Dear Paul
----- Original Message -----
From: Paul Olivier
To: Discussion of biomass cooking stoves
Sent: Wednesday, March 14, 2012 1:38 AM
Subject: Re: [Stoves] radiant heat capture, total heat measurement
Alex,
I took three sets of temperature readings with and without the dome.
With Without
Reading 1 - 500 C 563 C
Reading 2 - 473 C 578 C
Reading 3 - 470 C 571 C
All measurements were taken at the same height above the burner.
With the dome, the probe remained its normal color.
Without the dome, the probe got red hot.
The burner that I am using is a Belonio burner.
In a first step I added a burner housing to the Belonio burner.
In a second step I added the dome.
I can't imagine that the burner housing alone accounts
for the much better boiling time that I get in comparison to Belonio.
I am totally at loss in explaining these temperature readings.
# The above results seem consistent with the hypothesis I presented in my
posting of 13 March, 8:37 AM ADT. Basically: The Belonio blue flame has low
luminosity, while with the dome, it is heated by the non luminous blue flame
gases, and the "loss by radiadiation from the dome" cools the gases. You seem
to have missed the posting or it point. Accordingly, I include a copy below.
Best wishes,
Kevin
Paul
*****************************************************************************
----- Original Message -----
From: "Kevin" <[email protected]>
To: "Discussion of biomass cooking stoves" <[email protected]>
Sent: Tuesday, March 13, 2012 8:36 AM
Subject: Re: [Stoves] radiant heat capture, total heat measurement
> Dear Andrew
>
> I think your very last comment is very important, and that its importance
is
> being overlooked.
> "Yes the glowing dome will radiate more power than the blue flame."
>
> A "blue flame" has very poor flame radiation characteristics. A yellow or
> red flame has very superior flame radiation characteristics. "Flame
> Luminosity" basically equals better radiation characteristics.
>
> One way to look at it is that "Blue Flames are too smart by half." :-)
There
> is a gain in completeness of combustion, and probably higher temperature
for
> "products of combustion", and reduced sooting of pots, BUT there is a
> significant loss in luminosity, and heat transfer to the pot by radiation.
> The Mesh Dome, heated by direct convection of the "blue flame" then is in a
> position to add a "radiation contribution" to heat transfer capability.
>
> It would be a very interesting experiment to take a "flame temperature" of
> Paul Oliver's system, with, and without the dome. My guess is that the
> "flame temperature" of the "Blue Flame", and the gases leaving the dome
> would be similar, and relatively low, even though the actual thermocouple
> measured temperature of the gases would be high. In very simplistic terms
> (for illustrative purposes only)
> 1: Blue Flame temperature by radiation measurement: 1000
> 2: Gas temperature above dome (radiation) 1000
> 3: Thermometer temperature of both gases 1500
> 4: Flame Emissivity of 1: and 2: .2
> 5: Flame emissivity for luminous flame: .8
>
> Thus, if some of the pyrolysis gases were diverted away from the "blue
flame
> conditions", and were allowed to increase the flame luminosity, there could
> potentially be an opportunity to "have your cake and eat it." More
> specifically, the addition of some "luminous fractions" to the flame could,
> for example increase flame luminosity to say .6. but with a drop in actual
> gas temperature to say 1300 because of incompleteness of combustion.
>
> In other words, "Heat Transfer capability to the Pot" would be:
> 1: Blue flame: 1500 x .2 = 300
> 2: Blue + Yellow" flame conditions = 1300 x .6 = 780
>
> For a "Blue Flame + Radiation Dome, conditions might be
> 1300 x .4 = 510
>
> (NOTE: All these numbers are arbitrary and purely illustrative, to explain
> the concepts)
>
> So.... if the concepts are correct, then it would seem that the best way to
> make a stove would be to make one with a burner that produced BOTH yellow
> flame(for luminosity) and a blue flame (for completeness of combustion).
>
> Does that "hang together for you?
>
> Best wishes,
>
> Kevin
>
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