[Stoves] Explaination of downdraft in TLUD updraft stoves --- was --Re: Mis-information
Paul Anderson
psanders at ilstu.edu
Fri Mar 23 20:05:01 CDT 2018
Hugh,
Thanks for the reply. I am forwarding it to the Stoves Listserv.
The impact of the air being drawn in (creating a draft onto the ignited
stick) should be able to be checked by shielding the flame from the
direct draft.
To all: How can we get copies of these messages to Heath Putnam for
his input?
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 3/22/2018 5:41 PM, Hugh McLaughlin wrote:
> Paul,
>
> I am unconvinced. One of the comments (the first - Arthur Noll)
> provides an explanation - it is the air being drawn into the base
> (primary air inlets) that stimulate the burning at the bottom.
>
> Hugh
>
> Noll's comment is copied below:
>
> That is interesting, but I'm not convinced that pyrolysis products are
> coming out of the bottom. You don't see any smoke coming out the
> bottom until you put the flaming stick in there. The stick could be
> producing the smoke that hits the bottom of the can, turns sideways
> and joins the flow of air, much of which is rising up the sides
> between the containers, while smaller amounts are going in to the
> wood. If it were correct that products of pyrolysis were going down
> and then up, I would expect to see a significant amount of smoke
> coming out the bottom and up the sides all the time, not just when the
> stick was put in. And I would expect to see soot and tar
> precipitating out on the surfaces between the containers. Pyrolysis
> produces a combination of gases, smoke, soot and tar. It is messy. I
> have built these stoves and this area is always clean, even after many
> burns, just like what you have is clean. I have always felt that the
> smoke, tar and gas from the pyrolosis was rising up, and the preheated
> air coming out the secondary air holes, going into this mixture of
> flammable gas and vapor, made the jets of flame. I don't think it
> makes any difference whether you have a jet of air going into a mass
> of flammable gas or if you have a jet of flammable gas going into a
> mass of air, both can give you a jet of flame.
>
>
> On Thursday, March 22, 2018 9:05 AM, Paul Anderson
> <psanders at ilstu.edu> wrote:
>
>
> *Explanation of downdraft in the fuel chamber of TLUD (UP draft) stoves.*
> Paul S. Anderson, PhD21 March 2018
> **Stovers,Previously I wrote:
> *******************
> This link takes you to [what I am calling Video A.)
> https://www.youtube.com/watch?annotation_id=annotation_1962734105&feature=iv&src_vid=wzN-cYR84_Y&v=b0vM9aD78XY
> Same fellow. and showing clearly UPdraft. Side by side comparisons.
> Well worth watching.
> That is dated 2015. I hope that somebody will delve into this further.
> *****************************
> First, we all should thank Heath Putnam for his research and for
> reporting it publicly. He also provided an earlier video that lh
> cheng saw and called to our attention:
> https://www.youtube.com/watch?v=wzN-cYR84_Y
> This I am calling Video B. Although dated earlier, it is better to
> watch Video A first.
>
> After sleeping on this question last night, I think I have an
> explanation. And it also would explain what Nate Mulcahey presented
> as the "Everything Nice Stove" which he claimed was not a TLUD stove
> and claimed to be a downdraft flow of the pyrolytic gases (or Opposite
> draft). Putnam's work shows (but does not explain) the answers about
> downdraft in updraft TLUD stoves.
>
> The big clue (revealed in video (A) above) is the difference between
> the two trial units. The difference is a sealed bottom that enables a
> "co-mingled air supply zone" for somewhat restricted primary and
> secondary air versus abundant secondary air that arrives separately
> from the supply of primary air.
>
> If the primary air entry is direct or very nearly direct and
> sufficient even with a small, restricted flow, it will sustain the
> migratory pyrolytic front (MPF), and all the air and gases will flow
> upward. This is the CLASSIC description of TLUD operation.
>
> But consider the case of a TLUD-design stove that has a closed bottom
> (or is sitting reasonably tightly on a flat surface that prevents
> entry of abundant air) AND also has somewhat limited entry (via 4
> holes in Putnam's glass outer cylinder) of air for *_BOTH _*primary
> and secondary air into a space (a "co-mingled air supply zone") from
> which BOTH types of air must be drawn. Therefore, the only exit is
> upward. The only DRAFT for the stove is powered by the flame of the
> burning gases at the top.
