Jetboil cold weather heat exchanger

[Bob Moulder]

That is the province of “Mythbusters” and “Jackass”…

Ain’t gunna happen with sober and semi-intelligent adults ;^)

I would NOT show this to a kid.

[Jerry Adams]

One other calculation and I’ll stop : )

David and Bob heat up the canister with a lighter.  Other people put it in sleeping bag.  The question is, how much does it cool from evaporative heat loss?

Assuming 7 g of fuel and 386 J/g to vaporize, it takes 2702 J to vaporize 7 g of fuel, which is what it takes me to boil a pint of water.

The specific heat of butane is 1675 J/kgK, and steel is 500 J/kgK.

A best case would be a full 228 g canister of butane.  steel canister weighs 5.4 ounces.  Vaporizing that 7 g of fuel would lower the temperature 5.9 C = 10.6 F.  I heat up 4 pints total, so that would be 42.4 F.  If the canister started at 75 F, it would cool to 32.5 which is still warm enough to work.  This is a reasonable strategy.

A worst case would be a 1/4 full 110 g canister.  Steel canister weighs 3 ounces.  Vaporizing 7 g of fuel would lower the temperature of canister 30 C = 54 F.  If the canister started at 75 F, it would come pretty close to heating up just one pint.  But you could heat up with Bic lighter to about 75 F before each pint of water you wanted to boil.

Why doesn’t the U.S. just switch to metric and get the pain over?  It’s like it’s better to just quickly rip off that band-aid and the pain is over : )

 

 

[Jim Sweeney]

A sad note re the earlier reference to “growing a pair.”  Though it’s always seemed an amusing biological impossibility,  I now must hope it isn’t.  I was attempting to solder some thin copper directly to a full canister, which, because I only have two hands, was held between my knees.  Apparently I’ll be able to leave the hospital in a few weeks, and then we’ll just have to see about the “growing.”

[David Thomas]

To be clear, I love the idea of the “Moulder Strip” and its rumored precedent, the “Gross Wire”.  Good to a lower temp, no muss, no fuss.  And I’m enjoying imagining tweaks to make it even better.  And I’ll give it go in the garage pretty soon.

My reason for interjecting the mini-Bic alternative is that some times, “Stuff Happens!” and you’re in a setting too cold for your fuel canister’s mix.  Without your Moulder Strip.  I want people to know that you can always:

Pop it in your sleeping bag for a long time.

Pop it under your armpit for less time.

Put it in warm or actually any liquid water.

Hold a small flame under it for a short time.

And be, as they say, “Cooking with gas!” again.

Jim, I was briefly considering posting, as a joke, a proposal to solder a bit of aluminum plate onto one’s cold-weather canisters with a hole drilled for 10-gauge copper or aluminum wire in it already.  Insert the wire, fire up the stove, you’re good.  But if I explain that it is a JOKE, never to ACTUALLY be done in practice because of EXPLOSIONS!; it kind of ruins the joke.

That said, a small pre-drilled plate EPOXIED (not soldered) onto a canister makes a better thermal connection without the bother of a strap to hold it on.

[Jerry Adams]

I just soldered a copper wire to a canister

but it was empty and I screwed on a stove and opened valve to let any pressure out

 

[David Thomas]

“opened valve to let any pressure out”

Be aware that any orifice can only allow gases to escape at the speed of sound.  The gas molecules can’t go faster than the speed of sound regardless of how much pressure is behind them because there’s no more “push” when all the gases behind them are going the same speed.  The density of the gas times the speed of sound times the cross-sectional area is the maximum mass flux through the orifice.

If the canister was “empty” in the sense it only had butane gas in it, you’d be fine.  It wouldn’t get far above atmospheric pressure with the valve open.

But to be clear: if there were still liquid butane in the canister, a torch flame could boil it so rapidly as to exceed the mass flow rate of the wide-open valve because it wasn’t spec’d as a pressure-relief valve, but as a control valve for flame level (a pretty low mass flow rate).

Bonus info:  For most gases and common temperatures, mass flow across a valve will increase as delta P increases until delta P is about 15 psig.  Then it won’t increase any more even as vessel pressure increases.   You can (if you’re really careful and wearing your big-girl panties) see this in a canister stove.  Set a low flame level with a room temperature canister.  Heat up the canister, say in a 140F water bath.  The flame level doesn’t change!  Even though you have clearly increased the pressure behind the valve, it was already going at sonic speeds through the valve orifice.

