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Flat 1x1 meter plate. Heat source indicated by red arrow. The rest is in space. No sun exposure at all.

Parallel plates

Some of the photons will exit through the gaps between plates. No problem. My question is about the photons that do make it from plate to plate.

One photon leaves the first plate and is received by the second. Is this transfer of heat 100% efficient? If not, why? If the energy does not go into heat, where does it go?

A variant of this question would be a hypothetical sphere heat source inside a much larger hollow sphere in space. Is heat transfer through radiation from the small sphere in the center to the larger outer sphere 100% efficient?

Let's define the term: "100% efficient" is taken to mean that one unit of energy carried away by a photon from the source delivers one unit of energy to the destination.

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  • $\begingroup$ It depends on what the plate is made of and its thickness. It can block or reflect infrared photons or just pass through depending on the material. $\endgroup$ – Star Man May 21 '20 at 16:31
  • $\begingroup$ What material would allow 100% of IR to pass through? $\endgroup$ – martin's May 21 '20 at 19:48
  • $\begingroup$ Nothing will allow 100% of IR to pass through but different materials will block more and other will block less. $\endgroup$ – Star Man May 21 '20 at 22:10
  • $\begingroup$ If there is a continuous source of heat X then temperatures will rise until equilibrium is established and thermal radiation to space equals X. Each layer has a temperature and produces its own thermal radiation in addition to transmitting and reflecting thermal radiation from the source and from other layers. This has to be set up as a mildly complicated set of equations and solved carefully to find the equilibrium or steady-state inter-layer fluxes and temperatures. $\endgroup$ – uhoh May 21 '20 at 22:37
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    $\begingroup$ I’m voting to close this question because it belongs in the physics SE. While it is vague, it could be edited to be more focused. Regardless, it doesn't belong here. $\endgroup$ – Anton Hengst May 22 '20 at 22:11

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