Paul Scherrer Institut
  • Villigen, Switzerland
Recent publications
The catalytic combustion of H2/CO/O2/N2 mixtures over PdO was investigated at pressures 3 to 10 bar, H2:CO volumetric ratios 1:5 to 3:1, and global equivalence ratios φ = 0.13 and 0.23. The catalyst surface temperatures were controlled to 540–690 K, a range especially important for hybrid hetero-/homogeneous combustion approaches with large gas turbines at idle or part-load operation and for microreactors with recuperative small-scale turbines. In situ Raman measurements determined the major gas-phase species concentrations over the catalyst boundary layers in a channel-flow reactor, thermocouples monitored the surface temperatures, and surface characterization identified the catalyst oxidation state (PdO) and surface morphology. A 2-D CFD code with a detailed catalytic reaction mechanism simulated the experiments. Simulations and measurements of the combustion of the individual fuel components revealed pressure dependencies ∼p0.74 and ∼p0.10 for the CO and H2 reactivities, respectively, at the investigated equivalence ratios. In the combustion of H2/CO blends, transition temperatures (TTRAN) were identified, below (above) which H2 inhibited (promoted) chemically the oxidation of CO. The transition temperatures decreased with increasing H2:CO volumetric ratio, pressure, and equivalence ratio. Sensitivity analysis indicated that the H2 and O2 adsorption reactions had the larger inhibiting effect on CO oxidation, particularly at lower pressures. Comparisons with other noble metals showed that the PdO transition temperatures were higher than those on Pt and Rh. Even though this behavior favored Pt and Rh for the ignition of syngas in practical catalytic burners, the H2 and CO kinetic coupling (H2 inhibition) was considerably weaker on PdO at T < TTRAN, thus rendering PdO also potentially suitable for low temperature syngas ignition.
The catalytic (heterogeneous) and gas-phase (homogeneous) combustion of C3H8/O2/N2 mixtures over rhodium was investigated experimentally and numerically at 5 bar and at fuel-rich equivalence ratios φ = 2.0-3.5 relevant to propane Catalytic Partial Oxidation (CPO). In situ spatially-resolved Raman measurements of major gas-phase species concentrations and Planar Laser Induced Fluorescence (PLIF) of formaldehyde were applied in an optically accessible channel-flow reactor to monitor the catalytic and gas-phase processes, respectively, while accompanying 2D simulations were carried out with detailed hetero-/homogeneous chemical reaction mechanisms. Due to the high gas-phase reactivity of propane, homogeneous chemistry could not be ignored over most of the reactor's oxidation zone length (upstream zone where the deficient reactant oxygen is not fully consumed). The presence of gas-phase chemistry deteriorated the otherwise high catalytic syngas (H2 and CO) selectivities over the oxidation zone. Raman measurements of major gas-phase species concentrations over the restricted oxidation zone length without appreciable gas-phase chemistry showed that the catalytic reaction mechanism slightly underpredicted (overpredicted) the H2 (CO) formation. The same behavior was also attested over the remaining length of the oxidation zone where combined catalytic and gas-phase chemistry was present. The production of considerable amounts of H2 at the highest investigated equivalence ratio of 3.5 accelerated the onset of homogeneous ignition and the formation of strong flames. The discrepancies between measured and predicted homogeneous ignition distances were less than 6.8% in all cases, illustrating the validity of the employed hetero-/homogeneous kinetic schemes. Contrary to past methane CPO studies, the contribution of gas-phase chemistry and the formation of strong flames in propane CPO was detrimental to syngas production.
Magnetoelectric phenomena are intimately linked to relativistic effects and also require the material to break spatial inversion symmetry and time-reversal invariance. Magnetoelectric coupling can substantially affect light–matter interaction and lead to non-reciprocal light propagation. Here, we confirm on a fully experimental basis, without invoking either symmetry-based or material-specific assumptions, that the optical magnetoelectric effect in materials with non-parallel magnetization ( M ) and electric polarization ( P ) generates a trilinear term in the refractive index, δ n ∝ k ⋅ ( P × M ), where k is the propagation vector of light. Its sharp magnetoelectric resonances in the terahertz regime, which are simultaneously electric and magnetic dipole active excitations, make Co 2 Mo 3 O 8 an ideal compound to demonstrate this fundamental relation via independent variation of M , P , and k . Remarkably, the material shows almost perfect one-way transparency in moderate magnetic fields for one of these magnetoelectric resonances.
