[Stoves] radiant heat capture, total heat measurement
Kevin
kchisholm at ca.inter.net
Thu Mar 15 12:36:09 CDT 2012
Dear Paul
----- Original Message -----
From: Paul Olivier
To: Discussion of biomass cooking stoves
Sent: Thursday, March 15, 2012 3:31 AM
Subject: Re: [Stoves] radiant heat capture, total heat measurement
As you all recall, Belonio and I, using the same reactor and the same burner,
report a difference in boiling times.
I was bringing a liter of water to a boil in about half the time that Belonio was reporting.
I assumed this was because of the dome.
But this assumption now appears to be completely wrong.
The dome does not reduce in any way the amount of time it takes to bring a liter of water to a boil.
In an experiment this morning, I took the dome off the burner
and put the pan of water at exactly the same height as if the dome were in place.
I did a second experiment with the dome in place.
The boiling times were exactly the same with or without the dome.
I apologize to you all in leading you to think that thermal radiation was making a big difference.
# No problem!! You raised some interesting questions relating to stove operation and improvement.
So now the only thing that remains to account for the difference
in boiling times between Belonio and me is the burner housing that I put around the burner.
# OK!! A 50% reduction in boiling time is very significant. What can you now tell us that will enable us to apply it to other stoves and combustion conditions?
Thanks!
Kevin
The burner housing feeds secondary to the burner holes.
What you see here:
http://www.youtube.com/watch?v=nZDt8DfgSls
appears to be just as efficient as what you see here:
http://www.youtube.com/watch?v=yO3jcbQj-GI
Here is a picture of the burner with burner housing:
http://dl.dropbox.com/u/22013094/150%20Gasifier/Boiling/IMG_1024a.JPG
The two parts are welded together.
Also I did another test in which I boiled water without the dome -
but this time at about one inch lower than the dome pan height.
This put the pan one inch closer to the flames.
Again there was no difference at all in boiling times.
Also I took several temperature readings:
1.. with the probe as close as possible to the blue flames: 646 C (probe turned red)
2.. with the dome in place and at the top of the dome: 463 C
3.. with the dome removed but with the probe at the same height as if the dome were there: 532 C (probe turned red)
4.. with the dome and with a pan of water above it: 390 C (probe situated in between the two)
Thanks.
Paul
On Thu, Mar 15, 2012 at 9:26 AM, Tom Miles <tmiles at trmiles.com> wrote:
Alex, Paul,
One option is to use a suction pyrometer in which you pull the hot gas past
the thermocouple in a tube. The tube limits the radiation so you get a
better picture of the true temperature. Temperatures can be about 90C (200F)
higher in the suction pyrometer than in a boiler or free air. A simple
version can be made with compressed air venture drawing air through a pipe
with a thermocouple inside it.
Tom
-----Original Message-----
From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Alex English
Sent: Wednesday, March 14, 2012 6:18 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] radiant heat capture, total heat measurement
Paul,
So this makes sense. The screen radiates away heat leaving a cooler gas
beyond.
If your thermocouple were smaller or shielded the difference would likely be
even greater because the thermocouple looses more heat from radiation when
it is hotter.
Or are there other reasons, too?
Alex
On 14/03/2012 7:36 PM, Paul Olivier wrote:
> There are problems with what I have written below.
> Let me again.
>
> Without the dome, the probe encounters hot gases and registers a
> temperature of 563 C.
> It turns red hot and starts emitting thermal radiation.
>
> With the dome, the probe encounter hot gases as well as thermal radiation.
> But it only registers a temperature of 500 C.
> It does not turn red hot.
> Therefore the probe does not absorb thermal radiation from the dome
> very well.
>
> Thanks.
> Paul
>
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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/
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