Caldera cone efficiency across different pot types

Dave,

I wonder if we are sometimes splitting hairs when looking at efficiency.

I have two cones, on with a SP Mini Solo and one with a Foster Keg. What is more important to me is that I can slide the cone completely inside the Keg, and it extends 1/2 way out of the SP. So packing it is more important to me.

>I wonder if we are sometimes splitting hairs when looking at efficiency.

That's what I'm wondering too.

Hey Dave-
Yup, I'm a gear geek. I have experimented with this. I have found that a wider pot is more efficient, even with the Caldera system. I had a MSR Titan kettle, now use an Evernew 0.9L short. Between the two in what I believe are the same conditions I'm getting about 2-3ml fuel more efficiency out of the wider pot per pint boiled. Could this be an abberation of some kind? Sure. But I've also noticed a similar difference on my canister stove. And it's easier to eat out of a wider pot, I think. Anyhoozit-
Cheers-
Brad

I know Dave was asking specifically about the C. Cone, but my follow-up Q is:

Is efficiency more a function of windscreen position (vertically), diameter (space around the pot), and shape (cone vs. cylinder), than the diamteter of pot? The hypothesis is the windwscreen (or Cone) reflects or directs heat "vertically" on both wide and narrow pots, cancelling out any advantage pot diameter has. Alchy stoves–at least the commercial ones–have about the same flame ring dia., so the answer would affect a majority of alchy stove users.

Someday I'll experiment with the MSR Kettle vs. the SP Solo, as both weight the same (lidless). I keep eyeing my Solo since it seems easier to pack, but I've only used it with a cannister stove.

Of course, the advantage of a wider pot is stability–especially on Red Bull stoves.

I suspect the future of "pots" to simply heat water will be a coil of tit. tubing arranged in a cone-shape to maximize surface area to the flame of the alchy stove–but then that's probably splitting a split hair.

I asked TrailDesigns about this before purchasing a cone last year. I was considering the Snow Peak 900 vs. the Snow Peak Mini Solo, pots of approximately equal capacity but different dimensions. I received this reply from Rand:

"Honestly, only very few pots do we see much of a performance difference…..and the SPMS [Snow Peak Mini Solo] and SP900 [Snow Peak 900] aren't two of them. When you get into really wide aluminum pots….then you might pick up a little bit of performance…..but most of the titanium pots don't really show anything that couldn't also be accounted for in experimental error.

"Now, with that said, you can make things worse on yourself if you bias the stove over to one side of the cone. That way most of the heat will just shoot up the side and out the vent. But so long as you are hitting the base of the pot, you are going to be pretty good either way you go….not enough to make up 1.3oz"

btw, I found the folks at TrailDesigns wonderful to work with. Very willing to answer questions and accommodate requests. They even arranged to hand deliver a Tri-Ti to me on short notice for a JMT hike. Great product, nice people.

Wow. Sounds like pot dimensions are largely a myth similar to the heat transfer myth of Al. vs. Ti. Except for "easier to eat out of" comment, I have no compelling reason to choose one pot over the other based on dimensions alone.
Thanks!

>>Sounds like pot dimensions are largely a myth

Not so fast dude.

Just got this from Rand via email:

"Pot size…..The prevailing wisdom is that wider pots are better. This is most definitely true for stereotypical stove setups because they don't capture and contain the heat against the sides of the pot like the Caldera Cone. With a wider bottom, the flame can hit the center and expand out and heat a larger area before escaping to the atmosphere because it isn't contained. Inside the Caldera, once the hot gasses flow off the edge of the bottom of the pot, they are constrained to travel up the sides continuing to heat the pot. As a consequence, the Caldera is less sensitive to pot diameter than traditional systems. It is possible you might see a little benefit on a test bench, but in the field, I doubt you are going to see much. NOW, with that said, the one thing that you do need to be careful of with the skinnier pots is to ensure the stove is centered. If you get the stove off-center where it is just going up the side and out the vents it will be much less efficient. In short, even though we sell Evernew, I wouldn't recommend you buy a new pot just for efficiency."

Not a myth, but less applicable to caldera set-ups by the sounds of it, eh?

Actually sounds like me and Rand agree: the best efficiency is achieved with conical "windscreen" that's centered around the pot to reflect heat against the sides, regardless of its diameter, as long as combustion isn't affected. Height, angle, and top/bottom dimensions of the windscreen are perhaps more critical with narrower pots.

Now where's that frustum formula and that big piece of aluminum I've saving for my new windscreen?