The dynamic phenomena in pneumatic conveying are investigated by the object-oriented simulation (OOS) method, which is discrete. deterministic and transient for the particulate phase. The fluid phase is considered by a pseudo bidirectional way, separated from the solid phase. The dynamic effects between the two phases are considered by bidirectional terms such as the drag force on the particles and the momentum generation in the fluid. The proposed model regards the effects of bidirectional coupling and tridimensional movement of the particles. Furthermore, collisions among particles are considered, which provide complex dynamic patterns. The object-oriented properties of the model enable it to deal with polydispersed mixtures, making it adequate for segregation studies in pneumatic transport. It is pointed out that the model investigated could be enlarged to include the effects of heat and mass transport.