Search

Explosion venting is a frequently used measure to mitigate the outcome of deflagration in closed environments. Despite the effort to improve engineering formulas and CFD tools used to predict the vent area needed to meet the desired enclosure protection, work has still to be done to reliably predict the outcome of a vented gas explosion. Blind-prediction exercises recently published by the HYSEA project show a large spread in the predictions by engineering models, including semi-empirical correlations and computational fluid dynamics (CFD) tools. University of Pisa performed experimental tests in a 25 m3 facility in inhomogeneous conditions and with the presence of simple obstacles constituted by plates bolted to HEB beams. The present paper is aimed to share the results of hydrogen dispersion and deflagration tests and discuss the comparison of maximum peak overpressure generated with different blockage ratio and repeated obstacles rows. Description of the experimental setup includes all the details deemed necessary to reproduce the phenomenon with a CFD tool.

University of Pisa performed hydrogen releases and deflagrations in a 1.14 m3 test facility, which shape and dimensions resemble a gas cabinet. Tests were performed for the HySEA project, founded by the Fuel Cells and Hydrogen 2 Joint Undertaking with the aim to conduct pre-normative research on vented deflagrations in enclosures and containers used for hydrogen energy applications. The test facility, named Small Scale Enclosure (SSE), has a vent area of 0,42 m2 which can host different types of vent; plastic sheet and commercial vent were tested. Realistic levels of congestion are obtained placing a number of gas bottles inside the enclosure. Releases are performed from a buffer tank of a known volume filled with hydrogen at a pressure ranging between 15 and 60 bar. Two nozzles of different diameter and three different release directions were tested, being the nozzle placed at a height where in a real application a leak has the highest probability to occur. Three different ignition locations were investigated as well. This paper is aimed to summarize the main features of the experimental campaign as well as to present its results.

This paper summarises the results from a blind-prediction benchmark study for models used for estimating the consequences of vented hydrogen deflagrations, as well as for users of such models. The work was part of the HySEA project that received funding from the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) under grant agreement no. 671461. The first blind-prediction benchmark exercise in the HySEA project focused on vented explosions with homogeneous hydrogen-air mixtures in 20-foot ISO containers. The scenarios selected for the second blind-prediction study focused on vented deflagrations in inhomogeneous hydrogen-air mixtures resulting from continuous stratification of hydrogen during vertical jet releases inside 20-foot ISO containers. The deflagrations were vented through commercial vent panels located on the roof of the containers. The test program included two configurations and four experiments, i.e. two repeated tests for each scenario. The paper compares experimental results and model predictions and discusses the implications of the findings for safety related to hydrogen applications. Several modellers predicted the stratification of hydrogen inside the container during the release phase with reasonable accuracy. However, there is significant spread in the model predictions, especially for the maximum reduced explosion pressure, and including predictions from different modellers using the same model system. The results from the blind-prediction benchmark studies performed as part of the HySEA project constitute a strong incentive for developers of consequence models to improve their models, implement automated procedures for scenario definition and grid generation, and update training and guidelines for users of the models. publishedVersion

University of Pisa (UNIPI) conducted a series of vented deflagration tests at B. Guerrini Laboratory. The tests were part of the experimental campaign performed by UNIPI for the European HySEA project (Hydrogen Safety for Energy Applications). Experiments included homogeneous hydrogen-air mixture contained in an about 1 m3 enclosure, called SSE (Small Scale Enclosure). The mixture concentration was variable between 10% and 18% vol. During the deflagrations, structural response was investigated by measuring the displacement of a test plate. The collected data were used to validate the FE model developed by IMPETUS Afea. In this paper experimental facility, displacement measurement system and FE model are briefly described, then comparison between experimental data and simulation results is discussed.

