MSR Windboiler – Completed Review

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longri
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Re: MSR Windboiler – Completed Review

Post by longri » Sat Dec 06, 2014 9:17 am

hikin_jim wrote:Actually only about 3 psig is required for decent pressure on an upright canister stove.
Try this:

Take your stove and open the valve. Press the canister side to your lips and blow as hard as you can. How much air got through? A human can blow with a pressure of about 2-3 psi.








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Re: MSR Windboiler – Completed Review

Post by hikin_jim » Mon Dec 08, 2014 11:57 am

At sea level, the boiling point of water is 212 Fahrenheit. At 10,000 feet elevation, the boiling point of water is about 193 Fahrenheit, a decrease of 19 degrees. The boiling points of propane, isobutane, and butane (or a mixture thereof), fall by the same amount. Therefore, if a stove can be reasonably operated at temperature "X" at sea level, the same stove can be operated at about the same level of effectiveness at 10,000' elevation at a temperature of "X" minus (roughly) 20.

The rule of thumb, and it is just that, a rule of thumb, is that one can operate a stove approximately 2 Fahrenheit degrees colder for every 1,000 feet of elevation gain. Note the use of the word "approximately" and the use of the phrase "rule of thumb."

I'm stepping away from a PSI based argument here. Pick whatever PSIG one feels is appropriate at sea level, and one should have that same PSIG at 10,000' in temperatures that are 20 Fahrenheit degrees colder. If one wants a PSIG of 5, very well, choose a fuel mix and go out in an appropriate temperature for that fuel mix for 5 PSIG at sea level. With that same fuel mix, one should be able to still get 5 PSIG at 10,000' in temperatures 20 degrees colder than at sea level.

Likewise for 10 PSIG, 15 PSIG, etc. Whatever PSIG one desires can be had if one goes out in temperatures appropriate for one's fuel mix.

Naturally, there are variations in air pressure due to factors other than elevation alone. There also variations in canister content. These are not "reagent grade" fuels. The percentages of propane and isobutane may vary. Other gasses such as propylene (if memory here serves) may be present. Even in canisters labeled as only containing isobutane, some n-butane will typically be present. Therefore, the closer one operates to the lower operating limit of a stove's temperature range, the more one should be prepared to take steps to mitigate the effects of cold on canisters.
1. Select a fuel that is labeled isobutane/propane only (contains no n-butane)
2. Start with a warm canister (sleep with it, put it under your shirt, etc.)
3. Warm the canister (put it in a bowl of water, use a chemical hand warmer, etc.)
4. Shield the canister from cold winds (place it in a sheltered spot, use a wind block, etc.)
5. Insulate the canister from the ground

HJ
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Re: MSR Windboiler – Completed Review

Post by hikin_jim » Mon Dec 08, 2014 12:09 pm

markskor wrote:Your chart seems to show that increasing altitude affecting the lowering of the temperature window for "decent" canister gas ignition, (you called this slack?).
The use of the word "slack" was perhaps not the best choice of words. What I means is that one typically has more pressure in a canister than just that derived from isobutane alone. Isobutane boils at 11F, but there's also propane in the canister which boils at -44F. Now, the propane does boil off at a faster rate than the isobutane, leaving one with only isobutane at the end of the canister. But for much of the life of the canister, one has propane, therefore a higher pressure, and therefore one can operate in colder temperatures.

Also, one typically uses a canister stove above sea level. Those camping in Death Valley take note! :)

So, given the propane content and the fact that one is usually higher than sea level, one typically has more pressure in the canister than would be implied by my 20F lower operating limit advice, a lower operating limit based on isobutane alone. The difference between the pressure of isobutane alone at 20F and the actual fuel + the effects of elevation is what I meant by "slack". Perhaps "margin for error" or "pressure over and above the lower operating limit of a stove" would be better terms.

However, canisters do empty and propane does burn off faster, so I typically say "20 F" as the lower operating limit knowing that this is a fairly conservative number.

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°

Post by longri » Mon Dec 08, 2014 3:47 pm

hikin_jim wrote:At sea level, the boiling point of water is 212 Fahrenheit. At 10,000 feet elevation, the boiling point of water is about 193 Fahrenheit, a decrease of 19 degrees. The boiling points of propane, isobutane, and butane (or a mixture thereof), fall by the same amount....

...The rule of thumb, and it is just that, a rule of thumb, is that one can operate a stove approximately 2 Fahrenheit degrees colder for every 1,000 feet of elevation gain. Note the use of the word "approximately" and the use of the phrase "rule of thumb."

I'm stepping away from a PSI based argument here. Pick whatever PSIG one feels is appropriate at sea level, and one should have that same PSIG at 10,000' in temperatures that are 20 Fahrenheit degrees colder.
Your rule of thumb is inaccurate.

At 10,000 feet water boils 18.8°F lower than at sea level but isobutane boils 16.5° lower and propane only 14.7° lower. So your estimate of a 2°F drop per 1000 feet is too optimistic; it should be closer to 1.6°F.

It's kind of beside the point since the fuel isn't going to be at ambient temperature. Still air doesn't contain or conduct enough heat. The canister is cooled by fuel vaporization and heated by proximity to the flame, immersion in water and/or warming of the cooking environment (e.g. vestibule). How these factors balance is the key to success in the cold.

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Re: MSR Windboiler – Completed Review

Post by longri » Mon Dec 08, 2014 4:05 pm

Yesterday, out of curiosity, I tested the flow rate through a Snowpeak canister stove. The MSR canister I used was on the low side, 80% empty. So the full throttle pressure was about half of what a new canister would have produced.

