Forum Index » Editor's Roundtable » Thermal Feedback in Upright Canister Stoves


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David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: Re: The Chemical Engineer gets pedantic. And no one is surprised. on 03/06/2013 15:55:44 MST Print View

>:"Fair question. I was including the requirement to heat the fuel up from, say, 20 C to wherever it boils."

Got it. While for fuels gaseous at ambient temps (propane, often butane), you primarily need to provide the latent heat, for high-boiling compounds, you need to provide a lot of sensible heat as well. Yes, then diesel would need to absorb more heat to boil than white gas than butane. Also, because the deltaT is less between the burner flame and heavier fuel to be heated and because the heated fuel vapor will have more losses once it leaves the vaporizer section, you'd need an even larger convective or conductive heat exchanger to heat that fuel.

Stephen Parks
(sdparks) - M

Locale: Southwest
Thermal feedback regulation on 03/06/2013 19:51:04 MST Print View

Hello all, this is my first post at BPL!

I had some thoughts on regulating the thermal feedback to the inlet tube based on temperature. Don't discard your heat shunt concept just yet.

You might be able to achieve regulation (preferably automatic regulation) by either varying the thermal conductivity of some parts of the stove, or by varying the exposure to thermal energy of some parts.

To vary the thermal conductivity of the structure, it would be nice to have a material that has a thermal conductivity with a strong and inverse dependence on temperature. As the temperature of the conducting parts rose, the conductivity would decrease, thereby reducing the thermal energy transmitted to the fuel. Unfortunately, I don't know of any such materials.

But, varying the exposure of the inlet tube and connected parts may be possible. In this case, you would want something to move as the temperature rose. What I imagine here is one of your flat metal shunts made out of bi-metal sheet. As the temperature of the shunt rose, the shunt would bend away from the flame, reducing its exposure and consequently the amount of heat conducted down to the inlet tube. The regulation would vary smoothly with temperature. Alternatively, you might find a shape memory alloy that would bend out of the way at an appropriate temperature. This deflection could potentially be much greater than with the bimetal, but all the deflection would occur over a narrow temperature range, which might be ok or even desirable. Or, you could go low-tech and just put your shunt on a hinge and manually flip it out of the way or adjust it once the stove is warmed up, at least for initial testing. You would probably want the rest of the stove to be designed to contribute relatively little heat transfer to the inlet tube, so that the moving component could have maximum control of thermal feedback.

You might think of other variations on this theme.

-Stephen

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Re: Thermal Feedback in Upright Canister Stoves on 03/06/2013 20:30:25 MST Print View

Hi Stuart

> a hole thru' the centre of a brass M5 bolt and then brazed the SS vaporiser tube
> into the hole. The bolt with tube then screws into the aluminium base
Yes, I played around with this idea too, but I had trouble getting it miniaturised and hermetic. It remains possible though.

> a little anaerobic threadlock for good measure.
That bit worried me. Most anaerobic threadlocks are based on methacrylate, which has a limited tenperature range. Maybe a silicone sealant could be used instead?

Maybe I will have another look some time.

Cheers

Jim Sweeney
(swimjay) - MLife

Locale: Northern California
thermocouple shunt on 03/06/2013 20:33:10 MST Print View

Stephen, that's something along the lines of what I was proposing. Great minds think alike.

Unfortunately, so do mediocre ones.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Thermal feedback regulation on 03/06/2013 20:33:14 MST Print View

> flat metal shunts made out of bi-metal sheet.
Novel! I imagine it could work.
But sourcing the material ...

Cheers

Jim Sweeney
(swimjay) - MLife

Locale: Northern California
bi metal coils on 03/06/2013 20:51:30 MST Print View

not sure if they could be made to work in this application, but bi-metal coils are at the heart of most house thermostats, and there's probably a mature technological base that knows how to manipulate their properties.

T N
(tordnado) - MLife

Locale: Europe
Bi-metal, now were talking! on 03/07/2013 00:44:28 MST Print View

Bi-metal sounds very interesting and it should not be hard or expansive to source.

