[Stoves] Fwd: RE: Explaination of downdraft in TLUD updraft stoves ---was--Re: Mis-information
Paul Anderson
psanders at ilstu.edu
Sun Apr 1 09:12:11 CDT 2018
Dear Kirk and all,
Kirk wrote to "All" but it seems to have come only to my address. So I
am sending to the Stoves Listserv Kirk's message (including his
attachment drawing), to which I provide my response after his message
has been read.
PSA
-------- Forwarded Message --------
Subject: RE: [Stoves] Explaination of downdraft in TLUD updraft stoves
---was--Re: Mis-information
Date: Sun, 1 Apr 2018 00:13:11 -0700
From: Kirk H. <gkharris316 at comcast.net>
To: Paul Anderson <psanders at ilstu.edu>
All,
I have been trying to think how down-draft might be possible in this
stove. I am not convinced that the Venturi effect alone could do it
working against the draft. The attached drawing might explain how it is
possible. What do you think?
Kirk H.
Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for
Windows 10
________________________________________
Reply by Paul is below:
Kirk and all,
I have previously posted my thoughts that the co-mingled
primary/secondary air (two purposes of air that are not with separate
entrances) means that the venturi effect is causing a lowering of air
pressure inside the bottom part of the sealed fuel chamber.
To test that hypothesis on paper, take your diagram and place a number
of small (2 - 3 mm) holes into the bottom of the fuel chamber (and
therefore with access to ambient air). It will be functioning as a
normal TLUD stove, not as a downward sucking (DS) stove. To test that
hypothesis in the real world, have a functioning DS stove with maybe 6
holes in the bottom, closed off with screws. Remove one screw.
observe. Remove a second screw and observe. Remove more and more
screws. That is one test.
Prediction, the DS function will weaken with the removal of each screw,
until there is an equilibrium of air pressure inside the bottom of the
chamber, and then (maybe with one more screw being removed) the primary
air will rise through the fuel. Be alert that there might not be any
glowing pyrolysis (normally at the MPF) to allow the creation of a MPF
(pyrolytic front) as in a normally operated TLUD stove. Be prepared to
re-gnite the upper flame (if needed) to prevent a smoke event.
The second test is to have a cold start of a "DS stove with open
bottom-holes" that is loaded with fuel, and do a standard top ignition.
And watch to see if the TLUD or DS process occurs.
I think that I am correct. The venturi effect on those lower side hole
can still be operational, but it will be pulling out sideways some of
the true primary air that is entering from the bottom. The result will
be no reduction of the air pressure inside the fuel chamber, and TLUD
operation will dominate.
Paul
__________________________
*From: *Paul Anderson <mailto:psanders at ilstu.edu>
*Sent: *Saturday, March 24, 2018 6:34 AM
*To: *Discussion of biomass cooking stoves
<mailto:stoves at lists.bioenergylists.org>; gkharris316 at comcast.net
<mailto:gkharris316 at comcast.net>
*Subject: *Re: [Stoves] Explaination of downdraft in TLUD updraft stoves
---was--Re: Mis-information
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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