Teori Praktik Niklas Lagström is product manager at Primus. When I talked to him I figured he was the right person to solve all my wintertime gas canister problems. Like; Can you use canister stoves in deep cold? And should you try to insulate the canister from the cold or not? As usual it turned out that there are no simple answers.
By Jörgen Johansson
Jörgen: Niklas, could you tell us something about who you are and how you've become product manager at Primus?
Niklas: I have always been using outdoor products since I grew up and was early interested in scouting, climbing and sea kayaking. One of my other interests are technical product development and how to improve the things I used. While I studied to master of science I started to work at Naturkompaniet (the largest outdoor retailer in Sweden) and later on, I got picked up by Primus when they where looking for a product manager. Now, I can use all my interests during my work, which is a fantastic position!
Jörgen: When we met recently we talked about using canister stoves in winter and whether to use insulation on the canisters or not. So I thought it would be interesting to get some advice on how to use my canister stove optimally for winter trips. For several years now, I've been amazed at how well my top mounted canister stove Primus Micron works even when it's really cold. In winter I wrap a piece of cell foam around the canister, which you've told me sometimes is really stupid and sometimes work really well, depending on the outside temperature.
Niklas: Well, it can be both a good and a bad idea to insulate the gas cartridge. As I guess you all know, gas cartridges work worse and worse the colder it gets. In addition to that, the physical basics about gas are that it needs heat to get from liquid to gas. The heat normally comes from the surrounding air but if it is really cold outside, or the cartridge is insulated, all heat must be taken from the liquid. Colder liquid means less pressure and soon there will be NO pressure.
On the other hand, if the container is much warmer than the surroundings, it will lose less heat to the surrounding air if it is insulated – and this heat can be used for keeping the pressure up!
Is it good to insulate the cartridge? Short answer is “it depends...”.
Jörgen: Let me describe how I handle my canisters today. When I don't use the stove, the canister is in the front pocket of my anorak or in my sleeping bag. I'm guessing that due to this my canister almost never is colder than, say 5 Celsius, when I start to cook.
Niklas: This is a good start. When the gas cartridge is warmer than the surrounding air, it may be a good idea to insulate the gas cartridge. If after the cooking, the temperature in the gas cartridge is still higher than the surroundings, then the insulation helps all the time.
Table below shows how much a certain amount of liquid gas lowers in temperature if the cartridge is fully insulated. For example, if you have 100 gram of gas left in you cartridge, cook in five minuter (uses 13 gram of gas) will lead to a decrease of the gas cartridge with 22 degrees plus (or minus) the decrease of temperature given by the surrounding temperature.
Jörgen: OK, let's move on to how I cook. I never cook for long, I just bring water to the boil. Usually only 0,2-0,5 liters depending on if it's cocoa, coffee or rehydration of a freeze dried meal. However, in winter I have to melt snow for drinking water, which means producing something like 1-1,5 liters of water morning, noon and evening. This takes it's time. Let's say it's -5 Celsius where I am.
Niklas: This is where insulation becomes a bad idea. Melting snow uses a lot of gas, and this means that the gas cartridge itself will decrease its temperature a lot… If you have the half full (100-150 gram gas left) cartridge I mentioned earlier, and cooking for 10 minutes, this means that the decrease in temperature due to the use of gas will be somewhere around 30-40 degrees. Then, the -5 Celsius around is much warmer and would be much better for the cartridge.
Jörgen: OK, let's say it's -20-25 degrees Celsius, what should I do differently?
Niklas: Now, insulation becomes interesting again! Since the surrounding temperature together with the decrease of temperature due to gas use will become lower than the gas boiling point, you will have problem to get the gas out of the cartridge. If you only have the impact of the decrease of temperature made by the used gas (and starting at plus 5 degrees as you said), the cartridge will just reach the surrounding temperature and therefore, insulation is a good idea!
Jörgen: OK, so to sum this up I have to take into consideration the temperature of the canister, outside temperature and how long the burner will be running. And we've only been talking about me, travelling solo. If I'm cooking for two the burner time increases and the advantage of using isolation on my canister decreases. Is that about right?
Niklas: Yes, that is completely right!
Jörgen: Dear reader, right now I’m sitting here, hoping that Niklas has a nice Christmas vacation without any thoughts whatsoever about canisters and temperatures. I’m also trying to sum up what he told me and to see if I can formulate some practical ideas. So far these are my conclusions:
- The gas boiling temperature is -15 C. This means that below this temperature you do not get any gas out of the canister. If you turn it upside down (which you cannot do with a top mounted canister stove) you can get liquid out of it. If the surrounding temperature is lower than -15 C, but the cartridge is warmer, it is a good idea to insulate the cartridge, since no heat can be taken from the surrounding air to gasify the contents in the canister.
- If the start temperature of the gas is high, say +10 C and the ambient temperature is -10 C you start out cooking with an insulated cartridge. It will take around 5-6 minutes (depending on a lot of factors) before the use of the gas has decreased the gas temperature to -10 C. Then you should remove the insulation to slow down the continued decrease in gas temperature.
- So, if the start temperature of the gas is higher than the surrounding air, insulation is always a good idea. The problem is knowing when the gas no longer is warmer then the ambient air.
- If the start temperature of the gas is the same as the surrounding air, insulation is always a bad idea, since the cartridge itself will become colder than the surrounding air, which we want to avoid.
- And to complicate things; if I use a windscreen that totally surrounds stove and canister the heat from the flame bouncing of the bottom of my pot will add some heat to the canister, helping it to stay warmer for longer. Or forever, depending on outside temperatures, amount of gas and…
By the way, a lot of things are done with canisters that Primus really can’t recommend. Like windscreens that totally surround pot and stove, which can cause overheated canister that could explode. Some people using canisters connected to the burner with a hose also put the canister into the pot were they are melting snow or heating water in order to raise the temperature of the gas inside. I have also seen different contraptions of metal working on the principle that part of it sits inside the flame of the burner and conducts heat to the canister, around which the rest of the metal is tighly cinched.
I don’t know if I’m less confused now than before, but I suppose that I am confused on a higher level. Have to talk about this with Niklas when he’s back…
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