Picture: http://www.google.se/imgres?imgurl=http://www.hilli1.de/Physik/Folien/Waerme1/Bimetall.gif&imgrefurl=http://www.hilli1.de/Physik/Folien/Waerme1/Bimetall.htm&h=660&w=514&sz=23&tbnid=oZjbVetxRYXVOM:&tbnh=89&tbnw=69&zoom=1&usg=__IAb2lOT2K7tr0ORmGJq8mXWP4rc=&docid=1VfhP_GJPe_5DM&hl=sv&sa=X&ei=FkY4Uf6QO4vesgbykYCYBA&ved=0CEAQ9QEwBQ&dur=670

Edited by tordnado on 03/07/2013 00:49:57 MST.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Or just metal rods. on 03/07/2013 01:45:14 MST Print View

It doesn't even have to be bimtallic in the traditional sense of two alloys continuously bonded to each other. Simply two metal rods triangulated with a narrow base would, if allowed to pivot, bend away from the hot side. The hot rod could be either a conductor of heat to a vaporizer or the vaporizer tube itself. The cold rod could be a turnbuckle to field tune it for ambient temps or different fuel types ( butane, white gas, diesel, yak's milk, etc).

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Or just metal rods. on 03/07/2013 11:58:07 MST Print View

So, what is the heat of vaporization of yak's milk?

--B.G.--

Stephen Parks
(sdparks) - M

Locale: Southwest
Re: Re: Thermal feedback regulation on 03/08/2013 20:04:04 MST Print View

>Novel! I imagine it could work.
>But sourcing the material ...

I don't usually give novel ideas away. If you make it big in the stove industry, you owe me some CNC play time...

Here's some useful info on bimetals. These guys would probably send you some samples if you tell them you are developing a product.

http://www.cladit.com/tech.html

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Thermal feedback regulation on 03/08/2013 20:50:00 MST Print View

> http://www.cladit.com/tech.html

f a s c i n a t i n g...

Cheers

Hikin' Jim
(hikin_jim)

Locale: Los Angeles, CA, USA
Re: Thermal feedback regulation on 03/08/2013 22:52:56 MST Print View

Roger,

Very interesting what you've learned by experimentation (and frustration at times, no doubt). Sounds like it's all about the heat and consequent pressure within the canister although I still wonder some about the Jetboil Sol (although I suppose if I'm really curious I can do a bit of experimentation).

Interesting bit about the difficulty of sealing a pre-heat loop. The FMS-118 Volcano at least has the sealing right (although it seems they've got the diameter a bit too big).

I do notice the Kovea Moonwalker uses a shunt instead of a pre-heat loop. The one thing I don't like about this arrangement is that the whole stove gets quite hot and takes a while before I can reasonably pack it away, but the Moonwalker has a lot of metal. Smaller, UL style stoves will likely not have this problem.

It's late, and I don't have any particularly brilliant insight to add (would that I did), but I thank you for writing yet another article that very few people are in a position to write. It is such articles that make BPL such a great place to be a part of (well, and the people too of course).

HJ
Adventures In Stoving

Hikin' Jim
(hikin_jim)

Locale: Los Angeles, CA, USA
Re: Re: Thermal Feedback on 03/08/2013 22:59:35 MST Print View

Actually, Kevin, you apparently are a stove designer. I think you just designed a SVEA 123.

Here's our own HikinJim priming one with denatured alcohol:

http://www.youtube.com/watch?v=TfRRs4x51k8

But the alcohol used is more like 3 ml on a cool day. Maybe two such treatments ( 2 x 3 ml) in snow-camping conditions.

E-gads! Is that old thing still out there? That was B.T. (before tripod). I hope you take motion sickness meds before viewing.

The idea of priming a remote canister stove with alcohol has merit, particularly one that is designed for it. For example, the WindPro is really a white gas stove (the Simmerlite) that has been repurposed for use with canister gas (and it outlived its parent, the Simmerlite, which alas has been discontinued). The WindPro's head will hold alcohol and it has a small priming cup. Very interesting. Suppose one filled the head with alcohol and ignited it. The edge of a cold canister could be held into the flame. The flame would a) heat the canister and b) heat the pre-heat loop. One would then open the valve, and voila! no-flare inverted start ups with plenty of pressure. Conceivably, one could operate in very low temperatures this way. Adding a bit of fiberglass wick, as on a Whisperlite Internationale, would increase the vaporization of the alcohol which could be quite balky in cold weather. Hmm. Interesting.

