[Stoves] Request to get partners in a possible TLUD stoveimprovement project

kgharris kgharris at sonic.net
Tue Aug 18 15:25:51 CDT 2015


Ron and All,

I do use swirl in the Wonderwerk Strata test combustors.  The swirl  is not for mixing.  Mixing is done first by the Venturi gas mixer arrangement, which uses both draft and Venturi vacuum to mix the gasses.  Thank you Ron Larson for your suggestion of using a pipe across the wood gas column, which eventually led to an adaptation of the Venturi gas mixer for the TLUD stove.  This gas mixer does a supurb job of mixing the gasses, so when the flame enters the swirl, it is already thoroughly mixed.  The swirl is for three purposes:  first to give the flame a longer path to finish burning, second to concentrate the heat for better burn, and three to shorten the height of the flame.

I did some experimenting with using tangential secondary air entrances to create swirl to mix the gasses.  It sort of worked at low speeds, but at higher speeds it seperated the cooler, heavier air from the hotter, lighter wood gas by acting like a centrifuge.  The air moves to the outside and the wood gas to the inside.  This is why the Strata combustor mixes the gasses first, and then swirls the resulting flame second.  This combination works very well.  The Strata combustor that I took to stove camp in July turned in one run at 1mg/min particulates, which is good.  This was at about 3 kw but above this the particulates and CO went up rapidly.  I am now testing an upgraded design (using some ideas those who helped me at stove camp came up with) which seems to make it to my target 5 kw, (It boiled 5 liters of water in 14.5 minutes.  The flame looked quite clean, blue and yellow.).  I will know for sure when Aprovecho tests it.  

The stationary fan which creates the swirl resides directly above the Venturi mixer array.  I have found that the closer the fan is to the mixer, the better it works, so the lower tips of the fan touch the mixer array.  The blade design is very simple.  It is a disk of sheet metal, with six radial slits located evenly around the disk.  The blades formed are each curved into a smooth, gentle curve.  This smooth gentle curve can make use of the Coanda effect.  This effect is that a gas moving along a surface tends to stay close to the surface.  It does not work if there is a sharp bend in the blade or if the blade is too tightly curved.  The flame stays close to the gently curved blade all along its length and leaves the blade at its trailing edge at a very flat angle.  This gives a very high quality swirl.  If the flame is too large it can overload the mixer and fan.  The buoyancy (draft) becomes so strong that it overcomes the Coanda effect and pushes the flame away from the blade early, giving a steeper, less desirable swirl angle.  As a result of this I have been thinking about Rons idea of using a helix shaped blade, which would hold the flame into a spiral.  This would be more complex to build and may increase flow resistance.  I have also been thinking of Julian Winters widening of the combustor, with a wider stationary fan, which would lower the flow resistance.  I have tried this before with good results.  Both arrangments will need testing.

The mixer array is at the bottom of the combustor, the stationary fan is just above the mixer array.  This leaves the rest of the combustor for the swirling flame.  The combustor I am testing now is 5" (13cm) tall.  This is great for the 3kw flame, but a little short for a 5 kw flame as it is exiting the combustor.  I will need to add a little height, perhaps another inch (2.5 cm) will work.  

I hope this adds to the discussion.

Jon Andersen gave me my battle cry,
"Watch out propane!!!"

My best wishes to all,
Kirk

  ----- Original Message ----- 
  From: Ronal W. Larson 
  To: Discussion of biomass 
  Sent: Tuesday, August 04, 2015 6:13 PM
  Subject: Re: [Stoves] Request to get partners in a possible TLUD stoveimprovement project


  Dean:


  I want to emphasize - no making of a new stove intended.  This is to be only an addition to stoves that (hopefully, but not necessarily) have already been tested.  Looking for a breadth of existing designs.  Hopefully these are already in the best “balance” they could achieve.  This is to see whether that can be improved.


  What have you seen in swirl approaches?


  What have you seen in turbulence enhancers?


  Thanks for the quick feedback.


  Ron




  On Aug 4, 2015, at 6:52 PM, Dean Still <deankstill at gmail.com> wrote:


    Hi Ron,


    In my opinion, reducing emissions in a TLUD or any stove requires testing with emissions equipment. The great stove combines many factors working together. "Swirl" is only one part. Kirk gets good results when everything is in balance. "Swirl" is not powerful enough to overcome problems in the balance.


    I completely agree that anyone with tin snips and emission equipment and  perseverance can make low emission stoves. If you are lucky it takes a shorter time. So what? Even if you are unlucky it happens eventually. Drink more coffee.


    Best,


    Dean


    On Tue, Aug 4, 2015 at 5:40 PM, Ronal W. Larson <rongretlarson at comcast.net> wrote:

      Stove list  cc Kirk

              From what I can understand, the lowest emission (particulates, CO is easy) values from TLUDs have been from stoves designed and tested (last week) by Kirk Harris.  One reason seems to be that he has achieved a swirl, using (as described on this list often) a fan blade shape.

              I recall a few other uses of the term “swirl”, but know of no significant tests like those by Kirk.

              In recent conversations, Kirk has agreed to be part of an off-list TLUD stove group to investigate a different means of achieving swirl. It seems to be cheap and applicable to most TLUD stoves.

              The main advantage of a swirl is more flame time spent in the stove;  to get low emissions, hot gases, not flames, need to be hitting the cook pot.

              The proposed approach also should increase turbulence.  I do not recall any TLUD that tried to achieve turbulence  (to get the mixing needed for shorter path lengths and more complete combustion).  Anybody know of designs to achieve turbulence other than added disk or washer shapes?

              The reason for not saying much now is to save list members’ time and energy. This is not a guaranteed approach.

               Anyone joining should want to see this open-source (no patents).

              Anticipated time commitment for a first design - a few hours with tin snips.  Metal cost a buck or two.  Probably can work with clay as well.

              If anyone knows of past swirl or turbulence experiments (or modeling) in TLUDs, your input now could save Kirk and I (and anyone else wanting to join) a lot of time - especially if those results were negative.

      Ron

              feel free to call 303-526-9629, if that would help.
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    -- 

    Dean Still
    Executive Director
    Aprovecho Research Center
    PO Box 1175
    76132 Blue Mountain School Road
    Cottage Grove, OR 97424
    (541) 767-0287
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