Testing Moulder Strips at -15F/-26C

[David Thomas]

Ben (and everyone):

DON’T USE A MOULDER STRIP IN WARM WEATHER!!!

There’s no need to, and there is definitely risk of providing too much thermal feedback.  In warm weather, we should all check the canister temperature with a bare finger and it shouldn’t be hot to the touch, at least not down where the liquid is.  If it is, open up your windscreen a lot or shut it down till it cools off.

Are you wearing shorts?  Are people sunbathing?  No Moulder Strip.

Is there snow on the ground?  Was it 0F last night?  Do you have skis on?  Consider a Moulder Strip.

Yes, mostly you are replacing the heat of vaporization of the fuel.  Yes, that is a function of fuel usage (low, medium, or high stove output).  But there are other mitigating factors.  That canister is out in the cold.  If the canister started to get much warmer than ambient, there will be more heat losses off its exterior.  That’s why Bob and Gary sometimes see better results with smaller canisters: less surface area (plus a shorter MS length).

The DOT rating is for 50C = 122F.  If you somehow got the liquid up to 50C, the WHOLE canister – top, sides and bottom – will 50C / 122F.  There’s a lot of heat loss off of a 122F object on a 0F day.  Drop trou at 0F and a few parts of your 98.6F anatomy will make it clear that there’s a lot of heat loss going on.

Looks at the close-up photo of the CMS – there’s a droplet of ice on the steel canister (above the liquid level).  That tells me the liquid butane is at or below 32F.  Otherwise the >32F liquid butane would boil into >32F vapor butane which would condense on the inside of the canister (preferentially on the coldest spots) until the whole exterior of the canister was at the temperature of the liquid butane.

You’re right that heat conduction down the MS is mostly a function of flame temperature, not flame setting.  I’m not worried about excessive heat transfer (if used at or below freezing), but I’ve often observed an equilibrium be reached at the lower limits of a particular MS.  The marginal MS can’t keep up with the evaporation rate of the butane, so the butane cools a few more degrees, the pressure drops, and the flame level decreases, even with the same valve position.  And it putters along at the lower level till you run out of fuel.

Everything I said above is for isobutane or a butane/propane mix.  If you are refilling canisters with n-butane, then a Moulder Strip or any of the other techniques Gary documented in his recent article may be helpful at 32F to 45F, maybe even 50F at high flame settings, especially with no windscreen.  Like back in the day when we cursed at those 100% n-butane Bleut cartridges because (1) they crapped out below 45F and (2) once pierced, you couldn’t remove the stove head.

[David Thomas]

“a quick google search suggests you anneal aluminum at 750°F.. a bit higher than my oven goes.”

“Honey, why do you have the oven on self-clean for a second time this week?  And where did Phoebe’s ruler for Geometry go?”

[Bob Moulder]

Ben,

There is no reason someone would be using this device at 60°F, let alone 100°F. This is strictly for cold weather, which I would define as 45°F and below, because with some fuels—notably n-butane—some reduction of performance can be seen once evaporative cooling kicks in. While propane/isobutane blends don’t really need a lot of help at 45°F, I have seen improved performance at that relatively mild temperature.

However, knowing that the potential for misuse/abuse abounds, I tested it at 75°F ambient with both a MiniMo and BRS, both running full bore for 30 minutes, using both the copper strip AND cozies. Yes, I monitored with 2 thermometers on the canister—one near the copper strip and one on the opposite side of the canister—and very frequently I did the Touch Test on the top of the canister. It got pretty warm, but did not exceed the 122°F (50°C) temperature deemed safe by DoT.

My rather extensive empirical observations tend to agree with your epiphany that thermal feedback heat might be—to a point—independent of ambient temperatures. I say this because when testing n-butane at -5°F the stove (BRS-3000T with 110g canister) continued to run at full power until the fuel was completely exhausted, same as it did at +20°F. A few weeks ago in the Adirondacks I was running a MiniMo with n-butane in a 220g canister right around 0°F and got the same performance.

All this applies to the performance of the stove AFTER the canister is warm enough to run, AND while using a cozy. When running the larger canisters at approximately 20°F and lower WITHOUT a cozy, there will be a drop-off in performance. This is why I say “To a point…”  But with adequate insulation of the cozy there’s no telling what the lower ambient temperature limit might be.

