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Safety assessment of MLI super-insulation systems for cryogenic liquid-hydrogen tanks in fire scenarios
No full textIn the context of green energy transition, cryogenic tanks featuring MLI systems are emerging as a leading solution to store hydrogen in heavy-duty vehicles. However, the integrity of such tanks can be jeopardized by fire. In such a scenario, MLI materials degradation can occur, leaving the tank unprotected from the fire heat flux, with consequent rapid pressurization and a high risk of failure. This study presents an assessment of aluminum-based MLI for liquid hydrogen cryogenic tanks under fire exposure based on the estimation of the time to mechanical failure of the equipment. This is calculated through an innovative model that simulates the thermomechanical response of the tank, including the MLI thermal degradation and the pressure-relief valve (PRV) operation. The application to several case studies that consider a typical LH2 tank featuring a wide range of MLI configurations demonstrated the likelihood of failure in case of exposure to a hydrocarbon pool fire, providing also comprehensive insights into the impact of the insulation characteristics and operating conditions on the time to failure
Effective elastic moduli and failure mechanisms of a random assembly of thin walled glass microbubbles
No full textIn this work a methodology is presented to estimate the elastic properties and failure mechanisms of an assembly of random, brittle microbubbles. The approach is based on the mechanics of frictionless micro-contact between hollow spherical shells by employing relations from classical shell theory and verified by two dimensional axisymmetric Finite Elements. The estimated values are in agreement with available experimental values. Moreover, a granular type analytical homogenization model provides an isotropic elastic constitutive law to be used for the macroscopic deformation of an assembly of glass micro-bubbles when it is compressed by external loads. In addition, approximate estimates are also proposed for two important micro-failure mechanisms of such assemblies that relate either to the splitting or to the buckling of a brittle spherical shell, prior its complete crushing. The results are novel and are expected to enhance the application of glass microbubbles directly in acute thermal insulation problems such as liquid hydrogen storage
Mechanical properties of 3D printed concrete: a RILEM TC 304-ADC interlaboratory study — flexural and tensile strength
No full textThis paper discusses the flexural and tensile strength properties of 3D printed concrete, based on the results of a RILEM TC 304-ADC interlaboratory study on mechanical properties. These properties are determined using different testing techniques, including 3- and 4-point flexural tests, splitting tests, and uniaxial tension tests, on specimens extracted from large 3D printed elements in accordance with a prescribed study plan. The relationship between compressive and flexural or tensile strengths, cast or printed samples, different types of tests, and different loading orientations, are analysed to understand the influence of 3D printing. As expected, the strength can reduce significantly when the main tensile stress is acting perpendicular to the interface between layers. The role of deviations from the standard study procedure, in terms of the time interval between the placing of subsequent layers, or the adoption of a different curing strategy, are also assessed. While the increased time interval significantly impacts the strength in the critical direction, the use of variable curing conditions does not seem to have a clear-cut effect on the strength ratios of the printed to cast specimens. Additionally, the paper looks at the variability in the results for the printed specimens, in order to emphasize the need for multiple replicates for obtaining a proper result. An extensive insight into the aspects affecting the variability is presented in the paper. Finally, with the limited dataset available for specimens tested at a larger scale, it is difficult to arrive at a clear understanding of the role of specimen size (i.e., greater number of layers)
Behavior of a LH2 storage tank under fire