[Bob Moulder]

Hey guys, I just want first to say thanks for all the effort, ideas and suggestions to make the HX strip better, but I’m hoping that you will first give the system a shot in its basic form to see how it works without any embellishment. While thermal conduction through the HX strip and thermal contact with the canister are often mentioned, neither of these has been a problem at any point in my testing, with many dozens of runs in some very cold weather, both in my ‘lab’ and in quite a few field trips. So before you solder/screw/glue/tattoo anything to the canister, consider what that means when the canister runs out of fuel, and that it probably would have not been necessary in the first place, and you’re stuck with option #2 — you’re screwed. :^)

I recently started experimenting with using a hi-temp neoprene for the cozy, that being in the form of a cut-down Jetboil Flash pot cozy. REI sells spares, and they fit the 4oz canisters quite nicely. I have ordered some stock 3mm neoprene foam from a place in Seattle (seattlefabrics.com) so that I can make some custom cozies, also for the 8oz and 16oz fuel canisters. It was far too warm this afternoon at 37°F to do a real test, but this cut-down JB  cozy really worked well.

[David Thomas]

I love how this thread has stretched to 156 ever geekier posts.  When, really, it could have started and stopped with “Oilcamp makes a cheap HX pot” and “Use a Moulder Strip in Winter”.

[Bob Moulder]

But to be clear: if there were still liquid butane in the canister, a torch flame could boil it so rapidly as to exceed the mass flow rate of the wide-open valve because it wasn’t spec’d as a pressure-relief valve, but as a control valve for flame level (a pretty low mass flow rate).

Funny thing about this. The other night when I did the first tests with n-butane at 13°F, I finished the last run by simply removing the HX strip and letting the flame die out all by itself, leaving the stove’s fuel valve wide open all night to experience first-hand what would happen to the n-butane… In short, nothing — there was plenty of fuel remaining the next morning because it doesn’t vaporize below 31°F, but it was pretty neat to experience that little “Science 101” lesson.

But yeah, I’d be really careful about soldering or torching a canister, “empty” or not.  (altho “Bic-ing” is OK sometimes!)

[David Thomas]

“leaving the stove’s fuel valve wide open all night”

A few times a week a 700-foot-long LNG tanker goes by my house (I live on the shore of Cook Inlet).  If Alaska builds a NG pipeline from the North Slope, it will terminate 6 miles from my house and then it will be one or two LNG tankers a day.  Rather than provide refrigeration to keep the methane below its boiling point (-259F), they simply allow it boil off and feed the resulting vapor into the ship’s engines.  That keeps those huge tanks very, very cold for the voyage to Japan.

[Stuart R]

Solid materials start to glow red above 525 Celcius (977F). This is called the Draper temperature, named after the guy who first measured it. So I guess aluminium could glow red just before it melted.

[Bob Moulder]

Keeping this thread updated as a ‘repository’ for HX strip-related developments, HERE is a link to the latest tweaks to the system, mainly the modular cozy with neoprene wrap, silicone heat shield and Velcro cinch strap combined as a unit.

Photo: BRS-3000T stove running full blast at -5°F (-20.5°C) on n-butane

[Paul McLaughlin]

Bob, have you tried your strip with a 450gm canister, especiall one close to empty? planning a trip that needs that much fuel, and would like to save weight by carrying one big boy instead of two 220’s.

[Roger Caffin]

they simply allow it boil off and feed the resulting vapor into the ship’s engines.

How very clever … Rather than burning #6 bunker fuel, which is one of the filthiest fuels around, they burn clean LPG. Cute.

Cheers

 

[Bob Moulder]

Bob, have you tried your strip with a 450gm canister, especiall one close to empty? planning a trip that needs that much fuel, and would like to save weight by carrying one big boy instead of two 220’s.

No, I have not, Paul, but based upon my experiences with 110g and 230g canisters I would not recommend it for use in very cold weather with a 450g canister. There’s simply too much heat-sumping surface area, mass and volume for the strip to ‘keep up with’.

However, when you think about it, the weight penalty for two 230g canisters is not all that big when you add in the weight of a larger cozy. A 450g canister weighs (empty) about 195g. Two empty 230g canisters weigh about 290g, so you’re looking at about  a 100g increase, offset by about 20g for the cozy.

So, for your scenario, after the small weight offsets the penalty would end up being about 80g/2.8 oz.

[edit to correct my arithmetic — forget algebra, I can’t even handle simple addition/subtraction]

[Stuart R]

My reason for interjecting the mini-Bic alternative is that some times, “Stuff Happens!” and you’re in a setting too cold for your fuel canister’s mix.  Without your Moulder Strip.  I want people to know that you can always:

Pop it in your sleeping bag for a long time.

Pop it under your armpit for less time.

Put it in warm or actually any liquid water.

