Re: Wonderful Fans/extra water

[AJH <andrew.heggie@dtn.ntl.com>]

On Tue, 4 Jun 2002 10:10:51 +0000,
kenboak@stirlingservice.freeserve.co.uk wrote:

>Stovers,
>
>Despite a period of absence from the list, I have been following your discussion regarding fans.

Nice to hear from you again Ken, I lost you after my last e-mail.
Having now tried a couple of flash steam monotube boilers I could use
some analysis of my figures.
>
>Might I suggest a simple idea using a jet of steam to entrap a greater volume of air up through a chimney and thus creating a forced draft using the steam ejector principle. 

I use my steam aspirator to provide the combustion air pressure for
two reasons.
1) A steam ejector as used on a steam engine requires a chimney, as
you have seen my burners work slightly pressurised and without a
chimney. The pan gets in the way of a chimney, though Rogerio and Dean
have posted on progress with sunken pots with flues.

2) With relatively poor heat exchange surfaces the cookstove rejects
heat at a relatively high temperature, this tends to mean induced
draft flue gas movers need considerably more power, though they act in
addition to a chimney effect.


>
>Alternatively using 2 computer fans mounted on a common shaft, one being driven by the jet of steam in turbine mode, the other used as a fan to create the draft.  We used to make steam turbines as kids from old cocoa cans - before we had the luxury of computer fans with precision bearings.

Computer fans I have seen have plastic blades which potentially will
melt. An axial steam turbine coupled to a centrifugal fan could well
work and be formed from tincanium, bearings would be a problem. There
would be no need for a common shaft as such as they could be formed on
the same "propeller", like the bypass fan on a jet.

What price per watt will you be able to get one of your engines down
to?
>
>On a completely different subject,  when bone dry wood is "roasted"  in an oxygen depleted atmosphere, and begins to pyrolise - will some of the byproducts of pyrolysis break down to create additional water vapour as a results of the chemical cracking of the cellulose material?  

Yes, Tom Reed has often posted in the past that the various stages of
"cooking" wood into charcoal are akin to removing water molecules from
the idealised "wood molecule". Consider that the wood was formed by
the tree taking water from the ground, carbon dioxide from the air and
using the energy from photons combining them to a sugar which is
further combined to make the collection of carbohydrates we know as
wood, expiring the oxygen as a by product. This is photosynthesis.

Pyrolysis is the splitting of this wood back into its constituent
parts, one part left in the absence of oxygen for complete combustion
is charcoal. This charcoal is the "fixed" charcoal of the original
sample of wood and comprises some 25-70% of the original carbon in the
wood depending on conditions in the carboniser.

If the char sample is pure you will see that the amount of water
vapour given of via pyrolysis is exactly the same as if the whole
sample had been burnt and will amount to about 50% of the dry weight
of the original wood.
>
>I recently observed a great deal of water vapour released from a "dry" wood sample - much more than I expected, and I wondered if other Stovers had had experience of this.

Be aware that with british hardwoods and uk climate it is unusual to
have a sample better than 15% mc wwb even if it has been stored under
cover.

AJH

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