Search

This paper presents intermediate-scale experimental tests of a small 2 x 2 array of ceramic foam absorbers at CIEMAT-PSA (SSPS-CRS tower). Receiver air outlet temperaturesof up to 900 ºC have been reached. The experimental activities are supported by CFD simulations in order facilitate the selection process of the foam geometry for the final eCAPTure receiver prototype (333 kW thermal), which will be installed at the same location. more...

This paper presents the experimental evaluation of two volumetric solar absorber concepts. It compares the thermal performance of conventional foam absorbers with that of an innovative rotary disc absorber design. The moving absorber showed advantages regarding air temperature stability at the outlet and better operability compared to the foam absorber. Unfortunately, it is shown that the innovative rotary disc design in its present form is not competitive, neither in terms of thermal performance, nor regarding mechanical reliability and robustness. The future task is therefore to optimize the mechanical design regarding thermal fatigue, in order to obtain a robust and durable rotary absorber that can be thoroughly evaluated experimentally. more...

Continuous direct foaming techniques for ceramics promise economical and ecological advantages compared to other manufacturing routes. No additional template is needed to generate a foam structure, and no fugitive pore formers have to be burned out. Using only air as the pore former, much lower emissions of waste gases can be achieved during the heat treatment of the foam. The challenge of the direct foaming technique is the control of the metastable wet foam state where foam destabilization processes can change or destroy the foam structure. Complex rheological and microscopic measurements were developed to investigate the relationship between rheological parameters and foam stability. It could be shown that the storage modulus G' is the dominant factor describing the stability of the wet foam. The shear-thinning behavior and the value of the viscosity of the slurry define the possible foam porosity in dependence of the manufacturing parameters of the foaming device. Foamability and foam stability are rheological contrary to each other. The Sauter diameter D32 was used to characterize the pore size. Theoretical calculations of the Sauter diameter D32 could be verified by experimental data. Suitable parameters are shown to produce stable foams with high porosities. more...

A new technology to coat open-celled foams homogeneously by using a vertical centrifuge and shear-thinning slurries is presented. The technology is exemplified by a complex multilayer-coated foam for catalytic applications (Fig. 3). Furthermore, a new calculation model for the estimation of coating thickness and for quality assessment is introduced and proved by comparing the calculated and experimental data. Based on these results, various material combinations are shown, e.g., layers made of rough particles, zeolites, activated carbon, γ-Al2O3, perovskites, mullite, and yttria–alumina–garnet on SiC–, Al2O3–, or cordierite foams. Theses “functionalized foams” can be used for a wide variety of practical applications, e.g., as adsorbents and catalysts in environmental engineering, as preforms for metal matrix composites, and for special purpose applications that require corrosion and oxidation resistance. more...

The structure and phase formation of porous liquid phase sintered silicon carbide (porous LPS-SiC), containing yttria and alumina additives have been studied. The present paper is focused on the system Y-Al-Si-C-O. The systems Al-Si-C-O and Y-Si-C-O have been studied in previous papers [J. Eur. Ceram. Soc. (in press) parts I and II]. The reaction products of the interaction of Al2O3 /Y2O3 with SiC and resulting microstructures were analysed by model experiments. The influences of different sintering atmospheres, namely argon and Ar/CO and different temperatures have been investigated. Thermodynamic calculations and sintering experiments reveal that silicides or carbides can be formed in addition to stable oxides. The main parameters controlling the formation of the different reaction products are the free carbon content, the oxygen activity and the temperature. Using CO containing atmospheres, the decomposition of the oxide additives can be effectively suppressed and stable porous LPS-SiC can be produced. more...

The ecological disaster which has overtaken Vietnam as the result of 17 years of war has been exacerbated by continuing deforestation and hunting for food and trade. The country's two zoos and seven national parks lack adequate resources. This paper reports on the work of the Munster Zoo as an intermediary between the wildlife authorities in Vietnam and European zoos. The resulting co-operation has provided support for particular projects for threatened species and enabled the provision of equipment and finance, as well as training at home and overseas for national park personnel. more...

Cellular materials have become increasingly interesting for applications in combustion environments. Improvements like high power efficiency and low emissions are the main targets of technological development in combustion processes. However, despite scientific and technical success in developing new or improved burner concepts over recent years, a lot of problems remain to be solved in the field of materials science: due to the high power density of the burners the materials are subjected to high loads in terms of thermal shock, temperature and corrosion, especially in so-called porous burner technology. This article shows some examples of research and development strategies and results in developing improved cellular ceramics. more...

Hybrid foams consist of two different interpenetrating or particulate-embedded foam-material classes and, therefore, an enhanced multifunctionality of the material and of the final product can be expected. This paper illustrates the concept of hybrid foams with two selected examples. The cells of an open-cell steel host-foam are filled either with a polymer foam or a newly developed direct ceramic foam. The results of compression tests and non-destructive resonance-frequency-damping analyses are presented. An improvement in the deformation is observed for the metal-polymer hybrid foam, while the deformation behavior changes from brittle to ductile for the metal-ceramic hybrid foams. Additionally, the damping and Young's modulus of the metal foam are enhanced by the interpenetrating direct foamed ceramic. more...

High porosity permeable materials have been manufactured on the basis of the highly uniform structure of foamed polyurethane since the 1950 s. This paper shows the development of open cell foams based on all kinds of steels, titanium alloys, and also open-cell molybdenum foams made by a powder metallurgical replication technique. Such materials show a wide range of physical and mechanical properties, which may be adapted to various requirements. The automotive industry, for example, needs high-temperature resistant materials with high permeability and good strength for catalytic conversion. For orthopaedic implants, the network-like metal foams made of titanium, tantalum, or steel exhibit a bone-like structure. The powder metallurgical replication route represents an economic method to process open-cell metal foams with a unique combination of properties for a wide range of applications. more...

