Pots With Heat Exchangers

[Mario Caceres]

Thanks Dan, what performance did you get with that cone?.  Looking at the picture IMHO it does not appear to have much in the way of air intake / exhausts.

For a straight up windscreen (that doesn’t work as pot support) I have used with good results a 0.25″ “uniform-ish” gap around the pot.  So if we were to try to have the same area on a conical windscreen, we are looking at somewhere between 2 or 3 rows of 0.25″ holes (I think that is what you get on a standard paper hole-punch?).

i.e lets assume that we have a pot with a 5.6″ in diameter: (Like the grease pot or evernew 0.9L short and wide)
Pot Diameter = 5.6″ (or pot radius (R) = 2.8″)
Area of 0.25″ gap = 4.39 square inches (2 x 3.1416 x R x 0.25″)

so if we use 0.25″ punch-holes in our cone, how many we need to match the same area?

Punch-hole diameter = 0.25″ (or radius (r) = 0.125″)
Each punch-hole has an area of 0.049 square inches (= ((r^2)*3.1416)

So we need 89 holes.  Depending how we space them we need between 2 and 3 rows.

If you look at the caldera cones by trail designs they don’t use round wholes but rectangles which are staggered so they don’t compromise the strength of the cone and allow to support the weight of the pot, but if you where to put them on a row, it looks like they would be about 0.25″ imaginary line.  I’ve never seen a caldera cone in person, just looking at the pictures.  Perhaps somebody that owns a caldera cone can confirm what is the height of those exhaust vents.

[DAN-Y]

The holes are 1/2″ dia. Had sufficient incoming air using the Starlyte Stove. The Starlyte stove supports the pot. 1/4″ gap all around the top between pot and top of windscreen.

Here is an easy way to cook Ramen (for me)…and you can eat it right out of the grease pot. No freezer bags to recycle for those that are concerned about their disposal.

I used 2 packages of Ramen, 2 cups of water and 1/2 ounce of fuel. 9.5 min. later the ramen was completely cooked ready to eat. During the cooking, the noodles soak up plenty of seasoning and taste great. The remaining water can be used to heat additional food products.

https://www.whiteblaze.net/forum/showthread.php/56087-ZMart-Cook-Kit-and-Ramen-Noodles?highlight=zmart

[Mario Caceres]

Oh, I see, you have a gap around your pot.  Looking carefully at your picture I see the gap. I’m still undecided about a cone vs a straight up screen.  I like that the cone works as pot support (when sized to do so), but you loose flexibility.  It has to be optimized for a particular pot / stove.  On the straight up screen you have the flexibility of being able to adjust the circumference of the screen and use if with different pots but then you need an additional pot support.

Thanks for the link, looks great.   Brilliant your idea of cooking the eggs on the lid :-) so you are not wasting that heat.  I noticed how much heat goes thru the lid, this is why I have the carbon felt “hat”, so I can slow down that heat waste a little.

[James Marco]

“James, did you notice the decrease in the grams of fuel used and time to boil in the 3rd test?”

Dan, yes. I varied the lower diameter of the wind screen and played with the air-inlets. But, opening the air inlets only works sometimes. In winds, it failed miserably. I stacked the inlets all on one side, under some conditions, there was actually a wind induced down draft. Then I used a dual screen (cone with aluminum foil inside partially.) But this was too many parts for hauling around and cooking, and, way too fiddly. There is also the overall difference in temperature of the stove. Starting at a slow speed for about two minutes then gradually picking up speed as it heated, then dying off as the fuel became less and less (hence the two cone design) means different air inlets. This means you need to adjust the air inlets to the phase of the burn. Too fiddly, iffy and dedicated time. But, in a lab, a free flow of air inlet with a restricted exhaust vent worked about the best. Unless you are camping in still air, it doesn’t really work all the time, though. Near the limits of fuel/water boiled things get real finicky and fiddly. Like I say, using it outside at <32f it would get the water to 180 or so and never boil…I tried several times with over an ounce of fuel. In a lab, it worked well with 3/8oz. But often enough I use water that is brown with tannic acid or somewhat silty. I want a full boil to be sure…

[DAN-Y]

But, opening the air inlets only works sometimes. In winds, it failed miserably. I stacked the inlets all on one side, under some conditions, there was actually a wind induced down draft.