No full textAs the world moves towards green energy production, effective storage and transportation solutions become essential. To support this transition, energy carriers with minimal or zero environmental impact are required. Liquified hydrogen represents a promising candidate due to its emissions-neutral properties. However, its highly flammable nature necessitates adherence to strict safety codes and standards. Storing hydrogen often requires advanced super-insulation materials. To enhance the safety of cryogenic hydrogen storage tanks under extreme conditions, such as those encountered during fire accidents, it is crucial to understand the thermal behaviour of the tank. Predicting pressurization and potential failure in advance demands a robust and comprehensive model. However, still such models suffer lack of detailed heat transfer models which account for various sub-processes during an accident scenario. Hence, this study introduces a comprehensive model for the pressurization of cryogenic tanks equipped with multi-layer insulation (MLI) systemsin the event of fire, which comprises several sub-models. These sub-models account for heat transfer phenomena through the thermal insulation at nominal conditions and its thermal degradation during fire exposure, the fluid, the internal pressurization, and the performance of the pressure relief valve. This study provides valuable insights into the safety and the behaviour of hydrogen storage tanks under thermal loads
Optimization of local backside released micro-ring resonators for sensing applications using silicon photonic integrated circuits in a SOI technology
No full textThe integration of photonic sensors into compact systems requires space-efficient solutions, such as the backside release of waveguides on silicon-on-insulator (SOI) platforms. This study presents the design, fabrication, and characterization of fully backside-released micro-ring resonators (MRRs) using the IHP SG25H5EPIC technology. The performance of rib and strip waveguides released by either dry or wet etching of the buried oxide (BOX) layer is evaluated. While wet etching provides low-loss release of rib waveguides, dry etching is required for the release of strip waveguides but results in increased waveguide losses and reduced quality factors. The effects of these release methods on critical coupling conditions, extinction ratio (ER), full width at half maximum (FWHM), and sensor performance are analyzed. The findings confirm that both etching strategies yield structures suitable for photonic sensing, with backside release enabling co-integration with microfluidic and optoelectronic components. These results contribute to the advancement of high-performance, integrated silicon photonic sensors
Optimization of local backside released micro-ring resonators for sensing applications using silicon photonic integrated circuits in a SOI technology
No full textPhotonic micro-ring resonators (MRR) are widely studied for their high sensitivity across applications like environmental monitoring, healthcare, and chemical analysis. Their evanescent field sensing requires partially unembedded waveguides compatible with CMOS processing. Our approach uses local backside etching with an additional buried oxide (BOX) etch to release waveguides while preserving the back-end of line (BEOL) structure, enabling spatial separation of the sensing area and electronics. The BOX etch critically affects sensor performance, as waveguide surface roughness can alter MRR properties and coupling. We analyzed MRR design variations, comparing wet and dry etching techniques for their effects on optical performance across rib and strip waveguides in quasi-TE and quasi-TM modes. Wafer-level measurements show that backside-released MRR achieve high extinction ratios with slightly reduced quality factors, advancing high-sensitivity photonic sensors
Feasibility Study on the Direct Detection of Per- and Polyfluoroalkyl Substances (PFAS) with Surface-Assisted Flowing Atmospheric-Pressure Afterglow Mass Spectrometry (SA-FAPA-MS)
No full textPer- and polyfluoroalkyl substances (PFAS) are a large class of thousands of synthetic chemicals that are used worldwide. However, growing environmental and human health concerns in the last two decades have led to more stringent regulatory requirements and the development of quantitative analytical methods for PFAS detection. Today, standardized and powerful methods exist, e.g., for the determination of PFAS in water, sludge, compost, soil, and drinking water (DIN 38407-42, DIN 38414-14, ISO 21675, and DIN EN 17892). While liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) is often used, blank levels, sample preparation, and total analysis times can be challenging. [1] Here, ambient desorption/ionization mass spectrometry (ADI-MS) is considered interesting because it requires only minimal sample preparation and was able to reduce total analysis time in other types of applications. [2] Previously, we used a plasma-based pin-to-capillary flowing atmospheric-pressure afterglow source (FAPA) [3] to probe samples directly from thin-layer chromatography (TLC) plates and to perform quantitative analysis and mass spectral imaging [4].
