If, as in the above question, you have a cylinder within a cylinder, there won't be any space for air to flow up the sides of the pot. Yes, the conical nature of the Caldera Cone does provide for stability, but that's not the main reason for the cone shape. The conical shape creates separation between the walls of the pot and the walls of the cone so that heated air can be directed up the sides of the pot, transferring heat to the pot as it goes.

In your blog you say
Well, a straight-wall will most definitely work , given adequate gap (10mm, or 8mm-12mm) I refer you to Pot Skirt Investigation, ETHOS 2010

I believe what the cone shape does better than a straight wall is promote swirling (venturi effect) at lower temperatures. This might mean slightly cleaner combustion; this might mean longer use-life for the cone; though I believe the difference at this scale is insignificant

I agree with your analysis of the purposes the cone serves
1. Entraps heat near the pot.
- yup, the air entering from the bottom robs heat from the cone (prevents cone melting), ie, the cone preheats primary combustion air (aluminum is reflective)

2. Protects against wind.
- yup, it protects the flame from blowing out
- the holes control the maximum amount of air available for combustion, and thus, maximum firepower

3. Controls internal air flow to maximize heat transfer.
- yup, it forces the hot gasses to scrape against sides of pot to maximize heat transfer (its a hot skirt)


You should definitely check out ( via translate.google.com ) All-round all-weather stove "The most comprehensive all-weather stove"
I really like the cardboard and aluminum foil prison its insulative and reflective

No screws or epoxy!! Pop-Up Foster’s Pot and Fin Shells , its a great folding/flanged/aluminum potskirt/windscreen, with 12.5 grams of alcohol ( 1 tablespoon ) it cooks 200 grams of rice in 400 grams of water ( 400 ml ) in a 750ml pot, using LannyPlans Builds an Alcohol Beverage-Can Stove


And this TLUD The Pop-Up Two Buck Stove , esentially the beefier version of the Pop-Up Foster's Pot

Great work Jim. Much appreciated.

Blake

EMP mentioned "promote swrling" and that popped a question in my mind : the Swiss volcano stove has a ribbed wall ( otherwise straight up, not conical) so what is the purpose of those ribs in the wall ?? Strength of the wall ?? Swiriling ??

Also, have you compared the caldera conical design with the volcano straight up design ??

mmmm ... I think there are many variables to compare , like the ribbed /vs/ straight walls, the diameter of the pot ..etc. In the volcano stove , the cooking pot has a larger ratio of surface area to volume, but in the caldera, you have a larger area at the bottom of the pot, where most of the heat is.