Muons are particles with a spin of ½ that can be implanted into a wide range of condensed matter materials to act as a local probe of the surrounding atomic environment. Measurement of the muon’s precession and relaxation provides an insight into how it interacts with its local environment. From this, unique information is obtained about the static and dynamic properties of the material of interest. This has enabled muon spin spectroscopy, more commonly known as muon spin rotation/relaxation/resonance (μSR), to develop into a powerful tool to investigate material properties such as fundamental magnetism, superconductivity and functional materials. Alongside this, μSR may be used to study, for example, energy storage materials, ionic diffusion in potential batteries, the dynamics of soft matter, free radical chemistry, reaction kinetics, semiconductors, advanced manufacturing and cultural artefacts. This Primer is intended as an introductory article and introduces the μSR technique, the typical results obtained and some recent advances across various fields. Data reproducibility and limitations are also discussed, before highlighting promising future developments. Muon spin spectroscopy examines how muons interact with their local environment through measurement of the muon’s precession and relaxation. This provides unique information about the static and dynamic properties of a material. This Primer gives an introductory overview to muon spin spectroscopy, describing how muons are produced and used experimentally in various applications.
The critical region of unmoderated molten salt reactors consists in a cavity filled with a liquid fuel. The lack of internal structure implies a complex flow structure of the circulating fuel salt. A preliminary core shape optimization has been performed during the EVOL European project to limit recirculation and hotspots. This optimization was based on a Reynolds Averaged Navier Stokes (RANS) approach, but the latter only provides time-averaged values for velocity and temperature. However, the power stability is sensitive to thermal fluctuations induced by the flow turbulence itself, even at steady state without pump flow rate or heat extraction variation. This phenomenon is studied using a Detached Eddies Simulation approach to solve the turbulence in the reactor and get a time dependent temperature distribution and then the reactivity fluctuations. A new geometry is proposed to limit the total power fluctuations from 7.5% for the preconceptual EVOL geometry down to 1.2%.
The electrification of heating, cooling, and transportation to reach decarbonization targets calls for a rapid expansion of renewable technologies. Due to their decentral and intermittent nature, these technologies require robust planning that considers non-technical constraints and flexibility options to be integrated effectively. Energy system models (ESMs) are frequently used to support decision-makers in this planning process. In this study, 116 case studies of local, integrated ESMs are systematically reviewed to identify best-practice approaches to model flexibility and address non-technical constraints. Within the sample, storage systems and sector coupling are the most common types of flexibility. Sector coupling with the transportation sector is rarely considered, specifically with electric vehicles even though they could be used for smart charging or vehicle-to-grid operation. Social aspects are generally either completely neglected or modeled exogenously. Lacking actor heterogeneity, which can lead to unstable results in optimization models, can be addressed through building-level information. A strong emphasis on cost is found and while emissions are also frequently reported, additional metrics such as imports or the share of renewable generation are nearly entirely absent. To guide future modeling, the paper concludes with a roadmap highlighting flexibility and robustness options that either represent low-hanging fruit or have a large impact on results.
This work focuses on tests for control reserve of a novel Power-to-Gas-to-Power platform based on proton exchange membrane technologies and on pure oxygen instead of air in the re-electrification process. The technologies are intended as a further option to stabilize the power system, therefore, helping integrating renewable energy into the power system. The tests are based on the pre-qualification tests used by Swissgrid, but are not identical in order to capture the maximum dynamics by the plants. The main characteristics identified are the ramping capabilities of ±8% per unit per second for the electrolyzer system and ±33% per unit per second for the fuel cell system. The ramping capabilities are mainly limited by the underlying processes of polymer electrolyte membrane technologies. Additionally, the current and projected round-trip efficiencies for Power-to-Gas-to-Power of 39% in 2025 and 48% in 2040 are derived. Furthermore, during the successful tests, the usage of oxygen in the present Power-to-Gas and Gas-to-Power processes and its influence on the dynamics and the round-trip efficiency was assessed. In consequence, fundamental data on the efficiency and the dynamics of the Power-to-Gas-to-Power technologies is presented. This data can serve as basis for prospective assessments on the suitability of the technologies investigated for frequency control in power systems.
This paper presents the results of large-eddy simulation (LES) of a downward wall jet that encounters an upward flow in a vertical rectangular channel, named negative buoyant fountain (NBF). The downward jet fluid has higher temperature than the opposing upward stream so that the influence of the buoyancy force on the physics of the mixing process can be investigated. Two subgrid-scale models available in the OpenFOAM platform, i.e. the dynamic k-equation model (DKM) and the wall-adapting local eddy-viscosity (WALE) model, are used for cross-comparison. The numerical results of the time-averaged and fluctuating velocity fields agree satisfactorily with the experimental data. The LES results form an accurate, high-resolution, three-dimensional database of buoyant turbulent mixing, which has expanded the sparse flow field measurements provided by the experiment, hence the numerical database could be used to validate the Reynolds-averaged Navier–Stokes (RANS) simulation method and to contribute to the turbulence modeling. In particular, the statistics of turbulent heat flux have been analyzed and various turbulent heat flux models have been a priori tested based on the LES numerical database. Such information could be useful for RANS simulation guidelines or for deriving anisotropic turbulent heat flux models applicable for turbulent buoyant flows sharing the similar principal flow structures in complex geometries.
