Browsing by Author "Vartia, Olli"

Porous structures, such as foams make excellent thermal insulators. This happens because thermal transfer by conduction is hindered by the voids in the material. However, heat can still radiate through the material or just past the voids. Due to Stefan-Boltzmann law, heat transfer by radiation can be especially significant for large temperatures, and it follows that thermal transfer models that account for radiation may be necessary in some cases. Several existing models for radiative thermal transfer in porous materials, such as continuum models and Monte Carlo, have been used in the past. What many of these models tend to have in common, is that they are highly specific to the systems they were originally made for and require some rather limiting approximations. A more general method which would only require knowing the material and the geometry of the system would be useful. One candidate for such a method, discrete dipole approximation for periodic structures, was tested. In the discrete dipole approximation a structure is discretized into a collection of polarizable points, or dipoles and an incoming electromagnetic planewave is set to polarize it. This has the benefits that it accurately takes into account the target geometry and possible near field effects. It was found that this method is limited for high wavelength, by computation time and for small wavelengths by errors. The cause of the errors for small wavelengths was not entirely caused by the discretization and remains not fully understood.