Numerical simulation on high-temperature supercritical CO2/gaseous H2O mixture flowing over a single reactive spherical char particle

Abstract

Based on PR-DNS (Particle Resolve-Direct Numerical Simulation) method, the gasification process of a single spherical char particle moving in high-temperature supercritical CO2/gaseous H2O atmosphere at 9 MPa is conducted, and related mechanism on the reaction-affected drag of the sphere, flow field and interphase thermal as well as mass transfer near sphere surface is presented. The reaction temperature and Re (Reynolds number) of the fluid flowing over the sphere are variable within the range of 1273.15–1673.15 K and 10–200, respectively. The mass decomposition source on the sphere surface (Stefan flow), reaction heat, heat radiation between fluid species and char, porous inert ash layer and variations on physical properties of fluid mixture near the sphere surface are taken into account, while the Pseudo-Steady-State approach is employed for handling the particle shrinking. The results indicate that the higher reaction temperature leads the smaller drag coefficient, while enhances the performance of heat transfer compared with that of non-reactive cases. Due to the relative strength between convective heat transfer and endothermic effect of heterogeneous reaction, variation laws of temperature on the sphere surface vs. Re differs from each other under different reaction temperatures. Higher temperature and lower Re leads the higher surface Damköhler numbers, which indicates that the heterogeneous reactions in gasification process have normal characteristic of reactions in the kinetically-controlled regime. Porous inert ash layer increases resistance to flow as well as diffusion of species, and the variations in relative concentration of fluid reactants can also result in varied influences on above variables.