And a convienient source of warm water when your stove won’t light is:

Urine

[Jim Sweeney]

And many ships are now fueling themselves by boiling off their urine.

[David Thomas]

I agree that the weight penalty isn’t huge for the 230-gram canisters versus the 450s, but for a long trip, I’m draw to the 450s for their noticeably lower price per gram of fuel.  It’s kind of like buying green beans: the 14-ounce small can, the 28-ounce big can and the huge 6-pound #10 don’t differ much in price.

Last I looked at my local store:

110-gram canister: $4.99

220-gram canister: $5.99

450-gram canister: $7.99

So, for a pound of fuel:

Four 110-gram canisters: $20

Two 220-gram canisters: $12

or one 450-gram canister: $8

[Bob Moulder]

Refilling with N-butane, I’ve got the cost down to $3.25 per pound for all sizes. :^)

110g canister = $0.82, 230g = $1.64, 450g = $3.25

But “canister season” (winter!) is all but finished here and soon it’ll be Esbit and alcohol. Maybe some wood as well.

[Bob Moulder]

And a convienient source of warm water when your stove won’t light is:

Urine

And when your dinner is finished cooking you’re going to want to be really hungry!

[David Thomas]

“Refilling with N-butane, I’ve got the cost down to $3.25 per pound for all sizes. :^)”

Or refill with propane for $0.60/pound.  And you can leave the Moulder Strip at home.  But never, EVER, let the canister get over 70F.

No, really, don’t do this.  Dropping hot Top Ramen on your canister, or dozens of other mishaps or a moment of inattention would create a bomb.

[Jerry Adams]

and the generic 220g from Fred Meyers is $3.99 : )  I just used a mostly full 220 g canister at 22 F without problem,

I’d argue the 450 g canister would be better for cold.  A mostly empty 220 g will cool down 12 F while boiling a pint of water.  A full 220 g will cool down maybe 2 F.  So you can use a full canister at 10 F colder than an amlost empty one.  A half full 450 g would be the same as a full 220 g.

[Gary Dunckel]

” A half full 450 g would be the same as a full 220 g.”

No it wouldn’t, Jerry. Are you ignoring Bob’s comment about the effect of a greater canister surface area of the 450 g. canister, which will enhance cooling? Bob and I have both found that the 110 g. canisters function in cold temperatures (near 0* F) significantly better than the 220 g. ones do. Bob’s neoprene cozies (as well as my own) work well with both the 110 and 220 gram canisters. But when you consider the extra weight needed for a cozy and copper strip for the tall 450, well…I wouldn’t consider it given what I’ve learned from my own tests.

Some of the engineers on BPL seem to be guessing as to how this “Moulder Strip” concept functions, without actually trying it themselves. The exception, of course, is David Thomas, who always posts some good stuff that adds to the quality of this thread.

 

[Bob Moulder]

@ David, yikes, yeah, don’t do propane, lol!

@ Jerry, anything will work well at fairly cold temps as long as there is enough propane content remaining. Even at 22°F, however, if the stove runs longer than about 4-5 minutes the performance will start to fall off due to cooling from vaporization. If long burn times are needed for melting snow, obviously some sort of external heat will be required, especially when the fuel level is low. I recall that the very first serious test I conducted was at 23°F (first post in this thread), and an almost full 100g MSR canister died out fairly quickly without external heat, even with relatively high propane content.

Based on everything I’ve seen, I’d bet a hot dinner that a 450g canister with 28g of fuel remaining would not be able to boil 2 pints at 22°F ambient even with the canister starting at 70°F (absent an external heat source). IMO, sustained low fuel level performance is ‘the acid test’.

[Jerry Adams]

I’ve only tested 220 g canisters, at about 1/8, 1/2, and 1 full.  I’ve done the 1/8 and 1/2 with an aluminum “Moulder strip” which worked fairly good, but it hasn’t been really cold.  I always go 3 minutes at a fairly high level boiling 1 pint, then I take off 10 minutes to drink my tea/coffee.

I think an even bigger factor than the small amount of propane is the heat capacity of the butane in the  canister.  Like I said, a 1/4 full canister will cool down 12 F during a 3 minute burn time.  If the lowest temp that will produce enough evaporation of butane is 20 F, and you start less than 32 F, it will drop down to that 20 F and then the flame will drop to almost nothing because little butane is evaporating.  With a full canister, it only drops 2 F, so you could start at 22 F or higher, and the butane will never get down to that 20 F point, so it will work fine.  A full canister will work at a 10 F colder temperature.

I think a half full 450 g canister would work the same as a full 220 g canister, but that’s just guessing.

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