CFD analysis for an overpressure buildup phenomenon of sri hydrogen explosion test at fuel lean and fuel rich conditions in an open space

Abstract

A computational fluid dynamics (CFD) calculation for a hydrogen explosion test with a complicated obstacle tube geometry of pitch 21.3 mm and diameter 99.1 mm at fuel lean and fuel rich conditions was performed to establish a CFD analysis methodology for a hypothetical hydrogen explosion accident between a very high temperature reactor (VHTR) and a hydrogen production facility. We firstly developed the CFD analysis methodology with an error range of about 34% at the hydrogen stoichiometric condition on the basis of SRI's hydrogen explosion test results. The proposed CFD analysis methodology consisted of the standard k- turbulent model for a turbulent flow, eddy dissipation model (EDM) constants of A=10 and B=0.8 for a combustion flow, a time step size of 0.01 ms with backward Euler 2nd order for a transient flow and a cell length of 10 mm around the obstacle tube approximately equaled to a large length scale of eddy. A spark ignition model was developed to simulate a high ignition energy of 40 J induced by an electric device for 2 ms in the hydrogen explosion test based on an energy conservation law. However, the EDM model constants of A=10 and B=0.8 was modified to A=7 and B=0.8 for the fuel lean and fuel rich conditions because the main idea of the turbulence mixing rate in the EDM cannot cover the variation of combustion energy due to the hydrogen concentration difference from the stoichiometric condition to the fuel lean or fuel rich conditions. The calculated error range of the CFD analysis methodology was about 7% from the simulation results of SRI's hydrogen explosion test at the fuel lean and fuel rich conditions. Therefore, it is known that a CFD analysis with the EDM may be used as an accurate evaluation tool to predict overpressure buildup if the EDM constants may be properly chosen according to the hydrogen concentration.