[Stoves] radiant heat capture, total heat measurement
rongretlarson at comcast.net
rongretlarson at comcast.net
Sat Mar 10 19:11:05 CST 2012
Paul:
Apologies in advance for some probably dumb questions and suggestions below.
----- Original Message -----
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.
<blockquote>
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?)
</blockquote>
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 ]
<blockquote>
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:
<blockquote>
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:
<blockquote>
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:
<blockquote>
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/
</blockquote>
--
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/
</blockquote>
--
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/
</blockquote>
--
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/
</blockquote>
--
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/20120311/65e2264b/attachment.html>
More information about the Stoves
mailing list