[Stoves] Heat transfer and in-line water heater

[Paul S. Anderson]

Dear All,

Dean and Tom and Crispin and Phillip and 2 Andrews and others have given good
comments that I am trying to digest.

Tom mentioned radiant heat at 500 C and above being so important.  Yes.  But 30
degrees C for bath water up to 100 C for boiling and higher to do most baking
at under 300 deg C.  Even frying can be under 500 C, but not likely to get
those temperatures via convection or non-special conduction.  So that
lower-value heat really can be quite useful.  If only we can capture it. 
Consider:

Use aluminum.  Aluminum is so common in cookware in developing societies.

Cover the pot because so much heat is lost from the open tops.

Wider-bottom pots/vessels.

Insulation

Slowness (dwell time) of the hot emissions long enough to impact an item (pot or
food) that is surrounded (as in baking or in an immersed/sunken pot).

All of the above are NOT allowed or favored in the standard water boiling test. 
Instead, the requirements (needed for comparibility) are for Stainless steel,
uncovered, uniform diameter, not specially insulated pots, and "get vigorously
moving gases into contact with the pot" because need to get to boiling at least
reasonably fast.

So our important efforts concerning clean-burning cookstoves (and testing them)
do not encourage much work on these other important points that should be part
of our work on improved cookstoves.

Kudos to Allen B. of Oregon and Dale Andreatta of Ohio for their ongoing work on
heat transfer.

So, how do we get these issues to be considered more and in conjunction with
other aspects?  It is all about "application of the heat" and the "human
factors of what people want", and not about combustion or fuels.

Example:  At my location in India, there is concern about the cost of simple
heating of bath water, especially in the cool months.  Basically, water for
bathing is heated separately from cooking activities.  What I am doing is
trying to place a very simple water heater into the flow of the exit gases. 
Because I am focused now on a forced-air TLUD, my stove is not dependent on the
creation of draft by the exit gases.  I can cool (utilize the heat) the exit
gases in:

an aluminum (or even copper) container of water (for bathing or washing) that
has plenty of surface area but an almost closed top in an insulated widened
chamber of the exit chimney where the gases can move slowly to give up that
heat, with no intention of boiling the water (just get it hot so it can be of
used for bathing directly or after mixing with cold water), and be available
during or soon after every cooking event/meal (so possibly during most to the
day and evening).

I do not know now well this will work.  No data yet and possibly only partial
data before I must leave here.  But worth some effort, and maybe pick up an
extra 10% of the heat (just guessing:  is anyone able to give guidelines on
this?)  What I am doing is hardly new.  Old wood-burner stoves had a water tank
at one end for heating water, and some had tanks on chimneys.

By the way, to keep the costs down, my unit is made of two standard
square-topped tins (5 gallons - 20 liters, I think) for vegetable oil.  I have
seen and used such recycled tins in other countries, especially in my Bolivia
work.  First tin is the outer body (24 by 24 by 32 cm high).  Second tin is cut
to provide the cylindrical inner surface of the "chimney" into which the water
container (perhaps 8 liters??) is inserted.  The space between the two metal
surfaces is filled with any of the following:  mineral wool, ashes, or just
dead-space of air.  Hot gases enter into the inner cylinder from the bottom or
from a side-entrance down low, pass upward around the water container, and exit
either through another side-entrance up high or simply exit via a gap at the
top.  I will be checking for any condensation/accumulation of nasty stuff, but
I expect very little from the TLUD combustion of woodgas.

BTW, my son Simon (age 23) arrived today to assist me until we leave on 20 Dec.

Paul
-- 
Paul S. Anderson, Ph.D., Geography professor - Emeritus
Telephone:  USA-309-452-7072 (residence and office)
Internet site:  www.ilstu.edu/~psanders
For my gasifier stoves info, go to:
http://bioenergylists.org/contributors#Paul_Anderson



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