Half a croissant, on a plate, with a sign in front of it saying '50c'
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Fuel Efficient Stove

Some help from a heat exchanger
  (+3)
(+3)
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Instead of having the pot or pan sit on a cast iron support, it would sit on a bowl or cone shaped piece of insulating, heat resistant ceramic, with concentric circular ridges.

Each ridge would be flat on top, and sloped downward toward the burner on the inner side. Inside each ridge would be a circle of air holes, which would act as an exhaust for the combustion gasses; a knob would control which circle of holes would be used (the preferred one being the largest circle which is still smaller than the pot). The air would pass from the circle of holes, through a high efficiency countercurrent heat exchanger, through an exhaust fan, and up the flue.

In the meantime, an air intake fan would blow fresh air (possibly taken from outide the house) through that same heat exchanger, then to the burner.

Since heat is being recirculated from exhaust to intake, we can produce a much higher temperature using the same amount of fuel, or produce the same temperature using much less fuel.

As a side benefit, we no longer need to use the oven hood for some cooking tasks, since less heat enters the kitchen.

goldbb, Mar 15 2009

'S kinda the same, not enough for an mfd... http://www.jetboil....rsonalcookingsystem
As per usual, if you want to find out what's at the cutting edge of technology, go look at mountaineering, backpacking, hunting or adventuring equipment. Basically an efficiency optimised boiler for mountain climbing, very (very) fuel efficient. Easily use this concept for home. [Custardguts, Mar 15 2009]

Injector Pump http://en.wikipedia.org/wiki/Injector
Let momentum do the work for you. [eight_nine_tortoise, Mar 17 2009]

[link]






       I like the thought behind this [+]. However I think it needs a picture to fully describe it. If the cone angle is too small you would have to reach a long way down to get the pans in and out (would it have a cutout for the handle?). I also think you would need to make sure that the seal between pan and cone was very good to ensure no heat loss into the room through escaping combustion gases and also that the restrictions down the exhaust system did not lead to to much back pressure lifting the pan or starving the combustion process of airflow.
eight_nine_tortoise, Mar 15 2009
  

       I agree with the above, this is well trodden territory so I'd need to see a drawing to understand how this fairs against ideas in this category, so please illustrate as this is a vitally important area that needs improvement in the third world though for there you may have to use SS instead of ceramic.
MisterQED, Mar 15 2009
  

       See link for comparable, similar but not the same device for mountain climbing. These things are all the rage with people who don't like carting around kilos and kilos of fuel. Very fuel efficient (up to like 1/3 consumption, or something like that) - but christingly expensive. Think a thermos with an optimised burner/flue underneath.   

       Something like this could easily be adapted for home use, save fuel/electricity costs. Remember, Tall and narrow pots are more efficient than short wide ones.
Custardguts, Mar 15 2009
  

       Would it be better to have multiple burners (only using one at a time) in between the ridges, and exhaust through the centre using an extractor fan to pull in air and draw the working fluid through the system. Using flow meters on the gas feed and exhaust gases you could also optimize the air/fuel mixing and heat exchanger flow.
Skrewloose, Mar 16 2009
  

       The cone would be very shallow, nearly flat; the top surface of each ridge would be about 1/4 inch wide, whilst the vertical parts of the ridges would be about 1/16 inch high.   

       Regarding a tight seal between pot/pan and the cone: since there's both an air intake fan and an exhaust fan, the flows of air can be balanced even if the seal isn't perfect.   

       As to the jetboil thingy... I don't see any description of what, exactly, makes it more fuel efficient than any other burner.   

       Skrewloose, I don't see how it would be either better or worse to have a circular ring of burners and a central exhaust, versus a central burner, and ring of exhausts. Well, except for cost.   

       I do agree that appropriate sensors in the system would allow air/fuel mixing to be optimized (by controlling fuel flow and fan speed).   

       I'd probably also want air pressure sensors, one between the intake fan and heat exchanger, the other between the heat excanger and exhaust fan.   

       Monitoring these would allow us to detect if the pot has been removed, and allow us to turn the gas flow down or off. It might also detect clogged exhaust holes, which would activate an appropriate warning light/noise.   

       And perhaps an oxygen sensor -- a stove should never burn a rich fuel mixture, which would consume 100% of the oxygen while sending unburnt fuel into the exhaust; it should always be slightly on the lean side (with some unused oxygen going out the exhaust).   

       In a normal stove with an open flame, we can visually see if there wasn't enough air mixed into the fuel prior to combustion, since the flame will be yellow instead of blue; however, when combustion is out of sight, a sensor becomes necessary.
goldbb, Mar 16 2009
  

       Could the ceramic be transparent? Then you could see the flame and not need to rely on sensors. Don't use up the resources you save in fuel by adding expensive to make and replace parts. I think a system that balances flows by good design is much more elegant. Try the venturi effect with an injector pump [link] around the flame to promote flow instead of a fan.
eight_nine_tortoise, Mar 17 2009
  

       The only reason I suggested ceramic, as opposed to, let's say, metal, is that it's not only heat resistant, but a moderately good thermal insulator (a ceramic coffee mug will feel less hot than a glass one; and I wouldn't even think of putting coffee in a solid metal cup). The only transparent ceramic I know of is the stuff Corell plates are made of... which is quite glass-like, and would *probably* (I don't know for sure) be as poor as glass.   

       As for the venturii effect, could it force the air through the heat exchanger?
goldbb, Mar 17 2009
  

       Trangia, anyone?
simonj, Mar 17 2009
  

       Sorry, I'd got confused about the operation, I thought you were pre-heating the fuel, rather than the air. The central burner makes much more sense now. I assume you'd have a single exhaust fan and valves controlling the portion of flow through the different radius exhausts.   

       [goldbb] - The only gas in the system under a significant pressure here is going to be the fuel, and I don't think I'd be happy mixing the air and fuel before they got to the 'underpan chamber', as there's potential for back-burning.   

       A sudden thought comes to me... rather than concentric rings, could you use a single spiral of ridges? This would even up the heat delivered if there was a bad seal on one side of the pan.
Skrewloose, Mar 18 2009
  

       I was thinking of each ring of exhaust holes (going from the middle outwards) being just a little bit higher than the previous one; the pan would only sit flat (and not rock) if it's centered, ruducing the likelyhood of a poor seal.   

       By using a circle, and selecting the largest circle which isn't larger than the pan, the hot air moves the maximum distance across the bottom of the pan, without diluting the air going to the heat exchanger, with (cool) room air.   

       You probably could use a single spiral ridge; a side benefit of doing so would be to eliminate the need for the user to turn a selector knob to choose which ring of exhaust ports to use.   

       But if you did use a spiral, it would be pulling some of the hot air from very near the burner out the exhaust, befre it could move across the bottom of the pan (wasting that heat) and, at the same time, pulling cool air, from the very edge of the spiral (beyond the edge of the pan) out the exhaust (diluting the hot air going to the heat exchanger, and reducing how much the fresh air will be heated).   

       If you made a spiral which ascended from the middle outwards, the pan would be sure to wobble. If the spiral was flat, there'd be less assurance of the user placing the pan as centrally as possible.
goldbb, Mar 18 2009
  
      
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