A method to characterize asymmetrical three-stage creep of ordinary refractory ceramics and its application for numerical modelling

During operation, thermomechanical stresses occur in refractory linings. Under elevated stress and temperatures, these ceramics experience primary creep, which can further proceed to the secondary and tertiary creep stages. This necessitates a characterization of their three-stage creep behavior. Hence, two advanced uniaxial tensile and compressive creep testing devices are utilized. The Norton-Bailey creep equations and an inverse identification procedure are applied for the evaluation of the creep curves. To account for the full three-stage creep behavior in thermomechanical modelling activities, a creep-stage transition criterion is identified and subsequently implemented together with the Norton-Bailey creep-strain rate representations in a new developed creep model. The finite element simulation results from different creep testing procedures are in accordance with the corresponding experimental results of a magnesia-chromite refractory ceramic. The study also reveals the temperature-dependent asymmetrical creep behavior of the material in terms of the creep-strain rates and critical creep strains.     

Experimental-numerical study and optimization of sound insulation of a finite composite cylinder

The aircraft fuselage is idealized as a composite cylinder, its vibroacoustic properties are studied both experimentally and numerically, and a minimization of the inner pressure of a composite cylinder is conducted with the genetic algorithm (GA). In the optimization, the Acoustic Transfer Vector (ATV), which comes from the boundary element method, builds the relationship between the structural surface velocity and the sound pressure at the specific filed points. Results show that the noise reduction obtained by the experimental and numerical methods have a good agreement; the optimization method which combines GA and ATV show high efficiency and robustness; increase of the bending stiffness of the cylinder can improve the noise reduction at low frequencies; both the reduction of weight and the increase of noise insulation can be achieved by the optimization of the layup at different regions of the cylinder individually.     

Arduino-based slider setup for gas–liquid mass transfer investigations: Experiments and CFD simulations

The implementation of traditional sensors is a drawback when investigating mass transfer phenomena within microstructured devices, since they disturb the flow and reactor characteristics. An Arduino based slider setup is developed, which is equipped with a computer-vision system to track gas–liquid slug flow. This setup is combined with an optical analytical method allowing to compare experimental results against CFD simulations and investigate the entire lifetime of a single liquid slug with high spatial and temporal resolution. Volumetric mass transfer coefficients are measured and compared with data from literature and the mass transfer contribution of the liquid film is discussed.     

Creep testing of carbon containing refractories under reducing conditions

Mechanical testing of carbon containing refractories at high temperatures requires measures to protect the sample from oxidation. Therefore, special setups for tensile and compressive creep testing were developed to prevent the oxidation of carbon in the sample. A MgO-C refractory was selected for a case study. These developments allow the quantification of the tensile and compressive creep behaviour of MgO-C refractories at temperatures up to 1500?°C. The creep parameters are determined by an inverse evaluation method for the obtained experimental data. They enable the consideration of creep in a thermomechanical finite element simulation of refractory linings in service.     

Financial and Ecological Evaluation of Hydrogen Production Processes on Large Scale

Hydrogen is widely seen as energy carrier of the future. Different technologies are under development to produce hydrogen at competitive cost but with significantly reduced carbon footprint. Two conventional technologies, namely, methane steam reforming and coal gasification, are compared based on product cost and carbon footprint with four new technologies, i.e., metal‐oxide cycle, water electrolysis, biomass gasification, and methane pyrolysis. To evaluate the carbon footprint for methane pyrolysis, system extension and differential methods are applied. For the boundary conditions selected here, methane pyrolysis yields very good values for product cost and carbon footprint. Therefore, a cross industry technology development of methane pyrolysis was initiated.     

The effectiveness of coincidence site lattice criteria in predicting creep cavitation resistance

The coincidence site lattice (CSL) concept is often used in microstructural characterization by researchers studying grain boundary engineering as a method for improving the performance of polycrystalline materials. It is assumed that a high degree of shared lattice sites in the boundary between two grains will result in improved mechanical properties. For practical application of the CSL concept to experimental results, a maximum deviation from ideal CSL orientation relationships must be defined to distinguish potential CSL boundaries from random boundaries that are not likely to exhibit “special” properties. Several different maximum deviation criteria have been proposed in the literature. In this study, four of these criteria are investigated for their effectiveness in predicting the creep cavitation resistance of boundaries of different CSL character in three model alloys: pure Cu, Cu-Bi, and Cu-Sb. Bi and Sb strongly segregate to Cu grain boundaries and are detrimental to creep life. The experimental observations are compared to simulation results for a non-textured polycrystal. It is observed that only boundaries related to cubic annealing twins (Σ3 and Σ9) exhibit special resistance to creep cavitation, that boundaries with Σ > 3 are affected by the presence of segregants, and that the fraction of non-Σ(3,9) boundaries tracks closely with what would be expected from a random polycrystal. It is shown that more restrictive criteria result in more reliable characterization of the fraction of cavitation-resistant boundaries only because they exclude more non-Σ(3,9) boundaries from the analysis.     

Performance analysis of a steady flamelet model for the use in small-scale biomass combustion under extreme air-staged conditions

Small-scale biomass boiler development is often based on empirical methods resulting in high efforts for experimental test runs using several prototypes. CFD simulations are able to reduce both, development time and efforts for tests and prototypes, supposing that the models reliability is high and its computational effort is low. Extreme air-staging with an initial gasification stage and a subsequent fuel gas burnout in a downstream gas-burner is a promising new method to reduce NO_X and PM emissions in small-scale biomass boilers. Gasification conditions in the first combustion stage lead to high accumulation of gaseous tars in the fuel gas contributing challenges for combustion simulation because common CFD models use 2 or 3-step global methane reaction schemes to describe combustion chemistry. In this work, the performance of a computationally inexpensive steady flamelet model (SFM) together with a detailed reaction mechanism (18 species, 42 reactions) was scrutinized. In order to evaluate the performance of the SFM, two furnace designs were examined, running under different load shifts and various excess air ratio. Comparative numerical simulations were performed with classical species transport models. The numerical simulations and the experiments for validation were carried out on a wood-chip boiler with a heat output of 40 kW. Results show that flue gas temperature, flame shape, main flue gas concentrations and NO_X can be quantitatively predicted. The SFM shows also reasonable good predictions for CO variation trends. With the present approach, calculation time can be reduced by 90% compared to commonly used models (EDC). The SFM provides sufficiently accurate results within 24 h using a standard processor consisting of six cores (mesh size 1.5 million elements). Thus, the presented model is a perfectly suitable method for applied science and industrial research.     

A large-scale investigation of lateralization in cortical anatomy and word reading: Are there sex differences?

The authors report findings of a large-scale, multitask investigation of sex differences in both structural asymmetries and lateralization of word reading. Two hundred participants were tested in eight divided visual field lexical tasks, and each received a structural magnetic resonance imaging scan. The authors examined whether there was evidence for sex differences in overall measures of neuroanatomical and behavioral lateralization, in specific language tasks and brain regions, and in variation in asymmetry within and across tasks and brain regions. There was very little evidence for sex differences on any behavioral measure. The few indications of sex differences in the current report accounted for 2% or less of the individual variation in asymmetry and could not be replicated in independent subsamples. No sex differences were observed in the asymmetry of structures in Broca's and Wernicke's areas such as pars triangularis, pars opercularis, the planum temporale, planum parietale, or Heschl's gyrus. There were also no sex differences in the variability of neuroanatomical asymmetries within or between brain regions. However, a significant relationship between planum temporale and behavioral asymmetry was restricted to men. (PsycINFO Database Record (c) 2010 APA, all rights reserved)