>
> Consider the case of a functioning TLUD stove when the MPF is below a
> layer of charcoal about 3 to 6 cm down from the top, with another 7 to
> 12 cm of raw fuel below the MPF. The pyrolysis occurs, and the hot
> gases tend to rise upward through the layer of char and into the zone
> of the cooking flame. But the flame requires secondary air, which
> can only come up in the ring (annulus) between the two cylinders, and
> it does come up. This is the vast majority of the total supply of air
> (about 5 units for secondary to 1 unit of primary air). In fact,
> that natural draft by the flame is pulling the air from the
> "co-mingled air supply zone" (that one place of air supply which is
> also feeding the primary air). There is therefore a reduction of air
> pressure below the MPF, and that means less movement of the primary
> air upwards.
>
> The result is that there is sufficient lower pressure that SOME of the
> pyrolytic gases move downward. Probably some swirling also, or some
> channels of gases going down but with SOME (at least some) primary air
> (the O2 is the important part) moving to the MPF.
> With a little bit of time, some of the pyrolytic gases reach the entry
> holes of the primary air and leak outward into the "co-mingled air
> supply zone" where there is fresh air entering and where those gases
> can be combusted (as shown in the Putnam demonstration in Video B).
> Impressive. And if there is no flame down there, those pyrolytic
> gases can be pulled upward to become part of the upward flowing
> secondary air THAT IS NOW PRE-MIXED (-but rather diluted to some
> unknown amount -) WITH COMBUSTIBLE GASES. Nice trick, and you can
> see Putnam's demonstration of a taller, stronger flame (Video A).
> This is important. Pre-mixing is to be encouraged. But it should be
> understood and done intentionally to attain consistent results.
>
> BUT in the described simple setup, production of the pyrolytic gases
> is suffering. There is a somewhat deficiency of primary air. That
> could be forgiven (or overlooked or ignored) except for one very
> important factor:
>
> When the downdraft is occurring, the stove user loses some control
> over the fire. The draft from the burning gases is now regulating
> (in part) the operations of the TLUD stove. The normal control of a
> TLUD fire is by closing off some primary air, or using a small fan,
> but these are no longer as effective because of the co-mingled air.
> As the flame at the top changes when there is downward flow (shown by
> Putnam), there is a ripple effect to the air flows. Adjust, then
> adjust again, and then adjust again.
>
> You can look at the Champion TLUD (only one hole for primary air
> entry) or the Quad or the Troika (by Awamu) with only one entry for
> primary air, or some of the other more established true TLUD stoves.
> The Peko Pe by Wendelbo also keeps the two air sources separate.
> Then look at Putnam's variation and at the Everything Nice stove
> and see how the primary and secondary air are comingled and subjected
> to the draft created at the top of the stove.
>
> Also consider what would happen if there actually was sufficient
> downward draft for the FULL reversal of the air flow in the fuel
> chamber. At the top there is flame. And how is there any O2
> surviving in that flame so that it could go downward enough to go
> through the 3 to 6 (and deeper) layer of hot charcoal in order for O2
> to reach FROM ABOVE the top side of the MPF and to sustain that MPF
> for sending gases further downward? And then those pyrolytic gases
> would need to go out through what were the primary air inlet holes,
> and then be mixed with secondary air (but never catching fire because
> somehow there was not a spark there, even at the end of the batch with
> red-glowing coals????), and then rising in the annulus between the two
> cylinders, and only when entering the area of the main flame would
> those gases combust. But this supposition of FULL reversal of the air
> flow is impossible because there are no pyrolytic gases moving upward
> from the MPF.
> Conclusion: In a TLUD stove, there can be PARTIAL downward drafting
> of the created pyrolytic gases when caused by natural draft of
> secondary air to counteract the flow of primary air. This is
> educational, but what is possible is not necessarily desirable or
> practical.
> --
> Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
> Email: psanders at ilstu.edu <mailto:psanders at ilstu.edu>__Skype:
> paultlud Phone: +1-309-452-7072__Website: www.drtlud.com
> <http://www.drtlud.com/>
>
>
>
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