[Stoves] Effect of ambient temperature on low power stove testing

[Crispin Pemberton-Pigott]

Dear Kirk

 

All that is well noted.

 

I don't have an answer for your last questions, but I do recommend that you
do one of two things.

 

If you have money, get a combustion analyser with a pressure meter measuring
in 0.01 millibars and measure the draft directly between the primary air
inlet holes and the fuel bed, or anywhere else you please.

 

This is easy to do by soldering in a pipe where you want to make a
measurement, even in a confined space, and connecting it to the combustion
analyser sample pipe using a short piece of rubber tube.

 

It is quite easy to get a draft of 0.20 millibars which means a 20:1 change
on the display. 

 

Alternatively, get well-measured temperatures and the vertical distances
between points of interest and enter the values in the Draft Calculator
downloadable from this website. It will calculate the individual drafts of
segments of the stove and give an overall total as well. The segments can be
indicated as positive (+1) or negative (-1) depending on the flow direction.
I think it accepts 5 or 8 segments, there are a couple of version floating
around.

 

Regards
Crispin

 

All,

 

It appears to me that the effect of ambient conditions on a TLUD-ND
operating at low power is quite complex.  The excellent responses to this
thread have pointed to several possibilities.

 

1.  The heat loss from the stove and pot to the atmosphere is reduced
because the temperature difference is less.  (Thank you Prof Lloyd)

 

2.  At higher ambient temperatures the primary and secondary air is
effectively pre-heated before it enters the stove.  This leads to a hotter
pyrolysis front, faster wood gas production, and a larger secondary flame.
(Thank you Crispin)

 

3.  Higher ambient temperatures may be accompanied by higher humidity, which
reduces evaporation from the pot.  How does higher humidity effect the
flame?  (Thank you Crispin)

 

4.  If I might add another, higher ambient temperatures are often
accompanied by higher barometric pressure, which would increase the
vaporization temperature so the pot will heat up slightly.  It will also
increase the vaporization temperature of the volitiles in the fuel, slightly
increasing the fuel temperature.  This may seem very small, but the stove
operates on buoyancy pressure differences measured in single digit Pascals,
so a change in barometric pressure may be more than the pressure differences
that drive the stove.

 

The total effect of a combination of these could be considerable.

 

Kirk H.

 

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