Effective Permeability and thermal conductivities of graded sintered open cell metallic foams via a multiscale procedure

Abstract

Within an interdisciplinary research group metal foams are investigated, which are meant to be used as effusion cooled wall elements in a combustion chamber of an advanced high efficiency gas turbine. Two of the properties of the metal foams which determine the thermodynamic behaviour of the wall elements are permeability and thermal conductivity. These two properties depend highly on the porosity of the metal foam. Changing the porosity of a metal foam along a direction leads to a gradient in the porosity and thermal conductivity. This grading of metal foams enables adjusting material properties accordingly to the position within the wall element. Metal foams with a gradation in one direction are fabricated and local material properties are determined. The local topology is determined via X-ray tomography. The homogenised thermal conductivity is measured using a Transient Plane Source Technique, also known as HotDisk, and the permeability is measured with a pressure drop experiment. The measurements are done at different positions along the gradation. The experiments demonstrate that the topology of metal foams can be varied within the same foam sample and that properties of the foams like permeability and thermal conductance change accordingly.