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Saarland University, Germany, reports that its engineers are using shape memory alloys to develop a new method of cooling in which heat and cold are transferred by a nickel-titanium alloy. An extensive series of tests have yielded results that are now being exploited to develop a prototype cooling circuit that will further increase the efficiency of the process. If a nickel-titanium wire or sheet is deformed or pulled in tension, the crystal lattice structure can change, creating strain within the material. This change in the crystal structure, known as a phase transition, causes the shape memory alloy to become hotter. If the stressed sample is allowed to relax after temperature equalization with the environment, it undergoes substantial cooling to a temperature about 20 Centigrade degrees below ambient temperature. ‘ "The basic idea was to remove heat from a space – like the interior of a refrigerator – by allowing a pre-stressed, super-elastic shape memory material to relax and thus cool significantly. The heat taken up in this process is then released externally to the surroundings. The SMA is then re-stressed in the surroundings, thereby raising its temperature, before the cycle begins again," explains Stefan Seelecke, Professor for Intelligent Material Systems at Saarland University. In the experimental and modelling studies carried out so far, the researchers at Saarland University and the Center for Mechatronics and Automation Technology (ZeMA) in Saarbrücken have demonstrated that this type of cooling works, and that it can be used in practice. They used a model system to determine how to optimize the efficiency of the cooling process, examining such factors as how strongly the material has to be elongated or bent in order to achieve a certain cooling performance, or whether the process is more effective when carried out slowly or more rapidly. A thermal imaging camera was deployed to analyze precisely how the heating and cooling stages proceed. The German Research Foundation, which has been funding the project for the last three years, has agreed to invest a further 500,000 euros. In total, the project has brought around 950,000 euros in funding to the region.

Kuhn K.,Laboratory for Measurement Technology | Kuhn K.,FESTO | Pignanelli E.,Laboratory for Measurement Technology | Pignanelli E.,Center for Mechatronics and Automation | Schutze A.,Laboratory for Measurement Technology
IEEE Sensors Journal | Year: 2013

Based on a low-cost micro-machined infrared (IR) source with subsequent gas specific filter, photoacoustic absorption (PA) measurements were investigated in a nonresonant operating mode of a gas cell. In addition, nondispersive IR (NDIR) transmission measurements based on a thermopile detector were used to expand the measurement range, but also for an inherent self-monitoring scheme of the system. Compared to other systems using expensive laser sources for stimulation of acoustic pressure waves in a resonant mode of operation, the approach is based on low-cost components. The IR source was modulated in the frequency range between 1 and 10 Hz. To achieve enhanced resolution and a good signal to noise ratio the sensor raw data-both for transmission as well as absorption measurements-were evaluated using discrete Fourier transformation. By combining PA and NDIR transmission measurements a wide concentration range is achieved, e.g., 100-20 000 ppm of carbon dioxide for a measurement cell with a length of 9 cm. Whereas the NDIR transmission measurement is suitable for monitoring higher concentrations, the PA measurement offers better detectivity at lower gas concentrations. Furthermore, the modular system allows the realization of a self-monitoring scheme by comparing the signals measured with both approaches, thus omitting the need for a second filter at a reference wavelength. © 2012 IEEE. Source

Weber O.,Center for Mechatronics and Automation | Weber O.,Saarland University | Weinmann M.,Saarland University | Natter H.,Saarland University | Bahre D.,Saarland University
Journal of Applied Electrochemistry | Year: 2015

The electrochemical dissolution of three cast iron types in NaNO3 electrolyte was investigated by cyclic voltammetry, chronoamperometry, and numerical simulations. The measurements were performed with commercially available materials with different iron matrix compositions and graphite particle shapes: lamellar graphite particles in a ferritic/perlitic matrix, spheroidal graphite particles in a ferritic matrix, and spheroidal graphite particles in a ferritic/perlitic matrix. With regard to electrochemical machining (ECM) applications, the measurements were performed in different kinds of flow cells which realize the high electrolyte flow of an ECM experiment. It could be shown that the electrochemical dissolution was especially influenced by the microstructure of the cast iron and the pH of the electrolyte. Electrochemical measurements as well as numerical simulations show that the graphite geometry and the matrix structure are responsible for inhomogeneities of the electric field in the outer sample surface region which were formed during the dissolution process. The resulting shape of the electric field is responsible for different dissolution mechanisms. The kinetics of the dissolution reaction was influenced in the same manner. Finally, it was found that an alkaline electrolyte pH impedes the dissolution process, whereas no significant difference can be observed between acidic and neutral electrolytes. © 2015, Springer Science+Business Media Dordrecht. Source

Weber O.,Saarland University | Weber O.,Center for Mechatronics and Automation | Natter H.,Saarland University | Bahre D.,Saarland University
Journal of Solid State Electrochemistry | Year: 2015

In this paper, a new layer-based simulation method for predicting the steady-state current of a pulse electrochemical machining (PECM) process is described. The basic concept of the method is a simple two-layer model consisting of a porous oxide and an adsorption layer. The oxide layer of PECM-machined samples, characterized by Raman spectroscopy and electron microscopy measurements, shows a similar structure as the oxide layer formed in electrochemical impedance spectroscopy (EIS) measurements. Therefore, the electronic equivalent circuit developed according to EIS results was used as analogy for the description of the overall impedance of the PECM model. The difference between the assumed layers of a PECM and EIS measurement is modeled with a material-dependent adjustment function. In this way, the calculated values of the equivalent circuit elements can be directly derived from experimental PECM data. It could be shown that the procedure allows the calculation of the steady-state current of PECM processes for different work conditions (e.g., pulse on-times, pulse frequencies). The procedure is applied to the electrochemical dissolution of three different types of cast iron in NaNO3 electrolyte on realistic machining conditions. All samples were characterized according to their chemical composition, graphite particle morphology/structure, and their anodic dissolution behavior. © 2015 Springer-Verlag Berlin Heidelberg Source

Zapp N.,Saarland University | Weber O.,Center for Mechatronics and Automation | Weber O.,Saarland University | Natter H.,Saarland University
International Journal of Electrochemical Science | Year: 2015

The corrosion behavior and the electrochemical dissolution of three different cast iron types and one high purity iron sample in NaNO3 electrolyte (25°C, 1 M, pH: 7) were investigated by comparing three different cell setups: a relatively simple beaker-cell, a small-sized capillary flow-cell and a high-current gap-cell. The electrochemical cell types differ in electrolyte flow rate, size of the measured sample surface and applied current density. The work aims at investigating the electrochemical dissolution of inclusion containing materials (cast iron) and the evolution of a strategy that allows the determination of process parameters used for the design of electrochemical machining (ECM) processes. All samples were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy and scanning electron microscopy. Electrochemical characterization was carried out by cyclic voltammetry and chronoamperometry experiments. It could be shown that the electrochemical dissolution behavior was dominated by the matrix structure and the geometry of the included graphite particles. The determination of corrosion potential and -current were mainly influenced by the electrolyte flow rate. Our new flow cell design (gap-cell) is suited for an easy and fast electrochemical characterization of materials under high current densities. © 2015 The Authors. Source

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