[Stoves] Secondary combustion.

[Crispin Pemberton-Pigott]

Dear Dr Tom and All

I have been looking at the speed at which the incoming secondary air
increases in temperature and happily found this
http://www.people.fas.harvard.edu/~yhuang/research/thesis.pdf which says
(page 46/155) that the collection of heat by air from a radiative source is
highly dependent on the moisture content and in fact the temperature of that
moisture (Planck effect) with a substantial portion of broadening of
spectral lines of absorption being caused by Lorentz and Doppler broadening,
both strongly affected by temperature.

Let's suppose cold air through a small jet heats very rapidly from the
moment it emerges from the hole. It will expand rapidly with all sorts of
perturbations commencing and lots of chaotic mixing. Good news. It is taking
heat out of the fire, one way or another. Will this grossly affect the fire?
I guess that also depends on the moisture content, but if we say that the
ultimate temperature is 1500 K then then total energy in the secondary air,
preheated or not, is a pretty small portion of the total.

If that small portion could produce a significant difference in CO
combustion, then it would matter.

Regards
Crispin still thinking about it

Dear Tom and all.

I work with industrial  gas furnaces,

Some use a mixture of gasses with H2, CO, CO2, CH4 with traces of C2's to
C4'4's. -  with a HV as low as 16 MJ/m3.  Others burn Natural gas with a HV
of 40 MJ/m3.  Some have preheated air and some do not.

All run with a minimum of excess air, with about 1.5 to 2% O2 in the flue
gas and very low CO.

The common factor in all these flames is the 3 T's .  Turbulence,
temperature and time.  All having turbulent mixing,  A well insulated
combustion chamber, and a large area for the flame to burn to completion.

This is the scenario that we need to try and emulate as far as possible in
the secondary flame of our stoves. How close we can get to this is the big
question.

Regards,
John Davies

-----Original Message-----

From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Thomas Reed
Sent: 31 July 2011 01:38 PM
To: stoves at lists.bioenergylists.org; Paul Anderson; Hugh McLaughlin
Cc: stoves at lists.bioenergylists.org
Subject: Re: [Stoves] Stoves Digest, Vol 11, Issue 38

Crispin and All

Let's explore the plus and minus of preheating secondary air.  




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