[Stoves] Stoves Digest, Vol 47, Issue 25
Luis Osorio
laosorio at gmail.com
Thu Jul 24 17:38:38 CDT 2014
Dear Julien,
I would think viscosity of gases increases with temperature due to the
ashes on them nearing the point of softening.
Regards,
Luis Osorio
Mobile:+57 300 615 1434
On Thu, Jul 24, 2014 at 1:00 PM, <stoves-request at lists.bioenergylists.org>
wrote:
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> Today's Topics:
>
> 1. Re: Trials on TLUD Gas Burners - Burner Diameter
> (Crispin Pemberton-Pigott)
> 2. Trials on TLUD Gas Burners - Burner Diameter (Julien Winter)
> 3. Re: Trials on TLUD Gas Burners - Burner Diameter
> (Crispin Pemberton-Pigott)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 23 Jul 2014 19:07:08 -0400
> From: Crispin Pemberton-Pigott <crispinpigott at outlook.com>
> To: "'Discussion of biomass cooking stoves'"
> <stoves at lists.bioenergylists.org>
> Subject: Re: [Stoves] Trials on TLUD Gas Burners - Burner Diameter
> Message-ID: <COL401-EAS138DE80B078EB1CF3D71D18B1FE0 at phx.gbl>
> Content-Type: text/plain; charset="utf-8"
>
> Dear Julien
>
>
>
> This is a good and helpful report with a lot of practical experience built
> in.
>
>
>
> On slide 7 it says ?However, heating air decreases its density, so air
> velocity must increase to maintain the quantity of oxygen mixing with
> pyrogas.?
>
>
>
> It is probably worth mentioning, because it is against common sense, that
> increasing the temperature reduces the density but increases the viscosity.
> Getting the right size hole is not quite as simple as a pro-rata change in
> area. That plus of course the shape of the entry hole changes the flow (a
> lot).
>
>
>
> @Paul S Anderson, what do you think of us putting together a chart with a
> diameter/flow plot for different levels of draft?
>
>
>
> Question: In slide 18, it gives the burn rate per unit time per unit
> volume. I can?t grasp that easily. Is the density somehow detectable in
> there? What is the mass loss rate in g/minute? While I realise that
> meaningful interpretation requires knowing the volume of fuel involved, I
> was trying to calculate the water mass out of the burn rate to see what the
> ?real burn rate? was. It is difficult to do that as the mass per unit time
> is not the metric.
>
>
>
> Is there some other way you can report the burn rate for different fuel
> moisture levels?
>
>
>
> It would be helpful, if you stick to the mg/minute/cm2 and first factor
> the mass loss raw data for the moisture content so it is mgDRY. In that way
> we can calculate the fuel burn rate and then, using the moisture level,
> calculate the true realisable energy (potential) value.
>
>
>
> Performing this calculation sometimes gives surprises. From the look of
> the curves, the energy available drops as well as the burn rate. This is
> intuitive but not always the case. One thing to take a lesson from is the
> investigation which shows that 15% moisture fuel usually has lower PM
> emissions in most devices than 10% or 5%, but increasing it above 15% more
> sees the level rise. For each stove type there is an optimum.
>
>
>
> For the TLUD?s with a different burner design, there is probably a
> different optimal moisture level.
>
>
>
> Thanks for sharing the presentation.
>
>
>
> Regards
>
> Crispin
>
>
>
>
>
> Hi Stoves;
>
>
>
> In May, I reported to this listserv on some tests I had done with a
> menagerie of gas burners.
>
>
> http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/2014-May/008665.html
>
>
>
> My tinkering has continued, and some results are attached as a pdf that
> show some interesting features of ND-TLUDs. For example, the best I could
> do for a turndown was about 2x, and turndown is very sensitive to primary
> air supply.
>
>
>
> These tests follow from the earlier work were is was shown that placing a
> concentrator disk below the secondary air inlets did not result in a flame
> concentrated above the aperture in the disk. Instead, pyrogas moved
> radially outward to the underside of the secondary air holes, and became
> entrained in the jets of secondary air.
>
> In addition, I was using gas burners that were 1.2 x larger than the
> diameter of the TLUD combustion chamber so as to get more space to
> manipulate secondary air, and more space for the gas flame to develop.
