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: [email protected] 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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