The removal of particles from the hot gas in many advanced coal fired power plants works at high temperatures. To ensure a guaranteed lifetime of about 16000 h the effect of combustion or gasification atmosphere and temperature on the thermal and mechanical properties of the filters has to be studied. This was done for different commercially available and newly developed materials. The materials were exposed to oxidizing and reducing atmospheres with and without ash. Afterwards the properties of these materials were compared to those of new materials and the damage mechanisms were investigated to give hints for a further material development. more...

This paper describes the manufacture of an oxidation protection layer for reticulated silicon carbide foams. The produced foams are investigated by light microscopy, XRD and electrical measurements. The protection efficiency is estimated by weight change, image analysis and electrical resistance. The results indicate a feasible way to protect SiC foams against oxidation. more...

Siliziumcarbid (SiC) ist ein relativ neues nichtoxidisches Keramikmaterial. Es wird getestet, ob unterschiedlich vorbehandeltes SiC im Vergleich zu einer Aluminiumoxid-Keramik (P80) eine geringere Beeinflussung der die Keramik passierenden Losung hervorruft. Hierzu wird ein Kationenstandard, ein Anionenstandard und eine Bodenlosung verwendet. Negativ fallt auf, dass beide Keramiken nahezu unabhangig von der Vorbehandlung Na und Al abgeben. Bezuglich Anionen und geloster organischer Inhaltsstoffe zeigt SiC meist gunstigere Ergebnisse. Es erscheint daher lohnenswert, durch Minimierung von Sinteradditiven und optimierte Konditionierung die Eigenschaften von SiC weiter zu verbessern, um es zur Herstellung von Saugkerzen mit vorteilhaften Eigenschaften verwenden zu konnen. Siliciumcarbide — is it an alternative to suction cups made of aluminumoxide? Siliziumcarbide (SiC) is a novel non-oxide ceramic material. We tested differently preconditioned SiC and aluminum-oxide ceramics (P80) with respect to their influence on the solution passing through. For this we used a cation standard, an anion standard and a soil solution. Both ceramics released considerable amounts of Na and Al. However, in most cases SiC showed better results for anions and dissolved organic carbon. Therefore it may be a promising task to improve the properties of SiC by minimizing sinter additives and optimized conditioning procedures, and develop improved suction cups. more...

This work targets the numerical and experimental evaluation of ceramic foam as solar absorber material for solar thermal power generation. Two different 1-D model types with local thermal non-equilibrium (LTNE) have been developed independently at CENER and Fraunhofer-IKTS. The modeling of radiation propagation inside the foam is considered via two approaches. One approach is based on a discrete-ordinate solution of the radiation transport equation; the other imposes the solar flux defining an exponential attenuation, as derived from Bouguer’s law, and considering thermal radiation transport according to Rosseland’s diffusion approximation. Both models have been successfully checked for consistency against experimental data obtained at a 4 kW solar simulator. Then, the models have been run applying automatic scripts, performing a large number of parameter variations, optimizing for the absorber thermal efficiency. It is important to note that single, double and triple layer absorber configurations have been studied, since previous works found that a decreasing porosity in direction of flow can enhance absorber performance. The parametric optimization studies have shown that the porosity of the foam is strongly related to the obtained thermal efficiency. The higher the porosity of the foam, the higher is also the absorber thermal efficiency. A broad plateau-like efficiency maximum can be observed for cell densities between 30 and 50 PPI (pores per inch). When applying a multi-layer configuration, no significant correlation can be observed between efficiency and the properties of the second or third layer. Only the parameters of the first layer seem to determine the thermal performance. This leads to the conclusion that an optimized single-layer configuration is the absorber of choice. If necessary, a second layer could be applied to satisfy mechanical stability aspects. more...

The structure and the electrical properties of porous and dense liquid-phase sintered silicon carbide ceramics (LPS-SiC), containing yttria and alumina additives, have been studied. The electrical resistance of LPS-SiC-materials varies in a wide range. This paper is focused on the influence of porosity on the electrical resistance of the sintered SiC. The porosity was controlled by the SiC grain size. Porous LPS-SiC materials were found to have substantially lower electrical resistance in comparison to dense materials of the same type. The structure of the materials was investigated by XRD and FESEM. The porous materials consist of large grains due to the coarser starting powders in comparison to the dense materials. This results in a reduction of the dissolved and re-precipitated fraction of the SiC during sintering. Using the in-lens SEM mode, the high conductivity of the formed rims of the SiC grains could be shown. These observations reveal that the rim volume of dense LPS-SiC is much more extended than the rims of porous materials showing the higher conductivity. more...

Micro reaction technology offers the possibility to improve the flexibility, selectivity, and mobility of chemical reactions in the chemical industry, process engineering, or pharmaceutical industry. In comparison with conventional chemical devices, the scale down to a millimeter or micrometer scale will result in remarkable time and cost savings, especially in the area of research and development of smaller- and medium-sized enterprises and at universities. The Fraunhofer Alliance Modular Micro Reaction System (FAMOS), consisting of six Fraunhofer institutes, has developed a software-based micro reaction toolkit provided with all essential elements of conventional chemical devices, e.g., micro reactors, micro mixers, or analyzing modules. All these elements are arranged on a single platform. Besides modules made of other materials, ceramics play a dominant role in micro reactor components. Their chemical and thermal resistance show a number of advantages for application in micro reaction technology, especially in such cases when aggressive media are combined with high temperatures. For this reason, ceramic micro mixers and reaction modules containing multichannel plates for screening of catalysts or ceramic self-heating foam structures were developed. This contribution will introduce the modular micro reaction system FAMOS such as different ceramic modules. It will show the development of the modules including construction, shaping, covering, and testing. more...