HJ
Adventures In Stoving

Hikin' Jim
(hikin_jim)

Locale: Los Angeles, CA, USA
PowerMax or 7/16ths UNEF or Camping Gaz on 03/09/2013 00:25:55 MST Print View

Roger,

I just noticed this elsewhere on BPL regarding your MYOG canister remote stove:

Works with standard screw-thread canisters, French Campingaz canisters, and Coleman Powermax canisters, all in full winter mode. This means I can use it virtually anywhere around the world.
I noticed the PowerMax canister in the photo here in your article (of which I have laid in a goodly supply), but your stove also works with standard threaded and Camping Gaz? Now, that's nice.

How did you do it? Do you have a connector that fits over the rim around the valve, something along the lines of how an MSR SuperFly connector works? Is the pin any different between a PowerMax, Camping Gaz, or standard threaded stove?

HJ
Adventures In Stoving

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: PowerMax or 7/16ths UNEF or Camping Gaz on 03/09/2013 02:01:00 MST Print View

Hi Jim

All the details, in great and gory (or glorious) depth, will be revealed soon. The connector is more like the French Campingaz one than the Superfly. I tried the Superfly and was, frankly, a bit scared of the way MSR had done it. Things flexed ... It was not an option for me.

The pin - you would not believe how much trouble that gave me! The Lindal valves are all different. Yes, a solution was found, and yes, it will be in the article to come.

Fwiiw: I have been using my winter stove for 6 - 9 months now.

Cheers
(Yes, I know I'm mean not giving all the details now ...)

Rex Sanders
(Rex) - M

Locale: Central California Coast
Why not 100% propane in canisters? on 03/09/2013 10:51:55 MST Print View

IANASG (I am not a stove geek), so maybe this is a dumb question:

Given all the troubles vaporizing butane, why not make light canisters with 100% propane specifically for winter use?

Why are Coleman-style propane steel canisters the only ones on the market anywhere close to backpacking size?

(Edit) And to answer my own question:

http://www.backpackinglight.com/cgi-bin/backpackinglight/canister_stove_faq

Edited by Rex on 03/09/2013 10:56:30 MST.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
A pound of propane takes a pound of steel. on 03/09/2013 12:12:40 MST Print View

As the link you added explains, pure propane is so high pressure, it requires thicker steel. About exactly the weight of the propane regardless of size (14 oz. 16 oz, 20-pound/4.5-gallon, 80-pound, etc).

There are about three people on this very gear-heady site that I'd trust to load their own lighter canisters for winter-only use and be damn sure they never got above room temperature during transit and use. Those safety margins are used for good reason as HikinJim, RogerC, and I have all proved at times.

Now if someone offered a refillable 200-gram fuel weight aluminum or titanium propane canister, I'd order a handful.

Kevin Schneringer
(Slammer) - MLife

Locale: Oklahoma Flat Lands
Natural Gas? Efficient and clean on 03/09/2013 13:01:19 MST Print View

I own a Chevy Siverado that I had converted to Run on Natural Gas. It has a polymer tank that is wrapped in fiberglass and carbon fiber.
It has a fill pressure of 3600 PSI.

I just use public fill stations but there are several types of home filling stations.

It would be nice to just have a small refillable bottle to use with my stove! No more issue with low temps and no more canisters in landfills.

Maybe 3M or GE see an ultralight mini tank in there future?

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Natural Gas? Efficient and clean on 03/09/2013 14:06:19 MST Print View

> It has a polymer tank that is wrapped in fiberglass and carbon fiber.
Bring it on!!!!!

But the cost of production would likely be swamped by the cost of development and insurance and safety testing and getting approvals and ...
Sigh.

Cheers

Kevin Schneringer
(Slammer) - MLife

Locale: Oklahoma Flat Lands
Yep on 03/09/2013 14:18:27 MST Print View

Roger that is most definitely the problem!
It is amazing what is out there just waiting
Well my son can look forward to such high tech gear!
In 25 years who knows what possible