[Stoves] radiant heat capture, total heat measurement

Sat Mar 10 18:30:24 CST 2012

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.
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.

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.
This gives me reason to believe that the transfer of convective heat is
much more efficient when a dome is present.
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.

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
>>>>
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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/
>

-- 
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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