Direct numerical simulation of liquid sodium droplet combustion in forced convection air flow

In case of sodium leakage in liquid metal fast breeder reactor, the liquid sodium comes out in droplet form from a pipe accompanied with ignition and combustion Combustion heat and reaction products might affect integrity of steel liners in piping rooms. A direct numerical simulation code, COMET, is developed to simulate the combustion of a liquid sodium droplet. The extended MAC method coupled with a higher-order upwind scheme is used to calculate reacting compressible flow. Multicomponent counter diffusion of chemical species, mass and energy transfer by sodium evaporation, and heat transfer by radiation and thermal conductivity are calculated coupling with the flow. Chemical reaction of sodium, oxygen and water vapor is calculated by using the equation-solving methods of equilibrium constants. Thermodynamic properties of the mixed gas are evaluated based on the molecular transport theories. By using COMET, the single droplet combustion of liquid sodium in forced convection air flow is numerically simulated. Spatial distributions such as combustion heat, temperature, pressure, and chemical species behaviors such as formation, decomposition and transport are analyzed and discussed. The change of the droplet diameter agrees closely with the d-square law that has been experimentally observed and theoretically derived. (author)