3 psig: 1.2 g/min
5 psig: 1.5 g/min
10 psig: 2.1 g/min
22 psig: 3.6 g/min (full throttle at 61°F)

At 3 and 5 psig it was kind of a weak flame. Given how much fuel is necessary to melt snow and bring it to a boil it would be a long weight at the lower flow rates.

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Re: °

Post by hikin_jim » Mon Dec 08, 2014 5:22 pm

longri wrote:At 10,000 feet water boils 18.8°F lower than at sea level but isobutane boils 16.5° lower and propane only 14.7° lower. So your estimate of a 2°F drop per 1000 feet is too optimistic; it should be closer to 1.6°F.
Over a 3,000 meter elevation gain from sea level, the boiling point of hydrocarbons like propane, isobutane, and n-butane is depressed by about 9 degrees Celsius. Converting to Fahrenheit comes out to about 1.6, so I'll buy your number, but the difference between using your number versus the one I used over a 10,000 foot elevation gain is 4 degrees Fahrenheit, an amount which isn't going to have a huge impact on the operation of a stove. In addition, I can work with 2 in my head, and it's easy to remember. It's a rule of thumb not a precise calculation.
longri wrote:It's kind of beside the point since the fuel isn't going to be at ambient temperature. Still air doesn't contain or conduct enough heat. The canister is cooled by fuel vaporization and heated by proximity to the flame, immersion in water and/or warming of the cooking environment (e.g. vestibule). How these factors balance is the key to success in the cold.
Agreed. But you have to understand enough about how canisters work in order to successfully deal with the cold.

I usually tell people that above 50F/10C, you don't really need to worry about mitigating the effects of evaporative cooling as the fuel vaporizes. I tell people that they shouldn't expect an upright canister stove to work well throughout the life of the canister at less than 20 F/-7 C -- and that's using isobutane. These are round numbers. Yes, there are any number of factors that can affect those numbers. The point is that with a few simple numbers, the average person can have some rough rules of thumb that they can remember and use in the field.

To get really precise numbers, you'd have to know the exact temperature, the exact mix of fuel (which changes over time as the propane burns off at a faster rate and to be fully understood requires the calculation of the molar fractions), the exact barometric pressure of the air, the amount of heat loss due to convection, the amount of heat loss due to conduction, and on and on. For the average person, good luck. And out in the field? It's just not practical.

For field usable, practical values:
-Above 50F/10C, don't get too worried about canister cooling for normal boiling of say a liter or less of water.
-Think of 20F/-7C as the lower operating limit of a stove, and then adjust that by about 2 degrees F colder per 1000 feet above sea level, and don't use fuel with n-butane in it. The performance will degrade as one approaches the lower operating limit. Cold weather canister techniques are important as one approaches the lower operating limit (don't use n-butane, warm the canister before use, supply mild heat to the canister during use, insulate from the ground, protect from wind).

If the average person stays within those parameters, they should be fine.

Obviously, one can use can use an upright canister stove as cold as they like so long as they have good cold weather canister techniques. Screw up when it's really cold, and you could be in for a world of hurt. For that reason I generally recommend 20F/-7C as a practical lower limit.

HJ
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Re: MSR Windboiler – Completed Review

Post by oldranger » Tue Dec 09, 2014 9:14 am

Wow you guys must have too much time on your hands! :D my rule of thumb is that if is going to be so cold that the functioning of my stove is questionable I will stay home and snuggle up with my wife! A man should have his priorities in order.

Thanks for the discussion, though.

Mike
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Re: MSR Windboiler – Completed Review

Post by hikin_jim » Tue Dec 09, 2014 9:33 am

oldranger wrote:Wow you guys must have too much time on your hands! :D my rule of thumb is that if is going to be so cold that the functioning of my stove is questionable I will stay home and snuggle up with my wife! A man should have his priorities in order.
:lol:

You're definitely a smarter man that we are.

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Re: °

Post by longri » Tue Dec 09, 2014 11:44 am

hikin_jim wrote:...the difference between using your number versus the one I used over a 10,000 foot elevation gain is 4 degrees Fahrenheit, an amount which isn't going to have a huge impact on the operation of a stove.
When on the edge of acceptable stove function I think 4 degrees matters.

hikin_jim wrote:Pick whatever PSIG one feels is appropriate at sea level, and one should have that same PSIG at 10,000' in temperatures that are 20 Fahrenheit degrees colder.
Jim, it doesn't scale that way. The P-T curve is logarithmic. As the temperature drops the pressure differential narrows so you won't get the same fuel flow rate.

edit: Here's a chart to illustrate. You can see that at sea level and 20° a full canister is at about 13 psig whereas at 10,000 feet and 0° it's at about 8 psig. To get the same pressure at 10,000 feet the fuel temperature would have to be about 10°, not zero.
fuel_mix_temp_elev.jpg

hikin_jim wrote:In addition, I can work with 2 in my head, and it's easy to remember. It's a rule of thumb not a precise calculation.
So then make it 1° per 1000 feet. It's no less precise and the arithmetic is even easier. Since your rule is mostly for beginners, don't you think it's wiser to err on the conservative side instead of being overly optimistic?
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Re: MSR Windboiler – Completed Review

Post by longri » Tue Dec 09, 2014 11:48 am

hikin_jim wrote:To get really precise numbers...
I know very well that this can't be reduced to an exact formula. But that's not an argument for a hand waving sciency approach either. Why not simply state what works, based on experience? I don't do calculations when I go camping. Do you?

The thing is, when I apply your rule of thumb I find it doesn't jibe with my experience.

[edit: typo]
Last edited by longri on Wed Dec 10, 2014 5:39 pm, edited 1 time in total.

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