Karlsruhe Institute of Technology

This work presents a numerical investigation of the applicability of the product of formaldehyde (CH 2 O) and hydroxyl radicals (OH), denoted as CH 2 O ⋅ OH, as a marker for the local heat release rate (HRR) in CH 4 flames over a broad range of boundary conditions. Both laminar freely propagating one-dimensional and premixed counter-flow CH 4 flames were simulated using several detailed reaction mechanisms. The analysis systematically varied the oxidizer composition (from air to pure oxy-fuel), equivalence ratio ( Φ ), inlet temperature, pressure, and strain rate. The correlation between the CH 2 O ⋅ OH profiles and the HRR was quantified using the Pearson correlation coefficient. Overall, the study confirms CH 2 O ⋅ OH as a practical and reliable HRR marker in CH 4 flames, particularly under high-temperature and high-pressure oxy-fuel conditions. The results show that in slightly rich CH 4 -air flames (about Φ = 1.5 ), CH 2 O ⋅ OH provides an accurate estimate of the HRR. In oxygen-enriched and pure oxy-fuel flames, the strongest correlation shifts to ultra-rich conditions (about Φ ≈ 3.0 ). Increasing pressure enhances the correlation at lower equivalence ratios, whereas preheating weakens the correlation locally but expands the overall range of validity. Although increasing strain rate generally degrades the correlation, CH 2 O ⋅ OH remains a robust marker under technically relevant turbulent conditions (strain rates below 10,000 s − 1 ), maintaining Pearson correlation coefficients of approximately R ≈ 0.9 even close to extinction. This demonstrates the strong feasibility of using CH 2 O ⋅ OH for HRR estimation in highly turbulent flames. The demonstrated robustness of CH 2 O ⋅ OH highlights its suitability as an HRR marker, providing valuable insights for experimental diagnostics. • CH 2 O ⋅ OH confirms as robust HRR marker across a wide range of conditions including variations in oxidizer content, equivalence ratio, preheat temperature, pressure, and strain. • For CH 4 -air flames, the highest correlation between CH 2 O ⋅ OH and HRR occurs at slightly rich mixtures ( Φ ≈ 1.5), while in CH 4 /O 2 flames, the strongest correlation shifts to ultra-rich conditions ( Φ ≈ 3.0). • Elevated pressure generally improves the correlation at leaner mixtures but narrows the range of high correlation, whereas preheating shifts the optimal equivalence ratio to richer conditions and broadens the applicability range. • Even under high strain rates (up to 10,000 s − 1 , relevant for turbulent flames), CH 2 O ⋅ OH maintains a strong correlation (R ≈ 0.9) with HRR, highlighting its suitability for turbulent combustion diagnostics. • The results of this study are intended to support and guide experimental diagnostics by identifying reliable marker regimes.

Numerous industrial applications such as aluminum smelters, electrolysis plants and large data centers, require DC feeding currents of several hundred kA. Within the project DEMO200, a demonstrator for a superconducting single-pole 200 kA DC busbar was developed, including suitable current leads. The demonstrator consists of ten identical modules, each with a current capacity of 20 kA. The ten modules are electrically connected in series since a 200 kA DC source was unavailable for testing purposes. Thus, the magnetic self-field effects and Lorentz forces are the same as in the parallel target configuration, but a 20 kA source is sufficient. The demonstrator has a length of 2 m and its ten modules are each based on sixty 12 mm wide REBCO superconducting tapes. The modules are joined in a compact structure with a diameter of 300 mm which withstands thermal contraction and the large Lorentz forces. The demonstrator's design operation temperature was 70 K, but finally the tests were conducted at 77 K. Despite this shortcoming, DEMO200 carried a current of 10 x 18.9 kADC. The current leads and low ohmic connectors complied with the requirements. As a result, SuprAl, a 600 m long busbar, is now being built for TRIMET in Hamburg and is also presented.

• Nusselt correlation for homogeneous heating describes azimuthally inhomogeneous heating. • Mixed convection is observed for heat flux orientation non-parallel to gravitation. • Buhr criterion underestimates the onset of mixed convection in a horizontal flow. An experimental study of the heat transfer on mixed convection in a turbulent liquid metal flow with azimuthally inhomogeneous heat flux distribution is presented. A horizontal nickel tube is heated in different sections to investigate the influence of heat flux orientation relative to gravity on heat transfer in a liquid metal flow. Four semi-circumferential heat flux distributions (top, bottom, right and bottom right half) are examined. These configurations emulate the azimuthally inhomogeneous heat flux profile that is characteristic of receiver tubes in concentrated solar power plants. The working fluid is a near eutectic alloy of gallium, indium, and tin (GaInSn, P r = 0.03 , ϑ melt = 11 ∘ C ). The Péclet number is varied within a range of 2.4 × 10 2 < P e < 3 × 10 3 , while the Rayleigh number is 1.6 × 10 3 < R a q < 8.2 × 10 3 . For all four heat flux distributions, the correlation for the azimuthally averaged Nusselt number 〈 N u 〉 can be confirmed. The temperature difference along the circumference of the tube reveals mixed convection for heating directions opposing the direction of gravitational acceleration for P e < 7.2 × 10 2 . Based on this quotient, the applicability of the Rayleigh number, the Buhr parameter, the Buoyancy parameter, and the Richardson number as criteria for the determination of mixed convection in liquid metals is discussed. New correlations for the critical Rayleigh number and limits for the Buhr parameter are established.

