Heat Exchange Stove Shootout: Part 3Heat Exchanger Stoves

[Tony Beasley]

Hi Roger

>My tests show the neoprene cosy has virtually no effect on the heating rate.

At warmer ambient temperatures this may be correct, at very cold temps I am not sure, we need to test the neoprene cosy at -20C.

>But a lid has an enormous effect.

I long time ago I did some tests boiling water with and without lids and at warmer ambient temps the lid made very little difference but at cooler temps it did.

If we can work out how to do affordable controlled cold temperature tests a series of tests on the above would be good.

Tony

[Michael Ray]

I went through about the same amount of fuel (45 g, maybe a few less), but I boiled 3 L of water in about 9.5 min this time. This was with the canister inverted the entire time (I had just rotated the connection and this was my test for leaks). It was cooler today, but water had no ice added. This time of course I used a lid.

Perhaps closing the valve a bit would have saved some fuel as it still seems to have no effect on the flame or sound after about 3/4 turn. I suspect the valve orifice is the limiting factor at that point. I did notice the delay with the canister inverted, which didn't occur when it was right side up. Anyway, I think 3 L in 9.5 minutes is likely normal performance. Not sure about how much fuel that should take though.

One other variable this time was I was using a partial 8 oz canister rather than a new 4 oz one from before. Both MSR brand so that SHOULD not make any difference.

[Roger Caffin]

Hi Tony

> warmer ambient temps the lid made very little difference but at cooler temps it did.

I was testing out a canister stove some years ago – not sure which one. I had it on a very low simmer, and just for the fun of it I tried running the rig with no lid. The water got to ~90 C and sat there. It would/could not get any higher. (Yes, the stove could do a very nice simmer.)

So after about 2 minutes just sitting there I stuck the lid back on. It shot up to boiling quite quickly.

I repeated the experiment with and without the lid after turning the stove off at 100 C. The difference in rate of cooling was very significant.

Cheers
-20 C – hum … :-)

[Hikin’ Jim]

Roger Caffin wrote >

Hi Jim

You didn't ask about wisdom.

My tests show the neoprene cosy has virtually no effect on the heating rate. But a lid has an enormous effect.

Cheers

lol. Well, I suppose I didn't ask about wisdom did I.

Interesting. Doesn't at least the neoprene prevent heat loss while say, simmering? Or is the neoprene just a very fancy pot protector?

Speaking of lids, that's a big gripe I have with the GCS pot lid. It pops off and doesn't stay fully sealed when it gets hot. I just set it on top rather than fully sealing it, which is probably going to trap most of the heat I'd lose through evaporation (which I believe is the major component of heat loss), but for such a fancy and none-to-cheap pot you'd think they could have a better lid.

[Roger Caffin]

Hi Jim

Well, all my tests suggest that the neoprene cozy is just another marketing gimmick, at least when you are using a stove of reasonable power. It ?might? be of some use when using a micro open alky and taking 15 min to boil a litre … maybe.

Yeah, I know, 'all' the stove companies include a neoprene cozy these days, and surely they wouldn't try to sell you something you don't really need? Ahem. (But the cozy can take a huge logo screen-printed on it…)

Actually, with the titanium pots like the MSR Titan series, the heat conductivity is so low going up the side wall that there is not a lot of heat loss from there anyhow. I can grab the top edge of my 1.3 L Titan pot quite happily, so convection-based heat loss from the side walls is not going to be real great. Thick-walled aluminium pots might lose a whisker more, but what BPL member uses thick walled pots? The thin walled HAA pots should not lose too much heat from the side walls, I think, but I need to actually measure the heat loss before saying any more. (Tony may have done this already?)

Cheers

[Hikin’ Jim]

So it makes little difference in terms of fuel used and time taken whether one cooks with a neoprene cozy or not? Lol, the things they'll do for marketing. Well, at least on the JB PCS I suppose it helps to keep from burning one's hands when holding the pot/mug. Speaking of which, it seems like if the sides of the pot feel hot to the touch, they must be losing heat, yes? But it's just insignificant, is that it?

How about with multi-step meal preps where I might need to set the heated pot aside for a time while I work on antother step? Would a sitting pot benefit any from the cozy?

Maybe I'm really stretching here, loooking for some shred of value for the neoprene. :) Maybe I should just peel it off and save the weight.

[Roger Caffin]

Hi Jim

> if the sides of the pot feel hot to the touch, they must be losing heat, yes? But
> it's just insignificant, is that it?
I assume that you have a windshield around your pot. In that case the air coming up the sides between the pot and the windshield is probably hotter than the pot.

> Would a sitting pot benefit any from the cozy?
I do this myself, and yes, some insulation may help. Two buts:
* I find that the contents of my Ti pot are still hotter than I can comfortably eat after 10 minutes standing
* There are much lighter ways to insulate a pot than a neoprene cozy. I often use my bush hat – zero extra weight.

