[Stoves] Heat / cook stove - proposed design

[Crispin Pemberton-Pigott]

Dear Darren

 

Based on the hopper size, and presuming you have about 4 metres of chimney,
that size is probably going to be enough air to heat a home. Do you have a
kW rating in mind? I think you should be able to get 40 kW from it. Do you
want that much?

 

>>The area of the hole should be about 30 x 120mm.


The primary air hole should be 30x120mm?  With a valve so its adjustable?

Yeah, a sliding plate should be OK. It doesn't have to fit perfectly. The
point about the location of the air inlet is that the air should be able to
pass up into the lower portion of the fuel and then cross the bottom of the
hopper, and exit the left side (is the drawing you sent) into the flaming
area. At that point the passage should be constricted to about 20,000 mm^2
then the secondary air can be admitted above the constriction. Not much,
because some of the air passing through the slot will be secondary air. The
hopper should have no air leaks into it at all.  I hope you saw the stove
from Eastern Canada that Kevin passed around. That top was good - it had a
woven seal.

 

>>Lastly, constrain the entrance into the combustion area (where the
secondary air enters) to about 1/3 of the area of the hopper. Keep it
square-ish, definitely not long and thin as is often seen in furnaces. 


>You mean the 'throat' from hopper (A) to combustion area (B).  Third of the
hopper width >would be about 7cm.  7x7 then?

No, a third of the area, not a third of the dimension. If you have 20 x 30
cm = 600 cm^2 then 1/3 = 200 cm^2 = about 140 x 140. My little model says
14.5 x 14.5 but that is a bit big, just looking at it (subjective opinion).
If you only want 20 kW, meaning a max of 20 and sometimes 4, make the
constriction smaller, say 100 x 100mm. That constriction is perhaps 100 to
125mm above the lower end of the grate, just as you drew it.



Put the secondary air entrances where it starts to expand (because there is
additional draft there). 



you mean straight away after the 'throat'?

Your drawing is correct. Just bring all gases and flames into a smaller
space than the surface area of the grate.  It is by no means the gas flow
constriction on the whole system. It is a permanent method of getting the
combustion efficiency up. In the GTZ 7 series I put ceramic plates on each
of the 4 sides tapering open to about 230 x 100. The height is about 220 or
so - not all that important because it is regulated a bit by the oiliness of
the fuel. More oil, longer flame, so a longer space to burn in.

 

About the bricks, you can use any bricks. Go for the hardest, strongest
bricks you can find, if you can't get genuine low thermal expansion
materials. Put them in a way so that when they crack they don't fall out of
place.

 

Oh yeah, put a damper on the chimney that can cut the cross-section by 75%
max.

 

Regards

Crispin

 

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