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You are currently reading a thread in /sci/ - Science & Math

Thread replies: 20
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File: Mloxon.jpg (29 KB, 183x288) Image search: [iqdb] [SauceNao] [Google]
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How the fuck does a gas mantle obey thermodynamics?

> absorbs infrared radiation
> emits higher energy radiation (light)
> no temperature difference, only heat
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It has low emissivity in the IR spectrum
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>>7780233
>emits higher energy radiation (light)

Yeah, no. Higher FREQUENCY =/= higher energy.
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>>7780289
Are you for reals?
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>>7780233
>no temperature difference, only heat

i dont even...
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>>7780233
offhand, if it works the way you say it does, i would venture that it is a multi-photon absorption process to an excited state with a single drop back to ground state.

such a system is not common but it does exist. tends to be a bit inefficient for obvious reasons (needs multiple photons simultaneously) but maybe there is a special property of the radioactive materials in the mantle which overcome this limitation.

>>7780289
stop posting
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>>7780337
ok read up on it a bit more.

its not a fluorescence process. the IR photons are simply absorbed, and once the temperature of the bulk material is high enough, it begins emitting light.

This means that if it were simply radiative processes, more IR photons would need to be absorbed (but not simultaneously) than visible photons could be emitted. Thats fine tho, you cant see the heat but the light emitted could still be plenty bright.

However, its not simply radiative. Any heat transfer will do, so the convective transfer from the heated air will also be a significant source of energy, allowing more of the chemical energy from the burning fuel to be utilized in light production.
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>>7780372
not a simple fluorescence process, i mean.

heat is absorbed and converted to vibrational energy in the material. when this energy is high enough, it results in an electronic excitation which in turn produces a visible light photon.

the material is special in that very little of the vibrational energy is re-released again as heat.
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>>7780375
>heat is absorbed and converted to vibrational energy

I hate to be a nazi, but heat IS vibrational energy.

Also the way you just described this thing makes it seem like a reverse-entropy machine. Taking heat energy and converting it to light.
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>>7780400
heat in a molecule is vibrational energy.

radiative heat is IR-radiation.

so by saying "heat is absorbed" I am saying IR-radiation is absorbed and vibrational energy is transferred.
the more you know.
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>>7780400
>reverse entropy machine

no. it requires more energy in than energy out. a certain amount of the heat energy is trapped in the molecule and will eventually be released again (as heat) albeit at a much lower rate.
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>>7780412
Thanks for clarifying.
>>7780415
You've mixed up entropy with the first law. Obviously no new energy is created by this conversion from heat to light.

For reference, a lightbulb has to be at 2700K to emit the light which it does. That is a lot of heat energy needed in order to make the material emit light. This is standard of all metals. What allows this material to convert heat to relatively high-energy photons with such efficiency?
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>>7780420
no, i didnt.

for every high energy photon that is released, the total entropy of the system must be increased. this is contained in the statement that it needs more energy in than it puts out.

look at the entire system. how do you heat the mantle? by burning a chemical fuel. that is a massive increase in entropy. only some of that is pushed into higher energy photons. net effect: increase in entropy.

this is not a violation of thermodynamics. supposed "reverse entropy machines" (life for example) are all net-increasers of entropy when you take into account the entire system and not just the machine iteself.
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File: emission spectrums.png (53 KB, 1024x614) Image search: [iqdb] [SauceNao] [Google]
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>>7780440
I've made too many assumptions. Apologies.

Well that concludes the gas mantle saga.
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>>7780448
not a problem at all, better you ask and learn than sit on your assumptions.
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>>7780448
btw, i am working with CeO2 in my current project and your questions here just enlightened me to a property that may have quite some significance to my results.

so thank you, actually
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>>7780451
Ha well in that case glad to help anon
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>>7780448
is pic related why we use tungsten as light globe filaments?
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>>7780535
that and the fact that it has an incredibly high melting point.
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>>7780540
thanks anon, i learnt something today
Thread replies: 20
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Thread DB ID: 418541



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