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Post by peterberg on Apr 2, 2012 6:25:26 GMT -8
@dk,
I do know quite a bit about performance and temperatures in rocket stoves, and I do know what insulation can do to the performance of an already nice working experiment. Insulation is not a stop gap, it's a way to achieve the highest possible temperature in a carefully designed combustion chamber. I've seen the difference with and without, using the same design. And yes, mud isn't an insulator at all, some other substances are way better than that.
But, when somebody's postulating insulation isn't necessary and the loss of heat is neglectable, I won't buy that.
That's not to say your design isn't capable of smokeless combustion, by the way. Testing it is the only way to know what level of hydrocarbons is released.
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Post by Deleted on Apr 2, 2012 9:08:52 GMT -8
The Maths do not work in favor of small things with insulation.
Insulation increases the circumference by 8 times the thickness in square cross sections.
With round cross sections it is a bit better.
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Post by peterberg on Apr 2, 2012 10:04:31 GMT -8
The Maths do not work in favor of small things with insulation. Insulation increases the circumference by 8 times the thickness in square cross sections. The cross sectional area will be increased when adding insulation, yes. What do you mean by that? Are you trying to say: because of that the insulation won't insulate and the temperature won't rise? |
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Post by Deleted on Apr 2, 2012 10:24:28 GMT -8
In extreme cases, like the example with harddrives and bitumen, the temperature could even fall.
To compensate for the increased surface one would habe to use extremely good and usualy also extremely expensive insulation for small things.
Because of this Suncus etruscus needs to eat up to two times it's own body weight daily
and can still only survive by using some aditional enegy saving tricks.
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Post by peterberg on Apr 2, 2012 12:23:19 GMT -8
In extreme cases, like the example with harddrives and bitumen, the temperature could even fall. To compensate for the increased surface one would habe to use extremely good and usualy also extremely expensive insulation for small things. Because of this Suncus etruscus needs to eat up to two times it's own body weight daily and can still only survive by using some aditional enegy saving tricks. Very interesting, especially about the Suncus etruscus, said to be the smallest mammal of the world, but not terribly relevant in this case. Mainly because I'm talking about a specific situation, not about the extreme cases you mention. You have done the math and the theory, I've done the measuring and the outcome is different from yours. Without insulation the highest temperature inside the 10x10 cm steel feed tube reached 820 C. Adding insulation in the form of exfoliated vermiculite, about 5 cm of it and all else equal, around the feed tube and the burn tunnel let the temp rise to 1150 C, measured by a digital thermometer rated 1370 C maximum. By that moment the sensor died quietly because it was rated 1000 C only. The temp rose to that level in mere seconds after inserting the sensor, so I would think the real temp was even higher. Theories aside, it looks like insulation do work as an insulator in these specific circumstances, don't you think? |
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Post by Deleted on Apr 3, 2012 0:17:54 GMT -8
Yes.
However I do not belive DK could sell a lot of his small devices with this kind of insulation.
Suncus etruscus was meant as an example for the hefty price tag for small and moveable things.
The small animal can not afford more or better insulation, as the price would be it's live.
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Post by dkrocketstoves on Apr 3, 2012 10:14:59 GMT -8
From Aprovecho Research Centers own paper.
Insulation
An unexpected discovery from these experiments is the effect of insulation on the efficiency of the rocket
stove. First, it was shown that adding perlite insulation increases efficiency by about 2 to 5 percent over an
uninsulated 4.5” diameter stove. However, super insulating the stove with two layers of fiberglass blanket
insulation does not increase efficiency, but instead caused performance to actually decrease by as much as
3% for the 9” high stove.
on my small DK stoves,I have found that adding insulation slows the cooking times down.
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Post by peterberg on Apr 3, 2012 23:46:50 GMT -8
From Aprovecho Research Centers own paper. That's a paper I haven't seen yet, can you provide a link? Increasing the combustion temperature and everything else being equal, the efficiency will decrease because of higher heat loss through the exhaust. That's exactly one of the problems I've stumbled into. When more heat is produced the heat exchanger ought to be upgraded as well. |
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Post by Deleted on Apr 4, 2012 2:26:17 GMT -8
That supports what I have said.
The ARC paper as well.
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Post by Deleted on Apr 4, 2012 5:07:10 GMT -8
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Post by Rinchen on Apr 4, 2012 5:27:45 GMT -8
From the same page
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Post by Deleted on Apr 4, 2012 6:53:41 GMT -8
ROFL For a research center that explanation is plainly ridiculous and a shame. Insulation -> low mass Super insulation -> super low mass or none at all (vakuum). If mass could be an explanation it would affect the biggest piece the most, not the medium. I did not think one could take that serious.  |
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Post by dkrocketstoves on Apr 4, 2012 10:19:18 GMT -8
From Aprovecho Research Centers own paper. That's a paper I haven't seen yet, can you provide a link? This is for small cooking stoves (open top) not mass heaters. |
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Post by Deleted on Apr 5, 2012 5:16:30 GMT -8
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Post by woodburner on Apr 5, 2012 8:51:51 GMT -8
I think fibreglass is not a good insulator at rocket stove temperatures. It might work up to perhaps 200ºC, but after that performance drops off because there is enough energy to move the air around in the relatively large voids. The spec for this material is only around 500ºC. For higher temperatures and better performance www.advancedthermalsupplies.com.au/products/thermal/#1 would be a starting place. There are stiff boards available to and I was able to make a rocket stove from 1" board, burn for 10 mins and then pick it up with bare hands. That's insulation. I see the problem with mild steel stoves is that if they are run hotter, by using lots of insulation, then the stove wont survive for long. |
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