How were you able to determine the wind induced a down draft?

Increasing air intake is a time consuming process for me. Increase a small amount and then do 3 tests to determine repeat ability.

In stove design we need to determine how well the stove performs “on the bench” we have to have a starting point. Once we have a good stove design “on the bench”, it is then up to us to do everything we can to preserve the heat being directed at the pot…add windscreen, place pack close to stove set-up, place stove set-up next to tree or boulder/rocks. First things first. Get it right in calm conditions and go from there. Right now I have the right burner to provide the heat. Fuel in and won’t spill out. When burner is cooled, place cap on to preserve unused fuel.

If winds are too great, we may opt to do a no-cook meal, adapt to the situation;-)

[James Marco]

“How were you able to determine the wind induced a down draft?”

By watching it. I could see the heat blowing OUT of the lower air-inlets in a heavy (~10-15mph) wind.

“In stove design we need to determine …”

Been there. That was where I was at when I first tried alky back when my kids were little (<5 or 6.) That was close to 35 years ago.

Nope. Even if I run out of alky, I make a wood fire for coffee. Gotta have macaroni or rice for supper, too.

 

 

[Eric Blumensaadt]

BTW, speaking of meals (I live to eat, not vice-versa.;o) I just saw a receipe  for either lobster chunks or shrimp chunks in Mac ‘n Cheese. If you have a high quality M&C this would be great at camp B/C you can buy shrimp in retort pouches or re-hydrate dehydrated shrimp from an Asian food store.

OK, back to stoves. BPL needs to set up a testing lab.

Wait – Roger Caffin already has a stove lab. So Roger, please collect all the various HX pot designs you can and test those suckers. We want to know which one is really worth the money. And please test them on a “normal” canister burner, not a JB or MSR dedicated HX stove.

[Roger Caffin]

Hi Eric

One problem with testing ALL the HX pots is that vendors keep coming up with new designs. I have one or two Jetboil pots and a Reactor pot. After testing those pots I concluded that the increase in fuel efficiency was unlikely to ever compensate for the increase in pot weight, but I have not looked at the weights of more recent designs.

A secondary problem is maintaining a constant flame between test runs, but that has been solved by logging the canister weight during the run.

Are we concerned about the cost of the pots vs their efficiency, or the balance between extra pot weight and reduced fuel weight? I would only be concerned with the latter. You buy a good pot and 4 years later you won’t remember the cost.

If the world wants me to test some newer pots, it can be done, but ‘the world’ needs to supply the pots. SWMBO does not think we need any more pots you see … (and she may be right).

So, what pots are we talking about?

Cheers

[Mario Caceres]

I wonder how those carbon felt windscreens work to block winds yet providing enough air to run the stove. I think they may work similar to waterproof membranes, that do not allow rain to go thru, but do allow perspiration to get out (at least in theory).  On the other side, is clear that a metallic windscreen close to the pot not only blocks the wind, but helps reflect some of the heat back into the pot walls (which the carbon felt windscreen does not).  Perhaps the best windscreen would be to have an aluminum windscreen with very generous intakes (covered with carbon felt), maybe even have the aluminum windscreen lifted above the ground, and then on the bottom part covered by a strip of carbon felt.

Something like this …

To keep the cone elevated above the ground (providing plenty of air for the stove) one could use something like this….

But instead of having a canister stove, one would have the alcohol stove and pot support.  Again the gap between the bottom of the aluminum windscreen and the ground would be covered by a carbon felt strip…. Hot air would go up and be reflected by the aluminum part back to the pot walls, and finaly escape thru air vents on top of the windscreen.  Any excess heat building on the bottom of the “cone” (Thermal feedback) would escape thru the carbon felt which is porous reducing the problem of overheating the stove (Which as mentioned by James, creates a problem accelerating the stove)

Again, I have not technical expertise in this matters and not sure if the above would work…I’m just thinking out loud…

[Roger Caffin]

All these hypothetical windscreen designs … mostly fail when there is any wind.

I use a 3/4 wrap of solid foil spaced about 10 – 15 mm from the pot. The open 1/4 is downwind and allows access for air and to the valve. The windscreen reaches to about 1/2 way up the pot or a bit more. I have a couple of tiny (3 mm) holes at the bottom edge, through which I poke micro-stakes to anchor the windscreen in position. Very simple and very reliable.

