Whiteburn's Wanderings

One man's wanderings backpacking around Scotland plus the odd digression

Winter Fuel

After my recent dawdle in the Cairngorms I weighed the remains of my 230g Primus gas canister (-480g when full) & reckoned I’d used 150g of gas for a 2 night trip.  I wasn’t really surprised given the amount of snow I’d melted but it did bring to mind this phenomenon was something the average backpacker may be unfamiliar with.

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Whatever the stove/ fuel I use I reckon as a rough guide I’ll use at least double the amount of fuel in winter than in summer, part of this will be down to my increased consumption of hot drinks but the most significant is melting snow.

The science bit.

The amount of energy needed to heat water is a simple calculation:

Energy required = Temperature change * 4.2 Joules/ gram

Example, summer heating water from say 10C to 100C

[(100-10) * 4.2] = 378 Joules of energy per gram.

Turning snow into hot water needs a lot more energy:

Firstly,

The energy input need to change state, snow/ ice into water (latent heat) = 334 Joules/ gram

Secondly,

The energy needed to raise the water to the needed temperature, as above.

Example, winter melting ice (0C) & heating to 100C

334 + [(100-0) * 4.2] = 754 Joules of energy per gram

The efficient melting of snow does requires some water in the pot in the first place so I’m careful not to run out.  I carry an insulated water bottle which I’ll top up during every snow melt (unless I’m certain of finding a supply), the bottle gets stashed inside the bivi overnight or even inside the sleeping bag.

The key message is find liquid water if you can, it saves a lot of fuel

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This entry was posted on February 11, 2015 by in Gear and tagged , .
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