Forum Index » Editor's Roundtable » Lightweight Stove Systems for Group Cooking Part 2: Considering Fuel Needs for Cold Temperatures


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James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Re: HE pot on 12/25/2013 18:48:11 MST Print View

Yeah, maybe. I first posted several years ago on the Backpacking light list at Yahoo, now pretty much defunct. It was discussed here several times. The pots were just "Plain Jane" aluminum. K-Mart (Stanco) grease pots. Anodizing means some sort of hard mineral coating. This, invariably, does not do well with forming.

Doric Swain
(skibug) - M
Convoluted pot base design for increased heat transfer. on 12/31/2013 22:22:26 MST Print View

Hey James,

Most interesting: "At about 15-17% better efficiency, it works on all stoves except for very slow heats"

I would have thought this is of major significance - a 15% efficiency improvement means around 30 grams, or about an ounce, weight saved for a medium sized gas canister. Even more for alcohol. On long, or group, or cold expeditions, many would consider this significant, and worth some money - look at how much people will pay for (eg.) torches and titanium pots that result in smaller weight savings.

Furthermore, I can only suppose that a large company with an R&D budget (or someone like Roger Caffin) could possibly turn this into a 20 - 25% improvement with the most efficient designs/shapes and materials.

Thanks for your work and reply, I genuinely admire your effort to think and experiment outside the square - let's hope some manufacturers are prepared to do the same!

Skibug

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Turbulence is our friend on 01/01/2014 00:09:02 MST Print View

Dimpling or pressing in ridges in a pot bottom isn't necessarily just about surface area. Something that creates turbulence generally improves heat exchange.

I played a little with vortex generators on the sides of a beer-can pot and it definitely helped, especially with a very full pot (full pots have more wetted vertical sidewall for heat exchange). Also, because it wasn't in the flame proper, it wasn't so hot there, so I managed with foil tape - very cheap and fast to fabricate, I could tuck the materials in my wallet like a business card if I wanted to modify a found beer can on site.

I'd suggest (this just occurred to me), that rather than tweaking the bottom of the pot, the pot supports could be arranged so as stir up the hot gases. All the pot supports I can think of are strictly radial. If they had angled vanes to mix the flow a little, that energized boundary layer wouldn't be so insulating. Another cool thing - twisted pot supports needn't weigh much more at all. And they would benefit any pot you put on the stove whereas HX fins only help on one pot.

This addresses one of those blind spots we develop when we focus on "base weight" = lighter stove, lighter pot. But HX fins on the pot, a better fuel efficiency on the stove, and insulation to let you seep your pasta all save fuel which DOES weigh something on your back.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Turbulence is our friend on 01/01/2014 08:34:26 MST Print View

Yeah, turbulence has an effect too. It seems that on the pots, the totals I get with a 12/10 stove include both, though. I never tried to seperate them. Even using the baffles on the stove doesn't really seperate the two.

There are several designs for doing exactly what you describe on Zen Stoves. Anyway, it appears that the side mounted fins increase angular flow, while decreasing vertical flow, leading to an increased heat density of the gasses surrounding the pots. It would help a bit, but, I never tested for any of that.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Turbulence is our friend on 01/01/2014 09:51:46 MST Print View

It seems like what you don't want is layer of hot gas next to pot, another layer further out - there will be less heat transfer for that layer to pot

So, what you want is vertical turbulence, not sideways. A vortex will produce sideways turbulence, although there will also be vertical so maybe it doesn't matter.

The simplest structure would be a ring of wire. Maybe halfway out from the center. Positioned in the middle of the hot gases. With the right diameter wire to produce good turbulence.

Or, the burner could have some jets that point more vertical, and some that point more sideways, combined you'de get vertical turbulence.

If the pot was bigger diameter, there'de be more surface area on the bottom (good) but it would be less deep on the sides so there'de be smaller area absorbing heat. Maybe the pot above the water level would absorb heat that eventually gets into the water. Playing with pot diameter may yield efficiency.

Fins on side of pot may be more important than on bottom, for example:

windscreenhx

Maybe bigger or smaller channels would be better. This also keeps the hot gas next to the pot better. Maybe some dimples or whatever would increase turbulence in the channel.

I know this is doing something, because my oatmeal sticks to the inside of the pot where the aluminum touches the pot. I measure maybe 10% or 15% efficiency, but that's right at the edge of my measurement accuracy.