Truth to tell, most of my windscreens are modified Trail Designs ones from ages ago. The versions with square air-holes were just fine once I taped up the holes with high-temp electro-plating tape (wt added about 1 g).

KISS!

Cheers
PS: yeah, heresy, I know.

[DAN-Y]

Thank you James.

I did another test today, added more air intake at base, made no difference, boiled 4 cups using 21 grams fuel, 19.5 min. to rolling boil.

The rest of the thread is for you canister users. :-)

[Mario Caceres]

Roger, that is the role of the carbon felt (I hope)…. to block the wind (yet, allowing air for proper combustion).  I remember seeing a video of a guy having a small fan blowing and did not get to the stove flame…. and of course as usual I can not find that video.  I think one of the main complains about carbon felt whole windscreens is that they are lumpy and don’t have structure, but this would not be much of an issue if it’s just a small strip about 1″ tall.

[Roger Caffin]

Hi Mario

Too complex for a simple-minded person like me.
Especially at 2,000 m at 6 pm in a snow storm.

Cheers

[Mario Caceres]

Perhaps, Roger, I also like and, most of the time, I live by the K.I.S.S principle…. but I’m also a “tinkerer” and this is how I have my fun :-).  I just ordered some carbon felt to try this idea.  Perhaps when I put it in a model / mock-up it will not appear as complicated as my poor english manages to explain in words.  I just tried to use a hair blower over my carbon felt hat, and it really stop any air from going thru and get to the flame of my stove.  So the idea looks promising (to me).  Again I need more material for testing the whole concept.

[Roger Caffin]

Hi Mario

Absolutely no problem at all with experimenting. I am, after all, a career experimental research scientist. :)

The distinction between ‘experimenting in a scientific manner’ and ‘having fun’ is an interesting one. Most research scientists don’t believe that there is any difference. Which explains a lot of things.

Photos and results, please!

Cheers

[David Thomas]

Roger, you go on relatively short trips and with relatively small parties.  I often have trips with 6-10 people, a corresponding amount of hot water needed, and while we’ve brought chainsaws and gotten through 18 inches of ice to get liquid water, if the ice is >24″ inches, deep, then we’re melting snow for EVERYTHING and heating up some of it for hot water.

And on some of my trips, we sled the gear in not many miles so are somewhat insensitive to total weight, but the faster melt/boil times are always appreciated.

Weekend backpacking in the California Sierra, in summer, for 1-2 people?  I don’t know of a HX pot that will come out ahead of just bringing a little more fuel.

Even on a 10-day section of the PCT, for one person, it seems doubtful if your only criteria is weight.  Remember, you carry your fuel for HALF the trip miles, on average, while you carry your pot weight for all the miles.

But if cost is an issue, you only buy the pot once and for ever after save 30-50% of your fuel.  Here’s a $25 pot which will pay back over $60 of fuel consumption – a dozen 110-gram canisters or seven 450-gram canisters (for those of us who refill our own canisters).

If you really want to help save the planet through more efficient cooking, use one of these pots in your kitchen.  And you’ll get dinner ready sooner.

[Roger Caffin]

Hi David

you go on relatively short trips and with relatively small parties.
Yes, it is very very rare that there are more than the two of us. That’s how we go.

However, I am not so sure about the ‘short trips’ bit. We have some short ones for sure (3 nights to a week), and then we get into the 1 month, 2 month and 3 month long trips. Nothing so far over 3 months.

Digging through snow for water? Yep, but only to about 12″, and it was not ice. Sometimes we know there is no water around, so we melt.

Cost of fuel over the years? Sorry, but I really can’t get excited about it. It can take 6 hours driving to get where we are going sometimes (our alpine region), and the cost of that fuel is orders of magnitude greater.

So what else should I do with our savings? Pass it on to our children? They don’t want it, and have said so. Everyone’s priorities are different.

Cheers

[James Marco]

“I did another test today, added more air intake at base, made no difference, boiled 4 cups using 21 grams fuel, 19.5 min. to rolling boil.”

