Jetboil cold weather heat exchanger

[Bob Gross]

"Yeah, thinner material does conform better, but maybe you can do a bit of hammering at home first?"

In the past, I have done this using a heavy solid copper wire and beating it a little flat. For this current experiment, I started with a copper pipe fitting. I used a Dremel tool to cut it, and then I straightened it out to give me a heavy flat strip. Using a hand sledge and a concrete garage floor, I hammered the edges thinner so that they would conform better to the canister shape. The main thickness of the copper is good for transporting the heat. It's kind of heavy. This piece weighs more than 1 ounce, and that doesn't even include the attachment wire.

For milder conditions, I'll bet that aluminum might work similarly.

–B.G.–

[David Thomas]

Roger: yes, the stuff is like albino gorilla snot.

Bob: aluminum is lighter per heat-carrying capacity, but copper is good to a much higher temp.

[Bob Gross]

Yes, David, I think that we sat in the same physics class.

That's probably why most heat sinks are made of extruded aluminum, not copper.

–B.G.–

[Bob Moulder]

Contact is pretty darn good with the thin sheet. After folding it the edges can be flattened easily just with a thumbnail and it is also easy to bend a curve into the strip. The slight cushioning effect of the silicone also helps it hug the can even better.

I was aware of the heat sink paste but wanted to keep it as simple as possible.

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[Jerry Adams]

I think your velcro will make sufficiently good contact – heat sink goop is too messy

I think #18 steel wire loop of just the right diameter works pretty good too, although the velcro strip will push on a longer length of wire

Wire doesn't have a very big contact area – strip is better. Although pounding it flat (as in one of your pictures and Bob said) helps.

[Bob Gross]

"aluminum is lighter per heat-carrying capacity, but copper is good to a much higher temp."

What temperature on a scale of butane stove flame temperatures?

By the way, some copper that is probably not acceptable is sold at some home repair stores. It is a copper foil with adhesive backing, but it is far too thin to accomplish much in heat transport.

–B.G.–

[Jerry Adams]

Good point Bob – I've had aluminum in the butane flame and it was just fine
– maybe glowed red

Aluminum melts at 1200 F, but aluminum oxide melts at a much higher temperature

[David Thomas]

>"That's probably why most heat sinks are made of extruded aluminum, not copper."

I suspect it is due to the lower cost to manufacture – lower temperatures involved, but more so, the lower materials cost.

I bet there is a market for copper heat sinks (because they would work better): gamers who over-clock their processors.

In general, a heat conductor can be thought of a pipe to carry heat. For simply carrying heat, it is all about cross-sectional area (for a given material). But, as Roger notes, flat stock dissipates more heat to the air than a round(-ish) cross section.

I'd start with about 10- or 12-gauge copper wire, maybe folded in a tight U and pounded flat on the bottom end. A broccoli-bunch rubber band to secure it to the bottom of the canister and (if you want to get super fancy), a bit of high-temp wrap (scavenged from a hair dryer, for instance) between the canister-contact point and the flame zone. For something with more heat-carrying capacity, I'd use 3/16" or 1/4" copper tubing, hammered flat on the bottom. I like the idea of some JB-weld on the flat bit to conform to the canister curvature. Probably wax the canister as "form release" while the JB-Weld cures.

Any pre-mix blue flame can oxidize aluminum and melt the pure aluminum (but not the oxide). But maybe not with the "heat sink" aspect: the rest of the Al rod extending into cold air and onto the tank.

This is something I'd mock up and test, but we haven't had Winter here, yet. Almost every day since Fall has been in the 30's F.

Edited to fix typo.

[Bob Gross]

"10- or 12-gauge copper wire"

Yes, solid copper, not stranded. Solid will hold itself stiff longer. Pound it about halfway flat.

If you want to simplify it, use a loop of wire. The middle is in the flame, then it is doubled and extends down to the canister. Then you can form a loop there and extend the wire all the way around the canister so that you can tie it off tight. If you want to make it more weight-efficient, then the wire that goes around the canister can be thin steel wire since it is much stronger for a given weight.

You probably want to keep the wire long enough so that it will fit to a small canister or large canister.

I have some aluminum wire here as well, although I haven't tried it yet.

–B.G.–

[Bob Moulder]

With my newly developed confidence in the MiniMo with HX for cold weather stoving, I decided to rely upon it solely for my recent trip to the Adirondacks, the first time ever that I was not using a Whisperlite or XGK in those woods.

The temperatures ranged from a high of about 23F Friday afternoon to a low of 3F Sunday morning. In order to validate the performance of the HX device, I did not make any effort at any point to pre-warm the fuel canisters, one of which was a 110g MSR and the other a Primus Power Gas 100g.

All water (except for 1 liter carried in) was from melting snow, and if I were as good at managing fuel as some of you veteran canister users, one canister would have sufficed. However, a couple of times I let the meltwater get far warmer than necessary, and a couple of times the water was boiling furiously and wasting fuel because I wasn't 'at the ready' with more snow to melt, so I ended up needing a teensy amount of fuel from the Primus canister.

