Porous materials for solar thermal and spin-off applications

This presentation gives an overview on latest research activities in the field of hot gas flow through highly porous materials. The overall objective is to describe the thermal behaviour of these kinds of materials when applied as solar air receivers for solar tower technology. In this application, concentrated solar radiation heats up the material, which continuously transfers the energy to an air circuit. After that, the hot air feeds a steam turbine process. Since equivalent physical processes as well as similar materials are involved a number of spin off activities such as effusion cooling, particle filtration and micro heat exchanger arose from the solar application. The presentation includes a short description of the solar application as well as the further activities and the corresponding material requirements. In all of these applications the temperature and fluid velocity distribution inside the porous material is of special interest. Methods to analytically or numerically calculate these quantities are presented. An appropriate modelling of the physical processes requires a precise determination of homogenized material properties such as effective heat conductivity, volumetric heat transfer coefficient and permeability constants. Methods to determine these quantities experimentally as well as results of selected materials are shortly presented. Finally, an outlook on perspectives and future activities is given