Clausthal University of Technology

In this paper a new modeling approach for denitrification and similar processes, which depend on the geochemical gradient between the air-filled larger pores in a soil and a water-filled matrix, is presented. The new modeling approach is capable of taking soil structural properties (obtained e.g. from X-ray CT) into account without requiring a high-resolution simulation. The model approach is explained and its application is demonstrated by simulating denitrification experiments conducted with repacked soil samples to assess the challenges and possibilities of the new approach. The main result of the modeling is that the nitrous oxide emission measured in the experiment can not be explained by a limited supply with oxygen alone at a carbon turnover rate derived from carbon dioxide emissions. It is additionally necessary that the microbial activity is concentrated in localized hot spots to create anaerobic conditions. This is confirmed by analytical solutions.

Distinctive propagation characteristics of millimeter wave (mmWave) bands require channel sounding for link management. Reported mmWave channel-sounder setups support only simplex operation while depending on bulky and expensive lab equipment; especially for frequency domain channel sounding (FCS), which can be performed with simple hardware. This work presents a solution in the form of a 60 GHz modular front-end designed using off-the-shelf components with tailor-made passive circuits and high-frequency interconnections, all compatible with printed circuit technology. An FCS setup is developed using two units of the designed transceiver front-ends, which can sweep 6 GHz bandwidth with 1 MHz resolution. An antenna duplexing circuitry is also presented, which enables each front-end unit to use a single transmit-receive antenna ensuring a high correlation between the round-trip channels. To the best of the authors’ knowledge, this work reports the first FCS setup, which preserves channel reciprocity in round-trip sounding. The application of the designed system is showcased through a channel reciprocity key generation (CRKG) algorithm, which exploits the high correlation between the forward and receive channels to demonstrate a physical layer security system functional at 60 GHz.

This chapter provides the overview for the relevance of this book, showing the urgent need to transform food supply chains towards more sustainable and circular systems to combat climate change, geo-politically driven food poverty, particularly in Mediterranean region. It analyses and maps citrus by-products supply chains, showing the supply, value chain, and logistics network design in various countries, such as Egypt, Tunis, Turkey, Jordan, and Algeria. Based on this mapping, the weak points for sustainability are identified, while showing the alternative transformation pathways utilizing, e.g. technological advances and life cycle assessment methods towards innovative business models. Moreover, consumer perceptions for sustainable food intake as well as small-scale farming practices, including optimal use of irrigation and pesticides are strongly considered in designing the biological and technological circular supply chain systems. Political and managerial recommendations are derived from sustainability analysis of various future scenarios to design and implement transformation strategies optimally and efficiently.

This book explores the application of integrated sustainability assessment methods in both operational and strategic decision-making processes within food supply chains (FSCs), with a specific focus on citrus supply chains (CSCs). It emphasizes evidence-based practices and encourages decision-makers to implement data-driven approaches to enhance the sustainability, resilience, and circularity of FSCs. To facilitate the implementation of data-driven solutions, the advanced data analytics methodologies have been envisaged to forecast crop yields accurately, optimize supply chain processes, and minimize crop wastage, while opening new markets for citrus by-products. These data-driven solutions empower stakeholders with valuable insights to make informed decisions and achieve operational excellence, meanwhile offering healthy and sustainable nutrition to the consumers. The development of consumer-driven, efficient, and innovative supply chains is crucial for the growth of citrus and fruit consumption in Europe. Furthermore, the information on the different roles along the supply chain can help in understanding the dynamics of the industry, inform decision-makers about leveraging benefits, and identify areas for collaborative innovation mechanisms to enable circular transformation.