> Maybe I should just peel it off and save the weight.
Well, you could run some experiments with a thermometer. See what works for you. Don't just trust me!
(But do always question what the vendor claims!)

Cheers

[Hikin’ Jim]

Roger Caffin Wrote: >

I assume that you have a windshield around your pot. In that case the air coming up the sides between the pot and the windshield is probably hotter than the pot.

Which brings up another thought. If one is using a windscreen and the air moving up the sides of the pot is hotter than the pot itself, then the neoprene might actually be decreasing the amount of heat getting to the pot. lol.

At this point we're probably talking about hairs too fine to split. I guess the general ideas is that the neoprene isn't particularly essential.

[Huzefa @ Blue Bolt Gear]

I think cozy would be of significant benefit only when using jetboil outside the vestibule in wind without windscreen.

[Tony Beasley]

Part 1: It is often assumed that using a windshield it directs the heat from the flame up the side of the pot and therefore the sides will absorb heat into the water, this may be so with some stove systems but this may not necessarily be so with all stoves systems at all settings.

I have just run some tests measuring the gas temperatures up the sides of a pot with and without a wind screen and at different valve settings.

These tests are far from comprehensive and only one test per setting was conducted, a comprehensive set of tests would take more time than I have available to me at the moment.

Stove used a Kovea Supalite Titanium. Pot used a Snow peak Ti 1liter, Windshield very old modified MSR Whisperlite.

The first tests where done with a suspended windscreen that covered the pot and burner, The canister was not covered, the windshield was placed around the pot with about 1-1.5cm gap and the hot gas temperature probe was placed at the top to measure the hot gasses coming out the top gap (see picture 1).

Picture 1

The tests where done in my garage under windless conditions at an ambient temperature of around 10C.

Results Windshield

Chart 1

Three tests where done using different control valve settings, slow, medium and fast, the medium setting as around what I use in the field.

Slow setting: 6.2g/80C, 10m 45s/80C.
Medium setting: 6.3g/80C, 5m 20s/80C
Fast setting: 7.2g/80C, 2m 59s/80C

Results: with the slow test the gas temperature did not raise much above around 40C, there is some evidence in the gas result line that the gas temperature is actually rising as the water temperature rises therefore it maybe taking heat away from the water in the pot.

The same could be said for the medium test but to a much lesser extent.

With the fast test some heat would be absorbed into the water from the sides but more gas was used.

Note that in all tests the gas temperature measured went up and down randomly, I am not sure exactly what is going on but I think that cooler air is being entrained with the hot gasses.

With chart 2 the probe was placed in three places and temperatures recorded, the first was with no windscreen (No WS top HR and No WS top gas) and was placed at the bottom of the pot 15 mm from the bottom 3 mm from the side (see picture 2), the second (No Ws bott HR and No WS bott Gas) also with no windscreen the probe was placed at the top (picture 3) 3 mm from the sides, the third placing was with a windscreen and the probe was placed at the top as per tests in graph 1.

Picture 2

Picture 3

Chart 2: HR= heating Rate, Gas = gas temperatures.

WS top setting: 6.3g/80C, 5m 20s/80C
No WS top setting: 6.2g/80C, 5m 10s/80C
No WS bottom setting: 6.5g/80C, 4m 45s/80

With all three tests the settings where set at about what I would set the stove in the field (this is not exact science but with canister gas stoves it is very difficult to exactly to repeat tests.)

Results: It can be noted that with the top placed probes the measured gas temperature where lower than the bottom placed probe , my thoughts on this is that as the hot gas travel’s up the sides it mixes with the cooler surrounding air cooling the gas down, surprisingly this also happens when the windshield is used some of this heat loss my be from contact with the windshield but my guess is that as the hot gasses travel up th sides it entrains cooler air.

When I find time I will do some similar tests with my flux ring pot to look at the gas temperatures up the sides and to see if I can see if using the neoprene cozy makes any difference.

Conclusion: As pointed out in my earlier discussions these tests are not comprehensive but they show that in a windless environment using a windshield makes very little if any difference to the efficiency of a canister stove system, in a windless environment the main influence on efficiency is the valve setting

[Roger Caffin]

Very interesting! Thank you Tony.
Makes sense – although I don't often have a windless environment!

Cheers

[Derek Goffin]

My take on those results is I do not have to carry such a tall windshield. one inch above the bottom of the pot may be enough, even in windy conditions. Extrapolating to flux ring pots, the air temperatures up the sides of the pot, after the heat exchanger can only be lower than for none flux ring pots. A Windshield's job is apparently to buffer the inlet air and the flame rather than the sides of the pot

[Tony Beasley]

Hi Derek,

>My take on those results is I do not have to carry such a tall windshield. one inch above the bottom of the pot may be enough, even in windy conditions.

My test on the STD windshield design show that in strong wind they may not be that efficient, I suspect that the wind travelling over the top of the windscreen causes a sucking effect, the hot gasses are then sucked up faster than normal causing loss of efficiency. But at the moment this is only a theory, I have to do some more tests to prove this.

