CFD Prediction for an Overpressure Buildup Phenomenon of SRI Hydrogen Test in an Open Space

Abstract

A computational fluid dynamics (CFD) calculation for a hydrogen explosion test with a complicated obstacle tube geometry of pitch 21.3mm and diameter 99.1mm at a stoichiometric condition was performed to establish a CFD analysis method for a hypothetical hydrogen explosion accident between a very high temperature reactor (VHTR) and a hydrogen production facility. We developed a spark ignition model to simulate high ignition energy of 40J induced by an electric device for 2 ms in the hydrogen explosion based on an energy conservation law. We performed a sensitivity calculation by varying a constant value of the eddy dissipation model (EDM), a time step size, and a cell length size around the obstacle tube to evaluate an effect of each factor on the flame propagation and overpressure buildup phenomenon. The CFD results of the flame front time of arrival (TOA) and overpressure were compared with those of the test data. The comparison results showed that the spark ignition model with a radius of 6 cm, a pressure of 105.7 kPa, a temperature of 1000 K, a turbulent mixing time of 2 ms, and an assumption of the 10% product mass fraction can reasonably initiate the hydrogen flame propagation in the CFD calculation. As for the CFD analysis method, the EDM constants of A = 10 and B = 0.8, the time step size of 0.01 ms, the cell length of 1 cm around the obstacle tube predicted the measured flame front TOA and peak overpressure with an error range of about 27.8% and 53.3%, respectively. Therefore, it is known that the CFD analysis with the EDM may be used as an accurate evaluation tool to provide the 3-dimesnional information of the flame front TOA and overpressure buildup phenomenon if the CFD analysis method is properly chosen.