Jetboil cold weather heat exchanger

I'm no physicist James, I always leave at least one error for "the reader" to find.

I don't understand your comment about at 0F it will never boil.

If you have a 10-12 minute burn time with canister stove, and it's 0 F outside, your water won't boil?

I've never gone much below 20 F. At that point, ice crystals start forming in my cold water bottle, lid freezes on and I can't unscrew it,… I prefer to look at weather reports and find a place that's not that cold : )

It was 0degF this morning out on the deck so I decided to do a video showing the HX strip in action.

I left the stove/canister out all night. THIS VIDEO shows the start-up of the stove (after a little warming of the canister by hand…) and the subsequent burn, still boiling 2 cups of 48degF water in about 2.5 minutes. I had the digital scale out to weigh the canister for fuel consumption but it would not work in the very cold temperature.

THIS VIDEO was made to show what happens when the HX device is removed and what happens when it is re-installed. The difference is pretty dramatic.

Edit: If you want to skip forward to about 7 minutes in the video, that is where the HX strip is re-installed.

Hey Jerry, try it. The same flame as you use all summer will simply warm the water up at 0F. The warmer it gets, the more it radiates heat…there's about a hundred degrees difference in outside air temp.

Next time it's real cold : )

I'm not going to do the maths, but I predict that the radiative heat loss from the pot to be insignificant – the pot is just not hot enough. Heat gain or loss from the pot is all about convection. The pot gains heat by convection from the hot combustion gas (and a tiny bit of radiation from the hot burner). This is increased by surface area – hence fins on HX pots. Pots can also lose heat by convection from the upper pot wall, especially in wind, hence the insulating pot cosy used by Jetboil etc.

I'm with Stuart, except that if you leave the lid OFF, evaporation will be a killer!

Cheers

Definitely very little radiative heat loss, at least from the MiniMo.

The MiniMo remained in the same spot for 2 dinners and 2 breakfasts and snow melting duties, and there wasn't a melted flake of snow to be found in the small, sheltered area where the stove was operating.

Big contrast with something like the Whisperlite which bounced gobs of radiant energy off the burner and the bottom of a standard aluminum pot. Even with a proper windscreen there was lots of melted snow in the stove area.

But that's the old Whisperlite. Perhaps the latest models are better, but I don't know.

> Big contrast with something like the Whisperlite which bounced gobs of radiant energy
> off the burner and the bottom of a standard aluminum pot.
Not proven. It could very easily have been swirling hot air.

In fact, with a windscreen, there is likely to have been even more hot air circulating inside the screen.

Cheers

Though one question I have which occurred to me while listening to the boiling sound as I dipped a canister in warm water…When these canisters get too hot is there a typical failure mode? Top blows out? Bottom dimple inverts?

"When these canisters get too hot is there a typical failure mode?"

Oh, you will know it.

How about KABOOM!

I had a mere Bic lighter that got overheated one time and its butane contents were liberated. I heard the explosion from about 150 yards away.

–B.G.–

When these canisters get too hot is there a typical failure mode?

You DO NOT want to find out!

If you look at the photo a few posts above, you'll notice that I have a thermometer probe to monitor the canister temperature. This was during one of the first tests. It took quite a few tests for me to get comfortable with the idea of not monitoring, and even then I frequently touched the canister to check…

I have monitored canister temperatures many times with ambient temperatures up to 45degF and the canisters have never gotten anywhere near hot enough to explode. Typical running temperature (measured on the opposite side of the canister) is ~56degF. Very safe.

However as I have mentioned before, these are the results with my setup. Anyone doing this kind of experimentation is well advised to make temperature monitoring the first priority.

Hi rm

> When these canisters get too hot is there a typical failure mode?
We have a special article just for that:
http://www.backpackinglight.com/cgi-bin/backpackinglight/exploding_gas_canisters_the_hazard_of_overheating.html

The short answer is yes: very, very loud.

Cheers

Having had the opportunity now to actually use the JB MiniMo with HX strip on a few trips, an update is in order.

First of all, I am still happy to say that this is the external heat solution for canister stoves that I was aiming for. Even when starting with a partially full canister (approx. 1/2 full or more) I have been able to start and run the stove with no pre-warming of the canister down to +3F. The key, of course, is the remaining propane content which determines whether not there will be any combustion at lower temperatures. It takes some heat to get the heat-shunt feedback loop going — but surprisingly little!

However, another thing I noticed is that when fuel levels are less than approx 50%, the 8-oz canisters are noticeably slower to warm up compared to the 4-oz canisters, which is understandable with these canisters' larger volume and surface area. Therefore they are more likely to need a 'kick-start' with a little pre-warming inside a jacket, if they are not kept in the foot of the sleeping bag at night, and they burn more robustly if there is an insulating cozy around them to prevent loss of heat to the surrounding cold air.

This morning it was fairly cold (+7F, approx -13C) and I did a test starting with a cold 8-oz canister w/cozy with only 17g of fuel remaining. As expected, it did not start at +7F with no propane remaining in the mix. After warming with bare hands for about 30 seconds (yeah… ouch!) it started weakly and took a while to warm up, but after about 5 minutes it was running at a very acceptable level. Not blowtorch, considering the starting temperature and the low level of fuel remaining, but it boiled water and burned almost all the gas. (It was somewhat windy, and I caught a faint whiff of the scent that is added to butane.)

The quick take-away from this is that it still helps to use a cozy in very cold temperatures, especially when using a larger canister with very little fuel remaining in it. And if you start with a reasonably warm canister (say 40F) there will be no problem at all achieving a roaring burner right from the git-go — no matter the fuel level — that will burn until the last molecule is consumed.

A quick, local overnight trip to do some gear testing provided an opportunity to field test the cozy with the 8-oz canister.

