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Posers and Puzzles

Posers and Puzzles

  1. Subscriber sonhouse
    Fast and Curious
    16 Feb '06 03:02
    Always wondered how much heat a candle really has, one of these
    days I will take out my digital TC guage and measure it, like
    have a few cc's of water in a metal can and watch the temperature
    rise over time, that should do it I think. Anyone know offhand in
    advance? I can use that to see how close I came.
  2. 16 Feb '06 03:40
    sory no idea
  3. Standard member XanthosNZ
    Cancerous Bus Crash
    16 Feb '06 19:16
    Originally posted by sonhouse
    Always wondered how much heat a candle really has, one of these
    days I will take out my digital TC guage and measure it, like
    have a few cc's of water in a metal can and watch the temperature
    rise over time, that should do it I think. Anyone know offhand in
    advance? I can use that to see how close I came.
    You need a closed (in actuality semi-closed as practically a completely closed system can't exist) system.
  4. Subscriber sonhouse
    Fast and Curious
    16 Feb '06 22:16
    Originally posted by XanthosNZ
    You need a closed (in actuality semi-closed as practically a completely closed system can't exist) system.
    Yeah, it is impossible to be even within ten percent I am sure but
    it is an interesting sounding amateur experiment, not that big a deal.
    You could use a thimble sized container and just measure how fast
    the water heats up. 1 BTU as you no doubt know, is the amount
    of heat that changes the temp of a pint of water one degree F.
    Time is not involved, with the caveat that you don't want to take
    too long to make the measurement, the candle will eventually die
    out at least. So you could make a BTU/hour measurement, Have to
    figure what a thimble full of water is, how many it would take to
    make a pint, etc. Not exactly rocket science, I am just curious.
  5. Standard member XanthosNZ
    Cancerous Bus Crash
    17 Feb '06 00:22
    Originally posted by sonhouse
    Yeah, it is impossible to be even within ten percent I am sure but
    it is an interesting sounding amateur experiment, not that big a deal.
    You could use a thimble sized container and just measure how fast
    the water heats up. 1 BTU as you no doubt know, is the amount
    of heat that changes the temp of a pint of water one degree F.
    Time is not involved, wi ...[text shortened]... s, how many it would take to
    make a pint, etc. Not exactly rocket science, I am just curious.
    That would be a horrible setup. First you'd be heating the thimble too. Second not all the heat would be directed into the thimble full of water you'd also heat up the wax of the candle and the air in the room.

    Also no one in their right mind uses BTUs anymore. Joules (or perhaps kJ) makes much more sense. A unit based on a pound of water and a degree Fahrenheit? Ridiculous in this day and age.

    Now if you were sensible you could just work out the theoretical value by looking up the delta H for

    C60H122 + (90.5)O2 -> (60)CO2 + (61)H20

    This is the theoretical amount of heat released when one mole of wax burns to completion. We are assuming in this case that the wick contributes next to nothing in terms of heat energy. Now it's simply a matter of finding how many moles of wax burns in the time you wish. Weight the candle, burn it for the set time, reweight and work out how many moles the difference in weight is. Multiply the equation by the number of moles and you have the total amount of energy released. If you were to do the experiment you would end up with a smaller value as you lost heat that you can't accurately account for.
  6. Subscriber sonhouse
    Fast and Curious
    17 Feb '06 03:48 / 1 edit
    Originally posted by XanthosNZ
    That would be a horrible setup. First you'd be heating the thimble too. Second not all the heat would be directed into the thimble full of water you'd also heat up the wax of the candle and the air in the room.

    Also no one in their right mind uses BTUs anymore. Joules (or perhaps kJ) makes much more sense. A unit based on a pound of water and a degree ou would end up with a smaller value as you lost heat that you can't accurately account for.
    Well when I speak of BTU, I always convert to other formats, that
    was just the first thing that popped up. Could have used calories
    or Kilocalories too, once you have it in one regime its easy enough
    to convert, just rolling numbers around. Also I was thinking about that,
    I can see the problems with that setup, just a first thought
    experiment. Its a matter of getting the heat available to the
    device being measured. There was an interesting experiment
    where the guy was not going for calories or joules or such but
    convection currents and had a container closed off that was
    1 mm^3, very small, filled with water and I think he did oil too.
    He used a simple arangement of tiny TC gauges inside the liquid
    and was able to graph the convection currents inside by graphing
    the temperature changes. I did a similar experiment at work when
    we had to test some photonics circuitry (Erbium doped waveguide
    amplifiers) that had to have a heat stress test for 24 hours.
    It was what we called the bomb. It was a pressure vessel capable of
    withstanding over 10,000 PSI and got that by using DI water and
    just heating it, and it had a TC probe holder, kind of like a test tube
    sticking into the small chamber, a cylinder about 150 mm wide by
    450 mm high, very thick SS. I was able to chart the internal
    convection currents by charting the TC probe readings. It was
    interesting to see, obviously liquid phase followed by gaseous phase
    currents inside, we were not going for huge pressures, only about
    2 atm., and about 110 degrees C. That was baby stuff for that device
    though! It went on for 24 hours to 72 hours simulating lifetime checks.
    Funny thing was, we thought the performance of the circuit would
    have deteriorated but some of the devices got better! Go figure.
  7. Subscriber AThousandYoung
    It's about respect
    17 Feb '06 20:56
    Originally posted by XanthosNZ
    That would be a horrible setup. First you'd be heating the thimble too. Second not all the heat would be directed into the thimble full of water you'd also heat up the wax of the candle and the air in the room.

    Also no one in their right mind uses BTUs anymore. Joules (or perhaps kJ) makes much more sense. A unit based on a pound of water and a degree ...[text shortened]... ou would end up with a smaller value as you lost heat that you can't accurately account for.
    I think American engineers use the British system still. It is definitely odd to see their equations for me, since I studied biochemistry and we used the metric system.
  8. 18 Feb '06 00:32
    Heaters and Air Conditioners are still rated in BTU's, at least in America