[Stoves] radiant heat capture, total heat measurement

Ron Larson rongretlarson at comcast.net
Sun Mar 11 01:04:47 CST 2012


Paul:

   Much clearer now.  Thanks.

   One last suggestion.   If you successfully boiled as in the short video with the radiant dome, and then quickly removed the cook pot and radiant dome, how would the flame appearance change (assuming no change in fan speed).   If still operating reasonably well, could you then repeat the same boiling test, but now without the dome?

    Would it, alternatively, be possible to get near what you deem the same power level, by changing fan speeds?  (Maybe have to use a scale and the same time derivative of weight?)

    Few more inserted questions below.

On Mar 10, 2012, at 8:38 PM, Paul Olivier <paul.olivier at esrla.com> wrote:

> Ron,
> 
> Let me try to explain things a bit more exactly.
> 
> The fan speed needed to light the biomass is generally higher than at any other time in the batch cycle.
> This assures that the biomass lights quickly.
> 
> Once the biomass is well lit, then the fan speed is turned down,
>  and the burner is placed on top of the reactor.
> If the operator turns it down to just the right degree,
>  the flames within the reactor come through the burner holes,
>  and there is no lighting of the gas.
> 
> It takes a while for the flames within the reactor to go out, 
>  and for all the burner holes to be ignited fully and uniformly.
> 
> The next step is to place the dome above the burner.
> At this point I have to turn down the fan once again.
> The previous speed is no longer needed to obtain a uniform burning of the gases at the burner holes,
>  and generally at the previous speed, too much gas is produced for the dome to handle.
         [RWL1 -  This is surprising to me.  I could have guessed less gas with the dome (more flow resistance).

> It is important, of course, to get total combustion of the gases within and underneath the dome,
>  and if too much gas is being produced, of course the fan has to be turned down.
> Most movements of the fan have to be quite small.
> 
> Therefore the speed regulator of the fan has to move in small increments.
> Otherwise the operator has no control over the process.
> I have no idea how someone can operate a gasifier or pyrolyzer without an incredibly tight control over the flow of primary air.
> A fan with a good speed regulator makes things so easy.
> The fan in normal operation consumes less than one watt of electricity.
> 
> If I turn the fan way down, it is possible to reach a point where there are no longer any flameletts at the burner holes.
> All that is left is a cloud of burning gas at the apex of the dome.
> If I turn the fan back up, fingers of flame begin to move down from the cloud of burning gas to the burner holes,
>  and eventually all of the burner holes ignite again.
> This results in a good turn-down ratio.
       [RWL2- Fascinating!   I guess a much wider turn-down ratio with the dome?]

> Without the protection provided by the dome, it would be impossible for a cloud of burning gas to form.
> Small movements of air around the burner would blow away and extinguish the cloud.
> 
> The burner housing feeds secondary air to the burner and to the dome.
> I do not think that the dome would work without the burner housing.
> If I raise the dome a few mm's above its point of contact with the housing,
>  the dome does not work at all.
> I was so lucky when I first placed a strainer above the burner and burner housing:
>  the diameter of the strainer and the diameter of the burner housing matched perfectly.
> Here is a picture of the burner with burner housing and the wire mesh dome
> http://dl.dropbox.com/u/22013094/150%20Gasifier/Boiling/IMG_1024.JPG
     [RWL- Nice clean photo. Can you provide a description of the path for a typical secondary oxygen molecule getting to the flame let lower edge (relative to the burner housing - which perhaps Prof Belonio did not have?)
> 
> The aperture of the dome can be either too big or too small.
> If too big, the gases pass right through the dome with being fully combusted, and the dome is black rather than red.
> If too small, the flow of gas is restrained so much that the fan has to be turned too low.
> If too low, the specific rate of gasification is, in turn, too low, 
>  and the temperature within the reactor is not high enough to produce H2 and CO in high quantities.
> If H2 and CO are not the predominant gases, then a lot more secondary air is required to burn the gas.
    [RWL- This last part not clear.  It would be nice to have a gas analyzer.]

