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<div class="moz-cite-prefix">Julien,<br>
<br>
Good observations for us to consider. <br>
<br>
I do raise one issue: If a stove is SPECIFIC for use with
pellets (as an example), the proof that the stove does not work
well with other fuels is not the needed scientific testing. <br>
<br>
In fact, there might be some pellets that are not acceptable as
fuel for the stove. For example, years ago I tried pelletized pet
feeds and they did not pyrolyze well at all. <br>
<br>
But in fact the customer for the stove wants the stove to be
reliable for the known and available type of pellets. Period.
Full stop. How would you envision the testing for such as
situation? At what point in the testing cycles is it reasonable
to declare some solid findings?<br>
<br>
Paul<br>
<pre class="moz-signature" cols="72">Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
Email: <a class="moz-txt-link-abbreviated" href="mailto:psanders@ilstu.edu">psanders@ilstu.edu</a>
Skype: paultlud Phone: +1-309-452-7072
Website: <a class="moz-txt-link-abbreviated" href="http://www.drtlud.com">www.drtlud.com</a></pre>
On 2/18/2015 11:42 AM, Julien Winter wrote:<br>
</div>
<blockquote
cite="mid:CALv4xTzF+KHNgtN8RgM-hHVQL_ymfVT8LdxAaRXVjz1cPKWKyQ@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>I haven't got as far as water-boiling tests yet, because I
have been working on fundamental issues of burner design, and
that takes a while.</div>
<div><br>
</div>
<div>However I can see a some problems with the way stoves are
being tested.</div>
<div>1) Measurements made over the course of a run are
autocorrelated.</div>
<div>2) Proper testing of a stove involves a range of fuels.</div>
<div>3) Test to find the boundaries of failure, not success.</div>
<div>In summary, proper testing of a stove, prior to
manufacturing thousands, or making it an exemplar for millions
can't be done with one test. It takes many tests; tests that
try to find out not only where the stove succeeds, but most
importantly, where it fails.</div>
<div><br>
</div>
<div>1) AUTOCORRELATION and Correlation vs. Independent
Observations.</div>
<div><br>
</div>
<div>Autocorrelation, or serial correlation, is a statistical
term use to say that two observations, for example, of
temperature, are not independent, because they are related in
space or time. Autocorrelation can be a good thing to study
if you are looking at spatial patterns in soils, but it can be
a problem if you are trying to measure properties of a stove.</div>
<div><br>
</div>
<div>If we are trying to measure energy transfer during boiling,
followed by energy transfer during simmering, all in the same
run, then these two measurements of energy transfer will
be autocorrelated. They are autocorrelated, because there
history to the combustion reaction, especially in a TLUD. In
a TLUD, the depth of char increases over time, and changes in
temperature. This change can alter the chemical composition
of the pyrogas. In TLUDs and other stoves burning thick
pieces of fuel, char combustion can increase over time.</div>
<div><br>
</div>
<div>Now it may be that boiling followed by simmering is so
common that energy transfer from fire to pot over this the
sequence should be measured. However, if we a primarily
interested in how efficient energy is transferred at different
power levels, then having a separate run for each power
level would make the observations at different power
levels independent of each other.</div>
<div><br>
</div>
<div>There are actually two different turndowns to measure:</div>
<div>a) the turndown of fuel consumption rate</div>
<div>b) the turndown of energy transfer rate to a pot</div>
<div><br>
</div>
<div>2) A RANGE OF FUELS</div>
<div><br>
</div>
<div>It is important to test stoves over a range of fuels,
because they behave quite differently depending on moisture
content, volatile content, particle thickness and shape. In a
ND-TLUD the fire in wood chips invariably, channels; with
thick fuel (e.g., sticks) there is char combustion on the
surface while the interior pyrolysis; and, if air spaces are
vertical then a very strong draft develops in the fuel bed.
Channeling of the ignition can increase as primary air is cut
back, especially in wood chips. </div>
<div><br>
</div>
<div>Across all these fuels there is >5 fold change in
ND-TLUD gasification rate. In other words, turndown is not
properly represented by a single fuel.</div>
<div><br>
</div>
<div>3) TEST FOR FAILURE NOT SUCCESS</div>
<div><br>
</div>
<div>Critical testing of stove should try to find where it
fails. Although it is useful to see where a stove succeeds,
repeated observations of success is not critical testing. </div>
<div><br>
</div>
<div>Scientist are encouraged to design critical experiments
that reject hypotheses, not confirm them. If, under critical
test, our hypothesis is not rejected then it is probably
true. We owe this line of reasoning to the philosopher, Karl
Popper. Queen Elizabeth (of England) gave him a knighthood,
therefore, he must the right!!</div>
<div><br>
</div>
<div>In the case of cookstoves, we should cover a range of
conditions (fuels and turndowns) to see where they fail.
Using a single fuel is not subjecting a stove to critical
testing.</div>
<div><br>
</div>
<div>To use a more simplistic example, let us say that a
European looks in the sky and sees only white swans, and comes
up with the hypothesis that "all swans are white". To
confirm the hypothesis is not the way to go. We can count
thousands of white swans in the skies of Europe, and we still
haven't put our hypothesis to a critical test. We have to
devise a circumstance or an experiment, where our
hypothesis could fail. So lets search all corners of the
Planet to see if we can find a non-white swan. Lo, in
Australia, the swans are black. The crucial point here is
that in our critical test, we only had to see one black swan
for us to reject our hypothesis that "all swans are white";
all the thousands of white swans, previously seen, now count
for naught. </div>
<div><br>
</div>
<div><br>
</div>
<div>To test cookstoves (i.e., ND-TLUDs) on wood pellets is to
count white swans.</div>
<div><br>
</div>
<div><br>
</div>
<div>To conclude: before a cookstove is promoted as an
exemplar, or sold by the thousands, there is a lot of testing
to be done to characterize stove performance over a range of
conditions. One water-boiling test just doesn't make the
grade.</div>
<div><br>
</div>
<div>Cheers,</div>
<div>Julien.</div>
<div><br>
</div>
<div>P.S.: Scientists must really get inventors and engineers
pissed-off. Not only do the want to try to break the stove,
they want to do it four times so that they can say, "Yup, I am
95% sure that your stove is broken."</div>
<div><br>
</div>
<div><br>
-- <br>
</div>
<div class="gmail_signature">
<div dir="ltr">Julien Winter<br>
Cobourg, ON, CANADA<br>
</div>
</div>
</div>
<br>
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