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<DIV><FONT size=4 face=Calibri>Dear Teddy</FONT></DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=cookswelljikos@gmail.com
href="mailto:cookswelljikos@gmail.com">Cookswell Jikos</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=stoves@lists.bioenergylists.org
href="mailto:stoves@lists.bioenergylists.org">Discussion of biomass cooking
stoves</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, March 03, 2014 2:14
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Stoves] Turn down by moving
the pot</DIV>
<DIV><BR></DIV>
<DIV dir=ltr>Dear Kevin,
<DIV><BR></DIV>
<DIV>Thank you very much for this, I have been thinking about that quite alot
in regards how people in Kenya (and E.A) cook ugali (a polenta maize flour
type of food). It starts out liquid but ends up a solid - how much will the
size (diameter) of the source contribute to cold/hot spots during this
conversion? Is a graduated turn down function or a simple high/low better for
controlling this? </DIV>
<DIV> </DIV>
<DIV><FONT size=4 face=Calibri># In my opinion, an adequate "turn-down ratio"
is absolutely required for such cooking.</FONT></DIV>
<DIV><FONT size=4 face=Calibri></FONT> </DIV>
<DIV><FONT size=4 face=Calibri># There is an "upper limit" to the temperature
in the pot, which is the temperature beyond which the ugali will scorch
or burn to the bottom of the pot. There is also a "lower limit" to the
temperature in teh pot, below which the ugali will not cook adequately. As
long as the stove can be operated in a manner to ensure that the temperature
within the pot is always within this "window", then the stove system can
accomplish its desired function, which is, of course, cooking
food.</FONT></DIV>
<DIV><FONT size=4 face=Calibri></FONT> </DIV>
<DIV><FONT size=4 face=Calibri># At the early stage, when the food is in a
"fluid" state, it can be heated intensely, because the "fluid food" covects,
and carries teh heat to the remainder of teh pot by convection or actual
movement of the fluid. Under these conditions, the temperature of the inside
face of the pot bottom is likely no more than about 5 degrees C above the
boiling point of water at that location. </FONT></DIV>
<DIV><FONT size=4 face=Calibri></FONT> </DIV>
<DIV><FONT size=4 face=Calibri># In the latter stages of cooking, when the
ugali has thickened, it is less able to move by convection, and the heat
transfer mechanism changes over to heat transfer by conduction... heat is
transferred from teh pot bottom, through the cooked ugali on the bottom of the
pot, to nearby ugali, which is not yet cooked. At this point, the "heat
to the pot" must be reduced, because its rate of transfer from the inside of
the pot is greatly reduced, to prevent burning or scorching of the food.
Obviously, if heat is being applied to theoutside face of the pot at a
rate of say 3 watts per square centimeter, and if it is being removed from the
insde face of the pot at a rate of 1 watt/cm^2, then the temperature of the
inner pot face will increase, and burning is likely.</FONT></DIV>
<DIV><FONT size=4 face=Calibri></FONT> </DIV>
<DIV><FONT size=4 face=Calibri># Here would be a neat experiment for you to
try...</FONT></DIV>
<DIV><FONT size=4 face=Calibri>==> Mix up teh ingrredients for a batch of
ugali, and put some of it in a large frying pan that it too big for the heat
source, only to a depth of say 2.5 cm. Place the oversized pan of "raw ugali"
over teh heater, so that only one side of teh pan is heated, and turn on teh
source of heat, and watch what happens. Eventually, you will see a zone of
burned ugali, surrounded by a zone of "over-cooked" ugali, then a zone of
"propertl cooked ugali", followe by a zone of "undercooked ugali", followed by
a zone of "raw ugali." If you noted the temperatures and times during the
test, you could learn a great deal about cooking ugali.</FONT></DIV>
<DIV><FONT size=4 face=Calibri>==> This experiment should vividly
demonstrate the need for a "good" turn-down ratio.</FONT></DIV>
<DIV><FONT size=4 face=Calibri></FONT> </DIV>
<DIV><FONT size=4 face=Calibri># A "graduated turn-down", ie, "infinitely
variable", like a propane stove, is clearly superior to a "stepwise turn-down"
capability, in that the former allows the the inside of the pot surface to be
kept at the maximum temperature below which the ugali will not burn, and
thus will lead to the shortest possible cooking time. </FONT></DIV>
<DIV><FONT size=4 face=Calibri></FONT> </DIV>
<DIV><FONT size=4 face=Calibri>Hope this helps.</FONT></DIV>
<DIV><FONT size=4 face=Calibri></FONT> </DIV>
<DIV><FONT size=4 face=Calibri>Kevin</FONT></DIV>
<DIV><BR></DIV>
<DIV>Thanks, </DIV>
<DIV><BR>Teddy </DIV></DIV>
<DIV class=gmail_extra><BR clear=all>
<DIV>
<DIV dir=ltr>
<DIV><B>Cookswell Jikos</B><BR><A href="http://www.cookswell.co.ke"
target=_blank>www.cookswell.co.ke</A></DIV>
<DIV><A href="http://www.facebook.com/CookswellJikos"
target=_blank>www.facebook.com/CookswellJikos</A></DIV>
<DIV><A href="http://www.kenyacharcoal.blogspot.com"
target=_blank>www.kenyacharcoal.blogspot.com</A></DIV>
<DIV>Mobile: +254 700 380 009 <BR></DIV>
<DIV>Mobile: +254 700 905 913</DIV>
<DIV>P.O. Box 1433, Nairobi 00606, Kenya</DIV>
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<DIV><FONT color=#008000 face="Tms Rmn">Save trees - think twice before
printing</FONT><FONT color=#008000 size=1 face="Tms Rmn">.</FONT><BR></DIV>
<DIV><BR></DIV>
