Performance of Hydrogen Storage Tanks of Type IV in a Fire: Effect of the State of Charge

The use of hydrogen storage tanks at 100% of nominal working pressure (NWP) is expected only after refuelling. Driving between refuellings is characterised by the state of charge SoC <100%. There is experimental evidence that Type IV tanks tested in a fire at initial pressures below 1/3 NWP, leaked without rupture. This paper aims at understanding this phenomenon. The numerical research has demonstrated that the heat transfer from fire through the composite overwrap at storage pressures below NWP/3 is sufficient to melt the polymer liner. This melting initiates hydrogen microleaks through the composite before it loses the load-bearing ability. The fire-resistance rating (FRR) is defined as the time to rupture in a fire of a tank without or with blocked thermally activated pressure relief device. The dependence of a FRR on the SoC is demonstrated for the tanks with defined material properties and volumes in the range of 36–244 L. A composite wall thickness variation is shown to cause a safety issue by reducing the tank’s FRR and is suggested to be addressed by tank manufacturers and OEMs. The effect of a tank’s burst pressure ratio on the FRR is investigated. Thermal parameters of the composite wall, i.e., decomposition heat and temperatures, are shown in simulations of a tank failure in a fire to play an important role in its FRR

Spontaneous Ignition of Cryo-Compressed Hydrogen in a T-Shaped Channel System

Sudden releases of pressurised hydrogen may spontaneously ignite by the so-called &ldquo;diffusion ignition&rdquo; mechanism. Several experimental and numerical studies have been performed on spontaneous ignition for compressed hydrogen at ambient temperature. However, there is no knowledge of the phenomenon for compressed hydrogen at cryogenic temperatures. The study aims to close this knowledge gap by performing numerical experiments using a computational fluid dynamics model, validated previously against experiments at atmospheric temperatures, to assess the effect of temperature decrease from ambient 300 K to cryogenic 80 K. The ignition dynamics is analysed for a T-shaped channel system. The cryo-compressed hydrogen is initially separated from the air in the T-shaped channel system by a burst disk (diaphragm). The inertia of the burst disk is accounted for in the simulations. The numerical experiments were carried out to determine the hydrogen storage pressure limit leading to spontaneous ignition in the configuration under investigation. It is found that the pressure limit for spontaneous ignition of the cryo-compressed hydrogen at temperature 80 K is 9.4 MPa. This is more than 3 times larger than pressure limit for spontaneous ignition of 2.9 MPa in the same setup at ambient temperature of 300 K

Two Notes on the Notion of Education by Theodore Metochites and in the Patristic Tradition of the Middle Byzantine Period

Introduction. John Polemis thought that in On Education the notions of logos, paideia and theoria were synonymous. Meanwhile, Igor P. Medvedev stressed in his trail-blazing book the variety of meanings of theoria in the Late Byzantine period. Relying upon his ideas and evidence, we would like to underline, in our turn, Metochites’ diversification of meanings of this notion. As a skillful conductor or musician, he was able to tune into different waves when speaking about mundane or ecclesiastical affairs. In a number of points, he diverged from traditional Orthodoxy. Methods. Using the traditional set of historical, philosophical, and hermeneutic methods, as well as those of comparative religious and cultural studies, we try to single out and analyze in some detail different layers of meaning in the treatise under discussion. If our author had made digressions into theological knowledge, it does not mean that he would have given himself completely to theology alone, as the basic line of his reasoning remained philosophical and mundane. As compared to what his fellow-Churchmen, like Callistos I, wrote on the issue of education, Metochites’ ideas turn to be a rather clear-cut continuation of the ancient paideia and not especially spiritual knowledge derived from the Christian Revelation. Analysis. Thus, in his cosmological deliberations Metochites ran a risk to turn the world-creating power of God into something temporary and liable to change. He certainly did not learn well the lessons of the patristic tradition represented, e.g., by Ps.-Maximos’ Chapters Full of Knowledge dating back to the 7th – 8th centuries. This led to the fact that he had not recognized the operations of divine world-ordering energy in the created universe, and thus had confirmed the old assumption of H.-G. Beck that Metochites were unfamiliar with Ps.-Maximos the Confessor. At the same time, some Theodore’s ideas come close to those uttered by Ps.-Maximos. Both authors criticize indeed the notion of a pure and self-contained contemplation (which expresses the negative meaning of theoria) unattached to a person’s struggle with passions and vices. Even more intriguing is their common use of a widespread patristic concept of “cultivating the land of one’s mind” (or: “heart”). Given the fact of Metochites’ pronounced admiration of Orthodox monasticism (see, e.g., Ch. 13 of On Education), this parallel may not be incidental. It seems to be traceable to the common Biblical and ancient roots of the Byzantine spiritual culture. Results. If it is difficult to unambiguously resolve the issue of Ps.-Maximos’ or Metochites’ influence exerted to his counterpart, it is not to say, however, that there was not a high degree of cohesion and integrity within the philosophical and theological synthesis of the middle- and late Byzantine patristic tradition and spiritual culture in general. It is within this framework that a scholar should analyze Metochites’ ideas as expressed in On Education and elsewhere