The computational fluid dynamics (CFD) code DESC has been used to simulate a series of dust explosion experiments performed in an 18.5 m 3 vessel equipped with vent ducts of varying cross sections and lengths. The motivation behind the work is 3-fold: to validate the CFD code, to gain increased understanding of the parameters affecting dust explosion venting through ducts, and to investigate the validity of empirical correlations found in various standards and guidelines for design of explosion protection systems. Although the results from simulations agree reasonably well with experimental observations, DESC tends to underpredict the reduced explosion pressures for scenarios with vent ducts with diameters significantly larger than the vent openings. These discrepancies may be a result of inherent limitations in the model system, but poor repeatability and limited access to detailed experimental data complicates the analysis. Results from experiments and simulations are compared with predictions from various standards and guidelines for design of vent ducts in industry: EN 14491, VDI 3673, NFPA 68, and the methodology developed by FM Global. The correlations in NFPA 68, derived from the same set of experiments in the 18.5 m 3 vessel, yield the most accurate predictions. The FM Global method underestimates the reduced explosion pressure for the largest vent diameter and rear ignition and yields conservative results for smaller duct diameters. Neither experiments nor simulations support the concept of a critical duct length prescribed in EN 14491 and VDI 3673.

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This dissertation describes the development and validation of a methodology for estimating the consequences of accidental dust explosions in complex geometries. The approach adopted entails the use of results from standardized tests in 20-litre explosion vessels as input to the combustion model in a computational fluid dynamics (CFD) code, and the subsequent validation of the model system by comparing with results from laboratory and large-scale experiments. The PhD project includes dedicated laboratory experiments designed to explore selected aspects of flame propagation in dust clouds, and to reveal similarities and differences between flame propagation in gaseous mixtures and mechanical suspensions of combustible powder in air. v Scientific environment The philosophiae doctor (PhD) project started in January 2004. The work progressed under the principal supervision of Professor Rolf K.