The agricultural supply chain involves various activities and processes that facilitate the flow of food products from farms to consumers, including various logistics activities such as packaging and transportation. Sustainable operational practices within the food supply chain play an essential role in delivering fresh and high-quality agricultural products to consumers with fresh and high-quality agricultural products, while optimizing resource utilization, minimizing food loss, and supporting healthy nutrition of the consumers. This chapter aims to discuss the key operational practices and the associated logistics activities along the citrus supply chain to increase sustainability and circularity within the food systems. To achieve this, the chapter reviews the operational and agricultural practices published in the literature, including journal papers, book chapters, and conference papers, which focused specifically on the citrus supply chains and their relationship to citrus loss and waste. Overall, most of the reviewed studies focused on the agricultural practices at the farm level and operational practices in the processing stages, but rarely on the downstream of the supply chain. It has been concluded that the different operational practices have their benefits and challenges, and the choice of methods would depend on various factors such as the available resources, the specific requirements of the citrus variety, and the target market’s regulations. Recommendations for future research were also provided.

Porphyry deposits of the Cu-Mo-Au-Re metal spectrum mainly occur in arc settings, but only some segments of the same arc host significant metal resources. The factors controlling the variable metal endowment in magmatic arcs remain unclear. Here, we conducted zircon U-Pb age, trace element, and Hg isotope studies on the ore-bearing (i.e., fertile) and coeval barren granitic rocks from the Upper Triassic Yidun arc, eastern Tibetan Plateau. The results show that the barren granites from the northern Yidun arc display normal arc magma features, and have low oxygen fugacities (ΔFMQ= -3.7 to -0.5), low water contents. Their negative Δ¹⁹⁹Hg values (-0.20 to 0.02‰) indicate that they were mainly derived from continental basement rocks. The fertile granites from the southern Yidun arc exhibit adakitic geochemical affinity (i.e., high Sr/Y and La/Yb ratios), high oxygen fugacities (ΔFMQ = 0.2 to 2.7), and high water contents. Their positive Δ¹⁹⁹Hg values (-0.07 to 0.23‰) indicate an oceanic source of the Hg and suggest that they were derived from an enriched mantle source modified by oxidizing, subduction-related fluids/melts. The contrasting characteristics of fertile and barren granites indicate that magma sources likely have a critical control on the metallogenic potential of arc magmas, with slab-derived fluids imprinting high fO2 and volatile contents for the formation of productive intrusions in arc settings. Arc magmas derived from oxidized and water-riched magma sources have a predisposition to form porphyry Cu deposits, and should be regarded as priority targets for porphyry deposit exploration.

The welding of steel grades relies primarily on the interaction of the weld metal with doped oxygen components of the shielding gas. This mainly serves to decrease the viscosity and reduce the surface tension of the melt in order to achieve an adjusted material transition. Interference with the ambient atmosphere is undesirable in this context. In order to prevent material-related changes in the microstructure, slag initiators are admixed which promote the precipitation of low-density oxides on the weld seam surface. Manufacturing technology is increasingly striving to eliminate the interaction of atmospheric oxygen in the production process. It is primarily intended to counteract the negative effects of oxygen during manufacturing. For this objective, silane-doped gases for subtractive manufacturing processes and additive manufacturing via the PBF-LB/M process have been considered. Small amounts of silane in conventional inert shielding gases allow partial pressures of oxygen that are comparable to a high vacuum. In the scope of this publication on investigations for welding applications, blind welds on S355 substrate plates were performed using G3Si1 filler material. In addition to the recommended M21, an argon shielding gas with 1.5% silane doping and argon 4.6 are applied for welding. Apart from the observation of the resulting energy input, the weld seams are metallographically characterized. For this purpose, the formation of silicates on the weld seam surface and the development of the weld seam within the base material are investigated. The volume of the weld seam is reduced as a result of the silane doping compared to the M21 application. The composition of the weld metal is significantly influenced by the silane content, leading to an increased manganese content in particular. The silane doping results in an intensified formation of an acicular bainitic structure and an accompanying hardening within the weld metal.

We present a condition under which the thermal quasi-geostrophic (TQG) model possesses a solution that is holomorphic in time with values in the Gevrey space of complex analytic functions. This can be seen as the complex extension of the work by Levermore and Oliver (1997) for the generalised Euler equation but applied to the TQG model.

