Clever woodburning stove

[Treeview]

I wonder...how much effect altitude has on the heat output of an open fire that anyone on this forum will experience.

What is the actual percentage difference in temperatures 'under the pot' at camping altitudes. Now...if people are actually climbing or doing mountaineering it might be something to actually think about.

here are some things that I found:

Bolivian Andes 17,100' Western Cordillera; highest treeline in the world on the slopes of Sajama Volcano (Polylepis tarapacana)

Scotland 1,600' Strong maritime influence serves to cool summer and restrict tree growth

This is interesting academically but I wonder how interesting it might be in a practical sense.

To me, I'll just add a bit more wood to the fire...and wait a little longer to cook.

[Treeview]

Why not use a pressure cooker to heat water and cook?

I've seen cook time studies on lightweight backpacing forums that show how using a pressure cooker saves time and fuel. The fuel savings off sets the added weight in a lightweight cook kit. when you're chasing grams it's easy to find the benefits.

[eamarquardt]

We're on a roll!!!!!!

No definitive answers though.

Cheers,

Gus

[Engineer Guy]

The theoretical Posted above - that a Fire COULD be as well-fed and hot at higher Elevations - doesn't/can't exist w/o some Gas Density-enhancing 'assist' like a Bellows.

Imagine a Mole of Gas [a standard volume] as anything from a Liter Bottle to a Sugar Cube. That is, use whatever image suits you. The definition of lower pressure at higher Elevations is that there's less Gas in a given volume. This means there's less Oxygen to feed a Fire in the unassisted Atmosphere.

Consider using a Choke on a Yard Tool around the House. When the Fuel/Air mixture is 'off', there is necessarily incomplete combustion and resulting soot and/or unburnt Gas smell and Engine flooding. So, 'the same' Fuel/Air mixture at high Elevations as at Sea Level is a fantasy. A non-starter. For example, some Generators, etc., have to be re-Jetted for efficient use above Elevation 'x' to account for less Air. Their Electrical output is de-rated accordingly since the lesser Combustion results in less available energy.

The logical end to this effect is noted in the Post above. At low enough Pressure [Pressure being Gas Density in a standard Volume], combustion is not sustainable. That illustration or end point is the ultimate in a cooler Fire: no sustainable Fire at all.

Less Gas density also results in less effective [partial] Heat transfer to the Pot or Food. Taking advantage of this effect is why Vacuum Flasks have evacuated Walls at modest, sub-Atmospheric Pressure.

[Treeview]

Could a setup be designed to incorporate a venturi?

In the orginal picture I see that the infeed tube is smaller than the 'chimney' part. Of course, most/all of the cross section of the infeed will be jammed full of fuel. That willchange the airflow.

What I wonder...is...at what elevation and what fuel load will elevation be the limitation? And...at what percentage of efficiency?

Truly...this is NOT rocket science but the physics applies. Rockets need a higher efficiency and control of unknown variables. Cooking with wood sure doesn't need to be THAT accurate unless there is no wood or fuel. Just using one of these tube stoves will increase efficiency compared to an open fire.

[eamarquardt]

I still kinda think that if you burn the same amount of fuel (propane, gasoline, wood) yer gonna get the same amount of heat as the chemical reaction hasn't changed. Given the combustion we're talking about is in open air, I don't think that there will be "incomplete" combustion to any great extent due to a lack of available oxygen (at the altitudes we're likely to be camping). If your propane or gasoline stove is pumping out the same amount of fuel, there will be more than enough oxygen in the air to provide for complete combustion, and yer gonna get the same amount of heat. I think.

Here is a web site that makes an interesting point that the heated air, due to its being less dense, has less capacity to carry heat. I kinda think that the transfer of heat to the cooking vessel by the thinner air might be more of a factor than the supposition that the flames are "cooler" due to less oxygen being available for combustion. Again, within the limits of the altitudes folks are actually camping at.

The "Rocket Scientist" said that you lose about 3% of heating capacity in a typical heater per 1000 feet in altitude (although the article cited below says 4%, who ya gonna trust). It might be that the regulator used to regulate the fuel gas might be producing a gauge pressure (pressure compared to outside pressure) versus an absolute pressure (meaning if the outside pressure decreases the regulator puts out the same pressure when compared to the outside atmospheric pressure but when the outside pressure drops the absolute pressure of the fuel gas also drops). If the pressure of the fuel gas is lower, less gas will flow through the fixed orifice, and as less fuel is being burned, less heat will be produced.

http://www.achrnews.com/articles/select ... tude-homes

As I stated earlier, I think that there is "more to it" than the one supposition that the flames of the fire are cooler.

