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<DIV><FONT size=4 face=Calibri>Dear Kirk</FONT></DIV>
<DIV><FONT size=4 face=Calibri></FONT> </DIV>
<DIV><FONT size=4 face=Calibri>Simple stuff can indeed be complex when one digs
into it.</FONT></DIV>
<DIV><FONT size=4 face=Calibri></FONT> </DIV>
<DIV><FONT size=4 face=Calibri>However, there is definitely a "Delta P", or
"pressure difference" that causes air to flow in and hot gas to flow out.
Perhaps you couldn't measure the pressure difference because your manometer was
not precise enough? Small pressure differences are difficult to measure with a
"Standard" U-Tube Manometer, with vertical legs. What about using an "Inclined
Manometer"?</FONT></DIV>
<DIV><FONT size=4 face=Calibri></FONT> </DIV>
<DIV><FONT size=4 face=Calibri>Very simply, get a 2"x4" stud, 92" long.
Accurately set it level on the floor. Get a 1" board piece, and plane it down to
.92" thickness, and use it to prop up one end of the 2"x4" stud. The slope of
the 2x4 will be exactly 1.00%. Lay the water tube... clear vinyl tubing with
water that was coloured with a bit of coffee, on the "inclined board. Thus, a
pressure difference of say .500" Water Gage would drive the water column 50" up
the tube at the slope of 1.00% . You can "Educate the 2x4" by marking it with
divisions every 1.00 inches... each "inch of reading" would represent a "Delta
P" of .01" Water gage.</FONT></DIV>
<DIV><FONT size=4 face=Calibri></FONT> </DIV>
<DIV><FONT size=4 face=Calibri>You could do the same thing with a yard stick,
but in this case you would prop up the 36" end by 0.36" to get the 1% slope.
However, you could only measure a "Delta P" of .3" Water Gage.</FONT></DIV>
<DIV><FONT size=4 face=Calibri></FONT> </DIV>
<DIV><FONT size=4 face=Calibri>Once you get into it, you can probably figure out
the details easily.</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>
<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=kgharris@sonic.net href="mailto:kgharris@sonic.net">kgharris</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, April 14, 2014 3:56
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [Stoves] Thoughts and questions
about Buoyancy</DIV>
<DIV><BR></DIV>
<DIV>
<P style="MARGIN: 0in 0in 10pt; tab-stops: 45.0pt" class=MsoNormal><B
style="mso-bidi-font-weight: normal"><SPAN
style="LINE-HEIGHT: 115%; FONT-SIZE: 14pt"><FONT face=Calibri>Thoughts and
questions about Buoyancy <o:p></o:p></FONT></SPAN></B></P>
<P style="MARGIN: 0in 0in 0pt; tab-stops: 45.0pt" class=MsoNormal><SPAN
style="LINE-HEIGHT: 115%; FONT-SIZE: 14pt"><FONT face=Calibri>I would like to
pose some thoughts and questions to the group about buoyancy.<SPAN
style="mso-spacerun: yes"> </SPAN>I have been trying to think this
through for some time and would like to get some input.<B
style="mso-bidi-font-weight: normal"><o:p></o:p></B></FONT></SPAN></P>
<P style="MARGIN: 0in 0in 0pt; tab-stops: 45.0pt" class=MsoNormal><SPAN
style="LINE-HEIGHT: 115%; FONT-SIZE: 14pt"><FONT face=Calibri><SPAN
style="mso-tab-count: 1">
</SPAN>I used a manometer with attached probe to test my TLUD for gas pressure
variations, measuring to .01 inch of water column, hoping to learn more about
what goes on inside the stove.<SPAN style="mso-spacerun: yes"> </SPAN>I
found no variations in pressure. The stove was at atmospheric
pressure throughout.<SPAN style="mso-spacerun: yes"> </SPAN>I could not
confirm any pressure variations within the functioning stove.<SPAN
style="mso-spacerun: yes"> Can anyone confirm or disprove the results of
this test? Because I found no pressure variations</SPAN>, I had to find
a mechanism which could move the gasses without pressure difference.<SPAN
