Investigation of appropriate mesh size and solid angle number for CFD simulating the characteristics of pool fires_with experiments assessment

In order to implement NFPA 805 in the performance-based fire design for nuclear power plants (NPPs), a reliable computational fluid dynamics (CFD) fire model is needed. However, numerical treatments including mesh size and number of solid angles significantly influence the accuracy of CFD predicted results of the thermal-hydraulic behaviors involved in fire scenarios. Therefore, the majority of this paper is to investigate appropriate mesh size and solid angle number used for CFD simulating the characteristics of pool fires. Based on the present sensitivity studies of different mesh sizes and solid angle numbers, appropriate numerical treatment could be selected by comparing the predicted results of flame height and radiative heat flux for the pool fires. Two experiments with pan sizes of 20 and 30 cm, respectively, are also conducted to assess the CFD predicted results obtained using these selected mesh size and number of solid angles. Good agreement between the experiments and predictions clearly shows that the optima mesh resolution for the flame height and radiative heat flux is at the normalized mesh size (R*, ratio of the mesh size to the flame characteristic diameter) = 0.077 and 500 solid angles for thermal radiation are sufficient to reasonably capture the radiative characteristics from the pool fires with the size less than 30 cm. Herein, solid angle means included angle between rays from thermal radiator.