[Stoves] Somewhat urgent question¿ Interior cross sectional area of a plancha stove.

[Dean Still]

Dear Charlie,

This reply will be short because I'm heading out of town. I don't type as
fast as you do, anyway.

So, in my opinion:

1.) When we start designing a stove we build a prototype after checking with
local cooks to see what they want. Checking with the local cooks takes as
long as needed or as much time as we have (weeks to months). The prototype
starts with equal cross sectional area. Then we test it (WBT) under the
emission hood changing the gaps. This can take weeks or longer until the
stove has the best balance between fuel used, CO and PM to boil 5 liters and
simmer it for 45 minutes. We use both the standard 7 liter flat bottomed pot
and local pots. If we notice a big difference we design the stove to best
suit the local pots, like round bottom pots in India.  Also using the
standard pot gives us a way to compare the stove to make sure it is as good
as other similar stoves.

2.) Then the prototype is given to local cooks to get their input using
local food, local wood, local pots, etc. (CCT) The feedback is then
incorporated into a new prototype which is tested as above. The process goes
back and forth between WBT and CCT until the stove pleases local cooks and
also uses less than 850 grams wood, makes less than 20 g of CO, and less
than 1500mg of PM. So we and funders can feel confident that we have an
improved stove.

Durability of materials is harder. If you can throw a super heated floor
tile into a cold bucket of water and it doesn't crack it will probably last
long enough to please folks. Great if you can make the floor tile combustion
chamber easily replaceable.

Testing, developing of prototypes in the field determines gaps, materials,
configurations. If we don't have a way to test emissions, then using the CCT
to compare new and traditional stoves is great too. In my opinion, the new
stove should improve fuel used by at least one third to one half and make
considerably less observable smoke. The cooks should hopefully want to take
the stove home without a rich funder standing close by with possibly more
goodies, etc.

Best of luck, my dear friend!

Dean



-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of Charlie Sellers
Sent: Wednesday, August 08, 2007 10:35 AM
To: Discussion of biomass cooking stoves
Subject: Somewhat urgent question¿ Interior ross sectional area of a plancha
stove.

I can get to town/electricity every few days and am on line on and off for a
few hours right now.  The dimensions of our planch stove design here in Peru
are somewhat limited by the dimensions of the types of hollow brick
available (I can only cut tile - or break bricks in a clumsy fashion - and
have only simple tools) so various dimensions of the stoves are limited.
Particularly the chimneys - only scrap iron pipe or stacked hollow bricks
are here - so I want to be a little flexible in the open area of the stove
at various places in the cross section.

One ¨rule¨of the rocket is constant cross sectional area throughout the
stove but it seems that the exit/chimney really only needs a larger area
than the rocket entrance - true?  I use the analogy of a river flowing into
a new channel - if the area diminishes then smoke backs up into the room.
And if the new channel is smaller then the flow out needs everything is
fine.  And if there is a temporary wide spot inside the stove then there is
no problem, as long as the exit is larger than the entrance?
   
  I am trying to increase the size of the combustion chamber as much as I
can, since the plancha will slow the time to boil (and other perceived
problems), to increase the firepower a little.  But I only have limited size
possibilities for either the entrance and exit, and I don´t yet know how to
exactly take into account that there is an expansion of gas as it heats, and
there is a net increase in gas volume during combustion.  How does the equal
area rule take such things into account¿  I am taking some risks, but as
long as I increse the chimney area I hope to be fine.  As always, I want the
best conditions to increase the burning of the smoke before it leaves.
   
  Any advice on whether commercial floor tiles can generally be the walls of
the combustion chamber¿  What exactly is baldosa tile¨¨ - specifications¿  I
tested mine (and also the hollow bricks) in a very hot fire with no
problems, but success in the longer run is too important to take too many
risks.
   
  thanks in advance!
   
  Charlie
   


http://improvedstoves.blogspot.com/ - just R&D related to fuel efficient
biomass stove issues
  http://travelswithcharlie.blogspot.com/ - most recent travel posts
http://new.photos.yahoo.com/csellers42/ - travel photos, of everywhere -
click on the country albumns on the left
http://huiplesofguatemala.blogspot.com/ - my textile project in Guatemala -
what colors!
http://travelswithcharlie2.blogspot.com/ - older travel posts, including
Nepal travelogue 
http://ewbappropriatetechnology.blogspot.com/ - just posts for the ATDT of
the EWB-SFP; AT for developing countries

       
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