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<div class="moz-cite-prefix">Crispin,<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
Or you can see how many different efficiencies you can fit on the
head of a pin.<br>
<br>
Heuristically yours,<br>
Alex<br>
<br>
On 13/10/2013 11:21 AM, Crispin Pemberton-Pigott wrote:<br>
</div>
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<p class="MsoNormal">Dear Friends<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">As we are, at the CAU stoves conference,
talking about thermal efficiency tomorrow, here is something
to think about.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">++++++++<o:p></o:p></p>
<p class="MsoNormal">Efficiency is a ratio, but of what to what?
Let us follow the heat and decide which ‘efficiency’ we want
to report. <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<ol style="margin-top:0mm" start="1" type="1">
<li class="MsoNormal" style="mso-list:l1 level1 lfo1">Heat
available in the raw fuel if it was to be burned completely<o:p></o:p></li>
<li class="MsoNormal" style="mso-list:l1 level1 lfo1">Heat
available in the dry portion of the raw fuel<o:p></o:p></li>
<li class="MsoNormal" style="mso-list:l1 level1 lfo1">Heat
available from the fire considering incomplete combustion<o:p></o:p></li>
<li class="MsoNormal" style="mso-list:l1 level1 lfo1">Heat
available to the pot, at the pot in the hot gas stream
passing by<o:p></o:p></li>
</ol>
<p class="MsoNormal" style="margin-left:36.0pt"><o:p> </o:p></p>
<ol style="margin-top:0mm" start="5" type="1">
<li class="MsoNormal" style="mso-list:l0 level1 lfo2">Heat
transferred to the pot – all of it<o:p></o:p></li>
<li class="MsoNormal" style="mso-list:l0 level1 lfo2">Heat
transferred to the pot and subsequently lost from the pot
into the surrounding environment<o:p></o:p></li>
<li class="MsoNormal" style="mso-list:l0 level1 lfo2">Heat
absorbed the pot material changing its temperature<o:p></o:p></li>
<li class="MsoNormal" style="mso-list:l0 level1 lfo2">Heat
absorbed by the water – all of it<o:p></o:p></li>
<li class="MsoNormal" style="mso-list:l0 level1 lfo2">Heat
absorbed by the water changing its temperature <o:p></o:p></li>
<li class="MsoNormal" style="mso-list:l0 level1 lfo2">Heat
absorbed by the water and evaporating water (whether the
water is hot or not)<o:p></o:p></li>
<li class="MsoNormal" style="mso-list:l0 level1 lfo2">Heat
absorbed by the water and lost from the water (by radiation,
not by evaporation)<o:p></o:p></li>
<li class="MsoNormal" style="mso-list:l0 level1 lfo2">Heat
absorbed into the food and being absorbed chemically
(transforming it into cooked food)<o:p></o:p></li>
</ol>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">System efficiency [Overall thermal
efficiency] is (7+9+10+12)/1. [When boiling water only
#12=0]<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Heat transfer efficiency is …. ? Which one
is the one you were thinking of when asked about ‘thermal
efficiency’?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">+++++++++<o:p></o:p></p>
<p class="MsoNormal">Regards<o:p></o:p></p>
<p class="MsoNormal">Crispin<o:p></o:p></p>
</div>
<br>
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