In this paper, we discuss how windows in Euclidean time can be used to isolate the origin of potential conflicts between evaluations of the hadronic-vacuum-polarization (HVP) contribution to the anomalous magnetic moment of the muon in lattice QCD and from e+e−→hadrons cross-section data. We provide phenomenological comparison numbers evaluated from e+e−→hadrons data for the window quantities most commonly studied in lattice QCD, complete with the correlations among them. We discuss and evaluate modifications of window parameters that could be useful in dissecting the energy dependence of tensions in the HVP integral and emphasize that further optimizations require a precise knowledge of the full covariance matrix in lattice-QCD calculations as well.
Application of wood ash to forests can restore pools of phosphorus (P) and other nutrients, which are removed following whole tree harvesting. Yet, the mechanisms that affect the fate of ash-P in the organic layer are less well known. Previous research into the extent to which ash application leads to increased P solubility in the soil is contradictory. We combined synchrotron P K-edge XANES spectroscopy, µ-XRF microscopy, and chemical extractions to examine the speciation and solubility of P. We studied organic horizons of two long-term field experiments, Riddarhyttan (central Sweden), which had received 3, 6, and 9 Mg ash ha⁻¹, and Rödålund (northern Sweden), where 3 Mg ash ha⁻¹ had been applied alone or combined with N every-three years since 2003. At the latter site, we also determined P in aboveground tree biomass. Overall, the ash application increased P in the organic layer by between 6 and 28 kg P ha⁻¹, equivalent to 17–39 % of the initial P content in the applied ash. At Rödålund, there was 4.6 kg Ca-bound P ha⁻¹ (9.5 %) in the ash treatment compared to 1.6 kg ha⁻¹ in the ash + N treatment and < 0.4 kg ha⁻¹ in the N treatment and the control. At Riddarhyttan, only the treatment with the highest ash dose had residual Ca-bound P (3.8 kg ha⁻¹). In contrast, the ash application increased Al-bound P (p < 0.001) with up to 15.6 kg P ha⁻¹. Moreover, the ash increased Olsen-P by up to two times. There was a strong relationship between the concentrations of Olsen-P and Al-bound P (R² = 0.83, p < 0.001) as well as Fe-bound P (R² = 0.74, p = 0.003), suggesting that the ash application resulted in an increased amount of relatively soluble P associated with hydroxy-Al and hydroxy-Fe compounds. Further, there was an 18 % increase in P uptake by trees in the ash treatment. By contrast, repeated N fertilization, with or without ash, reduced Olsen-P. The lower P extractability was concomitant with a 39 % increase in plant P uptake in the N treatment, which indicates elevated P uptake in response to higher N availability. Hence, the application of wood ash increased Al-bound P, easily available P, and P uptake. N fertilization, while also increasing tree P uptake, instead decreased easily available P and did not cause a shift in soil P speciation.
We report an operando neutron imaging study of a commercial ICR 10440 Li ion battery during charge and discharge. The cylindrical battery with a spiral configuration is composed of a multiphase layered oxide cathode and graphite anode. In spite of a two-dimensional nature of the projection data of this time-resolved study, structural and functional details of the neutron radiography study were successfully uncovered and visualized. The spatially resolved measurements with a resolution of 40 µm enabled to observe Li redistribution between the electrodes as well as a circulation of the electrolyte between the central column and the electrode layers at different states of charge (SoC) and at different current rates. Furthermore, ex-situ tomographic studies of the battery revealed the fine details of the structural inhomogeneity within the cell.
A new thermal lattice Boltzmann scheme for the simulation of heat transfer and phase change in multiphase flows based on the pseudopotential formulation is introduced. The model includes a novel elaboration of the equilibrium distribution function, source term, and off-diagonal elements of the relaxation matrix. The resulting equation formally recovers the macroscopic advection-diffusion equation for energy transport avoiding unwanted non-physical terms. Moreover, the thermal diffusivity can be controlled using relaxation factors and free parameters of the equilibrium distribution. The new model is applied to simulate the stratification of a van der Waals fluid and the one-dimensional Stefan problem. In particular, the predictive capability of the model is tested against real experimental conditions, finding good agreement in the bubble growth rate and the wall-temperature dependence of the departure diameter.