> The temperature within the reactor running on rice hulls should be about 1,000 C.
> 
> This still leaves behind a lot of biochar,
>  since the bonds between the amorphous silica and lignin with the rice hull are not so easily broken.
> 
> Does this make a bit more sense?
    RWL - A bit.  It is not yet clear how to perform a test to separate the radiant and convective components of the heat transfer.
  Best of luck.    Ron

>  
> Thanks.
> Paul
> 
> 
> 
> On Sun, Mar 11, 2012 at 8:11 AM, <rongretlarson at comcast.net> wrote:
> Paul:
> 
>    Apologies in advance for some probably dumb questions and suggestions below.
> 
> 
> From: "Paul Olivier" <paul.olivier at esrla.com>
> To: rongretlarson at comcast.net
> Cc: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>, "Andrew Heggie" <ajheggie at gmail.com>, "Crispin Pemberton-Pigott" <crispinpigott at gmail.com>
> Sent: Saturday, March 10, 2012 5:30:24 PM
> 
> Subject: Re: [Stoves] radiant heat capture, total heat measurement
> 
> See comments.
> 
> On Sun, Mar 11, 2012 at 6:52 AM, <rongretlarson at comcast.net> wrote:
> Paul:
> 
>    All correct below about water boiling timing - if the rice hull characteristics (size, density, etc), their height in the stove body, and the fan types and speeds are identical.  You will have a better story if the test can be repeated on the same day, with and without a strainer. 
> 
> I agree.
>  
> If necessary, buy a second one, and snip out all the "strainer" material from the frame.  This last as a joke - but there should be a way to get a more guaranteed comparison of the impact of radiation  (where you are using just a stop-watch).
> 
>    Is there any chance that the strainer either causes a faster or slower burn (higher or lower power out?)   
> 
> It is impossible to light the burner with the strainer in place.
>    [RWL1  -  I have a propane tank "torch" which can put out quite a long flame.  Or could a very long "match" do this?  It is not clear why the "in-place" lighting should be impossible.  It would be nice to keep the fan speed constant between runs.  But maybe this is a small problem.  I just worry about accurately replicating the power out level - which "should be" almost entirely independent of the strainer.  But this "supposed "independence" doesn't seem to be borne out in your observations.  Can anyone explain why power level goes up (if it does) with the (air-flow blocking) strainer in place]
> 
> So in lighting a burner, I have to run it for a short while without the strainer.
> And when I put the strainer on the burner, I always have to turn down the fan.
>    [RWL2 -  Or what would happen?   The strainer is sending a lot more energy back towards the flamelets - and probably doing a better job of preheating the secondary air.  If things were set just right for the "strainer-in" mode, and then you removed the strainer, what would the new flame look like (no changes in fan speed, etc)?   I think your next three sentences require my same responses/questions (but if not, maybe you can rephrase something.)
> 
> 
> To get full and uniform ignition at all burner holes without the strainer, a certain fan speed is required.
> But to get full and uniform ignition at all burner holes with the strainer, a lesser fan speed is required.
> With the strainer the flames are far more consistent and stable. 
> 
> The flames acquire structure and are not easily influenced by the wind.
>     [RWL3:  Your observation re wind could relate to  the issue/explanation in my RWL2 - of the flamelet hole region being a lot hotter and thereby able to "hold" better.   With and without the strainer, an IR thermometer (or other) should show a big temperature difference in the "plate" containing the flamelet holes (right terminology not remembered).
> 
>      
> This gives me reason to believe that the transfer of convective heat is much more efficient when a dome is present.
>     [RWL4:  This not clear.  Does "transfer of convective heat" mean to the cookpot?  I would say you are reducing (not increasing) the convective heat transfer - but this is more than made up by the radiative heat transfer.    This confusion on my part relates also to your next sentence on "more efficient".]
> 
> 
>    So with a more efficient transfer of heat by convective means
>  and with the whole new dimension of thermal radiation that comes into play,
>  a lot more heat makes it into the pot.
>     [RWL5:   All the above trying to get a better quantitative handle on "lot more".
> Random thought.  You brought up the issue of these ideas being used in a thermophotovoltaic (TPV)  device.   Maybe one with some light pipes would allow us to separate the convective and radiative phenomena.
>    End this time.    Again, apologies.    Ron]
> 
> You need to time the duration of the same fuel loading to completion I guess - as another part of the test.  Along with all the usual weights, etc.
