Papers by Author: Thomas Fiedler

Abstract: In this paper, the increase of the effective thermal conductivity of paraffin based heat sinks is investigated by making use of cellular metallic matrixes with open cells which are introduced in the thermal low conductive paraffin wax. Lattice Monte Carlo analyses are conducted on different model geometries of such composites composed of a cellular matrixes and paraffin wax. The dependence of the effective thermal conductivity on the cell geometry and the metal foam matrix material is analysed. Furthermore, a diamond coating is simulated in order to estimate its influence on the effective thermal conductivity.

Abstract: In this paper, a Lattice Monte Carlo method is used to determine the effective thermal conductivity in two dimensional models of adhesively bonded metallic hollow sphere structures (MHSS). In contrast to earlier approaches, more realistic distributions of spheres without the simplification of cubic symmetric arrangements are considered in this study. For the Monte Carlo analyses, two-dimensional periodic lattices representing different cutting planes through MHSS are generated. Therefore, an algorithm is used which sequentially fills the lattice by adding cut spherical shells and inclusions in the matrix. Another focus of this work is the analysis of the influence of different geometric circle distributions on the effective thermal conductivity. The findings of the random arrangements are also compared to a regular primitive cubic arrangement and with a Maxwell-type approach.

Abstract: The effective conductivity of 2D porous materials with temperature dependent matrix properties is investigated by two different approaches: namely, a numerical and an analytical method. A model with disjoint parallel cylindrical pores in a representative cell is considered. The numerical method is represented by the finite element method. In the scope of the analytical method, the nonlinear boundary value problem which describes conducting properties of the materials is solved by the methods of complex analysis, and the effective conductivity is represented in an explicit form via the solution of this problem. The values of the effective conductivity obtained by two these methods are compared.

Abstract: In this paper, the Finite Element and lattice Monte Carlo methods are used to calculate the effective thermal conductivity of two models of a composite: circular and square inclusions arranged in a square planar arrangement. A new lattice Monte Carlo method based around Fick’s First Law is also presented. Excellent agreement is found between these quite different methods. It is also shown that the results are in excellent agreement with the century-old Maxwell Equation.

Abstract: Hollow sphere structures (HSS) constitute a group of innovative materials which are characterised by more constant material properties compared to classical cellular metals [1]. Their big potential lies within multifunctional applications where combinations of their proper- ties yield symbiotic advantages. In the scope of this paper their effective thermal conductivity is investigated. In addition to the analysis of the dependency of this material parameter on the conductivities of the base materials and the sphere wall thickness, special focus is given to the influence of the morphology of joining.

Abstract: This paper is on the geometrical effective thermal conductivity of hollow metal sphere structures. Two different technologies of joining, namely adhesive bonding and sintering, are considered. The spheres are arranged in the nodes of a cubic primitive lattice and connected by an adhesive layer, respectively directly joined by sintering. Furthermore, the influence of the cell wall thickness of the spheres on the thermal conductivity is investigated.

Abstract: This paper is on the investigation of adhesively bonded metallic hollow sphere structures. Two different approaches, namely experimental analysis and finite element cal- culations are applied and the findings of both attempts are compared. In the scope of the numerical approach the influence of the mechanical properties of the adhesive on the me- chanical response of the structure is analysed. Based on these results, suggestions for design parameters are derived.

Abstract: In this paper, the geometrical effective thermal conductivity of porous materials is investigated based on two different approaches: the finite element method as a representative for numerical approximation methods and an analytical method for 2D homogenised models based on a solution of the respective boundary value problem. It is found that the relative conductivity is practically independent of the specific shape or topology of the inclusions. Only the morphology (closed-cell or open-cell) of the structure slightly influences the conductivity. Furthermore, it is shown that a small perturbation of the circular inclusions of 2D models increases the effective conductivity.