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Not sure what geometry you're thinking of. Whatever idea it is, you're stuck dealing with Kirchoff's law, which says optical emissivity and absorptivity are the same number at any given wavelength. I.e., you can't create "one-way trap doors" for heat flow—that would be a Maxwell's demon. Stacking multiple surfaces isn't a way to circumvent this.

If it's just an asymmetric shape, with different material surfaces pointed in different directions, than that of course is permitted.

https://en.wikipedia.org/wiki/Kirchhoff%27s_law_of_thermal_r...

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WalterBright 4 hours ago | parent [-]

Kirchoff's law doesn't say which direction it emits in. As shaped charges can alter the direction of where the blast wave goes, I suspect an analogous behavior of a heat shield can direct where the emissions go. I.e. as you say, an asymmetric shape.

PS I haven't done thermo in nearly 50 years!

	▲	perihelions 4 hours ago \| parent [-]
		V-groove radiators are a really neat, unintuitive design, which gets strong directionality out of thermal radiation. It's the thermal design SPHEREX went with—the space telescope that went up a few weeks ago, that was all over HN. That's: a cavity that's a thin wedge in between two slightly angled plates, where the interior surface coating is partly emissive, and partly infrared-reflective—it can reflect the thermal radiation it emits. That means specular reflections, following geometric optics, so it works like a horn for light—beams it out the sides in a narrow cone. (.pdf) https://ttu-ir.tdl.org/server/api/core/bitstreams/71aee1e9-3...