h a l f b a k e r yMake mine a double.
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
Please log in.
Before you can vote, you need to register.
Please log in or create an account.
|
Let us freak out the world by passively concentrating heat, from within a closed box of air, into a pipe in the center. This appears to violate a thermodynamics law. Over a long time period, the law rules, but for a short while (a million years?) entropy can be reversed. With today's technology, this
seems stupidly simple to do. Modern materials science is awesome.
First, I will describe the laughably simple device. When you are done laughing, read the description of how it works. Maybe wrinkle your brow as you think, "That can't be right!?" Then do some calculations and blow your mind. I just finished picking up the pieces of my mind before writing this.
Start with some flat, square, plate mirrors, of material that reflects infrared light well. Assemble these into a cube with the mirrored surfaces on the inside. Run a pipe, with material on the outside that absorbs infrared light, from the center of one face of the cube to the center of the opposite face. Maybe put thermometers on the box and on the pipe. Don't block the path of light bouncing around inside of the cube. That is it. You can laugh now.
Infrared light (photons) is emitted by molecules inside of the cube. Any of those photons which strike a side at an angle other than 45 degrees is redirected through multiple reflections until it strikes the pipe in the center. Concentration efficiency drops due to photons striking other air molecules or being absorbed by the sides due to imperfect reflection or missing the pipe due to diffusion. The temperature difference is further reduced due to conduction losses from the pipe to the air inside the cube. Conduction losses can be minimized if you put a vacuum tube, made of material that passes infrared, around the pipe. How big of a temperature differential can be developed before the pipe radiates as much as it gains is beyond my ability to calculate. I suppose I'll have to invest a little money into experiments to find out. How hot do you think it will get?
In this house we obey the laws of thermodynamics!
https://www.youtube...watch?v=Dc-m9dumEaw
[Voice, May 28 2022]
[link]
|
| |
//Infrared light (photons) is emitted by molecules inside of
the cube. Any of those photons which strike a side at an
angle other than 45 degrees is redirected through multiple
reflections until it strikes the pipe in the center.// |
|
| |
What prevents this process from being bi-directional? I'm
not talking about the same photon being directed back the
way it came; I'm just saying that, if air molecules in the
cube randomly shed photons which hit the pipe, why don't
the molecules of the pipe (including air molecules inside
the pipe) also randomly shed photons which hit air
molecules in the cube? |
|
| |
Maxwell's Demon can stop embellishing his LinkedIn profile;
his job is safe. |
|
| |
It is possible to move heat around a closed system. Only total entropy must rise. |
|
| |
Okay, so you reflect infra-red into a pipe, which absorbs it and gets hotter. Then you use a Stirling engine to generate power from the temperature difference. I can't figure out why it won't work, so I'll have to look it up. |
|
| |
Even if you can't use a Stirling engine doesn't this constantly use energy within itself getting colder relative to the outside? That's a second violation. |
|
| |
So the internet tells me you can have infinite energy movement, you just can't extract energy from the system. So somehow using a Sterling engine breaks this down, and somehow passive reflection and absorption can't perform work that isn't provided by breaking down the materials. |
|
| |
So you make your box and pipe. You put in an engine. The pipe heats up. The engine runs. But the engine will not emit more heat than the temperature difference generates. As a closed system this reaches equilibrium with a tube hotter than its surroundings. When you add the Stirling engine the tube, engine, and surroundings each find their temperature. |
|
| |
//I can't figure out why it won't work// One of my favourite statements. |
|
| |
Why will it get hot? Why the cube? Why a pipe? Isn't this device topologiclly equivalent to holding a rock in front of a mirror? In fact the mirror is superfluous, just have a rock. Does it spontanelously heat up because of photons emitted by the air striking it? |
|
| |
@pertinax, It is bi-directional. What makes it workable is the relatively huge gaps between air molecules. More photons hit the pipe than hit the air molecules. |
|
| |