<DIV><BR></DIV>
<DIV><BR><BR><BR></DIV></DIV></DIV><BR><BR>
<DIV class=gmail_quote>On Sat, Mar 1, 2014 at 5:47 AM, Kevin C <SPAN
dir=ltr><<A href="mailto:kchisholm@ca.inter.net"
target=_blank>kchisholm@ca.inter.net</A>></SPAN> wrote:<BR>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote><BR>Dear Paul<BR><BR>I've seen Crispin's reply, and mine
comes from a different angle... hopefully, it will hve an element of
"contribtory helpfulness".<BR><BR>There are two fundamental "cooking tasks",
in the sense that:<BR>1: The product being cooked/heated is perfectly fluid,
such that heat applied to one part of a pot will be transferred by
"convective stirring", such that the entire pot contents are virtually at
the same temperature. Examples would be heating/boiling water, making tea,
or perhaps a "watery soup", boiling an egg, cooking whole potatoes,
etc<BR>2: The product being heated or cooked is viscid and does not "move
around" by convection in the pot. Examples would be cooking rice, frying an
egg, cooking a stew.<BR><BR>In the former case, where the product can move
by convection, and is not subject to burning, then moving the pot to the
side of the stove will reduce the total heat energy picked up by the pot in
a given period of time. For example, if the stove was operating at a
constant heat input rate equivalent to 3 watts per square cm. of pot bottom
area, then moving the pot so that only half the pot was in the heat, it is
clear that the "heat to the pot" would be cut in half. The energy would be
supplied at the same intensity, but to only half the area. The desired
heating task would be accomplished. However, since the fuel burn rate was
the same, and "half the cooking work" was being done, fuel utilization would
be halved. (When cooking an egg or potatoes by boiling, the food does not
move, but the water can circulate freely.)<BR><BR>In the second case, where
the food could not move by convection, when the pot was moved partially off
the stove heating area, with the same heating energy density of 3 watts per
square cm, a "cooking failure" is likely, in that the food in the "hot area"
would be cooked and possibly burned, while the food that was not above the
heated area would be partially cooked or raw. The system would fail as a
"cooker". On the other hand, if the heat input rate could be modulated, all
of the pot bottom could be receiving heat, and there would be no areas of
"overcooking or burning" and no areas of "raw or partially cooked
food."<BR><BR>A "good turn-down ratio" is necessary for the stove to
function properly, when attempting to cook foods that cannot rely on
convection of water throughout the pot, for proper cooking.<BR><BR>To see
the problem vividly, try to cook rice, or stew, or a fried egg on an
electric stove operating on "High Power", and then attempt to control heat
input to the pot by removing part of the pot from the burner.<BR><BR>If a
stove does not have an adequate "built in turn-down ratio", the problems may
be avoided by elevating the pot above the stove, allowing the inflow of
"side air" to dilute the intensity of the stove heat reaching the pot. That
would work, but it would be bad for stove efficiency.<BR><BR>Best
wishes,<BR><BR>Kevin<BR><BR>Quoting Paul Anderson <<A
href="mailto:psanders@ilstu.edu"
target=_blank>psanders@ilstu.edu</A>>:<BR><BR>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>
<DIV>On 2/26/2014 2:25 PM, Crispin Pembert-Pigott wrote:<BR></DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex; PADDING-LEFT: 1ex"
class=gmail_quote>There are many ways to control the power getting into
the pot -- not only lowering the fire. But one way or another control
needs to be exercised by the cook.<BR><BR></BLOCKQUOTE>
<DIV>
<DIV class=h5>Stovers,<BR><BR>One way to have less heat entering the pot
is to move the pot off to the side so that only part of the heat has any
contact with the pot. The results of this are:<BR><BR>1.
The SAME amount of energy / fuel is released in the combustion
chamber, AND<BR><BR>2. LESS water is boiled away from the simmering
pot.<BR><BR>As I understand the WBT procedures, doing this would result in
more favorable efficiency numbers than if the pot was boiling vigorously
on the full impact of the fire, and losing much water.<BR><BR>Can someone
please confirm this for me. And perhaps give an example where
the ONLY VARIABLE THAT CHANGES IS THAT THE POT BOILS OFF SIGNIFICANTLY
LESS WATER if the pot is placed to the side. I am thinking of the
difference in the amount of water in the pot being even 2 or 3 liters less
between the two examples.<BR><BR>Yes, these types of stoves could exist,
as in an example of a TLUD without any turn down of primary air and with a
pot support that allows the pot to be shifted to the side (such as on 2
pieces of rebar).<BR><BR>When we have clarification about this, we can
then discuss if moving the pot should be a factor in stove testing.
And also if the amount of remaining water after simmer should be a
factor.<BR><BR>Paul<BR><BR>Doc / Dr TLUD / Prof.
Paul S. Anderson, PhD<BR>Email: <A href="mailto:psanders@ilstu.edu"
target=_blank>psanders@ilstu.edu</A><BR>Skype: paultlud
Phone: +1-309-452-7072<BR>Website: <A
href="http://www.drtlud.com"
target=_blank>www.drtlud.com</A><BR><BR><BR></DIV></DIV></BLOCKQUOTE><BR><BR><BR><BR>______________________________<U></U>_________________<BR>Stoves
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