NotReallyKelvin
Materials
- Jun 20, 2014
- 6
A few vague references out there say you can't just state a thermal conductivity for a bulk material, for example insulation used in building construction, because it depends on thickness. Anybody know what this is getting at? Trivially, packing a flexible insulation into a smaller volume spoils its resistivity, and if manufacturing methods change for different weight insulations their intrinsic properties may change, and making stacks of sheet insulation may give different effective bulk conductivities for the stack because all the contact conductances between layers need accounting for, and if thermal radiation penetrates the sample then thermal conductivity will poorly model the system behavior. But references make it sound like it's the fault of Fourier's law itself.
Another example concerns layers of silicon in integrated circuit manufacture. There is a new issue, Kapitza resistance, involving resistance at atomically perfect bonds because the mechanism of conduction changes or because phonons scatter at the interface due to lattice discontinuities. For example alternating layers of bismuth and diamond create great resistance because the conduction mechanism alternates between the electron gas and phonon conduction. Maybe this reference is just failing to consider these interfaces separately from the bulks, but it doesn't sound like it.
So -- Fourier's law might be repealed, or what?
Thanks!!
Another example concerns layers of silicon in integrated circuit manufacture. There is a new issue, Kapitza resistance, involving resistance at atomically perfect bonds because the mechanism of conduction changes or because phonons scatter at the interface due to lattice discontinuities. For example alternating layers of bismuth and diamond create great resistance because the conduction mechanism alternates between the electron gas and phonon conduction. Maybe this reference is just failing to consider these interfaces separately from the bulks, but it doesn't sound like it.
So -- Fourier's law might be repealed, or what?
Thanks!!