Modified Kovea Syder for confined pot supports

[James Marco]

Yes, Roger. But what drives the conduction or convection? I know, I know…combustion.

Combustion is when two or more atoms or molecules combine releasing their excess energy by falling into a more stable state…the energy released is usually heat or IR though some small bit is visible light.

IR scatters in a sphere heating the gasses making them less dense, so they rise. And so on…

Same thing really…all driven by the energy release or IR.

[DAN-Y/FANCEE FEEST]

I had to transfer the comment James made here for reference so I don’t have to back and forth to read and re-read. I finished testing. I used up all of the 440 grams of fuel to boil 17 litres of water.

I quote for reference:

Dan, yes.

“James, that radiation is from the outside of the pot, the water inside is not radiating heat outward, the water is still absorbing….correct? yes or no :-)”

Dan,  Not to be a pain in the butt, but Yes and No. Metal absorbs say 99.9999999999999999999999999% of IR radiation (not a correct value.) Some IR manages to slip through directly, though depending on the thickness, density, blah, blah, blah… it is undetectable, generally.

IR is a radiation or enrgy. It absorbed by almost any mass. (Though some is actually transparent to it.) For metals, in general, what happens is it is absorbed, increasing the “heat” state. Heat can be interpreted in various ways: molecular vibratiion, lengthening of electron shells (exitatation), and/or even loss of electrons (ionization) and in extreme heat plasma. Anyway, the heat is retransmitted in a 360 degree probability sphere…some will go back the way it came, some will escape to the next atom. Some of the IR is duplicated as the atom “relaxes” and electrons drop back to their non-excited states. This releases the IR photon to the next atom with the same probability’s all over again. Sometimes it will only release part of the energy as a lower order photon and keeping part as “excitation”. Sometimes it will simply convect to another atom as Brownian movement or molecular “bumping.”  Generally we say the pot gets hot. Anyway, there is no set formula for determining which will happen, only probabilities of possible dispositions for the added additional energy. The transfer of heat from water to metal to the outside is NOT instantaneous, though. Conduction is a measure for the SPEED at which this happens. (Metals form a different structure, but still the rules apply.) So looking at the total pot structure, you can envision the heat as being radiated from the outer surface. But it may have been produced from the second or third or fourth or fifth or some other layer of atoms UNDER the surface, not necessarily from the surface layer of atoms. But, assuming the pot has several thousand layers in its thickness, it will be difficult to know the difference. And, the IR will likely be at a different frequency than the IR released from the water, or the IR released from the flame. This is just basic laser physics as far as the frequency and it is based on the composition of the material releasing the photon…skip it…

Anyway, you can see that water and the pot act the same, except, you deal with two different materials. The water still radiates heat. It may be picked up by the other water molecules, and/or the pot. This “starts” the above heat transfers. There is no actual start, though (at least above absolute zero,) just an increase in what is already happening either in the plus (heating) direction or minus (cooling) direction.  Newtonian views are usually enough, but they can fail for the last 10-20% of efficiencies.  My example with the paint is one such, even though it is only 7-10%.

Anyway, the actual thermodynamics says heat flows in both directions at all times. The water radiates heat and it also absorbs heat. It radiates to the pot as it absorbs from the pot. The pot absorbes from the flame and radiates to the flame.  The hotter something is the more it radiates.The difference between the input and output indicates the plus or minus direction of the heat flow (not correct terminology, but easily understood.) Most of the heat produced by a stove starts as IR. It pays to understand it at least in general terms. Is that better, Dan?

I’ll be back with final boil times and comments.

 

[James Marco]

Yeah, I’m typically all wet…again.    Thanks Dan!

[Jon Fong / Flat Cat Gear]

I used up all of the 440 grams of fuel to boil 17 litres of water.

