Modelling heat transfer in porous structures, under the influence of fluid flow, among other things
The research activities of the working group “Multiphysics Materials Modelling: Microstructure – Heat and Mass Transfer”, led by Dr. rer. nat. Anastasia August, include the modelling of the heat transfer in porous structures, which, among other things, is influenced by fluid flow. The improvement of the efficiency of heat exchangers, heat collectors and heat storage systems, in dependence of the microstructure and the material properties, is the objective of the work. During the reproduction of the processes, the phase transformation processes of the fluid medium are considered. The work of the research group focuses on the development of an optimal structure of the participating porous materials, such as the structure of a metal foam.
Photograph: Dr. Marco Berghoff
Important Research Projects
Metal foams are materials with excellent properties. They look like beer froth, but without the beer, and basically without partitions between the individual bubbles. Only where three or more bubbles meet is it that material still does exist. These so-called ligaments form an irregular solid mesh, which still possesses many properties of the base material – metal: thermal conductivity, stability, electrical conductivity, and even more properties, such as the lightness, the reduced demand for base material, and especially the large surface, compared to the volume. This surface, for example, enables the heat to be exchanged by the air, which surrounds the ligaments. Because of this property, in connection with the good thermal conductivity of metal, metal foams are very popular in our research within the KIT programme “Energy Efficiency, Materials and Resources”.
Solar thermal energy
Black objects are able to absorb solar energy extremely well. The skin of a polar bear is black, so that it is able to absorb as much energy as possible from the sunlight at the North Pole. The white hairs of its fur, which allow the sunlight to pass through, serve as an insulation of the polar bear's own body heat. On the basis of this principle, heat collectors, consisting of textile spacer fabrics, are developed in the project “Solar Thermal Energy”, in cooperation with the Institute of Textile Technology and Process Engineering, Denkendorf https://www.uni-stuttgart.de/forschung/orp/inst_profile/we/itv.html, which is the project partner. Besides the generation of energy, the storage of energy does, of course, also play an important role. In the second part of the project, new storage systems are examined: small, thimble-sized buckets, filled with paraffin, which are to be positioned directly beneath the textile collector. During melting, paraffin stores the latent heat, and releases it again during solidification. At the CMS, we examine the eligible systems by means of computer simulations, and make suggestions for improvement, with regard to their geometry.
Porous water pipes
Using energy resources in the most efficient manner is an important challenge of the future. In materials sciences, this results in a search for efficient, affordable and practical materials for heat conduction and storage. Metal foams provide a promising solution for energy transmission and energy storage problems, as they possess the capacity to allow fluids to permeate, on the one hand, and a large surface, on the other hand. This enables fluids and other possible fillings to be heated more efficiently. Hereby, the objective is to achieve a heat transfer, which is as high as possible, while, at the same time, the pressure drop is as low as possible. First, these foams are designed in computer simulations, in which the material is tested for different conditions, such as changes in temperature or pressure, as well as for the influence of different pore sizes. Subsequently, a 3D printer is used to produce a model for the investment casting of the optimal foam.
Metal foams are used in the design of water pipes, which release their energy to the water in a more efficient manner.
InSel: Innovative foam structures for an efficient lightweight design
The research project InSel (innovative foam structures for an efficient lightweight design) is a research initiative in Baden-Wuerttemberg, for research on lightweight design, which consists of an association of different universities, extramural institutions and companies, in which the IAM of the KIT is involved. It includes joint research, but also the communication of research results to companies, as well as the networking of the members of the project InSel with other research projects. Thereby, the following three aspects are of primary importance for the members of the project InSel:
Because of the steady advancement of technology, porous structures are popular materials, whose development, however, poses a challenge, such as the development of composites.
The project InSel is supposed to enable the development of porous materials, which so far have not been developed sufficiently. This especially increases the competitiveness of medium-sized companies.
This aspect includes the communication of knowledge to other companies. Moreover, with this interdisciplinary approach, the communication among researchers is to be strengthened.
At the CMS, we participate in the project by performing computer simulations in the field of polymer foams, which serve as preforms during the casting of particularly fine-pored and monodisperse metal foams.