[Stoves] Radiant heat and heat transfer

[IPC]

Dear Frank

It is most of the heat the pots feel.  It comes from the flame (which you
see as a radiant heat source because it is luminous) and from the hot gas,
and it bounces off the walls,and flows just about everywhere.  In order to
be able to see it you need something that will let you visualize the
infrared spectrum.  Convection plays a quite small part, and conduction even
less (to the pot surface).  

The critical part about radiant heat transfer is that it varies as the
fourth power of the absolute temperature, and that makes it big.  One of the
terrifying things about nuclear weapons is that they have a surface
temperature around 8000 deg C - compare the sun at around 5700 deg C - and
the fourth power really comes into play. At Hiroshima the glaze on the roof
tiles boiled before the blast wave hit them.  Now that really is Heat
Transfer - but it illustrates the point that radiant heat transfer can
dominate quite easily.

Hope that helps

(Dr)Philip Lloyd
Energy Research Centre
University of Cape Town
Private Bag Rondebosch 7701
South Africa
Tel +27 (0)21 650 3896
Fax +27 (0)21 650 2830
e-mail philip.lloyd at uct.ac.za 

  

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of frank
Sent: 26 November 2007 09:16
To: Discussion of biomass cooking stoves
Subject: [Stoves] Radiant heat and heat transfer

Stovers,

Trying to understand radiant heat in our biomass stoves. Is this the heat
produced within the 'line of sight' of the combustion: and also heat
transfered by metal to water?
If a stove having several pots lined up its the first one in line of sight
that gets the radiant heat and the others get heat by convection from air
(that doesn't work very well?)?

What I am wondering is if one was to start a fire using dry wood then, once
going well, added wet wood the heat produced would travel via steam (radiant
heat?) to the second and third pots (out of combustion sight) and condense
on the cold metal surface transferring the heat to the metal-water So using
wet wood (or adding water mist to the hot gases
produced) aid in getting heat to more places on the pot (back side) and to
pots located at greater distances? It may take heat away to produce the
steam but that is not lost heat unless it makes it past the pots without
being used?

Just wondering

Thanks
Frank




--
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com



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