> 
>   Presumably the impact of a lid will make a difference in the times - but not the ratio of times.
> 
>    If you can prove twice the power level to the cook pot, that will be amazing.  
> 
> Ron
> 
> From: "Paul Olivier" <paul.olivier at esrla.com>
> To: rongretlarson at comcast.net
> Cc: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>, "Andrew Heggie" <ajheggie at gmail.com>, "Crispin Pemberton-Pigott" <crispinpigott at gmail.com>
> Sent: Saturday, March 10, 2012 3:40:40 PM
> 
> Subject: Re: [Stoves] radiant heat capture, total heat measurement
> 
> Ron,
> 
> The burner I am using is the burner that Belonio developed for rice hulls.
> I use the same number of holes and the same hole diameter as he proposed.
> I added a burner housing that reduces the length of the diffusion tail.
> But I do not think that the burner housing makes much of a difference until it is coupled with the radiant dome.
> 
> With his burner, Belonio reported an average time of over 8 minutes to bring a liter of water to a boil.
> Since my burner is a Belonio burner, 
>  since the diameter of my reactor is the same as his,
>  I am confident that the dome allows the boiling time to be reduced by 50%.
> Last week I sent a video of the dome in operation to Belonio,
>  and he was quite positive about this development.
> 
> I plan to do more boiling tests next week with a proper boiling pot with a lid.
> I wonder how much of a difference a lid might make.
> I plan to use a pot with a whistle that will begin to blow when a certain pressure has been reached.
> When the whistle blows, I will stop my stopwatch.
> Otherwise I do not know exactly when to say that water has begun to boil.
> I hesitate to use a standard water boiling pot because the bottom appears to be too reflective.
> I need a boiling pot with a lid and a whistle that can adsorb thermal radiation efficiently.
> Also I wish I had a thermocouple that could withstand temperatures as high as 800 C.
> 
> What I really want to test at this point is dome-shaped ceramic foam.
> 
> Thanks.
> Paul
> 
> On Sun, Mar 11, 2012 at 4:08 AM, <rongretlarson at comcast.net> wrote:
> Paul etal
> 
>   Nice short 13 second video.  Very clear.
> 
>    Is it possible to repeat a timed boiling test with the only difference being whether there is a strainer in or out?    Might also try different pots, artificially changing the pot height, etc   Anything to give more numerical values.
> 
>    This is is to more exactly quantify your earlier observation that the input energy seemed to be about a doubling.
> 
> Ron
> 
> From: "Paul Olivier" <paul.olivier at esrla.com>
> To: rongretlarson at comcast.net
> Cc: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>, "Andrew Heggie" <ajheggie at gmail.com>, "Crispin Pemberton-Pigott" <crispinpigott at gmail.com>
> Sent: Saturday, March 10, 2012 1:33:24 PM
> 
> Subject: Re: [Stoves] radiant heat capture, total heat measurement
> 
> Ron,
> 
> This is not a very good video clip, but it does show the entire 150 gasifier:
> http://youtu.be/8IcXDAK37gA  
> This is a rough prototype made by hand.
> The mass-produced product should look better.
> 
> Also I do not envision that this gasifier be operated as a stand-alone device.
> For safety reasons it should be set within a counter-top enclosure, as seen here:
> http://dl.dropbox.com/u/22013094/150%20Gasifier/Jpegs/008.jpg
> 
> Thanks.
> Paul
> 
> On Sun, Mar 11, 2012 at 2:48 AM, Paul Olivier <paul.olivier at esrla.com> wrote:
> Ron,
> 
> I did yesterday an experiment with aluminum foil to reflect back up the thermal radiation emitted from the dome.
> The aluminum starts to wrinkle and crack well before the burn is complete.
> 
> Also I tried yesterday a wire mesh of an aperture of 30 mesh.
> This did not work as well as what I am using now (a stainer that I bought in the market).
> I have yet to find the factory that makes this strainer,
>  and I do not have the instrument that is needed to measure its aperture.
> 
> Ron, I think that the foam that you have found offers the most promise.
> I am sure that this foam will deliver more radiant energy than stainless steel wire mesh.
> Also I hope to employ a type of funnel that would surround the dome and 
>  focus the laterally emitted thermal radiation toward the pot.
> Finally the pot has to absorb and not reflect.
> 
> Thanks.
> Paul
> 
> 
> 
> On Sun, Mar 11, 2012 at 1:58 AM, <rongretlarson at comcast.net> wrote:
> Andrew, Paul, Crispin, list:
> 
>    1.   The last several paragraphs below are coming out more negatively on radiant heat capture than I think are appropriate.  Remember, the initial information provided by Paul Olivier on March 2, when he said:
> 
> "When a wire mesh dome is placed on top of the burner and burner housing, 
>  this roughly doubles the amount of heat being transferred to a pot:"
> 
