jetboil fluxring

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russb
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jetboil fluxring

Postby russb » Thu Jan 31, 2008 4:45 pm

I have a question for anyone who is familiar with the jetboil system. How does the fluxring increase the efficiency of the stove? Someone please correct me in my error, but it seems that if adding more metal to the pot especially so close to the heat source, the metal will absorb more heat and thus less will be transferred to the water. How does this increase the fuel efficiency, it seems like it should decrease it. What am I missing?

oops56
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Re: jetboil fluxring

Postby oops56 » Thu Jan 31, 2008 5:12 pm

As i see it. Its like a windscreen but a heat screen holds the heat in on area and transfer it i think.I made a alcohol stove to work on it the flame got to spread out to hit the fins to much straight up no good
Image

The left one is a side burner reg the right one i added a ring to get it to hit the fins

Image
Man play with fire man get burnt

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zelph
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Re: jetboil fluxring

Postby zelph » Thu Jan 31, 2008 11:21 pm

Any heat absorbed is transfered to the water, the more absorbed tha more transfered. As long as the inside wall of the pot is cooler than the outside it will continue to transfere heat to the water as fast as it can. The fins are grabbing all the flames heat as it can before it passes away to the outside and up and away. The more caught by the pot the better.

I wish I had one of those pots!!!!!! :D
http://www.woodgaz-stove.com/

oops56
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Re: jetboil fluxring

Postby oops56 » Thu Jan 31, 2008 11:31 pm

zelph wrote:Any heat absorbed is transfered to the water, the more absorbed tha more transfered. As long as the inside wall of the pot is cooler than the outside it will continue to transfere heat to the water as fast as it can. The fins are grabbing all the flames heat as it can before it passes away to the outside and up and away. The more caught by the pot the better.

I wish I had one of hose pots!!!!!! :D


You wish to much just do it . :roll: :roll:
Man play with fire man get burnt

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zelph
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Re: jetboil fluxring

Postby zelph » Thu Jan 31, 2008 11:40 pm

oops56 wrote:
zelph wrote:Any heat absorbed is transfered to the water, the more absorbed tha more transfered. As long as the inside wall of the pot is cooler than the outside it will continue to transfere heat to the water as fast as it can. The fins are grabbing all the flames heat as it can before it passes away to the outside and up and away. The more caught by the pot the better.

I wish I had one of hose pots!!!!!! :D


You wish to much just do it . :roll: :roll:


I spent my allowance on some other stove related stuff at an army surplus store up in MN 2 days ago :mrgreen:
http://www.woodgaz-stove.com/

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zelph
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Re: jetboil fluxring

Postby zelph » Thu Jan 31, 2008 11:55 pm

Just wanted to show a pic of the flux ring. It aint all that much metal

Image[
http://www.woodgaz-stove.com/

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russb
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Re: jetboil fluxring

Postby russb » Fri Feb 01, 2008 7:17 am

A few more questions then... So the fluxring just stops any loss of heat from escaping to the side? Does this mean that if the flame maintains 100% contact with the bottom of the pot, there will be no loss, or is it the radiant heat loss to the side the issue? Since the idea is that the ring must transfer the heat to the water, the specific heat (and mass) of the fluxring must be minimized thus the material and design are important?

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zelph
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Re: jetboil fluxring

Postby zelph » Fri Feb 01, 2008 11:12 am

russb wrote:A few more questions then... So the fluxring just stops any loss of heat from escaping to the side? Does this mean that if the flame maintains 100% contact with the bottom of the pot, there will be no loss, or is it the radiant heat loss to the side the issue? Since the idea is that the ring must transfer the heat to the water, the specific heat (and mass) of the fluxring must be minimized thus the material and design are important?


It does'nt stop heat loss, It gathers all it can while the heat is passing through the fins.

The radiator in your car has fins wrapped around/attached to copper tubes that absorb heat in the tubes and passes it on to the air around it. In the winter the fins pass a great deal to the air causing your car heater to have a hard time warming the air inside your car.
http://www.woodgaz-stove.com/

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russb
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Re: jetboil fluxring

Postby russb » Fri Feb 01, 2008 12:44 pm

The process of gathering the heat and then transferring it, instead of letting the heat escape to the air would be decreasing the heat loss (ie increasing efficiency). That is what I meant, Sorry for not being clear. Or am I missing the point of the fluxring? I thought its intended purpose was to increase the efficiency of the stove?

