Topic of the month August 2009


Figure 1: Meaningful visualization of a water-steam flow within a safety-relevant component at 50 times the normal pressure and a temperature of 264 degrees Celsius. Source: Forschungszentrum Dresden - Rossendorf e.V.

The requirements profile of materials that are to be used in the form of cables, wires or contacts is extremely varied, especially with respect to their thermal properties. Properties like high temperature strength, sub-zero toughness or thermal expansion – it’s all in the names: Temperature and heat are frequently key requirements for selecting the right candidate for a specific application. Recent scientific findings demonstrate how these material characteristics are increasingly understood and how technological research and development can turn them into real products.

Customized thermal expansion

Many high-technology products contain components and assemblies that consist of materials with different thermal expansion coefficients. Under extreme temperature conditions or due to process-related waste heat – systems with this kind of characteristics can be frequently found in the relevant industries for the wire and TUBE trade shows –, this fact can lead to time-consuming and costly damage in plants: Overheating, deformation or breakage are only a few examples of possible failure modes. An intelligent solution would be to find a way to match the thermal expansion coefficients of different materials to each other.

This step has recently been taken by scientists at the Fraunhofer-Institute for Production Engineering and Automation (IPA) in Stuttgart. The materials specialists demonstrated that a significant reduction of the expansion coefficient of metals can be achieved when carbon nanotubes are incorporated in the metal matrix, leveraging the negative thermal expansion coefficient of this class of materials. Using a powder-metallurgical process, the scientists produced innovative compound materials from these carbon nanotubes and a number of different metals such as copper and aluminum. They achieved surprising results with the characterization of the expansion behavior using dilatometric methods.

The impacts are conclusive. The most obvious results were achieved with the addition of so-called Single Walled Nanotubes (SWNT). With a three per cent aluminum compound, it was possible to reduce the thermal expansion coefficient by up to 20 per cent compared to conventional aluminum – and that over a wide temperature range.

In the future, the possibility to reduce the thermal expansion coefficient of metals through the addition of carbon nanotubes will be preferred for applications that require complex material combinations to work reliably. This may e.g. include high-performance switches, heat sinks, electrical interconnection components as well as cables and contacts.

Hot films: Visualizing water-steam flows


Figure 2: Reduction of the thermal expansion coefficient of metallic materials through the incorporation of carbon nanotubes (CNT). Source: Fraunhofer Institute for Manufacturing Engineering and Automation (IPA).

Fluid-gas flows are a key component of critical processes in chemical process technology, in nuclear plants and in nearly all areas of the oil and energy industry. The understanding of existing flow processes and the possibility to analyze and evaluate them are essential to make reliable statements about the safety of plants and processes.

For a very long time, it has been technically impossible to visualize the flow of water and steam over large areas at high pressures and high temperatures. Of course, conventional cameras cannot be used here to take a picture since they cannot see through the metallic materials used for the plant components.

Recently, scientists and engineers at the Forschungszentrum Dresden - Rossendorf e.V. presented a newly developed test technology that enables experiments within the context of these critical issues. The experimental setup is characterized by a special chamber that matches the pressure of the atmosphere contained in this chamber to the pressure within the item under test. In this manner, the materials, components and assemblies in this segment are not exposed to high differential pressures and can be provided with large transparent viewing ports, either in central locations or at particularly interesting points. The use of high-performance, high-speed video cameras permits the generation of most meaningful data and images with high spatial and temporal resolution at these points. Partners from all parts of the world have already signed cooperation agreements with the Forschungszentrum Dresden - Rossendorf e.V that allow them to use the technology in their projects. The experimental data gained in this manner may e.g. be used to develop flow calculation methods such as Computational Fluid Dynamics (CFD) Codes as well as for three-dimensional flow simulation.

Dr.-Ing. Christoph Konetschny
Material- und Nanoexperte
www.materialsgate.de


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