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Bryce Nerland
(bnerland) - F

Locale: Southeast
Caldera Style windscreen for Canister Stove on 02/06/2008 09:26:35 MST Print View

Last night I made a Caldera- style windscreen for my Vargo Jet Ti Canister Stove and 1.3L Evernew Ti Pot. I prefer cannister stoves on longer trips where weight saving from fuel is greater than weight savings from lighter equipment, but have never liked the windscreen set-ups I could find for canister stoves. To make the windscreen it I simply traced my Caldera Cone on a piece of aluminum flashing and cut it out. I put a lot of holes in the cone for it to breathe. I searched the forums and couldn't find anyone who had tried this. My obvious concern would be that the canister would get too hot inside (even with the venting) and explode. I am very hesitant to actually try this. Any thoughts?

Edited by bnerland on 02/06/2008 09:42:58 MST.

Michael Crosby
(djjmikie) - MLife

Locale: Ky
TEST CAREFULLY on 02/06/2008 10:13:39 MST Print View

I have done a few tests with the standard alcohol cone I bought and found that the inside gets VERY hot. In my first trial, I set it up on a 2x12 pine board and ended up catching the board on fire where the stove sat.
A friend of mine is a gunsmith and has had people ask him to find the hottest loads that their revolver can handle. He explains that that the only way to do this is to fasten the revolver to a tree, use a long string to activate the trigger while increasing the powder load until the cylinder explodes.

Vick Hines
(vickrhines) - F

Locale: Central Texas
Re: TEST CAREFULLY on 02/06/2008 10:26:53 MST Print View

Special care is needed when using a cannister stove with a cone. You are very likely to overheat the cannister. The consequences are dire; you are likely to leave the gene pool much sooner and more painfully than you would like.

There is a trick with cones. If the cone does not have adequate vents at the top, the flame will spread on the ground around the burner. This is due to the back pressure created by a cushion of hot air at the top of the cone.

The solution, of course, is to add a few more vents or to increase the size of the existing vents. One efficient way to increase air flow is to join adjacent holes to create oval vents. It does not take much enlarging to increase the efficiency of the vents significantly. If you simply punched holes around the top ot the cone, they are very likely to be too small. Remember that approximately 1/8 inch of the hole diameter does not move air because of the 1/16 inch (approximately) boundary layer. If you enlarge the holes cautiously, you can avoid the undesirable effect of venting too much heat too fast. There is a balance to be sought.

Edited by vickrhines on 02/06/2008 10:37:42 MST.

Joshua Mitchell
(jdmitch) - F

Locale: Kansas
Wow... yeah... I'd be really careful... on 02/06/2008 12:31:21 MST Print View

there are a LOT of issues with running a canister stove inside of a tightly enclosed area. Running it inside a fully enclosed cone would really NOT be advised... as has mentioned it gets very hot just with alcohol...

May I recommend looking at doing something more like a 'wind break' rather than a windscreen? ALA Jim Wood's Kite Screen?

Roger Caffin, I believe, has an article about making an aluminum wind break. I also posted some concept pics of staking out my Tri-Ti as a windbreak...

Edited by jdmitch on 02/06/2008 12:32:32 MST.

Tony Beasley
(tbeasley) - MLife

Locale: Pigeon House Mt from the Castle
Re:Caldera Style windscreen for Canister Stove on 02/06/2008 14:42:50 MST Print View

Hi Bryce,

Brett from Japan has done some work on using cones on a canister stove, I am unable to find his postings on the topic in his 1400 post, but from memory the cone did not come down below the top of the canister therefore the canister does not over heat.

Hi Vick,

I am making a low profile remote canister stove for a cone style windshield and while trying to understand how a Cone works I did some testing with a canister stove under a cone with temperature probes through the sides at different levels, the cone only came down to the top of the canister, the first test had no holes at the top. I found that the hot gases stratified with the coolest layer on top, this stayed that way even until boiling was reached, I could not make it over turn.

The one thing that I did notice was there was a much higher temperature around the base of the pot than there is if there was with no cone.

I drilled some small holes around the top of the cone and repeated the tests, I found very little change in the above results (as you pointed out boundary layer thickness stopping the flow through the holes) so I made the holes bigger and more numerous re-tested and so on until I started seeing the stratification breakup, what I did notice is that the temperature at the base of the pot was higher in all tests and the temperature increased up the sides too as the bigger hole improves gas flow, all this is good for better heat transfer in to the water.

I did not try oval holes and thanks for the tip and also thanks for the figures of how thick the boundary layer is, I have measured them at the base but not the top.

Tony

Joshua Mitchell
(jdmitch) - F

Locale: Kansas
Re: Stratification and Cones... on 02/06/2008 15:00:57 MST Print View

Tony,

If the cone only comes down to about pot level or below, that's one thing. The concern is if much of the canister is covered by the cone (I believe you're familiar with this, I'm just making a clarification statement for other's benefit)

Also, the stratification you're seeing makes sense as the hot gases likely lose a bit of heat in moving up and around the pot. There will likely be a net transfer of gasses up, but they'll lose some energy as they move.

Also, there isn't much thermal mass above the water line to retain heat and transfer it back into the area of the cone.

Gasses always move from the driving force away from the dirving force. Yes, the gasses below are technically hotter, but they are still driving the total gas flux upwards. It's not a matter of 'hot gasses will always be on top', they're just trying to get to the top and as they do so they're losing heat to the liquid.

If there were holes up and down the cone (so that the gases could go somewhere other than straigh up) you might see more what you would expect. However, right under the pot will always be the hottest as that the 'driving source' of the gasses and everything is expanding out from that point.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Caldera Style windscreen for Canister Stove on 02/06/2008 17:38:41 MST Print View

> My obvious concern would be that the canister would get too hot inside (even with the venting) and explode. I am very hesitant to actually try this. Any thoughts?

Yes indeed. Assuming the use of a standard design cone, I would expect that the canister might explode after about 4 - 6 minutes.

This might be considered rather dangerous ... (serious understatement!)

Brett .
(Brett1234) - F

Locale: CA
Calderas and canisters on 02/06/2008 18:53:26 MST Print View

Tony, I simply allowed the pot to stick in the caldera cone as ususal; and lift it all on and off the canister burner as necessary to pour, etc.. With my setups, the cone has enough friction to stick to the pot just under the rim, and since the canister stove is on top of the canister, there are a few inches of clearance under the cone to keep the canister cool yet still block the wind.
This is not an authorized use of the cones according to the manufacturer, but IMO it is yet another reason to buy cones for your pots.
In addition to canisters use, my titanium cone is acceptable for alcohol, esbit, canister, and even direct wood fires. 4 in 1.