Tony

[Derek Goffin]

Hi Tony,
I am interested because We persuaded myself to buy a eta packlite and I intend to lighten it. One of the first candidates is the windshield. It would help a lot to understand windshields. The existing windshield is only 60mm tall yet 91 grams heavy and is mounted about 25 mm off the floor. A standard windshield that fitted in the pot when packed, would be limited to 80mm. The top of the flux ring when on the stove is about 70mm off the floor.

On another issue: help from anyone who has a packlite. Does the brass mixture tube from the jet to the burner unscrew at the elbow? Is the brass round base below the elbow solid? Can it just be cut off without exposing the internal cavity. The purpose of the round base appears to be to support the burner, but the burner is supported by a split pin and has very little weight on it.

[Larry Risch]

Isn't the ETA Power fuel consumption of 7.9 / liter MORE than 6+ for the average remote or upright??!!

[Larry Risch]

Looks like you put the minutes to boil in for the fuel per liter in that one chart, I can't see that chart while posting but the 6+ numbers should be 11.6 and 13.3 from the earlier chart. I get a bit different # of liters for the ETA power, the only one I checked, 24 liters and 92 liters, about the same.

[Larry Risch]

The weight difference of the stoves/pot is constant for the trip, while the fuel difference only reaches its maximum near the end of the trip, assuming you take the same amount of fuel for either system. (This favors Ti pots)

Another way to look at this is how many canisters you are going to take. Using your figures the ETA Power ,229 g fuel , / 7.92 is 28 liters, while the average upright and remote would get between 17 to 19 liters. So if you need to take an extra canister (12 oz) it becomes closer weight wise , but you also save some cost on fuel and waste of canisters? Partial canisters? Margin for error?

EDIT: In this case as the stove with the Ti pot burns more fuel the difference of the extra fuel weight should go down, except for the extra canister weight itself remains the same.

Winter time more fuel used to melt snow for drinking water. Snow is hard to melt?

[Roger Caffin]

Hi Larry

I am not sure what you are asking. Please help me.

The Eta Power has a fuel consumption of 7.9 g per litre water, while the average for the Uprights (ie no heat exchanger pot) was listed as 11.6 g of fuel. I am not sure where you got the 6+ figure from?

Cheers

[Derek Goffin]

Larry has noticed what I pointed out earlier:

Sorry to persist Roger, perhaps you should look at the table in your report! Performance or efficiency surely means that higher numbers are better. Fuel per litre would be lower numbers are better. In the column the more efficient heat exchanger stoves have higher numbers but it is headed fuel per litre that is surely wrong, a typo, not just a slightly wrong word.

Under "efficiency in real life" Larry points out that his example the eta power uses 7.9 grams per liter whereas the average upright uses 6.5 grams per litre. As we know that heat exchanger stoves use less fuel to boil a litre something is wrong.

[Roger Caffin]

Hi Larry and Derek

OK, now I get it. I think something happened along the way such that the last two lines in the published table under the heading 'Efficiency in Real Life' has the wrong figures. The values for the Uprights and Remotes are actually the time to boil from a previous table I think! Oops!
I will have this corrected ASAP – my thanks to you for seeing this.
(Edit: Addie tells me this has now been corrected.)

Now to the issue of the word 'efficiency' Derek suggests that 'Performance or efficiency surely means that higher numbers are better. Fuel per litre would be lower numbers are better.'

Well, not always. That is one definition of fuel efficiency, bolstered by the American practice of talking about 'miles per gallon' when discussing cars. But the rest of the world (which is all metric) measures a car's fuel efficiency in terms of 'litres per 100 km'. That's the same as grams per litre boiled.

You see, there is NO formal definition of the term, so it can mean anything you want it to – as the Duchess said to Alice. I take efficiency to mean using as little fuel as possible.

I suspect this argument may not have a satisfactory resolution, as we are proceeding from different origins. But can you suggest a better term which could be added to the article?

Cheers
Roger

[Derek Goffin]

Hi Roger,
If you amend those 2 incorrect figures I have no argument with your meaning. I was just trying to explain why I knew they were wrong.

[Larry Risch]

Derek:

"The is a typo in Roger's report. Under "Efficiency in real life" the column fuel/litre shows instead efficiency which is a sort of reciprocal."

I think Derek was thinking if the numbers are right the label is wrong?

Efficiency =C.L / g (oz) was about the same as the boil times for the average upright and average remote, 6+

I assumed the words were right but did not understand the numbers.

[Derek Goffin]

Larry,
You are right

[Tomas Reinhardt]

Where is Part 4 ?

[Roger Caffin]

> Where is Part 4 ?

Still coming. My flow got interrupted when we headed off to Switzerland for 6 weeks in July. :-)

I have some higher-priority stuff to complete, then I will fire up the pots (so to speak). Anyone else noticed how the week flies past so fast?

Cheers

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