> This work suggested that is was possible to increase the diameter of the
> gas burner even further. The current trials put this to the test. Here is
> an abstract of the study:
>
>
>
> ABASTACT
>
> Gas burners for a natural draft, top-lit updraft gasifier (ND-TLUD) were
> assessed for visible flame characteristics and their effect on gasification
> rate. Two main design options were tested: diameter of the burner and
> preheating secondary air. Burners were tested on wood chip fuel that varied
> in moisture content, and primary air was adjusted to get very low to
> maximal rates of gasification. Preheating secondary air had no visible
> effect on the gas flame nor did it alter gasification rate. Increasing the
> size of the gas burner from 1x to 1.2x the diameter of the TLUD
> significantly improved gasification rate, reduced flame height, and reduced
> visible smoke production. Further increasing burner diameter to 1.5x TLUD
> diameter didn?t cause a further increase gasification rate, and made the
> reaction unstable at low rates of primary air and high fuel moisture
> contents. Increasing the diameter of burners to at least 1.2x looked very
> promising for improving TLUD operation. Burners of 1.5x may be suitable
> for TLUDs that only run at high gasification rates. Larger diameter
> burners will likely cause less air pollution, and should be tested for CO
> and particulate emissions.
>
>
>
>
>
> Increasing the size of gas burners could be tested with some of Jock
> Gill's ideas for increasing flame temperature in the burner.
>
>
> http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/2014-May/008843.html
>
>
>
> All the best,
>
> Julien.
>
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> ------------------------------
>
> Message: 2
> Date: Wed, 23 Jul 2014 20:49:31 -0400
> From: Julien Winter <winter.julien at gmail.com>
> To: Discussion of biomass cooking stoves
> <stoves at lists.bioenergylists.org>
> Subject: [Stoves] Trials on TLUD Gas Burners - Burner Diameter
> Message-ID:
> <
> CALv4xTxHqzjmB+H35+1c-UYid13GQf2jWA9vj8e9MuZwikNF_Q at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Dear Crispin and Stovers;
>
> Thanks for your comments. They are very insightful, as always.
>
> You make a good point that I should mention viscosity. I have read that
> viscosity of gases increase as their temperature increases, but I don't
> know why. Does anybody have an answer and a reference?
>
> The reproduction of slide 18 may not be very clear. I am reporting all my
> gasification rates as mg/min/cm^2. Unless my equation is in error (side
> 14), this is loss of fuel dry matter / unit time / per unit area of TLUD.
> I divided by the area of the TLUD to give a 'specific' gasification rate
> that could be directly compared measurements on other TLUDs of different
> diameters.
>
> When designing an experiment, the researcher often wants to hold certain
> features constant, whilst varying an experimental factor. This often leads
> to situations which are not quite optimal. In my case, I held the diameter
> of the secondary air holes constant, whilst varying burner diameter. That
> way I was isolating the effect of diameter. However, under practical
> circumstances, it may be better to decrease the size of the secondary air
> holes as diameter decreases. Thus the 1x burner may work better with
> smaller holes. (I did try this on 16% moisture fuel with no success.) So
> a more thorough experiment would be to vary both hole size and burner
> diameter.
>
> I have varied hole size in another trial. The gasification rate increased
> when I increased hole diameter, but I decreased the number of holes to keep
> the total area for secondary air constant. I had 16x 1.45 cm, 12x 1.75 cm,
> and 8x 2.05 cm holes. However, this is another example of keeping
> something constant and producing an impractical consequence. If you
> increase the hole size, but decrease their number, the space between holes
> becomes too large; so in practical terms, you can't increase hole diameter
> and keep the total area for secondary air constant. The burner with 8 x
> 2.05 cm holes had to be scrapped.
>
> The good thing about small prototype TLUDs is that you can run many trials
> at low cost, and develop theories and hypothesis to be corroborated later
> on full size models. This trial had 90 experimental units for the lowest
> three moisture levels. I would not like to have tried that with a full
> size stove without having run prototypes first. However, when it comes to
> developing real world stoves, prototypes will not suffice. In the end, we
> have to get the response curves for changing the dimensions of working-size
> burners.
>
> The MOST IMPORTANT thing I have discovered is that if you mix canned chick
> peas with canned tomatoes, a lot of fried onions, and curry paste ... and
> eat this mix with rice several times a day for a few weeks, you will have a
> lot of tin cans. It helps to wash it down with coffee that comes in large
> cans.
>
> Cheers,
> Julien
>
>
> --
> Julien Winter
> Cobourg, ON, CANADA
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> ------------------------------
>
> Message: 3
> Date: Wed, 23 Jul 2014 21:24:47 -0400
> From: Crispin Pemberton-Pigott <crispinpigott at outlook.com>
> To: stoves at lists.bioenergylists.org
> Subject: Re: [Stoves] Trials on TLUD Gas Burners - Burner Diameter
> Message-ID: <COL401-EAS25B34299C1D744F6E37E8CB1FF0 at phx.gbl>
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> End of Stoves Digest, Vol 47, Issue 25
> **************************************
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