Filament winding is a manufacturing process used in the construction of fiber composite structures, where a thermoset resin impregnated bunch of fibers is deposited on a rotating mandrel. The evolving stress and strain states due to thermal and mechanical loads during the manufacturing process are of particular interest to avoid subsequent failure of the parts. In this first approach, the mechanical load within the fiber, mainly driven by the pre‐stressed fiber tension, is investigated. Thus, the development of the fiber tension and the pressure on the mandrel as a function of the number of windings is examined. Therefore, models based on the theory of large and small deformations are derived under certain assumptions, resulting in a boundary value problem. In case of large deformations, the boundary value problem using a three‐dimensional formulation based on incompressible, isotropic hyperelasticity does not yield a simple solution. Using a small deformation formulation on the basis of a one‐dimensional consideration an analytical solution can be found. The problems are described in curvilinear coordinates. From the derived models, the required quantities including the fiber tension, the pressure on the mandrel, also as a function of the number of windings, and the fiber elongation can be calculated.

With their high storage capacity and energy efficiency as well as the compatibilities with renewable energy sources, high‐temperature aquifer thermal energy storage (HT‐ATES) systems are frequently the target today in the design of temporally and spatially balanced and continuous energy supply systems. The inherent density‐driven buoyancy flow is of greater importance with HT‐ATES, which may lead to a lower thermal recovery efficiency than conventional low‐temperature ATES. In this study, the governing equations for HT‐ATES considering buoyancy flow are nondimensionalized, and four key dimensionless parameters regarding thermal recovery efficiency are determined. Then, using numerical simulations, recovery efficiency for a sweep of the key dimensionless parameters for multiple cycles and storage volumes is examined. Ranges of the key dimensionless parameters for the three displacement regimes, that is, a buoyancy‐dominated regime, a conduction‐dominated regime, and a transition regime, are identified. In the buoyancy‐dominated regime, recovery efficiency is mainly correlated to the ratio between the Rayleigh number and the Peclet number. In the conduction‐dominated regime, recovery efficiency is mainly correlated to the product of a material‐related parameter and the Peclet number. Multivariable regression functions are provided to estimate recovery efficiency using the dimensionless parameters. The recovery efficiency estimated by the regression function shows good agreement with the simulation results. Additionally, well screen designs for optimizing recovery efficiency at various degrees of intensity of buoyancy flow are investigated. The findings of this study can be used for a quick assessment and characterization of the potential HT‐ATES systems based on the geological and operational parameters.

Power‐to‐methane (PtM) offers an efficient opportunity for surplus renewable energy storage, but heat management is a major challenge for conducting the highly exothermic methanation reaction. To address this challenge, this study presents the first successful demonstration of core‐shell catalyst pellets in a pilot‐scale reactor for CO 2 methanation. Experiments in a wall‐cooled fixed‐bed reactor are conducted with diluted and undiluted reactant feed under systematic variation of cooling temperature and inlet gas flow rate. The results show that core‐shell catalyst pellets significantly reduce the hot‐spot temperature while maintaining comparable reactant conversions to uncoated catalyst pellets at the same conditions. Additionally, core‐shell catalyst pellets allow for undiluted reactant feed at comparably low hot‐spot temperatures (approx. 600 °C).

A considerable number of different tools and operating materials are used in classical optics manufacturing. Moreover, further parameters such as environmental and process conditions contribute to material removal and surface smoothing in the course of production. A large potential variety of the final surface state of optics can thus be expected. Against this background, nominally identical fused silica optics surfaces purchased from different suppliers were investigated in the present work via x-ray photoelectron spectroscopy, laser-induced breakdown spectroscopy, infrared spectroscopy, ellipsometry, and atomic force microscopy. It is shown that the surfaces under consideration feature quite different types and degrees of contamination that can be attributed to the particularly used water and polishing agent. Moreover, slight differences in index of refraction and surface roughness were detected. The presented data thus confirm the expectation that the surface state of an optical component might depend on its origin. The findings are intended to sensitize users regarding such a potential impact, for example, when switching to other suppliers for bought-in parts and outsourced precision optics items.

