[Stoves] radiant heat capture, total heat measurement

Paul Olivier paul.olivier at esrla.com
Thu Mar 15 01:31:37 CDT 2012


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.

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.
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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