In this work, a feasibility study for the direct detection of PFAS with FAPA-MS is reported. Selected PFAS samples were directly probed on functionalized TLC surfaces (normal-phase silica, reversed-phase-modified silica, cyano [CN]-modified silica, and dimethyl [RP2]-modified silica, diol modified silica, and amino [NH2]-modified silica). The suitability of the surfaces was evaluated and the compatibility of different solvents with the surfaces was studied. CN-HPTLC and RP2-TLC surfaces showed the best performance for direct PFAS detection with FAPA-MS. In addition, direct analysis of PFAS mixtures and selected matrices was performed with little sample preparation and short analysis time
Feasibility Study on the Adsorption of Environmental Contaminants onto Fresh and Aged Microplastics
No full textMicroplastics (MPs) refer to plastic particles, fibers, or beads with sizes ranging from 100 nm to 5 mm in size. Their pervasive distribution as environmental contaminants have escalated into a significant global concern. Primary MPs are intentionally produced particles for industrial and commercial applications, such as exfoliants in personal care and cosmetic formulations. In contrast, secondary MPs are generated through the fragmentation and degradation of larger plastic materials, due to environmental weathering processes. [1]
Due to their high surface area-to-volume ratio and hydrophobic nature, MPs have the potential to serve as vectors for the accumulation and transport of diverse organic contaminants, including polycyclic aromatic hydrocarbons (PAHs), perfluoroalkyl substances (PFAS), pharmaceuticals and personal care products (PPCPs), as well as trace metals such as silver, cadmium, chromium, and copper. In the environmental, MPs are subject to aging processes driven by factors such as temperature, ultraviolet radiation, oxygen, and chemical interactions with environmental toxins. This aging can induce significant alterations in their physicochemical properties, which, in turn, can affect the adsorption behavior. [2]
Classical and alternative analytical methods such as high-performance liquid chromatography (HPLC) and ambient desorption/ionization high-resolution mass spectrometry (ADI-HR-MS) can help to study the adsorption potential. ADI-HR-MS allows rapid sample analysis with minimal preparation, providing results in under a minute, much faster than traditional chromatographic techniques. [3]
This study aims to investigate the influence of aging and particle size on the ability of microplastics to act as vectors for environmental contaminants. Microplastics were prepared in-house and subjected to controlled aging conditions for 12, 24, 36, and 48 hours. Subsequently, the aged MPs were exposed in plastic-free containers to model solutions to simulate co-contaminants in the environment. Adsorption onto synthesized secondary microplastics, varying in size and aging status, was investigated at different time intervals with ambient MS and time-of-flight secondary ion mass spectrometry
Creep Phenomena During Initial Loading of Type 4 Composite Pressure Vessels
No full textA poster presentation on the impact of creep phenomena during initial loading on the safety of type 4 composite pressure vessels. A statistical evaluation of slow burst tests shows an increase of the survival rate of initially loaded composite pressure vessels (sustained load and increased pressure) compared to the ones tested in a brand-new state
Insights into Mechanochemical Solid-State Ball-Milling Reaction: Monitoring Transition from Heterogeneous to Homogeneous Conditions
No full textAs mechanochemical synthesis has advanced significantly, there has been intense interest in understanding the underlying mechanisms of these reactions. Given that many mechanochemical processes are conducted in the solid-state without solvation yet sometimes yield faster reactions than those in solution, we sought to address the following question: Are mechanochemical reactions homo- or heterogeneous? To investigate, we employed a model system involving the mixing and copolymerization of l-lactide (LLA) and d-lactide (DLA), monitored through powder X-ray diffraction (PXRD), nuclear magnetic resonance, and differential scanning calorimetry. In situ and ex situ PXRD analyses of the mixture of LLA and DLA showed that vibratory ball milling rapidly transformed the initially heterogeneous lactide mixture into a homogeneous phase within one min due to collisions between the balls and the jar. By varying the milling conditions, we were able to regulate the level of mixing, which subsequently influenced the copolymerization outcomes. In the solid-state ball-milling copolymerization of LLA and DLA in the presence of a catalyst and initiator, multiblock copolymers of poly(l-lactic acid) and poly(d-lactic acid) were formed within one min during the early stage of the reaction, when incomplete mixing of the monomers led to a process governed by phase heterogeneity. In contrast, prolonged polymerization promoted conditions approaching homogeneity, ultimately yielding atactic poly(lactic acid). This transition from heterogeneous to homogeneous reactions is a distinctive feature compared to conventional homogeneous reactions, potentially leading to mechano-exclusive reaction designs