I was extremely pleased with the results. As expected, after leaving the stove/canister out all night it was somewhat sluggish when firing it up at 3F Sunday morning, but the HX strip worked its magic and it was chugging along at full speed in very short order. I didn't time it, but I would estimate it was within 2 minutes of lighting.

MiniMo with HX strip

Chugging along happily at 3F following a cold start!

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Yes, it was fairly cold…

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[Jerry Adams]

wow, that worked really good

I hate it when I get distracted and let my water boil furiously for a while without noticing it.

[Bob Moulder]

I forgot to mention… in the photos it looks as if the canister is sitting directly on the snow, which is not the case. It was covered up by the snow, but there is actually a piece of 1/4" CCF under the canister.

Especially with this smaller pot, I'm going to have to watch it more closely because it brings the liquid to a boil in such a hurry. I found it interesting that small bubbles were forming at the bottom of the pot even as a blob of unmelted snow floated at the top of the water!

This is a great solo setup but not practical for 2 or more people; it would require constant attention for quite a while to make water for two.

One problem I had was with the large number of spruce needles and various other forms of flotsam in the snow. At first I didn't think much of the lid on the MiniMo, but it turned out that the pasta strainer did a pretty good job of filtering out most of the larger chunks.

Ok, this is just cool. Nice accomplishment with a JB!

[Bob Moulder]

John, seems I'm pretty close to getting the no-muss, no-fuss cold weather setup I was aiming for.

I don't know if I'll get the chance to test it at -20F this year, but if it maintains this kind of performance at that temperature I am getting rid of all other winter stove setups. It works that well. But at -20 I might have to warm up a partially-used canister a bit just to get it to light…

I'm looking to get the 1.8L Sumo cup, however, to make it useful for 2-man winter outings.

[jimmer ultralight]

Looks like it worked just fine..;)

It would be intersting to see how much it would improve fuel consumption versus running a plain setup in the same temps..

[Jerry Adams]

A plain setup (upright canister) would quickly slow to nothing at 20 F.

Shouldn't affect fuel consumption. The heat of vaporization is 1% of the heat of combustion, so if you siphoned away 1% of the combustion heat to vaporize the fuel, you'de consume an extra 1% of fuel.

[jimmer ultralight]

Jerry,
You missunderstood my post..

I thibk it will perhaps IMPROVE fuel economy because it is burning better vsporized fuel.

Such a test would be a good one for Hikin' Jims blog.

[Bob Moulder]

Hi, Jimmer/Jerry:

To Jerry's comment, in my opening post describing my test burn on the deck at +10F, I observed that starting with a brand new canister at room temperature (+72F), and without using any kind of warming trick, the stove burned strongly for a couple of minutes and then noticeably diminished in performance until it was for all practical purposes not putting out any heat at all at around 8 minutes. So Jerry's right – the stove just stops. This is why I was more than a little surprised in the Adirondacks when the stove cold-started at 3F… but that was a very fresh (although not totally full) canister with a considerable percentage of propane remaining. A well-used canister with a small amount of propane remaining would likely need a little pre-warming to kick-start it until the HX strip becomes effective.

Jimmer, I'm almost (because I haven't actually tested ;^o) certain that fuel economy (overall stove efficiency) is improved because, especially when it is very cold, there are going to be increased radiation/convection heat losses to the surrounding environment. So at a very low flame setting the whole system might barely be keeping up with environmental heat loss and not actually warming the water in the pot, in which case the efficiency would be practically ZERO. This is why the integrated pot cozies are such a good idea. But, as others have observed, there is a certain, optimal 'sweet spot' somewhere below full blast where the system is more efficiently absorbing heat from the burner without having excess heat wasted by running around the sides of the pot. But this kind of heat loss is hugely mitigated by the fins on HX pot bases, so it probably matters a lot less.

Quite a few canisters of fuel were burned getting to this point, and I don't plan to do a whole lot more testing unless I have a golden opportunity with easy access to some sub-zero conditions. I'm going to try to find some of the 'summer' Primus canisters to see how they work in the cold with the HX strip. Campmor might have them.

Obviously this HX concept is well known to stove and stove accessory manufacturers, so I'm assuming they avoid it due to liability concerns for a feature that is of interest to only a small segment of their market. There's no shortage of nitwits out there.

Edited to edit my editing.

[Jerry Adams]

Same here – tried on my patio

20F just slowed to nothing so never boiled

Efficiency improved a little, when the stove was slower. I weighed the canister before and after to see how much fuel was consumed. Repeated a couple times to make sure I wasn't just measuring random variation. Too lazy to find the thread – maybe a year ago?

When the stove runs slower it's more efficient. The hot gasses flow around the pot closer so transfer more heat to the pot. When you turn the stove up, there are more hot gasses that flow over bigger area so transfer less heat to pot.