Another explanation is that I'm, typically, just making it more complicated than it really is but its always fun to know the truth and learn something new.

We need some serious controlled experiments to really determine what is going on.

You'll, though, get no argument from me that it takes longer to cook foods at altitude but mostly because water can't get as hot as it can at sea level.

Cheers,

Gus

[eamarquardt]

Why not use a pressure cooker to heat water and cook?

I've seen cook time studies on lightweight backpacing forums that show how using a pressure cooker saves time and fuel. The fuel savings off sets the added weight in a lightweight cook kit. when you're chasing grams it's easy to find the benefits.

For some types of cooking a pressure cooker would address the issues of cooking at altitude. I've found, though, that cooking bread, brownies, cupcakes, and the like in a pressure cooker to be less than optimum.

Everything in life is a compromise. IE: I can either hurt like crazy or take my meds and be dazed and stoned. It just which is the "lesser" evil.

Cheers,

Gus

[eamarquardt]

Why not use a pressure cooker to heat water and cook?

I've seen cook time studies on lightweight backpacing forums that show how using a pressure cooker saves time and fuel. The fuel savings off sets the added weight in a lightweight cook kit. when you're chasing grams it's easy to find the benefits.

For some types of cooking a pressure cooker would address the issues of cooking at altitude. I've found, though, that cooking bread, brownies, cupcakes, and the like in a pressure cooker to be less than optimum.

Everything in life is a compromise. IE: I can either hurt like crazy or take my meds and be dazed and stoned. It just which is the "lesser" evil.

Cheers,

Gus

[Treeview]

[It just which is the "lesser" evil.

Or...as Captain Jack Aubrey says, 'The lesser of two weevils'

http://tinyurl.com/Jack-Aubrey-weevils

[warnmar10]

Air is less dense at altitude so, all else being equal, more air must pass through the system to support the same intensity of combustion at altitude as at sea level.

[Treeview]

Air is less dense at altitude so, all else being equal, more air must pass through the system to support the same intensity of combustion at altitude as at sea level.

Yup...I learned that in high school physics...but...at what elevation does it make a difference in campfire heat?

My guess is that there is way more O2 in the air up to an elevation approaching 10k feet or so that is needed. At some elevation the needs of a woodfire are going to suffer...but, would that even be a consideration?

[eamarquardt]

[It just which is the "lesser" evil.

Or...as Captain Jack Aubrey says, 'The lesser of two weevils'

http://tinyurl.com/Jack-Aubrey-weevils

Yes but as I remember they were "special racing weevils".

Cheers,

Gus

[warnmar10]

Air is less dense at altitude so, all else being equal, more air must pass through the system to support the same intensity of combustion at altitude as at sea level.

Yup...I learned that in high school physics...but...at what elevation does it make a difference in campfire heat?

My guess is that there is way more O2 in the air up to an elevation approaching 10k feet or so that is needed. At some elevation the needs of a woodfire are going to suffer...but, would that even be a consideration?

The key is "all else being equal". Essentially it is unknowable unless we can compare equal fuel sources at sea level and 10k or whatever. If it turned out to be a problem I think I would just adjust the fuel, but that's me.

[McDave]

Well that was just too good to just let it lay there. Let's see if we can get it jump started. I'll go first.
Rocket Stove, Schmocket Stove. Where I come from we call it a Dakota Hole. No welding, No pipe. Nothing to pack around. Nearly smokeless. Time tested and true. And it's Free!
Here ya go. Get knowed up.
http://survivaltopics.com/the-dakota-fire-hole/

Also, pertaining to the time/temp./altitude discussion, lets remember that the fuel really only holds the fire. The real power is in the oxygen. Does it take longer to boil or not. Glass half full or half empty.? If it has a hole at the top, the glass is always full. It may be air or liquid , but it is always full.

McDave

[GPW]

You can dig two holes in the ground and make the same thing … ( camping )
Wolf is Right , the insulation makes it work much more efficiently …