1,720,973 research outputs found
Insulation Materials Used in Tanks for the Storage of Cryogenic Fluids in Fire Scenarios
No full textNon-combustible MLI based insulation behavior under fire condition - Experimental and numerical investigation
Full text linkThe number of applications that demand zero-emission energy carriers, such as liquified hydrogen (LH2), is increasing worldwide. LH2 is typically transported or stored under cryogenic conditions. Storage in such conditions requires super thermal insulations which maintain very low boil-off for a prolonged time. Multi-Layer insulation (MLI) finds widespread use in cryogenic applications, designed to effectively restrict heat inleak towards cryogenic fluids. However, recent studies evidenced that exposure to high heat fluxes, such as in the event of a fire accident, can cause the thermal degradation of the insulation material, resulting in the severe collapse of its heat resistance performance. Therefore, the risk of rapid tank pressurization and its connection to the risk of BLEVE may be possible. This study proposes a numerical model to assess the performances of aluminum-based MLI materials under fire conditions. The model offers insights into the total heat transfer rate through the insulation, serving as
Analysis of High Temperature Degradation of Multi-layer Insulation (MLI) Systems for Liquid Hydrogen Storage Tanks
Full text linkThe interest in hydrogen-based green energy is increasing worldwide, and the same is true for hydrogenpowered vehicles. Among the possible solutions to store hydrogen in such vehicles, cryogenic tanks equipped with multi-layer insulation (MLI) are the most promising to increase the amount of energy stored per unit volume. However, MLI is affected by severe deterioration when exposed to an external source of heat such as a fire following a car accident, leaving the tank unprotected and leading to failure in a relatively short time. In this work, a one-dimensional model to evaluate MLI thermal degradation when a liquid hydrogen tank is exposed to fire is presented. The relevance of taking MLI degradation into account when simulating the pressure increase
due to external fire exposure is here demonstrated through the analysis of several case studies. The results show that MLI systems performance depletes within a few minutes of exposure to hydrocarbon poolfire
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
An experimental and numerical study on liquid fragmentation induced by an accidental industrial explosion
No full textIn a process involving hazardous liquids, if a chemical runaway reaction happens inside a tank, an explosion may occur and spreads the bulk liquid around the exploded vessel. Following the rapid ejection, the liquid will be fragmented into droplets both by the high-speed gas flow and blast propagation. The droplets dimension are directly related to the extent of the dispersion of toxic liquids and/or the combustion risk of a flammable aerosol thus produced. Therefore, it is of crucial relevance to study the phenomena involved in fragmentation, understanding the role played by hydrodynamic instabilities occurring at the liquid-high-pressure gas interface. Moreover, liquid fragmentation is supposed to be strongly dependent on the blast overpressure and the amount of liquid affected by the explosion. The present work analysed these aspects, simulating the impact of an explosion over a liquid layer using the shock tube facility. Firstly, a 1-D numerical model has been implemented to simulate the shock tube problem. Although the presence of viscosity effects was detected, a good match between model and experimental data was found in simulating the closed shock tube. Subsequently, the original shock tube set-up has been appropriately modified to accommodate the liquid on the top. Thus, the different overpressure behaviour in presence of water instead of a closed wall at the end of the tube was investigated. The comparison with the numerical model has allowed appreciating the water layer acts as a solid wall when reflecting the incident shock wave. Direct visualization of the fragmentation phenomenon and the instabilities has been achieved by using high-speed cameras. Several tests have been performed changing the mass of water involved and the pressure impulse impacting it, observing the correlation interacting between these parameters and the liquid acceleration throughout an image processing software
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Modelling Fire Response of Cryogenic Liquid Hydrogen Tanks Equipped with Multilayer Insulation (MLI) Systems
No full textIn the context of the growing global interest in hydrogen-based green energy, cryogenic tanks equipped with multi-layer insulation (MLI) are emerging as a leading solution for storing hydrogen in vehicles. The integrity of these systems might be threatened during fire exposure. This can trigger the degradation of the MLI materials and induce rapid pressurization of the tank with a high risk of catastrophic failure. In this work, a novel lumped model to simulate the thermal response of MLI-equipped cryogenic liquid hydrogen tanks is presented. The model integrates the accurate database “Coolprop” for hydrogen thermodynamic properties and sub-models for detailed simulation of MLI degradation, providing a realistic simulation of the experimental data obtained under normal operating conditions. The application of the model to several case studies considering different numbers of MLI layers and tank geometries demonstrates that aluminum-based MLI offers scarce protection in case of exposure to a hydrocarbon poolfire
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
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