[Amps] Black Heat Shields

[Roger (K8RI)]

On 12/20/2010 12:20 AM, Mike Saculla wrote:
> If any of you discover a material that absorbs heat faster than it radiates it, please let me know. We
> can become millionaires together. Conservation of energy in the universe - materials absorb and radiate
> energy at the same rate.
>
> Jim, I like your analogy, except that at some temperature the outer layers of the carbon would begin
> to ablate off and the box would slowly vaporize. Now, if the box was a perfect sphere, and you
> instantly heated the outer surface of that sphere super hot, the ablation of the outer surface would
> cause an equal and opposite reaction, the sphere would implode and fusion would occur.
>
> This is the concept of Inertial Confinement Fusion, or Laser Fusion as it sometimes called. It's what
> we are trying to do at my place of employment. We have the largest laser in the world - it's over a
> football field long and three stories high. Google NIF Laser, NIF short for National Ignition Facility.
Now all yah gotta do is figure out a way to load those little spheres at 
60 cps, then recharge and fire the lasers at 60 cps without dumping the 
national electric grid. <:-)) Who's going to break even first.  Us or 
the UK? or is that one in continental Europe?

73

Roger (K8RI)
> Mike K6MDS
>
>
> One final comment, for those wonder how something that absorbs radiation can
> also emit radiation. Imagine what would happen if that didn't happen.
> Suppose, for example, we take a graphite box and set it in outer space so
> that the sun shines on it. In outer space, there's no convective heating or
> cooling (let's ignore the solar wind, meteor dust, and other minor
> complications), so the only way heat can enter or leave the graphite box is
> by radiation. If the graphite didn't emit radiation, then it would keep
> absorbing sunlight and get hotter and hotter. Its temperature would keep
> rising, until it became white hot and then blue hot, and then finally so hot
> the carbon atoms would fuse and it would explode like a hydrogen bomb (in
> this case a carbon bomb). Of course, that doesn't happen and the reason is
> that the graphite box eventually reaches thermal equilibrium; the energy it
> absorbs exactly equals the energy that it emits. If we replace the graphite
> with, say, a block of wood, then the same thing will happen. But because
> wood isn't as good an absorber of radiation as graphite, it won't get as hot
> when it reaches equilibrium. In other words its equilibrium temperature will
> be lower. And, if we put a glass mirror in outer space, it won't heat up
> much at all, because it will absorb only tiny bit of energy. However, even
> that tiny bit gets reradiated, and if one measures the spectrum of the
> radiated energy, it will look very much like a blackbody spectrum. So the
> bottom line is that all things absorb radiation to some degree, thermalize
> it, and reradiate it back out.  A theoretical blackbody does this perfectly,
> everything else less so, to varying degrees, but the basic concept is the
> same. And it's a good thing Mother Nature works this way, because if she
> didn't the universe as we know it wouldn't exist and we wouldn't be having
> this conversation.
>
>
>
> End of lecture. Tnx for the bandwidth!
>
> 73.
>
> Jim W8ZR
>
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