Numerical and experimental results of pressure piling using flammable mixtures within enclosed volumes including obstacles

The design of electric valve actuators for explosion proof (Ex d) hazardous environments, whereby an explosive event must be contained, is examined in this study. Combustion within these small enclosed volumes is complex due to
the irregular geometries developed in the design process, effectively producing a series of baffles (obstacles). These obstacles lead to a scenario whereby combustion within the enclosed interconnected vessels produces a phenomenon
know as pressure piling. Furthermore, if the correct criteria is met, it will result in a deflagration to detonation transition (DDT). Two simple cylindrical vessels connected by a transmission pipe, with the first primary vessel (ignition source) having a larger volume than the second vessel, are presented here to induce the pressure piling phenomenon. OpenFOAM has been utlised to simulate the combustion process using the solver rhoReactingFoam [1]. Simulation results are compared to a set of experimental results to validate the solver accuracy. A further unique experiment that includes obstacles, representing blockage ratios (BR’s) of 30% and 60%, has been conducted and presented here to further verify the accuracy of the numerical solver. The results demonstrates that the impact that obstacles have on pressure piling. The introduction of baffles increases flame acceleration (FA) and the over pressure by a factor of approximately 1.5, in most cases. Pressure trace results are presented of three fuels with different combinations of obstacles. Understanding the mechanisms of pressure piling will eventually lead to design techniques to control the effects of the over pressures produced by these types of internal geometries.