Starting out, the partially-full canister contained 164g of fuel (compared with an empty canister weight of 151.5g, with cap).

I wanted to burn off lots of fuel for dinner and for melting snow so that the canister fuel level would be low in the morning, so I tried to be as wasteful as possible. I had coffee, soup, water for my pooch’s dehydrated dog food, water for my dehydrated people food, a couple of liters of water for the following morning… all using snow and brought to a complete boil and then some. I had no scale, but after all that I would estimate the amount of fuel remaining at about 80g, so substantially less than half.

(Back at home, fuel remaining is 65g, so 99g total used for this trip – extremely wasteful!)

The temperature got down to +2F and the stove/canister sat out all night, so it was pretty cold. As expected, it did not start without a little warming, which was achiefed by wafting my warm breath over the top part of the canister without removing it from the cozy or detaching the stove. Ice formed on the top of the canister, indicating heat transfer. I did this for about 1.5 minutes and the stove started with a very weak flame. I thought it might go out (there was also a gentle breeze) but I just let it alone while the HX strip did its thing. It took a few minutes for a solid flame to build up, but after a total time of about 8-9 minutes there was a very robust flame.

Starting with a warmer canister kept in the foot a sleeping bag overnight would, of course, result in full power output from the start, which, combined with the HX strip and cozy, would maintain full performance to the last bit of fuel.

And all this done without “Magical Mystery Blotter Paper”!

Field test at +2F

Edited to add snide remark about “Winter Gas”.

>"it did not start without a little warming, which was achieved by wafting my warm breath over the top part of the canister. . .for about 1.5 minutes"

I like to direct the flame of a Bic lighter onto the bottom of the canister. With such a cold canister, you get great heat transfer not just from the sensible heat of the hot air from the flame, but also from condensation of the water vapor in the combustion gases. In 3-5 seconds, you're ready to light the burner and let the HX strip do its thing.

I find a Bic lighter much more comfortable in pocket, armpit or some body orifice than a 220-gram canister. But HYOH, WYOC (warm your own canister).

Thanks, David, good tip. I'll use that for a quick kick-start. One less thing to keep in the foot of the sleeping bag.

Ok, first question. How can I get one? Bob, if you still have some spare copper, I'll happily buy one. We can keep it as a personal gift transaction and as testing equipment so you won't be held liable for anything stupid I do. (if you are worried about that).

Second…I mainly want one b/c I didn't like the water bath method. Though, I did it sub optimally. I don't have a picture from my trip with it (when it was around 20*F outside), but I had my jetboil sol like this ->

I was able to get two burns (both night and morning) of 2 cup freezing cold water, and the water I put into the cup was at 32* (it was basically ice bath water…I carried in the water I needed for an overnighter so I wouldn't have to boil it, but I didn't bury the water bottles during the night so they had quite a bit of ice in them in the morning).
However, after the 2 boils, the gas canister and the orange cup both had ice formed on them, so I had to keep them separate from my jetboil in a plastic bag so it wouldn't get water on the rest of my gear when it defrosted during the day.

Not sure how others do a water bath….do they just use a larger cup with warmer water so ice doesn't form?

I'm thinking I'll still need a different solution for a longer trip where I'll need to melt snow. The 800ML cup of a jetboil would be infuriating to melt water….especially for more than 1 person.

I have a .9L evernew sidewinder caldera cone setup, though that would still stink for melting water (plus using a ton of alcohol…and just how long alcohol would take to melt the snow), though I'm trying to get a 1.3L setup.

As an aside…if I was just going to boil water, would a starlyte stove in a caldera setup work fine as long as I had a CCF pad with aluminum foil on the bottom?

Also, Jerry said this ->

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I was thinking the water is best. I forget who it is that filled upside down canister with water, then put a lid on it, then turned it right side up, but I haven't found the right size lid. Because of this thread, I'm now thinking the aluminum strip might be better.

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Interesting idea….though I can't find the thread that the idea came from, and my quick search didn't find a suitable cap. Though I would think I would have the same problem where the water underneath the canister would freeze just like my water bath…

I'm in NH doing some day hikes. I'll be home late Wednesday and can PM for info to send you some material later this week.

"my quick search didn't find a suitable cap"

same here – whenever I see a plastic cap now, I see if it will fit…

I tried a plastic bag with rubber band to keep it on

You have to add a bit of your warm water occasionally to keep it from freezing. The heat of combustion for butane is 100X the heat of vaporization, so you only need to use 1% of your warm water.

You can use aluminum

Theoretically, you need a little thicker aluminum to conduct the same amount of heat, compared to copper, but even with thicker aluminum it would weigh less

If you PMed me your address I'd mail you a couple scraps – price would be to post anything useful you learn

Thank you very much to both of you. I'll be happy to post my experience with whatever I can get rigged up.

And, for the aluminum….would the trick be with it that if I get the strip of metal too close to the burner, that the burner would melt the aluminum but not the copper?

I've had strip of aluminum in flame without melting

Maybe adjust position so it's not in the main part of the flame?

If it's too much into the flame, it will interphere with burning? Roger will tell you you're quenching the flame creating inefficiency and CO ? : )

Exactly. Copper goes to MUCH higher temperatures than aluminum. I've melted the tips of some experimental aluminum HX fins in butane flames. Thicker aluminum helps, though, because more heat is conducted away from the hot end. PM me if you want some copper bits to play with. I'll be back from a father-daughter GCNP trip in a few days.

"BTW, I forgot to mention that the silicone sheet material came from some ice cube tray covers purchased at Bed Bath & Beyond"

Silicon pot holders and non-stick sheets for cookie baking pans (kind of like reuseable parchment paper) are other retail sources of silicon. From memory, I think it's good to 495F continuous, 525F intermittently.