A comprehensive uncertainty analysis methodology has been established for the modeling of stationary neutron flux oscillations induced by fuel rods vibration in a zero-power reactor. The methodology includes uncertainty propagation and sensitivity analysis. The target event is based on an actual experimental campaign at the CROCUS zero-power reactor and corresponds to the simultaneous oscillation of 18 metallic uranium fuel rods in the periphery of the core. Both the uncertainty propagation and the sensitivity analysis commonly use a large part of the entire analysis process, from the selection of uncertain parameters to the actual code simulations. Applying a random sampling-based approach, the input parameters are sampled N times from their distribution information and used as inputs for N noise simulations using CORE SIM +. The quantity of interest (QoI) is the amplitude of the Auto-Power Spectral Density at various detector locations, which is normalized by the amplitude of the Cross-Power Spectral Density of the reference detector. Their uncertainties are determined following the 4th order Wilks’ formula for two-sided limits. Through the determination of correlations among QoI at the installed detector locations, it is demonstrated that the neutron noise near the area of oscillating fuel rods (noise source) have different behavior compared to the neutron noise further away from the noise source. The following sensitivity analyses are carried out using multiple correlation coefficients within grouped parameters. As expected from the QoI correlations, the QoIs at two different locations (near and far from the noise source) are influenced by different input parameters. Near the noise source, the QoI uncertainty is driven by the uncertainties in the position of the noise source, while the uncertainties in the nuclear data for U-235 and U-238 are the leading contributors further away from the source. This paper provides general information on how to perform the uncertainty analyses for neutron noise simulations, as well as quantitative estimates of the computational uncertainty required for the validation of the computer programs under development for the simulation of neutron noise.
Nodal diffusion codes have been successfully used for decades as a primary tool of commercial power reactor design, safety calculations and plant cycle simulations. The large-size, small-leakage property of these reactor cores and the appropriately generated and applied auxiliary parameters (such as albedos, discontinuity factors etc.) provide a calculation environment, where diffusion theory is fairly accurate, giving the industry the ultimate advantage of fast neutronic computation. Recently, several efforts have been made to extend this methodology to small-core, high-leakage research reactors, in which the validity of diffusion theory is not straightforward. In this paper, the appropriate generation of the diffusion coefficients and their effect on the overall performance of the simulations are investigated in light of recent developments. For the numerical analysis, the two-dimensional DIMPLE benchmarks and the BME TR core benchmark problems were chosen. Group constants were generated with the Serpent 2 Monte Carlo code, while nodal diffusion calculations were carried out with the PARCS code. The results were assessed in terms of multiplication factor, assembly level power and two-group flux distributions.
Evaporative cooling is a promising concept to reduce the fuel cell system volume and mass significantly. This paper investigates the interactions between the fuel cell stack and the balance of plant in an evaporatively cooled polymer electrolyte fuel cell system (PEFCS). For this, a zero-dimensional PEFCS model, comprising the fuel cell stack, air compressor, charge air cooler, humidifier, hydrogen recirculation blower, condensing radiator and water separator has been developed and analyzed. Two evaporative cooling system architectures are compared to conventional, liquid cooling. Optimal operating conditions are determined by a numerical optimization of the net system power output. Main results show that evaporative cooling works on the system level over a wide range of operating conditions. The optimum system power and highest efficiencies are achieved at high temperatures (80–90 °C), low pressure (125–150 kPa) and a corresponding cathode stoichiometry between 1.5 and 3, allowing for a closed water loop at the same time. The air compressor shows an increased power demand, compared to conventional cooling and the exhaust gas condenser is identified as the one critical component for evaporative cooling. Its performance is key to an efficient operation and closed water loop at all ambient conditions.
Calcium aluminosilicate hydrate (C-A-S-H) is the binding phase of both blended cement-based and alkali-activated materials. The intrinsic mechanical properties of non-cross-linked C-A-S-H are important while experimentally unvalidated. Here, the properties are for the first time measured using high-pressure X-ray diffraction. The incompressibility and bulk modulus K0 of C-A-S-Hs are correlated to their nanostructure and stability using nuclear magnetic resonance and X-ray absorption spectroscopies. Al coordination in stable C-A-S-H (Al/Si = 0.1) cured for 546 days is purely tetrahedral (AlIV), while in metastable C-A-S-H (Al/Si = 0.05) cured for only 182 days is both AlIV and pentahedral (AlV). The stable C-A-S-H is stiffer along the a,b,c-axis with higher K0 relative to C-S-H. Short-curing-induced metastable C-A-S-H (Al/Si = 0.05) shows expanded interlayer and softer c-axis, thus lower K0 than C-S-H and the stable C-A-S-H. Our results highlight the stiffening effect of AlIV incorporation and the negative influences of insufficient curing on the nanomechanical properties of non-cross-linked C-A-S-H at Ca/Si = 1.