@Voice, You seem to be conflating the closed system demonstration with the energy extraction mode. The closed system demonstration is only meant to illustrate how ambient heat energy can be concentrated to create a steep temperature gradient from what was a flat gradient, without adding more energy to the system. It is only possible to use energy within a closed system when you are within, and thus part of, that closed system. |
|
| |
As part of the larger system that we live in, the thing may be usable because it concentrates heat from its surroundings. While the pipe gets hotter, the air gets colder. The mirrors also get colder. Then the outside of the box is warmed by the outside air. It's a heat pump with no moving parts. A Stirling engine runs when the temperature difference between one end and the other is large enough. You can do work as long as the engine receives enough heat on one side and dumps it fast enough on the other side. This contraption is roughly equivalent to having water flow uphill by itself, no pumps needed, except at the atomic level. |
|
| |
@pocmloc, You almost got it. It is the topology that makes it happen. To start with, a rock does spontaneously heat up because of photons emitted by the air striking it. It is called "radiant" heating. Radiant heating is part of how a rock warms up to the same temperature as the room it is in. It is a pipe for convenience in drawing off energy to do work. Any object in the center of any mirrored, regular polyhedron will do for a demonstration. It is a cube for convenience in constructing it. Even a rectangle would work. As long as all of the side planes of the polyhedron are all tangent to some spheres that have the same center point, the focal point will be that center point. |
|
| |
Why will it get hot? Hold a rock in front of a mirror and a laser pointer to represent the infrared source. There are at most two specific directions you can point the laser to light up the rock without changing the location of the laser. Photons emitted at random are very rarely going to be traveling in the right direction to hit your rock. Therefore the rock doesn't get hot. With the rock at the center, and the laser pointer anywhere within the mirror lined regular polyhedron, that probability is reversed. There will be very few directions you can point the laser that will 'not' light up the rock. Because almost all of the emitted photons will end up striking the rock now, the rock will heat up very much faster. |
|
| |
But you didn't mention a laser pointer in your original idea. |
|
| |
If you have a laser pointer then you can get heat much more efficiently by taking out the batteries are connecting them to a resistance coil of wire. |
|
| |
When I was young I thought you could make a sort of flash bulb using
"one-way glass". You'd make a cube (or other convex hull), and light
could get in but not out. So it would build up, and when you broke it
the light would all come out at once.
Now I know that it's really semi-silvered glass, and light goes both
ways with equal probability. (And also that the light won't bounce
around forever, it would get absorbed of course.) |
|
| |
I think this has the same sort of flaw. Things which absorb heat
radiate it just as well. Without an exchange of energy with the
environment, the inside of the pipe will remain the same temperature
as the inside of the closed box. |
|
| |
-pocmloc, You are annoying me. I hope you are doing it on purpose. |
|
| |
-Loris, As materials get hotter, they radiate heat away even faster. This is why the idea may be of no use. At some point the pipe will lose heat as fast as it gains heat from the air and the box. The big question is, "How much hotter than the ambient temperature will the pipe get before the losses equal the gains?" If it gains heat at all, the concept is valid, but if the heat gain is too small, then the concept is also useless. When I can afford some IR mirrors I will build it, measure it and find out. Until then it is only a half-baked idea. |
|
| |
My suspicion is that the whole thing will simply sit at ambient.
But I've been wrong a lot lately. |
|
| |
Sure.
You can trap stray photons in a single place so that it heats up and radiates hotter than its surroundings. |
|
| |
As simple parabolic dish with some charcoal at its focal point shows this. |
|
| |
Not sure what is new other than trying to make a one-way mirror behave the way charcoal would. It should radiate more slowly than it collects. There is no amplification, just storage. |
|
| |
[2 fries], does the charcoal-in-a-dish still work if the parabolic
dish is covered so that no external energy source (such as
sunlight) is shining into it? |
|
| |
Ah I see now. In that case, no. |
|
| |
Max was one of only a few people I enjoyed having
exchanges with here, and now they're all either
dead; have deleted their accounts or just don't
post anymore. I don't post that much either
anymore for a variety of reasons. |
|
| |