UKC

/ Heat Exchanger Pots / Snow melting

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purplemonkeyelephant - on 11 Jan 2018

Currently I only have a 1L pot for my stove so am looking to get something around 2-3L for daily snow melting to minimise the amount of melts and boils needed each time. My current pot has a heat exchanger and I've read a lot about the pros and cons but to me it seems better to have one that not, even it's a bit heavier. The problem is that my stove is fairly small and so large pots with a HE won't sit on the HE but on the base of the stove. Does it matter whether the stove legs are on the heat exchanger or pot base? There isn't really any mention of it in the Primus manuals, just a symbol on my Eta pot showing not to do it. Using the flat base of the pot puts the burner closer to the contact surface, does that reduce efficiency? Should I get a flat based pot or is it still worth getting a HE even if it doesn't match my stove exactly? Wish Primus would actually return emails, phone calls etc!


matthew - on 11 Jan 2018
In reply to purplemonkeyelephant:

> Using the flat base of the pot puts the burner closer to the contact surface, does that reduce efficiency?

Having the flame too close to the pot does reduce efficiency. It seems that the pot cools the flame, resulting in incomplete combustion. As well as fuel consumption, carbon monoxide emissions are also increased and could be harmful in even a partially enclosed space. It is reportedly a design fault with many of the micro stoves on the market.

To work properly, a heat exchanger needs to be a reasonable match with the stove. There is something to be said for the smaller pot. Apart from being lighter, it is much easier to get hot and you can have a drink while you are waiting for the next one.

purplemonkeyelephant - on 12 Jan 2018
In reply to matthew:

Interesting, so would you say it's more efficient to do multiple boils in my small pot - or one big boil in a 2/3L pot? My little pot is super efficient, but I figured repeatedly emptying it into flasks would be a big waste of heat. 

matthew - on 21 Jan 2018
In reply to purplemonkeyelephant:

Apologes for the delay replying. I've found that a 3 litre takes more than 3 times as long to heat as a 1 litre and is therefore less efficient but it may depend on the stove, windshield and conditions.

purplemonkeyelephant - on 21 Jan 2018
In reply to matthew:

Interesting! I did a test boiling 1L of water in my new 2.35L pot and it actually came out more efficient than my smaller 1L pot (12g, 9g fuel respectively). It has a bigger heat exchanger which may explain the difference, it would be interesting to do a test boiling 2L of water and seeing if the efficiency drops off. 

Stefan Jacobsen - on 21 Jan 2018
In reply to purplemonkeyelephant:

> ... it would be interesting to do a test boiling 2L of water and seeing if the efficiency drops off. 

Do it and let us know!

purplemonkeyelephant - on 22 Jan 2018
In reply to Stefan Jacobsen:

Just boiled 2L of water, took about 6.3 minutes and 18g of fuel so it would seem fairly linear up to this amount of water. 

matthew - on 22 Jan 2018
In reply to purplemonkeyelephant:

Sounds like the bigger pot / heat exchanger is more efficient with your stove in practice - presumably it's losing less at the sides when the heat is turned up.

Portion size is more relevant in adverse conditions as the rate of heat loss becomes increasingly significant compared with the power of the stove. A stove that's powerful and well shielded might be less affected. It would be interesting to measure the effect of cold and wind.

Stefan Jacobsen - on 22 Jan 2018
In reply to purplemonkeyelephant:

What about 2x1 liter with the smaller pot?
What stove did you use?
Did the pot size affect the proximity of the pot to the flame?

 

HardenClimber - on 23 Jan 2018
In reply to purplemonkeyelephant:

The more chance the flame has to play on a cold surface the more carbon monoxide you produce. In 'bad' weather this could be (and has been) serious. The closer the pot to the burner the more likely there is to be incomplete combustion. Gets worse with altitude, but I'm sure it can be achieved in a snow hole etc...

 

There is a good link near the bottom (think msr have changed their products)

https://www.ukclimbing.com/forums/expedition+alpine/warning_heat_re_exchanger_pots_at_altitude-465983#x6482162

purplemonkeyelephant - on 23 Jan 2018
In reply to Stefan Jacobsen:

> What about 2x1 liter with the smaller pot?

Well I assume it would be the same as doing 1 boil, twice? I doubt any residual heat would make a difference by the time you put cold water in the pan. Perhaps a warm stove might run more efficiently on the second boil but I didn't see it worth testing.

> What stove did you use?

Primus Spider

> Did the pot size affect the proximity of the pot to the flame?

The heat exchanger is bigger so maybe a touch, but I'd say it was negligible compared to my normal Primus Eta Pot. As Matt says it's probably more to do with the bigger surface area collecting more heat. 

 

purplemonkeyelephant - on 23 Jan 2018
In reply to matthew:

Yeah I guess the bigger the pot the stronger the heat-sink effect!


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