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Active Heat Cancellation?

Posted by: Akkman - Fri Dec 15, 2006 12:03 pm
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Active Heat Cancellation? 
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Post Active Heat Cancellation?   Posted on: Fri Dec 15, 2006 12:03 pm
I was just wondering if such a thing was possible.

We all have probably heard of active noise cancellation by using another sound wave to cancel out the first. I was wondering if heat, which I understand to be vibrating molecules, if it would be possible to cancel those vibrations also?

If such a thing were possible, could you make an electric heatshield from it?


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Post    Posted on: Fri Dec 15, 2006 1:30 pm
Seems unlikely. The source of the vibration is physical contact with a foreign object displacing the molecules. This being the spacecraft itself.

I wouldn't however rule out some method to displace the transfer of heat to the object.


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Post Re: Active Heat Cancellation?   Posted on: Fri Dec 15, 2006 10:08 pm
Akkman wrote:
I was just wondering if such a thing was possible.

We all have probably heard of active noise cancellation by using another sound wave to cancel out the first. I was wondering if heat, which I understand to be vibrating molecules, if it would be possible to cancel those vibrations also?

If such a thing were possible, could you make an electric heatshield from it?


Something like this is done on an atomic scale in research labs, when laser beams are used to "trap" and cool small amounts of matter (creating so-called optical molasses). But you need a comparably vast amount of laser energy to extract a tiny bit of thermal energy from your sample; so it's not practical for the application.

The first problem with heat is that, unlike sound, the matter moves in an unpredictable way; it's only the electromagnetic field that has predictable, easily measurable waves. You can't stop the molecules vibrating because there's too many of them and they're not enough in sync. Rather, what you need would be a kind of heat wave interferometer near your heat source. It sounds fairly remote to me, but maybe not ultimately ( very long term) impossible.

The second problem is that a process that generates, say, a few megawatts of heat will produce only a few kilowatts at best of noise; typically even less. So you need only moderate acoustic power to cancel out strong (>100 Db) noise, but to cancel out the heat of, say, a rocket engine, you'd have to produce the same heat flux again. This really limits your options. It miiiiight work out if you have a very special situation, say a very thin heat-conducting structure that has one end in a hot environment and the other needs to be cold, but I'm very sceptical about this.

Happy Weekend anyway :)
Max

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Post    Posted on: Sat Apr 11, 2009 3:14 pm
The idea of active heat cacelation in principle sounds interesting to me although the idea posted initially seems to be unrealistic.

But isn't the comcept of cooling suggested and conceived by t/Space something like active heat cancellation? Those psrts of the vehicle heated are cooled by water.

That means the water wil be heated. To what temperatured? Wil it be turned into steam? Then something might be done by the steam? Might it be turned into a jet causing deceleration or directing the vehicle so that the heated surface is minimized? Might the steam be used to drive a power source that might cause magnetic cooling? ...

Wouldn't that be active heat cancellation as well?



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


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Post    Posted on: Sat Apr 11, 2009 3:45 pm
Energy can not be created or destroyed it can only change form. Anything moving in air is going to create heat. I suggest removing the air. Everything has a resonate frequency I suggest a field of resonance around the object that disrupts the Nitrogen atoms. How do you do that? The atoms the object is made of must resonate at this frequency and maintain structural integrity. Can we do that? I don't know yet.

Monroe

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Post    Posted on: Tue Apr 14, 2009 12:28 pm
The SF book Sundiver by David Brin has a 'sunship' which uses a form of active heat disipation. It converts the heat from the hull to electricity (however you want to do that), then uses the electricity to power a laser, which fires out behind the craft 'getting rid of' the energy as a laser beam.

You just have to be careful where you aim the laser.


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Post    Posted on: Tue Apr 14, 2009 6:49 pm
JamesHughes wrote:
The SF book Sundiver by David Brin has a 'sunship' which uses a form of active heat disipation. It converts the heat from the hull to electricity (however you want to do that), then uses the electricity to power a laser, which fires out behind the craft 'getting rid of' the energy as a laser beam.

You just have to be careful where you aim the laser.

That could work, if you had a laser that was powered by heat, with a high efficiency. All lasers we know have a really bad efficiency, like less than 10%. The rest is waste heat.


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