Bushwalk Australia

There may be a very obvious answer to this question... but here goes anyway...

If my upright canister stove isn't working well, e.g. in the snow, what's wrong with providing a bit of insulation around it to keep the canister warmer? I've kept a canister inside my sleeping bag as a starting point, but if it's so cold so as to not be functioning properly, surely a bit of CCF around it won't be enough to overheat the canister? If I apply the 'ouch' test, and remove the insulation in the very unlikely event of the canister warming up, what's the flaw in my thinking?

No flaw, but an insulated base is what I have made, I will be able to use it for both the XGK-EX and the Pocket Rocket.
Aluminium flashing / plywood CCF all held together with a scrape of silicon. I have no experience with new gas stoves but if it's really cold I will use a windscreen and be careful. I see very little distinction between using a sheltered space and using a small windshield

I thought that canister got cold from the liquid to gas endothermic reaction/state change that happened as the gas was used off the top. The canister gets cold because of the liquid changing to gas inside, and needs to be kept warm enough (with warmth from outside the canister) for the propane to keep changing to gaseous state. Therefore I dont think it will work, the canister needs heat from something.

I thought there was something on the Roger Caffin bushwalking 'FAQ' but I cant find it now. Putting the canister in a small bowl of luke warm water should work.

Thanks for thoughts

Maelgwn wrote:The canister gets cold because of the liquid changing to gas inside, and needs to be kept warm enough (with warmth from outside the canister) for the propane to keep changing to gaseous state. Therefore I dont think it will work, the canister needs heat from something.

But if the canister is insulated from the outside, so not losing extra heat, it shouldn't get colder than 'normal', should it? (physics was not my forte, though)

Unless you are in way, way below zero degree temperatures (where it wont work regardless anyway), then insulating it will indeed actually make it colder believe it or not! It won't be loosing heat less, it will be absorbing it less as the ambient temp will quickly be warmer (or less cold) than the canister!

Now a bit of insulation with one of those chemical hand warmers inside would be a different story...

I've never done it but others have suggested sitting the cannister in a container of water in the past. This should help as the heat from the (cold) water will be more efficiently absorbed by the canister.

Mealgwns right and I should have remembered that, still insulating from the cold ground should help

Just sit that canister in a bowl of water and don't use butane only cartriges.
(a mix containing propane and or Iso Butane will do)

Sorry ,by the time I uploaded my comment it had already been suggested.
(I can't see the Edit button right now...)

Agree with all of the previous comments.

The canister can also be warmed up by judicious use of a windshield. Used carefully this will send reflected heat from the bottom of your pot down into the canister.

Done carefully, the canister can be kept warm, particularly if it is on some sort of insulated base. If not done carefully, pyrotechnics could result, which is why manufacturers say "No,No"

A safe level of heat can be judged simply by touching the top of the canister frequently with your fingers. Your call and your responsibility.

People with the necessary skills to break a cannonball would be best not to use this method

Ms. Tortoise, they're right. The liquid fuel is evaporating inside the canister to make the gas and that makes the canister colder. It's the same as when you stand in front of a blowing fan when you're wet. You feel cooler wet than you would if you were dry because the water is evaporating off of your skin.

I usually just use a reflective metal windscreen and do fine at -10°C.

Franco wrote:Just sit that canister in a bowl of water and don't use butane only cartriges.
(a mix containing propane and or Iso Butane will do)

+1 for this
Water will only change temperature slowly compared to air and therefore it will keep the canister from getting too cold for a fair while, long enough to cook at meal.
Agree with others, insulating the canister will only make the problem worse.

Thanks everybody. I think I'm getting it now. Thanks for the practical stuff and the explanations.

As I'll usually be using cold mountain water - how much difference do you reckon it'd make warming the water a bit first?

and... if I use the water, is there still any point keeping the canister above zero in my sleeping bag overnight?

Yes tortoise "up the jumper" if you are in really cold conditions (personally have never done it ) however it is a good idea,water unless it is frozen ie ICE is still water and works !! don't ask me why I am just an old Fart who has done it and it worked
corvus

corvus wrote:Yes tortoise "up the jumper" if you are in really cold conditions (personally have never done it )

I have done it, i confess, but wasn't sure if it was entirely necessary. Using the water will be more comfy I reckon.

don't ask me why I am just an old Fart who has done it and it worked
corvus

Old Fart's experience happily accepted

If my upright canister stove isn't working well, e.g. in the snow, what's wrong with providing a bit of insulation around it to keep the canister warmer?

Well, basically, the insulation is not going to achieve anything useful. It may even be counterproductive.

The contents are cooling down because they are losing energy when the fuel evaporates inside. Sure, the canister may start off warm (which is good), but boiling the fuel off to drive the stove soon cools the liquid fuel down. If you insulate the canister, there is nothing to warm the contents up, unless you let it get a bit of radiation from the stove. That requires constant monitoring to be safe, but it is often done by experienced stove users and does work. The CCF would just get in the way there. Alternately, as many have done, put the canister in a bowl of luke-warm (not hot!) water and get some energy into it that way.

The best info on winter stove use is to be found (imho) at www.backpackinglight.com. There are extensive technical articles there. Disclosure: I wrote most of them, so I am biased.

Cheers

Hi Corvus

water unless it is frozen ie ICE is still water and works !!

