Speaker
Description
Phonon transport is fully determining the elastic wave propagation and the thermal conductivity in non-metallic crystalline solids. A typical phonon spectrum involves phonons with a mean free path from nanometers up to millimeters [1], which are frequently comparable or larger than the relevant material or structural length scales. At this length scales, the diffusive picture is replaced by the so-called ballistic one, and most phonon scattering is caused by boundaries and interfaces [2]. Phonon transport modelling needs, then, to go beyond the simple Fourier heat equation. Furthermore, suppose the relevant length scales become even smaller, like in short-period superlattices. In that case, phonons’ interaction with interfaces becomes weaker because they can coherently tunnel through the structure because of wave effects.
In this talk, the new lattice Boltzmann method, the worm-LBM [3], developed to simulate the ballistic phonon transport regime efficiently, will be presented. Moreover, the impact of ballistic and coherent effects on the effective thermal conductivity will be discussed in the framework of time-domain thermoreflectance measurements and molecular dynamics simulations.
[1] J. P. Freedman et al., Universal phonon mean free path spectra in crystalline semiconductors at high temperature. Scientific Reports 3 (2013)
[2] L. Mitterhuber, R. Hammer, T. Dengg, and J. Spitaler. Thermal characterization and modelling of AlGaN-GaN multilayer structures for HEMT applications. Energies 13 (2020)
[3] R. Hammer, V. Fritz, and N. Bedoya-Martínez, The worm-LBM, an algorithm for a high number of propagation directions on a lattice Boltzmann grid: the case of phonon transport. Accepted in Int. J. Heat Mass Transf. (2021)
| Speaker Country | Austria |
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