Jetboil cold weather heat exchanger

[Roger Caffin]

> Not sure how others do a water bath….do they just use a larger cup with warmer
> water so ice doesn't form?
I use my GSI plastic dinner bowl. When dinner is ready I drink the cool water in the bowl then eat my dinner. Very simple.,
Yes, ice can start to form after a while: move a few spoonfuls of hot water from pot to bowl.

I MUCH prefer a small bit of light 3-ply to a CCF pad: the 3-ply is rigid and far more stable.

Cheers

[Roger Caffin]

> 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 ? : )
Chuckle. The latter bit might be true.

But you don't need to stick the Al strip right into the flame: just have it vaguely 'touching' the side or underside of the flame. Plenty hot there, and minimal CO generated as the upper part of the flame will continue on its way.

I rather like the Cu/Al strip plus foam cozy idea. Neat.

Cheers

[Jerry Adams]

Okay, I mailed you a strip of aluminum flashing

also a thicker strip of aluminum

also a length of steel wire – I just put that on the outside to hold strip against canister. Make it the right length so it just barely fits so it holds aluminum strip tightly against canister

the materials would eventually make their way to recycle and the postage was $2.50 so don't worry about cost – PIF

[DGoggins]

Thank you Jerry! I'm sure I'll bother you again with metallurgy questions later…

Right now though, so as I understand it, it doesn't matter if the canister is 145*F next to the aluminum tab, as long as the opposite side of the canister doesn't get too hot as well, then I should be fine?

And, the "hand/pain" test would be sufficient (so as long as I can place my hand on the canister, it should be under 140*f), I should be ok. I do have a thermometer to use anyway though.

[Jerry Adams]

I think what you don't want hot is the butane inside.

Maybe the canister could be a little hot right next to the tab? But if there's butane inside, the canister external temperature should be the same as the butane.

Above the butane level the canister might get warm?

But, you don't want to risk it blowing up. All you need is for the butane to be above 25 F or 30 F. If there's any chance it's too hot, move the metal tab away from the flame. If the butane is too cold, that is, if the stove slows way down, then move the tab closer to the flame.

[David Thomas]

Yes, 140F is the hold-on-to-it limit. Yes the canister, below the fuel line on the opposite side reflects the liquid butane temperature (which determines the vapor pressure). Yes, 140F is okay (think car interior on a hot sunny day), but (1) I wouldn't want it any higher and (2) as Jerry points out, the benefit is getting it above freezing. More than that doesn't help. And carries some risk of going too high if, unnoticed, you get more thermal feedback.

[Jerry Adams]

so, it doesn't matter if the canister is hot at the top, where it's above the level of butane inside the canister?

[David Thomas]

Jerry, correct. Hot metal on the top conducts poorly through the stratified gas or to the lower metal (the hot vapor above won't exchange with cooler vapor below).

You can see this happen on the BBQ propane tank during use. The top of the tank, above the liquid level, is close to ambient (or even warm in the sun), but at high vaporization rates, the liquid gets cold and you can feel the liquid level by running your hand down the side. Sometimes, you can even see the liquid level due to condensation or ice forming on the lower part of the tank.

But the pressure of that gas – hot or cold – is determined by the temperature of the liquid. So feel the bottom of the canister. If it feels hot to the touch, dial back your HX or radiant feedback. If it feels cold to warm, you're fine.

[Roger Caffin]

> it doesn't matter if the canister is 145*F next to the aluminum tab, as long as the
> opposite side of the canister doesn't get too hot as well, then I should be fine?
Chancy.

The DoT regulations require that the canister never fail at 50 C (122 F). The 'ouch' touch response starts a bit under that. So I recommend that the canister should never get hotter than you can touch.

However, the copper strip is never in perfect contact with the canister, so if it gets to 145 F I don't think there will be much of a problem. Yes, check the other side of the canister.

What David wrote is a pretty good guide too.

Cheers

[Jerry Adams]

So, does it matter if the top of the canister is hot?

As long as the butane inside the canister is below 122 F? And the canister that the butane is against, on the opposite side of the tab, should be very close to the temperature of the butane?

[David Thomas]

Jerry, all correct.

[Bob Moulder]

Jerry, I did many temperature checks with the copper strip in addition to the touch test to relieve my well-founded paranoia about canister overheating. I also re-tested when I started using the cozy for very cold temps and it got a few degrees warmer (and warmed up more quickly). But even with burns of 1/2 hour or so it never got remotely warm enough to cause a problem. The heat at the site of the strip/canister contact area dissipates very rapidly into the rest of the canister so the average temperature remains well within safe limits. At least that's my experience.

[Bob Moulder]

Photo to detail relationship… the strip needs to bend around a little at the top because of the concavity of the burner.

