Computation of mass transfer coefficient and Sherwood number in circulating fluidized bed downer using computational fluid dynamics simulation

In this study, the Eulerian–Eulerian computational fluid dynamics simulation with the kinetic theory of granular flow model was successfully used to compute mass transfer coefficients and Sherwood numbers in a circulating fluidized bed downer using the concept of additive chemical reaction and mass transfer resistances. The simulation was also used to determine the ozone molar concentration, axial gas velocity and solid volume fraction.The effects of reaction rate constant and circulating fluidized bed downer height were investigated. The mass transfer coefficients and the Sherwood numbers had minimum values at moderate or central value of each effect. The low mass transfer coefficients and Sherwood numbers were observed due to the formation of solid particle sheet or loose solid particle cluster. In addition, the system flow and chemical reaction behaviors were discussed using the obtained mass transfer characteristics. For high reaction rate constant case, the ozone molar concentrations were decreased with the increasing of the system height. This is because mass transfer dominances the system. For low reaction rate constant case, the ozone molar concentrations were slightly changed with the system height. This is the chemical reaction control.

► The downer reactor was simulated using computational fluid dynamics (CFD) model.
► The mass transfer coefficients and the Sherwood numbers were successfully computed.
► The effects of reaction rate constant and downer height were investigated.
► The low Sherwood numbers were observed due to loose particle cluster formation.
► The flow and reaction were discussed using obtained mass transfer characteristics.