[Stoves] radiant heat capture, total heat measurement

Paul Olivier paul.olivier at esrla.com
Sat Mar 10 16:40:40 CST 2012


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
>>>
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>>>
>>
>>
>> --
>> 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/
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