[Stoves] Nozzles for TLUDs Re: venturi system -ratios of air and gas?

[Paul Anderson]

Dear Kirk,

WONDERFUL MESSAGE by you below.   Stimulates several thoughts and some 
comments.

1.  I will be at the Apro Open House, and will bring with me a 
concept-prototype of a combustor that relates to several of your 
comment, but maybe not as expected.  The concept comes from Kevin Adair 
(not a member of Stoves Listserv) with whom I am working on a TLUD-ND 
project with his NGO in Haiti.   The major change is to have a "nozzle" 
where the concentrator hole is located.   Think of a short, squat 
hour-glass of metal through which the created gases must pass.

2.  Kirk's comment about the thick metal impacting the ability of the 
flame to pass is interesting.   But instead of preventing passage from 
below upward, use it to prevent passage from above downward.   It that 
happens, and if the flame is above and cannot get down below the 
concentrator, then the mixing might be improved (longer time to mix).   
And a better flame above?   These are specculation thougthts.   Perhaps 
someone could computationally model this?   But instead, we can just 
make some and have real-world results much sooner.   This can be a topic 
for the ETHOS and Apro events this month.

3.  There are a number of variables to consider about the nozzle approach.
a.  Diameter of the minimal hole in the hourglass.
b.  Height of hourglass above the concentrator.
c.  Height below the concentrator.
d.  Possible use of more than one nozzle.
e.  Material of the nozzle and maybe with perforations.
f.   Probably a few more variables.

4.  I am very interested in knowing more about
> One of my burner/combustors did work on a forced air rice hull
> TLUD, cleaning up some smoke that was being produced. 
Please bring those materials, etc to the Apro gathering.

5.  I expect to be at the Baymont Inn by 2 PM on Friday 29 Jan.

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype:   paultlud    Phone: +1-309-452-7072
Website:  www.drtlud.com

On 1/10/2016 8:27 PM, kgharris wrote:
> Dr. Boll and All,
>
> I am following the discussion on Venturi ratios with interest. The 
> Venturi has been part of my efforts for over a year. The discussion of 
> pressurized gas Venturi mixers has a very good point for us in TLUD 
> experimenting, it shows that mixing by the Venturi is possible and 
> efficient. The important question for us is can it be adapted for 
> TLUDs. I believe the answer is yes. A TLUD Venturi mixer would look 
> very different from a pressurized gas Venturi mixer. This is because 
> the gasses in a TLUD, not being pressurized, do not reach the same 
> high velocity as the pressurized gas jet exiting a small hole. The 
> pressure drop created in a TLUD would not be as much of a pressure 
> drop as the pressurized gas system and so must have more mixing area. 
> My experiments have been promising, but I have not had the equipment 
> to do thorough testing to prove the Venturi is working as intended. In 
> their latest newsletter, Aprovecho has described new equipment they 
> have for testing gas velocity. The meter could also be used to test 
> for a Venturi vacuum to prove or disprove the TLUD Venturi concept I 
> am working with. I will be at Aprovecho for their open house in early 
> February and with their help we can design a test which will answer 
> this question: "Can the Venturi effect be used in a TLUD to provide 
> similar quality mixing as in a pressurized gas system". Until then I 
> can share some thoughts which may be of some interest.
>
> My designs have the Venturi section after the main secondary burn so 
> the gasses are already burning at this point. Thus this is not a 
> premixed flame because it is already burning, but also it
> is not a diffusion flame because there is active mixing going on. A 
> pre-mixed flame is not possible in a TLUD because the mixture is above 
> combustion temperature and so burns as it is mixed. I suppose it could 
> be called "mixing while burning" or perhaps "concurrent mixing". I 
> have found that the results in a Venturi combustor should rival 
> premixing. As long as the system is not overloaded with too much wood 
> gas it burns super clean as per tests at Aprovecho. High power levels, 
> apparently unlike lower power levels, seem to break off large 
> quantities of soot size particles of carbon, probably at the pyrolysis 
> front. I suspect this has something to do with thermal stresses in the 
> char at higher pyrolysis temperatures. These particulates are 
> difficult to burn completely. The Wonderwerk system is able to handle 
> some of this, but at this point in its development it doesn't seem to 
> be able to burn an excess of these particulates.  It is easier to have 
> super clean combustion at lower power levels.  Perhaps, 
> hypothetically, having a larger fuel chamber area and operating it at 
> a lower power level will produce enough gas to have a high power 
> secondary flame without the excess soot.
>
> The Venturi in my designs is created by directing the gas through a
> restricted area causing it to accelerate, which is accompanied by the
> Venturi effect drop in pressure. The restriction cannot be too tight 
> or a back pressure is
> created. I have been designing the open area through the restriction at
> about half the cross-sectional area of the fuel chamber/reactor, which 
> seems to work.
>
> I do not know the mixed ratio. I adjust it until it works but have no
> calculations for the ratio of gas to air.
>
> To my knowledge there are two things which keep flash back from 
> happening in
> a pre-mixed gas burner. One is that the speed of the gas is
> faster than the burn back speed of the flame. The other (more 
> important) is that the flame
> has difficulty getting through a hole where the thickness of the 
> material is
> equal to or greater than the diameter of the hole. This is because the 
> flame
> loses heat to the material, and so drops below combustion temperature 
> before
> it gets through the hole. This is the technique that made the old time
> miners safety lamps safe to use in a mine with a combustible level of
> methane. I have run into this principle as a problem in my 
> experiments. My design uses parallel pipes with spaces between. The 
> spaces between the pipes are the restricted area. Slits in the sides 
> of the pipes introduce air to the accelerated gasses passing through 
> these spaces. In one experiment I placed the pipes to close together 
> and the flame could not get through to maintain combustion above the 
> pipes. Lots of smoke resulted. Spreading the pipes out helped, but the 
> flame could only get through the center area. The cool air passing 
> through the pipes along the edge cooled flame and did not let it pass. 
> The air was heated when it reached the center so the flame was not 
> cooled and could pass. Widening the spaces at the edges and narrowing 
> them in the center allows the flame to pass evenly (see attachment of 
> a Wonderwerk test combustor turned upside down).
>
> The Venturi allows considerable turn-down. This is possibly because as 
> the
> power level gets lower, the gas flow is lower, and the Venturi effect is
> also less, so the gasses don't have as much chance to get diluted with 
> too
> much air.
>
> The Wonderwerk Venturi system seems to work best as an upper end 
> cleaning device for the
> flame, catching any particulates and tar that gets past the secondary. 
> As such it
> will have different effectiveness depending on how well the lower stove
> burns the gasses. One of my burner/combustors did work on a forced air 
> rice hull
> TLUD, cleaning up some smoke that was being produced.
>
> Best to All,
>
> Kirk
> Santa Rosa, CA. USA
>