[Stoves] Fwd: Re: Explaination of downdraft in TLUD updraft stoves ---was --Re: Mis-information
Paul Anderson
psanders at ilstu.edu
Sat Mar 24 11:40:44 CDT 2018
From Hugh McLaughlin to the Stoves Listserv (forwarded by Paul Anderson)
-------- Forwarded Message --------
Subject: Re: [Stoves] Explaination of downdraft in TLUD updraft stoves
---was --Re: Mis-information
Date: Sat, 24 Mar 2018 16:23:27 +0000 (UTC)
From: Hugh McLaughlin <wastemin1 at verizon.net>
Reply-To: Hugh McLaughlin <wastemin1 at verizon.net>
To: Paul Anderson <psanders at ilstu.edu>, Discussion of biomass cooking
stoves <stoves at lists.bioenergylists.org>, gkharris316 at comcast.net
<gkharris316 at comcast.net>, Hugh McLaughlin <wastemin1 at verizon.net>
All,
The World Stove is a TLUD - there is no central downward flow of vapors,
for two good reasons:
Thermodynamics: The proposed descending hot gases, oxygen-free, are
proposed to supply the necessary latent heat to convert the biomass to
char. That heat duty is estimated at 5% of the heat of combustion (to
heat the biomass to 400C and vaporize the wood gas). Please don't cite
the exotherm from the formation of the graphene structures - they amount
to about a 50C temperature rise at best. One simply cannot get the
necessary flow of inert gas down the column of fuel to keep the
carbonization going - without diluting the wood gas to a energy density
below the level necessary to support combustion.
Fluid Dynamics: The density of a column of vapor inside the fuel stack
is less than the density of the column of vapors in the annulus of the
stove. In the absence of some overriding pressure gradient, the vapors
follow the path of least density, with increased temperature resulting
in decreased density of the local vapor. If this phenomenon is dictating
flows, then the cold outside air is splitting and going to both the
primary air entrance and up the secondary air pathway.
World Stove advocates, in the form of Nathaniel, there is a Bernoulli
effect (https://en.wikipedia.org/wiki/Bernoulli's_principle).
Unfortunately, at any reasonable vapor flows for a tiny stove, the
Bernoulli effect is far below the magnitude necessary to reverse the
flow in the fuel stack from buoyancy-driven upflow to postulated downflow.
I admire the attention Nathaniel has brought to the Stove Community, but
his claim of uniqueness from commonplace TLUD technology is unsupported
by the (cruel) science of the situation. The utilization of forced draft
does not materially change the above analysis.
Hugh McLaughlin, PhD, PE
On Saturday, March 24, 2018 9:34 AM, Paul Anderson <psanders at ilstu.edu>
wrote:
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/>
On 3/24/2018 7:39 AM, Ronal W. Larson wrote:
> Kirk et al
>
> You have it partially correct - but we are not talking about a TLUD.
> There is no MPF (Moving Pyrolysis Front). Rather, the pyrolysis
> gases are created by the downward flowing (very) hot gases..
Incorrect. There is no way for the very hot gases that are the flame
at the top to go downward WITH O2 through a substantial layer of hot
charcoal and then reach the raw biomass fuel at temperatures that are
going to cause full-fledged pyrolysis (at least above 400 C) and
continue downward to exit through what are called "primary air inlets"
(but are claimed to be outlets).
>
> Besides N2, there is a fair amount of CO2 - but no O2. Much more gas
> comes out the bottom than enters (all valuable pyrolysis gases) .
> Possible only because of the Venturi effect - not iimportant in TLUDs.
>
> See http://www.charcoalproject.org/2010/05/a-man-a-stove-a-mission/ .
My very quick look at this did not find speciic content about proving
the downdraft issue. (If anyone finds specific content, please call
it to my/our attention.)
>
> and:
>
> https://foodtank.com/news/2017/05/nathaniel-mulcahy-worldstove-talks-clean-cooking-stoves/
Also an Info item, not a science item.
