The bubble formation and extent of particle mixing induced by a single bubble injected in a mono-disperse uidised bed at incipient uidisation conditions has been studied with a Two-Fluid continuum Model (TFM) using the Kinetic Theory of Granular Flow (KTGF) and com- pared with experiments and simulation results obtained from a Discrete Particle Model (DPM). The eect of dierent gas-particle drag models and frictional viscosity models on the bubble behaviour and extent of particle mixing has been assessed. To describe the extent of particle mixing well, a frictional viscosity model needs to be included, however, the currently available frictional viscosity models need further improvement