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Boiling water to save energy, start a low or high gaz setting?

  1. Aug 2, 2012 #1
    What is more efficient to bring water to a boil?

    1. Using the low setting on heat
    2. Going full blast to get it to boil as fast as possible

    For a vehicle, developing velocity is more economical with slow accelaration, but would it be the same with boiling water?

    Does it take less BTU to crank the heat slowly until it reaches a boil or put it on high right away?

    This question relates to a 50 000 BTU gaz burner to heat 40 liters of water for canning pickles.
     
  2. jcsd
  3. Aug 2, 2012 #2
    Generally, the higher temperature of the heater, the more efficient the thermal transfer. So I would go for the full tilt.

    But that assumes no "silly" losses, such as parts of the produced heat having no way or time to be absorbed with the tank.
     
  4. Aug 2, 2012 #3

    sophiecentaur

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    It would probably depend upon the size of the pan and the size of the gas ring. If I put our smallest pan on the large ring, you have to back the gas flow right down so that the flames actually play on the ban and don't just flare out round the sides.
    In principle, though, the higher the power, the quicker the water will heat up so the less time there is to lose heat to the surroundings. This would be easy to show if an electric kettle were used with different supply voltages.
    otoh, if you want to use the hot water at a specific time, you may be better off at a lower power setting, rather than waiting with the water at its highest temperature.
     
  5. Aug 2, 2012 #4
    ^ This would be my answer, and is probably the dominant process of wasting input energy.
     
  6. Aug 2, 2012 #5
    Thanks everybody,

    Actually the pot is commercial high chromium stainless steel, I'm in Thailand and this is restaurant grade ;) The burner is also a KB5 and very powerful.

    My question relates to fuel economy basically.

    The size of the burner is adequate for the pot and they are designe to work together.

    Taken that information:

    Will bring to boil very fast cost more or less propane than slowly bringing to a boil?

    Thanks,
    Bruno
     
  7. Aug 3, 2012 #6
    Since you're doing this routinely, why not test it for yourself. Determine the weight of the propane pot with a good scale. Do a couple of fast boilings and weigh again. Repeat with a couple of slow boiling and you'll have the answer.

    It's probable indeed that the prolonged time of heat loss would increase the required amount of propane with slow boiling. But the other mentioned effect, losses due to inefficient heat exchange at fast boling, cannot be ruled out.
     
  8. Aug 3, 2012 #7
    An accelerating vehicle is a much more complex process, and even then your statement is not necessarily true.

    How economically you accelerate depends on how efficient your engine is. It's actually most efficient at full throttle, but not necessarily at redline, so chances are you will waste more gas by flooring it and redlining every gear. But again, not necessarily. The variables which affect the efficiency of chemical to heat to mechanical energy conversion are quite many, which furthermore interact with and affect each other.

    When boiling water, there really isn't nearly as much room for inefficiency. After all, you're trying to turn chemical (or electric) energy into heat. Waste heat is basically what inefficiency IS is most applications, but here it just does more of what you want it to do. Worst thing that can happen is the heat goes somewhere else beside the water. This is why I would guess you're just better off cranking it all the way and let it boil as fast as possible, so that there's less time for the water to lose heat to the surroundings.
     
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