Hydrogen and the Containment

Integral large-scale experiments on hydrogen combustion are being carried out within the EC 5th Framework programme (Bielert et al., 2001) to promote understanding of the phenomena and for the development of analysis methods. These extend work carried out in the 4th Framework programme, which concluded that local information on the properties of reactive flow fields was necessary for modelling, and also that flame acceleration was important for transition from deflagration-to-detonation (DDT).

In the recent project, two different geometric scales are considered with the emphasis on different combustion regimes from slow to fast turbulent deflagrations.

Medium-scale tests with hydrogen-air mixtures were carried out within the DRIVER and TORPEDO facilities (Bielert et al., 2001), i. e. in simple geometric configurations. The objectives were to study the effects on: location of the ignition, changes in blockage ratio and channel cross-section, and venting.

Large-scale tests were conducted in the RUT facility, which aimed to study the processes of turbulent flame propagation in multi-compartment geometry and in non­uniform mixtures. This facility was of a scale commensurate with typical reactor length scales. Previous tests were mainly concerned with determining critical conditions for DDT (Breitung et al., 2000; Sidorov and Dorofeev, 1998). The present tests consider processes with lower flame speeds in both slow and fast deflagration situations.

To date, the data from these tests indicate specific effects of scale, multi­compartment geometry, mixture gradient effects and venting. The critical conditions for fast combustion regimes can be influenced by flow geometry, although a converging flow geometry does not especially promote this effect.

With regard to modelling, it has been found that lumped parameter codes do better at predicting slow flames, the computational fluid dynamics (CFD) codes do better at predicting fast deflagrations. There were, however, other phenomena which could not be adequately simulated by the codes, such as global quenching and pulsating flames.

Other work in the 5th Framework is aimed at investigating the effects of passive autocatalytic recombiners. The design and placing of these systems rely on a validated methodology for good prediction of hydrogen distribution under accident conditions.

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