But, IMVHO the current setup is, in fact, already inherently safe.

 

[Jerry Adams]

yeah, maybe worst case 45 F is where the stove slows down

maybe at intermediate temperatures like 25 F to 45 F, first use stove normally, and if it slows down, then use one of the cold weather techniques

[Roger Caffin]

thermal feedback heat might be—to a point—independent of ambient temperatures.

Well, let’s look at this as engineers or physicists. One end of the metal strip is in a flame at very roughly 1,000 C. The other end of the strip is at ambient, somewhere between -10 C and +10 C. So there is a temperature gradient of about 1,000 C. Do you really think that a variation of 10 C at the cold end is going to make much of a difference to the heat flow down the strip?

In any event, I totally agree with David and Bob and Jerry: you do NOT need any heat shunt or strip at all above 10 C (50 F). Using one in warm temperatures is just stupid – or dangerous.

Cheers

[Bob Moulder]

Do you really think that a variation of 10 C at the cold end is going to make much of a difference to the heat flow down the strip?

Good point, it doesn’t. The problem there is not the heat flow down the strip but the retention of heat in the canister which of course has a large surface exposed to ambient. When using a canister cozy this is largely mitigated… enough to permit a 220g canister to run full power until empty at -5°F with n-butane (and likely lower, but I have not had it out in colder temps than that…)

 

[Ben H.]

Thanks David and Bob and others for reiterating not using these things in warm weather.  I threw out 100°F from a Murphy’s law perspective.  You know some jacka$$ is going to do it so you better figure out what will happen.  I should have added some cautionary warnings not to be that jacka$$.

[David Thomas]

“let’s look at this as engineers or physicists”

The physicist would calculate how likely one state is versus another, using the usually combinatorial calculations I expect everyone in my household to know by age 10. They’d then relate that entropy change to energy units.

The engineer would grab his or her Butane-Mix-Canister Handbook and read the entry directly off the table in the 0F column and the 25%-full canister row in traditional units of British Thermal Units per fortnight.

[Bob Moulder]

LOL, well we always have to consider the Jackass Factor… there’s no shortage of contestants for the Darwin Award.

Funny thing, during my very extensive googling of “Alpine Bomb” I found many iterations of the copper heat shunt but no examples of anything actually exploding. It’s almost as if nobody ever thought to stick a cooking thermometer probe on the shunt and/or canister to measure the actual temperature. Based on everything I have seen, it would be almost (leaving some leeway for the boundless creativity of morons) impossible to intentionally cause an explosion with a heat shunt.

[Bob Moulder]

………which reminds me….. Roger C at some point in the past did indeed intentionally blow up some canisters and might be interested in testing this hypothesis. ;^)

[Roger Caffin]

@David: just so. :) :) :)

Bob: I suspect that most users of the original Alpine Bomb were at some altitude where the ambient was down around 0 C or lower. Bear in mind they started with the old Bleuet canisters which contain ‘pure’ n-butane. Mid-summer on a S-facing granite wall they might have been satisfied with sandwiches and water.

Yes, I did explode a canister to see how hot it had to get. My result, starting with only a small amount of fuel in the canister, was that it had to get to about 100 C before it popped. Further testing of more canisters was forbidden by my wife on the grounds of the noise involved. “There was some.”

Cheers

[David Thomas]

An update on the math competition: Drake’s score on the American Invitation Mathematical Examination that day in Fairbanks was 11th highest, nationally.  Plenty good enough to make the cut from that 5,000-student event to the 260-student USAMO this week: 3 questions in 4.5 hours on Wednesday and another 3 questions in another 4.5 hours yesterday.  He felt good about two proofs each day which is better than in past years, but without nailing 5 or 6 out of 6, I’m not studying Portuguese for travel to Rio this summer for the IMO (top six from each country).

[BlackHatGuy]

Congratulations to Drake!

[Roger Caffin]

Hi David and Drake
Way to go!
Cheers

[Bob Moulder]

Congrats to Drake!

What a huge accomplishment, and best wishes for the USAMO.

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