style="mso-spacerun: yes"> </SPAN>I am looking
at buoyancy.<SPAN style="mso-spacerun: yes"> </SPAN>Heavy gasses
fall and displace light gasses which rise.<SPAN
style="mso-spacerun: yes"> </SPAN>This does not mean that light
gasses have “lift” as in anti-gravity.<SPAN style="mso-spacerun: yes">
</SPAN>They are simply pulled down with less force by gravity than heavier
gasses.<SPAN style="mso-spacerun: yes"> </SPAN>A light weight gas, like
helium or fire gasses, placed in a vacuum chamber will fall, not rise.<SPAN
style="mso-spacerun: yes"> D</SPAN>o heavy gasses push the light weight
gasses up?<SPAN style="mso-spacerun: yes"> </SPAN>I am thinking of it as
a field of gravity where heavier gasses are pulled more by gravity than light
gasses, and so heavy gasses are pulled closer to the center of gravity than
light gasses (ie down).<SPAN style="mso-spacerun: yes"> </SPAN>So
buoyancy can only occur in a gravitational field and is an effect of
gravity.<SPAN style="mso-spacerun: yes"> </SPAN>But then in a state of
equilibrium the light gasses are sitting on top of the heavy gasses and thus
must be exerting a force on the heavy gasses, and vise versa the heavy gasses
must be pushing up on the light gasses.<SPAN style="mso-spacerun: yes">
</SPAN>This means pressure, and it would show up in the overall
atmospheric pressure and so would not be seen in my manometer tests, since
both ends of the manometer are subject to it.<SPAN
style="mso-spacerun: yes"> </SPAN>The question I raise is “Does the air
push up on the fire gases in the non-equilibrium situation inside the stove,
or is it a displacement where the air flows in and the fire flows out all due
to gravity?” <SPAN style="mso-spacerun: yes"> Either way it is clear that
a small bubble of light weight gas in a sea of heavier gas,
such as the situation with our stoves, cannot maintain its position
and must rise. </SPAN>If the heavy gas is pushing up on the light gas,
would not a pressure area have been detected by the manometer
test?<o:p></o:p></FONT></SPAN></P>
<P style="MARGIN: 0in 0in 0pt; tab-stops: 45.0pt" class=MsoNormal><SPAN
style="LINE-HEIGHT: 115%; FONT-SIZE: 14pt"><FONT face=Calibri><SPAN
style="mso-tab-count: 1">
</SPAN>I have read that the raising fire is caused by the difference in
altitude, that the atmospheric pressure on the bottom of our stoves is greater
than the atmospheric pressure on the top and so the fire rises.<SPAN
style="mso-spacerun: yes"> </SPAN>I find it difficult to believe that
the pressure difference in two feet of stove height is significant enough to
drive a high power fire, when the atmospheric pressure gradually changes over
ten miles of height.<o:p></o:p></FONT></SPAN></P>
<P style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt; tab-stops: 45.0pt"
class=MsoNormal><SPAN style="FONT-SIZE: 14pt"><FONT face=Calibri><SPAN
style="mso-tab-count: 1">
</SPAN>Exhaust gasses rising in a chimney do NOT create a vacuum below them
and thus pull air in to the stove, as the word draft implies.<SPAN
style="mso-spacerun: yes"> </SPAN>The atmospheric air falls into the
stove and displaces the hotter and thus lighter weight fire gasses.<SPAN
style="mso-spacerun: yes"> </SPAN>Another way to think of this is to
think of a tube held in a U shape.<SPAN style="mso-spacerun: yes">
</SPAN>Both ends of the tube are at the top and both are open to the
atmosphere.<SPAN style="mso-spacerun: yes"> </SPAN>If one leg of the U,
say the right side, is filled with heavy gas, and the left is filled with
light weight gas, the heavy gas will fall around the bend and then rise up the
left leg to a point of equilibrium.<SPAN style="mso-spacerun: yes">
</SPAN>This is the same as what is happening in our natural draft stoves, the
