2 ms·

Wouldn't the limiting factor be the outer layer? I'm not sure what layering would give you, or what adding a container would give you. For short bursts this may

by IanCal 2y ago

Wouldn't the limiting factor be the outer layer? I'm not sure what layering would give you, or what adding a container would give you. For short bursts this may make a difference but the steady state means the system as a whole needs to radiate out that energy somewhere. More mass gives some kind of ballast I guess but kilowatts of energy is just a lot to get rid of.

vlovich123 2y ago
It's not about ballast. Black body radiation, which I'm sure you know is the only way heat is dissipated in a vacuum (unless you're the Sun & even then it's still the primary way), is defined as: P = ε * σ * A * T^4 That's the constant, the emissivity of the material, the surface area A, and temperature. We want to increase the temperature differential above what the natural black body radiation can dissipate for a given device (let's take a space probe) and assume we can't change the material. The only thing we can play with is surface area. The point of the nitrogen gas is to leverage normal convection / conduction to dissipate into a larger gaseous volume which then naturally also has a larger surface area. This would then give you more surface area to dissipate across. The reason I'm thinking the layering with different pressure gradients might be useful is that it reduces the overall weight because you need less overall gas for a given dissipation profile (i.e. you need high density beside your heat source to transfer energy away quickly but less density further away because there's a larger surface area growing with the square of the distance away from the heat source). [1] https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law
- mppm 2y ago
  Convection depends on buoyancy and hence gravity, and conduction in nitrogen gas is extremely low, so I don't think your idea would work. You need a conventional radiator with forced circulation.

by IanCal 2y ago

vlovich123 2y ago

It's not about ballast. Black body radiation, which I'm sure you know is the only way heat is dissipated in a vacuum (unless you're the Sun & even then it's still the primary way), is defined as: P = ε * σ * A * T^4 That's the constant, the emissivity of the material, the surface area A, and temperature. We want to increase the temperature differential above what the natural black body radiation can dissipate for a given device (let's take a space probe) and assume we can't change the material. The only thing we can play with is surface area. The point of the nitrogen gas is to leverage normal convection / conduction to dissipate into a larger gaseous volume which then naturally also has a larger surface area. This would then give you more surface area to dissipate across. The reason I'm thinking the layering with different pressure gradients might be useful is that it reduces the overall weight because you need less overall gas for a given dissipation profile (i.e. you need high density beside your heat source to transfer energy away quickly but less density further away because there's a larger surface area growing with the square of the distance away from the heat source). [1] https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law

mppm 2y ago
Convection depends on buoyancy and hence gravity, and conduction in nitrogen gas is extremely low, so I don't think your idea would work. You need a conventional radiator with forced circulation.