Offshore wind generators are expected to exceed 15 MVA in the coming years, necessitating compact and light-weight step-up transformers. While high-temperature superconducting (HTS) transformers offer high efficiency and compact size, their complex AC loss behavior in large-scale devices is still not sufficiently understood. In this work, we present a comprehensive investigation on practical strategies for reducing AC loss in a 15 MVA HTS transformer based on the primary industrial criteria of efficiency, weight, and cost. We employed an efficient numerical method to model up to thousands of HTS tapes in low-voltage (LV) and high-voltage (HV) windings in detail. Using this framework, we evaluated the influence of key design and operating parameters on the AC loss, including winding height, axial gap between the cables, radial distance between HV and LV windings, winding height difference, number of parallel conductors, voltage per turn, magnetic flux diverters, and temperature. These analyses enable the development of four improved transformer designs at operating temperatures of 20 K, 70 K, and two configurations at 77 K that balance AC loss reduction with conductor cost and core weight. The results provide validated design principles and practical guidelines for developing next-generation HTS transformers that are compact, light-weight, cost-effective, and suitable for large-scale offshore wind energy systems. • Numerical framework developed for AC loss evaluation in HTS transformers • Impact of key operating and design parameters on AC loss quantified • Reduction of AC loss at winding ends is identified as key design strategy • Design trade-offs between AC loss, conductor length, and cost are analyzed • Optimized HTS transformer designs proposed for 20 K, 70 K, and 77 K

The landscape of modern computing systems is shifting towards architectures built by combining available services under the “everything as a service” paradigm. These architectures are deployed on distributed cloud-edge infrastructures, aiming to provide innovative services to a wide range of users. However, it is crucial for these systems to address environmental sustainability concerns. This poses challenges in operating such systems in open, dynamic, and uncertain environments while minimizing their energy consumption. To tackle these challenges, we propose a decentralized service assembly approach that ensures the assembly is energetically self-sustainable by relying on locally harvested and stored energy. In our contribution, we introduce a general service selection template that enables the derivation of different selection policies. These policies guide the construction and maintenance of the service assembly. To evaluate their effectiveness in meeting the sustainability requirements, we conduct a comprehensive set of simulation experiments, providing valuable insights.

A photovoltaic-powered membrane filtration (PV-membrane) system desalinates brackish water to produce drinkable water using sunlight but is prone to shutdowns – due to solar irradiance fluctuations – that reduce permeate quality and daily yield. Shutdowns occur at certain PV power deviation thresholds ( D th ) that, when identified, can be controlled to operate the system autonomously within certain windows of shutdown resilience during transient operation. This study introduces the resilient operating window (ROW) to investigate PV-membrane system operation under four different configurations – via two membranes (BW30 & NF90) and two pumps (SQFlex 0.6-3 N/20 bar & -2 N/12 bar) – using real-world solar conditions. The BW30/3 N configuration, operated at ~11 bar transmembrane pressure ( TMP ), achieved ~67% shutdown resilience while the NF90/3 N configuration at ~9 bar TMP (constrained) achieved 100% resilience & daily production gains of 8 L and 19 L, respectively, compared to reference uncontrolled operation. The -2 N pump enabled 100% resilience for both membranes, with reduced daily yield for NF90. Results highlight how D th influences shutdowns in PV-membrane systems, and how these can be mitigated for enhanced resilient operation during transient conditions without additional energy buffering support, essential for more robust autonomous PV-membrane water desalination systems. • PV-membrane pump resilient to shutdowns at low TMP set-point/high PV power • PV power deviations thresholds investigated for pump resilience boundary • Defined resilient operating windows for PV-membrane under transient operation • Enhanced resilience with control increases daily production with no energy buffering • Real-world demonstration ⇒ optimal membrane configuration under transient operation

Solid-state dewetting is the process by which thin solid films break up and retract on a substrate, forming nanostructures. While dewetting of single-crystalline films is understood as a surface-energy-driven process mediated by surface diffusion, polycrystalline films exhibit additional complexity due to the presence of grain boundaries. Most theoretical and computational studies have focused on single-crystalline dewetting. Here, we present the application of the grand-potential multi-phase-field model to the dewetting of thin polycrystalline films in three dimensions, reproducing the key phenomenology of this process. By considering isotropic interface/surface energy, we illustrate its consistency with predictions based on energetic arguments and the morphological evolution towards equilibrium. We also provide novel analytical criteria for the onset of three-dimensional dewetting, serving as fundamental theoretical benchmarks, and highlight the critical role of triple junctions. Moreover, we unveil the dewetting behavior of polycrystalline patches, extending the scenarios of their single-crystalline counterparts.