-60C out, with some condensation or both) and
> a flow meter to measure the thermal work done. A modern automated three way
> valve controlling the flow through a heat exchanger can regulate the return
> temperature precisely.
>
> The pot can be any pot with a non standards lid disc with in/out plumbing
> connections, glued with silicone to the top of the pot. It should withstand
> a few inches of water pressure with a stand pipe open to the atmosphere
> after the outflow thermocouple. The vapour losses then are outside of the
> measurement frame. The pot could be filled with water or be part filled and
> have a vapour/air head space. Flow rates and velocities could be high
> enough to eliminate biases between pots or to mimic natural convective
> patterns within the pot.
>
> All you need is a whole bunch of disc lids from 20 to ??cm in diameter in
> 1cm increments, or custom make them as the required.
>
> Or you can see how many different efficiencies you can fit on the head of
> a pin.
>
> Heuristically yours,
> Alex
>
> On 13/10/2013 11:21 AM, Crispin Pemberton-Pigott wrote:****
>
> Dear Friends****
>
>  ****
>
> As we are, at the CAU stoves conference, talking about thermal efficiency
> tomorrow, here is something to think about.****
>
>  ****
>
> ++++++++****
>
> Efficiency is a ratio, but of what to what? Let us follow the heat and
> decide which ‘efficiency’ we want to report. ****
>
>  ****
>
>    1. Heat available in the raw fuel if it was to be burned completely****
>    2. Heat available in the dry portion of the raw fuel****
>    3. Heat available from the fire considering incomplete combustion****
>    4. Heat available to the pot, at the pot in the hot gas stream passing
>    by****
>
>  ****
>
>    1. Heat transferred to the pot – all of it****
>    2. Heat transferred to the pot and subsequently lost from the pot into
>    the surrounding environment****
>    3. Heat absorbed the pot material changing its temperature****
>    4. Heat absorbed by the water – all of it****
>    5. Heat absorbed by the water changing its temperature ****
>    6. Heat absorbed by the water and evaporating water (whether the water
>    is hot or not)****
>    7. Heat absorbed by the water and lost from the water (by radiation,
>    not by evaporation)****
>    8. Heat absorbed into the food and being absorbed chemically
>    (transforming it into cooked food)****
>
>  ****
>
> System efficiency [Overall thermal efficiency] is (7+9+10+12)/1.   [When
> boiling water only #12=0]****
>
>  ****
>
> Heat transfer efficiency is …. ?  Which one is the one you were thinking
> of when asked about ‘thermal efficiency’?****
>
>  ****
>
> +++++++++****
>
> Regards****
>
> Crispin****
>
>
>
> ****
>
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