.

[Bob Moulder]

On a recent trip with a friend I took care of the stove needs, which for 2 of us meant using the taller, 1.8L Sumo vessel with the MiniMo stove.

Especially in the snow, further stability was called for, so I modified the cozy to accept the optional JB canister base legs. This set-up worked very well with the taller pot and operation was not affected in any way down to 4°F. Next morning the temperature had risen to 12°F (due to an arriving storm front) and the stove was ignited with no external heat and warmed up quite quickly to operating temperature. (Using the HX strip, of course!)

[DGoggins]

So, all I have is a sol AL, which is a 800ML aluminum cup. I would think that would barely be sufficient for solo use melting snow, or be too much of a hassle. I like the idea of buying a sumo companion cup for winter.

You have the aluminum sumo cup, correct? The TI sumo cup would have the same problem as the sol TI with melting snow where the fins would detach from the cup, right?

Can you let me know the weight of your sumo cup?

[Bob Moulder]

The Sumo cup with lid and bowl base weighs 319.4g (11.26oz). The canister base legs (recommended for use with the Sumo cup) weigh 27.4g (0.97oz).

The MiniMo cup with lid and bowl base weighs 284.8g (10.05oz).

These are both Aluminum.

Regards to HX fins detaching, this is pure speculation on my part but I very strongly suspect user error, whereby some way, somehow, the stove was running with no liquid in the pot. The only way they're going to detach is if the temperature exceeds the spot-welding temperature because there was no water in the pot. Used correctly, the energy is converted to steam. Relatively easy to do when melting snow because fresh snow tossed into the pot absorbs a lot of water and the bottom of the pot can end up dry when the snow sublimates straight from solid to vapor. Not good. Melting snow isn't rocket science, but there is a bit of a trick to it… mainly to pay attention and put in small amounts when there's little water in the pot, and more as the water level increases.

HOWEVER, for solo use I found the MiniMo cup (also .8L) totally adequate.

[Bob Moulder]

Addendum to the above, before someone jumps on me…

Also possible that the welding on the fins was defective, either by not getting hot enough to truly weld the 2 surfaces together, or not enough contact area at the welds.

However, I'd wager this explanation is vastly secondary to the user-error scenario.

[DGoggins]

Thank you for the quick reply.

Yeah…I guess I haven't weighed my jetboil sol AL cup in a while…with lid and base cup, it weighs 7.5 oz. Oh, that also includes using a jetboil zip neoprene sleeve instead of the sol sleeve. I guess I was getting used to recently weighing my evernew .9L titanium pot, which weighs 3.9 oz. Don't get me wrong…it doesn't have fins, or a sleeve, and its made of titanium, but just thinking of going up to almost 12 oz was a bit of a shock.

[Roger Caffin]

> Also possible that the welding on the fins was defective,

It was a combination of several things in my humble and personal opinion.

* Welding aluminium to titanium is not easy, and while Jetboil claimed to have mastered the process, there were doubts. Some of the ruined pots showed less than wonderful welds.

* Jetboil specified the Ti/Al pots for boiling water only – that would prevent the failures which happened, but it was a fundamentally stupid management decision to try selling such a pot into the general market. Users were going to cook, not boil, in those pots. I guess they had committed the investment to do the welding, and wanted an ROI.

* Jetboil used very thin alminium sheet for the fins. It was so thin that without really good heat-sinking at the pot end of the fins, which died not always happen, the tips in the flames could and did melt.

* Jetboil requested that users return damaged pots for evaluation. But once they had the pots in their hands, they refused to either replace OR RETURN the pots. In effect, they stole the customers' property. This was not well received.

So – a small amount of user error, but a huge amount of company error.
(Note: this only applies to the Ti pots with aluminium fins.)

Cheers

[Bob Moulder]

Roger, thanks for the clarification. That makes sense.

However, the fin design for Reactors and Windboilers is much more robust with significantly thicker material and much greater contact area, and also Al-Al, but I've seen photos of those after they've been run dry… also not pretty.

I hope Jetboil figures out a way to recompense the customers they stiffed, even if their position is that the product was misused… perhaps a very steep discount on a new stove.

On the bright side, the simmer capability of the MiniMo is quite good. This came in handy when the water was boiling and my mate hadn't yet dug out his dinner from his pack.

[Bob Moulder]

my jetboil sol AL cup in a while…with lid and base cup, it weighs 7.5 oz. Oh, that also includes using a jetboil zip neoprene sleeve instead of the sol sleeve.

John, obviously that's pretty good compared to the MiniMo cup at 10 oz… makes me wonder if JB is putting a little more material in the HX fins and pot base. I didn't think to compare the fins of the MiniMo and the Sumo.