Dan, that is about the sweet spot. Roughly 3/8oz fuel (10gm) for about 10 minutes for two cups. With or without a heat exchanger that appears to be the same. Longer burns with smaller flames means more heat is lost from the pot. Lots of insulation. Less time means more heat (and fuel.) So, there are a lot of different things going on. For example: air exchange as well as combustion with air works both ways. You need the new air to generate heat, but, exchanging air too rapidly can lower the total heat transferred to a pot by reducing flame heat. Too much heat trapping will lower system heat, by reducing combustion. Too little will cool off the pot and flame. Anyway, one of a host of factors.  All these have a sweet spot.

Hmmm…As far as carbon sheets go, add a 1″ strip of carbon to the bottom of any wind screen. This may work, but I would still be more worried about upper heat loss. The pot sidewalls, top, windscreen itself all radiate/conduct heat. Increasing the wind increases the heat lost by these mechanisms.

[DAN-Y]

I’m getting better efficiency using this big pot compared to the 2 cup Sterno Inferno. Interesting!

[DAN-Y]

Just stopped by to get a copy of my test results to pass on to an interested party.

Results in one spot for future use 

did 2 tests

4 cups water used in both tests

denatured alcohol was the fuel of choice

Starlyte XL3 burner was used as stove choice

Pot support was the one that came with the Sterno Inferno kit as seen in another thread.

1st

74 degree start water temp and 62 degree air temp

22 grams of fuel used to boil the 4 cups

16 min. to bring to rolling boil

2nd

68 degree start water temp and 58 degree air temp

20 grams of fuel to boil 4 cups

19 min to bring to rolling boil

I used a United States Postal Scale to weigh burner before and after test

Digital timer used for timing.

More tests tomorrow.

Pot is said to be made of magnesium/aluminum alloy

Note: 1 fluid ounce weighs 24.2 grams

So….less than 1/2 ounce of fuel used to boil 2 cups of water if you want to look at it that way.

Pot only, weighs 265 grams or 9.4 ounces and yet 4 cups were able to be boiled efficiently with less than 1 ounce of fuel.

4 cups water boiled each test

1st
24 grams fuel used
20.5 min.
start water 66/air 57

2nd
22 gr fuel used
19 min 40 sec to boil
start water 61, air 55

3rd
19 gr fuel used,
18 min 20 sec to boil
start water 58, air 54

 

[Eric Blumensaadt]

Dan Y.,

I remembered that my JB pot is the same 1.5 Liter pot you had a link for. I removed the folding handles and bought an extra neoprene cozy B/C the original was getting pretty singed from sitting on my Inferno wood burning Caldera Cone I use for melting snow. I don’t own a JB stove.

** Would it be worth it in terms of added efficiency to add a large “hose clamp” around the perimeter of the “Flux Ring”. (That would make it my “Flux Capacitor”?? ;o) At least the fins would be protected. Now they get bent “in transit”.

[DAN-Y]

Eric, I think it would work. Because it’s canister driven, heat would be forced in and out the fins causing an exchange. The slits in the hose clamp would allow some heat to flow thru. I like the way you think

Just in the interest of stove science, when I return home, I will reduce the size of my pot down to a 2 cup capacity and see if I can boil 2 cups using 8 grams or under of denatured alcohol. The handles will be removed and a different lid used. Nothing Ventured, Nothing Gained 

[Eric Blumensaadt]

Dan,

When I bought my Trail Designs Sidewinder I got the 3 cup pot/stove combo. Since then I have found that 3 cup size just about the practical limit for using ESBIT, my fav fuel for a Caldera Cone stove. That pot is wider than it is tall, proven to be the most heat efficient shape for a pot.

When using the Inferno insert in the Sidewinder for wood burning the stove is so hot that I sit the 1.5 L. Jet Boil  pot on top, resting on its fins, and easily melt snow. That Inferno gassifier wood burning setup is just amazingly hot. I have to set the stove on a ti sheet, a high heat painted plywood “plate” AND  heavy branches to keep it from melting the snow beneath.

 

[DAN-Y]

Eric, how do you prevent the HX fins from getting fowled by the wood fire soot? Spray them with soap first :-))))

[DAN-Y]

Eric, I hacked my pot down to a 3 cup size.

What is your best test results using your 3 cup pot with the caldera Cone with 2 cups and 3 cups of water? Fuel by weight using alcohol and cubes if esbit used?

The hack:

[Author]

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