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<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>
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style="LINE-HEIGHT: 115%; FONT-SIZE: 14pt"><FONT face=Calibri><SPAN
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</SPAN><SPAN
style="mso-spacerun: yes"> </SPAN></FONT><o:p></o:p></SPAN></P></DIV></BODY></HTML>