[Stoves] Concentrators in ND TLUDs

[Paul Anderson]

Bob and all,   ( I am sending to the Stoves Listserv because the 
discussion merits a wider audience. Please read Bob's message first 
(below my comments.)

Paul writes:
I like your analysis of the options.   And there are additional 
variations such as fins or "mixers" that could increase the turbulence.

I am not in favor of forcing the gases to the outside.   My reasoning is 
that when the gas flow is low (intentionally or otherwise), there can be 
loss of the flame on one side of the "ring-gap" and the flaming side is 
not able to re-ignite the extinguished side, allowing un-combusted gases 
to escape.

I think that the Reed-Larson 1996 natural draft IDD (now called TLUD) 
was not very successful because of the outside gap instead of the 
concentrator hole.   That led (I believe) Tom Reed to shift his efforts 
to force air units.   On the other hand, Paal Wendelbo's Peko Pe of the 
1990s in Uganda had a concentrator hole in the middle.   I do not know 
when or how he started using the concentrator disk.

I do know that my own early experiments were NOT very successful until 
2005 when I (prompted by discussions with Tom Reed about mixing) first 
used the concentrator disk in the prototype "Champion" stove I took to 
Stove Camp where it won the Cat Pee Award for cleanest emissions.

Having said that, I must point out that the Belonio style of very 
successful rice husk gasifiers (with forced air only for the primary 
air) has a ring of holes (not a gap).   I will look further into this 
when I have such units in hand.

I agree with Bob that MUCH more useful experimentation is needed about 
this highly crucial aspect of TLUD stoves.   But there are no funds for 
such research (unless CSU will be looking into this), so I am sticking 
with the reliable concentrator disk in my stove project in Uganda.

Paul   (I will be home from Uganda by Tuesday night)

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

On 2/22/2013 4:28 PM, Robert Fairchild wrote:
>
> *ND TLUD Concentrators*
>
> It seems to me there are several possible concentrator designs for 
> natural draft TLUDs. How many have been tried?
>
> Two dimensional concentrators include the ring (concentrating gasses 
> to the middle) and the disk (forcing gasses to the outside). It seems 
> to me that the disk might give better mixing and cleaner combustion as 
> the width of the space would be narrower. (With a 6” cylinder, a ring 
> with a 4” center hole has the same area as the gap around a 4½” disk. 
> With the ring the secondary air needs to penetrate 2”, with the disk 
> only ¾”)
>
> Three dimensional concentrators are the full venturi (back to back 
> buckets –see attached photo, I tried it and it works just fine), half 
> venturi, inverted venturi, and half inverted venturi.
>
> The half venturi – bottom bucket only - expanding to full cylinder 
> above with ring. This might increase turbulence for cleaner combustion.
>
> The inverted venturi (back to back cones in the center – think 3D 
> disc) and the half “inventuri” - bottom cone only. Again, the half 
> version might increase turbulence for cleaner combustion. The inverted 
> venturi, like the disc gives a shorter secondary air penetration 
> distance than the true venturi.
>
> (Note: a venturi creates suction (to pull in more secondary air) at 
> the constriction, Bernoulli “Where the speed is greatest the pressure 
> is least”. It does, however, remove some energy (increases friction 
> losses) and slows the primary gasses from how fast they would flow 
> without the venturi.)
>
> Of course a disc or inverted venturi will need to be supported in the 
> center of the cylinder with three or more radial supports.
>
>  Thoughts?
>
>  Bob
>

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