I just looked up the specific heats of both Al and Ti.

Al= .9J/gK
Ti= .52J/gK

Tony
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Re: jetboil fluxring

Postby Tony » Fri Feb 01, 2008 4:14 pm

Hi russb,

I have a question for anyone who is familiar with the jetboil system. How does the fluxring increase the efficiency of the stove? Someone please correct me in my error, but it seems that if adding more metal to the pot especially so close to the heat source, the metal will absorb more heat and thus less will be transferred to the water. How does this increase the fuel efficiency, it seems like it should decrease it. What am I missing?

I just looked up the specific heats of both Al and Ti.

Al= .9J/gK
Ti= .52J/gK



The most important parameter in heat transfer of a pot is CONDUCTION ( it would be best to look it up on the net as it would take a lot to fully explain here).

The transfer of heat by conduction if found to depend on

1. The area through which heat transfer takes place.
2. the temperature difference of the faces through which the heat is passing.
3. the time taken for the heat ransfer.
4. the thickness of the material through which the heat is passing.
5. the type of material.

the coefficient of thermal conductivity (W/m K) is the figure used in the heat transfer equation not specific heat, but with pots it is not that important as the thickness of a pot is very thin ( my testing Ti pots are more efficent that Al but Ti has a much poorer coefficient Al=206 W/m K Ti=15 W/m K, I think the better efficiency of Ti could be because of the rougher surface finish on the Ti pot.)

I also think that the flux ring not only gives the pot more surface area bit it slows down the flow of hot gasses over the bottom of the pot which also adds to the heat transfer.

FYI
Here are some results from testing a standard pot and a 1.5 liter JetBoil pot on a Cat Can side burner stove that I made, the stove is not the most efficient but is fast heating.

Both tests were done under the same conditions and technique, ambient 21.5C, 600m elevation and fuel used Methylated Spirits 95% ethanol (denatured Alcohol), I used 0.8 grams of fuel to prime which is taken into account in the results. The two pots that I used are as close to the same diameter that I could get, JB = 165 mm and Billy pot 157 mm, the Billy volume is 2 liters, the neoprene cozy was NOT used on the JetBoil pot.

Results
Billy pot (g/C)/0.5 liter = 0.226grams (g/80C)/0.5 liter = 18.1 grams
JetBoil pot (g/C)/0.5 liter = 0.156 grams (g/80C)/0.5 liter = 12.48 grams
JetBoil stove (g/C)/0.5 liter = 0.0548 grams (g/80C)/0.5 liter = 4.38 grams

(JB 1.5l pot) With this Cat Can Side Burner stove the Billy pot used 45% more fuel than the JetBoil pot.

Note 1: 12.5 grams is a typical amount of fuel that is used to boil 0.5 liters of water in most of the alcohol stove that I have tested with Standard pots but they are usually much slower to boil.

Note 2: I put the JetBoil stove test results in as a comparison to compare the Standard JetBoil configuration with the alcohol JB setup.

Note 3: [(g/80C)/0.5 liter = grams of fuel used to heat 0.5 liter of water 80C] and [(g/C)/0.5 liter = grams of fuel to raise 0.5 liters of water 1C] (efficiency numbers) are numbers that I use to compare stoves and systems. I feel this is a fairer way of looking at efficiency as the efficiency equation does not take into account the mass of fuel used only the amount of heating energy in the fuel.

Note 4: This test must be looked at with some caution as it is for this particular Cat Can Side Burner alcohol stove other alcohol stoves behave differently with the JetBoil pot, more tests with other alcohol stoves will be published at a later date.

Conclusions: The flux ring can make a big difference to the efficiency of some alcohol stove pot systems. For some alcohol stove users the extra weight of the JetBoil flux ring pot verses the fuel savings might be worth looking at.

I hope this helps you a bit

Tony

Image
Time vs temperature rise curve
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Standard pot on stove
Image
JetBoil pot on stove


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