The reason is very simple. Butane boils around 0 C at sea level (slightly lower at altitude). Liquid water is of course above 0 C, although sometimes not by much. Anyhow, the water is warmer than the boiling point of the butane, and it can supply heat energy to the butane.

Yeah, sound funny saying that ice-cold water is 'warm', doesn't it? All things are relative.

Cheers

Excellent explanation - thanks, Roger
I really must get around to subscribing, but can't figure payment options yet (I'm such a netophobe with my credit card )

I am a side sleeper. I have always found that sleeping with the canister between my legs (and buying good quality Iso-butane like Elemental), has always been enough.

If I wanted really prolonged use which could cool the canister too much, I would just use a wind shield or warm water.

rcaffin wrote:The contents are cooling down because they are losing energy when the fuel evaporates inside.

The contents are actually adsorbing energy not losing it. The change in state from a liquid to gas is endothermic and so therefore takes energy in the form of heat from it's surrounds, same as the cold plate in a fridge.

Forgive me please I failed physics but had an innate feeling that a water "bath" was the answer , did try a can "cosy" not much good other than ground insulation. Did make a big mistake 20 odd years ago leaving my Primus Gas conversion and Can for our Trangia outside under the cooking tarp in snow in winter to find it a bit frozen next morning,fortunately the lake was not frozen and I collected water and did the can bath ,it worked and we had a warm drink and feed.
corvus

Scottyk wrote:

rcaffin wrote:The contents are cooling down because they are losing energy when the fuel evaporates inside.

The contents are actually adsorbing energy not losing it. The change in state from a liquid to gas is endothermic and so therefore takes energy in the form of heat from it's surrounds, same as the cold plate in a fridge.

That's a good point, but take note that it isn't nice to correct a physicst on matters pertaining to physics.

While we're being correct I'm pretty sure that energy is absorbed not adsorbed.

Another equally uninteresting point is that while most of the cooling is due to the state change, something on the order of 10% is caused by adiabatic expansion and around 1% is due to the Joule-Thompson effect.

Oh crap, I meant Thomson.

(what happened to the edit button?)

Orion wrote:
(what happened to the edit button?)

was looking for that myself!

here it is :


now, where is the ANY key ?

I've used gas cylinders in the snow for a few years. I keep the cylinder in my sleeping bag overnight, and then heat some water enough to get some warm water. I sit the gas cylinder in a bowl and pour the warm water around the cylinder. Works a charm.

Scottyk wrote:The contents are actually adsorbing energy not losing it. The change in state from a liquid to gas is endothermic and so therefore takes energy in the form of heat from it's surrounds, same as the cold plate in a fridge.

I still can't edit. What's up with that?

So one more point is that the fuel can vaporize without any absorbed energy. If the fuel is fully insulated, for example, the temperature goes down but the total energy will be the same. Which brings me to my question about putting the canister in water (a technique I have never needed to use):

If the air is below freezing doesn't it make sense to fully insulate the canister+water combination?

I still can't edit. What's up with that?

Did you try my button ?



(the edit button disappeared sometime last week)

Orion wrote:
If the air is below freezing doesn't it make sense to fully insulate the canister+water combination?

It gets complicated here
If you light your stove and have a pressure gauge fitted to the bottle then you can use that pressure reading to get an evaporation temp (if you have a pressure/temperature chart for that fuel) and if that evaporation temp is above the ambient air temp then yes is would be good to insulate the whole assembly however once the water reached the same temp as the canister then gas stops flowing. The evaporation temperature of a butane mix is I would guess a long way below most ambient temps encountered and that mean no insulation.
To confirm these assumptions you would need to fit a gauge to the bottle when you are using it and then gain a pressure/temperature chart for your fuel but I have a feeling that the vapour temp for the mix will be pretty low when a burner is running and so no insulation required.

So if you want to fit a gauge to your bottle when using it and then get a chart for your mix then........ or just stick it in a pot of water and use it!

Franco wrote:Did you try my button ?

Err, uhh, no thanks, Franco.

Scottyk wrote:

Orion wrote:
If the air is below freezing doesn't it make sense to fully insulate the canister+water combination?

It gets complicated here
If you light your stove and have a pressure gauge fitted to the bottle then you can use that pressure reading to get an evaporation temp (if you have a pressure/temperature chart for that fuel) and if that evaporation temp is above the ambient air temp then yes is would be good to insulate the whole assembly however once the water reached the same temp as the canister then gas stops flowing. The evaporation temperature of a butane mix is I would guess a long way below most ambient temps encountered and that mean no insulation.
To confirm these assumptions you would need to fit a gauge to the bottle when you are using it and then gain a pressure/temperature chart for your fuel but I have a feeling that the vapour temp for the mix will be pretty low when a burner is running and so no insulation required.

So if you want to fit a gauge to your bottle when using it and then get a chart for your mix then........ or just stick it in a pot of water and use it!

I actually have charted vapor pressure versus fill % of various canisters in the past. The exact temperature varies, but the point is that there is a point where a canister, at a given fill percentage and elevation, will not have positive pressure if at the ambient temperature. And in that situation the air is just going to be a heat sink.

But I take it from your response that you don't insulate when using water. I guess the other part of this is that you're probably relying to some extent on reflected heat from the flame and insulating would get in the way of that.

I've never even tried a little dish of water but instead just used the reflected heat by itself.