Understanding the phase and interphase behavior at equilibrium and during the mass transfer between two adjacent fluid phases is relevant for optimizing and designing efficient separation processes. This study experimentally investigates the interfacial and transport behavior of systems comprising tri-ethylene glycol (TEG) and methane (CH 4 ) under conditions relevant to the gas dehydration process. A comprehensive review of the interfacial tension (IFT) and diffusivity of systems involving non-polar and polar compounds at elevated pressures was studied. However, a research gap exists, particularly concerning the interfacial tension of systems involving TEG, TEG + water, and different types of gases as well as the diffusivity of CH 4 in TEG. To address this gap, this study presents new data on mixture densities, interfacial tension, and drop volumes of TEG and TEG + water in CH 4 and CH 4 + CO 2 mixtures at temperatures ranging from 20 to 50 °C and pressures up to 250 bar using the oscillating U-tube and pendant drop methods, respectively. Additionally, time-dependent fluid mixture densities and TEG droplet volumetric expansion, coupled with an analytical approach for the binary diffusion were applied to determine the CH 4 solubility and diffusivity in TEG. The results show that IFT and drop volume of TEG and TEG + water in CH 4 and CH 4 + CO 2 mixtures decrease with increasing pressure. The presence of water increases the IFT of TEG-CH 4 up to $\sim$ ∼ 5mN/m, while CO 2 reduces it by $\sim$ ∼ 2mN/m. Interestingly, the IFT and drop volume of TEG-CH 4 show no significant change at elevated pressures when temperatures rise from 20 to 50 °C. IFT remains relatively constant over time at moderate pressures but decreases by $\sim$ ∼ 3mN/m at an elevated pressure of 150 bar, suggesting methane solubilization into TEG to have a significant influence which is confirmed by TEG drop volume expansion. The diffusivity of CH 4 in TEG at 150 bar and 50 °C is determined to be in the range of 10 –10 m ² /s, which is in agreement with the diffusivity of CH 4 in liquids of similar viscosity, i.e. according correlations may be applied as good engineering practice. To the best of our knowledge, there is no such comprehensive work on the properties of fluid mixtures relevant in gas dehydration processes published up to date.

The disodium salt of 9,10‐anthraquinone‐2,7‐disulphonic acid (2,7‐AQDS) is an interesting platform for developing anthraquinone derivative negolytes for aqueous organic flow batteries. Recently, ammonium sulphate supporting electrolytes have been considered for improved stability and solubility. This work advances the 2,7‐AQDS/ferrocyanide flow battery with an ammonium sulphate supporting electrolyte (pH 5) by studying the suitability of six commercially available cation exchange membranes: E‐620, NR‐212, FS‐930, F‐1075‐PK, F‐1850 and N‐115. Cell cycling under galvanostatic regime plus potential hold was performed to determine coulombic efficiency, energy efficiency and accessible capacity for each membrane as well as capacity fade rate for three selected membranes under extended operation. Cell cycling under galvanostatic control only was carried out to observe transient membrane behavior alongside accessible capacity and apparent capacity fade rate. It was found that the capacity set by the limiting negolyte is consistent with 1.5 electrons per 2,7‐AQDS molecule and that energy efficiency shows a simple direct relationship to membrane thickness, with one exception. Meanwhile, four membranes displayed similar apparent capacity fade rates at this laboratory scale irrespective of their thickness, with capacity loss explained in terms of crossover. The best overall performance was attained by the thinnest membranes, E‐620 and NR‐212.

To investigate the MgLiq ↔ FeSol (Bcc and Fcc) equilibrium up to high temperatures, a suitable protocol for the thermodynamic study of volatile elements was developed. Pure magnesium was melted between 700 and 1450 °C (973 and 1723K) in a low-carbon steel sealed crucible (C35), itself sealed in a tantalum crucible to prevent magnesium leakage. The concentration of iron was characterised by inductively coupled plasma–atomic emission spectroscopy (ICP-AES) and the distribution of iron precipitates was examined by x-Ray tomography. The liquidus composition was measured up to 1450 °C and the results obtained confirm the trend in the literature with, however, significant differences above 1000 °C where a lower Fe solubility is measured in comparison with previous thermodynamic descriptions and the scarce available experimental data in this temperature domain. The existing Calphad model of the binary system was then re-evaluated.