Experiments were carried out inside a 25 m3 vented combustion test facility (CVE) with a fixed vent area sealed by a plastic sheet vent. Inside the CVE, a 0.64 m3 open vent box, called RED-CVE was placed. The vent of the RED-CVE was left open and three different vent area were tested. Two different mixing fans, one for each compartment, were used to establish homogeneous H2 concentrations. This study examined H2 concentrations in the range between 8.5% vol. to 12.5% vol. and three different ignition locations, (1) far vent ignition, (2) inside the RED-CVE box ignition and (3) near vent ignition (the vent refers to the CVE vent). Peak overpressures generated inside the test facility and the smaller compartment were measured. The results indicate that the near vent ignition generates negligible peak overpressures inside the test facility as compared to those originated by far vent ignition and ignition inside the RED-CVE box. The experiments with far vent ignition showed a pressure increase with increasing hydrogen concentration which reached a peak value at 11% vol. concentration and then decreased showing a non-monotonic behaviour. The overpressure measured inside the RED-CVE was higher when the ignition was outside the box whereas the flame entered the box through the small vent.

Explosion relief panels or doors are often used in industrial buildings to reduce damages caused by gas explosions. Decades of research have contributed to the understanding of the phenomena involved in gas explosions in order to establish an effective method to predict reliably the explosion overpressure. All the methods predict a monotonic increase of the overpressure with the concentration of the gas in the range from the lower explosion limit to the stoichiometric one. Nevertheless, in few cases, a non-monotonic behaviour of the maximum developed pressure as a function of hydrogen concentration was reported in the literature. The non-monotonic behaviour was also observed during experimental tests performed at the Scalbatraio laboratory at the University of Pisa, in a 25 m3 vented combustion test facility, with a vent area of 1,12 m2. This paper presents the results obtained during the tests and investigates the possible explanations of the phenomena.

Explosion relief panels or doors are often used in industrial buildings to reduce damages caused by a gas explosion. Decades of research produced a significant contribution to the understanding of the phenomena involved. Among the aspects that need further research, interactions between acoustic oscillations and the flame front is one of the most important. Interactions between the flame front and acoustic oscillations has raised technical problems in lots of combustion applications as well and has been studied theoretically and experimentally in such cases. Pressure oscillations have been observed in vented deflagrations and in certain cases they are responsible for the highest pressure peak generated during the event. At Scalbatraio laboratory of Pisa University a test facility (CVE) was built in order to investigate vented hydrogen deflagrations. This paper presents an overview of the results obtained during several experimental campaigns. The tests are analysed with the focus on the investigation of flame acoustic interaction phenomena. Qualitative and quantitative analysis is presented and the generated possible physical phenomena are investigated.

At the DIMNP (Department of Mechanical, Nuclear and Production Engineering) laboratories of University of Pisa (Italy) a pilot plant called HPBT (Hydrogen Pipe Break Test) was built in cooperation with the Italian Fire Brigade Department. The apparatus consists of a 12 m3 tank connected with a 50 m long pipe. At the far end of the pipeline a couple of flanges have been used to house a disc with a hole of the defined diameter. The plant has been used to carry out experiments of hydrogen release. During the experimental activity, data have been acquired about the gas concentration and the length of release as function of internal pressure and release hole diameter. The information obtained by the experimental activity will be the basis for the development of a new specific normative framework arranged to prevent fire and applied to hydrogen. This study is focused on hydrogen concentration as function of wind velocity and direction. Experimental data have been compared with theoretical and computer models (such as CFD simulations).

There are currently projects and demonstration programs aiming at introducing Hydrogen powered Fuel Cell (HFC) vehicles into the market. Regione Toscana has been cofounder of the project “H2 Filiera Idrogeno”, whose goal is to achieve a clean and sustainable mobility through HFC vehicle studies covering their production, storage and use. Among the goals of the project was the substitution of the electric propulsion system with a hydrogen fuel cells propulsion system. This work presents a brief overview of the necessary modifications of the electric propulsion version of a Piaggio Porter to host a H 2 fuel cell and experimental studies of realistic H 2 releases from the vehicle. The scenarios covered H 2 unintended releases underneath the vehicle when at rest and focused on three types of releases, diffusive, major and minor, that might reach the interior of the vehicle and potentially pose a direct risk to the passengers.