>    2.  I think this doubling has little to do with the exchange below (and a few earlier that are similar).  Radiant heaters are  widely sold because of their efficiency in heat transfer - in many cases involving zero convection.  Given we have only one (above) piece of data for one stove, the chances are that a doubling is not the maximum we can achieve.  
> 
>    3.  I would look at this as a conservation of energy problem. We know that we can transfer more energy to the pot if the radiator is hotter.   There may be catalysts that we can employ.   We know how to use reflectors and obtain high absorption (and sometimes simultaneously low emissivity)
>      In my reading on ceramic foam, I found that some foam is being employed so as to have gas combustion take place inside the foam!.  
> 
>    4.   I hope that others can perform some experiments along these lines.
> 
> Ron
> 
> From: ajheggie at gmail.com
> To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>
> Sent: Saturday, March 10, 2012 3:31:17 AM
> 
> Subject: Re: [Stoves] radiant heat capture, total heat measurement
> 
> On Fri, 9 Mar 2012 12:25:49 +0200, Crispin Pemberton-Pigott wrote:
> 
> >>...and passes visible light and higher frequency infra red from hot bodies,
> >like the sun, 
> >
> > 
> >
> >Most of it, the rest makes it warmer (absorbs).
> 
> Yes that which it absorbs make it warmer but equally as a warm body at
> equilibrium it will be re emitting longer wavelength IR.
> >
> > 
> >
> >>but absorbs the lower energy infra red from cooler bodies like earth and
> >our bodies.
> >
> > 
> >
> >Yes, and because it is warm, and active in the IR, it also emits IR but with
> >a low emissivity. In other words if you know the emissivity, you can read
> >the temperature with an IR gun.
> 
>  it is emitting a different (lower) frequency from which it has
> absorbed.
> >
> > 
> >
> >But more to the point I was saying that at a lower (non 90°) angle, it
> >starts to reflect radiation from the top of the surface. Look at glass at a
> >low angle and it looks like a mirror.
> 
> Agreed
> >
> > 
> >
> >The point is that when reflecting heat, if the incident angle is past a
> >critical value, it reflects pretty much all of it so the issues Kevin
> >mentioned about the mirroring on the back don’t come into play.
> 
> This depends on the refractive index of the two materials, going from
> a lower to higher there is always some light transmission, the other
> way round and you have total reflection, this is how a light fibre
> works.
> >
> > 
> >
> >Paul’s question was about reflecting the heat. So the principles are the
> >reflectivity, surface finish, incident angle and emissivity. While a stove
> >may be good at sending IR radiation towards the pot, pots are not all that
> >good at picking it up, actually. Stainless steel pots are quite reflective
> >and do better picking up heat by convection.
> 
> The major salient point is that radiation from heating something by
> flame/flue gases is only ever going to extract a minor portion of the
> heat in the gas stream. Consider a black body in the gas flow, it can
> never be hotter than the gas flow downstream of it, as you make it
> hotter it radiates more heat but the rejected gas flow is also hotter,
> either way you still need to have the convection do most of the work.
> AJH
> 
> _______________________________________________
> Stoves mailing list
> 
> to Send a Message to the list, use the email address
> stoves at lists.bioenergylists.org
> 
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
> 
> for more Biomass Cooking Stoves,  News and Information see our web site:
> http://www.bioenergylists.org/
> 
> 
> 
> 
> -- 
> Paul A. Olivier PhD
> 27C Pham Hong Thai Street
> Dalat
> Vietnam
> 
> Louisiana telephone: 1-337-447-4124 (rings Vietnam)
> Mobile: 090-694-1573 (in Vietnam)
> Skype address: Xpolivier
> http://www.esrla.com/
> 
> 
> 
> -- 
> Paul A. Olivier PhD
> 27C Pham Hong Thai Street
> Dalat
> Vietnam
> 
> Louisiana telephone: 1-337-447-4124 (rings Vietnam)
> Mobile: 090-694-1573 (in Vietnam)
> Skype address: Xpolivier
> http://www.esrla.com/
> 
> 
> 
> -- 
> Paul A. Olivier PhD
> 27C Pham Hong Thai Street
> Dalat
> Vietnam
> 
> Louisiana telephone: 1-337-447-4124 (rings Vietnam)
> Mobile: 090-694-1573 (in Vietnam)
> Skype address: Xpolivier
> http://www.esrla.com/
> 
> 
> 
> -- 
> Paul A. Olivier PhD
> 27C Pham Hong Thai Street
> Dalat
> Vietnam
> 
> Louisiana telephone: 1-337-447-4124 (rings Vietnam)
> Mobile: 090-694-1573 (in Vietnam)
> Skype address: Xpolivier
> http://www.esrla.com/
> 
> 
> 
> -- 
> Paul A. Olivier PhD
> 27C Pham Hong Thai Street
> Dalat
> Vietnam
> 
> Louisiana telephone: 1-337-447-4124 (rings Vietnam)
> Mobile: 090-694-1573 (in Vietnam)
> Skype address: Xpolivier
> http://www.esrla.com/
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20120311/c85520cd/attachment.html>


More information about the Stoves mailing list