>
> and
>
> https://www.youtube.com/watch?v=QsH_Gh-n2Mg
This is the FORCED AIR Lucia stove and is not relevent to the current
conversation.
See further down my reply to Noil (or was the Neil), and Crispin and Kirk.
>
> I will look for more technical descriptions. Note these above
> emphasize the biochar part of cooking.
>
> Ron
>
>
>> On Mar 24, 2018, at 1:52 AM, Kirk H. <gkharris316 at comcast.net
>> <mailto:gkharris316 at comcast.net>> wrote:
>>
>> All,
>> I like Noll’s remarks. If down-draft was occurring the gasses would
>> cool as they pass through the unburned fuel and so the vapors would
>> condense and become smoke. There would be lots of smoke exiting the
>> primary holes. This is not happening in the video. Creosote would
>> soon coat the entire bottom and annulus portions of the stove and
>> clog the primary air openings. Creosote may also coat the unburned
>> fuel and so restrict the air flow. Also the unburned fuel would get
>> hotter and hotter and possibly begin pyrolysing in mass.
VERY good point. Something that can be studied via observation without
lots of expensive equipment.
>> Paul’s question about how air would get to the MPF from above is
>> unanswered. The air would have to pass through the flame. This may
>> be possible because the flame is a gas and gasses are permeable. But
>> as the air passes through the flame, the oxygen would get used up so
>> only nitrogen would descend into the fuel and the MPF would go out.
>> Crispin remarks that it would have to be an air restricted situation
>> for down-draft to occur and only around the edges. This sounds true,
>> and you would not get much fire power in an air restricted
>> situation. And remember how TLUDs go out when turned down too much?
>> Would whatever this is have the same problem?
Yes, such a flow is to be considered. I visualize it as a donut.
Primary air upward through the donut hole and then some pyrolytic gases
downward as an annulus (the sides of the donut. Also to be studied.
>> With adequate primary air to keep the MPF going, adequate secondary
>> air, and an open top the gasses inside would be actively interacting
>> with the outside atmosphere. All the gases, including near the edge
>> of the chamber are hotter than the atmosphere and subject to rising
>> via buoyancy, although perhaps at different rates.
>> It is unlikely that it is down-draft.
CLARIFICATION: Downdraft has at least two meanings. One can be the
movement of gases, such as some pyrolytic gases moving downward in the
fuel column (what we are discussing). The other is as in a downdraft
gasifier there the hot gases exit the gasifier by going downward THROUGH
the bottom layer of red-hot (white hot) charcoal.
So the wording could be It is unlikely that it is down-draft
[gasification] Which it is not in this case. OR It is unlikely
that [there] is down-draft [of some gases within the column of fue.].
(which is what is being discussed.)
NOTE: This is te the most vigorous TECHNICAL-BASED DISCUSSION on the
Stoves Listserv for quite some time. I like it!!
Paul
>> Kirk H.
>> Sent fromMail <https://go.microsoft.com/fwlink/?LinkId=550986>for
>> Windows 10
>> *From:*Paul Anderson <mailto:psanders at ilstu.edu>
>> *Sent:*Friday, March 23, 2018 6:09 PM
>> *To:*Hugh McLaughlin <mailto:wastemin1 at verizon.net>;Stoves and
>> biofuels network <mailto:Stoves at lists.bioenergylists.org>
>> *Subject:*Re: [Stoves] Explaination of downdraft in TLUD updraft
>> stoves ---was --Re: Mis-information
>> 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 <mailto:psanders at ilstu.edu>
>> Skype: paultlud Phone: +1-309-452-7072
>> Website:www.drtlud.com <http://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> <mailto:psanders at ilstu.edu>wrote:
>> *Explanation of downdraft in the fuel chamber of TLUD (UP draft)
>> stoves.*
>> Paul S. Anderson, PhD 21 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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