heavier atmosphere rushes into the stove and displaces the lighter gasses of
the fire.<SPAN style="mso-spacerun: yes"> The primary air is able to
rise through the fuel in the stove like the heavy gas in the U tube is able to
rise in the left leg. </SPAN>But since the incoming air is heated by the
fire and becomes buoyant, it is itself displaced by more air from the
outside.<SPAN style="mso-spacerun: yes"> </SPAN>A point of equilibrium
cannot be reached until the fire is extinguished and the stove is
cooled.<o:p></o:p></FONT></SPAN></P>
<P style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt; tab-stops: 45.0pt"
class=MsoNormal><SPAN style="FONT-SIZE: 14pt"><FONT face=Calibri><SPAN
style="mso-tab-count: 1">
</SPAN>A taller chimney creates more draft because it contains a taller column
of light weight gasses, which means a taller column of heavier atmosphere
outside the chimney.<SPAN style="mso-spacerun: yes"> </SPAN>This gives
more height difference for gravity to act on.<SPAN
style="mso-spacerun: yes"> </SPAN>Buoyancy strength in this
situation depends on the weight (density * gravity)
difference between the gasses, and the column height.<SPAN
style="mso-spacerun: yes"> </SPAN>A chimney two feet tall will have
twice the weight difference of gas to act on as a chimney one foot tall.<SPAN
style="mso-spacerun: yes"> </SPAN>Thinking in terms of electricity,
stacking the volumes of gas on top of each other is like batteries in series
and stacking them side by side is like batteries in parallel.<SPAN
style="mso-spacerun: yes"> </SPAN>The batteries in series will double
the voltage like the air volumes stacked above each other in a chimney will
double the buoyancy head.<o:p></o:p></FONT></SPAN></P>
<P style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt; tab-stops: 45.0pt"
class=MsoNormal><SPAN style="FONT-SIZE: 14pt"><FONT face=Calibri><SPAN
style="mso-tab-count: 1">
</SPAN>A fire temperature of 1600 F with air temperature at 50 F to 100 F
creates considerable difference in density and weight between the fire and the
air.<SPAN style="mso-spacerun: yes"> </SPAN>A hot air balloon rises at
only 250 F, or a temperature difference of 200 F with the air, about
1/8<SUP>th</SUP> of the difference the fire in our stoves creates.<SPAN
style="mso-spacerun: yes"> </SPAN>The density of the gasses in the fire
is about 1/4<SUP>th</SUP> that of the atmosphere.<SPAN
style="mso-spacerun: yes"> </SPAN>One could expect to see a very lively
fire based on buoyancy as the driving force.<SPAN
style="mso-spacerun: yes"> </SPAN>This is my conclusion, buoyancy is the
driving force in our natural draft stoves, and most likely in an open fire as
well.<SPAN style="mso-spacerun: yes"> </SPAN>I do not know how this will
effect stove design, but it does help me to understand how a natural draft
stove operates.</FONT></SPAN></P>
<P style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt; tab-stops: 45.0pt"
class=MsoNormal><SPAN style="FONT-SIZE: 14pt"><FONT
face=Calibri></FONT></SPAN> </P>
<P style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt; tab-stops: 45.0pt"
class=MsoNormal><SPAN style="FONT-SIZE: 14pt"><FONT
face=Calibri><o:p>Kirk</o:p></FONT></SPAN></P>
<P style="LINE-HEIGHT: normal; MARGIN: 0in 0in 0pt; tab-stops: 45.0pt"
class=MsoNormal><SPAN style="FONT-SIZE: 14pt"><FONT face=Calibri><o:p>Santa
Rosa, CA. USA</o:p></FONT></SPAN></P>
<P style="MARGIN: 0in 0in 10pt; tab-stops: 45.0pt" class=MsoNormal><SPAN
style="LINE-HEIGHT: 115%; FONT-SIZE: 14pt"><FONT face=Calibri><SPAN
style="mso-tab-count: 1">
</SPAN><SPAN
style="mso-spacerun: yes"> </SPAN></FONT><o:p></o:p></SPAN></P></DIV>
<P>
<HR>
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