Topological crystalline insulators (TCIs) with hourglass fermion surface state have attracted a lot of attention and are further enriched by crystalline symmetries and magnetic order. Here, we show the emergence of hourglass fermion surface state and exotic phases in the newly discovered, air-stable ErAsS single crystals. In the paramagnetic phase, ErAsS is expected to be a TCI with hourglass fermion surface state protected by the nonsymmorphic symmetry. Dirac-cone like bands and nearly linear dispersions in large energy range are experimentally observed, consistent well with theoretical calculations. Below TN ∼ 3.27 K, ErAsS enters a collinear antiferromagnetic state, which is a trivial insulator breaking the time-reversal symmetry. An intermediate incommensurate magnetic state appears in a narrow temperature range (3.27 K - 3.65 K), exhibiting an abrupt change in magnetic coupling. The results reveal that ErAsS is an experimentally available TCI candidate and provide a unique platform to understand the formation of hourglass fermion surface state and explore magnetic-tuned topological phase transitions. This article is protected by copyright. All rights reserved.
Water management by gas diffusion electrodes is a fundamental aspect of the performance of electrochemical cells. Herein, we introduce the characteristic constrictions size as a descriptor of the microporous layers...
Koopmans spectral functionals aim to describe simultaneously ground-state properties and charged excitations of atoms, molecules, nanostructures, and periodic crystals. This is achieved by augmenting standard density functionals with simple but physically motivated orbital-density-dependent corrections. These corrections act on a set of localized orbitals that, in periodic systems, resemble maximally localized Wannier functions. At variance with the original, direct supercell implementation (Phys. Rev. X 2018, 8, 021051), we discuss here (i) the complex but efficient formalism required for a periodic boundary code using explicit Brillouin zone sampling and (ii) the calculation of the screened Koopmans corrections with density functional perturbation theory. In addition to delivering improved scaling with system size, the present development makes the calculation of band structures with Koopmans functionals straightforward. The implementation in the open-source Quantum ESPRESSO distribution and the application to prototypical insulating and semiconducting systems are presented and discussed.
Sub-surface clay samples are difficult to characterize using conventional methods so non-invasive Nuclear Magnetic Resonance (NMR) techniques were used to evaluate in a preserved state the pore structure, porosity, water mobility, and affinity of various clay systems. Within the CLAYWAT project launched by the NEA Clay Club, some of the most advanced NMR techniques were applied to samples from 11 clay-rich sedimentary formations (Boom Clay, Yper Clay (both Belgium); Callovo-Oxfordian shale, Upper Toarcian (both France); Opalinus Clay from two sites (Switzerland); Queenston Fm., Georgian Bay Fm., Blue Mountain Fm. (all Canada); Boda Clay (Hungary); and Wakkanai Fm. and Koetoi Fm. (Japan)). The degree of induration within this suite of samples varies substantially, resulting in a wide porosity range of 0.02–0.6. The key finding is the determination of pore-size distribution by NMR cryoporometry in the range of 2 nm–1 μm with the native fluid present in the pore space for most samples. The water volume in pore sizes of <2 nm could also be measured, thus providing a full description of the porosity system. A specific preparation by sample milling was applied to the preserved original cores minimizing disturbances to the samples in terms of water loss. The water content measured by NMR relaxation was comparable to values obtained by drying at 105°C. In general, the narrow T2 distributions indicate that water was diffusing throughout the pore network during the magnetization lifetime, implying that T2 distributions cannot be considered as proxies for the pore-size distributions. For the set of samples considered, the T1/T2 varied between 1.7 and 4.6, implying variable surface affinity. Finally, for most samples, a pore-shape factor of ~2.4, intermediate between a sheet (1) and a cylinder (4), was deduced.
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1,013 members
Rasmus Ischebeck
  • Department Large Research Facilities (GFA)
F. Grillo Ruggieri
  • Center for Proton Therapy (CPT)
Erik J. Berg
  • Research Department General Energy (ENE)
Teguh Citra Asmara
  • Swiss Light Source (SLS)
5232, Villigen, Switzerland
Head of institution
Prof. Dr. Joël Mesot
0041 56 310 21 11
0041 56 310 21 99