If you do it in sunlight, and look at the shadow, you can see where the hot gasses go and, when you turn it up, they go all over the place rather than staying next to pot. Sort of a poor man's Schlieren photography.

I forget, maybe 10% more efficient at slower speed. Good trick if you're low on fuel and want to get everything you can out of it.

[jimmer ultralight]

Jerry,

The thing is, when you run a stove.in cold weather IT CANNOT run full power.

How hot was it when you did your tests turning the stove "down"? In sub.freexing temps, mother nature already turns it down. Even with.the HX you are only running about 2/3 the temp you would at 70 degrees.

Remember, fuel efficiency is based on the amount of water actually boiled per ounce. In sub freezing weather "ovrrheating" the pot is not a problem. Overcomming the constant heat drain of the pot surfaces exposed to the freezing air and wind, is.

I still say that in below freezing temps, fuel efficiency would improve with the HX strip.

[Bob Moulder]

My impression from using it in 'respectably' cold temps – well below freezing – is that the fuel efficiency is pretty darn good. And the performance was certainly not lacking.

I really expected to use more fuel than I did. The only precise number I have is total fuel consumed between the two canisters, which was 141 grams, but I have no idea how much snow was melted, water was heated/boiled, nor how long it took. It was an actual trip and my only goal was to see if it worked well and was reasonably fuel efficient.

[Jerry Adams]

I measured the weight of water to make sure it was the same every time.

I measured the weight of the canister before and after to get amount of fuel used. I made sure and wiped off any condensed water on outside of canister, but that was insignificant.

I measured the temperature before and after. I had a lid with a hole and a thermometer tip through hole. Little piece of wire around thermometer probe to keep it the same distance from the bottom – about half way between bottom and top of water, and half way between center and outside of pot. I waited a few seconds after turning off because the temperature rises a few more degrees. This should also equalize any differences between different places in the water volume.

I tried to do 180 degree F temperature difference from before to after, but each time was a few degrees different, but I normalized that out. I calculated the amount of fuel to raise 15 fluid ounces of water 180 degrees F. That's the amount required to fill up my thermos to make tea.

I've tried the strip of aluminum (works good), a copper wire (not big enough for enough heat transfer but a bigger wire would have woked but weighs more), and a container of water (works best, but more of a hassle).

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.

When I turned it down, it took 6 minutes to boil instead of the normal 3 minutes. This is with enough heat exchanger so it will run that hot. 6 minutes used 10% less fuel.

If you look at a shadow in sunlight you can see what's going on. With 3 minutes boil time, the hot gasses go all over. With 6 minutes, they stay closer to the pot.

It's all basic chemistry or physics or whatever – the butane gives off so much heat when it combusts, and then some of the heat blows away into the air. It doesn't matter what temperature it's at. At least to first order.

Yeah, if it's colder, there will be a little more radiative heat loss, but I don't think that's significant.

Numbers are what I remember off top of head, but there was a 10% reduction in amount of fuel used when I doubled boil time.

Also, if you only heat up to 190 F or so, where it starts making hissing noise, and then let it sit for 1 minute (or several) it will kill any bugs and save another 10%. (Since none of this is necesary and you can drink untreated water just fine, you could just not heat it up at all and save 100%, except that doesn't make for good tea or oatmeal – just kidding).

[Bob Moulder]

And then there's the type of pot used (HX pot is a huge difference, I found!), wind screen and wind screen design and how it's integrated with the pot and actual wind conditions…

Then, you're dealing with thermometers, timers and scales, writing down data… OY!!

Objective testing requires a lot of work. Figuring out a test protocol to isolate one of the factors can take a lot of thought.

During the first tests with the HX strip the primary objective was simply to see if there was a gross effect, i.e. whether the thing worked at all. While the stove was running I would remove it, watch as stove performance decreased, re-install it and observe the increase in performance, and do this a few times as an entire canister of fuel burned to make sure it continued to work at different fuel levels.

You've gotta have a bit of insane geek in your DNA to do this when the temperature is in the teens and the wind is blowing. Especially while having a gin&tonic. ;-)

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[jimmer ultralight]

Even if it's exact effect on fuel consumption is not qauntified,at least the HX strip does its intended job and allows an canister stove to work better in lower temps.

Good work..;)

[James Marco]

Jerry a few comments:
1) Heating and cooling always happen. It is the difference between the two that counts.

2) Heat transfers geometrically, ie more heat is transferred closest to the flame.

3) At 10-12minute burns for 16oz at 70F, the radiant heat loss is not really important. It is based on the differential between the water and pot and outside environment. At 0F it will never boil, even at 30min. It just does not supply enough heat for that. The radiant heat loss is enough to prevent it. So, radiant losses can be important. I think JetBoil was the only company to recognize that by supplying a built in cozy (until the new MSR stoves) for use while you are cooking.
4) In a "perfect" world, cutting the heat by 50% should give you a 50% fuel savings, but double the time it takes to boil. As you found out, it doesn't work out that way, though.

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