16 Feb 06
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.
16 Feb 06
Originally posted by sonhouseYou need a closed (in actuality semi-closed as practically a completely closed system can't exist) system.
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.
16 Feb 06
Originally posted by XanthosNZYeah, it is impossible to be even within ten percent I am sure but
You need a closed (in actuality semi-closed as practically a completely closed system can't exist) system.
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.
17 Feb 06
Originally posted by sonhouseThat 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.
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.
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.
17 Feb 06
1 edit
Originally posted by XanthosNZWell when I speak of BTU, I always convert to other formats, that
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.
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.
17 Feb 06
Originally posted by XanthosNZI 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.
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.