Robust parameter estimation methodology for heterogeneous catalytic reactors

Modeling of Exhaust-Gas Aftertreatment Systems is an important tool for improved understanding and thus improved performance and durability. The challenges for accurate modeling of the multi-scale reactor are many and one important challenge is the interplay between mass transfer and kinetics. Although intrinsic kinetics (without effects from mass transfer) are possible to obtain by analysis of the washcoat separately, many challenges (e.g. washcoat distribution, ageing effects) are best studied using the monolith reactor structure.In this study, a 1+1D diesel oxidation catalyst model was tuned to synthetic catalyst activity test (SCAT) bench data using a robust parameter estimation algorithm based on response surface methodology (RSM). The final residuals (SSE) were compared with experimental uncertainties to enable a statistical F-test to assess the model fit. Two different design of experiment (DoE) design matrices were compared to evaluate potential interaction effects between parameters. While the choice of DoE had different benefits, problems with each design could easily be circumvented.Several parameter estimation cases were compared to investigate the importance of some key algorithm choices:(a) the choice of a weight function for the residual calculation. A weight function sensitive to the experimental observation distribution obtained different fits with different parameter sets.(b) The importance of carefully designed experimental observations. Simulations with catalysts containing an inert washcoat layer proved invaluable for tuning of internal mass transfer coefficients.(c) The importance of experimentally measured constants as initial guesses. The use of intelligent gravimetric analysis (IGA) showed to give a much more suitable initial guess for tortuosity compared to literature data.For all cases, the model fit gave insignificant F-test values (experimental uncertainties were larger than the model residuals), rendering that none of the parameter sets could be rejected. To demonstrate the significance of the different cases, the final parameter set for each case were compared through comparison of ratios of classical timescales, showing the experimental conditions for the various controlling regions of mass transfer and kinetics

Modelling of non uniform washcoat in catalytic monolith reactors

For advances in the design of exhaust aftertreatment systems, modelling can be a valuable tool. There have been various efforts in modelling the diesel oxidation catalyst (DOC) with varying degree of complexity. The simplest 1D models discretize the monolithic channel axially and use an effectiveness factor to account for different washcoat geometries. The more complex 1+1D models also resolve the catalyst washcoat which makes them able to better predict efficiency of e.g. layered catalysts. However, the vast majority of these 1+1D models assume the washcoat to be a uniform slab with homogeneous properties. Thus, they cannot identify tangential washcoat variations which have been found to have substantial effects on washcoat diffusivity (1). In this work a new parallel 1+1D reactor model has been developed. Similar to the sectionalizing method presented by Papadias et al (2), the washcoat is sliced into multiple tangential sections based on an evenly distributed angle. The model then solves each section of the washcoat independently – assuming that no mass is transferred between each section. Preliminary results (see figure 1) compare NO light-off simulations using the original 1+1D model and the parallel model using 3 sections. If the washcoat properties for each section are kept constant, then the conversion efficiency of the parallel model is slightly decreased because of the increased diffusive resistance of the thicker corners. However, if including the local porosity of each section (where the corners show a 13% increase in local porosity based on SEM images), the conversion efficiency of the parallel model is significantly higher because of the increased pore diffusivity in the corners. The proposed methodology enables analysis of local washcoat properties. The results are important for high performance modelling towards zero emission vehicles

Repräsentativer Schulhausbau in der zweiten Hälfte des 19. Jahrhunderts - Zwei Beispiele aus der Stadt Luzern und der Stadt Zürich

In Switzerland, a variety of demographic, social, pedagogical, political, and economic changes led to an increased demand for schoolroom in the second half of the 19th century. The school system played a crucial role in this early phase of the young liberal federal state which became manifest in the construction of prestigious school buildings. The process of defortification and incorporation of villages into cities generated new public spaces for modern school buildings, which had one main purpose: to create well-educated citizens. This paper analyses these processes by examining the making of two school buildings in Lucerne (1857) and Zurich (1897).+repphzhbib2018

Guidance for implementation of ethics and integrity training

The report is a summary of the results of participant breakout sessions to identify best practices and key elements for the implementation of training programmes for researchers in ERI. It is a guidance document for research integrity and ethics practitioners in academia. It identifies the key themes that lead to good practices and essential principles for an effective and successful approach to training. The report focuses on a hands-on approach with a checklist to help create an effective ERI training programme and provides links to relevant resources that help build that training

Use of 3D-printed mixers in laboratory reactor design for modelling of heterogeneous catalytic converters

A method for identifying radial concentration maldistribution in synthetic catalyst activity test (SCAT) benches, is presented, where spatially resolved concentration measurements are not available. The developed methodology was successfully tested for an injection-based SCAT. To resolve the radial concentration maldistribution a static mixer was designed, 3D-printed and inserted upstream the test sample. The methodology could also prove the effectiveness of the mixer, which did not only resolve the concentration maldistribution but also avoided causing reaction disturbances. The resulting increased axial dispersion from the turbulence created by the static mixer was evaluated using a 3D CFD model in Ansys Fluent 19. The axial dispersion of the injection-based SCAT bench was compared to a premixed SCAT bench through classical Aris-Taylor calculations. The results from the axial dispersion calculations show that the injection-based design with the use of a static mixer is far superior to the premixed design – both with regards to pulse broadening but also time delay. This is highly desirable for modelling studies towards zero emission exhaust aftertreatment

Impact of changes in bond structure on ovonic threshold switching behaviour in GeSe2

Raman spectroscopy measurements are performed on sputtered GexSe1x thin films to identify bond presence. A large amount of homopolar bonds are found, including Ge–Ge bonds that can be attributed to Ge clustering. A time-resolved approach to Raman spectroscopy is explored to observe the effect of the high power-density laser on the sample material. Several methods are then used to tailor the structural bond homogeneity (homopolar–heteropolar bonds): annealing, varying sputter deposition pressure and the addition of dopants. In particular doping can reduce homopolar bond presence and increase heteropolar bonds presence. The impact of each dopant is supported by calculations of bond enthalpies according to Pauling equation using the approach of Lankhorst/Bicerano–Ovshinsky. Finally, in order to correlate the structural bond presence to the Ovonic Threshold Switching behaviour of (doped) GexSe1x thin films, both DC and pulsed (AC) measurement are performed on metal–insulator– metal (MIM) type test structures. It is found that minimizing homopolar bond presence is beneficial for the leakage current and electrical stability of the materia

Impact of changes in bond structure on ovonic threshold switching behaviour in GeSe2 (vol 35, pg 151, 2020)

Correction for 'Impact of changes in bond structure on ovonic threshold switching behaviour in GeSe2' by Jonas Keukelier et al., J. Mater. Chem. C, 2021, DOI: ; 10.1039/d0tc04086j