That’s ~13 grams per 500 ml.  the stove must be running at full throttle.  In my Bobcat System with the Kovea Spider, I can boil 500 ml using about 5-6 grams.  I think that this goes to point out that Ryan’s proposed  F values will indicate if a system is hot, but not if it is efficient.  I’ll stick with efficient.  My 2 cents.

 

[DAN-Y/FANCEE FEEST]

I have nothing further to add.

 

[James Marco]

Wow, yeah, I agree Jon. I hadn’t computed anything yet, Thanks!

 

[Roger Caffin]

That’s ~13 grams per 500 ml. the stove must be running at full throttle.
Eek!
Not good!
But we KNOW that running flat out is seriously INefficient.

Cheers

[Ben H.]

…I think that this goes to point out that Ryan’s proposed  F values will indicate if a system is hot, but not if it is efficient.  I’ll stick with efficient.  My 2 cents.

I agree completely Jon.  The F value conflates power and efficiency and doesn’t do a very good job of describing either.

 

 

[fred L]

Hi Dan and others,

I made a windshield resembling the one in your video a while ago, with a kovea spyder. The windshield seals to the pot and has exhaust holses right undeneath, like in your design. I tried this as opposed to leaving a big gap between the shield and the pot to try to save fuel (as discussed earlier in this thread). For me that worked well on really low stove settings in no wind, but I kept having issues with exhaust gasses entering the stove intakes in windier moments. I believe that gusts of wind passing into the intakes created a flow inside the windshield that moved exhaust gasses down into the intakes. As there is no physical separator between the intakes and the exhaust fumes, a rather light gust of wind was sufficient to strangle the stove, as any exhaust gasses entering the intakes will suffocate it because it depletes the supply of oxygen.

Did you have similar issues?

Did this simply happen because i might have had a bad balance where i had too few holes for exhaust to exit, or is this an integral issue when feeding the flame in the same space as exhaust gasses flow?

Is it technically sound to keep tinkering to find a sweet spot with varying sizes and locations for intake and exhaust holes in a design when there is little to no gap between the pot bottom and the windshield ? or will this always yield a system optimized for a narrow range of external conditions ?

Solving it is simple though, the normal opening between the windshield and pot wall just makes sure the exhaust gasses exit fast enough for it to not be a problem.

A physical separator like in the trangia is a second solution, but will always require more metal.

[DAN-Y/FANCEE FEEST]

Fred, show us a photo of your windscreen please.

I had fun doing my testing. It’s a very efficient set-up. If I were to do scientific testing the results would be amazingly efficient. It could easily boil 500 ml using about 5-6 grams.

[fred L]

Here you go!

The lower line of holes goes around like 90% of the circumference and the top one all around. When wind passed by the burner it made hissing noises, not because it was physicaly blowing the flame out, but I believe it moved exhaust gas into the intakes. It did sustain boils on the tiniest flame though, witch i really liked. So it was great for long cooks in good weather.

[DAN-Y/FANCEE FEEST]

Nice workmanship on the screen/support.

Looks like the very top row of holes is being blocked by the bottom of pot. The hissing noise was the stoves way of saying “give me more exhaust holes”  ;)

Some of the “Sheldon Cooper’s” on this forum can probably give a detailed explanation of the hissing.😁

I like how the Kovia can be made to simmer.

[fred L]

yes, I assume that the combusted gasses have bigger volume than the air required to burn them, so my ratio was definately off :) also the holes are only like 5,5mm in diameters, i’m not big on fluid mechanics but I assume fewer but bigger holes with the same area will have less gas touch the hole perimeters and thus create better flow. Punching those holes also got old fast … The stamp you used, seems like it was something to make holes for product packaging?

[DAN-Y/FANCEE FEEST]

When wind passed by the burner it made hissing noises, not because it was physicaly blowing the flame out, but I believe it moved exhaust gas into the intakes.

I believe “half” the burner head was without flame and that is what was causing the hissing.

Let’s call it “Raw gas hiss”  or RGH

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