# Optimizing surface geometry for thermal radiation

I'm working on vacuum technology for a scientific project and one of the challenges is to optimize the cooling of 2500°C metals in vacuum. I'm wondering if it would be useful to design a grating on the surface of the metal for improved thermal radiation (bigger surface -> better thermal radiation) which would approximately look like this:

Unfortunately I haven't found any papers on this using Google. So the question is if

1. this is a viable option for better cooling at all
2. how the surface should ideally look like (if the angle is too high, a thermal ray would be just absorbed by the adjacent peak) and if you use a blaze layout (not typically used for radiation ;)) how big the ideal angle should be
• I wonder if any sort of microstructure would last long on a metal surface that is 2500°C hot. Mar 13, 2015 at 12:19

If your surface would be a perfect black body, there is pretty much nothing to do. As you said, more radiation is initially generated from the surface, but also more is self-absorbed. These two effects exactly compensate each other. Indeed, if you would put this object into to a thermal radiation bath, the II law of thermodynamics tells us that the object must always radiate as much as it absorbs. Two bodies of the same macroscopic shape (perhaps one with this grating and other without) absorb the same amount of radiation, thus they must also radiate equally.

However, if your surface is not a perfect black body, your idea actually works to some extent. The rougher the surface, the more an incoming ray will have to bounce before escaping, increasing the probability of absorption. Thus our surface becomes darker. Darker surface radiates more.

If you mean 'accelerate' rather than 'optimize' and if you are in an environment where there is no radiation coming back (as in empty space for example), then increasing the surface area will increase the radiated energy since the process depends on the temperature of the surface as well as the surface area. The orientation of the surface should be such that it does not reflect onto itself only. If you have radiation exchange on the other hand, the exchange will depend on the relative surfaces orientation as well and you need to look up formulae for what is known as the 'shape factors'.