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

Reduce convection losses in gas stoves and use the waste heat to heat the intake air
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Gas stoves are the most popular cooking stoves around the world. The heat from a gas stove is more controllable than an electric hotplate. It is also cheaper and usually more efficient (the in efficiency of an hotplate comes from production and transmission losses of electricity).

Yet a gas stove is a very inefficient device in itself. The inefficiency comes from the use of open flames in the stove. The flame is essentially hot gases. The hot gases are only able to partially transfer its heat to the cooking pot. The rest is lost to the surroundings. This can be easily verified by the fact that the surroundings of a gas stove is significantly warmer than the surroundings of a electric hotplate. The kitchen also gets uncomfortably hot in warm climates.

The open flames of a gas stove is a significant fire hazard. The exhaust from the stove may also buildup dangerous levels of carbon-dioxide in a closed in environment.

I propose an efficient stove design which keeps the flames in a closed chamber. After the hot gases of the flame heats the cooking pot, it is used to preheat the intake air. The exhaust escapes through a chimney which can be ducted outside to keep the kitchen cool and safe.

Please follow the links for illustrations.The cooking pot should make a more or less good seal with the stove when the pot sits on top. Thus the convection loss is stopped.

The stove has two chambers separated by a flower shaped thin aluminum wall. The intake air enters through the bottom of the stove and rises through the inner chamber. The hot exhaust travels down the outer chamber and exits to the chimney. The suction of the updraft in the long chimney helps the hot exhaust to travel down the chamber. A small fan on the chimney can help start the updraft. While the hot air is travelling down, it exchanges some of its heat to the intake air rising through the inner chamber. The large surface area of the flower shaped wall facilitates the heat exchange. The outer wall of the stove may be covered with some kind of insulation to reduce heat loss.

As the intake air is heated as it rises through the inner chamber, the convection current helps it move up wards. The gas enters in to the burner located at the top of the inner chamber through a venturi and create more suction for the intake air.

The actual gain in efficiency is hard to reckon with out lots of experimentation. This was supposed to be my winter project. Never got the time to finish it. I built a model with candles and aluminum foils. It seems to work, but I never had the time to do a controlled experiment. Feel free to try it yourself.

One possible improvement idea is to have corrugations in the flower shaped wall between the inner and outer chamber for better heat exchange.

The design was done in Solidworks. I can post the file on request. (cc)(science commons)

kneeslider, Feb 01 2010

Stove top-trimetric view http://www.postimag...mage.php?v=Ts18Qrar
[kneeslider, Feb 01 2010]

Burner bottom view http://www.postimag...mage.php?v=Ts18QSC0
[kneeslider, Feb 01 2010]

Burner top view http://www.postimag...image.php?v=Pqwq7br
[kneeslider, Feb 01 2010]

Stove bottom-trimetric view http://www.postimag...image.php?v=gxSGhR0
[kneeslider, Feb 01 2010]

Inefficient Gas Stove LPelletG_20Stove
[normzone, Feb 01 2010]

Prior (halfbaked) art. Fuel_20Efficient_20Stove
Very similar, especially the heat exchanger part [goldbb, Feb 03 2010]

[link]






       hmm.. getting only fish bones. Why no comments?
kneeslider, Feb 02 2010
  

       You might be able to get more comments (or votes if that's what you're really after) with a bit of marketing.   

       Tell us how much heat is lost in a regular gas stove and how much more efficient you expect yours will be. What are other ideas that have been tried/suggested to improve the efficiency of a gas stove?   

       I like your illustrations, and am looking forward to more of your ideas.
xaviergisz, Feb 02 2010
  

       Votes does not matter much (although croissants taste good). But I really appreciate and enjoy critical opinions, be that positive or negative.   

       I updated the post about efficiency losses in the regular stoves and why my design should be better.   

       If I knew the quantitative efficiency gain it would have either been a baked or a charred project. I have not experimented enough to make a comment about it.
kneeslider, Feb 03 2010
  

       I have questions about the increased risk of scorching since the heat is concentrated over a smaller area at the base of the pot, one advantage of the open flame model is the hot air moving up the sides of the pot or pan, which also allows you to use pans with a larger surface than the burner area.   

       You would also have a risk that if your air supply was inadequate you could get a gas build-up which would flashover when the pot was removed. This one can probably be designed out, but it is a concern.
MechE, Feb 03 2010
  

       I don't know what all the negativity is about, this looks great. (+)   

       Couldn't you just cover the stove tops with a thin SS sheet, so you always have a seal and you could spread out the heating? I commonly use both a 6" diameter pot and a 12" diameter pan and would like even heating on both. Maybe leave one open for those with a Wok.
MisterQED, Feb 03 2010
  

       Sometimes fish are the mark of an excellently-described idea here, for god knows what reason.   

       I wonder what the efficiency of an old gas-powered cast-iron stove would be?
RayfordSteele, Feb 03 2010
  

       [MechE] Scorching may be prevented by using different size stoves for different cooking pot sizes- a 6 inch stove for pots of 6 to 8 inches, a 9 inch stove for pots of 9 to 12 inches. The burner is almost the same size as the stove, so a cooking pot of comparable size will not probably scorch. Also thicker walled pots may be used.   

       I agree that flash over is a concern. Although, intuitively I think it's unlikely. Large slots have been cut out at the bottom of the stove for intake air. Updraft should be strong enough to create enough suction for the intake. But without experimentation, I cannot say anything for sure.   

       [MisterQED] I actually came up with the idea when I recently started using a hotplate. So at first I also thought about covering the stove top but abandoned it for several reasons.   

       1) A covered top will always leave some air trapped between the pot and the cover. This reduces conductivity. (It is one of the reasons hot plates take a lot of time to heat up a cooking pot, but a induction heater of the same wattage does much better.)   

       2) A covered top will require a flat bottomed pot. I designed it primarily to be used in third world countries where people mostly uses round bottomed cooking pots.   

       3) I wanted to keep the production cost as low as possible (possibly within 10 dollars) and also opted for the simplest possible design. If the top is not covered, the outer wall of the stove may be built from an aluminum pot.
kneeslider, Feb 04 2010
  
      
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