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Dear Julien</div>
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What a great set of links!</div>
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There is a LOT of water in air a lot of the time. We plan the SeTAR style diluter to anticipate / deal with 140 g/m^3 and bring it down to 14 or less with dry air dilution. </div>
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In spite of the large amount I doubt <span style="font-size: initial; text-align: initial; line-height: initial;">
it varies it much because O2 is larger and heavier. </span></div>
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<span style="font-size: initial; text-align: initial; line-height: initial;">It is possible to get 600 deg of preheat which about doubles the viscosity. Flow through a hole is however not linear with viscosity. Heh heh. </span></div>
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<span style="font-size: initial; text-align: initial; line-height: initial;">Now you know why stovers like James Robinson have degrees in aeronautical engineering. </span></div>
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<span style="font-size: initial; text-align: initial; line-height: initial;">Regards </span></div>
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<span style="font-size: initial; text-align: initial; line-height: initial;">Crispin
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<div><b>From: </b>Julien Winter</div>
<div><b>Sent: </b>Saturday, July 26, 2014 10:00</div>
<div><b>To: </b>Discussion of biomass cooking stoves</div>
<div><b>Reply To: </b>Discussion of biomass cooking stoves</div>
<div><b>Subject: </b>[Stoves] Trials on TLUD Gas Burners - Viscosity of Heated Air</div>
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<div>Hi Stovers;</div>
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<div>In an earlier correspondence, Crispin mentioned that when air temperature increases, there is an increase in the viscosity of air as well as decreased density (and oxygen concentration), and that will have implications for the design of TLUD stoves that
preheat secondary air.</div>
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<div>I looked further into why air viscosity increases with temperature.</div>
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<div>An explanation can be found in the <u><font face="Tahoma"><font face="Tahoma">The Physics Hypertextbook</font></font></u><u><font face="Tahoma"><font face="Tahoma">
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<p><font></font><a href="http://physics.info/viscosity/"><u><font color="#0000ff" face="Tahoma"><font color="#0000ff" face="Tahoma"><font color="#0000ff" face="Tahoma">http://physics.info/viscosity/</font></font></font></u></a></p>
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<p>"While liquids get runnier as they get hotter, gases get thicker. (If one can imagine a "thick" gas.) The viscosity of gases increases as temperature increases and is approximately proportional to the square root of temperature. This is due to the increase
in the frequency of intermolecular collisions at higher temperatures. Since most of the time the molecules in a gas are flying freely through the void, anything that increases the number of times one molecule is in contact with another will decrease the ability
of the molecules as a whole to engage in the coordinated movement. The more these molecules collide with one another, the more disorganized their motion becomes."
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A table of dynamic viscosity of dry air can be found here:</p>
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Kadoya, K; Matsunaga, N; Nagashima, A. 1985. Viscosity and thermal-conductivity of dry air in the gaseous-phase. Journal of Physical and Chemical Reference Data 14: 947-970
<a href="http://www.nist.gov/data/PDFfiles/jpcrd283.pdf">http://www.nist.gov/data/PDFfiles/jpcrd283.pdf</a></p>
<p>For dry air at 0.1 MPa pressure, their table gives:<br>
temperature = {250.0, 300.0, 350.0, 400.0, 450.0, 500.0, 550.0, 600.0, 650.0, 700.0, 750.0, 800.0, 850.0, 900.0, 950.0, 1000.0, 1100.0, 1200.0} °K<br>
viscosity = {16.06, 18.57, 20.90, 2.3.10, 25.17, 27.13, 29.02, 30.82, 32.57, 34.25, 35.88, 37.47, 39.01, 40.52, 41.99, 43.43, 46,22, 48.91} 10E-5 Pa · s</p>
<p>An online calculator for thermodynamic state variables of air can be found here:<br>
Peace Software <a href="http://www.peacesoftware.de/einigewerte/luft_e.html">http://www.peacesoftware.de/einigewerte/luft_e.html</a></p>
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The calculator values are very close to those of Kadoya et al. (1985) above.<br>
When the temperature of dry air increases from 25°C to 300°C, the dynamic viscosity increases from 18.48 to 29.86 10E-6 Pa s, or 1.6 times.</p>
<p>I haven't yet found data for air containing water vapor.</p>
<p>The conclusion is that the secondary air entry ports into the pyrogas burner of a TLUD may need to be larger for preheated secondary air than for ambient secondary air.</p>
<p>Cheers,</p>
<p>Julien.</p>
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<div dir="ltr">Julien Winter<br>
Cobourg, ON, CANADA<br>
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