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| Stoves Archive for May 2002 |
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| 102 messages, last added Tue Nov 26 17:31:37 2002 |
[Date Index][Thread Index]
Re: Temperature dilution
On Thu, 30 May 2002 23:54:09 +0200, "Crispin" <crispin@newdawn.sz>
wrote:
>
>I like the idea of a steam powered air injector. I have drawings...!
I am glad someone else thinks the idea has possibilities, I have been
pushing the idea for a while now. IMO natural draught plus a dry fuel
with a high volatiles content will be the cheapest route. The expense
of forced draught seems likely to be justified on poorer (low
volatiles and/or wet) fuels.
Tom Reed pointed to the Dasifier which uses compressed air through a
simple ejector, Vernon Harris had previously suggested that the
science of ejectors was quite a bit more sophisticated. I thought a
well designed ejector would enhance performance.
As to the drawings, I did nothing sophisticated and see little reason
most tincanium fanatics could not have a try. I took a propane burner
rated at 325g of propane per hour. This has a 0.5mm orifice, which is
far too large but any smaller makes fouling a problem. The screw
thread seems to be a standard BSP one, I attached 2.5m length of 10mm
cunifer brake pipe into the burner. The pipe was coiled around a 100mm
tin can. The other end I attached to a plastic spray can, I believe a
can filled with *rainwater* and pressurized by a bicycle tyre inflator
would work as well.
Now current observation is that while it produces a draught sufficient
to run the fire it is no where near as effective as a small 12v fan.
Currently I put this down to insufficient steam heating, I can see
droplets of water being discharged with the steam. I think the water
capacity of the flash steam coil is too high. To reduce this I have
acquired a length of diesel fuel injector steel pipe, this is 6mm od
with a 2mm wall thickness.
Now the theory is that a propane ejector entrains a volume ~23 times
the forcing flow, given the differences in mole weights of steam and
propane a much smaller mass of steam at high temperature should do the
same job, as long as the velocity of steam through the orifice stays
subsonic.
The propane burner only expects to discharge into ambient pressure, so
a high back pressure is going to be a problem. My stove has been
measured to only require a back pressure of ~5mm of water gauge (I
only measure water gauge and do not have a ready conversion to pascals
or bar) and I do not believe this to be a problem. I now wish to
develop the idea into somethim=ng more robust and less prone to
blockage.
I also feel the helical coil is not the best configuration and wish to
try a spiral coil which will double as a pan hob proceeding into an
expanding spiral helix in the superheating section.
Of course the assumption is that steel brake pipe or injector pipe is
available from scrap vehicles as well as a means of jointing them. I
have used braze which will survive the temperature in my tincanium
stove (~650C). To make this device at UK prices from new materials
means the steam coil is in the order of 10 times the cost of all the
other materials.
AJH
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