Anything with HX is going to be significantly heavier. I was testing with some 1L and 1.8L Primus Eta pots when experimenting with the HX strip and they're also quite heavy. Even the plastic lids on those things are heavy… definitely not targeted for the UL crowd.

[Tony Ronco]

Adding to the somewhat off-topic discussion on Jetboil's manufacturing approach for their heat exchanger cups …

Based on my observations of Jetboil's products … Jetboil connects their Al Cups to their Al Heat Exchanger Fins via resistance welding. The witness marks of the process are clearly visible both on the fins and on the inside bottom of the cup. This is the way that makes the most economic & ease of implementation sense. It also provides a better thermal interface …

However, while Jetboil may claim their weld their Ti Cups to their Al Heat Exchanger fins, visual inspection of their 1st generation cups would indicate otherwise: they appear to be joined via brazing. It is certainly possible to weld Ti to Al, but there is a lot to be concerned about using the process to mass produce units: the difference in CTEs, the thin intermetallic interface, Kirkendall voids, and galvanic corrosion. It would have been much easier, more economic for them to just braze the units together. Visual inspection of their 1st generation product does show clear indications of braze flash and does not show any witness marks from their in house resistance welding operation used for their aluminum cups … or for that matter, any typical welding indicators that I could readily see.

As it is reasonable to assume that brazing is the case, then in terms of a failure mode for Ti-Sol cups, the liquidus temperature of the braze material is obviously less that the aluminum fins (in order to join everything without the melting the fins in the first place).
I suspect the following has a primary role: if the cup gets too heated then a compromised braze thermal interface can develop between the pot and the fins from braze reflow & gravity) resulting in localized melted fins (due to the heat build up from the compromised conduction path). Since the fins have very little thermal mass, they'll heat up very quickly if they can NOT dissipate the heat fast enough. The effect is pronounced in the aluminum because the liquidus temp of aluminum is 1,221°F (660.3°C) which is far less than titanium at 3,034°F (1,668°C).

In an attempt to redeem this thread drift (*smile*), here is a table of the JetBoil cups weights per my postal scale:

EDIT: Updated table of cup weights. Also added speculation on the Ti-Sol failure mode.

[Bob Moulder]

Thanks, Tony! Very interesting insights.

There is certainly a wealth of knowledge and experience on this forum.

[Gary Dunckel]

…I want to be like Bob. No, not that Bob (-B.G-), but rather Sir Moulder of the Land of Icy Boils. He is a gentleman, spells correctly with a gift for the written word, and he is quite the MYOG guy. (I did ask my local angel if I could grow up to be like you, Bobby G., but she said there was only room on this planet for one geezer like you at any given time). So, on to my point:

Yesterday, I found some .04" thick copper sheet at my local mega hardware store (McGuckin's). They sell 14" x 1" strips, which was perfect, and I bought a couple pieces to use to emulate Bob's heat exchanger thingy. Here are a couple that worked out pretty well:

After bending and contouring the copper strip to pretty well maximize contact with the side of the canister, I secured it with a 1/2" piece of Velcro. I wasn't sure if the hot copper would melt the Velcro, so I placed a small piece of carbon felt between it and the copper strip. I tried to make these so that each strip would work with a couple of different stoves. In this case they were the SP Giga and the BRS-3000T. The setup for the 110 g. canister weighs 21 grams, and the one for the 220 g. canister is 25 grams.

We have had a spring cold snap for the past few days, so it was about 33-35* F early this morning in Boulder. Not frigid by any means, but it would probably be the last coldish temperatures until next December, so it would have to do.

I was rather amazed as to how well Bob's idea worked. The copper got quite hot over its entire length (I couldn't touch it), but 3/4" away the canister was only a bit warm and certainly comfortable to the touch. After 4-5 minutes of burning, the entire top of the canister was slightly warmer than ambient, but nowhere near dangerous, and the far side of the canister was a bit less "warmed up.". Of course, during frigid temperatures, the canister would be even cooler. I have no doubt that this is a safe and efficient way to beef up a canister stove's performance in such conditions.

I think that you have hit a home run with your simple and effective design, Bob, and I want to thank you for teaching us how to do it.

edit: spelling

[Bob Moulder]

After 4-5 minutes of burning, the entire top of the canister was slightly warmer than ambient, but nowhere near dangerous, and the far side of the canister was a bit less "warmed up."

Thanks, Gary!

This is key, IMO, and also a product of quite a bit of testing up to 45°F ambient and as low as -6°F.

It's the Goldilocks Principle in action… it gets warm enough but is not capable of getting too warm. :^)

Glad to see someone else give this a good effort and witness its effectiveness as I did numerous times this past winter.

I promise, the lower the ambient temperature the happier you will be!

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