DIY Skirted pot query

[Edward John M]

Absolute weight isn’t an issue with me. As light as practicable is.

It also depends on the groups size naturally. In a longish trip there will naturally be trade-offs between pot size and shape. Fuel saved with a bigger and heavier system might be worthwhile With the MSR I would naturally use the widest based pot that MSR state as the maximum and the Firemaple 4.7litre pot is what I have been using for a couple of seasons now.

https://www.ebay.com.au/itm/Fire-Maple-4-4L-cooking-pot-for-camping/323593587629?hash=item4b57ae4bad:g:ZG0AAOSwiSVcD6Cp:rk:1:pf:1&frcectupt=true

 

Well above your 7 ounces James but we have different needs so not comparable. What I am interested in is overall efficiency, theoretical now but important in a year and a half

[Jerry Adams]

Yeah Rene, that’s what I meant.  Ryan went into quite a bit of detail how to measure grams of fuel used to boil a measured quantity of water.  In a reproducible manner.

Ryan also had some IR pictures that show how the hot exhaust gasses can get blown away rather than sticking next to the pot where heat can be transferred.

Must have been James that talked about inducing turbulence to get better efficiency.  I forget who said what.  I forget what I said : )

If inducing turbulence could improve efficiency, then maybe a burner that’s has a more turbulent output would be more efficient than a burner that had a more laminar flow output.

[James Marco]

Yeah, maybe around 2007-8(?) I posted a diagram from an earlier post I made on Yahoo’s email list about that (circa 1999 or so.) I believe Dan Y, might have been someone else, pointed out that corners work well to break up laminar flow, also.

[Jerry Adams]

So, does that make sense if you could break up flow to induce turbulence to improve efficiency

that you could induce turbulence right out of the burner?

or, to put it another way, some burners have more turbulent output so would be more efficient?

[James Marco]

I don’t think it makes enough difference to really count at the burner level. Several years ago there was quite a lot of spin inducing “vortex” burners (especially alcohol stoves) out there. Designs and actual stoves based on those designs were fairly common. Indeed, the BRS-3000 has a spin inducing burner at the flame/fuel/air mix junction. You can do similar with drilling a fine hole, then reaming it sideways with a somewhat larger polished needle on alcohol burners. This may effect the overall heat production/heat transference slightly, but not enough that anyone has been able to measure it while camping that I have heard about.

While some stoves (the discontinued Reactor for example) use flame to mix with their mesh/fill to provide a large amount of thermal energy (unusually high IR, but also exhaust gas convection,) the biggest advantage is overlooked. A dual layer pot with a turbulence inducing corner about the lower 20% of the pot. Still, the large CO emission as reported by Roger C. means there is some inneficiency in the heat production, possibly due to flame quenching, possibly due to insufficient oxygen at low flow velocities (when the stove is turned down ), possibly a combination of both or other things.

Anyway, however the heat is produced (WG, Kero, canister, alky, etc,) there is always the notion that the heat MUST be transferred through some substance to the target, water. I am ignoring IR here because this is radiation like sunlight or x-rays and follows more quantum rules. Laminar flow is great for clearing used materials from the system using traditional conductive/convective rules(exhaust gasses), basically, allowing heated gasses to flow up and fairly fast along some surface rapidly. Turbulence is induced where we want to hamper this movement (corners, vortex inducers, etc.)  I don’t believe it matters one way or the other where the turbulence is induced, before reaching the pot, or, after reaching the pot.  We are looking at side effects of inducing the turbulence. Less efficient combustion for example using the Reacter as an example. Using a full, tall, thin “Beer Can” pot means good laminar flow of heated gas along the sides for the full length of the filled pot; these  achieve good efficiency of heat transfer also. Both low laminar flow rates and high laminar flow rates can be shown to be efficient for boiling water. A heat shield/wind screen can do both by redirecting the turbulence back to the pot. Well, all have been shown to be efficient mechanisms for boiling water.

By increasing turbulence you also increase disbursion of the heated gas: less efficient. But, any fins or disruptive elements added in the flow also pick up heat adding to the effect of heat exchanger. It works. I am sure you can come up with example where laminar flow decreases the efficiency of heating a pot.

Generally we always look at heating air as well as heating the pot. So, we have two materials in between the heat source and the water. Increasing IR with a flame can decrease efficiency because IR travels in a statistical 360 degree spherical pattern. Not real great for directing heat to a pot bottom without a heavy duty reflector (which gets hot and re-radiates IR…)

So, it seems we want a blend of these methods, both the inefficiencies of IR to gas in a flame and the direct IR against the pot bottom (allowing all else to escape) and the convective heat transfer of hot gasses to the pot which can be directed by design. In any wind, we ant more IR, in any calm we want more convenction. Thin highly conductive pots provide better conductance than thick less conductive pots. And so on. Again, different strokes…

 

[DAN-Y/FANCEE FEEST]

John, how are you doing with your pot skirt project? I have one that looks real promising for Toaks Light 650 pot. I made one for a Fosters beer pot and it tested positive.

Have you finalised on the pot size that you will for sure use?

Canister stoves are turbulent. When the burning gases are forced against the wall of the skirt turbulence abounds and heat is sent upwards between the walls……turbulant all the way up and out. Once the rising heat passes beyond the lip of the pot it starts to swirl inward over the lid of the pot.

 

[DAN-Y/FANCEE FEEST]

John inspired me to give some thought to making a pot skirt.

It holds firmly to the pot, full length of a Toaks Light 650ml pot. It has 4 verticle ribs that act as heat exchange fins and keep the windscreen an ideal spacing from pot to allow exhausting gases to pass close to the pot. The pot has handles. Slide skirt onto pot all the way up to rim of pot, place onto brs 3000 canister stove, turn gas on and light.

[DAN-Y/FANCEE FEEST]

This thread has a lot of good info on the use of pot skirts.

Posting photos again to make sure they are visible.

video:

[DAN-Y/FANCEE FEEST]

Vertical ribs act as heat exchangers. Titanium has tested to be very stable after being subjected to 1/2 hour burn times. The windscreen/skirt has been tested with 3 different stoves. All stoves performed well.

https://www.youtube=rgtzBQ2vvf0

[DAN-Y/FANCEE FEEST]

These are the 3 stoves that fit inside the skirt. All canisters were consumed during testing.

 

 

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