[Stoves] mixing of gasses of different pressures

[Daniel]

Kirk, sorry, but for some reason I cannot open attachments on this list. 

What you need to study is fuel injection models or rocket nozzle design to understand natures complex ways of mixing and dissolving one gas into another.

  Turbulence can be folding of layers of gasses, but it can also be any chaotic stirring of the pot.  There are advantages to various schemes to mix with with gas. I attended a hour long seminar once on pesticide spray nozzles and the droplet patterns. At different pressures, fluids ( including liquids and gasses) behave totally different emerging from the same design of nozzle. At a low pressure the fluid follows the sides of the nozzle with droplets ( or gas bubbles) mostly sticking together in large drops. As the pressure increases the droplets break up and scatter according to the design of nozzle. Sometimes the flow breaks up then recombines.
Heat has the effect of making gasses like " thinner" liquids. It breaks up surface tension. At high temperatures, the molecular turbulance may be more important than the macro blending caused by nozzle shape.  Gasses naturally want to reach a blended equilibrium. The lighter the gas ( think hydrogen) or the hotter the gas, the faster that equilibrium is reached.
Another factor is the centrifuge effect with rotating swirling causing thinner and thinner layers to blend with each other. Many forges and waste oil burners use this effect to promote hot, clean burning.
Babbington  burners use high pressure gas emerging from a " blow hole" this breaks up fluid flowing over the hole. 

Hot and cold fluids can sometimes behave like mixing oil and water due to the viscosity differences. This can help or hurt your mixing depending on design but usually the closer in temperature the faster the mixing. Cold hydrogen will mix with hot air faster than hot CO2 because the molecules are smaller.

Dr. Reed used to always remind us that gas mixing is relative to " time, temperature, and turbulance".

To understand what is happening in your devise, use colored smoke and a viewing window.  Or make a model to replicate the process. You can do worse than to study die poured into a creek, flowing around rocks.
. I learned a lot about fluid dynamics watching snow blowing around objects at night under street or headlights. - Dan Dimiduk.

Sent from my Verizon 4G LTE Droid
On Feb 26, 2019 1:20 PM, "Kirk H." <gkharris316 at comcast.net> wrote:
>
> All,
>
> I have some questions about the mixing of gasses of different pressures.  This question arises from my efforts to mix wood gas and air in a TLUD-ND.  When two gasses of different pressures meet (such as higher pressure atmospheric air and lower pressure wood gas), there are two things that I can see happening.  One is that the higher pressure gas expands and compresses the lower pressure gas (expansion and compression).  The other is that, since gasses are permeable, being mostly open space, that the molecules of the higher pressure gas penetrate in between the molecules of the lower pressure gas (I am calling this injection, since one dictionary definition describes forcing one fluid into another by using pressure).  It seems to me that some of both will occur, some molecules hitting each other (expansion and compression) and some missing (injection).  Expansion and compression will not mix the gasses, but injection will mix them on a molecular level.  Injection would give excellent mixing since it brings the molecules together to react (not just folding them over into regions of each gas like turbulence).  I have been designing my mixing system to use injection.  Does anyone know if injection actually is real?  How much penetration is possible?  Is there another name for it that I don’t know?  I think some call it entrainment, but it seems to me that entrainment is a result of injection.  Does diffusion operate at the same time across the pressure gradient?
>
> Kirk H.
>
> Sent from Mail for Windows 10
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